全文获取类型
收费全文 | 5497篇 |
免费 | 485篇 |
国内免费 | 88篇 |
出版年
2022年 | 28篇 |
2021年 | 100篇 |
2020年 | 74篇 |
2019年 | 87篇 |
2018年 | 83篇 |
2017年 | 84篇 |
2016年 | 103篇 |
2015年 | 208篇 |
2014年 | 249篇 |
2013年 | 287篇 |
2012年 | 434篇 |
2011年 | 368篇 |
2010年 | 223篇 |
2009年 | 203篇 |
2008年 | 288篇 |
2007年 | 325篇 |
2006年 | 280篇 |
2005年 | 251篇 |
2004年 | 249篇 |
2003年 | 185篇 |
2002年 | 175篇 |
2001年 | 117篇 |
2000年 | 103篇 |
1999年 | 78篇 |
1998年 | 67篇 |
1997年 | 38篇 |
1996年 | 31篇 |
1995年 | 44篇 |
1994年 | 60篇 |
1993年 | 52篇 |
1992年 | 59篇 |
1991年 | 67篇 |
1990年 | 75篇 |
1989年 | 72篇 |
1988年 | 58篇 |
1987年 | 75篇 |
1986年 | 57篇 |
1985年 | 42篇 |
1984年 | 48篇 |
1983年 | 30篇 |
1982年 | 43篇 |
1981年 | 23篇 |
1980年 | 27篇 |
1979年 | 33篇 |
1978年 | 32篇 |
1977年 | 29篇 |
1976年 | 35篇 |
1974年 | 31篇 |
1973年 | 27篇 |
1972年 | 31篇 |
排序方式: 共有6070条查询结果,搜索用时 265 毫秒
1.
2.
Oussama El Far Béatrice Marquèze Christian Leveque Nicole Martin-Moutôt Bethan Lang John Newsom-Davis †Akira Yoshida †Masami Takahashi Michael J. Seagar 《Journal of neurochemistry》1995,64(4):1696-1702
Abstract: In Lambert-Eaton myasthenic syndrome neurotransmitter release is reduced by an autoimmune response directed against the calcium channel complex of the nerve terminal. Autoantibodies were detected by immunoprecipitation assays using solubilized receptors labeled with ligands selective for N-type (125 I-ω conotoxin GVIA) and L-type ([3 H]PN200-110) calcium channels. Sera with a high antibody titer (>3 n M ) against rat brain N-type channels contained autoantibodies that immunoprecipitated neuronal and muscle L-type channels. These IgG fractions stained a 55-kDa protein in immunoblots of purified skeletal muscle dihydropyridine receptor, suggesting that they contain autoantibodies against the β subunit of the calcium channel. A distinct antibody population in the same fractions reacted with a nerve terminal 65-kDa protein that is unrelated to the β subunit and displays properties similar to those of synaptotagmin. 相似文献
3.
Sylvia Hofmann Sabine Kraus Tsering Dorge Michael Nothnagel Georg Miehe 《Journal of Biogeography》2014,41(11):2162-2172
4.
E Lang G I Szendrei I Elekes V M Lee L Otvos 《Biochemical and biophysical research communications》1992,182(1):63-69
Serine416 of human tau protein is believed to be phosphorylated in Alzheimer neurofibrillary tangles. We synthesized a fragment of tau, consisting of amino acids 408-421 in both non-phosphorylated and serine416-phosphorylated forms. Circular dichroism in a trifluoroethanol-water mixture indicated a beta-turn----beta-pleated sheet conformational transition upon phosphorylation. The beta-structure formation is intermolecular and can be inhibited by addition of Ca2+ ions or a phosphorylated tripeptide, but not with its non-phosphorylated analog. The presence of the phosphorylated tau peptide did not facilitate the formation of beta-pleated sheets of a phosphorylated neurofilament fragment. Multivalent cations induced a conformational transition of this phosphorylated neurofilament peptide, but the effect was less specific than the transition induced in the tau fragment, and it could also be reversed with the competing phosphorylated tripeptide. 相似文献
5.
6.
7.
A diet (KSC-25) to be sterilized by irradiation was formulated to contain 66% moisture and to provide the required nutrients for growing rats. Analyses of the irradiated dry diet provided data to evaluate its nutrient content. The diet was evaluated for its ability to supply all nutrients, including water, required by immature rats. Sixteen Sprague-Dawley rats were fed the high-moisture diet with or without access to a water bottle. Rats (n = 16) fed an irradiated purified diet in a meal form with access to a water bottle were the control animals. Feed efficiency, food and water consumption, and growth rate data were collected during the 28-day study. Organ weights were collected on day 28. The test diet met or exceeded the National Research Council (NRC) estimated nutritional requirements for immature laboratory rats. The 66% moisture KSC-25 diet provided all nutrients, including water, required by weanling male Sprague-Dawley rats for growth equivalent to the established purified diet. 相似文献
8.
John M. Robinson Sylvia A. Larrimore David W. Craft H.E. Heath Gary L. Sloan 《Biochemical and biophysical research communications》1982,109(3):730-737
The extracellular protease, endopeptidase, and hexosaminidase produced by were neither induced nor repressed by amino acids but required a tryptic digest of casein for their production. Catabolite repression of exoenzyme production by glucose was not affected by exogenous cyclic adenosine 3′, 5′-monophosphate but was partially relieved by di- or monobutyryl derivatives of this compound. 相似文献
9.
Altitudinal gradients are frequently used to study environmental effects on species diversity. Recent quantitative studies on Lepidoptera focussed on tropical mountain systems and often reported unimodal diversity peaks at “mid-elevations”;, a pattern also often found in other taxa. Here we used methodologically comparable, nocturnal Macrolepidoptera samples from the Swiss Alps to analyze environmental correlates of diversity. Using seasonal data (monthly samples from April to November at altitudes between 600 and 2400 m a.s.l.) allowed to decouple altitude and some climate variables for analyses. We found that the altitude–diversity pattern changes with season. In spring and autumn, diversity decreased with increasing altitude, while we found a unimodal peak of diversity at mid-elevations during summer. This excluded all hypothetical causes of diversity variation that do not allow for seasonality. Temperature was an important correlate of diversity, whereas precipitation was not. These results were separately corroborated for the two most common families (Noctuidae and Geometridae). However, diversity patterns of the two families were not particularly close, and unexplained variance of climatic explanations was substantial in all cases. The patterns of faunal overlap did not explain the unimodal diversity pattern, and we claim that we lack a generally valid explanation for this common phenomenon. 相似文献
10.