全文获取类型
收费全文 | 12442篇 |
免费 | 935篇 |
国内免费 | 2篇 |
专业分类
13379篇 |
出版年
2023年 | 52篇 |
2021年 | 87篇 |
2020年 | 91篇 |
2019年 | 88篇 |
2018年 | 222篇 |
2017年 | 267篇 |
2016年 | 311篇 |
2015年 | 383篇 |
2014年 | 443篇 |
2013年 | 634篇 |
2012年 | 979篇 |
2011年 | 1010篇 |
2010年 | 535篇 |
2009年 | 363篇 |
2008年 | 772篇 |
2007年 | 822篇 |
2006年 | 722篇 |
2005年 | 633篇 |
2004年 | 590篇 |
2003年 | 609篇 |
2002年 | 571篇 |
2001年 | 325篇 |
2000年 | 349篇 |
1999年 | 188篇 |
1998年 | 109篇 |
1997年 | 89篇 |
1996年 | 99篇 |
1995年 | 94篇 |
1994年 | 100篇 |
1993年 | 91篇 |
1992年 | 95篇 |
1991年 | 97篇 |
1990年 | 100篇 |
1989年 | 83篇 |
1988年 | 82篇 |
1987年 | 81篇 |
1986年 | 81篇 |
1985年 | 86篇 |
1984年 | 85篇 |
1983年 | 85篇 |
1982年 | 73篇 |
1981年 | 80篇 |
1980年 | 77篇 |
1979年 | 73篇 |
1978年 | 68篇 |
1977年 | 67篇 |
1976年 | 53篇 |
1975年 | 36篇 |
1974年 | 41篇 |
1973年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
Shashank Gupta Regine Utoft Henrik Hasseldam Anja Schmidt-Christensen Tine Dahlbaek Hannibal Lisbeth Hansen Nina Fransén-Pettersson Noopur Agarwal-Gupta Bj?rn Rozell ?sa Andersson Dan Holmberg 《PloS one》2013,8(10)
Multiple Sclerosis (MS) is a progressive autoimmune inflammatory and demyelinating disease of the central nervous system (CNS). T cells play a key role in the progression of neuroinflammation in MS and also in the experimental autoimmune encephalomyelitis (EAE) animal models for the disease. A technology for quantitative and 3 dimensional (3D) spatial assessment of inflammation in this and other CNS inflammatory conditions is much needed. Here we present a procedure for 3D spatial assessment and global quantification of the development of neuroinflammation based on Optical Projection Tomography (OPT). Applying this approach to the analysis of rodent models of MS, we provide global quantitative data of the major inflammatory component as a function of the clinical course. Our data demonstrates a strong correlation between the development and progression of neuroinflammation and clinical disease in several mouse and a rat model of MS refining the information regarding the spatial dynamics of the inflammatory component in EAE. This method provides a powerful tool to investigate the effect of environmental and genetic forces and for assessing the therapeutic effects of drug therapy in animal models of MS and other neuroinflammatory/neurodegenerative disorders. 相似文献
972.
Angela Oppelt Viola H Lobert Kaisa Haglund Ashley M Mackey Lucia E Rameh Knut Liestøl Kay Oliver Schink Nina Marie Pedersen Eva M Wenzel Ellen M Haugsten Andreas Brech Tor Erik Rusten Harald Stenmark Jørgen Wesche 《EMBO reports》2013,14(1):57-64
Although phosphatidylinositol 5‐phosphate (PtdIns5P) is present in many cell types and its biogenesis is increased by diverse stimuli, its precise cellular function remains elusive. Here we show that PtdIns5P levels increase when cells are stimulated to move and we find PtdIns5P to promote cell migration in tissue culture and in a Drosophila in vivo model. First, class III phosphatidylinositol 3‐kinase, which produces PtdIns3P, was shown to be involved in migration of fibroblasts. In a cell migration screen for proteins containing PtdIns3P‐binding motifs, we identified the phosphoinositide 5‐kinase PIKfyve and the phosphoinositide 3‐phosphatase MTMR3, which together constitute a phosphoinositide loop that produces PtdIns5P via PtdIns(3,5)P2. The ability of PtdIns5P to stimulate cell migration was demonstrated directly with exogenous PtdIns5P and a PtdIns5P‐producing bacterial enzyme. Thus, the identified phosphoinositide loop defines a new role for PtdIns5P in cell migration. 相似文献
973.
