全文获取类型
收费全文 | 6615篇 |
免费 | 909篇 |
国内免费 | 2篇 |
出版年
2022年 | 48篇 |
2021年 | 69篇 |
2020年 | 45篇 |
2019年 | 66篇 |
2018年 | 97篇 |
2017年 | 71篇 |
2016年 | 127篇 |
2015年 | 270篇 |
2014年 | 244篇 |
2013年 | 326篇 |
2012年 | 403篇 |
2011年 | 393篇 |
2010年 | 286篇 |
2009年 | 216篇 |
2008年 | 305篇 |
2007年 | 369篇 |
2006年 | 409篇 |
2005年 | 383篇 |
2004年 | 381篇 |
2003年 | 374篇 |
2002年 | 351篇 |
2001年 | 180篇 |
2000年 | 108篇 |
1999年 | 125篇 |
1998年 | 84篇 |
1997年 | 84篇 |
1996年 | 81篇 |
1995年 | 71篇 |
1994年 | 65篇 |
1993年 | 73篇 |
1992年 | 86篇 |
1991年 | 78篇 |
1990年 | 63篇 |
1989年 | 68篇 |
1988年 | 61篇 |
1987年 | 77篇 |
1986年 | 79篇 |
1985年 | 64篇 |
1984年 | 55篇 |
1983年 | 61篇 |
1982年 | 36篇 |
1981年 | 54篇 |
1980年 | 44篇 |
1979年 | 59篇 |
1977年 | 35篇 |
1975年 | 39篇 |
1974年 | 43篇 |
1973年 | 44篇 |
1972年 | 37篇 |
1971年 | 38篇 |
排序方式: 共有7526条查询结果,搜索用时 15 毫秒
91.
A method for the quantitative determination of cycasin from cycad flour by gas-liquid chromatography is described. The flour is extracted with 70% ethanol and the residue from the dried extract is directly trimethylsilylated. Androsterone was found to be an excellent internal standard. The average content of cycasin from ten separate analyses of one lot of flour was . The method is rapid, sensitive, and not hindered by contaminating compounds. 相似文献
92.
James R. Wells 《Brittonia》1967,19(4):391-394
Polymnia mcvaughii from Jalisco, Mexico, is described as new. This herbaceous species appears to belong in the mainstream of evolution within the genus. It exhibits marked affinities to several species, but most closely resemblesP. oaxacana Schultz-Bip. Illustrations of important features are included, along with a list of key characteristics. 相似文献
93.
94.
95.
The aims, content, and organisatory structure of a proposed interdisciplinary ecosystem research project in the Wadden Sea
of Schleswig-Holstein (W. Germany) are briefly presented. The project will include research on both fundamental as well as
applied aspects of the Wadden Sea ecosystems and their interaction with local human activities. In contrast to most of the
other completed or currently running ecosystem research projects on tidal coasts, a considerable part of the scientific work
will also deal with aspects of ecosystem management and protection of the various marine and semiterrestrial habitats of the
Wadden Sea. Considerable attention is paid to theoretical and methodological aspects of research on ecosystems and landscape
units. In particular, the adoption of a hierarchical view of complex biological and environmental systems is recommended.
Presented at the VI International Wadden Sea Symposium (Biologische Anstalt Helgoland, Wattenmeerstation Sylt, D-2282 List,
FRG, 1–4 November 1988) 相似文献
96.
97.
Andrea Streit reas Faissner Bernd Gehrig Melitta Schachner 《Journal of neurochemistry》1990,55(5):1494-1506
The monoclonal L5 antibody reacts with an N-glycosidically linked carbohydrate structure which is present on the neural cell adhesion molecule L1, neural chondroitin sulfate proteoglycans, and other not yet identified glycosylated proteins. Using this antibody, we isolated and characterized proteoglycans from adult mouse brain and cultured astrocytes biosynthetically labeled with Na2 35SO4 and a 3H-amino acid mixture. Our data suggest that the L5 proteoglycans of both sources are identical in their biochemical properties. The apparent molecular mass of the L5 proteoglycan is approximately 500 kDa. Digestion of the iodinated L5 proteoglycan from mouse brain and of the [35S]methionine-labeled L5 proteoglycan from cultured astrocytes with proteinase-free chondroitinases ABC and AC revealed three major core proteins with apparent molecular masses of approximately 380, 360, and 260 kDa. These represent molecularly distinct protein cores. 相似文献
98.
Natural history of experimental woodchuck hepatitis virus infection: molecular virologic features of the pancreas, kidney, ovary, and testis. 总被引:2,自引:0,他引:2 下载免费PDF全文
B E Korba T L Brown F V Wells B Baldwin P J Cote H Steinberg B C Tennant J L Gerin 《Journal of virology》1990,64(9):4499-4506
The kinetic patterns of woodchuck hepatitis virus (WHV) infection were monitored in the pancreas, kidneys, ovaries, and testes. Groups of woodchucks experimentally infected with a standardized inoculum of WHV were sacrificed at different times over a 65-week period beginning in the preacute phase of viral infection and continuing to the period of serologic recovery or the establishment of chronic infections and subsequent hepatocellular carcinoma (B. E. Korba, P. J. Cote, F. V. Wells, B. Baldwin, H. Popper, R. H. Purcell, B. C. Tennant, and J. L. Gerin, J. Virol. 63:1360-1370, 1989). Tissues from an additional group of long-term (2 to 3 years) chronic WHV carriers which had been infected with the same WHV inocula were also examined. Viral DNA replication intermediates were found in all four tissues during the acute phase of WHV infection. However, WHV DNA replication intermediates were observed only in the kidneys of a small proportion of the chronically infected animals. Following the acute phase of infection, WHV DNA was present only in the pancreas, kidneys, and ovaries of the chronically infected woodchucks. A progressive evolution of different WHV genomic forms related to the replicative state of WHV was observed in these tissues. Histologic evaluation of these four tissues revealed only minimal, localized lesions which were not correlated with the state of WHV activity. The observations compiled in this study further extend the tissue tropism of WHV. 相似文献
99.
Summary Ion: solute cotransporters frequency are incapable of achieving equilibrium between the solute accumulation and the transmembrane difference of the electrochemical potential of the ion. The presence of uncoupled flows of ion and solutes (leaks) is often advanced as an explanation. Here an alternative is discussed. The net accumulation of solute may be so slow that equilibrium can never be attained at finite times (e.g., several hours). Cotransporters may exhibit strong product inhibition, and the net influx of solute approaches zero far from equilibrium. The inherent slowness of net transport under these conditions is termed catalytic inefficiency. The likelihood that galactoside: H+ cotransport inEscherichia coli, hexose: H+ cotransport inChlorella vulgaris, andd-glucose: Na+ cotransport in brush-border membranes exhibit catalytic inefficiency is examined. The existence of strong product inhibition complicates the determination of the stoichiometry of cotransport and the characterization of chemically modified or mutant cotransporters. 相似文献
100.