全文获取类型
收费全文 | 112319篇 |
免费 | 2135篇 |
国内免费 | 888篇 |
专业分类
115342篇 |
出版年
2022年 | 99篇 |
2021年 | 204篇 |
2020年 | 174篇 |
2019年 | 192篇 |
2018年 | 12160篇 |
2017年 | 11010篇 |
2016年 | 7866篇 |
2015年 | 1242篇 |
2014年 | 1008篇 |
2013年 | 1311篇 |
2012年 | 5609篇 |
2011年 | 14197篇 |
2010年 | 12720篇 |
2009年 | 8778篇 |
2008年 | 10802篇 |
2007年 | 12422篇 |
2006年 | 1371篇 |
2005年 | 1527篇 |
2004年 | 1887篇 |
2003年 | 1929篇 |
2002年 | 1599篇 |
2001年 | 743篇 |
2000年 | 655篇 |
1999年 | 352篇 |
1998年 | 214篇 |
1997年 | 190篇 |
1996年 | 171篇 |
1995年 | 147篇 |
1994年 | 165篇 |
1993年 | 194篇 |
1992年 | 208篇 |
1991年 | 210篇 |
1990年 | 205篇 |
1989年 | 180篇 |
1988年 | 185篇 |
1987年 | 168篇 |
1986年 | 164篇 |
1985年 | 181篇 |
1984年 | 177篇 |
1983年 | 186篇 |
1982年 | 137篇 |
1981年 | 126篇 |
1980年 | 131篇 |
1979年 | 149篇 |
1978年 | 117篇 |
1977年 | 125篇 |
1976年 | 110篇 |
1973年 | 96篇 |
1972年 | 300篇 |
1971年 | 320篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
A comparison was made between a hay fed group, consisting of 23 ewes, and a grass silage fed group of 22 ewes, all pregnant. Excretion of Listeria monocytogenes (Lm) in the faeces and milk, antibody titres in sera and whey and delayed hypersensitivity against Lm, and several blood components were determined. The animals had previously been exposed to Lm, and Lm was isolated from the faeces from several animals when the experiment started. No significant difference in number of excretors between the 2 groups was found during the experimental period. The haemagglutination titres in both sera and whey were low and on the same level in both groups. The titres were higher in animals with 1 foetus than in animals with more than 1 foetus. In the first part of the experimental period the silage group had a reduced number of lymphocytes, lower total serum protein values and higher serum iron values, compared with the hay group. The silage group also had a stronger delayed hypersensitivity reaction against Lm than the hay group, and in the silage group the reaction was significantly stronger in ewes with 3 or more foetuses than in ewes with 1 foetus. In conclusion, the combined effect of some of the changes found in animals fed grass silage may leave them more susceptible to infections. 相似文献
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.
From three Fouquieria sp. 12 iridoid glucosides were isolated and identified. Eight of these were structurally related to galioside (monotropein methylester), while four were hydroxy substitution products of deoxyloganin. In three cases the glucoside occurred together with the corresponding 10-O-acetate. 相似文献
8.
9.
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
10.
Erwan Stephan Stéphane Delanaud Cécile Bisch Jean-Pierre Libert Frédéric Telliez 《Journal of electromyography and kinesiology》2008,18(1):160-168
We present here a new, dedicated mechanical device for monitoring quick-release movements of the wrist. The ergometer was designed to easily assess musculotendinous properties during wrist flexion. Maximal voluntary contractions (MVC) and quick-release (QR) movements during wrist flexion were performed on 14 subjects. A validation of the ergometer, using a test-retest methodology, was performed to assess its reliability and sensitivity. The device has been technically and biomechanically validated in a range of situations, including inertia measurement (mean inertia was found 0.0119+/-0.0012 N m s(2) rad(-1)) and appearance of the unloading reflex. Our results indicate that the device provides highly reliable, sensitive evaluation of wrist muscle stiffness (intraclass correlation coefficient for inertia, maximal voluntary contraction and stiffness index were 0.873, 0.994 and 0.930, respectively). Its portability facilitates measurement of the influence of repetitive, occupational activity on the musculotendinous complex of the wrist flexors. 相似文献