全文获取类型
收费全文 | 28837篇 |
免费 | 2857篇 |
国内免费 | 17篇 |
专业分类
31711篇 |
出版年
2021年 | 307篇 |
2020年 | 228篇 |
2019年 | 258篇 |
2018年 | 314篇 |
2017年 | 312篇 |
2016年 | 500篇 |
2015年 | 853篇 |
2014年 | 883篇 |
2013年 | 1235篇 |
2012年 | 1403篇 |
2011年 | 1386篇 |
2010年 | 1062篇 |
2009年 | 824篇 |
2008年 | 1082篇 |
2007年 | 1098篇 |
2006年 | 1038篇 |
2005年 | 1067篇 |
2004年 | 1143篇 |
2003年 | 1020篇 |
2002年 | 973篇 |
2001年 | 850篇 |
2000年 | 830篇 |
1999年 | 816篇 |
1998年 | 419篇 |
1997年 | 411篇 |
1996年 | 426篇 |
1995年 | 364篇 |
1994年 | 306篇 |
1993年 | 349篇 |
1992年 | 743篇 |
1991年 | 586篇 |
1990年 | 631篇 |
1989年 | 638篇 |
1988年 | 527篇 |
1987年 | 512篇 |
1986年 | 451篇 |
1985年 | 476篇 |
1984年 | 480篇 |
1983年 | 360篇 |
1982年 | 326篇 |
1981年 | 312篇 |
1980年 | 282篇 |
1979年 | 375篇 |
1978年 | 312篇 |
1977年 | 308篇 |
1976年 | 234篇 |
1975年 | 255篇 |
1974年 | 279篇 |
1973年 | 231篇 |
1971年 | 203篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
A. Verrips Gerry C. H. Steenbergen-Spanjers J. A. F. M. Luyten R. A. Wevers John H. J. Wokke Fons J. M. Gabreëls Bert G. Wolthers Lambert P. W. J. van den Heuvel 《Human genetics》1997,100(2):284-286
We report a new mutation in the sterol 27-hydroxylase (CYP 27) gene in a Dutch family with cerebrotendinous xanthomatosis:
a G→A transition in the splice donor site in intron 4. This mutation leads to skipping of exon 4, resulting in a loss of 66
amino acids in the CYP 27 enzyme molecule.
Received: 15 March 1997 / Accepted: 26 March 1997 相似文献
44.
45.
46.
47.
A general in vitro cloning system was established for four Helleborus species: H. argutifolius, H. foetidus, H. niger and H. orientalis. The plant material was introduced in vitro from axillary buds. A Murashige and Skoog (MS)—based medium (Murashige and Skoog
1962) was used supplemented with 2% (w/v) sucrose, 2-isopentenyladenine (2-iP) and 6-benzylaminopurine (BA). Multiplication
rates depended on the genotype and varied from 1.3 for H. foetidus till 3.8 for H. niger. The first results showed that the rooting phase could be done ex vitro. Rooting was induced by a drench for one week in
a solution of indole-3-butyric acid (IBA -3 mg l−1) and 1-naphthaleneacetic acid (NAA-1 mg l−1) at 5°C. 相似文献
48.
49.
Mutant 5 S rRNA genes were expressed in Saccharomyces cerevisiae to further define the function of the ribosomal 5 S RNA. RNA synthesis and utilization were assayed using previously constructed markers which have been shown to be functionally neutral and easily detected by gel electrophoresis. Most mutations were found not to affect the growth rate because they were poorly expressed or could be accommodated effectively in the ribosomal structure. Two of the mutants, Y5A99U56U57 and Y5U90i5 adversely affected cell growth as well as protein synthesis in vitro. Polyribosome profiles in both of these mutants were substantially shorter, and an analysis of the ribosomal subunit composition revealed a significant imbalance with a 25-35% excess in 40 S subunits. Kinetic analyses of RNA labeling indicated very low cellular levels of mutant RNA either because it was poorly expressed (Y5U90i5) or rapidly degraded before being incorporated into mature 60 subunits (Y5A99U56U57). The results suggest that the 5 S RNA is required for the assembly of stable ribosomal 60 S subunits and raise the possibility that this RNA or, more likely, its corresponding ribonucleoprotein complex is critical for subunit assembly or even RNA processing. 相似文献
50.
Abstract cDNA-RNA liquid hybridization analysis was used to compare the RNA sequence homology between two members of the Nudaurelia β virus family, Trichoplusia ni virus ( T.ni V) and Dasychira pudibunda virus ( D.p V). Heterologous hybridization experiments demonstrated that these viruses shared little sequence homology. Using oligo(dT) chromatography and oligo(dT)12–18 as a primer for cDNA synthesis it was shown that neither T.ni V nor D.p V RNA genomes possess a poly(A) tract at the 3' end. 相似文献