全文获取类型
收费全文 | 1469篇 |
免费 | 57篇 |
国内免费 | 239篇 |
出版年
2024年 | 3篇 |
2023年 | 11篇 |
2022年 | 15篇 |
2021年 | 29篇 |
2020年 | 24篇 |
2019年 | 44篇 |
2018年 | 21篇 |
2017年 | 47篇 |
2016年 | 30篇 |
2015年 | 71篇 |
2014年 | 71篇 |
2013年 | 61篇 |
2012年 | 73篇 |
2011年 | 86篇 |
2010年 | 75篇 |
2009年 | 86篇 |
2008年 | 99篇 |
2007年 | 105篇 |
2006年 | 101篇 |
2005年 | 97篇 |
2004年 | 75篇 |
2003年 | 72篇 |
2002年 | 60篇 |
2001年 | 48篇 |
2000年 | 42篇 |
1999年 | 27篇 |
1998年 | 31篇 |
1997年 | 33篇 |
1996年 | 19篇 |
1995年 | 13篇 |
1994年 | 35篇 |
1993年 | 19篇 |
1992年 | 14篇 |
1991年 | 20篇 |
1990年 | 13篇 |
1989年 | 17篇 |
1988年 | 10篇 |
1987年 | 8篇 |
1986年 | 11篇 |
1985年 | 7篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1976年 | 3篇 |
1974年 | 3篇 |
1966年 | 1篇 |
1952年 | 1篇 |
排序方式: 共有1765条查询结果,搜索用时 15 毫秒
21.
Marcel Weber 《Biology & philosophy》1996,11(1):67-88
Enzyme directed genetic mechanisms causing random DNA sequence alterations are ubiquitous in both eukaryotes and prokaryotes. A number of molecular geneticist have invoked adaptation through natural selection to account for this fact, however, alternative explanations have also flourished. The population geneticist G.C. Williams has dismissed the possibility of selection for mutator activity on a priori grounds. In this paper, I attempt a refutation of Williams' argument. In addition, I discuss some conceptual problems related to recent claims made by microbiologists on the adaptiveness of molecular variety generators in the evolution of prokaryotes. A distinction is proposed between selection for mutations caused by a mutator activity and selection for the mutator activity proper. The latter requires a concept of fitness different from the one commonly used in microbiology. 相似文献
22.
Yamazaki Masaaki; Ono Ayako; Watanabe Koji; Sasaki Kuniaki; Tashiro Hiroyuki; Nomura Toru 《DNA research》1995,2(4):187-189
Most ofthe human Not I linking clones identified to date areconsidered to be derived from CpG islands because ofthe recognitionsequence of this enzyme, and CpG islands have been reportedto be located around the 5' regions of genes. As a pilot study,we determined the complete nucleotide sequence (41,924 bp) ofa human cosmid clone (LL21NC02Q7A10) containing the marker D21S246originating from a Not I linking clone. As a result of sequenceanalysis, we successfully mapped and revealed the genomic genestructure for KIAA0002 previously reported as a cDNA clone.This gene consists of 15 exons and was shown to exist at theD21S246 locus on human chromosome 21q21.3q22.1. Theseresults demonstrated that genomic marker-anchored DNA sequencingis a useful approach for the human genome project. 相似文献
23.
铜绿假单胞菌PIC-N萘降解基因的研究 总被引:1,自引:0,他引:1
铜绿假单胞菌(Pseudomonasaeruginosa)PIC-N对萘、邻苯二甲酸、水杨酸等有较强的氧化能力。发现该菌株以禁为底物可诱导产生芳香烃分解酶系。菌株中存在一个57.4kb的质粒,经限制性内切酶HindⅢ处理可产生7个片段,用限制性内切酶EcoRⅠ处理可产生8个片段。将以限制性内切酶HindⅢ部分酶切的片段克隆至大肠杆菌质粒pMFY43上,获得29个克隆株。通过对含有菌株PIC-N质粒HindⅢ片段的7个重组质粒进行限制酶分析,绘出了该质粒HindⅢ内切酶7个切点的酶切图谱。 相似文献
24.
