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   117603篇
  免费   1985篇
  国内免费   816篇
  2023年   207篇
  2022年   358篇
  2021年   712篇
  2020年   522篇
  2019年   591篇
  2018年   12393篇
  2017年   11137篇
  2016年   8330篇
  2015年   1989篇
  2014年   1823篇
  2013年   2109篇
  2012年   6191篇
  2011年   14625篇
  2010年   13074篇
  2009年   9168篇
  2008年   11098篇
  2007年   12609篇
  2006年   1594篇
  2005年   1602篇
  2004年   2007篇
  2003年   1891篇
  2002年   1615篇
  2001年   653篇
  2000年   512篇
  1999年   310篇
  1998年   209篇
  1997年   172篇
  1996年   160篇
  1995年   130篇
  1994年   124篇
  1993年   135篇
  1992年   180篇
  1991年   170篇
  1990年   143篇
  1989年   107篇
  1988年   112篇
  1987年   91篇
  1986年   78篇
  1985年   77篇
  1984年   74篇
  1983年   83篇
  1982年   62篇
  1981年   50篇
  1980年   41篇
  1979年   58篇
  1978年   60篇
  1975年   63篇
  1973年   36篇
  1972年   267篇
  1971年   294篇
排序方式: 共有10000条查询结果,搜索用时 765 毫秒
201.
Software for fitting of NMR spectra in MATLAB is presented. Spectra are fitted in the frequency domain, using Fourier transformed lineshapes, which are derived using the experimental acquisition and processing parameters. This yields more accurate fits compared to common fitting methods that use Lorentzian or Gaussian functions. Furthermore, a very time-efficient algorithm for calculating and fitting spectra has been developed. The software also performs initial peak picking, followed by subsequent fitting and refinement of the peak list, by iteratively adding and removing peaks to improve the overall fit. Estimation of error on fitting parameters is performed using a Monte-Carlo approach. Many fitting options allow the software to be flexible enough for a wide array of applications, while still being straightforward to set up with minimal user input.  相似文献   
202.
203.
Advanced hepatic fibrosis therapy using drug-delivering nanoparticles is a relatively unexplored area. Angiotensin type 1 (AT1) receptor blockers such as losartan can be delivered to hepatic stellate cells (HSC), blocking their activation and thereby reducing fibrosis progression in the liver. In our study, we analyzed the possibility of utilizing drug-loaded vehicles such as hyaluronic acid (HA) micelles carrying losartan to attenuate HSC activation. Losartan, which exhibits inherent lipophilicity, was loaded into the hydrophobic core of HA micelles with a 19.5% drug loading efficiency. An advanced liver fibrosis model was developed using C3H/HeN mice subjected to 20 weeks of prolonged TAA/ethanol weight-adapted treatment. The cytocompatibility and cell uptake profile of losartan-HA micelles were studied in murine fibroblast cells (NIH3T3), human hepatic stellate cells (hHSC) and FL83B cells (hepatocyte cell line). The ability of these nanoparticles to attenuate HSC activation was studied in activated HSC cells based on alpha smooth muscle actin (α-sma) expression. Mice treated with oral losartan or losartan-HA micelles were analyzed for serum enzyme levels (ALT/AST, CK and LDH) and collagen deposition (hydroxyproline levels) in the liver. The accumulation of HA micelles was observed in fibrotic livers, which suggests increased delivery of losartan compared to normal livers and specific uptake by HSC. Active reduction of α-sma was observed in hHSC and the liver sections of losartan-HA micelle-treated mice. The serum enzyme levels and collagen deposition of losartan-HA micelle-treated mice was reduced significantly compared to the oral losartan group. Losartan-HA micelles demonstrated significant attenuation of hepatic fibrosis via an HSC-targeting mechanism in our in vitro and in vivo studies. These nanoparticles can be considered as an alternative therapy for liver fibrosis.  相似文献   
204.
205.
206.
This article contains a comparison of the profits of cultivating modern and traditional varieties of coconuts as a monocrop and as an intercrop, in ideal and in average growing conditions, with good and with average management. We carry out the analysis from a private (financial) and from a national (economic) perspective. The results show that intercropping generates more income than monocropping. In the conclusion we discuss why development organizations and Third World countries encourage monocropping.  相似文献   
207.
208.
209.
K Jo  M D Topal 《Nucleic acids research》1996,24(21):4171-4175
Substituting lysine for leucine at position 43 (L43K) transforms NaeI from restriction endonuclease to topoisomerase and makes NaeI hypersensitive to intercalative anticancer drugs. Here we investigated DNA recognition by Nael-L43K. Using DNA competition and gel retardation assays, NaeI-L43K showed reduced affinity for DNA substrate and the ability to bind both single- and double-stranded DNA with a definite preference for the former. Sedimentation studies showed that under native conditions NaeI-L43K, like NaeI, is a dimer. Introduction of mismatched bases into double-stranded DNA significantly increased that DNA's ability to inhibit NaeI-L43K. Wild-type NaeI showed no detectable binding of either single-stranded DNA or mismatched DNA over the concentration range studied. These results demonstrate that the L43K substitution caused a significant change in recognition specificity by NaeI and imply that NaeI-L43K's topoisomerase activity is related to its ability to bind single-stranded and distorted regions in DNA. A mechanism is proposed for the evolution of the NaeI restriction-modification system from a topoisomerase/ligase by a mutation that abolished religation activity and provided a needed change in DNA recognition.  相似文献   
210.
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