全文获取类型
收费全文 | 3570篇 |
免费 | 253篇 |
国内免费 | 1篇 |
出版年
2022年 | 22篇 |
2021年 | 50篇 |
2020年 | 45篇 |
2019年 | 39篇 |
2018年 | 44篇 |
2017年 | 41篇 |
2016年 | 93篇 |
2015年 | 149篇 |
2014年 | 160篇 |
2013年 | 233篇 |
2012年 | 274篇 |
2011年 | 251篇 |
2010年 | 151篇 |
2009年 | 135篇 |
2008年 | 203篇 |
2007年 | 199篇 |
2006年 | 189篇 |
2005年 | 198篇 |
2004年 | 187篇 |
2003年 | 164篇 |
2002年 | 165篇 |
2001年 | 37篇 |
2000年 | 29篇 |
1999年 | 33篇 |
1998年 | 35篇 |
1997年 | 39篇 |
1996年 | 20篇 |
1995年 | 26篇 |
1994年 | 33篇 |
1993年 | 27篇 |
1992年 | 30篇 |
1991年 | 25篇 |
1990年 | 30篇 |
1989年 | 26篇 |
1988年 | 26篇 |
1987年 | 21篇 |
1986年 | 23篇 |
1985年 | 20篇 |
1984年 | 26篇 |
1983年 | 24篇 |
1982年 | 27篇 |
1981年 | 20篇 |
1980年 | 22篇 |
1979年 | 24篇 |
1978年 | 15篇 |
1977年 | 18篇 |
1976年 | 23篇 |
1975年 | 19篇 |
1974年 | 23篇 |
1970年 | 14篇 |
排序方式: 共有3824条查询结果,搜索用时 31 毫秒
81.
Virginia E. Papaioannou John D. West Theodor Bücher Ingrid M. Linke 《Genesis (New York, N.Y. : 2000)》1981,2(3):305-315
We have used a sensitive electrophoretic technique for estimating the activity, or ratio, of two allozymes of the X-chromosome-linked enzyme phosphoglycerate kinase (PGK-1), in order to investigate the randomness of X-chromosome expression in the derivatives of the three primary cell lineages of the early mouse conceptus. The maternally derived Pgk-1 allele is preferentially expressed in the derivatives of the primitive endoderm and trophectoderm lineages at 6 1/2 days post coitum in Pgk-1a/Pgk-1b heterozygous conceptuses, and in the one informative 5 1/2-day heterozygous conceptus analysed. This evidence for preferential expression of the maternally derived X chromosome (Xm), so soon after the time of X-chromosome inactivation, favors the possibility that the preferential expression of Xm is a consequence of primary non-random X-chromosome inactivation, rather than a secondary selection phenomenon. The majority of embryos analysed at 4 1/2 and 5 1/2 days pc produced only a single PGK-1 band, corresponding to the allozyme produced by the Pgk-1 allele on Xm, although 50% of these embryos should have been heterozygous females. Possible explanations are discussed. 相似文献
82.
Wolfgang Hartmann Ingrid Tan Aloys Hüttermann Hans Kühlwein 《Archives of microbiology》1977,114(1):13-18
The properties of seven enzymes were studied in extracts from Myxobacter AL-1. The enzymes were isocitrate dehydrogenase (E.C. 1.1.1.42), succinate dehydrogenase (E.C. 1.3.99.1), alkaline phosphatase (E.C. 3.1.3.1), -glucosidase (E.C. 3.2.1.20), -glucosidase (E.C. 3.2.1.21), -galactosidase (E.C. 3.2.1.23), and N-acetyl-glucosaminidase (E.C. 3.2.1.30). Four of these enzymes: isocitrate dehydrogenase, -glucosidase, -glucosidase, and -galactosidase are cytosolic enzymes. Succinate dehydrogenase was found to be located on the cytoplasmic membrane system, whereas alkaline phosphatase and N-acetyl-glucosaminidase were considered as enzymes which bind the outer membranes resp. the cell wall. During the cell cycle, all enzymes have a pattern of discontinuous activity increase. Succinate dehydrogenase and isocitrate dehydrogenase exhibit a stepwise increase of activity, whereas the other enzymes follow the pattern of a peak enzyme. 相似文献
83.
