全文获取类型
收费全文 | 11892篇 |
免费 | 1684篇 |
国内免费 | 1篇 |
出版年
2021年 | 195篇 |
2020年 | 110篇 |
2019年 | 134篇 |
2018年 | 155篇 |
2017年 | 143篇 |
2016年 | 233篇 |
2015年 | 359篇 |
2014年 | 414篇 |
2013年 | 477篇 |
2012年 | 649篇 |
2011年 | 629篇 |
2010年 | 358篇 |
2009年 | 329篇 |
2008年 | 502篇 |
2007年 | 544篇 |
2006年 | 440篇 |
2005年 | 433篇 |
2004年 | 371篇 |
2003年 | 377篇 |
2002年 | 357篇 |
2001年 | 356篇 |
2000年 | 353篇 |
1999年 | 297篇 |
1998年 | 159篇 |
1997年 | 141篇 |
1996年 | 124篇 |
1995年 | 140篇 |
1994年 | 151篇 |
1993年 | 123篇 |
1992年 | 257篇 |
1991年 | 215篇 |
1990年 | 229篇 |
1989年 | 255篇 |
1988年 | 358篇 |
1987年 | 217篇 |
1986年 | 170篇 |
1985年 | 191篇 |
1984年 | 150篇 |
1983年 | 149篇 |
1982年 | 123篇 |
1981年 | 104篇 |
1980年 | 119篇 |
1979年 | 134篇 |
1978年 | 124篇 |
1977年 | 134篇 |
1976年 | 100篇 |
1974年 | 113篇 |
1973年 | 112篇 |
1972年 | 101篇 |
1970年 | 104篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
M. J. D. White 《Australian Journal of Entomology》1970,9(1):1-6
i
The essence of speciation lies in the origin of genetic isolating mechanisms. Argument has raged as to whether the primary isolating mechanisms which initiate specific divergence operate at the pre-mating or post-mating level and whether complete geographic isolation necessarily precedes divergence. Speciation is essentially a cytogenetic process and the role of chromosomal rearrangements as primary isolating factors has probably been underestimated in the past. But speciation depends on many factors such as population size, vagility and type of life cycle, so it is unlikely that any universal model is applicable. 相似文献
The essence of speciation lies in the origin of genetic isolating mechanisms. Argument has raged as to whether the primary isolating mechanisms which initiate specific divergence operate at the pre-mating or post-mating level and whether complete geographic isolation necessarily precedes divergence. Speciation is essentially a cytogenetic process and the role of chromosomal rearrangements as primary isolating factors has probably been underestimated in the past. But speciation depends on many factors such as population size, vagility and type of life cycle, so it is unlikely that any universal model is applicable. 相似文献
32.
33.
Jason C. White 《Arts Education Policy Review》2016,117(1):55-64
While there are many educational and experiential benefits to attending professional higher arts education programs, students who incur excessive student loan debt during their studies may experience unanticipated or poor professional outcomes either over the course of their artistic careers, shortly after the expiration of a loan grace period, or after they can no longer defer payments. To date, little to no research exists on the effects of an excessive student loan debt burden on professional arts careers. To address this gap in the higher arts education literature, and in an effort to facilitate scholarly discussion on the topic, this article identifies concerns, consequences, and potential interventions. 相似文献
34.
A Banerjee M A Jordan R F Luduena 《Biochemical and biophysical research communications》1985,128(2):506-512
Incubation of phosphocellulose-purified tubulin with GSH at 30 degrees C results in an inhibition of colchicine binding activity. GSSG has a protective effect against the GSH-induced loss of colchicine-binding. Incubation of tubulin with GSH at 30 degrees C results in the formation of abnormal tubulin polymers which are insensitive to cold. Such aggregation is insensitive to antimicrotubular drugs. Aggregation is inhibited by GSSG but not by DTT or mercaptoethanol. GSH-induced aggregation is very sensitive to the ionic strength of the assembly medium; both the aggregation and colchicine binding inhibition induced by GSH are inhibited at higher ionic strength. These results indicate a very complex interaction of GSH with tubulin. 相似文献
35.
36.
37.
38.
39.
P. White 《BMJ (Clinical research ed.)》1989,298(6682):1199-1200
40.
M. D. Furones † D. J. Alderman D. Bucke T. C. Fletcher ‡§ D. Knox ‡ A. White ‡§ 《Journal of fish biology》1992,41(6):1037-1041
Rainbow trout fed diets containing 7, 86 or 806 mg vitamin E kg−1 for 22 weeks were exposed to virulent Yersinia ruckeri by bath or injection. Mortalities were always least among those fed the highest concentration of vitamin E but serum antibody production was not affected by vitamin E levels. 相似文献