全文获取类型
收费全文 | 70047篇 |
免费 | 5827篇 |
国内免费 | 33篇 |
出版年
2022年 | 448篇 |
2021年 | 993篇 |
2020年 | 629篇 |
2019年 | 768篇 |
2018年 | 979篇 |
2017年 | 956篇 |
2016年 | 1576篇 |
2015年 | 2764篇 |
2014年 | 3029篇 |
2013年 | 3890篇 |
2012年 | 4942篇 |
2011年 | 4875篇 |
2010年 | 3194篇 |
2009年 | 2838篇 |
2008年 | 4027篇 |
2007年 | 4104篇 |
2006年 | 3846篇 |
2005年 | 3878篇 |
2004年 | 3802篇 |
2003年 | 3579篇 |
2002年 | 3511篇 |
2001年 | 947篇 |
2000年 | 726篇 |
1999年 | 924篇 |
1998年 | 1010篇 |
1997年 | 721篇 |
1996年 | 710篇 |
1995年 | 672篇 |
1994年 | 676篇 |
1993年 | 671篇 |
1992年 | 677篇 |
1991年 | 571篇 |
1990年 | 495篇 |
1989年 | 511篇 |
1988年 | 482篇 |
1987年 | 412篇 |
1986年 | 399篇 |
1985年 | 486篇 |
1984年 | 521篇 |
1983年 | 438篇 |
1982年 | 521篇 |
1981年 | 459篇 |
1980年 | 403篇 |
1979年 | 292篇 |
1978年 | 330篇 |
1977年 | 318篇 |
1976年 | 270篇 |
1975年 | 246篇 |
1974年 | 286篇 |
1973年 | 254篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
831.
A microdeletion of less than 250 kb, including the proximal part of the FMR-1 gene and the fragile-X site, in a male with the clinical phenotype of fragile-X syndrome
下载免费PDF全文
![点击此处可从《American journal of human genetics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Doris Whrle Dieter Kotzot Mark C. Hirst Antonella Manca Bernhard Korn Angela Schmidt Gotthold Barbi Hans-Dieter Rott Annemarie Poustka Kay E. Davies Peter Steinbach 《American journal of human genetics》1992,51(2):299-306
A gene designated "FMR-1" has been isolated at the fragile-X locus. One exon of this gene is carried on a 5.1-kb EcoRI fragment that exhibits length variation in fragile-X patients because of amplification of or insertion into a CGG-repeat sequence. This repeat probably represents the fragile site. The EcoRI fragment also includes an HTF island that is hypermethylated in fragile-X patients showing absence of FMR-1 mRNA. In this paper, we present further evidence that the FMR-1 gene is involved in the clinical manifestation of the fragile-X syndrome and also in the expression of the cellular phenotype. A deletion including the HTF island and exons of the FMR-1 gene was detected in a fragile X-negative mentally retarded male who presented the clinical phenotype of the fragile-X syndrome. The deletion involves less than 250 kb of genomic DNA, including DXS548 and at least five exons of the FMR-1 gene. These data support the hypothesis that loss of function of the FMR-1 gene leads to the clinical phenotype of the fragile-X syndrome. In the fragile-X syndrome, there are pathogenetic mechanisms other than amplification of the CGG repeat that do have the same phenotypic consequences. 相似文献
832.
833.
834.
Bart M. Nicolaï Jan F. Van Impe Peter A. Vanrolleghem Joos Vandewalle 《Antonie van Leeuwenhoek》1992,62(4):273-283
The mathematical model for the penicillin G fed-batch fermentation proposed by Heijnen et al. (1979) is compared with the model of Bajpai & Reuß (1980). Although the general structure of these models is similar, the difference in metabolic assumptions and specific growth and production kinetics results in a completely different behaviour towards product optimization. A detailed analysis of both models reveals some physical and biochemical shortcomings. It is shown that it is impossible to make a reliable estimation of the model parameters, only using experimental data of simple constant glucose feed rate fermentations with low initial substrate amount. However, it is demonstrated that some model parameters might be key factors in concluding whether or not altering the substrate feeding strategy has an important influence on the final amount of product.It is illustrated that feeding strategy optimization studies can be a tool in designing experiments for parameter estimation purposes. 相似文献
835.
