全文获取类型
收费全文 | 20070篇 |
免费 | 1003篇 |
国内免费 | 29篇 |
专业分类
21102篇 |
出版年
2023年 | 173篇 |
2022年 | 396篇 |
2021年 | 752篇 |
2020年 | 436篇 |
2019年 | 469篇 |
2018年 | 687篇 |
2017年 | 637篇 |
2016年 | 829篇 |
2015年 | 949篇 |
2014年 | 1200篇 |
2013年 | 1648篇 |
2012年 | 1756篇 |
2011年 | 1594篇 |
2010年 | 901篇 |
2009年 | 795篇 |
2008年 | 919篇 |
2007年 | 906篇 |
2006年 | 752篇 |
2005年 | 679篇 |
2004年 | 567篇 |
2003年 | 477篇 |
2002年 | 422篇 |
2001年 | 341篇 |
2000年 | 298篇 |
1999年 | 278篇 |
1998年 | 107篇 |
1997年 | 81篇 |
1996年 | 89篇 |
1995年 | 83篇 |
1994年 | 66篇 |
1993年 | 68篇 |
1992年 | 165篇 |
1991年 | 150篇 |
1990年 | 121篇 |
1989年 | 92篇 |
1988年 | 139篇 |
1987年 | 106篇 |
1986年 | 89篇 |
1985年 | 95篇 |
1984年 | 89篇 |
1983年 | 49篇 |
1982年 | 49篇 |
1981年 | 54篇 |
1980年 | 52篇 |
1979年 | 67篇 |
1978年 | 39篇 |
1977年 | 44篇 |
1976年 | 36篇 |
1973年 | 31篇 |
1972年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
891.
892.
893.
894.
Janus kinase 3 (Jak3) is a non-receptor tyrosine kinase known to be expressed in hematopoietic cells. Studies of whole organ homogenates show that Jak3 is also expressed in the intestines of both human and mice. However, neither its expression nor its function has been defined in intestinal epithelial enterocytes. The present studies demonstrate that functional Jak3 is expressed in human intestinal enterocytes HT-29 Cl-19A and Caco-2 and plays an essential role in the intestinal epithelial wound repair process in response to interleukin 2 (IL-2). Exogenous IL-2 enhanced the wound repair of intestinal enterocytes in a dose-dependent manner. Activation by IL-2 led to rapid tyrosine phosphorylation and redistribution of Jak3. IL-2-stimulated redistribution of Jak3 was inhibited by the Jak3-specific inhibitor WHI-P131. IL-2 also induced Jak3-dependent redistribution of the actin cytoskeleton in migrating cells. In these cells Jak3 interacted with the intestinal and renal epithelial cell-specific cytoskeletal protein villin in an IL-2-dependent manner. Inhibition of Jak3 activation resulted in loss of tyrosine phosphorylation of villin and a significant decrease in wound repair of the intestinal epithelial cells. Previously, we had shown that tyrosine phosphorylation of villin is important for cytoskeletal remodeling and cell migration. The present study demonstrates a novel pathway in intestinal enterocytes in which IL-2 enhances intestinal wound repair through mechanisms involving Jak3 and its interactions with villin. 相似文献
895.
Identification of the mechanisms underlying cellular plasticity in salamander cells is important because these may give pointers to the restricted regenerative ability of mammals. The myofibers from salamanders are remarkable for their ability to undergo cellularization and cell-cycle re-entry during regeneration. Here, we describe a detailed method for the isolation and culture of larval salamander myofibers in numbers suitable for cellular plasticity studies. The basic protocol for isolation and purification of cells can be completed in 4 h. 相似文献
896.
Maheshwari P Songara B Kumar S Jain P Srivastava K Kumar A 《Biotechnology journal》2007,2(8):1026-1032
Fast-growing callus, cell suspension and root cultures of Vernonia cinerea, a medicinal plant, were analyzed for the presence of alkaloids. Callus and root cultures were established from young leaf explants in Murashige and Skoog (MS) basal media supplemented with combinations of auxins and cytokinins, whereas cell suspension cultures were established from callus cultures. Maximum biomass of callus, cell suspension and root cultures were obtained in the medium supplemented with 1 mg/L alpha-naphthaleneacetic acid (NAA) and 5 mg/L benzylaminopurine (BA), 1.0 mg/L NAA and 0.1 mg/L BA and 1.5 mg/L NAA, respectively. The 5-week-old callus cultures resulted in maximum biomass and alkaloid contents (750 microg/g). Cell suspension growth and alkaloid contents were maximal in 20-day-old cultures and alkaloid contents were 1.15 mg/g. A 0.2-g sample of root tissue regenerated in semi-solid medium upon transfer to liquid MS medium containing 1.5 mg/L NAA regenerated a maximum increase in biomass of 6.3-fold over a period of 5 weeks. The highest root growth and alkaloid contents of 2 mg/g dry weight were obtained in 5-week-old cultures. Maximum alkaloid contents were obtained in root cultures in vitro compared to all others including the alkaloid content of in vivo obtained with aerial parts and roots (800 microg/g and 1.2 mg/g dry weight, respectively) of V. cinerea. 相似文献
897.
