全文获取类型
收费全文 | 2463篇 |
免费 | 75篇 |
国内免费 | 13篇 |
专业分类
2551篇 |
出版年
2015年 | 19篇 |
2014年 | 13篇 |
2013年 | 56篇 |
2012年 | 59篇 |
2011年 | 50篇 |
2010年 | 63篇 |
2009年 | 110篇 |
2008年 | 79篇 |
2007年 | 60篇 |
2006年 | 58篇 |
2005年 | 51篇 |
2004年 | 50篇 |
2003年 | 25篇 |
2002年 | 15篇 |
2001年 | 14篇 |
2000年 | 17篇 |
1999年 | 28篇 |
1998年 | 36篇 |
1997年 | 41篇 |
1996年 | 36篇 |
1995年 | 27篇 |
1994年 | 23篇 |
1993年 | 18篇 |
1992年 | 34篇 |
1991年 | 13篇 |
1990年 | 23篇 |
1989年 | 22篇 |
1988年 | 19篇 |
1987年 | 21篇 |
1986年 | 19篇 |
1985年 | 19篇 |
1984年 | 14篇 |
1983年 | 19篇 |
1981年 | 21篇 |
1980年 | 14篇 |
1979年 | 20篇 |
1977年 | 15篇 |
1971年 | 16篇 |
1959年 | 49篇 |
1958年 | 123篇 |
1957年 | 137篇 |
1956年 | 134篇 |
1955年 | 149篇 |
1954年 | 150篇 |
1953年 | 119篇 |
1952年 | 104篇 |
1951年 | 98篇 |
1950年 | 59篇 |
1949年 | 14篇 |
1948年 | 23篇 |
排序方式: 共有2551条查询结果,搜索用时 15 毫秒
961.
LOUISE E. M. VET RUURD DE JONG WILANT A. VAN GIESSEN J. H. VISSER† 《Physiological Entomology》1990,15(2):243-247
ABSTRACT Odour responses of parasitic insects, in search of their hosts, can change due to experience. Leptopilina heterotoma (Thomson) (Hymenoptera; Eucoilidae), a parasitic wasp of drosophilid larvae, is known to alter its preference for odours emanating from host food substrates through learning. These kinds of behavioural modifications in insects are assumed to be the result of complex processes in the brain. The results presented in this report, however, suggest that this learning-related behavioural variation is not restricted to brain processes but that it involves changes in sensitivity of olfactory receptor neurones. 相似文献
962.
963.
W. ALBERTIN P. MARULLO M. AIGLE A. BOURGAIS M. BELY C. DILLMANN D. DE VIENNE D. SICARD 《Journal of evolutionary biology》2009,22(11):2157-2170
Partial or whole‐genome duplications have played a major role in the evolution of new species. We have investigated the variation of ploidy level in a panel of domesticated strains of Saccharomyces cerevisiae coming from different geographical origins. Segregation studies and crosses with tester strains of different ploidy levels showed that part of the strains were well‐balanced autotetraploids displaying tetrasomic inheritance. The presence of up to four different alleles for various loci is consistent with a polyploidization mechanism relying on the fusion of two nonreduced meiospores coming from two S. cerevisiae strains. Autotetraploidy was also in accordance with karyotype and flow cytometry analyses. Interestingly, most bakery strains were tetraploids, suggesting a link between ploidy level and human use. The null or drastically reduced fertility of the hybrids between tetraploid and diploid strains indicated that domesticated S. cerevisiae strains are composed of two groups isolated by post‐zygotic reproductive barriers. 相似文献
964.
The Wachstein and Meisel incubation medium was used to detect ATPase activity in epimastigote, spheromastigote (amastigote), and bloodstream trypomastigote forms of Trypanosoma cruzi. Reaction product, indicative of enzyme activity, was associated with the plasma membrane covering the cell body and the flagellum of the parasite. No reaction product was found in the portion of the plasma membrane lining the flagellar pocket. The plasma membrane-associated ATPase activity was not inhibited by ouabain or oligomycin, was detected in incubation medium without K+, was inhibited by prolonged glutaraldehyde fixation, and its activity was diminished when Mg2+ was omitted from the incubation medium. The Ernst medium was used to detect Na+-K+-ATPase activity in T. cruzi. No reaction product indicative of the presence of this enzyme was detected. Reaction product indicative of 5'-nucleotidase was not detected in T. cruzi. Acid phosphatase activity was detected in lysosomes. These results indicate that a Mg2+-activated ATPase is present in the plasma membrane of T. cruzi and that it can be used as an enzyme marker, provided that the mitochondrial and flagellar ATPases are inhibited, to assess the purity of plasma membrane fractions isolated from this parasite. 相似文献
965.
966.
967.
DE MEYER R 《Archives de biologie》1952,63(4):455-514
968.
969.
970.