全文获取类型
收费全文 | 1700928篇 |
免费 | 166986篇 |
国内免费 | 1705篇 |
出版年
2021年 | 17373篇 |
2019年 | 16300篇 |
2018年 | 19268篇 |
2017年 | 18077篇 |
2016年 | 29371篇 |
2015年 | 43447篇 |
2014年 | 51592篇 |
2013年 | 77861篇 |
2012年 | 48615篇 |
2011年 | 39966篇 |
2010年 | 47827篇 |
2009年 | 47999篇 |
2008年 | 37167篇 |
2007年 | 36038篇 |
2006年 | 38942篇 |
2005年 | 39748篇 |
2004年 | 38712篇 |
2003年 | 36151篇 |
2002年 | 34028篇 |
2001年 | 54595篇 |
2000年 | 52724篇 |
1999年 | 46204篇 |
1998年 | 26699篇 |
1997年 | 26665篇 |
1996年 | 25677篇 |
1995年 | 25267篇 |
1994年 | 24916篇 |
1993年 | 24347篇 |
1992年 | 40047篇 |
1991年 | 38395篇 |
1990年 | 37228篇 |
1989年 | 37361篇 |
1988年 | 34360篇 |
1987年 | 33352篇 |
1986年 | 31088篇 |
1985年 | 32715篇 |
1984年 | 30131篇 |
1983年 | 26417篇 |
1982年 | 24487篇 |
1981年 | 23104篇 |
1980年 | 21705篇 |
1979年 | 26694篇 |
1978年 | 23462篇 |
1977年 | 22060篇 |
1976年 | 21037篇 |
1975年 | 21419篇 |
1974年 | 22574篇 |
1973年 | 22748篇 |
1972年 | 19627篇 |
1971年 | 18182篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
A method for estimating and comparing population genetic variation using random amplified polymorphic DNA (RAPD) profiling is presented. An analysis of molecular variance (AMOVA) is extended to accomodate phenotypic molecular data in diploid populations in Hardy-Weinberg equilibrium or with an assumed degree of selfing. We present a two step strategy: 1) Estimate RAPD site frequencies without preliminary assumptions on the unknown population structure, then perform significance testing for population substructuring. 2) If population structure is evident from the first step, use this data to calculate better estimates for RAPD site frequencies and sub-population variance components. A nonparametric test for the homogeneity of molecular variance (HOMOVA) is also presented. This test was designed to statistically test for differences in intrapopulational molecular variances (heteroscedasticity among populations). These theoretical developments are applied to a RAPD data set in Vaccinium macrocarpon (American cranberry) using small sample sizes, where a gradient of molecular diversity is found between central and marginal populations. The AMOVA and HOMOVA methods provide flexible population analysis tools when using data from RAPD or other DNA methods that provide many polymorphic markers with or without direct allelic data. 相似文献
993.
Nuclear ion channel activity is regulated by actin filaments 总被引:1,自引:0,他引:1
994.
995.
996.
997.
998.
999.
Y. Jiang 《Biochimica et Biophysica Acta (BBA)/General Subjects》1994,1201(1):76-84
Proteolysis of the hydroxylase component of soluble methane monooxygenase (MMO) with trypsin yielded a protein which retained 50% activity in a standard MMO assay. In an H2O2-driven assay, in which H2O2 replaced two of the protein components, NADH and O2 used in the standard assay, the proteolysed hydroxylase retained full activity for ethane, propane and propene, but had a 2–3 fold increase with methane as substrate. Several crosslinking reagents have been tested for their ability to stabilise the proteolysed form of the hydroxylase. Using polyoxyethylene bis(imidazolyl carbonyl) (Mr 3350) as the crosslinking agent, increased thermostability of the hydroxylase was observed. Activated methoxypolyethylene glycol (Mr 5000) was used to modify the hydroxylase which was now soluble in organic solvents as well as water and could be activated by H2O2. The glycol-modified hydroxylase functioned well in organic solvents in the catalysis of propene oxidation. 相似文献
1000.
Defects in RNA splicing and the consequence of shortened translational reading frames. 总被引:28,自引:8,他引:20 下载免费PDF全文
L. E. Maquat 《American journal of human genetics》1996,59(2):279-286