全文获取类型
收费全文 | 5213篇 |
免费 | 388篇 |
国内免费 | 481篇 |
专业分类
6082篇 |
出版年
2024年 | 9篇 |
2023年 | 71篇 |
2022年 | 175篇 |
2021年 | 308篇 |
2020年 | 206篇 |
2019年 | 230篇 |
2018年 | 252篇 |
2017年 | 180篇 |
2016年 | 232篇 |
2015年 | 314篇 |
2014年 | 390篇 |
2013年 | 391篇 |
2012年 | 481篇 |
2011年 | 428篇 |
2010年 | 274篇 |
2009年 | 264篇 |
2008年 | 275篇 |
2007年 | 252篇 |
2006年 | 194篇 |
2005年 | 145篇 |
2004年 | 161篇 |
2003年 | 134篇 |
2002年 | 91篇 |
2001年 | 76篇 |
2000年 | 78篇 |
1999年 | 73篇 |
1998年 | 43篇 |
1997年 | 46篇 |
1996年 | 46篇 |
1995年 | 40篇 |
1994年 | 29篇 |
1993年 | 27篇 |
1992年 | 26篇 |
1991年 | 17篇 |
1990年 | 17篇 |
1989年 | 19篇 |
1988年 | 8篇 |
1987年 | 9篇 |
1986年 | 9篇 |
1985年 | 10篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1979年 | 8篇 |
1975年 | 7篇 |
1974年 | 4篇 |
1971年 | 4篇 |
1970年 | 4篇 |
1969年 | 2篇 |
1966年 | 3篇 |
1965年 | 3篇 |
排序方式: 共有6082条查询结果,搜索用时 0 毫秒
991.
992.
993.
Mei-Ling Bai Daniel Schmidt Eckhard Gottschalk Michael Mühlenberg 《Journal of Ornithology》2009,150(1):255-263
We studied the nest site selection and distribution pattern at landscape level of the German Osprey population, and demonstrated
how to test the predictions of the ideal free distribution theory and its derivatives on such an expanding population. Information
about the location and breeding success of each Osprey nest site between 1995 and 2005 was collected through a long-term monitoring
programme. Data of land cover types were acquired from the administrations of each federal state and the CORINE Land Cover
database. The results showed that Ospreys preferred landscapes with more water bodies and forests. Such sites were also occupied
earlier and had higher local population density. However, in the study period of 11 years, there was a gradual shift from
forest-dominated landscapes to agricultural land-dominated landscapes. The breeding success increased over time, with no difference
in the breeding success between pairs nesting on trees and poles, whereas there was higher breeding success at nest sites
surrounded by more agricultural land and less forest. The more efficient foraging in eutrophic lakes in agricultural landscapes
was the most likely cause for the higher breeding success. The distribution pattern of the Ospreys did not match the resource
allocation, which deviated from the models tested. We suggested that the proximate cues used for nest site selection mismatched
site quality due to anthropogenic environmental changes. 相似文献
994.
Aiping Bai Zdzislaw M. Szulc Jacek Bielawski Nalini Mayroo Xiang Liu James Norris Yusuf A. Hannun Alicja Bielawska 《Bioorganic & medicinal chemistry》2009,17(5):1840-1848
Novel ω-N-amino analogs of B13 (Class E) were designed, synthesized and tested as inhibitors of acid ceramidase (ACDase) and potential anticancer agents deprived of unwanted lysosomal destabilization and ACDase proteolytic degradation properties of LCL204 [Szulc, Z. M.; Mayroo, N.; Bai, A.; Bielawski, J.; Liu, X.; Norris, J. S.; Hannun, Y. A.; Bielawska, A. Bioorg. Med. Chem. 2008, 16, 1015].Representative analog LCL464, (1R,2R)-2-N-(12′-N,N-dimethylaminododecanoyl amino)-1-(4″-nitrophenyl)-1,3-propandiol, inhibited ACDase activity in vitro, with a similar potency as B13 but higher than LCL204. LCL464 caused an early inhibition of this enzyme at a cellular level corresponding to decrease of sphingosine and specific increase of C14- and C16-ceramide. LCL464 did not induce lysosomal destabilization nor degradation of ACDase, showed increased cell death demonstrating inherent anticancer activity in a wide range of different cancer cell lines, and induction of apoptosis via executioner caspases activation. LCL464 represents a novel structural lead as chemotherapeutic agent acting via the inhibition of ACDase. 相似文献
995.
Establishment and characterization of a fibroblast cell line from the Mongolian horse 总被引:1,自引:0,他引:1
Lin-feng Li Wei-jun Guan Yue Hua Xiu-juan Bai Yue-hui Ma 《In vitro cellular & developmental biology. Animal》2009,45(7):311-316
A fibroblast line was successfully established from Mongolian horse ear marginal tissue by using a primary explant technique
and cell cryogenic preservation technology. Biological analysis showed the following: The cells were adherent and exhibited
density-dependent inhibition of proliferation; assays of microbial contamination from bacteria, fungi, and mycoplasma were
negative; the population doubling time of the cells was 33.9 h; and a 2n chromosome number of 64 at a frequency higher than
80%. A lack of cross-contamination of this cell line with other species was confirmed by isoenzyme analysis of lactic and
malic dehydrogenases. In order to study exogenous gene expression, four fluorescent proteins, pEGFP-N3, pEGFP-C1, pDsRed1-N1,
and pEYFP-N1, were transfected into the cells. The corresponding fluorescence was distributed throughout the cytoplasm and
nucleus 12 h after transfection. This cell line not only preserves the genetic resources of the Mongolian horse at the cellular
level but also provides valuable materials for genomic, postgenomic, and somacloning research in this species. 相似文献
996.
