全文获取类型
收费全文 | 1297篇 |
免费 | 118篇 |
国内免费 | 1篇 |
专业分类
1416篇 |
出版年
2023年 | 7篇 |
2022年 | 19篇 |
2021年 | 37篇 |
2020年 | 18篇 |
2019年 | 24篇 |
2018年 | 29篇 |
2017年 | 31篇 |
2016年 | 35篇 |
2015年 | 42篇 |
2014年 | 47篇 |
2013年 | 80篇 |
2012年 | 74篇 |
2011年 | 87篇 |
2010年 | 46篇 |
2009年 | 43篇 |
2008年 | 49篇 |
2007年 | 78篇 |
2006年 | 48篇 |
2005年 | 40篇 |
2004年 | 49篇 |
2003年 | 34篇 |
2002年 | 30篇 |
2001年 | 35篇 |
2000年 | 29篇 |
1999年 | 25篇 |
1998年 | 15篇 |
1997年 | 12篇 |
1995年 | 10篇 |
1994年 | 13篇 |
1993年 | 7篇 |
1992年 | 26篇 |
1991年 | 28篇 |
1990年 | 25篇 |
1989年 | 26篇 |
1988年 | 14篇 |
1987年 | 12篇 |
1986年 | 12篇 |
1985年 | 16篇 |
1984年 | 8篇 |
1983年 | 8篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 16篇 |
1978年 | 16篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1973年 | 7篇 |
1972年 | 10篇 |
1971年 | 9篇 |
1966年 | 7篇 |
排序方式: 共有1416条查询结果,搜索用时 0 毫秒
101.
Storz JF Bhat HR Kunz TH 《Evolution; international journal of organic evolution》2001,55(6):1215-1223
Population subdivision into behaviorally cohesive kin groups influences rates of inbreeding and genetic drift and has important implications for the evolution of social behavior. Here we report the results of a study designed to test the hypothesis that harem social structure promotes inbreeding and genetic subdivision in a population with overlapping generations. Genetic consequences of harem social structure were investigated in a natural population of a highly polygynous fruit bat, Cynopterus sphinx (Chiroptera: Pteropodidae), in western India. The partitioning of genetic variance within and among breeding groups was assessed using 10-locus microsatellite genotypes for 431 individually marked bats. Genetic analysis of the C. sphinx study population was integrated with field data on demography and social structure to determine the specific ways in which mating, dispersal, and new social group formation influenced population genetic structure. Microsatellite data revealed striking contrasts in genetic structure between consecutive offspring cohorts and between generations. Relative to the 1998 (dry-season) offspring cohort, the 1997 (wet-season) cohort was characterized by a more extensive degree of within-group heterozygote excess (F(IS) = -0.164 vs. -0.050), a greater degree of among-group subdivision (F(ST) = 0.123 vs. 0.008), and higher average within-group relatedness (r = 0.251 vs. 0.017). Differences in genetic structure between the two offspring cohorts were attributable to seasonal differences in the number and proportional representation of male parents. Relative to adult age-classes, offspring cohorts were characterized by more extensive departures from allelic and genotypic equilibria and a greater degree of genetic subdivision. Generational differences in F-statistics indicated that genetic structuring of offspring cohorts was randomized by natal dispersal prior to recruitment into the breeding population. Low relatedness among harem females (r = 0.002-0.005) was primarily attributable to high rates of natal dispersal and low rates of juvenile survivorship. Kin selection is therefore an unlikely explanation for the formation and maintenance of behaviorally cohesive breeding groups in this highly social mammal. 相似文献
102.
Loss of A-type lamin expression compromises nuclear envelope integrity leading to muscular dystrophy 总被引:28,自引:0,他引:28
下载免费PDF全文
![点击此处可从《The Journal of cell biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Sullivan T Escalante-Alcalde D Bhatt H Anver M Bhat N Nagashima K Stewart CL Burke B 《The Journal of cell biology》1999,147(5):913-920
The nuclear lamina is a protein meshwork lining the nucleoplasmic face of the inner nuclear membrane and represents an important determinant of interphase nuclear architecture. Its major components are the A- and B-type lamins. Whereas B-type lamins are found in all mammalian cells, A-type lamin expression is developmentally regulated. In the mouse, A-type lamins do not appear until midway through embryonic development, suggesting that these proteins may be involved in the regulation of terminal differentiation. Here we show that mice lacking A-type lamins develop to term with no overt abnormalities. However, their postnatal growth is severely retarded and is characterized by the appearance of muscular dystrophy. This phenotype is associated with ultrastructural perturbations to the nuclear envelope. These include the mislocalization of emerin, an inner nuclear membrane protein, defects in which are implicated in Emery-Dreifuss muscular dystrophy (EDMD), one of the three major X-linked dystrophies. Mice lacking the A-type lamins exhibit tissue-specific alterations to their nuclear envelope integrity and emerin distribution. In skeletal and cardiac muscles, this is manifest as a dystrophic condition related to EDMD. 相似文献
103.
