全文获取类型
收费全文 | 318608篇 |
免费 | 37376篇 |
国内免费 | 134篇 |
出版年
2018年 | 2748篇 |
2016年 | 3741篇 |
2015年 | 5067篇 |
2014年 | 5994篇 |
2013年 | 8632篇 |
2012年 | 9576篇 |
2011年 | 9746篇 |
2010年 | 6597篇 |
2009年 | 5892篇 |
2008年 | 8535篇 |
2007年 | 8962篇 |
2006年 | 8371篇 |
2005年 | 8078篇 |
2004年 | 8166篇 |
2003年 | 7903篇 |
2002年 | 7801篇 |
2001年 | 14292篇 |
2000年 | 14321篇 |
1999年 | 11475篇 |
1998年 | 4020篇 |
1997年 | 4129篇 |
1996年 | 3928篇 |
1995年 | 3799篇 |
1994年 | 3800篇 |
1993年 | 3689篇 |
1992年 | 9805篇 |
1991年 | 9386篇 |
1990年 | 9211篇 |
1989年 | 8940篇 |
1988年 | 8347篇 |
1987年 | 7985篇 |
1986年 | 7211篇 |
1985年 | 7319篇 |
1984年 | 6043篇 |
1983年 | 5301篇 |
1982年 | 4173篇 |
1981年 | 3691篇 |
1980年 | 3511篇 |
1979年 | 6094篇 |
1978年 | 4547篇 |
1977年 | 4272篇 |
1976年 | 3968篇 |
1975年 | 4295篇 |
1974年 | 4651篇 |
1973年 | 4715篇 |
1972年 | 4355篇 |
1971年 | 4065篇 |
1970年 | 3435篇 |
1969年 | 3334篇 |
1968年 | 2962篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
761.
The paper presents the analysis of the frequency, density, and distribution of recombination sites in the male meiosis of the domestic cat (Felis silvestris catus). The study was carried out using immunofluorescent staining of synaptonemal complex (SC) proteins, centromeric proteins and mismatch repair protein MLH1, a reliable marker of crossingover sites. We mapped 2633 sites of crossing over in 1098 individual autosomes. Based on these data, we estimated the total length of the genetic map of the domestic cat to be 2176 centimorgans. Positive correlation between the length of SC and the number of recombination sites common for mammalians was also found in the domestic cat. It was shown that this species was characterized by the highest density of recombination and the lowest interference in mammals. 相似文献
762.
763.
B Mao 《Biopolymers》1990,30(5-6):645-647
764.
The separation and estimation of ribonucleotides in minute quantities 总被引:11,自引:0,他引:11
MAGASANIK B VISCHER E DONIGER R ELSON D CHARGAFF E 《The Journal of biological chemistry》1950,186(1):37-50
765.
766.
B. K. Pierson S. J. Giovannoni D. A. Stahl R. W. Castenholz 《Archives of microbiology》1985,142(2):164-167
An unusual filamentous, gliding bacterium was found in a few hot springs in Oregon where it formed a nearly unispecific top layer of microbial mats. It contained a bacteriochlorophyll a-like pigment and an abundance of carotenoids. There were no chlorosomes or additional chlorophylls. The organism was aerotolerant and appeared to be photoheterotrophic. It was successfully co-cultured with an aerobic chemoheterotroph in a medium containing glucose and casamino acids. Although it has many characteristics in common with the genus Chloroflexus, the lack of chlorosomes and bacteriochlorophyll c and the aerobic nature of this organism indicate that it should be placed in a new genus. This conclusion is supported by 5S rRNA nucleotide sequence data. 相似文献
767.
Inositol 1,4,5-trisphosphate (IP3) induced rapid formation of thromboxane B2 in saponin-permeabilised human platelets: mechanism of IP3 action 总被引:2,自引:0,他引:2
The mechanism of IP3-induced activation of saponin-permeabilised platelets has been examined. Saponin permeabilization resulted in the leakage of low-Mr substances into and from the cells without loss of cytoplasmic proteins. Addition of IP3 rapidly induced a dose-related formation of thromboxane B2 and release into the medium, leading to the responses of shape change, aggregation and [14C]5HT release. These responses were inhibited by the thromboxane A2 receptor antagonist AH23848. The IP3-induced release of 45Ca from intracellular stores was not affected by indomethacin. Synthesis of thromboxane was inhibited if Ca2+ elevation was prevented by using Ca-EGTA buffers during permeabilization. These studies indicate that IP3-induced activation was due to Ca2+ mobilisation leading to phospholipase activation and thromboxane synthesis. 相似文献
768.
769.
N Flomenberg K Welte R Mertelsmann N Kernan N Ciobanu S Venuta S Feldman G Kruger D Kirkpatrick B Dupont R O'Reilly 《Journal of immunology (Baltimore, Md. : 1950)》1983,130(6):2644-2650
Five children with primary deficiencies of T cell function were studied to assess the effects of highly purified exogenous Interleukin 2 (IL 2) on their in vitro T cell responses. The lymphocytes from one child with Nezelof's T cell deficiency demonstrated absence of endogenous IL 2 production and improved proliferative responses to mitogen or alloantigen in the presence of exogenous IL 2. Moreover, during in vitro mixed lymphocyte culture in the presence of exogenous IL 2, his lymphocytes were able to develop into cytotoxic effector cells. A second child with Nezelof's syndrome demonstrated a different type of defect. The lymphocytes from this child had less impairment of endogenous IL 2 production. Although IL 2 increased the proliferation of his cells in response to PHA, similar augmentation was not seen after stimulation with OKT3 or alloantigen. In cell-mediated cytotoxicity assays, after mixed lymphocyte culture, natural killer-like activity was strongly boosted in the cultures that contained IL 2, but T cell-mediated cytotoxicity was not. The lymphocytes from three patients with severe combined immunodeficiency did not show improved proliferative responses in the presence of IL 2. Thus, only one of the five patients demonstrated the combination of defective endogenous IL 2 production, but preservation of the ability to respond appropriately to exogenous IL 2. This child may therefore have suffered from a T cell defect pathophysiologically similar to that seen in nude or aged mice. 相似文献
770.
Comparison of factor IX methylation on human active and inactive X chromosomes: implications for X inactivation and transcription of tissue-specific genes. 总被引:11,自引:2,他引:9
下载免费PDF全文
![点击此处可从《The EMBO journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Maintenance of dosage compensation for housekeeping genes on the human X chromosome is mediated through differential methylation of clustered CpG nucleotides associated with these genes. To determine if methylation has a role in maintaining inactivity of X-linked genes which show tissue-specific expression, we examined the locus for blood clotting Factor IX. The analysis encompassed 91% of the HpaII and HhaI sites in the 41-kb region that includes the presumed promoter region, 5 kb of 5'- and 4 kb of 3'-flanking sequences. Although there are sex differences in methylation of the locus in leukocytes, the methylation pattern in liver, where the gene is expressed, is essentially the same for loci on the active and inactive X chromosome. The lack of differences in methylation of active and inactive genes makes it unlikely that methylation within the locus has a role in expression of the Factor IX gene. These findings, along with the absence of clustered CpG dinucleotides within the Factor IX locus, suggest that functional differences in DNA methylation related to X chromosome dosage compensation may be limited to CpG clusters. In any event, dosage compensation seems to be maintained regionally, rather than locus by locus. 相似文献