Wang F Feng M Xu P Xiao H Niu P Yang X Bai Y Peng Y Yao P Tan H Tanguay RM Wu T 《Cell stress & chaperones》2009,14(3):245-251
Heat shock proteins (Hsps) can protect cells, organs, and whole organisms against damage caused by abnormal environmental
hazards. Some studies have reported that lymphocyte Hsps may serve as biomarkers for evaluating disease status and exposure
to environmental stresses; however, few epidemiologic studies have examined the associations between lymphocyte Hsps levels
and lung cancer risk. We examined lymphocyte levels of Hsp27 and Hsp70 in 263 lung cancer cases and age- and gender-matched
cancer-free controls by flow cytometry. Multivariate logistic regression models were used to estimate the association between
lymphocyte Hsps levels and lung cancer risk. Our results showed that Hsp27 levels were significantly lower in lung cancer
cases than in controls (16.5 vs 17.8 mean fluorescence intensity, P < 0.001). This was not observed for Hsp70 levels. Further stratification analysis revealed that lymphocyte Hsp27 levels were
negatively associated with lung cancer risk especially in males and heavy smokers. There was a statistical trend of low odd
ratios (95% confidence intervals) and upper tertile levels of Hsp27 [1.000, 0.904 (0.566–1.444) and 0.382 (0.221–0.658, P
trend = 0.001) in males and 1.000, 0.9207 (0.465–1.822) and 0.419 (0.195–0.897, P
trend = 0.036) in heavy smokers] after adjustment for confounding factors. These results suggest that lower lymphocyte Hsp27 levels
might be associated with an increased risk of lung cancer. Our findings need to be validated in a large prospective study.
Feng Wang and Maohui Feng contributed equally to this work. 相似文献
997.
Aims: To clarify the taxonomic status of strain ZG0656 and analyse the effects of its acarviostatin products on blood glucose levels in mammalian systems.
Methods and Results: Our program to screen for new α-amylase inhibitors led to the isolation of strain ZG0656. The polyphasic taxonomic study revealed that strain ZG0656 represents a novel variation of Streptomyces coelicoflavus , for which we propose the name S. coelicoflavus var. nankaiensis . Four chemically distinct α-amylase inhibitors, acarviostatins I03, II03, III03 and IV03, were isolated from strain ZG0656. Acarviostatins III03 and IV03 are both novel oligomers. All four acarviostatins are mixed noncompetitive porcine pancreas α-amylase inhibitors. Acarviostatin III03 is the most potent α-amylase inhibitor known to date. Moreover, in the in vitro and in vivo experiments, acarviostatins III03 showed significant inhibition of starch hydrolysis and glucose transfer to blood.
Conclusions: Strain ZG0656 is a novel variation of S. coelicoflavus, whose products are novel effective α-amylase inhibitors. Among the products, acarviostatins III03 could significantly depress blood glucose levels in mammalian systems and be developed towards a possible therapeutic agent for diabetes.
Significance and Impact of the Study: Acarviostatin III03 is the most potent α-amylase inhibitor known to date. The oligomer will benefit the research on the relationship between α-amylase and various inhibitors and will offer more choices in diabetes treatments. 相似文献
Methods and Results: Our program to screen for new α-amylase inhibitors led to the isolation of strain ZG0656. The polyphasic taxonomic study revealed that strain ZG0656 represents a novel variation of Streptomyces coelicoflavus , for which we propose the name S. coelicoflavus var. nankaiensis . Four chemically distinct α-amylase inhibitors, acarviostatins I03, II03, III03 and IV03, were isolated from strain ZG0656. Acarviostatins III03 and IV03 are both novel oligomers. All four acarviostatins are mixed noncompetitive porcine pancreas α-amylase inhibitors. Acarviostatin III03 is the most potent α-amylase inhibitor known to date. Moreover, in the in vitro and in vivo experiments, acarviostatins III03 showed significant inhibition of starch hydrolysis and glucose transfer to blood.
Conclusions: Strain ZG0656 is a novel variation of S. coelicoflavus, whose products are novel effective α-amylase inhibitors. Among the products, acarviostatins III03 could significantly depress blood glucose levels in mammalian systems and be developed towards a possible therapeutic agent for diabetes.
Significance and Impact of the Study: Acarviostatin III03 is the most potent α-amylase inhibitor known to date. The oligomer will benefit the research on the relationship between α-amylase and various inhibitors and will offer more choices in diabetes treatments. 相似文献
998.
Aims: To investigate the species-specific prevalence of vhhP2 among Vibrio harveyi isolates and the applicability of vhhP2 in the specific detection of V. harveyi from crude samples of animal and environmental origins.
