全文获取类型
收费全文 | 18602篇 |
免费 | 1642篇 |
国内免费 | 1篇 |
专业分类
20245篇 |
出版年
2023年 | 82篇 |
2021年 | 151篇 |
2020年 | 110篇 |
2019年 | 134篇 |
2018年 | 362篇 |
2017年 | 371篇 |
2016年 | 398篇 |
2015年 | 316篇 |
2014年 | 418篇 |
2013年 | 684篇 |
2012年 | 1293篇 |
2011年 | 1420篇 |
2010年 | 734篇 |
2009年 | 480篇 |
2008年 | 1207篇 |
2007年 | 1200篇 |
2006年 | 1145篇 |
2005年 | 1010篇 |
2004年 | 949篇 |
2003年 | 911篇 |
2002年 | 884篇 |
2001年 | 754篇 |
2000年 | 876篇 |
1999年 | 389篇 |
1998年 | 179篇 |
1997年 | 136篇 |
1996年 | 179篇 |
1995年 | 161篇 |
1994年 | 138篇 |
1993年 | 138篇 |
1992年 | 129篇 |
1991年 | 123篇 |
1990年 | 127篇 |
1989年 | 117篇 |
1988年 | 116篇 |
1987年 | 113篇 |
1986年 | 106篇 |
1985年 | 144篇 |
1984年 | 144篇 |
1983年 | 121篇 |
1982年 | 160篇 |
1981年 | 144篇 |
1980年 | 106篇 |
1979年 | 127篇 |
1978年 | 92篇 |
1977年 | 89篇 |
1976年 | 80篇 |
1975年 | 81篇 |
1974年 | 82篇 |
1973年 | 71篇 |
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
121.
Mero A Nykänen T Keinänen O Knuutinen J Lahti K Alen M Rasi S Leppäluoto J 《Amino acids》2005,28(3):327-335
Summary. This study was designed to determine the responses of muscle protein, serum amino acids, and strength performance to bovine colostrum supplementation in physically active men. The rest (R) group (n=6) and the exercise (E) group (n=6) carried out twice a 2-week experiment randomly assigned in a double-blind fashion with either placebo (PLA; consuming daily 20g maltodextrin) or bovine colostrum (COL; consuming daily 20g colostrum supplement) treatment with one month between. On the test day after the treatment period the measurements were carried out in fasting conditions and E carried out a strength training session (STS). The methods involved the infusion of ring-2H5-phenylalanine, femoral arterial and venous blood sampling, and biopsies from the vastus lateralis muscle. Serum concentration of essential amino acids during recovery was greater (p<0.05) in the COL groups compared with the PLA groups. Both muscle protein synthesis and breakdown increased (p<0.05) with COL. There were no differences in phenylalanine net balance or strength performance between the PLA and COL groups. It was concluded that a 2-week supplementation with bovine colostrum in physically active men increases serum concentration of essential amino acids but has no effect either on strength performance or protein net balance in fasting conditions during recovery after STS. 相似文献
122.
Micro and macro-habitat associations in saproxylic beetles: implications for biodiversity management 总被引:1,自引:0,他引:1
J Hjältén F Stenbacka RB Pettersson H Gibb T Johansson K Danell JP Ball J Hilszczański 《PloS one》2012,7(7):e41100
Restoration of habitats is critically important in preventing full realization of the extinction debt owed as a result of anthropogenic habitat destruction. Although much emphasis has been placed on macrohabitats, suitable microhabitats are also vital for the survival of most species. The aim of this large-scale field experiment was to evaluate the relative importance of manipulated microhabitats, i.e., dead wood substrates of spruce (snags, and logs that were burned, inoculated with wood fungi or shaded) and macrohabitats, i.e., stand types (clear-cuts, mature managed forests, and forest reserves) for species richness, abundance and assemblage composition of all saproxylic and red-listed saproxylic beetles. Beetles were collected in emergence traps in 30 forest stands in 2001, 2003, 2004 and 2006. More individuals emerged from snags and untreated logs than from burned and shaded logs, but species richness did not differ among substrates. Assemblage composition differed among substrates for both all saproxylics and red-listed saproxylic species, mainly attributed to different assemblage composition on snags. This suggests that the practise of leaving snags for conservation purposes should be complemented with log supplementation. Clear-cuts supported fewer species and different assemblages from mature managed forests and reserves. Neither abundance, nor species richness or assemblage composition differed between reserves and mature managed forests. This suggests that managed stands subjected to selective cutting, not clear-felling, maintain sufficient old growth characteristics and continuity to maintain more or less intact assemblages of saproxylic beetles. Thus, alternative management methods, e.g., continuity forestry should be considered for some of these stands to maintain continuity and conservation values. Furthermore, the significantly higher estimated abundance per ha of red-listed beetles in reserves underlines the importance of reserves for maintaining viable populations of rare red-listed species and as source areas for saproxylic species in boreal forest landscapes. 相似文献
123.
