全文获取类型
收费全文 | 26530篇 |
免费 | 2330篇 |
国内免费 | 8篇 |
出版年
2022年 | 165篇 |
2021年 | 341篇 |
2020年 | 221篇 |
2019年 | 281篇 |
2018年 | 383篇 |
2017年 | 313篇 |
2016年 | 587篇 |
2015年 | 1034篇 |
2014年 | 1057篇 |
2013年 | 1456篇 |
2012年 | 1770篇 |
2011年 | 1752篇 |
2010年 | 1211篇 |
2009年 | 979篇 |
2008年 | 1432篇 |
2007年 | 1544篇 |
2006年 | 1523篇 |
2005年 | 1478篇 |
2004年 | 1435篇 |
2003年 | 1350篇 |
2002年 | 1417篇 |
2001年 | 292篇 |
2000年 | 215篇 |
1999年 | 311篇 |
1998年 | 401篇 |
1997年 | 292篇 |
1996年 | 260篇 |
1995年 | 263篇 |
1994年 | 236篇 |
1993年 | 236篇 |
1992年 | 237篇 |
1991年 | 193篇 |
1990年 | 190篇 |
1989年 | 203篇 |
1988年 | 185篇 |
1987年 | 184篇 |
1986年 | 173篇 |
1985年 | 189篇 |
1984年 | 238篇 |
1983年 | 220篇 |
1982年 | 247篇 |
1981年 | 226篇 |
1980年 | 193篇 |
1979年 | 130篇 |
1978年 | 154篇 |
1977年 | 137篇 |
1976年 | 122篇 |
1975年 | 109篇 |
1974年 | 122篇 |
1973年 | 97篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
61.
Egg shell membrane protein contains significant quantities of the lysine-derived aldehyde, allysine, and its aldol condensation product. NaB3H4 reduction followed by alkaline hydrolysis of purified protein revealed that there were six residues/1000 of both allysine and the reduced aldol while only traces of desmosine and isodesmosine were detected. The amino acid composition of the membrane protein did not resemble that of mammalian elastin. 相似文献
62.
63.
Barbara Tillmann Pierre Jolic?ur Masami Ishihara Nathalie Gosselin Olivier Bertrand Yves Rossetti Isabelle Peretz 《PloS one》2010,5(4)
Congenital amusia is a neurogenetic disorder of music processing that is currently ascribed to a deficit in pitch processing. A recent study challenges this view and claims the disorder might arise as a consequence of a general spatial-processing deficit. Here, we assessed spatial processing abilities in two independent samples of individuals with congenital amusia by using line bisection tasks (Experiment 1) and a mental rotation task (Experiment 2). Both amusics and controls showed the classical spatial effects on bisection performance and on mental rotation performance, and amusics and controls did not differ from each other. These results indicate that the neurocognitive impairment of congenital amusia does not affect the processing of space. 相似文献
64.
65.
66.
The efficiencies of the estimators in the linear logistic regression model are examined using simulations under six missing value treatments. These treatments use either the maximum likelihood or the discriminant function approach in the estimation of the regression coefficients. Missing values are assumed to occur at random. The cases of multivariate normal and dichotomous independent variables are both considered. We found that in general, there is no uniformly best method. However, mean substitution and discriminant function estimation using existing pairs of values for correlations turn out to be favourable for the cases considered. 相似文献
67.
68.
Mary C. Orland 《Ecology letters》2003,6(8):716-720
Interactions between intrinsic processes and extrinsic fluctuations can positively impact population persistence in ways often not predicted by classic ecological models. These interactions only arise when the intrinsic and extrinsic processes operate on the proper relative scales in time or space. Both metapopulation theory and resonance/attenuation theory suggest that interactions which lower population variability will occur when the intrinsic and extrinsic process occur on similar time scales. I performed an aquatic protist microcosm experiment to investigate how the relative frequencies of extrinsic density perturbations and intrinsic resource pulses impacted population variability. Population variability was lowest in the treatments of intermediate frequency, in which the extrinsic fluctuations and intrinsic processes were on the same time scale. This result is consistent with general theoretical predictions, and empirically documents the importance of considering scale in interactions between intrinsic and extrinsic processes that positively impact population persistence. 相似文献
69.
70.