Methods and Results: A gene ( vhhP2 ) encoding an outer membrane protein of unknown function was identified from a pathogenic V. harveyi isolate. vhhP2 is present in 24 V. harveyi strains isolated from different geographical locations but is absent in 24 strains representing 17 different non- V. harveyi species, including V. parahaemolyticus and V. alginolyticus . A simple polymerase chain reaction method for the identification of V. harveyi was developed based on the conserved sequence of vhhP2 . This method was demonstrated to be applicable to the quick detection of V. harveyi from crude animal specimens and environmental samples. The specificity of this method was tested by applying it to the examination of two strains of V. campbellii , which is most closely related to V. harveyi . One of the V. campbellii strains was falsely identified as V. harveyi .
Conclusions: vhhP2 is ubiquitously present in the V. harveyi species and is absent in most of the non- V. harveyi species; this feature enables vhhP2 to serve as a genetic marker for the rapid identification of V. harveyi . However, this method can not distinguish some V. campbellii strains from V. harveyi .
Significance and Impact of the Study: the significance of our study is the identification of a novel gene of V. harveyi and the development of a simple method for the relatively accurate detection of V. harveyi from animal specimens and environmental samples. 相似文献
Methods and Results: A gene ( vhhP2 ) encoding an outer membrane protein of unknown function was identified from a pathogenic V. harveyi isolate. vhhP2 is present in 24 V. harveyi strains isolated from different geographical locations but is absent in 24 strains representing 17 different non- V. harveyi species, including V. parahaemolyticus and V. alginolyticus . A simple polymerase chain reaction method for the identification of V. harveyi was developed based on the conserved sequence of vhhP2 . This method was demonstrated to be applicable to the quick detection of V. harveyi from crude animal specimens and environmental samples. The specificity of this method was tested by applying it to the examination of two strains of V. campbellii , which is most closely related to V. harveyi . One of the V. campbellii strains was falsely identified as V. harveyi .
Conclusions: vhhP2 is ubiquitously present in the V. harveyi species and is absent in most of the non- V. harveyi species; this feature enables vhhP2 to serve as a genetic marker for the rapid identification of V. harveyi . However, this method can not distinguish some V. campbellii strains from V. harveyi .
Significance and Impact of the Study: the significance of our study is the identification of a novel gene of V. harveyi and the development of a simple method for the relatively accurate detection of V. harveyi from animal specimens and environmental samples. 相似文献
999.
Xiaochun Sun Guihua Bai Brett F. Carver 《Molecular breeding : new strategies in plant improvement》2009,23(2):311-321
Leaf rust, caused by Puccinia triticina Eriks., is an important foliar disease of common wheat (Triticum aestivum L.) worldwide. Pyramiding several major rust-resistance genes into one adapted cultivar is one strategy for obtaining more
durable resistance. Molecular markers linked to these genes are essential tools for gene pyramiding. The rust-resistance gene
Lr41 from T.
tauschii has been introgressed into chromosome 2D of several wheat cultivars that are currently under commercial production. To discover
molecular markers closely linked to Lr41, a set of near-isogenic lines (NILs) of the hard winter wheat cultivar Century were developed through backcrossing. A population
of 95 BC3F2:6 NILs were evaluated for leaf rust resistance at both seedling and adult plant stages and analyzed with simple sequence repeat
(SSR) markers using bulked segregant analysis. Four markers closely linked to Lr41 were identified on chromosome 2DS; the closest marker, Xbarc124, was about 1 cM from Lr41. Physical mapping using Chinese Spring nullitetrasomic and ditelosomic genetic stocks confirmed that markers linked to Lr41 were on chromosome arm 2DS. Marker analysis in a diverse set of wheat germplasm indicated that primers BARC124, GWM210, and
GDM35 amplified polymorphic bands between most resistant and susceptible accessions and can be used for marker-assisted selection
in breeding programs. 相似文献
1000.
The resurrection flowering plant Ramonda serbica inhabits the shallow organo-mineral soil that develops in crevices on northern-facing carbonate rocks in the gorges in the
Balkan Peninsula. This type of soil represents a complex substrate whose physical and chemical properties were found to be
well suited to the most important requirements for the growth and development of R. serbica as well as for the plant’s survival in the state of anhydrobiosis in periods of drought stress. Considerable amount of organic
matter (39.4%) in the soil resulted in the high field capacity (134 ml/100 g soil) as well as the slow changes in the amount
of its available water. The suitable soil hydric status, based on the organic remains, supports the slow dehydration of this
poikilohydric plant, which is extremely important in allowing the activation of the plant’s protective mechanisms. The pH
of the soil solution was slighty alkaline (7.7) mostly due to carbonates in its crystallographic structure. The large amount
of incompletely decomposed organic debris resulted in a marked difference between total and available nutrient concentration
in the soil. Still, the adequate content of nutrients in the leaves points to efficient mineral consumption by the plant roots.
The sufficient bioavailability of nutrients and water was also improved by vesicular–arbuscular mycorrhiza detected in R. serbica roots. 相似文献