H Gross C Hennard I Masouris C Cassel S Barth U Stober-Grässer A Mamiani B Moritz D Ostareck A Ostareck-Lederer N Neuenkirchen U Fischer W Deng H Leonhardt E Noessner E Kremmer FA Grässer 《PloS one》2012,7(8):e42106
The Epstein-Barr Virus (EBV) -encoded EBNA2 protein, which is essential for the in vitro transformation of B-lymphocytes, interferes with cellular processes by binding to proteins via conserved sequence motifs. Its Arginine-Glycine (RG) repeat element contains either symmetrically or asymmetrically di-methylated arginine residues (SDMA and ADMA, respectively). EBNA2 binds via its SDMA-modified RG-repeat to the survival motor neurons protein (SMN) and via the ADMA-RG-repeat to the NP9 protein of the human endogenous retrovirus K (HERV-K (HML-2) Type 1). The hypothesis of this work was that the methylated RG-repeat mimics an epitope shared with cellular proteins that is used for interaction with target structures. With monoclonal antibodies against the modified RG-repeat, we indeed identified cellular homologues that apparently have the same surface structure as methylated EBNA2. With the SDMA-specific antibodies, we precipitated the Sm protein D3 (SmD3) which, like EBNA2, binds via its SDMA-modified RG-repeat to SMN. With the ADMA-specific antibodies, we precipitated the heterogeneous ribonucleoprotein K (hnRNP K). Specific binding of the ADMA- antibody to hnRNP K was demonstrated using E. coli expressed/ADMA-methylated hnRNP K. In addition, we show that EBNA2 and hnRNP K form a complex in EBV- infected B-cells. Finally, hnRNP K, when co-expressed with EBNA2, strongly enhances viral latent membrane protein 2A (LMP2A) expression by an unknown mechanism as we did not detect a direct association of hnRNP K with DNA-bound EBNA2 in gel shift experiments. Our data support the notion that the methylated surface of EBNA2 mimics the surface structure of cellular proteins to interfere with or co-opt their functional properties. 相似文献
124.
Schollenberger L Gronemeyer T Huber CM Lay D Wiese S Meyer HE Warscheid B Saffrich R Peränen J Gorgas K Just WW 《PloS one》2010,5(11):e13886
The current view of peroxisome inheritance provides for the formation of new peroxisomes by both budding from the endoplasmic reticulum and autonomous division. Here we investigate peroxisome-cytoskeleton interactions and show by proteomics, biochemical and immunofluorescence analyses that actin, non-muscle myosin IIA (NMM IIA), RhoA, Rho kinase II (ROCKII) and Rab8 associate with peroxisomes. Our data provide evidence that (i) RhoA in its inactive state, maintained for example by C. botulinum toxin exoenzyme C3, dissociates from peroxisomes enabling microtubule-based peroxisomal movements and (ii) dominant-active RhoA targets to peroxisomes, uncouples the organelles from microtubules and favors Rho kinase recruitment to peroxisomes. We suggest that ROCKII activates NMM IIA mediating local peroxisomal constrictions. Although our understanding of peroxisome-cytoskeleton interactions is still incomplete, a picture is emerging demonstrating alternate RhoA-dependent association of peroxisomes to the microtubular and actin cytoskeleton. Whereas association of peroxisomes to microtubules clearly serves bidirectional, long-range saltatory movements, peroxisome-acto-myosin interactions may support biogenetic functions balancing peroxisome size, shape, number, and clustering. 相似文献
125.
