全文获取类型
收费全文 | 3786篇 |
免费 | 407篇 |
国内免费 | 1篇 |
专业分类
4194篇 |
出版年
2022年 | 28篇 |
2021年 | 61篇 |
2019年 | 38篇 |
2018年 | 43篇 |
2017年 | 28篇 |
2016年 | 85篇 |
2015年 | 115篇 |
2014年 | 148篇 |
2013年 | 159篇 |
2012年 | 196篇 |
2011年 | 184篇 |
2010年 | 106篇 |
2009年 | 112篇 |
2008年 | 163篇 |
2007年 | 155篇 |
2006年 | 138篇 |
2005年 | 120篇 |
2004年 | 137篇 |
2003年 | 129篇 |
2002年 | 126篇 |
2001年 | 98篇 |
2000年 | 100篇 |
1999年 | 77篇 |
1998年 | 45篇 |
1997年 | 28篇 |
1996年 | 28篇 |
1995年 | 36篇 |
1994年 | 33篇 |
1993年 | 46篇 |
1992年 | 80篇 |
1991年 | 71篇 |
1990年 | 68篇 |
1989年 | 67篇 |
1988年 | 67篇 |
1987年 | 62篇 |
1986年 | 43篇 |
1985年 | 50篇 |
1984年 | 68篇 |
1983年 | 49篇 |
1982年 | 38篇 |
1981年 | 35篇 |
1980年 | 45篇 |
1979年 | 45篇 |
1978年 | 46篇 |
1977年 | 42篇 |
1976年 | 54篇 |
1975年 | 44篇 |
1974年 | 39篇 |
1973年 | 46篇 |
1972年 | 30篇 |
排序方式: 共有4194条查询结果,搜索用时 0 毫秒
101.
Isolation and partial purification of the major abundant class rat seminal vesicle poly(A+)-messenger RNA 总被引:1,自引:1,他引:0 下载免费PDF全文
Per-Erik Mansson Donald B. Carter Alan B. Silverberg Douglas B. Tully Stephen E. Harris 《Nucleic acids research》1979,7(6):1553-1565
Total poly(A(+))-RNA (poly(A(+))-RNA(tot)) was isolated from rat seminal vesicle and its size distribution determined by 70% formamide 5-25% sucrose density analysis. One major peak was resolved in the 10-13 S region and accounted for approximately 35% of the total poly(A(+))-RNA applied. Preparative 1% SDS, 5-20% linear sucrose density gradients also resolved a single major peak in the 11S region (poly(A(+))(11S). Analysis of poly(A(+))-RNA(tot) and poly(A(+))-RNA(11S) under denaturing conditions on 2% agarose gel electrophoresis demonstrated two major components in both poly(A(+))-RNA populations. Size estimations for these components are 620 and 540 NT respectively. (3)H-cDNA was made to both poly(A(+))-RNA(tot) and poly(A(+))-RNA(11S). Back-hybridization of poly(A(+))-RNA(tot) and poly(A(+))-RNA(11S) to their respective (3)H-cDNA revealed a highly abundant class representing 41% and 85% of the sequences in their respective (3)H-cDNA's. The highly abundant class corresponded to 3-5 sequences present in 30,000-50,000 copies/cell. Invitro translation of poly(A(+))-RNA(11S) resulted in two major polypeptides coded for by the 620 NT long and 540 NT long poly(A(+))-RNA respectively.Images 相似文献
102.
Hydrogen evolution and uptake by nodules of soybeans inoculated with different strains of Rhizobium japonicum 总被引:16,自引:0,他引:16
Hydrogen evolved by nitrogenase may be recycled by a hydrogenase present in some legume nodules. Anoka and Portage cultivars of soybeans were inoculated with each of 8 and 24 strains, respectively, of Rhizobium japonicum and surveyed for H2 evolution and C2H2 reduction rates nodule weight, and plant dry weight. Six of the strains (3Ilb 110, USDA 122, USDA 136, 3Ilb 6, 3Ilb 142, and 3Ilb 143) which exhibited no H2 evolution in air were shown to take up H2. The relative efficiencies of nitrogenase energy utilization based on C2H2 reduction rates of nodules relative efficiences of nitrogenase energy utilization based on C2H2 reduction rates of nodules ranged from 0.96 to 1.0 for the six strains. Nodules formed by strain WA 5099-1-1 evolved small amounts of H2 in air and had a relative efficiency of 0.92. Nodules formed by the remaining 25 strains had relative efficiencies ranging from 0.41 to 0.80. A H2-evolving (3Ilb 123) and non-H2-evolving (3Ilb 143) strain were tested on seven soybean cultivars to determine the effect on the expression of hydrogenase. Nodules formed by strain 3Ilb 143 exhibited an efficiency of 1.0 on the following cultivars: Amsoy 71, Anoka, Bonus, Clark 63, Kent, Peking, and Portage. Relative efficiencies from 0.63 to 0.77 were determined for the five cultivars nodulated by strain 3Ilb 123. From the experiments with these cultivars, the capacity to recycle H2 produced from the nitrogenase system appears to be determined by the R. japonicum strain. 相似文献
103.
