全文获取类型
收费全文 | 9638篇 |
免费 | 878篇 |
国内免费 | 14篇 |
出版年
2023年 | 35篇 |
2022年 | 31篇 |
2021年 | 225篇 |
2020年 | 119篇 |
2019年 | 146篇 |
2018年 | 172篇 |
2017年 | 151篇 |
2016年 | 267篇 |
2015年 | 440篇 |
2014年 | 457篇 |
2013年 | 596篇 |
2012年 | 778篇 |
2011年 | 689篇 |
2010年 | 442篇 |
2009年 | 471篇 |
2008年 | 607篇 |
2007年 | 549篇 |
2006年 | 552篇 |
2005年 | 487篇 |
2004年 | 485篇 |
2003年 | 463篇 |
2002年 | 411篇 |
2001年 | 139篇 |
2000年 | 118篇 |
1999年 | 117篇 |
1998年 | 100篇 |
1997年 | 63篇 |
1996年 | 65篇 |
1995年 | 56篇 |
1994年 | 70篇 |
1993年 | 59篇 |
1992年 | 82篇 |
1991年 | 63篇 |
1990年 | 65篇 |
1989年 | 74篇 |
1988年 | 62篇 |
1987年 | 51篇 |
1986年 | 48篇 |
1985年 | 39篇 |
1984年 | 48篇 |
1983年 | 55篇 |
1982年 | 35篇 |
1981年 | 44篇 |
1980年 | 40篇 |
1979年 | 56篇 |
1977年 | 32篇 |
1976年 | 36篇 |
1975年 | 32篇 |
1974年 | 37篇 |
1973年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 968 毫秒
71.
Computer simulations are used to predict the behavior of pollen grains with different physical properties within the acceleration field created around the ovules of the gymnosperm Ephedra trifurca. A modelling procedure is given that (1) calculates the number of pollen grains captured by an ovule's pollination-droplet and (2) gives a correlation between pollination efficiency and the physical properties (= mass, size) of different types of pollen. Based on this procedure, the number of Ephedra pollen grains captured by micropyles can be less than the number captured from other species. However, the mass and size of Ephedra pollen grains appear to coincide with those predicted to yield a local maximum of pollination efficiency, i.e. slightly larger or smaller values of either mass or size would decrease the probability of capture. In addition, the properties of Ephedra pollen grains operate synergistically in the aerodynamic environment around ovules and are focused to collide with pollination-droplets. By analogy, the properties of Ephedra pollen coincide with those predicted for a localized adaptive peak. The physical properties of pollen grain types other than E. trifurca that can maximize pollen capture are not generally represented in the aerobiology of Ephedra during the pollination season. Therefore, the phenology of pollen release, community taxonomic-composition, and the physics of particle capture play collectively important roles in the reproductive success of Ephedra trifurca. 相似文献
72.
Determination of Rubella Hemagglutination-Inhibiting Antibody in Whole Blood 总被引:1,自引:0,他引:1 下载免费PDF全文
A technique is described for determination of rubella hemagglutination-inhibiting antibody in only 50 to 100 muliters of whole blood. 相似文献
73.
74.
75.
76.
77.
Vincent Marks Denys Fry P. A. L. Chapple Geoffrey Gray 《BMJ (Clinical research ed.)》1969,2(5650):153-155
Experience with urine analysis for morphine using thin-layer chromatography in 310 cases of real or possible heroin abuse showed that it was valuable not only in detecting improper drug use but also in monitoring treatment. The results of this test can be available routinely in 24, and exceptionally in five hours. A negative result implies that the subject has taken less than 10 mg. of heroin in the past 24 hours. 相似文献
78.
P. C. Vincent G. Borner A. D. Chanana E. P. Cronkite M. L. Greenberg D. D. Joel L. M. Schiffer P. A. Stryckmans 《Cell proliferation》1969,2(3):235-247
Some of the time parameters of the cell cycle in bovine thoracic duct lymphocytes have been estimated by analysing labeled mitoses curves, and by double labeling. The two methods gave similar estimates of Ts. Thus, Ts measured directly from labeled mitoses curves varied from 4 to 6 hr, while the estimates from double labeling were 4.8 and 4.5 hr. T G measured directly from labeled mitoses curves was 5 hr, and estimates of TG from the values of Ts ranged from 6.3 to 7.7 hr. The present data confirm the short generative cycle of large thoracic duct lymphocytes. Extracorporeal irradiation of the lymph (ECIL) had no detectable effect on the cell cycle or the fractional production rate of the lymphocytes. However, the calculated absolute production was reduced following ECIL, due to a decrease in the absolute number of cells present. The grain count over mitoses after ECIL was approximately one-half that found before ECIL. 相似文献
79.
80.
Studies of the toxicity of 2,4,5,6-tetrachloroisophthalonitrile (TCIN) to cells of Saccharomyces pastorianus and Neurospora crassa showed that 2 to 4 μg/ml of the toxicant were required to inhibit growth. Several thiol compounds reversed toxicity to growth. Glucose oxidation was severely impaired in treated cells of both test organisms. The toxicant at 2 or 4 μg/ml markedly reduced soluble thiol content of these cells. Bound thiol content was less affected in S. pastorianus cells than soluble thiol content. Uptake of toxicant by yeast cells was accompanied by formation of derivatives, some of which resembled those formed by reaction of glutathione with TCIN in vitro. Coenzyme A, glutathione, and 2-mercaptoethanol readily formed derivatives with TCIN in vitro. The nature of these derivatives was studied using 2-mercaptoethanol products as model substituents. Four derivatives were formed with 2-mercaptoethanol each with similar functional groups but showing dissimilar degrees of mobility during silica gel chromatography. Evidence indicated that these are derivatives of TCIN in which 1 to 4 of the halogens has been substituted by 2-mercaptoethanol. The mechanism of fungicidal action of TCIN is attributed to thiol inactivation. 相似文献