全文获取类型
收费全文 | 29142篇 |
免费 | 3695篇 |
国内免费 | 3篇 |
专业分类
32840篇 |
出版年
2021年 | 286篇 |
2018年 | 287篇 |
2017年 | 258篇 |
2016年 | 477篇 |
2015年 | 754篇 |
2014年 | 834篇 |
2013年 | 1070篇 |
2012年 | 1299篇 |
2011年 | 1201篇 |
2010年 | 771篇 |
2009年 | 743篇 |
2008年 | 1101篇 |
2007年 | 1087篇 |
2006年 | 1004篇 |
2005年 | 967篇 |
2004年 | 947篇 |
2003年 | 949篇 |
2002年 | 917篇 |
2001年 | 916篇 |
2000年 | 914篇 |
1999年 | 778篇 |
1998年 | 416篇 |
1997年 | 383篇 |
1996年 | 367篇 |
1995年 | 321篇 |
1994年 | 322篇 |
1993年 | 335篇 |
1992年 | 682篇 |
1991年 | 630篇 |
1990年 | 611篇 |
1989年 | 662篇 |
1988年 | 563篇 |
1987年 | 602篇 |
1986年 | 476篇 |
1985年 | 564篇 |
1984年 | 478篇 |
1983年 | 385篇 |
1982年 | 398篇 |
1981年 | 360篇 |
1980年 | 328篇 |
1979年 | 435篇 |
1978年 | 382篇 |
1977年 | 339篇 |
1976年 | 313篇 |
1975年 | 336篇 |
1974年 | 382篇 |
1973年 | 361篇 |
1972年 | 305篇 |
1971年 | 285篇 |
1969年 | 247篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
132.
Attachment and release of spermatozoa from the caudal isthmus of the hamster oviduct 总被引:2,自引:0,他引:2
Female hamsters were mated shortly after the onset of oestrus. At 3 or 6 h after mating, the right oviduct was flushed in situ with 30, 90 or 180 microliters medium to remove spermatozoa from the lumen, leaving only those firmly attached to the isthmic mucosa of the oviduct. When eggs were recovered from oviducts at 20 h after flushing the majority were fertilized, indicating that the spermatozoa that were firmly attached to the mucosa were capable of detaching and ascending to the ampulla to fertilize eggs. Neither the time of flushing nor the volume of flushing medium had a significant effect on the percentage of spermatozoa that remained in the isthmus after flushing. These results suggest that there is no change in the surface of the oviduct mucosa that causes the release of spermatozoa from the caudal isthmus near the time of ovulation. When incapacitated spermatozoa were introduced into the oviduct, many of them attached to oviductal mucosa, while capacitated spermatozoa did not. This indicates that it is a change in the sperm surface, rather than the mucosal surface, that causes the release of spermatozoa, i.e. spermatozoa remain attached to the isthmic mucosa until they become capacitated and then detach and migrate to the ampulla to fertilize the eggs. 相似文献
133.
Current studies suggest a genetic program governs the lifespan of each organism. Using cellular senescence as a model system, components of this program for aging have been sought. Human diploid fibroblasts, upon reaching senescence, express active inhibitors of DNA synthesis. It is believed that such inhibitors could be members of a new family of negative growth effectors involved in the pathway to senescence. Factors capable of inhibiting DNA synthesis in a similar manner have also been identified from human quiescent fibroblasts and liver cells as well as from quiescent rodent liver cells. The relationship of these inhibitors to previously identified negative growth effectors and aging are discussed. 相似文献
134.
Elaine F. Smith Andrew V. Roberts John Mottley Susan Denness 《Plant Cell, Tissue and Organ Culture》1991,27(3):309-313
Plantlets of Dendranthema grandiflora Pennine Reel were grown from nodal sections on Sorbarods saturated with liquid medium containing 0–3 mg 1–1 of various growth retardants. After 4 weeks they were transferred to compost and maintained at a relative humidity of 42% at 27.5°C. Wilting was assessed over a period of 3 h. Plantlets treated with paclobutrazol, flurprimidol, triapenthenol, chlorphonium chloride, uniconazol and ancymidol showed dose-related reductions in wilting up to a concentration of 3 mg 1–1. Responses to tetcyclacis and mepiquat chloride were weaker, and no responses to chlormequat chloride, BTS 44584 or diaminozide could be detected. These observations are compatible with an hypothesis that resistance to wilting derives from inhibited synthesis of gibberellins. 相似文献
135.
Smith JM 《Trends in ecology & evolution》1991,6(5):146-151
Recent research on sexual selection in animals has begun to indicate that 'handicaps' and 'honest signalling' may play more important roles than hitherto thought. This review reappraises theories of sexual selection in the light of these new developments. 相似文献
136.
Developmental expression and cellular localization of glucose transporter molecules during mouse preimplantation development. 总被引:7,自引:0,他引:7
M Aghayan L V Rao R M Smith L Jarett M J Charron B Thorens S Heyner 《Development (Cambridge, England)》1992,115(1):305-312
Two general mechanisms mediate glucose transport, one is a sodium-coupled glucose transporter found in the apical border of intestinal and kidney epithelia, while the other is a sodium-independent transport system. Of the latter, several facilitated transporters have been identified, including GLUT1 (erythrocyte/brain), GLUT2 (liver) and GLUT4 (adipose/muscle) isoforms. In this study, we used Western-blot analysis and high resolution immunoelectron microscopy (IEM) to investigate the stage-related expression and cellular localization of GLUT1, 2 and 4. The Western blot results demonstrate that GLUT1 is detectable in the oocyte and throughout preimplantation development. GLUT2 isoforms were not detectable until the blastocyst stage, while the GLUT4 isoform was undetectable in the oocyte through blastocyst stages. The present findings confirm previous studies at the molecular level which demonstrated that mRNAs encoding the same GLUT isoforms are detectable at corresponding developmental stages. GLUT1 and GLUT2 display different cellular distributions at the blastocyst stage as shown by IEM studies. GLUT1 has a widespread distribution in both trophectoderm and inner cell mass cells, while GLUT2 is located on trophectoderm membranes facing the blastocyst cavity. This observation suggests a different functional significance for these isoforms during mouse preimplantation development. 相似文献
137.
138.
139.
The discovery of apoptosis, a widespread and morphologically distinct form of physiological cell death, has had an extraordinary impact on cell biology. The importance of apoptosis stems from its active nature and its potential for controlling biological systems. The growing appreciation of the significance of this process has stimulated intense investigation into the molecular mechanisms involved and into its fundamental implications for developmental biology, immunology and oncology. 相似文献
140.
Prohibitin, an evolutionarily conserved intracellular protein that blocks DNA synthesis in normal fibroblasts and HeLa cells. 总被引:21,自引:7,他引:14
M J Nuell D A Stewart L Walker V Friedman C M Wood G A Owens J R Smith E L Schneider R Dell' Orco C K Lumpkin et al. 《Molecular and cellular biology》1991,11(3):1372-1381
Genes that act inside the cell to negatively regulate proliferation are of great interest because of their implications for such processes as development and cancer, but these genes have been difficult to clone. This report details the cloning and analysis of cDNA for prohibitin, a novel mammalian antiproliferative protein. Microinjection of synthetic prohibitin mRNA blocks entry into S phase in both normal fibroblasts and HeLa cells. Microinjection of an antisense oligonucleotide stimulates entry into S phase. By sequence comparison, the prohibitin gene appears to be the mammalian analog of Cc, a Drosophila gene that is vital for normal development. 相似文献