全文获取类型
收费全文 | 201352篇 |
免费 | 9202篇 |
国内免费 | 10955篇 |
专业分类
221509篇 |
出版年
2024年 | 275篇 |
2023年 | 1537篇 |
2022年 | 3473篇 |
2021年 | 5859篇 |
2020年 | 4037篇 |
2019年 | 5009篇 |
2018年 | 15351篇 |
2017年 | 13150篇 |
2016年 | 11661篇 |
2015年 | 7657篇 |
2014年 | 8607篇 |
2013年 | 9091篇 |
2012年 | 14426篇 |
2011年 | 21503篇 |
2010年 | 17188篇 |
2009年 | 13107篇 |
2008年 | 15453篇 |
2007年 | 16371篇 |
2006年 | 5030篇 |
2005年 | 4285篇 |
2004年 | 4189篇 |
2003年 | 3942篇 |
2002年 | 3214篇 |
2001年 | 2207篇 |
2000年 | 1953篇 |
1999年 | 1775篇 |
1998年 | 1103篇 |
1997年 | 1098篇 |
1996年 | 1005篇 |
1995年 | 859篇 |
1994年 | 819篇 |
1993年 | 661篇 |
1992年 | 850篇 |
1991年 | 660篇 |
1990年 | 484篇 |
1989年 | 452篇 |
1988年 | 377篇 |
1987年 | 363篇 |
1986年 | 267篇 |
1985年 | 291篇 |
1984年 | 167篇 |
1983年 | 180篇 |
1982年 | 112篇 |
1981年 | 85篇 |
1980年 | 61篇 |
1979年 | 78篇 |
1977年 | 59篇 |
1975年 | 62篇 |
1972年 | 296篇 |
1971年 | 294篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
1.
2.
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
3.
4.
5.
6.
7.
Characterization of phosphotyrosyl-protein phosphatase activity associated with calcineurin 总被引:3,自引:0,他引:3
J Chernoff M A Sells H C Li 《Biochemical and biophysical research communications》1984,121(1):141-148
Calcineurin purified from bovine brain is shown to possess phosphotyrosyl -protein phosphatase activity towards proteins phosphorylated by the epidermal growth factor receptor/kinase. The phosphatase activity is augmented by Ca2+/calmodulin or divalent cation (Ni2+ greater than Mn2+ greater than Mg2+ greater than Co2+). In the simultaneous presence of all three effectors, the enzymatic activity is synergistically increased. Ca2+/calmodulin activates the Mg2+-supported activity by decreasing the Km value for phosphotyrosyl -casein from 2.2 to 0.6 microM, and increasing the Vmax from 0.4 to 4.6 nmol/min/mg. These results represent the first demonstration that calcineurin can dephosphorylate phosphotyrosyl -proteins and suggest a novel mechanism of activation of this enzyme. 相似文献
8.
9.
E Giannazzo F Licata G Li Volsi G Mio F Santangelo M Scivoli 《Bollettino della Società italiana di biologia sperimentale》1992,68(11):677-683
A computer-assisted analysis of the spatial distribution of neurons having homogeneous characteristics is described in this paper. The camera lucida drawings of sections of a brain nucleus and the points representing the neurons labeled on the basis of a specific behavior of discharge rates were digitized on a personal computer Amiga 2000 or IBM compatible. Our software provided: a) the computerized, stereotaxically oriented reconstruction of the stored sections and of the plotted neurons; b) the identification within each section of the mass center (MC) of the units sharing a given behavior and of the area where the density of such neurons was maximal (MDA). The routine was tested on the spatial distribution of neuronal responses to serotonin in the lateral vestibular nucleus. 相似文献
10.
IN addition to its well known antiviral activity, interferon has recently been shown to inhibit the multiplication of tumour and mammalian cells in cell culture1–6. We report here the inhibition by interferon of DNA synthesis induced in mouse spleen lymphocytes by the non-viral stimuli phytohaemagglutinin (PHA) and allogeneic lymphocytes. These findings are in accord with our contention that interferon affects cell function and, furthermore, they suggest that by acting on lymphocytes, interferon plays a role in the immunological response of the host. 相似文献