首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   36332篇
  免费   3591篇
  国内免费   3507篇
  2024年   35篇
  2023年   438篇
  2022年   581篇
  2021年   1488篇
  2020年   1216篇
  2019年   1524篇
  2018年   1485篇
  2017年   1105篇
  2016年   1556篇
  2015年   2451篇
  2014年   2824篇
  2013年   2964篇
  2012年   3574篇
  2011年   3296篇
  2010年   2166篇
  2009年   1979篇
  2008年   2248篇
  2007年   2014篇
  2006年   1820篇
  2005年   1537篇
  2004年   1420篇
  2003年   1206篇
  2002年   981篇
  2001年   584篇
  2000年   479篇
  1999年   424篇
  1998年   334篇
  1997年   234篇
  1996年   221篇
  1995年   175篇
  1994年   189篇
  1993年   102篇
  1992年   133篇
  1991年   98篇
  1990年   104篇
  1989年   82篇
  1988年   55篇
  1987年   71篇
  1986年   39篇
  1985年   38篇
  1984年   41篇
  1983年   22篇
  1982年   16篇
  1981年   15篇
  1979年   8篇
  1977年   5篇
  1976年   8篇
  1974年   8篇
  1973年   7篇
  1966年   4篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
Bacillus thuringiensis NTB-1 isolated from soil samples in Korea produces ovoidal parasporal inclusions with proteins of approximately 24–40 kDa in size. Although serological study indicated that the isolate has a flagella (H) antigen identical with subsp. israelensis , it seemed to be non-insecticidal against Lepidoptera and Coleoptera as well as Diptera. To investigate the activity of non-insecticidal B. thuringiensis transformed with insecticidal crystal protein genes, cryIVD and cytA genes of B. thuringiensis subsp. morrisoni PG-14, highly toxic to mosquito larvae, were introduced into the isolate NTB-1. The expression of mosquitocidal crystal protein genes in NTB-1 was characterized by SDS–PAGE analysis and electron microscopy. The results showed that crystalline inclusions of host, CryIVD and CytA were stably expressed in the transformant. However, the mosquitocidal activity of transformant was similar to that of B. thuringiensis subsp. kurstaki Cry B harbouring cryIVD and cytA genes, demonstrating that a synergistic effect by an interaction of both introduced insecticidal and resident non-insecticidal crystal proteins was not observed.  相似文献   
4.
Cre/loxP technology is an important tool for studying cell type-specific gene functions. Cre recombinase mouse lines, including Agc1-CreERT2, Col2a1-Cre; Col2a1-CreERT2, Shh-Cre, Shh-CreERT2, and Osx-Cre, have been proven to be valuable tools to elucidate the biology of long bones, yet the information for their activity in postnatal intervertebral disc (IVD) tissues was very limited. In this study, we used R26-mTmG fluorescent reporter to systematically analyze cell specificity and targeting efficiency of these six mouse lines in IVD tissues at postnatal growing and adult stages. We found that Agc1-CreERT2 is effective to direct recombination in all components of IVDs, including annulus fibrosus (AF), nucleus pulposus (NP), and cartilaginous endplate (CEP), upon tamoxifen induction at either 2 weeks or 2 months of ages. Moreover, Col2a1-Cre targets most of the cells in IVDs, except for some cells in the outer AF (OAF) and NP. In contrast, the activity of Col2a1-CreERT2 is mainly limited to the IAF of IVD tissues at either stage of tamoxifen injection. Similarly, Shh-Cre directs recombination specifically in all NP cells, whereas Shh-CreERT2 is active only in a few NP cells when tamoxifen is administered at either stage. Finally, Osx-Cre targets cells in the CEP, but not in the NP or AF of IVDs tissues at these two stages. Thus, our data demonstrated that all these Cre lines can direct recombination in IVD tissues at postnatal stages with different cell type specificity and/or targeting efficiency, and can, therefore, serve as valuable tools to dissect cell type-specific gene functions in IVD development and homeostasis.  相似文献   
5.
6.
7.
A 45-year-old-male who had underlying ulcerative colitis and presented with fever and dry cough. Initially, the patient was considered to have invasive aspergillosis due to a positive galactomannan assay. He was treated with amphotericin B followed by voriconazole. Nevertheless, the patient deteriorated clinically and radiographically. The lung biopsy revealed eosinophilic pneumonia, and ELISA for Toxocara antigen was positive, leading to a diagnosis of pulmonary toxocariasis. After a 10-day treatment course with albendazole and adjunctive steroids, the patient recovered completely without any sequelae. Pulmonary toxocariasis may be considered in patients with subacute or chronic pneumonia unresponsive to antibiotic agents, particularly in cases with eosinophilia.  相似文献   
8.
华北地区针叶林下凋落物层化学性质的研究   总被引:10,自引:0,他引:10  
森林凋落物中贮积了大量的有机、无机养分物质,它是森林土壤自然肥力的重要来源之一。在森林生态系统中,养分物质的内部循环主要是通过凋落物来实现的。在分解、转化过  相似文献   
9.
Yan  Xue  Liu  Jia  Wu  Ke-Xin  Yang  Nan  Pan  Li-Ben  Song  Ying  Liu  Yang  Tang  Zhong-Hua 《Journal of Plant Growth Regulation》2022,41(6):2421-2434
Journal of Plant Growth Regulation - Early-spring plants are a special type of plant that complete their life cycle promptly in cold, early spring. Very little effort has been made into researching...  相似文献   
10.
ER oxidoreduclin 1α (ERO1α) is an oxidase, participating in formation of secretory and membrane proteins. However, the other physiological functions ERO1α is not well known. We found that ERO1α is high in the Leydig cells of the testis. Therefore, the purposes of the current study are to explore the role of ERO1α and the possible mechanisms in regulating cell proliferation, apoptosis, and testosterone secretion of Leydig cells. ERO1α was mainly localized in Leydig cells in the adult mice testes by immunofluorescence staining. Western blot analysis showed that ERO1α was higher in Leydig cells than that in the seminiferous tubules. The effect of ERO1α on cell proliferation, apoptosis, and testosterone secretion was detected by transducing ERO1α overexpression and knockdown lentiviruses into cultured primary Leydig cells (PLCs) together with hCG exposure. Flow cytometry analysis showed that ERO1α promoted cell proliferation by increasing cell distribution at the S phase and decreasing that at the G0/G1 phase. Western bolt analysis showed that ERO1α increased CDK2 and CDK6 expression. Cell apoptosis determination found that ERO1α inhibited PLC apoptosis. Western bolt analysis showed that ERO1α increased the ratio of BCL-2/BAX, and decreased BAD and Caspase-3 expression. Enzyme-linked immunosorbent assay analysis demonstrated that ERO1α enhanced testosterone secretion. Western bolt analysis found that ERO1α increased StAR, 3β-HSD, and CYP17A1 expression. Furthermore, ERO1α could activate the PI3K/AKT/mTOR signaling pathway. In summary, these results suggest that ERO1α might play proliferation promotion and antiapoptotic roles and enhance testosterone secretion in PLC, at least partly, via activation of the PI3K/AKT/mTOR signaling pathway.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号