25.
S. S. Sandhu F. J. de Serres H. N. B. Gopalan W. F. Grant D. Svendsgaard J. Velemínský G. C. Becking 《Mutation research》1994,310(2):257-263
In the first phase of a collaborative study by the International Programme on Chemical Safety (PRCS), four coded chemicals, i.e. azidoglycerol (AG, 3-azido-1,2-propanediol), methyl nitrosurea (MNU), sodium azide (NaN3) and maleic hydrazide (MH), and ethyl methanesulfonate (EMS) as a positive control were tested in four plant bioassays, namely the Arabidopsis embryo and chlorophyll mutation assay, the Tradescantia stamen hair assay (Trad-SH assay), the Tradescantia micronucleus assay (Trade-MCN), and the Vicia faba root tip assay. Seventeen laboratories from diverse regions of the world participated with four to six laboratories each using one plant assay. For the Arabidopsis assay, laboratories were in agreement with MNU and AG giving positive responses and NaN3 giving a negative response. With the exception of one laboratory which reported MH as weakly mutagenic, no mutagenic response was reported for MH by the other laboratories. For the Vicia faba assay, all laboratories reported a positive response for MNU, AG, and MH, whereas two of the six laboratories reported a negative response for NaN3. For the Trad-SH assay, MH was reported as giving a positive response and a positive response was also observed for MNU with the exception of one laboratory. NaN3, which exhibited a relatively high degree of toxicity, elicited a positive response in three of the five laboratories. AG was found positive in only one of the two laboratories which tested this chemical. For the Trad-MCN assay, MNU and MH were reported as positive by all laboratories, while four out of five laboratories reported NaN3 to be positive. Only one of three laboratories reported AG to be positive. The major sources of variability were identified and considered to be in the same range as found in similar studies on other test systems. Recommendations were made for minor changes in methodology and for initiating the second phase of this study. 相似文献
26.
A physical map and clone bank of the black pine (Pinus thunbergii) chloroplast genome 总被引:1,自引:1,他引:0
T. Wakasugi J. Tsudzuki S. Ito M. Shibata M. Sugiura 《Plant Molecular Biology Reporter》1994,12(3):227-241
Black pine chloroplast DNA is 119,707 bp long. The physical map is shown and the genes are listed. Plasmid clones covering
the entire DNA sequence have been ordered and available upon request. 相似文献
27.
L. Saoudi-Helis J. -P. Dubacq Y. Marty J. -F. Samain C. Gudin 《Journal of applied phycology》1994,6(3):315-322
A continuous culture ofIsochrysis aff.galbana clone T.iso, used to feedPecten maximus larvae at IFREMER (Brest, France), was carried out in a chemostat at its optimum temperature for growth (26 °C). Changes in pigments, lipid class (neutral, glyco- and phospholipids) and degree of fatty acid unsaturation were studied at three different growth rates (0.33, 0.5, 1 d–1). As predicted by chemostat theory, a slow growth rate produced higher cell numbers and higher biomass per unit volume. These cells were low in chlorophylla and carotenoids, but rich in neutral lipids. In contrast, cultures with a fast growth rate yielded lower cell concentrations, buth higher chlorophylla, carotenoid and membrane lipid contents per cell. Changes in polyunsaturated fatty acid distribution were related to differences in algal growth rates. Neutral lipids contained mainly saturated and monounsaturated fatty acids (C18:19) at low growth rates whereas they were enriched in polyunsaturated fatty acids, especially C22:63, at high growth rates. Therefore, it is suggested that the growth rate in continuous cultures be controlled so as to adjust the relative proportions of polyunsaturated fatty acids in lipid classes of the diet meant for larval nutrition.Author for correspondence 相似文献
28.
菜用香椿良种选育性状的模糊综合评判 总被引:1,自引:0,他引:1
采用模糊数学方法对菜用香棒16个不同种源的无性系从形态、颜色、香气、抗病性四个方面进行了综合评判,筛选出了接近选育目标的5个菜用优良无性系。 相似文献
29.
30.