全文获取类型
收费全文 | 6497篇 |
免费 | 765篇 |
国内免费 | 1篇 |
出版年
2023年 | 39篇 |
2022年 | 55篇 |
2021年 | 129篇 |
2020年 | 74篇 |
2019年 | 97篇 |
2018年 | 124篇 |
2017年 | 102篇 |
2016年 | 173篇 |
2015年 | 259篇 |
2014年 | 265篇 |
2013年 | 318篇 |
2012年 | 404篇 |
2011年 | 394篇 |
2010年 | 216篇 |
2009年 | 200篇 |
2008年 | 267篇 |
2007年 | 273篇 |
2006年 | 261篇 |
2005年 | 238篇 |
2004年 | 231篇 |
2003年 | 211篇 |
2002年 | 205篇 |
2001年 | 122篇 |
2000年 | 128篇 |
1999年 | 135篇 |
1998年 | 98篇 |
1997年 | 88篇 |
1996年 | 100篇 |
1995年 | 75篇 |
1994年 | 63篇 |
1993年 | 63篇 |
1992年 | 114篇 |
1991年 | 87篇 |
1990年 | 118篇 |
1989年 | 112篇 |
1988年 | 101篇 |
1987年 | 88篇 |
1986年 | 61篇 |
1985年 | 83篇 |
1984年 | 97篇 |
1983年 | 61篇 |
1982年 | 55篇 |
1981年 | 47篇 |
1979年 | 60篇 |
1978年 | 43篇 |
1977年 | 53篇 |
1973年 | 52篇 |
1972年 | 44篇 |
1970年 | 49篇 |
1969年 | 42篇 |
排序方式: 共有7263条查询结果,搜索用时 15 毫秒
1.
Marvin J. Allison Guillermo Focacci Calogero Santoro 《American journal of physical anthropology》1982,59(3):299-304
Burials and mummies of dogs from the Arica, Chile, area are described. It is concluded that these dogs were brought to this area 2500 years ago by shepherds from the highlands and are still present, relatively unchanged. 相似文献
2.
James B. Reid 《Animal behaviour》1982,30(4):1212-1216
A young captive rook, Corvus frugilegus, inserted a plug into a plug-hole in its aviary floor so that a pool of water formed, which was used by all four rooks in the aviary for drinking and bathing. The bird was selective about which, of six holes, it chose for insertion of the tool, choosing the appropriate one with respect to the water source. Days on which attempted or successful tool-use occurred were drier than other days, and days of successful tool-uses were also warmer. Availability of fresh water to the birds did not influence the occurrence of tool-use. 相似文献
3.
Internode length in Pisum. I. The effect of the Le/le gene difference on endogenous gibberellin-like substances 总被引:2,自引:0,他引:2
The allelopathic potential of the dry fruits of Washingtonia filifera (L. Linden) H. Wendl. was investigated. Leachates from fruits inhibited the germination of lettuce, wheat, red cabbage and cucumber seeds. The inhibitory effect was partly neutralized by kinetin (20 mg 1−1 ) and gibberellic acid (50 mg 1−1 ). The effect of kinetin was more pronounced at 25°C than at 20°C. Substances inhibiting germination were localized in the pericarp of the fruit and were resistant to high temperature. 相似文献
4.
5.
The cost of mutualism in a fly-fungus interaction 总被引:2,自引:0,他引:2
The movement ability of individuals has become increasingly important to a variety of ecological questions. In this study,
I investigate how plant structure and changes in body size through development affect the movement ability of a predaceous
stinkbug, Podisus maculiventris, on three species of goldenrod (Solidago spp.) representing a wide range of surface complexities. I adapt existing techniques for quantifying movement in two dimensions
to the study of movement on natural plant structures in three dimensions. These experiments indicate that plant structure
and insect size are significant factors affecting the movement ability of P. maculiventris. Changes in movement ability due to factors of ontogeny and different habitat structures suggest that the scale of an individual’s
ambit or ecological sphere of influence may vary within its lifespan. Considering the influence of ontogeny and habitat structure
on movement ability may be useful to investigations of population dynamics, foraging behavior, and pest management.
Received: 14 July 1999 / Accepted: 23 March 2000 相似文献
6.
7.
8.
9.
Targeting of porin to the outer membrane of Escherichia coli. Rate of trimer assembly and identification of a dimer intermediate 总被引:14,自引:0,他引:14
J Reid H Fung K Gehring P E Klebba H Nikaido 《The Journal of biological chemistry》1988,263(16):7753-7759
Porin, a transmembrane protein in the outer membrane of Escherichia coli, exists in a trimeric structure which is not dissociated during sodium dodecyl sulfate-polyacrylamide gel electrophoresis at 25 degrees C. This unusual stability was utilized in the study of the conformational changes which accompany the targeting of porin to the outer membrane. A delay of 16-44 s between completion of synthesis of a monomer and its assembly into a trimer was found from the ratio of monomers to trimers found in exponentially growing cells. Pulse-chase experiments showed that rapid processing of precursor OmpF molecules was followed by assembly into sodium dodecyl sulfate-resistant oligomers with a half-time of 20 s at 30 degrees C. An intermediate in assembly was isolated by immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis below 10 degrees C and was identified as a metastable dimer. 相似文献
10.
David G. Reid David M. Doddrell Dudley H. Williams Keith R. Fox 《Biochimica et Biophysica Acta (BBA)/General Subjects》1984,798(1):111-114
Uniformly 15N-labelled triostin A and echinomycin have been prepared by growing the producing organisms on enriched media and their 15N nuclear magnetic resonance spectra partially assigned by a combination of nuclear Overhauser effect and scalar coupling constant measurements. Selective feeding experiments using unlabelled L-tryptophan-supplemented media have shown that N-1 and N-4 of the quinoxaline rings have their origins in the indole and amino groups of tryptophan, respectively. 相似文献