Rajesh Kumar Tewari Soo Yeon Lee Eun Joo Hahn Kee Yoeup Paek 《Plant biotechnology reports》2007,1(4):227-235
Nitric oxide (NO) is a diffusible, gaseous signaling molecule. In plants, NO influences growth and development, and it can
also affect plant responses to various stresses. Because NO induces root differentiation and interacts with reactive oxygen
species, we examined the temporal effect of NO elicitation on root growth, saponin accumulation and antioxidant defense responses
in the adventitious roots of mountain ginseng (Panax ginseng). The observations revealed that NO is involved in root growth and saponin production. Elicitation with sodium nitroprusside
(SNP) activated O2
−-generating NADPH oxidase (NOX) activity, which most probably subsequently enhanced growth of adventitious roots of mountain
ginseng. A severe inhibition of NOX activity and decline in dry weight of SNP elicited adventitious roots in the presence
of NOX inhibitor (diphenyl iodonium, DPI), which further supports involvement of NOX in root growth. Enhanced activities of
antioxidant enzymes by SNP appear to be responsible for low H2O2, less lipid peroxidation, and modulation of ascorbate and non-protein thiol statuses in the adventitious roots of mountain
ginseng. Dry mass, saponin content and NOX activity was related with NO content present in adventitious roots of mountain
ginseng. 相似文献
898.
Kumar A 《Biotechnology journal》2007,2(5):543-545
Biotechnology is a life science-based technique especially used in agriculture, medicine and food sciences. It is generally defined as the manipulation in organisms to generate products for the welfare of the world. Biotechnology combines disciplines such as genetics, biochemistry, microbiology, and cell biology along with information technology, chemical engineering, robotics etc. It includes basic industries such as food processing, tissue culture, plant development and other sophisticated ones such as recombinant therapeutics and diagnostics. Biotechnology, globally recognized as a rapidly emerging and far-reaching technology, is aptly described as the "technology of hope" for its promise of food, health and environmental sustainability. In India, biotechnology employs more than 10 000 people and generates roughly US$ 500 million in revenue annually. The biotechnology market has increased its sales from Rs. 50 billion in 1997 to Rs.70 billion in 2000, and is expected to cross Rs. 240 billion by the year 2010. In India, the human health biotech products account for 60% of the total market; agribiotech and veterinary 25%, medical devices, contract research and development (R&D), reagents and supplies constitute the remaining 15% Moreover, to facilitate foreign investment, capital and government policies are being revised. Other important industries include industrial enzyme manufacture, bioinformatics, and medical devices. Biotechnology has had limited appeal so far on our capital markets, and we have less then a dozen biotech companies listed on the public markets. 相似文献
899.
Sucrose-inducible expression of hepatitis B surface antigen using potato granule-bound starch synthase promoter 总被引:2,自引:0,他引:2
U. K. S. Shekhawat T. R. Ganapathi G. B. Sunil Kumar L. Srinivas 《Plant biotechnology reports》2007,1(4):199-206
NT-1 cells of tobacco (Nicotiana tabacum L.) were transformed with pGBSSHBS and pGBSSHER expression cassettes wherein expression of hepatitis B surface antigen (HBsAg)
was driven by potato granule-bound starch synthase (GBSS) promoter. The transformed nature of the cells was confirmed by PCR
analysis. Expression of HBsAg was confirmed by RT-PCR and Western blotting and levels of expression were assayed by ELISA.
Transformed cell lines exhibited a sucrose-inducible pattern of HBsAg expression. NT-1 medium supplemented with 175 mmol L−1 sucrose gave the highest HBsAg expression of 198 ng g−1 FW after 8 days of induction. Different sugars, for example glucose, fructose, and palatinose, were also tested to study
the inducible nature of GBSS promoter. The results demonstrate that potato GBSS promoter can be used in heterologous host
systems like tobacco NT-1 cell suspension cultures for sucrose-inducible expression of recombinant proteins. 相似文献
900.