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   575635篇
  免费   6631篇
  国内免费   1851篇
化学   307507篇
晶体学   9271篇
力学   25229篇
综合类   18篇
数学   65903篇
物理学   176189篇
  2020年   4594篇
  2019年   5298篇
  2018年   6459篇
  2017年   6308篇
  2016年   9670篇
  2015年   6262篇
  2014年   9813篇
  2013年   26152篇
  2012年   18835篇
  2011年   23183篇
  2010年   16059篇
  2009年   15917篇
  2008年   21017篇
  2007年   21010篇
  2006年   19689篇
  2005年   17883篇
  2004年   16311篇
  2003年   14758篇
  2002年   14371篇
  2001年   16646篇
  2000年   12752篇
  1999年   10004篇
  1998年   8345篇
  1997年   8276篇
  1996年   7843篇
  1995年   7274篇
  1994年   6954篇
  1993年   6950篇
  1992年   7829篇
  1991年   7874篇
  1990年   7499篇
  1989年   7440篇
  1988年   7511篇
  1987年   7411篇
  1986年   6989篇
  1985年   9400篇
  1984年   9696篇
  1983年   7819篇
  1982年   8398篇
  1981年   8186篇
  1980年   7866篇
  1979年   8330篇
  1978年   8554篇
  1977年   8509篇
  1976年   8515篇
  1975年   7754篇
  1974年   7889篇
  1973年   8142篇
  1972年   5486篇
  1971年   4459篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
171.
Optics and Spectroscopy - 10.1134/S0030400X17050095  相似文献   
172.
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   
173.
174.
175.
176.
A uniform dispersion of reactants is necessary to achieve a complete reaction involving multicomponents. In this study, we have examined the role of plasticizer in the reaction of two seemingly unlikely reactants: a highly crystalline hexamethylenetetramine (HMTA) and a strongly hydrogen bonded phenol formaldehyde resin. By combining information from NMR, infrared spectroscopy and differential scanning calorimetry, we were able to determine the role of specific intermolecular interactions necessary for the plasticizer to dissolve the highly crystalline HMTA and to plasticize the phenol formaldehyde resin in this crosslinking reaction. The presence of the plasticizer increased the segmental mobility, disrupted the hydrogen bonded matrix, and freed the hydroxyl units, which further increased the solubility of the HMTA. Both the endothermic and exothermic transitions are accounted for in the calorimetric data obtained. For the first time, it is possible to obtain the effective molar ratio of each component needed to complete the crosslinking reaction efficiently. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1519–1526  相似文献   
177.
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   
178.
179.
180.
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