全文获取类型
收费全文 | 14877篇 |
免费 | 1443篇 |
国内免费 | 5篇 |
专业分类
16325篇 |
出版年
2023年 | 54篇 |
2022年 | 195篇 |
2021年 | 353篇 |
2020年 | 195篇 |
2019年 | 246篇 |
2018年 | 307篇 |
2017年 | 255篇 |
2016年 | 440篇 |
2015年 | 773篇 |
2014年 | 797篇 |
2013年 | 899篇 |
2012年 | 1200篇 |
2011年 | 1158篇 |
2010年 | 712篇 |
2009年 | 623篇 |
2008年 | 872篇 |
2007年 | 855篇 |
2006年 | 841篇 |
2005年 | 748篇 |
2004年 | 714篇 |
2003年 | 692篇 |
2002年 | 604篇 |
2001年 | 131篇 |
2000年 | 87篇 |
1999年 | 144篇 |
1998年 | 204篇 |
1997年 | 119篇 |
1996年 | 122篇 |
1995年 | 108篇 |
1994年 | 98篇 |
1993年 | 114篇 |
1992年 | 100篇 |
1991年 | 81篇 |
1990年 | 80篇 |
1989年 | 65篇 |
1988年 | 74篇 |
1987年 | 59篇 |
1986年 | 51篇 |
1985年 | 57篇 |
1984年 | 69篇 |
1983年 | 84篇 |
1982年 | 69篇 |
1981年 | 62篇 |
1980年 | 69篇 |
1979年 | 44篇 |
1978年 | 47篇 |
1977年 | 43篇 |
1976年 | 46篇 |
1975年 | 43篇 |
1974年 | 55篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Christine L. Truitt Elizabeth A. Weaver William G. Haldenwang 《Molecular & general genetics : MGG》1988,212(1):166-171
Summary The E-37 gene ctc was inactivated by a site-specific insertion into the Bacillus subtilis chromosome. The resulting mutation inhibited sporulation by 95% at elevated temperatures (48° C). If the ctc
- mutation is placed in a strain that carries a mutation in the closely linked but distinct spoVC gene, ctc now affects both growth and sporulation at elevated temperatures. Growth of the ctc
- spoVC285 strain was transiently inhibited when exponentially growing cultures were shifted from 37° C to 48° C. A similar, but less pronounced growth lag, was also seen in a B. subtilis strain carrying only the spoVC-285 mutation. This finding suggests that both the ctc and spoVC products function in vegetatively growing B. subtilis. 相似文献
52.
The joint probability distribution of the number of distinct (not identical by descent) genes from each founder of the Equus przewalskii population that survive in the five horses of the Calgary Zoological Gardens breeding group has been calculated. The dependence structure of this distribution is investigated, and informative marginal distributions are given, among them the distributions of the genetic contributions of each founder to the Calgary horses and the distribution of wild-type genes in these horses. The dependence pattern is found to be complex; there is no substitute for exact calculation of the full joint probability distribution of numbers of surviving genes. Probabilities of gene survival give a more complete summary of the genetic structure of a set of individuals than is provided by more routine measures such as heterozygosity or founder contributions. The feasibility of computing these probabilities for small groups of current individuals descended from few founders via long and complex pedigrees, provides a new approach to assessing such groups, and could be used also in selecting animals to form the founder stock of propagules for future reintroduction programs. 相似文献
53.
54.
Lakhu M. Keshvara Elizabeth M. Newton A. Heather Good Ole Hindsgaul Monica M. Palcic 《Glycoconjugate journal》1992,9(1):16-20
ELISA assays have been developed for (1–3)N-acetylgalactosaminyltransferase (blood group A transferase) and (1–3)galactosyltransferase (blood group B transferase) activities. In these assays, microtitre plates coated with the bovine serum albumin conjugate of a synthetic Fuc1–2Gal-R acceptor substrate are incubated with the appropriate nucleotide donor (UDP-GalNAc or UDP-Gal) and human serum as the enzyme source. The resulting trisaccharide products Fuc1–2(GalNAc1–3)Gal-R-BSA or Fuc1–2(Gal1–3)Gal-R-BSA are detected and quantified with monoclonal antibodies selected not to cross-react with the substrate structure. With less than a microliter of human serum, product formation is proportional to enzyme concentration and to time of incubation of up to 90 min. 相似文献
55.
Dieuwke B. van Dorp Alan F. Wright Andrew D. Carothers Elizabeth M. Bleeker-Wagemakers 《Human genetics》1992,88(3):331-334
Summary The results of linkage analysis in a family with X-linked retinitis pigmentosa (XLRP) are presented. Probe M27B (DXS255), localised to Xp11.22, was only loosely linked to XLRP, whereas pHOC3 (OTC), in the more distal Xp21.1 region, was tightly linked. In this family, the conditional probability of an RP3 locus (in Xp21.1–p11.4) was found to be 0.978 compared with 0.021 for an RP2 locus (in Xp11.4–p11.2). Risk assessment showed that 2 out of 4 at risk females showing no clinical abnormality have a high probability of being genetic carriers of XLRP. Some affected males have recurrent respiratory infections as a result of a condition indistinguishable from the immotile cilia syndrome; indeed, there is an association between XLRP and susceptibility to respiratory infections in the majority of affected males. The possibility that previously observed ciliary abnormalities in XLRP patients might be associated specifically with an RP3 locus abnormality is discussed. 相似文献
56.
We describe a human genomic cosmid clone, 56.1.1, that contains subtelomeric sequences present on multiple human chromosomes. In particular, using fluorescence in situ hybridization, we have identified 16 sites of hybridization on 12 chromosomes. In a sample of 8 unrelated individuals, 10 of these sites showed interindividual variation. Co-hybridization with other polymorphic probes allowed us to demonstrate cytologically heterozygosity at three sites in six individuals. The chromosomal distribution of hybridization sites in a family strongly suggests that these variants are inherited in a Mendelian fashion. These data show that subtelomeric repeats are a rich source of genetic variability. Possible mechanisms of generation of such variants are discussed. 相似文献
57.
58.
Summary We studied the influence of diet composition and breadth on the subsequent acceptability of three novel plants to sixth instarSchistocerca americana. Rearing diets of equal breadth differing in composition, and diets differing in breadth, significantly altered first meal length on some but not all of the test plants. These effects on palatability altered and at times reversed the palatability hierarchy of insects reared on different diets. The effects of rearing insects on broad diets were not produced by exposure to the plant odors alone, but apparently required contact with a diversity of plants while feeding. Switching diets for 24 h prior to testing did not alter preferences induced by rearing diets. The relationship of these patterns to induced preferences in other insects, and some possible mechanisms for generating induced preferences, are discussed. 相似文献
59.
Ejaculated, bovine sperm have been subjected to multiple partition in aqueous two-phase systems. This partition, carried out in a countercurrent fashion, reveals heterogeneity of the sperm population with respect to surface properties. The sperm, when partitioned in phase systems that detect non-change associated surface properties (change-insensitive) are largely distributed as two distinct populations. In charge-sensitive phase systems (which principally detect cell surface molecules carrying charge) the sperm do not show any obvious surface heterogeneity. Considerable heterogeneity is revealed in affinity-ligand phase systems containing palmitic acid coupled to one of the phase components-poly(ethylene glycol). There is a difference in surface heterogeneity between sperm which have been washed in buffer or left unwashed, direct from the ejaculate. This is indicative of weak adsorption of proteins to the sperm surface in seminal fluid. These results show that bovine ejaculated sperm is a heterogeneous cell population having unequal distributions of a number of different surface molecules. 相似文献
60.