全文获取类型
收费全文 | 1337298篇 |
免费 | 145378篇 |
国内免费 | 647篇 |
专业分类
1483323篇 |
出版年
2018年 | 11898篇 |
2016年 | 16420篇 |
2015年 | 22403篇 |
2014年 | 26357篇 |
2013年 | 37690篇 |
2012年 | 42322篇 |
2011年 | 43050篇 |
2010年 | 29575篇 |
2009年 | 27545篇 |
2008年 | 39077篇 |
2007年 | 40412篇 |
2006年 | 37747篇 |
2005年 | 36404篇 |
2004年 | 36086篇 |
2003年 | 34734篇 |
2002年 | 33879篇 |
2001年 | 55220篇 |
2000年 | 54914篇 |
1999年 | 44429篇 |
1998年 | 17348篇 |
1997年 | 17754篇 |
1996年 | 16834篇 |
1995年 | 15800篇 |
1994年 | 15462篇 |
1993年 | 15437篇 |
1992年 | 37298篇 |
1991年 | 36612篇 |
1990年 | 35852篇 |
1989年 | 35017篇 |
1988年 | 32399篇 |
1987年 | 31413篇 |
1986年 | 29144篇 |
1985年 | 29276篇 |
1984年 | 24396篇 |
1983年 | 21400篇 |
1982年 | 16652篇 |
1981年 | 15032篇 |
1980年 | 14169篇 |
1979年 | 23332篇 |
1978年 | 18678篇 |
1977年 | 16939篇 |
1976年 | 16087篇 |
1975年 | 17839篇 |
1974年 | 19240篇 |
1973年 | 18955篇 |
1972年 | 17182篇 |
1971年 | 15688篇 |
1970年 | 13574篇 |
1969年 | 13176篇 |
1968年 | 11673篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Hostile intercommunity relations, including attacking and killing extra-community infants of both sexes have occurred at most
wild chimpanzee sites. We describe three recent cases of intercommunity attacks on infants committed by members of the Ngogo
chimpanzee community in Kibale National Park, Uganda. Two of the attacks resulted in confirmed infanticides while a third
attack probably resulted in the infant's death. In common with previous accounts of chimpanzee infanticides, the attacks described
here occurred during boundary patrols outside the Ngogo community's usual range, adult and adolescent males were the main
participants, one infant was cannibalized after being killed, and the victims’ mothers did not accompany the attacking party
back to the Ngogo range. However, the patrol parties during each infanticide were larger than before and included females
from the Ngogo community. Our observations indirectly support both the range expansion and imbalance of power hypotheses,
which address why and under which conditions chimpanzee intercommunity encounters lead to aggression. These cases of intercommunity
infanticide add to the growing database of the phenomenon in wild chimpanzees. 相似文献
72.
Formation of rings from Drosophila DNA fragments 总被引:1,自引:0,他引:1
73.
J.G. Roddick 《Phytochemistry》1974,13(1):9-25
The literature relating to chemical, biochemical and biological aspects of the steroidal glycoalkaloid, α-tomatine, is reviewed. The alkaloid, which can be used as a starting compound for the synthesis of steroidal hormones, is toxic to a wide range of living organisms. The significance of tomatine to plants which elaborate it is discussed and some possible uses of the compound are mentioned. 相似文献
74.
Four myeloid cell lines (M1, WEHI-3B D+, FDC-P1, and 32D) were screened for the presence of J11d antigen. One of these cell lines, the myeloid leukemia M1, was found to express a high level of J11d antigen on the cell surface. Recombinant mouse leukemic inhibitory factor (rm-LIF), recombinant human LIF (rh-LIF), and steroids (hydrocortisone and dexamethasone) could induce M1 cells to undergo monocytic differentiation. The level of J11d antigen was greatly reduced after treatment of the cells with LIF or steroids. Western blotting revealed that the apparent molecular weight of the J11d antigen on M1 cells was 45-48 kDa. Furthermore, the level of J11d mRNA was also reduced during LIF-induced differentiation of M1 cells. 相似文献
75.
76.
77.
A. R. E. SINCLAIR 《African Journal of Ecology》1973,11(1):93-107
Censuses of buffalo and wildebeest in the Serengeti-Mara region have been carried out by various workers at intervals since 1958. The methods of these censuses, which normally employ a total count, are described and the errors inherent in such techniques are analysed in detail. After the appropriate corrections had been made the results showed that both populations have increased considerably over the years 1961–1971. 相似文献
78.
79.
T. B. Lapirova V. R. Mikryakova A. S. Mavrin G. A. Yinogradova 《Journal of Evolutionary Biochemistry and Physiology》2000,36(1):47-51
The paper presents data on a change in lysozyme content in tissues of spleen, liver and heart in fry of the Lena River sturgeon
exposed to the presence of sublethal concentrations of Hg2+, Cd2+, and Cu2+ under conditions of chronic experiment. It has been shown that the lysozyme content in fish tissues varies and has a phasic
character. The amplitude of fluctuations of this parameter depends on the moment of sampling, nature of the toxicant, and
structural-functional organization of the studied organs. 相似文献
80.
Staphylococcal gamma-hemolysin and leukocidin are bi-component cytolysins, consisting of LukF (or Hlg1)/Hlg2 and LukF/LukS, respectively. Here, we purified serum inhibitors of gamma-hemolysin and leukocidin from human plasma. Protein sequencing showed that the purified inhibitors of 62, 57, 50 and 38 kDa were the vitronectin fragments with truncation(s) of the C-terminal or both N- and C-terminal regions. The purified vitronectin fragments specifically bound to the Hlg2 component of gamma-hemolysin and the LukS component of leukocidin to form high-molecular-weight complexes with them, leading to inhibition of the toxin-induced lysis of human erythrocytes and human polymorphonuclear leukocytes, respectively. Intact vitronectin also showed inhibitory activity to the toxins. The ability of gamma-hemolysin and leukocidin to bind vitronectin and its fragments is a novel function of the pore-forming cytolysins. 相似文献