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   1095篇
  免费   62篇
  国内免费   2篇
  2023年   11篇
  2022年   18篇
  2021年   77篇
  2020年   60篇
  2019年   76篇
  2018年   51篇
  2017年   35篇
  2016年   37篇
  2015年   64篇
  2014年   68篇
  2013年   89篇
  2012年   78篇
  2011年   85篇
  2010年   37篇
  2009年   38篇
  2008年   40篇
  2007年   33篇
  2006年   28篇
  2005年   23篇
  2004年   24篇
  2003年   19篇
  2002年   14篇
  2001年   6篇
  2000年   7篇
  1999年   7篇
  1998年   9篇
  1997年   6篇
  1995年   2篇
  1994年   7篇
  1993年   4篇
  1992年   4篇
  1991年   9篇
  1990年   8篇
  1989年   3篇
  1988年   4篇
  1987年   6篇
  1986年   6篇
  1985年   2篇
  1984年   4篇
  1983年   3篇
  1982年   7篇
  1981年   4篇
  1980年   9篇
  1979年   10篇
  1978年   3篇
  1977年   6篇
  1976年   3篇
  1975年   3篇
  1974年   6篇
  1972年   4篇
排序方式: 共有1159条查询结果,搜索用时 318 毫秒
991.
992.
Journal of Plant Growth Regulation - Origanum vulgare L. is a valuable flavoring, mainly due to its important essential oils and is widely used in different industries. This study aimed to compare...  相似文献   
993.
The lignans (1-8) isolated from the roots of Vitex negundo Linn. were screened against the serine proteases alpha-chymotrypsin, thrombin and prolyl endopeptidase. Compounds 3 and 4 were found to be active only against alpha-chymotrypsin and were noncompetitive and competitive inhibitors of the enzyme, respectively. Ki values were found to be in the range 31.75-47.11 microM.  相似文献   
994.

Background  

Fibroblasts, as connective tissue cells, are able to transform into another cell type including smooth muscle cells. α1A-adrenergic receptor (α1A-AR) stimulation in rat-1 fibroblasts is coupled to cAMP production. However, the significance of an increase in cAMP produced by α1A-AR stimulation on proliferation, hypertrophy and differentiation in these cells is not known.  相似文献   
995.
Pseudomonas aeruginosa is a free-living and common environmental bacterium. It is an opportunistic and nosocomial pathogen causing serious human health problems. To overcome its predators, such as macrophages and environmental phagocytes, it utilises different survival strategies, such as the formation of microcolonies and the production of toxins mediated by a type III secretion system (TTSS). The aim of this study was to examine interaction of TTSS effector proteins of P. aeruginosa PA103 with Acanthamoeba castellanii by co-cultivation, viable count, eosin staining, electron microscopy, apoptosis assay, and statistical analysis. The results showed that P. aeruginosa PA103 induced necrosis and apoptosis to kill A. castellanii by the effects of TTSS effector proteins ExoU, ExoS, ExoT, and ExoY. In comparison, Acanthamoeba cultured alone and co-cultured with P. aeruginosa PA103 lacking the known four TTSS effector proteins were not killed. The results are consistent with P. aeruginosa being a strict extracellular bacterium that needs TTSS to survive in the environment, because the TTSS effector proteins are able to kill its eukaryotic predators, such as Acanthamoeba.  相似文献   
996.
997.
Interactions between tumorigenic cells and their surrounding microenvironment are critical for tumor progression yet remain incompletely understood. Germline mutations in the NF1 tumor suppressor gene cause neurofibromatosis type 1 (NF1), a common genetic disorder characterized by complex tumors called neurofibromas. Genetic studies indicate that biallelic loss of Nf1 is required in the tumorigenic cell of origin in the embryonic Schwann cell lineage. However, in the physiologic state, Schwann cell loss of heterozygosity is not sufficient for neurofibroma formation and Nf1 haploinsufficiency in at least one additional nonneoplastic lineage is required for tumor progression. Here, we establish that Nf1 heterozygosity of bone marrow-derived cells in the tumor microenvironment is sufficient to allow neurofibroma progression in the context of Schwann cell Nf1 deficiency. Further, genetic or pharmacologic attenuation of c-kit signaling in Nf1+/- hematopoietic cells diminishes neurofibroma initiation and progression. Finally, these studies implicate mast cells as critical mediators of tumor initiation.  相似文献   
998.
