全文获取类型
收费全文 | 12868篇 |
免费 | 304篇 |
国内免费 | 692篇 |
出版年
2024年 | 9篇 |
2023年 | 74篇 |
2022年 | 136篇 |
2021年 | 158篇 |
2020年 | 184篇 |
2019年 | 296篇 |
2018年 | 245篇 |
2017年 | 200篇 |
2016年 | 202篇 |
2015年 | 381篇 |
2014年 | 868篇 |
2013年 | 749篇 |
2012年 | 657篇 |
2011年 | 968篇 |
2010年 | 714篇 |
2009年 | 631篇 |
2008年 | 693篇 |
2007年 | 736篇 |
2006年 | 627篇 |
2005年 | 588篇 |
2004年 | 519篇 |
2003年 | 468篇 |
2002年 | 307篇 |
2001年 | 196篇 |
2000年 | 276篇 |
1999年 | 323篇 |
1998年 | 295篇 |
1997年 | 254篇 |
1996年 | 231篇 |
1995年 | 266篇 |
1994年 | 241篇 |
1993年 | 204篇 |
1992年 | 191篇 |
1991年 | 166篇 |
1990年 | 126篇 |
1989年 | 135篇 |
1988年 | 118篇 |
1987年 | 116篇 |
1986年 | 83篇 |
1985年 | 48篇 |
1984年 | 44篇 |
1983年 | 31篇 |
1982年 | 33篇 |
1981年 | 23篇 |
1980年 | 8篇 |
1979年 | 12篇 |
1978年 | 13篇 |
1976年 | 5篇 |
1973年 | 5篇 |
1972年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
141.
Fritz Rudert Wolfgang Zimmermann John A. Thompson 《Journal of molecular evolution》1989,29(2):126-134
Summary Various rodent and primate DNAs exhibit a stronger intra- than interspecies cross-hybridization with probes derived from the N-terminal domain exons of human and rat carcinoembryonic antigen (CEA)-like genes. Southern analyses also reveal that the human and rat CEA gene families are of similar complexity. We counted at least 10 different genes per human haploid genome. In the rat, approximately seven to nine different N-terminal domain exons that presumably represent different genes appear to be present. We were able to assign the corresponding genomic restriction endonuclease fragments to already isolated CEA gene family members of both human and rat. Highly similar subgroups, as found within the human CEA gene family, seem to be absent from the rat genome. Hybridization with an intron probe from the human nonspecific cross-reacting antigen (NCA) gene and analysis of DNA sequence data indicate the conservation of noncoding regions among CEA-like genes within primates, implicating that whole gene units may have been duplicated. With the help of a computer program and by calculating the rate of synonymous substitutions, evolutionary trees have been derived. From this, we propose that an independent parallel evolution, leading to different CEA gene families, must have taken place in, at least, the primate and rodent orders. 相似文献
142.
143.
J. J. M. Meulenberg W. A. M. Loenen E. Sellink P. W. Postma 《Molecular & general genetics : MGG》1990,220(3):481-484
Summary A generally applicable method is described for reintroduction of mutant plasmid-borne alleles to the chromosome of Klebsiella pneumoniae using bacteriophage . We, used this method to make stable chromosomal transposon insertions in genes for biosynthesis of pyrroloquinoline quinone in K. pneumoniae 相似文献
144.
Summary A cloned gene with an insertion, which was made by introducing cat, was ligated to the cloning site of the phage gt11. P1 phage grown on cells lysogenized with the recombinant phage could transduce the mutant gene into the original site on the Escherichia coli chromosome. 相似文献
145.
146.
147.
148.
Quantitative analysis of resistance in cotton to three new isolates of the bacterial blight pathogen
T. P. Wallace K. M. El-Zik 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1990,79(4):443-448
Summary Genetic variability for virulence of the bacterial blight pathogen [Xanthomonas campestris pv malvacearum (Smith) Dye] on cotton (Gossypium hirsutum L.) has been shown by the identification of 19 races of the pathogen based on disease reactions of a set of ten host differentials. This study was conducted to determine the inheritance of host resistance to three recently identified isolates of X. campestris pv malvacearum, which are virulent on the entire set of differentials. True leaves of Tamcot CAMD-E, LEBOCAS-3-80, Stoneville 825, and their f1, F2, and backcross progenies were wound-inoculated in the field with separate bacterial suspensions of the virulent HV3, HV7, and Sudan isolates of the pathogen. LEBOCAS-3-80 was replaced with S295, a new immune cultivar, for a greenhouse study in which both cotyledons and true leaves were inoculated. Disease reactions were rated on a scale of 1–10, and genetic models were proposed utilizing generation means analysis. Dominance, when significant, was in the direction of resistance in all but one cross-isolate combination. Digenic interaction components indicated a duplicate type. Narrow-sense heritability for resistance ranged from 0.59 to 0.68; therefore, primarily additive-genetic variability among the selected cutlivars was detected, indicating that breeding for improved resistance to these isolates is a practical goal.Contribution of the Department of Soil and Crop Sciences and the Texas Agricultural Experiment Station 相似文献
149.
150.
J. H. Roberds G. Namkoong T. Skrøppa 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1990,79(6):841-848
Summary A major concern arising from the culture of clonally propagated crops of forest trees is risk of catastrophic loss due to an agent or event not anticipated at the time of population establishment. Since danger of such a catastrophe depends to some degree on the genetic variability within clonal mixtures, attention has been focused on the number of clones needed to keep the risk of catastrophic loss below specified levels. In this paper, we describe a genetical analysis of susceptibility to a destructive agent and the effect that frequency of genes for susceptibility have on the number of clones needed to effectively manage this risk. As a part of the analysis, parameters representing the minimum unacceptable mortality rates in plantations () and acceptable levels of risk () are defined, and their effects on the number of single-pair matings needed for the production of clonal stock are evaluated. Dominance and recessive gene action models for a single two-allele genetic locus are investigated. Probabilities for plantation failure are functions of the gene frequency for the allele conferring susceptibility. These functions converge to zero for allele frequencies less than but to one for frequencies greater than or equal to . This convergence is periodic rather than monotonie, since probabilities for plantation failure increase rather than decrease over restricted ranges of increasing numbers of clones. Recessive and dominance gene actions are found to have different effects on the minimum number of clones needed to attain acceptable risk levels. For conditions in which substantial numbers of clones are required, selecting multiple clones per mating is an effective method for reducing the number of matings necessary to achieve acceptable risks.Paper No. 12480 of the Journal Series of the North Carolina Agriculture Research Service, Raleigh, NC 27695-7643, USA 相似文献