全文获取类型
收费全文 | 972篇 |
免费 | 123篇 |
专业分类
1095篇 |
出版年
2021年 | 6篇 |
2020年 | 6篇 |
2019年 | 7篇 |
2018年 | 7篇 |
2017年 | 7篇 |
2016年 | 12篇 |
2015年 | 25篇 |
2014年 | 16篇 |
2013年 | 30篇 |
2012年 | 39篇 |
2011年 | 34篇 |
2010年 | 16篇 |
2009年 | 34篇 |
2008年 | 25篇 |
2007年 | 31篇 |
2006年 | 25篇 |
2005年 | 38篇 |
2004年 | 34篇 |
2003年 | 24篇 |
2002年 | 28篇 |
2001年 | 27篇 |
2000年 | 31篇 |
1999年 | 31篇 |
1998年 | 19篇 |
1997年 | 16篇 |
1996年 | 13篇 |
1995年 | 17篇 |
1994年 | 8篇 |
1993年 | 10篇 |
1992年 | 22篇 |
1991年 | 29篇 |
1990年 | 28篇 |
1989年 | 28篇 |
1988年 | 18篇 |
1987年 | 23篇 |
1986年 | 23篇 |
1985年 | 20篇 |
1984年 | 15篇 |
1983年 | 12篇 |
1982年 | 11篇 |
1981年 | 19篇 |
1980年 | 14篇 |
1979年 | 16篇 |
1978年 | 22篇 |
1977年 | 17篇 |
1976年 | 12篇 |
1975年 | 12篇 |
1974年 | 13篇 |
1973年 | 15篇 |
1972年 | 6篇 |
排序方式: 共有1095条查询结果,搜索用时 15 毫秒
31.
A large, dominant pedigree of atrioventricular septal defect (AVSD): exclusion from the Down syndrome critical region on chromosome 21. 总被引:4,自引:0,他引:4 下载免费PDF全文
L Wilson A Curtis J R Korenberg R D Schipper L Allan G Chenevix-Trench A Stephenson J Goodship J Burn 《American journal of human genetics》1993,53(6):1262-1268
We describe a large pedigree of individuals with autosomal dominant atrioventricular septal defect (AVSD). The pedigree includes affected individuals and individuals who have transmitted the defect but are not clinically affected. AVSDs are a rare congenital heart malformation that occurs as only 2.8% of isolated cardiac lesions. They are the predominant heart defect in children with Down syndrome, making chromosome 21 a candidate for genes involved in atrioventricular septal development. We have carried out a linkage study in the pedigree by using 10 simple-sequence polymorphisms from chromosome 21. Multipoint linkage analysis gives lod scores of less than -2 for the region of trisomy 21 associated with heart defects, which excludes a locus within this region as the cause of the defect in this family. 相似文献
32.
33.
We examined factors affecting the duration of the staminate and pistillate phases in the protandrous flowers of Campanula rapunculoides L. (Campanulaceae). Under conditions of natural pollinator visitation, flowers experiencing low rates of pollen removal lasted significantly longer than flowers that had faster rates of pollen removal. Experimental manipulations showed that low levels of pollen removal resulted in extension of the staminate phase. Hand-pollinations in which we varied the amount and source of pollen showed that when the number of fertilized ovules within an ovary is low, senescence of the flower is delayed, resulting in extension of the pistillate phase. We also report on pollinator foraging patterns within the vertical inflorescences of C. rapunculoides and the limiting factor for seed set in this population. The results are relevent to recent suggestions that floral characters often serve to reduce interference between the sexual functions in cosexual plants. 相似文献
34.
Prostaglandin H Synthetase-Mediated Metabolism of Dopamine: Implication for Parkinson's Disease 总被引:2,自引:1,他引:1
† Michael B. Mattammal ‡§Randy Strong †Vijaya M. Lakshmi ¶Hyung D. Chung #Alan H. Stephenson 《Journal of neurochemistry》1995,64(4):1645-1654
Abstract: Differences in prostaglandin H synthetase (PHS) activity in the substantia nigra of age- and post-mortem interval-matched parkinsonian, Alzheimer's, and normal control brain tissue were assessed. Prostaglandin E2 (PGE2 , an index of PHS activity) was higher in substantia nigra of parkinsonian brain tissue than Alzheimer's or control tissue. Incubation of substantia nigra slices with arachidonic acid (AA) increased PGE2 synthesis. Dopamine stimulated PHS synthesis of PGE2 . [3 H]Dopamine was activated by PHS to electrophilic intermediate(s) that covalently bound to DNA, microtubulin protein, bovine serum albumin, and sulfhydryl reagents. When AA was replaced by hydrogen peroxide, PHS/H2 O2 -supported binding proceeded at rates similar to those observed with PHS/AA. Indomethacin and aspirin inhibited AA-mediated cooxidation of dopamine but not H2 O2 -mediated metabolism. PHS-mediated metabolism of dopamine was not affected by monoamine oxidase inhibitors. Substrate requirements and effects of specific inhibitors suggest cooxidation of dopamine is mediated by the hydroperoxidase activity of PHS. 32 P-postlabeling was used to detect dopamine-DNA adducts. PHS/AA activation of dopamine in the presence of DNA resulted in the formation of five dopamine-DNA adducts, i.e., 23, 43, 114, 70, and 270 amol/µg DNA. DNA adduct formation was PHS, AA, and dopamine dependent. PHS catalyzed cooxidation of dopamine in dopaminergic neuronal degeneration is discussed. 相似文献
35.