Six non-pregnant cows were allocated into 3 groups. Group 1 comprised a pair of lactating cows, whereas groups 2 and 3 each comprised a pair of non-lactating cows. The cows in groups 1 and 2 were dosed intraruminally by stomach tube with zinc oxide at 120 mg Zn per kg of bodyweight at weekly intervals for a period of 33 days. Each cow received a total of 4 doses of zinc oxide. Group 3 served as non-treated control group. Blood samples were collected from all 6 cows daily. Serum was analysed for concentration of calcium. Within 12–24 h of each zinc oxide administration the serum calcium of the lactating cows dropped dramatically indicating the existence of an antagonistic effect between Zn and Ca. The first Zn induced hypocalcaemic episode in the lactating cows was followed by a rise in serum calcium to a level above the pre-dosing level and above the mean value of the control group. The depth of the hypocalcaemic response decreased with the number of zinc oxide dosings. This effect was explained as a response from the stimulation of the calcium homeostatic mechanisms. In the Zn dosed non-lactating cows responses were similar but less clear. The perspective of these findings is discussed in relation to resistance towards parturient hypocalcaemia. 相似文献
974.
975.
Serhiy Pankiv Endalkachew A. Alemu Andreas Brech Jack-Ansgar Bruun Trond Lamark Aud ?vervatn Geir Bj?rk?y Terje Johansen 《The Journal of cell biology》2010,188(2):253-269
Autophagy is the main eukaryotic degradation pathway for long-lived proteins, protein aggregates, and cytosolic organelles. Although the protein machinery involved in the biogenesis of autophagic vesicles is well described, very little is known about the mechanism of cytosolic transport of autophagosomes. In this study, we have identified an adaptor protein complex, formed by the two autophagic membrane-associated proteins LC3 and Rab7 and the novel FYVE and coiled-coil (CC) domain–containing protein FYCO1, that promotes microtubule (MT) plus end–directed transport of autophagic vesicles. We have characterized the LC3-, Rab7-, and phosphatidylinositol-3-phosphate–binding domains in FYCO1 and mapped part of the CC region essential for MT plus end–directed transport. We also propose a mechanism for selective autophagosomal membrane recruitment of FYCO1. 相似文献
976.
Summary
Atriplex hymenelytra is an evergreen shrub distributed in the hot deserts of parts of Mexico and the southwestern United States. The leaves of the species have a number of characteristics that are adaptive in a hot, dry environment, some of which change seasonally. Steeply angled leaves reduce midday solar interception, yet result in relatively high interception when solar angles are low and vapor pressure deficits are at a minimum. The leaves substantially reduce their absorptance of incident radiation during the hot periods of the year by changing their moisture and hence dissolved salt contents. At these times the light intensity required for saturation of photosynthesis is low and a reduction in the radiation absorbed by the leaves therefore results in a greater water-use efficiency. 相似文献
977.
Hunting for willow ptarmigan (Lagopus lagopus) is a popular recreational activity in Norway, but studies of the hunters are limited. While large game management in Norway
is based on sound models and research, management of small game hunters and hunting have not been subject to the same rigour.
Compared to the extensive body of knowledge about ptarmigan behaviour and habitat preferences, the knowledge base on ptarmigan
hunters is very limited. We surveyed the habitat preferences of 3,056 hunters to identify preferred landscape categories using
pictures covering a range of landscape types. We also examined to which extent residence types and forms of hunting were related
to habitat preferences. Through factor analysis, we identified three categories of hunting habitat; mountain forest, low alpine
and high alpine. Mode of hunting is more important than residence status in terms of preferred habitat. Hunters using dogs
preferred mountain forest and low alpine habitats more than hunters without dogs. Hunters without dogs had a higher preference
than dog hunters for high alpine habitats. Hunters with mixed modes of hunting have wider habitat preferences. Residence status
only affects the perception of the mountain forest habitat. The results may have implications for management as land use and
place-based meanings are currently changing in many natural and rural landscapes, and hunting needs to be integrated with
other recreational uses. 相似文献
978.