Schwab U Seppänen-Laakso T Yetukuri L Agren J Kolehmainen M Laaksonen DE Ruskeepää AL Gylling H Uusitupa M Oresic M;GENOBIN Study Group 《PloS one》2008,3(7):e2630
Background
The effect of weight loss on different plasma lipid subclasses at the molecular level is unknown. The aim of this study was to examine whether a diet-induced weight reduction result in changes in the extended plasma lipid profiles (lipidome) in subjects with features of metabolic syndrome in a 33-week intervention.Methodology/Principal Findings
Plasma samples of 9 subjects in the weight reduction group and 10 subjects in the control group were analyzed using mass spectrometry based lipidomic and fatty acid analyses. Body weight decreased in the weight reduction group by 7.8±2.9% (p<0.01). Most of the serum triacylglycerols and phosphatidylcholines were reduced. The decrease in triacylglycerols affected predominantly the saturated short chain fatty acids. This decrease of saturated short chain fatty acid containing triacylglycerols correlated with the increase of insulin sensitivity. However, levels of several longer chain fatty acids, including arachidonic and docosahexanoic acid, were not affected by weight loss. Levels of other lipids known to be associated with obesity such as sphingolipids and lysophosphatidylcholines were not altered by weight reduction.Conclusions/Significance
Diet-induced weight loss caused significant changes in global lipid profiles in subjects with abnormal glucose metabolism. The observed changes may affect insulin sensitivity and glucose metabolism in these subjects.Trial Registration
ClinicalTrials.gov NCT00621205相似文献126.
Dehydrins are well known for being expressed in leaves during the course of developmental processes as well as under drought stress, being part of the protective machinery. Moreover, in seed physiology, dehydrins are classified as late embryogenesis‐related proteins (LEA protein), where they are thought to be responsible for persistence and longevity of seeds. Although both topics are a focus of modern plant biology, a direct linkage between these both areas is generally lacking. Based on an alignment of the chain of events, this paper will help to generate understanding that the occurrence of dehydrins in maturing seeds and leaves suffering drought stress is part of the same basic principle: basic principle: dehydrins are expressed in response to water shortage. Unfortunately, the related developmental process in seeds, i.e. maturation drying, has not been adequately considered as a part of this process. As a corresponding implication, the chain of events must be adjusted: the differences in dehydrin expression in orthodox, intermediate and recalcitrant seeds could be directly attributed to the occurrence or absence of maturation drying. The differences in dehydrin expression in orthodox, intermediate and recalcitrant seeds, and thus the differences in longevity, could be attributed to the occurrence or absence of a maturation drying. 相似文献
127.
Juhani Kaakinen Toivo Kuokkanen Janne Pesonen Ilkka Välimäki 《Soil & Sediment Contamination》2014,23(4):437-451
The mining industry is a very rapidly increasing production sector in Finland. Many new mines have been opened recently and others are in the planning phase. Mining legislation has been recently revised and compilation of an ID-directive (Industrial Emission Directive, 2010) required to implement environmental law revision is in progress. The aim of this study was to compare different digestion methods recommended by the Finnish Environmental Administration for threshold and guideline value determinations in the Finnish PIMA Decree (214/2007) and Government Decree (591/2006) concerning recovery of certain wastes in earth construction. Altogether six methods were tested, of which five were microwave-assisted acid digestion methods: ISO 11466, EPA Method 3051A (aqua region), EPA Method 3051A (HNO3), EPA Method 3051A (HNO3/HCl), and SFS-EN 13656, while one was a fusion method with lithium tetraborate (ASTM C 1391 - 95). The results showed that concentrations of heavy metals (As, Cd, Co, Cu, Ni, Pb, Sb, V, and Zn) can be determined reproducibly with standard methods, but the chemical method used can have a significant impact on the results. This conclusion is very important, because the measured heavy metal values can affect the classification and processing of waste materials, and thereby can significantly impact the cost of treatment. 相似文献
128.
