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   275756篇
  免费   2562篇
  国内免费   867篇
化学   132923篇
晶体学   3895篇
力学   14530篇
综合类   11篇
数学   50327篇
物理学   77499篇
  2020年   1720篇
  2019年   1918篇
  2018年   12371篇
  2017年   12305篇
  2016年   9407篇
  2015年   2991篇
  2014年   3814篇
  2013年   9345篇
  2012年   10084篇
  2011年   18065篇
  2010年   11100篇
  2009年   11483篇
  2008年   13462篇
  2007年   15493篇
  2006年   6875篇
  2005年   7277篇
  2004年   6951篇
  2003年   6956篇
  2002年   5808篇
  2001年   6358篇
  2000年   4886篇
  1999年   3651篇
  1998年   2916篇
  1997年   2831篇
  1996年   2778篇
  1995年   2549篇
  1994年   2402篇
  1993年   2250篇
  1992年   2875篇
  1991年   2787篇
  1990年   2720篇
  1989年   2746篇
  1988年   2770篇
  1987年   2775篇
  1986年   2648篇
  1985年   3284篇
  1984年   3277篇
  1983年   2558篇
  1982年   2680篇
  1981年   2735篇
  1980年   2520篇
  1979年   2863篇
  1978年   2852篇
  1977年   2963篇
  1976年   2800篇
  1975年   2544篇
  1974年   2483篇
  1973年   2462篇
  1972年   1692篇
  1968年   1712篇
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
71.
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   
72.
73.
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   
74.
Ni–Co alloys have a wide range of applications in various fields owning to their excellent physical, chemical, and mechanical properties. In this paper, we prepare Ni–Co alloy coatings on 316L stain steel surfaces by electroplating. We present a novel approach utilizing a nanosecond laser to induce microtextures on Ni–Co alloy coatings. We study experimentally the effects of laser power and scanning rate on the surface morphologies of Ni–Co alloy coatings. The results indicate that the shape and size of induced microtextures can be controlled by the laser power and scanning rate. The size of grains increases with increase in the work current of the laser (WCL) at a certain scanning rate. With the WCL constant, the size of grains decreases with increase in scanning rate while their average height increases. It is a simple and easily-controlled method for the fabrication of microstructures on Ni–Co alloy coatings, which has promising applications in investigations of the properties of microtextured surfaces, such as friction, adhesion, and wetting.  相似文献   
75.
76.
77.

The adsorption and photocatalytic degradation of Ethyl methylphosphonate (EMPA) on powdery TiO2 film has experimentally investigated using attenuated total reflection-infrared Fourier transform spectroscopy (ATR-FTIR) in ambient condition. Characteristic IR frequency as P-O-C vibration mode as EtO was observed by EMPA adsorbed at the surface of TiO2. By TiO2 photocatalysis, the adsorbed EMPA was decomposed to methyl phosphonic acid and phosphoric acid. The increment of IR intensity of which is assigned to Ti–O-P-O-Ti of EMPA was accompanied with increasing the IR peak intensity assigned to MPA. About that, we suggest that the appearance of the Ti–O-P-O-Ti of EMPA by the TiO2 photocatalysis is regarded as acceleration of the hydrolysis of EMPA by the surface OH groups of TiO2. The plausible adsorption structure and the photocatalytic reaction mechanism of EMPA at the surface of TiO2 photocatalyst were elucidated.

  相似文献   
78.
79.
80.
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