全文获取类型
收费全文 | 127445篇 |
免费 | 8898篇 |
国内免费 | 21篇 |
专业分类
136364篇 |
出版年
2023年 | 663篇 |
2022年 | 691篇 |
2021年 | 1475篇 |
2020年 | 1259篇 |
2019年 | 1339篇 |
2018年 | 3385篇 |
2017年 | 2965篇 |
2016年 | 3930篇 |
2015年 | 5723篇 |
2014年 | 5891篇 |
2013年 | 7846篇 |
2012年 | 9460篇 |
2011年 | 8787篇 |
2010年 | 5688篇 |
2009年 | 4423篇 |
2008年 | 7176篇 |
2007年 | 7036篇 |
2006年 | 6509篇 |
2005年 | 6069篇 |
2004年 | 5698篇 |
2003年 | 5222篇 |
2002年 | 4851篇 |
2001年 | 2591篇 |
2000年 | 2460篇 |
1999年 | 2164篇 |
1998年 | 1062篇 |
1997年 | 807篇 |
1996年 | 746篇 |
1995年 | 747篇 |
1994年 | 699篇 |
1993年 | 572篇 |
1992年 | 1419篇 |
1991年 | 1354篇 |
1990年 | 1187篇 |
1989年 | 1102篇 |
1988年 | 1019篇 |
1987年 | 873篇 |
1986年 | 824篇 |
1985年 | 904篇 |
1984年 | 782篇 |
1983年 | 620篇 |
1982年 | 518篇 |
1981年 | 497篇 |
1979年 | 662篇 |
1978年 | 530篇 |
1977年 | 448篇 |
1976年 | 459篇 |
1975年 | 490篇 |
1974年 | 510篇 |
1973年 | 509篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
D J Méwissen J H Rust J Rust 《Comptes rendus des séances de la Société de biologie et de ses filiales》1987,181(4):439-444
A total of 2,377 C 57 Bl/6M mice were assigned to control groups and experimental groups exposed to tritiated water administered as a pulse injection or in drinking water, at a dose of 1.0 microCi per injection or per ml of drinking water. Weanlings were observed for the duration of life span. Data analysis was based on two coefficient estimates (1) individual carcinogenic induction coefficient and (2) specific tumorigenic induction coefficient. The carcinogenic potency of tritium was found to be dual in nature in enhancing the absolute induction of lymphocytic lymphomas in both sexes as well as their relative induction in competition with reticulo-endothelial tumors of other types. 相似文献
42.
43.
The succinate dehydrogenase consists of only four subunits, all nuclearly encoded, and is part of both the respiratory chain and the Krebs cycle. Mutations in the four genes encoding the subunits of the mitochondrial respiratory chain succinate dehydrogenase have been recently reported in human and shown to be associated with a wide spectrum of clinical presentations. Although a comparatively rare deficiency in human, molecularly defined succinate dehydrogenase deficiency has already been found to cause encephalomyopathy in childhood, optic atrophy or tumor in adulthood. Because none of the typical housekeeping genes encoding this respiratory chain complex is known to present tissue-specific isoforms, the tissue-specific involvement represents a quite intriguing question, which is mostly addressed in this review. A differential impairment of electron flow through the respiratory chain, handling of oxygen, and/or metabolic blockade possibly associated with defects in the different subunits that can be advocated to account for tissue-specific involvement is discussed. 相似文献
44.
45.