Anatomical study of zygotic and somatic embryos of Tilia cordata 总被引:1,自引:0,他引:1
A comparative anatomical study was carried out on zygotic and somatic embryos of Tilia cordata Mill. to evaluate the effect of growth conditions on their development. Zygotic embryos (heart-shaped, torpedo, cotyledonary),
collected during two autumn periods, were examined to investigate the effect of growing season on embryo development. In comparison,
the influence of growth conditions on the development of somatic embryos in vitro was also studied. Treatment with abscisic acid (ABA) and polyethylene glycol-4000 induced the development of somatic cotyledonary
embryos similar to zygotic embryos with respect to morphology and anatomy, as illustrated by the differentiation of the apical
meristems and of the procambium. The pattern of accumulation of starch and protein was also similar in these embryos. Somatic
cotyledonary embryos that developed spontaneously without ABA showed defective accumulation of storage material and a general
failure to form the shoot apical meristem, leading to very low germination rates. Vacuolar phenolic deposits were observed
along the procambium of both zygotic and somatic embryos regardless of the maturation stage. Tracheid formation was observed
only in somatic embryos formed without ABA in the medium and in precociously germinated somatic embryos. Phenolic vacuolar
inclusions were frequently observed in epidermal cells of these embryos.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
129.
Laurence Carvalho Angelo G. Solimini Geoff Phillips Olli-Pekka Pietiläinen Jannicke Moe Ana Cristina Cardoso Anne Lyche Solheim Ingmar Ott Martin Søndergaard Gianni Tartari Seppo Rekolainen 《Hydrobiologia》2009,633(1):59-66
The Water Framework Directive (WFD) requires EU Member States to assess the “ecological status” of surface waters. As a component of ecological status, many European countries are developing a classification scheme for chlorophyll concentrations as a measure of phytoplankton biomass. The chlorophyll classification must be based on the degree of divergence of a water body from an appropriate baseline or ‘reference condition’. This article describes the development of a series of regression models for predicting reference chlorophyll concentrations on a site-specific basis. For model development, a large dataset of European lakes considered to be in reference condition, 466 lakes in total, was assembled. Data were included from 12 European countries, but lakes from Northern and Western Europe dominated and made up 92% of all reference lakes. Data have been collated on chlorophyll concentration, altitude, mean depth, alkalinity, humic type, surface area and geographical region. Regression models were developed for estimating site-specific reference chlorophyll concentrations from significant predictor ‘typology’ variables. Reference chlorophyll concentrations were found to vary along a number of environmental gradients. Concentrations increased with colour and alkalinity and decreased with lake depth and altitude. Forward selection was used to identify independent explanatory variables in regression models for predicting site-specific reference chlorophyll concentrations. Depth was selected as an explanatory variable in all models. Alkalinity was included in models for low colour and humic lakes and altitude was included in models for low colour and very humic lakes. Uncertainty in the models was quite high and arises from errors in the data used to develop the models (including natural temporal and spatial variability in data) and also from additional explanatory variables not considered in the models, particularly nutrient concentrations, retention time and grazing. Despite these uncertainties, site-specific reference conditions are still recommended in preference to type-specific reference conditions, as they use the individual characteristics of a site known to influence phytoplankton biomass, rather than adopt standards set to generally represent a large population of lakes of a particular type. For this reason, site-specific reference conditions should result in reduced error in ecological status classifications, particularly for lakes close to typology boundaries. 相似文献
130.
Pär Jonsson Hans Stenlund Thomas Moritz Johan Trygg Michael Sjöström Elwin R. Verheij Johan Lindberg Ina Schuppe-Koistinen Henrik Antti 《Metabolomics : Official journal of the Metabolomic Society》2006,2(3):135-143
A multivariate strategy for studying the metabolic response over time in urinary GC/MS data is presented and exemplified by a study of drug-induced liver toxicity in the rat. The strategy includes the generation of representative data through hierarchical multivariate curve resolution (H-MCR), highlighting the importance of obtaining resolved metabolite profiles for quantification and identification of exogenous (drug related) and endogenous compounds (potential biomarkers) and for allowing reliable comparisons of multiple samples through multivariate projections. Batch modelling was used to monitor and characterize the normal (control) metabolic variation over time as well as to map the dynamic response of the drug treated animals in relation to the control. In this way treatment related metabolic responses over time could be detected and classified as being drug related or being potential biomarkers. In summary the proposed strategy uses the relatively high sensitivity and reproducibility of GC/MS in combination with efficient multivariate curve resolution and data analysis to discover individual markers of drug metabolism and drug toxicity. The presented results imply that the strategy can be of great value in drug toxicity studies for classifying metabolic markers in relation to their dynamic responses as well as for biomarker identification. 相似文献