The cytology of Brachycome 总被引:1,自引:1,他引:0
C. R. Carter 《Chromosoma》1978,67(2):109-121
Over 1,000 plants of B. dichromosomatica have been counted. 10% of these carried one, two or three B chromosomes. The B chromosome is large, and though it is not heteropycnotic it condenses precociously at mitosis. It behaves regularly at mitosis, and when two are present they pair regularly at meiosis. Non-disjunction and preferential distribution of the B to the generative nucleus occurs at the first pollen grain mitosis, with very high frequency. This is corroborated by data from crosses, which also indicate that the transmission of the B through the female gamete is normal. — The frequency of B chromosomes in marginal populations of var. dichromosomatica is significantly higher than in central populations. In one population of var. alba the frequency of Bs increased significantly after two very dry seasons. It is suggested that both these cases of increased frequency were in response to a selective advantage of plants with Bs under arid conditions. — Plants with one B chromosome appear to be less fit than plants with 2 Bs. The combination of the calculated effects of the nondisjunction mechanism and the inferred relative fitness of the 0B, 1B and 2B plants, provides a reasonable explanation of the observed frequencies of the 0B, 1B and 2B plants in the populations studied. 相似文献
104.
105.
106.
107.
Cleavage of adeno-associated virus DNA with Sali,Psti and Haeii restriction endonucleases. 总被引:2,自引:0,他引:2 下载免费PDF全文
Duplex AAV-2 DNA was digested with SalI, PstI or HaeII restriction endonucleases and the cleavage sites were mapped. SalI cleaves AAV DNA at 0.310 map units, PstI at 0.106, 0.422 and 0.914 and the five HaeII sites were mapped at 0.110. 0.156, 0.181, 0.536 and 0.600 map units. These cleavage products will be useful for the isolation of specific regions from the AAV DNA, located outside of the stably transcribed region of the genome, and will also help to map more complex restriction enzyme cleavages. 相似文献
108.
Morphological changes in the chorion of the Medaka, Oryzias latipes, brought about by the hatching enzyme were examined by transmission as well as scanning electron microscopy. The structure of the intact chorion, especially its thick multilamellar inner layer, does not change during development until about 1 hr before the onset of hatching. As choriolysis proceeds, the inner layer of the chorion is digested to yield soluble proteins of relatively high molecular weight. During this process it appears that each lamella is successively solubilized from the inner surface of the chorion. Finally, a thin outer layer with accompanying villi and attaching filaments remains.Under the experimental conditions used, the enzyme was in direct contact with both the inner and outer layers of the chorion. Because of this, the enzyme could penetrate the outer layer and act on some peripheral parts of the underlying inner layer. Based on these morphological changes, a mechanism is proposed to account for the solubilization of the chorion by the hatching enzyme. 相似文献
109.
110.
Estrogen and the induction of lordosis in female and male prairie voles (Microtus ochrogaster) 总被引:1,自引:0,他引:1
Estrogen elicited lordosis in ovariectomized female prairie voles (Microtus ochrogaster). Treatment with estradiol benzoate (EB) was particularly effective if administered as multiple injections. Very high dose levels were not, in general, any more effective than lower doses. Individual animals typically showed lordosis within 24 to 48 hr following the onset of EB treatment and prolonged treatments did not increase the percentage of females responding to EB. Castrated male prairie voles did not respond with lordosis to repeated daily injections of 10 micrograms EB given for a period of 15 consecutive days. 相似文献