Thea Kristiansen Jens‐Christian Svenning Wolf L. Eiserhardt Dennis Pedersen Hans Brix Søren Munch Kristiansen Maria Knadel César Grández Henrik Balslev 《Journal of Biogeography》2012,39(7):1318-1332
Aim It is a central issue in ecology and biogeography to understand what governs community assembly and the maintenance of biodiversity in tropical rain forest ecosystems. A key question is the relative importance of environmental species sorting (niche assembly) and dispersal limitation (dispersal assembly), which we investigate using a large dataset from diverse palm communities. Location Lowland rain forest, western Amazon River Basin, Peru. Methods We inventoried palm communities, registering all palm individuals and recording environmental conditions in 149 transects of 5 m × 500 m. We used ordination, Mantel tests and indicator species analysis (ISA) to assess compositional patterns, species responses to geographical location and environmental factors. Mantel tests were used to assess the relative importance of geographical distance (as a proxy for dispersal limitation) and environmental differences as possible drivers of dissimilarity in palm species composition. We repeated the Mantel tests for subsets of species that differ in traits of likely importance for habitat specialization and dispersal (height and range size). Results We found a strong relationship between compositional dissimilarity and environmental distance and a weaker but also significant relationship between compositional dissimilarity and geographical distance. Consistent with expectations, relationships with environmental and geographical distance were stronger for understorey species than for canopy species. Geographical distance had a higher correlation with compositional dissimilarity for small‐ranged species compared with large‐ranged species, whereas the opposite was true for environmental distance. The main environmental correlates were inundation and soil nutrient levels. Main conclusions The assembly of palm communities in the western Amazon appears to be driven primarily by species sorting according to hydrology and soil, but with dispersal limitation also playing an important role. The importance of environmental characteristics and geographical distance varies depending on plant height and geographical range size in agreement with functional predictions, increasing our confidence in the inferred assembly mechanisms. 相似文献
46.
B Alexandre F Thiébaut M Allary E Boschetti C Séné J Saint-Blancard 《Revue fran?aise de transfusion et immuno-hématologie》1987,30(1):57-66
In this work the human plasma fibronectin was purified by affinity chromatography using a tandem column system. The first affinity column was filled with gelatin-Trisacryl whereas the second one contained heparin-Trisacryl. This double affinity chromatography demonstrated its high efficiency in term of purity and yield. Several analytical methods (electrophoresis, immunoelectrophoresis, F.P.L.C. and adhesion assay on cultured eucaryotic cells) evidenced in fact the high purity of the preparation as well as its biological behaviour in term of cell adhesion and spreading. The performances of the sorbents used facilitate the scaling up when large quantities of FNP are needed. 相似文献
47.
F Krizsa Z Borbényi E Arokszállásy I Cserháti 《Folia haematologica (Leipzig, Germany : 1928)》1980,107(4):683-687
The thrombopoietic serum activity was examined in rats during thrombocytopenia produced by bleeding or after treatment with antithrombocyte serum (ATS). 6 hours after both treatments the thrombopoietic activity of the serum, i.e. its content of thrombopoietin, is increased. After the ATS treatment of nephrectomized animals a similar increase of thrombopoietic activity as in normal animals could be achieved. In contrast to that, no similar increase of thrombopoietic activity was observed in nephrectomized animals after blood loss. According to the results of the authors the increase of thrombopoietic activity produced by different stimuli can be attributed to different mechanisms. 相似文献
48.
49.
50.
S. Goldenberg J.M. Salles V.T. Contreras M.P.Lima Franco A.M. Katzin W. Colli C.M. Morel 《FEBS letters》1985,180(2):265-270
The cell-free translation products of polyribosomal and post-polyribosomal mRNAs from the non-infective epimastigotes and the infective metacyclic trypomastigotes of the parasitic protozoan Trypanosoma cruzi were compared by two-dimensional polyacrylamide gel electrophoresis. The result show that although many polypeptides are conserved, quantitative and qualitative differences are observed between both differentiation stages. The results also indicate the existence of post-polyribosomal mRNAs in equilibrium with polyribosomal counterparts. The immunoprecipitation of the in vitro synthesized polypeptides with chagasic human serum and the serum raised against an 85-kDa glycoprotein (P2-WGA), potentially involved in the process of T. cruzi penetration into mammalian cells, shows that while the chagasic serum recognizes the same 72-kDa, 68-kDa and 46-kDa polypeptides in both differentiation stages, the anti-P2-WGA serum immunoprecipitates a single 48-kDa polypeptide from in vitro translation products of metacyclic trypomastigotes. 相似文献