全文获取类型
收费全文 | 4623篇 |
免费 | 346篇 |
国内免费 | 4篇 |
出版年
2022年 | 37篇 |
2021年 | 55篇 |
2020年 | 54篇 |
2019年 | 58篇 |
2018年 | 94篇 |
2017年 | 75篇 |
2016年 | 87篇 |
2015年 | 131篇 |
2014年 | 188篇 |
2013年 | 273篇 |
2012年 | 283篇 |
2011年 | 324篇 |
2010年 | 202篇 |
2009年 | 152篇 |
2008年 | 193篇 |
2007年 | 221篇 |
2006年 | 202篇 |
2005年 | 173篇 |
2004年 | 157篇 |
2003年 | 148篇 |
2002年 | 121篇 |
2001年 | 132篇 |
2000年 | 139篇 |
1999年 | 105篇 |
1998年 | 57篇 |
1997年 | 43篇 |
1996年 | 49篇 |
1995年 | 41篇 |
1994年 | 35篇 |
1993年 | 37篇 |
1992年 | 79篇 |
1991年 | 92篇 |
1990年 | 91篇 |
1989年 | 85篇 |
1988年 | 44篇 |
1987年 | 64篇 |
1986年 | 72篇 |
1985年 | 75篇 |
1984年 | 68篇 |
1983年 | 43篇 |
1982年 | 48篇 |
1981年 | 34篇 |
1980年 | 26篇 |
1979年 | 33篇 |
1978年 | 30篇 |
1977年 | 33篇 |
1976年 | 24篇 |
1975年 | 21篇 |
1974年 | 23篇 |
1972年 | 27篇 |
排序方式: 共有4973条查询结果,搜索用时 406 毫秒
51.
52.
53.
The nucleotide sequence of a rat liver glutathione S-transferase subunit cDNA clone 总被引:17,自引:0,他引:17
We have determined the nucleotide sequence of a cloned cDNA derived from liver poly(A) RNA of pentobarbital-treated rats encoding a glutathione S-transferase subunit. This cDNA clone pGTR261 contains one open reading frame of 222 amino acids, a complete 3' noncoding region, and 63 nucleotides in the 5' noncoding region. The cloned DNA hybridizes to rat poly(A) RNA in a tissue-specific fashion, with strong signals to liver and kidney poly(A) RNA(s) of approximately 1100 and approximately 1400 nucleotides in size but little or no hybridization to poly(A) RNAs from heart, lung, seminal vesicles, spleen, or testis under stringent conditions. Our sequence covers the cDNA sequence of pGST94 which contains a partial coding sequence for a liver glutathione S-transferase subunit of Ya size. Comparison of sequences with our earlier clone pGTR112 suggests that there are at least two mRNA species coding for two different subunits of the Ya (Mr = 25,600) subunit family with very limited amino acid substitutions mainly of conserved polarity. The divergent 3' noncoding sequences should be useful molecular probes in differentiating these two different but otherwise very similar subunits in induction and genomic structure analyses. Our results suggest that tissue-specific expression of the glutathione S-transferase subunits represented by the sequences of pGTR261 and pGTR112 may occur at or prior to the level of RNA processing. 相似文献
54.
55.
The Yc and Ya subunits of rat liver glutathione S-transferases are the products of separate genes 总被引:7,自引:0,他引:7
56.
P. Janardhan Reddy K. Vaidyanath 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1986,71(5):757-760
Summary The response of plant cells to salt stress was studied on embryo derived calli of rice (Oryza sativa L.) in order to identify cellular phenotypes associated with the stress. The feasability of selecting salt tolerant callus and its subsequent regeneration to plants was also studied. Callus was grown on agar-solidified media containing 0%, 1% and 2% (w/v) NaCl for 24 days. Parameters such as fresh weight, dry weight, soluble protein and proline content were measured. The callus growth decreased markedly with increasing NaCl concentration in the medium. The proline content was enhanced several fold in salt stressed calli. A prolonged exposure of callus to the salt environment led to discolouration and arrested growth in the majority of the calli and only a small number of callus cells maintained healthy and stable growth. These variants were subcultured every three weeks for a period of four months onto medium containing 1% NaCl to identify tolerant lines. At the end of the third cell passage, the tolerant calli were transferred to regeneration medium to regenerate plants. The regeneration frequency in the salt-selected lines was enhanced when compared to unselected lines. 相似文献
57.
58.
59.
60.
Research on the Bagatha tribe and the Malas and Madigas in India has been done for economic and social planning purposes in regard to family planning. Bagatha are mostly agricultural people where the nuclear family is prevalent and polygamy is popular as well as cousin marriage. The Madigas and Males (Harijans) are lower caste with the 1st being leather workers and the latter being agricultural helpers. The data was collected by direct interview of 202 tribesmen and 202 caste households with women from 15-49 years of age. The data collected on fertility include live births, child survival rate, fetal wastage, husband and wives education, income, and occupations. On mortality, the number of deaths, age at marriage, number of and intervals of pregnancies. As expected, educated and employed families show healthier and higher levels of fertility especially if the wife is educated. The wife shows more of the responsibility for family planning. The age at marriage and the number of pregnancies appears to have little effect on mortality. In the caste group the education level of the husband has little effect on fertility and again the wife has the primary responsibility in using family planning techniques. 相似文献