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   467955篇
  免费   3834篇
  国内免费   1106篇
化学   237495篇
晶体学   6951篇
力学   21654篇
综合类   17篇
数学   62999篇
物理学   143779篇
  2020年   3426篇
  2019年   3853篇
  2018年   11886篇
  2017年   12549篇
  2016年   10484篇
  2015年   4929篇
  2014年   6968篇
  2013年   17487篇
  2012年   16113篇
  2011年   25488篇
  2010年   16704篇
  2009年   16757篇
  2008年   22796篇
  2007年   25748篇
  2006年   13450篇
  2005年   17408篇
  2004年   13588篇
  2003年   12811篇
  2002年   10839篇
  2001年   11264篇
  2000年   8866篇
  1999年   6584篇
  1998年   5432篇
  1997年   5425篇
  1996年   5213篇
  1995年   4560篇
  1994年   4518篇
  1993年   4394篇
  1992年   5118篇
  1991年   5089篇
  1990年   4946篇
  1989年   4989篇
  1988年   4933篇
  1987年   4912篇
  1986年   4682篇
  1985年   6037篇
  1984年   6216篇
  1983年   4942篇
  1982年   5269篇
  1981年   5114篇
  1980年   4747篇
  1979年   5279篇
  1978年   5416篇
  1977年   5449篇
  1976年   5337篇
  1975年   4929篇
  1974年   4856篇
  1973年   4984篇
  1972年   3356篇
  1967年   3314篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
Copper oxide decorated multi‐walled carbon nanotube (MWCNT) modified glassy carbon electrode (GCE) was prepared for determination of isoniazid (INZ) in various matrices. The electrochemical behavior of INZ was tested with the aid of Cyclic Voltammetry (CV) and quantitative experiments were performed by using Linear Sweep Voltammetry (LSV). Morphological and structural characterization of the modified electrode was performed by utilizing Scanning Electron Microscopy (SEM), X‐Ray Photoelectron Spectroscopy (XPS) while electrochemical characterization was performed by using CV and Electrochemical Impedance spectroscopy (EIS). The proposed sensor exhibited well defined anodic peak at 0.30 V for INZ at pH 6.0 medium. Under the optimum conditions, a linear relation between INZ concentration and peak current was observed in the range of 2.0×10?7 to 5.0×10?5 M. Limit of detection was calculated as 1.0×10?8 M and repeatability and accuracy was found as 5.60 % and 91.0 % for 5.0 10?7 M INZ by using 3 successive measurement, respectively. Then, the analytic performance of the electrode developed was tested by analyzing commercial tablets, artificial human serum and urine samples. The results indicated that satisfactory recoveries was observed for all issue.  相似文献   
142.
143.
144.
The launch of the gamma-ray telescope Fermi Large Area Telescope (Fermi-LAT) started a pivotal period in indirect detection of dark matter. By outperforming expectations, for the first time a robust and stringent test of the paradigm of weakly interacting massive particles (WIMPs) is within reach. In this paper, we discuss astrophysical targets for WIMP detection and the challenges they present, review the analysis tools which have been employed to tackle these challenges, and summarize the status of constraints on and the claimed detections in the WIMP parameter space. Methods and results will be discussed in comparison to Imaging Air Cherenkov Telescopes. We also provide an outlook on short term and longer term developments.  相似文献   
145.
146.
The structure and properties of 12Cr1MoV steel irradiated with a zirconium ion beam were studied by optical microscopy, scanning electron microscopy, and micro- and nanoindentation. It is shown that the modification covers the entire cross-section of the irradiated specimens to a depth of 1 mm. The data on irradiation-induced structural changes are used to interpret the changes in mechanical properties of the irradiated specimens under static and cyclic loading. Particular attention is given to analysis of strain estimation by the digital image correlation method.  相似文献   
147.
148.
149.
150.
Influence of the nuclear energy structure, the conditions of fuel burnup, and accumulation of new fissile isotopes from the raw isotopes on the main parameters of a closed fuel cycle is considered. The effects of the breeding ratio, the cooling time of the spent fuel in the external fuel cycle, and the separation of the breeding area and the fissile isotope burning area on the parameters of the fuel cycle are analyzed.  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