Flash photolysis of DM-nitrophen generates an extremely large [Ca2+] transient ("Ca2+ spike") at the start of each Ca2+ "step." The Ca2+ spike greatly increases the speed of activation of the ryanodine receptor channel ("supercharging") and could be responsible for apparent channel adaptation. 相似文献
36.
The male determinant of self-incompatibility in Brassica oleracea is located in the pollen coating 总被引:2,自引:0,他引:2
Andrew G. Stephenson James Doughty Suzanne Dixon Carole Elleman Simon Hiscock Hugh G. Dickinson 《The Plant journal : for cell and molecular biology》1997,12(6):1351-1359
An in vitro bioassay has been developed to explore the role of the pollen coating in the pollen/stigma interaction in Brassica oleracea . In the assay, coating is removed from pollen grains, supplemented with protein fractions isolated from coatings of different S (self incompatibility) haplotypes, and then—using micromanipulation—interposed between individual pollen grains and the stigmatic surface. Normally, the coating used is of the same haplotype as the pollen in the experiment—thus constituting an 'extension' of its own coat—but carrying the supplemented protein fractions. Initial experiments confirmed preliminary data that the pollen coating contained the male determinant of self incompatibility (SI); not only did the addition of 'self' coating (i.e. that with the same S -haplotype as the stigma) prevent the success of a compatible cross pollination, but a 'cross' coating (i.e. that with a different S -haplotype from the stigma) could induce the germination and growth of self pollen. Protein supplementation experiments demonstrated that the pollen-held determinant is contained within the water soluble component of the pollen coat, while further analysis revealed that the active molecular species possesses an Mr 10 kDa. More extensive fractionation by gel filtration and reverse phase HPLC was used to isolate a family of basic, cysteine-rich proteins (PCP-A: P ollen C oat P roteins-class A)—one of which is known to bind to stigmatically-expressed components of the S -locus in Brassica . Introduction of the PCP-A protein fraction into the bioassay confirmed the male determinant of SI as a protein, and probably a member of the PCP-A protein family. 相似文献
37.
Stamatina E. Ziemba Shani Saks Yvonne Janviriya Robert S. Stephenson 《Cell and tissue research》1995,280(2):473-477
Photoreceptor cells that were mostly free of extracellular material and suitable for most electrophysiological study procedures were dissociated from whole heads of the fruit fly, Drosophila melanogaster, by a simple smash technique employing gentle chopping by a razor blade through Parafilm sheets. A variety of commonly available proteolytic and glycolytic digestion enzymes were tested as additions to the basic dissociation procedure described. With the aid of Nomarski interference contrast optics, periodic acid-Schiff staining, and fluorescent labeling and microscopy methods, it was determined that proteolytic enzymatic digestion does little to enhance the dissociation procedure, and instead, often damages the cells that one is attempting to recover. Unexpectedly, certain glycolytic enzymes, when added to the basic procedure, appear to enhance the recovery of intact viable Drosophila photoreceptors that are stripped of most extracellular material. Based on these results, a hypothesis concerning the biochemical nature of the extracellular matrix of the Drosophila retina is proposed. Drosophila photoreceptors are an interesting model system for the study of invertebrate phototransduction and photoreceptor cell biology because of their many well-characterized mutant strains. The technique described here should produce clean viable photoreceptors or ommatidia that respond to light, and that are suitable for patch clamping or cell culture. 相似文献
38.
39.
Feline leukemia virus: biochemical and immunological characterization of gag gene-coded structural proteins. 总被引:18,自引:12,他引:6 下载免费PDF全文
The major non-glycosylated structural proteins of feline leukemia virus have been isolated, and competition immunoassays have been developed for each. These proteins include the 27,000- to 30,000-molecular-weight major internal antigen designated p30, a 15,000-molecular-weight protein (p15), an acidic protein of 12,000 molecular weight (p12), and a highly basic 10,000-molecular-weight protein (p10). Immunologically and biochemically corresponding proteins of feline and murine leukemia viruses have been identified. and, on the basis of analogy to the known sequence of a prototype type C virus of mouse origin, the map order of the gag region of the feline type C viral genome has been tentatively deduced as NH2-p15-p12-p10-COOH. The demonstration of two feline leukemia virus gag gene-coded proteins, p15 and p12, expressed in the form of an uncleaved precursor in a mink cell line nonproductively transformed by feline sarcoma virus provides indirect support for the proposed sequence. 相似文献
40.
Translation of type C viral RNAs in Xenopus laevis oocytes: evidence that the 120,000-molecular-weight polyprotein expressed in Abelson leukemia virus-transformed cells is virus coded. 总被引:9,自引:6,他引:3 下载免费PDF全文
The genomic RNA of Abelson leukemia virus (AbLV) has been purified and translated in Xenopus laevis oocytes. The primary AbLV-specific protein synthesized is a polyprotein corresponding in molecular weight and immunological properties to a previously described p15 and p12 containing 110,000- to 130,000-molecular-weight polyprotein expressed in AbLV-transformed cells. In contrast, translation of woolly monkey sarcoma virus genomic RNA resulted in symthesis of a 55,000-molecular-weight polyprotein consisting of woolly helper virus p30, p15, and p12. These findings demonstrate the value of the X. laevis oocyte in vitro system for studies of translational products of replication-defective transforming viruses and establish the virus-coded nature of the nonstructural component of the 110,000- to 130,000-molecular-weight polyprotein expressed in AbLV-transformed cells. 相似文献