The diversity of rhizobia that form symbioses with roots of black locust (Robinia pseudoacacia L.), an economically important leguminous tree species, was examined by inoculating seedling root zones with samples of soil collected from the United States, Canada, and China. Bacteria were isolated from nodules, subcultured, and verified to be rhizobia. The 186 isolates varied significantly in their resistance to antibiotics and NaCl, their growth on different carbohydrates, and their effect on the pH of culture media. Most isolates showed intermediate antibiotic resistance, the capacity to use numerous carbohydrates, and a neutral to acid pH response. Isolates had greater similarity within sampling locations than among sampling locations. The isolates were grouped by using numerical taxonomy techniques, and representative strains of 37 groups were selected. The mean generation times of these isolates ranged from 3 to 9 h, and the protein profile of each of the 37 isolates was unique. Nitrogen fixation, total nitrogen accumulation, and plant growth varied significantly among black locust seedlings inoculated with the representative isolates. We conclude that great variation exists among Rhizobium spp. that nodulate black locust, and selection of strains for efficiency of the symbiotic association appears possible. 相似文献
836.
Analyses of wheat/rye addition lines by Southern blotting confirmed the presence of sequences related to theSec 1, Sec 2, andSec 3 loci on chromosomes 1R and 2R. Comparison of the 1R and 2R addition lines allowed the identification of -secalin genes atSec 1 andSec 2, respectively, while -secalin and -secalin genes atSec 1 were discriminated by comparative hybridization with three probes: -secalin, total -secalin, and 3 -secalin. The high molecular weight (HMW) secalin genes atSec 3 were identified using a homologous HMW subunit probe from wheat. Gene copy numbers were estimated as about 40–60 for -secalins, 5–10 for -secalins, and 2 for HMW secalins. Comparison of individual plants of cv. Gazelle showed a high degree of polymorphism, particularly for sequences related to -secalins and HMW secalins. 相似文献
837.
Peter C. Maloney 《Journal of bioenergetics and biomembranes》1990,22(4):509-523
Bacterial anion exchange now includes both carboxylate-linked reactions, in which there is an antiport of mono- and dicarboxylic acids, and Pi-linked reactions that build on phosphate (Pi) and organic phosphates. To illustrate the general features of this expanding class, this article discussed the biochemistry, physiology, and molecular biology of Pi-linked antiporters that accept glucose 6-phosphate (G6P) as their primary substrate. Kinetic and biochemical analysis suggsts that Pi-linked exchangers have a bifunctional active site that accepts a pair of negative charges. For this reason, exchange stoichiometry moves between the limits of 2:1 and 2:2 to reflect the ratio of mono- and divalent substrates at either membrane surface. This results in a particularly interesting reaction sequencein vivo, where, because cytosolic pH is relatively alkaline, one can expect the asymmetric exchange of two monovalent G6P anions against a single divalent G6P. In this way, an otherwise futile self-exchange of G6P gives a net flux driven (indirectly) by the pH gradient. Despite this biochemical and physiological complexity, Pi-linked carriers resemble all other secondary carriers at a molecular level. Indeed, sequence analysis leads one to infer a common (albeit low resolution) structural theme in which each functional unit has two sets of six trans-membrane helices separated by a central hydrophilic loop. Present examples show that this topology can derive from either a single protein, as is typical in bacteria, or from pairs of identical subunits, as found in mitochondria and chloroplasts. The finding of this common structure should make it possible to build detailed structural models that have implications for all membrane carrier proteins. 相似文献
838.
Reviewers for 1988 and 1989 相似文献
839.
840.
Lars Nitschke Karin Heeger Hans Bender Georg E. Schulz 《Applied microbiology and biotechnology》1990,33(5):542-546
Summary The -cyclodextrin glycosyltransferase (-CGTase) gene was isolated from a -library prepared from Bacillus circulans strain no. 8. It was subcloned into plasmid pTZ and expressed by its endogenous regulatory sequences in Escherichia coli JM 103. The structural gene was sequenced and showed an open reading frame for a polypeptide of 718 amino acid residues. The recombinant -CGTase had the same enzymatic properties as the extracellular CGTase (684 amino acid residues, corresponding to a mol. wt. of 74416) produced by B. circulans strain no. 8. The amino acid sequence showed the highest homology (74.6% identical amino acids) with the CGTase of B. circulans strain F-2, which had been erroneously described as an amylase. The homology with the enzyme from the alkalophilic Bacillus sp. strain no. 1011 was 71.4%. The amino acid sequence derived will be used for elucidating the three-dimensional structure of the enzyme.
Offprint requests to: H. Bender 相似文献