全文获取类型
收费全文 | 1370180篇 |
免费 | 123212篇 |
国内免费 | 1419篇 |
专业分类
1494811篇 |
出版年
2021年 | 17911篇 |
2019年 | 16204篇 |
2018年 | 17927篇 |
2017年 | 16714篇 |
2016年 | 28278篇 |
2015年 | 42618篇 |
2014年 | 50596篇 |
2013年 | 76977篇 |
2012年 | 37461篇 |
2011年 | 25990篇 |
2010年 | 43751篇 |
2009年 | 45115篇 |
2008年 | 24759篇 |
2007年 | 22562篇 |
2006年 | 27783篇 |
2005年 | 28759篇 |
2004年 | 27972篇 |
2003年 | 25449篇 |
2002年 | 23616篇 |
2001年 | 35127篇 |
2000年 | 32607篇 |
1999年 | 32576篇 |
1998年 | 25736篇 |
1997年 | 25523篇 |
1996年 | 25016篇 |
1995年 | 23165篇 |
1994年 | 22999篇 |
1993年 | 22136篇 |
1992年 | 28398篇 |
1991年 | 26588篇 |
1990年 | 25486篇 |
1989年 | 26345篇 |
1988年 | 24065篇 |
1987年 | 22885篇 |
1986年 | 21716篇 |
1985年 | 23553篇 |
1984年 | 23183篇 |
1983年 | 20491篇 |
1982年 | 20804篇 |
1981年 | 19940篇 |
1980年 | 18778篇 |
1979年 | 19336篇 |
1978年 | 18152篇 |
1977年 | 17277篇 |
1976年 | 16524篇 |
1975年 | 16053篇 |
1974年 | 16338篇 |
1973年 | 16695篇 |
1972年 | 14102篇 |
1971年 | 12818篇 |
排序方式: 共有10000条查询结果,搜索用时 2 毫秒
911.
912.
C-Type Virus Released from Cultured Human Rhabdomyosarcoma Cells 总被引:44,自引:0,他引:44
R. M. McALLISTER M. NICOLSON M. B. GARDNER R. W. RONGEY S. RASHEED P. S. SARMA R. J. HUEBNER M. HATANAKA S. OROSZLAN R. V. GILDEN A. KABIGTING L. VERNON 《Nature: New biology》1972,235(53):3-6
RD-114 virus, released from human rhabdomyosarcoma cells, has all the characteristics of a mammalian C-type virus. Immunological tests indicate that it differs from all known C-type viruses and is the most likely candidate for a human C-type virus yet described. 相似文献
913.
Effect of freezing on dehydrogenase activity and reduction of triphenyl tetrazolium chloride 总被引:5,自引:0,他引:5
P L Steponkus 《Cryobiology》1971,8(6):570-573
914.
915.
P K Kinnunen 《Chemistry and physics of lipids》1992,63(3):251-258
A model for the molecular mechanism of the fusion of lipid bilayers is described. A crucial feature of this model and related to the lamellar-->hexagonal phase HII transition is a novel, hypothetical lipid conformation, tentatively referred to here as extended. During fusion this conformation could manifest itself in the contact site between two vesicles in close proximity and involves the extension of the acyl chains of a phospholipid molecule in opposite directions, i.e. embedded into the two opposing bilayers while maintaining the headgroup in the interface. Although evidence for the occurrence of the extended conformation for phospholipids is sparse this conformation appears to be compatible with currently available experimental data. Of importance also is that the extended conformation allows for the fusion of two bilayer membranes to proceed with minimal exposure of the lipid hydrocarbon chains to water. It can also account for other features of membrane fusion such as lipid mixing in the intermediate state without mixing of the vesicle contents as well as for the molecular basis of the action of fusogenic lipids. 相似文献
916.
Populations of the Australian sleepy lizard, Tiliqua rugosa, near Mt. Mary, South Australia carry natural infestations of two tick species Aponomma hydrosauri and Amblyomma limbatum. In field experiments at two sites, 18 km apart, lizards with experimentally increased tick loads had smaller home ranges,
moved shorter distances in a day, and were found basking more but moving less often than lizards from which ticks were experimentally
removed. The results were consistent for adult lizards in two years, and for sub-adults in a third year. Laboratory trials
showed that juvenile lizards that had tick infestations had lower sprint speeds than uninfested siblings, and that adults
with tick infestations had less endurance than those that were uninfested. The results contrast with those of a previous survey
that showed that lizards with high tick loads had greater body size and remained longer at a site, but indicate that there
may be a balance, for lizards, between the fitness advantages in occupying habitats with high-quality resources, and the costs
from parasites that also prefer those habitats.
Received: 02 March 1999 / Accepted: 07 October 1999 相似文献
917.
Iu P Kostilenko 《Arkhiv anatomii, gistologii i émbriologii》1984,87(10):60-63
At various regimens of the secretory activity in the palatile salivary glands, changes occurring in the transversal profiles of the postcapillary venules, but not of the blood capillaries, are most noticeable. Under food stimulation of secretion, the former dilate essentially, that can demonstrate certain functional hyperemia developing in the palatine salivary glands. Some previous experiments concerning interpretation of principles on the microcirculatory bed spatial organization give a good reason to suggest that dilatation of the postcapillary venules is connected with an increased blood perfusion in the canals of the preferrable blood stream. The postcapillary dilatation is possible because blood from the precapillaries gets into the capacitance blood microvessels and its volume at that moment is greater than the capacity of the venous microvessels. A suggestion is made that filtrative function of the palatile salivary glands depends on development of the functional hyperemia. It is possible, that this mechanism is universal, since owing to it, reflectory reactions of the salivary glands directed to the immediate secure of the oral cavity with a necessary amount of liquor become possible. 相似文献
918.
G. F. Katekak 《Biologia Plantarum》1985,27(2-3):92-99
The chemical and stereochemical properties of phytotropins are described in terms of a receptor model, based on their ability
to bind to a receptor isolated from maize coleoptiles. Their root gravitropic properties are correlated with their ability
to bind to the receptor. It is suggested that their ability to inhibit auxin transport, without more, may not be enough to
explain their physiological effects. 相似文献
919.
920.
Infections of one and two Hymenolepis diminuta established in newly weaned rats continued to grow for the duration of the experiment (238 days), whereas infections of 5 worms per rat became asymptotic around Day 55 postinfection and remained at or below this level thereafter as shown by biomass and mean weight per worm measurements. Infections of 50 worms established in newly weaned rats became asymptotic around Day 28 postinfection and thereafter worms were lost from the rats. Initially the biomass fell with the loss of worms, but by Day 56 a new lower biomass persisted for the remainder of the infection period. This level was maintained, despite diminishing numbers of worms, due to the growth of surviving individuals to a weight exceeding the original weight at maturity by a factor of more than 2. Experiments using rats that were mature at the time of infection demonstrated that the same response occurred, but approximately 3 weeks earlier. 相似文献