全文获取类型
收费全文 | 535574篇 |
免费 | 61472篇 |
国内免费 | 295篇 |
出版年
2018年 | 5930篇 |
2017年 | 5446篇 |
2016年 | 8111篇 |
2015年 | 12162篇 |
2014年 | 13127篇 |
2013年 | 18275篇 |
2012年 | 21446篇 |
2011年 | 21138篇 |
2010年 | 13826篇 |
2009年 | 12119篇 |
2008年 | 18206篇 |
2007年 | 18608篇 |
2006年 | 16880篇 |
2005年 | 16346篇 |
2004年 | 15914篇 |
2003年 | 15056篇 |
2002年 | 14290篇 |
2001年 | 23061篇 |
2000年 | 23138篇 |
1999年 | 18651篇 |
1998年 | 6834篇 |
1997年 | 6939篇 |
1996年 | 6711篇 |
1995年 | 6128篇 |
1994年 | 6180篇 |
1993年 | 5912篇 |
1992年 | 14530篇 |
1991年 | 13777篇 |
1990年 | 13405篇 |
1989年 | 13187篇 |
1988年 | 11812篇 |
1987年 | 11311篇 |
1986年 | 10349篇 |
1985年 | 10229篇 |
1984年 | 8708篇 |
1983年 | 7511篇 |
1982年 | 5872篇 |
1981年 | 5348篇 |
1980年 | 4956篇 |
1979年 | 8145篇 |
1978年 | 6276篇 |
1977年 | 5737篇 |
1976年 | 5385篇 |
1975年 | 5702篇 |
1974年 | 6175篇 |
1973年 | 6018篇 |
1972年 | 5379篇 |
1971年 | 4987篇 |
1970年 | 4155篇 |
1969年 | 4095篇 |
排序方式: 共有10000条查询结果,搜索用时 703 毫秒
811.
A simple enucleation technique that facilitates autoradiographic and electron microscopic examination of cytoplasms is described. Cells were grown on commercially available plastic Leighton coverslips and these were centrifuged in the presence of cytochalasin B. The centrifugation requires no special holders and only a high speed centrifuge. Enucleation frequencies of greater than 90% were obtained for Chinese hamster fibroblasts and mouse B-82 cells. 相似文献
812.
To determine whether histone genes are coordinately regulated, histone mRNA concentrations were measured in exponentially growing L6 myoblasts, S-phase synchronized myoblasts and in differentiating myoblasts. The levels of various histone mRNA subspecies declined rapidly and coordinately once myoblasts were given the signal to differentiate. mRNA levels were reduced on average to 1-5% of the amount observed in exponentially growing cells by 48 h after the signal to differentiate. The reductions occurred in concert with the cessation of DNA synthesis as the cells differentiated. Inhibition of DNA synthesis by treating myoblasts with Ara-C or hydroxyurea resulted in a histone mRNA half-life of 10-13 min for each of the histones examined. One example of non-coordinate regulation was observed however among the H4 mRNA subspecies in S-phase synchronized cells. The levels of two major subspecies of H4 mRNA increased coordinately in S-phase compared to levels observed in cells growing exponentially. A third subspecies of H4 mRNA on the other hand was found to decline by 50%. These studies suggest that the majority of histone mRNA subspecies are under coordinate control, although one exception has been noted among the subspecies of histone H4. 相似文献
813.
R.E. Jonkers B. Oosterhuis R.J.M. Ten Berge C.J. Van Boxtel 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1982,233(1):249-255
A relatively simple assay with improved reliability and sensitivity for measuring levels of 6-mercaptopurine in human plasma is presented. After extraction of the compound and the added internal standard with phenyl mercury acetate, samples were separated by ion-pair reversed-phase high-performance liquid chromatography. On-line the analytes were oxidized to fluorescent products and detected in a flow-fluorimeter. The within-day coefficient of variation was 3.8% at a concentration of 25 ng/ml. The lower detection limit was 2 ng/ml when 1.0 ml of plasma was used. Mercaptopurine concentration versus time curves of two subjects after a single oral dose of azathioprine are shown. 相似文献
814.
The DNA of fifteen Italian cultivars of durum wheat (Triticum turgidum L. ssp. durum) were analyzed by in fluorescence amplified fragment length polymorphism (fAFLP) in order to obtain the characteristic fingerprintings
of genotypes and assess their genetic relatedness. Among 64 combinations of fluorescence labelled primers, three different
combinations were chosen as producing a total of 6630 AFLP fragments, 2277 (34.3 %) of them being polymorphic. By using this
fAFLP methodology a DNA fingerprinting of each durum wheat cultivar was generated for genotype identification. Analysis of
the genetic relationships show the low variability among durum wheat cultivars. 相似文献
815.
816.
Control of breathing in Sherpas at low and high altitude 总被引:2,自引:0,他引:2
Hackett P. H.; Reeves J. T.; Reeves C. D.; Grover R. F.; Rennie D. 《Journal of applied physiology》1980,49(3):374-379
817.
818.
819.
820.