The increasing demands on limited water supplies worldwide require the adoption of more efficient irrigation techniques for sustainable production in agriculture. Partial rootzone drying (PRD) is one of the techniques that offer potential saving of irrigation water. This technique involves alternate irrigation to two sides of a plant root system. The studies reported here investigated PRD irrigation regimes and the optimum time of starting PRD in potatoes grown in a protected environment. In the first experiment, plants of the potato cv. Estima were exposed to five different irrigation treatments and a fully watered control at tuber initiation. The treatment that performed most similar to the control was alternate PRD to field capacity (APRD100). This treatment produced similar total leaf area, haulm fresh and dry weights, plant water status and no significant yield reduction compared with the control plants. The APRD100 treatment utilised 29% less water and increased water use efficiency (WUE) by 19%. In the second experiment, the APRD100 irrigation was started at 2, 4, 6, 8 and 10 weeks after plant emergence. Vegetative growth and yield increased with the delay of the APRD100. APRD100 started at 6 weeks after emergence did not significantly reduce fresh tuber yield but received 21% less total water with a 19% increase in WUE. The results indicate that PRD may have potential use in the potato crop for conserving irrigation water with minimal loss of yield.  相似文献   
999.
The interaction of thiourea (Tu) with auranofin (Et(3)PAuSATg) and its analogue, Et(3)PAuCl has been studied using (13)C, (31)P and (15)N NMR spectroscopy. It is observed that Tu is able to replace both the ligands, Et(3)P and SATg(-) simultaneously from gold(I) in auranofin, forming [Et(3)P-Au-Tu](+) and Tu-Au-SATg complexes. However, no separate resonances for these species were observed either due to their rapid exchange with auranofin and thus giving only the average resonances or because the chemical shifts of either two species are same so that they cannot be resolved. The displaced SATg(-) is oxidized to its disulfide, (SATg)(2). However, some of the displaced Et(3)P is oxidized to Et(3)PO while the remaining reacts with Tu to form Et(3)P-Tu species, characterized by delta 31P of 1.0 ppm, assigned after an independent reaction between Et(3)P and Tu. In an experiment using a 0.05 M solution of auranofin, the Et(3)PO resonance appeared in auranofin spectrum after 4 days of addition of 1.0 equivalent of Tu, showing that the reaction is slow. A resonance for free Et(3)P is also detected in 31P NMR on the addition of CN(-). It is also observed that Tu reacts with Et(3)PAuCl to form [Et(3)P-Au-Tu](+) via displacement of Cl(-), consistent with an upfield shift of 6.2 ppm in >C [double bond] S resonance of Tu in (13)C NMR. In (15)N NMR, a smaller downfield, instead of an upfield shift, in NH(2) resonance of Tu on its addition to auranofin and Et(3)PAuCl indicates that it is not binding to gold(I) through nitrogen.  相似文献   
1000.
This is the first study demonstrating the efficacy of menstrual blood-derived stem cell (MenSC) transplantation via a neural guidance conduit, for peripheral nerve regeneration. The synthesized poly (?-caprolactone)/Gelatin conduit, filled with collagen type I and seeded with 3?×?104 MenSCs, was implanted into a rat’s 10 mm sciatic nerve defect. The results of hot plate latency, sciatic functional index and weight-loss percentage of wet gastrocnemius muscle demonstrated that the MenSC transplantation had comparable nerve regeneration outcome to autograft, as the gold standard of nerve bridging. The transplantation of MenSCs via a synthetic conduit could ameliorate the functional recovery of sciatic nerve-injured rats which make them a potential candidate for cell therapy of peripheral nervous system disorders.  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