Real-time metabolomic analysis of lactic acid bacteria as monitored by in vitro NMR and chemometrics
Parvaneh Ebrahimi Flemming Hofmann Larsen Henrik Max Jensen Finn Kvist Vogensen Søren Balling Engelsen 《Metabolomics : Official journal of the Metabolomic Society》2016,12(4):77
Introduction
Lactic acid bacteria (LAB) play an important role in the food industry as starter cultures to manufacture fermented food, and as probiotics. In recent years, there has been an increasing interest in using LAB cultures for biopreservation of food products. It is therefore of great interest to study the detailed metabolism of these bacteria.Objectives
This study aimed at developing an efficient analytical protocol for real-time in vitro NMR measurements of LAB fermentations, from sample preparation, over data acquisition and preprocessing, to the extraction of the kinetic metabolic profiles.Method
The developed analytical protocol is applied to an experimental design with two LAB strains (Lactobacillus rhamnosus DSM 20021 and Lactobacillus plantarum subsp. plantarum DSM 20174), two initial pH levels (pHi 6.5 and 5.5), two levels of glucose concentration (2.5 and 0.25 g/l), and two batch fermentation replicates.Results
The design factors proved to be strongly significant and led to interesting biological information. The protocol allowed for detailed real-time kinetic analysis of 11 major metabolites involved in the glycolysis, pyruvate catabolism, amino acid catabolism and cell energy metabolism. New biological knowledge was obtained about the different patterns of glutamine and aspartic acid consumption by the two strains. It was observed that L. plantarum consumes more glutamine at low pH (pH 5.5) whereas the opposite applies to L. rhamnosus. Regarding aspartic acid, both of the strains consume it higher at low pH, and overall L. plantarum consumes it more. L. rhamnosus did not consume aspartic acid at pH 6.5.Conclusion
The developed analytical protocol for real-time in vitro NMR measurements of bacterial metabolism allows a relatively easy investigation of different fermentation factors such as new strains, new substrates, cohabitations, temperature, and pH and has a great potential in biopreservation studies to discover new efficient bioprotective cultures.979.
Flodgren E Olde B Meidute-Abaraviciene S Winzell MS Ahrén B Salehi A 《Biochemical and biophysical research communications》2007,354(1):240-245
The free fatty acid receptor, GPR40, has been coupled with insulin secretion via its expression in pancreatic beta-cells. However, the role of GPR40 in the release of glucagon has not been studied and previous attempts to identify the receptor in alpha-cells have been unfruitful. Using double-staining for glucagon and GPR40 expression, we demonstrate that the two are expressed in the same cells in the periphery of mouse islets. In-R1-G9 hamster glucagonoma cells respond dose-dependently to linoleic acid stimulation by elevated phosphatidyl inositol hydrolysis and glucagon release and the cells become increasingly responsive to fatty acid stimulation when overexpressing GPR40. Isolated mouse islets also secrete glucagon in response to linoleic acid, a response that was abolished by antisense treatment against GPR40. This study demonstrates that GPR40 is present and active in pancreatic alpha-cells and puts further emphasis on the importance of this nutrient sensing receptor in islet function. 相似文献
980.
Does the colonization of new biogeographic regions influence the diversification and accumulation of clade richness among the Corvides (Aves: Passeriformes)? 下载免费PDF全文
Jonathan D. Kennedy Michael K. Borregaard Knud A. Jønsson Ben Holt Jon Fjeldså Carsten Rahbek 《Evolution; international journal of organic evolution》2017,71(1):38-50
Regional variation in clade richness can be vast, reflecting differences in the dynamics of historical dispersal and diversification among lineages. Although it has been proposed that dispersal into new biogeographic regions may facilitate diversification, to date there has been limited assessment of the importance of this process in the generation, and maintenance, of broad‐scale biodiversity gradients. To address this issue, we analytically derive biogeographic regions for a global radiation of passerine birds (the Corvides, c. 790 species) that are highly variable in the geographic and taxonomic distribution of species. Subsequently, we determine rates of historical dispersal between regions, the dynamics of diversification following regional colonization, and spatial variation in the distribution of species that differ in their rates of lineage diversification. The results of these analyses reveal spatiotemporal differences in the build‐up of lineages across regions. The number of regions occupied and the rate of transition between regions both predict family richness well, indicating that the accumulation of high clade richness is associated with repeated expansion into new geographic areas. However, only the largest family (the Corvidae) had significantly heightened rates of both speciation and regional transition, implying that repeated regional colonization is not a general mechanism promoting lineage diversification among the Corvides. 相似文献