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   13432篇
  免费   1174篇
  国内免费   11篇
电工技术   113篇
综合类   9篇
化学工业   5110篇
金属工艺   137篇
机械仪表   329篇
建筑科学   497篇
矿业工程   17篇
能源动力   363篇
轻工业   3278篇
水利工程   117篇
石油天然气   74篇
无线电   634篇
一般工业技术   1884篇
冶金工业   599篇
原子能技术   42篇
自动化技术   1414篇
  2024年   41篇
  2023年   148篇
  2022年   640篇
  2021年   1099篇
  2020年   453篇
  2019年   469篇
  2018年   518篇
  2017年   529篇
  2016年   588篇
  2015年   468篇
  2014年   648篇
  2013年   949篇
  2012年   909篇
  2011年   1034篇
  2010年   785篇
  2009年   720篇
  2008年   653篇
  2007年   628篇
  2006年   495篇
  2005年   359篇
  2004年   309篇
  2003年   283篇
  2002年   257篇
  2001年   166篇
  2000年   104篇
  1999年   141篇
  1998年   126篇
  1997年   132篇
  1996年   118篇
  1995年   88篇
  1994年   67篇
  1993年   71篇
  1992年   74篇
  1991年   63篇
  1990年   49篇
  1989年   44篇
  1988年   42篇
  1987年   33篇
  1986年   41篇
  1985年   41篇
  1984年   27篇
  1983年   27篇
  1982年   15篇
  1981年   19篇
  1980年   22篇
  1979年   22篇
  1978年   22篇
  1977年   15篇
  1976年   11篇
  1975年   13篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
The authenticity and traceability of meat products are issues of primary importance to ensure food safety. Unfortunately, food adulteration (e.g. the addition of inexpensive cuts to minced meat products) and mislabelling (e.g. the inclusion of meat from species other than those declared) happens frequently worldwide. The aim of this study was to apply a droplet digital PCR assay for the detection and quantification (copies μL−1) of the beef, pork, horse, sheep, chicken and turkey in meat products. The analysis conducted on commercial meat showed the presence of traces of DNA from other animal species than those declared. We show that the method is highly sensitive, specific and accurate (accuracy = 100%). This method could be adopted by competent food safety authorities to verify compliance with the labelling of meat products and to ensure quality and safety throughout the meat supply chain, from primary production to consumption.  相似文献   
44.
Cell therapy of the post-infarcted myocardium is still far from clinical use. Poor survival of transplanted cells, insufficient regeneration, and replacement of the damaged tissue limit the potential of currently available cell-based techniques. In this study, we generated a multilayered construct from adipose-derived mesenchymal stromal cells (MSCs) modified to secrete stem cell factor, SCF. In a rat model of myocardium infarction, we show that transplantation of SCF producing cell sheet induced activation of the epicardium and promoted the accumulation of c-kit positive cells in ischemic muscle. Morphometry showed the reduction of infarct size (16%) and a left ventricle expansion index (0.12) in the treatment group compared to controls (24–28%; 0.17–0.32). The ratio of viable myocardium was more than 1.5-fold higher, reaching 49% compared to the control (28%) or unmodified cell sheet group (30%). Finally, by day 30 after myocardium infarction, SCF-producing cell sheet transplantation increased left ventricle ejection fraction from 37% in the control sham-operated group to 53%. Our results suggest that, combining the genetic modification of MSCs and their assembly into a multilayered construct, we can provide prolonged pleiotropic effects to the damaged heart, induce endogenous regenerative processes, and improve cardiac function.  相似文献   
45.
46.
47.
48.
49.
Maria Ziolek   《Catalysis Today》2003,78(1-4):47-64
This review article is devoted to the materials containing niobium, which have been discovered or developed in the past few years and exhibit the potential application in heterogeneous catalysis. Niobium oxides and mixed oxides as well as sulfides, nitrides (oxynitrides), carbides (oxycarbides), and phosphates are considered. Among the catalytic processes in which Nb-containing materials were tested, liquid and gas phase oxidation is described in details, and the role of niobium in the prevention of the catalyst from SO2 poisoning is mentioned.  相似文献   
50.
An approach is presented to satisfy the demand for simple criteria, guidelines and models for the preliminary sizing of horizontal subsurface flow (SF) constructed wetland systems. This approach eliminates time-consuming calculations and iterations by providing graphical solutions for wetland system sizing. Therefore, it can be used for the preliminary assessment of new or performance evaluation of existing subsurface flow constructed wetland systems. The validity of this methodology is checked with data from existing systems and is found to be quite satisfactory. This methodology is combined with simple equations predicting the maximum wetland capacity in summer, so as to assist designers in sizing installations in tourist areas with increased summer populations. Furthermore, based on this methodology, a sensitivity analysis is performed of the area requirements for wastewaters of various strengths and various design conditions and performance criteria. The results provide a useful overview to engineers and further simplify the design methodology of new subsurface flow constructed wetland systems.  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