Bhat KM 《Genetics》1999,151(4):1479-1492
In a variety of tissues in eukaryotes, multipotential stem cells are responsible for maintaining a germinal population and generating a differentiated progeny. The Drosophila germline is one such tissue where a continuous supply of eggs or sperm relies on the normal functioning of stem cells. Recent studies have implicated a possible role for the posterior determinant gene nanos (nos) in stem cells. Here, I report that nanos is required in the Drosophila female germline as well as in the male germline. In the female, nos is required for the functioning of stem cells. In nos mutants, while the stem cells are specified, these cells divide only a few times at the most and then degenerate. The loss of germline stem cells in nos mutant mothers appears to be due to a progressive degeneration of the plasma membrane. Furthermore, following germ cell loss, the germaria in the nos mutant mothers appear to carry on massive mitochondrial biogenesis activity. Thus, the syncytia of such germaria are filled with mitochondria. In the male germline, the male fertility assay indicates that nos appears to be also required for the maintenance of stem cells. In these mutant males, spermatogenesis is progressively affected and these males eventually become sterile. These results indicate novel requirements for nos in the Drosophila germline. 相似文献
104.
Many fungi are known to secrete lectins, but their functional roles are not clearly understood. Sclerotium rolfsii, a soilborne plant pathogenic fungus capable of forming fruiting bodies called sclerotial bodies, secrete a cell wall-associated Thomsen-Friedenreich antigen-specific lectin. To understand the functional role of this lectin, we examined its occurrence and expression during development of the fungus. Furthermore, putative endogenous receptors of the lectin were examined to substantiate the functional role of the lectin. Immunolocalization studies using FITC-labeled lectin antibodies revealed discrete distribution of lectin sites at the branching points of the developing mycelia and uniformly occurring lectin sites on the mature sclerotial bodies. During development of the fungus the lectin is expressed in small amounts on the vegetative mycelia and reaching very high levels in mature sclerotial bodies with a sudden spurt in secretion at the maturation stage. Capping of the lectin sites on the sclerotial bodies by lectin antibodies or haptens inhibit strongly the germination of these bodies, indicating functional significance of the lectin. At the maturation stage the lectin interacts with the cell wall-associated putative endogenous receptor leading to the aggregation of mycelium to form sclerotial bodies. The lectin-receptor complex probably acts as signaling molecule in the germination process of sclerotial bodies. Using biotinylated lectin, the receptors were identified by determining the specific lectin binding to lipid components, extracted from sclerotial bodies, and separated on thin-layer chromatograms. Preliminary characterization studies indicated that the receptors are glycosphingolipids and resemble inositolphosphoceramides. These findings together demonstrate the importance of lectin-receptor interactions to explain hitherto speculated functional role of the lectins and also the glycosphingolipids of fungi. 相似文献
105.
106.
Background
Digital watermarking is a technique of hiding specific identification data for copyright authentication. This technique is adapted here for interleaving patient information with medical images, to reduce storage and transmission overheads. 相似文献107.
Bhat BA Ponnala S Sahu DP Tiwari P Tripathi BK Srivastava AK 《Bioorganic & medicinal chemistry》2004,12(22):5857-5864
A number of thiazolidine-2,4-diones derivatives having carboxylic ester appendage at N-3 were synthesized and their antihyperglycemic activity was evaluated. Many of these derivatives as well as their corresponding carboxylic acid showed significant improvement on post-prandial hyperglycemia in normal rats, in contrast to their poor agonist activity at PPARgamma. 相似文献
108.
109.
110.
C-Phycocyanin,a selective cyclooxygenase-2 inhibitor,induces apoptosis in lipopolysaccharide-stimulated RAW 264.7 macrophages 总被引:3,自引:0,他引:3
Reddy MC Subhashini J Mahipal SV Bhat VB Srinivas Reddy P Kiranmai G Madyastha KM Reddanna P 《Biochemical and biophysical research communications》2003,304(2):385-392
C-Phycocyanin (C-PC) is one of the major biliproteins of Spirulina platensis, a blue green algae, with antioxidant and radical scavenging properties. It is also known to exhibit anti-inflammatory and anti-cancer properties. However, the mechanism of action of C-PC is not clearly understood. Previously, we have shown that C-PC selectively inhibits cyclooxygenase-2 (COX-2), an inducible isoform that is upregulated during inflammation and cancer. In view of the reported induction of apoptosis in cancer cells by cyclooxygenase-2 inhibitors, the present study is undertaken to test the effect of C-PC on LPS stimulated RAW 264.7 mouse macrophage cell line. These studies have shown a dose dependent reduction in the growth and multiplication of macrophage cell line by C-PC. This decrease in cell number appears to be mediated by C-PC induced apoptosis as evidenced by flow cytometric and confocal microscopic studies. Cells treated with 20 micro M C-PC showed typical nuclear condensation and 16.6% of cells in sub-G(o)/G(1) phase. These cells also showed DNA fragmentation in a dose dependent manner. The studies on poly(ADP ribose) polymerase (PARP) cleavage showed typical fragmentation pattern in C-PC treated cells. This C-PC induced apoptosis in RAW 264.7 cells appears to be mediated by the release of cytochrome c from mitochondria and independent of Bcl-2 expression. These effects of C-PC on RAW 264.7 cells may be due to reduced PGE(2) levels as a result of COX-2 inhibition. 相似文献