A simple and selective assay for monomeric and filamentous actin is presented, based on the inhibition of DNAase I by actin. In mixtures of monomeric and filamentous actin, only the monomeric form is measured as DNAase inhibitor. The total amount of actin in a sample can be determined after depolymerization of F actin with guanidine hydrochloride. The assay is rapid enough to detect changes in the polymerization state of actin in vitro over time intervals as short as 3 min. Data characterizing unpolymerized and filamentous actin pools in extracts of human platelets, lymphocytes and HeLa cells are presented. 相似文献
84.
85.
86.
Peter Meyer Felicitas Linn Iris Heidmann Heiner Meyer Ingrid Niedenhof Heinz Saedler 《Molecular & general genetics : MGG》1992,231(3):345-352
Summary 30000 transgenic petunia plants carrying a single copy of the maize A1 gene, encoding a dihydroflavonol reductase, which confers a salmon red flower colour phenotype on the petunia plant, were grown in a field test. During the growing season plants with flowers deviating from this salmon red colour, such as those showing white or variegated phenotypes and plants with flowers exhibiting only weak pigmentation were observed with varying frequencies. While four white flowering plants were shown at the molecular level to be mutants in which part of the A1 gene had been deleted, other white flowering plants, as well as 13 representative plants tested out of a total of 57 variegated individuals were not mutants but rather showed hypermethylation of the 35S promoter directing A1 gene expression. This was in contrast to the homogeneous fully red flowering plants in which no methylation of the 35S promoter was observed. While blossoms on plants flowering early in the season were predominantly red, later flowers on the same plants showed weaker coloration. Once again the reduction of the A1-specific phenotype correlated with the methylation of the 35S promoter. This variation in coloration seems to be dependent not only on exogenous but also on endogenous factors such as the age of the parental plant from which the seed was derived or the time at which crosses were made. 相似文献
87.
The dissemination and viability of Gracilaria verrucosa spermatia were tested. Crosses were performed among three males and three females from Cape Gris Nez, northern France. Laboratory experiments show that spermatia have a mean fertile life of about five hours. Field studies show that spermatia are dispersed by stream and tidal currents and that fertilization can occur at least 80 m from a population. 相似文献
88.
H P Hohmann R Remy B P?schl A P van Loon 《The Journal of biological chemistry》1990,265(25):15183-15188
89.
The nonproteinogenic amino acid, cyclopentenylglycine, is found in certain Flacourtiaceae. This compound may be synthesized by two C1-chain elongations of -ketoglutarate via -ketopimelate (C5+2C1) or by condensation of C4 and C3 units (C4+C3), a pathway not involving -ketopimelate. The following experimental design elucidated the biosynthetic pathway: Idesia polycarpa callus cultures were freshly established from leaf petioles; synthetic -[1,2-14C]ketopimelate was added to the medium and cultures were incubated for 3 weeks. After isolation and separation of free amino acids from the tissues, the radioactivity incorporated into cyclopentenylglycine was determined. The results establish -ketopimelate as a precursor for cyclopentenylglycine, thus providing evidence for the C5+2C1 biosynthetic path. 相似文献
90.
Klaus Lange Konrad Keller Wolf-Dieter Ludwig Ingrid Monden Ingeborg Reinsch Ursula Brandt 《Journal of neurochemistry》1982,39(6):1594-1600
Previous studies have revealed two different kinds of regulation of glucose utilization in cell lines derived from the nervous system (Keller et al., 1981). We found glucose metabolism of C-6 glioma cells to be limited and regulated by membrane transport. In contrast, glucose utilization of C-1300 neuroblastoma (N2A) cells was limited by the known regulatory enzymes of the Embden-Meyerhof pathway. Under the given experimental conditions the "membrane-limited" C-6 glioma cells were characterized by periodically changing glucose transport rates and very low intracellular glucose concentrations, which remained constant in spite of widely differing transport rates. These findings suggest the close functional coupling between transport and phosphorylation required for the regulation of glucose transport by cellular metabolic needs. 相似文献