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   206173篇
  免费   1611篇
  国内免费   423篇
化学   106844篇
晶体学   2960篇
力学   10352篇
综合类   10篇
数学   22514篇
物理学   65527篇
  2021年   1996篇
  2020年   2055篇
  2019年   2604篇
  2018年   3705篇
  2017年   3706篇
  2016年   4899篇
  2015年   2431篇
  2014年   4411篇
  2013年   8801篇
  2012年   7071篇
  2011年   8332篇
  2010年   6587篇
  2009年   6758篇
  2008年   7873篇
  2007年   7861篇
  2006年   6958篇
  2005年   6168篇
  2004年   5830篇
  2003年   5351篇
  2002年   5306篇
  2001年   5701篇
  2000年   4202篇
  1999年   3188篇
  1998年   2735篇
  1997年   2814篇
  1996年   2579篇
  1995年   2260篇
  1994年   2360篇
  1993年   2256篇
  1992年   2557篇
  1991年   2627篇
  1990年   2536篇
  1989年   2592篇
  1988年   2525篇
  1987年   2526篇
  1986年   2397篇
  1985年   3046篇
  1984年   3115篇
  1983年   2614篇
  1982年   2592篇
  1981年   2550篇
  1980年   2347篇
  1979年   2738篇
  1978年   2698篇
  1977年   2902篇
  1976年   2894篇
  1975年   2683篇
  1974年   2626篇
  1973年   2729篇
  1972年   2080篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
92.
Doklady Mathematics - An Erratum to this paper has been published: https://doi.org/10.1134/S1064562421330012  相似文献   
93.
Ding  Q.  Yao  M.  Wu  Sh.  Zeng  M.  Xue  N.  Wu  D.  Xu  J. 《Journal of Applied Spectroscopy》2022,89(4):712-718
Journal of Applied Spectroscopy - Based on partial least squares (PLS) analysis, the effects of different smoothing points and different preprocessing methods on the accuracy and precision of the...  相似文献   
94.
Crystallography Reports - Nd1 – yEuyF3 – y crystals (y is the molar fraction of EuF2; 0 ≤ y ≤ 0.15) with a tysonite (LaF3) structure have...  相似文献   
95.
A new derivative of dioxouranium(VI) salen complex, [UO2(L)(pyridine)], where [L = N,N′-Bis(2-hydroxybenzylidene)-2,2-dimethyl-1,3-propanediamine] is synthesized and characterized by elemental analysis (C, H, N), FT-IR, ESI-MS spectrometry, UV/Vis, fluorescence, 1H and 13C NMR spectroscopy and thermal gravimetric (TG) study. Furthermore, the single crystal X-ray diffraction measurements of the complex were carried out at 100 and 273 K. The crystal structure measurements revealed that the complex has distorted pentagonal bipyramidal geometry with uranium atom located at the centre and bonded to two phenoxy oxygen and two azomethine nitrogen in tetradenate fashion and one nitrogen from pyridine making it seven coordinated. In addition, the photoluminescence property of the complex was also recorded.  相似文献   
96.
Russian Journal of Organic Chemistry - A procedure has been proposed for the synthesis of a series of substituted N-(1,3-thiazol-2-yl)-pyrimidin-2-amines and N-(pyrimidin-2-yl)thioureas by...  相似文献   
97.
Siberian Mathematical Journal - We consider a problem for a first-order differential equation in a Hilbert space. We replace the initial data with some condition that...  相似文献   
98.
In the present work, the use of cylindrical turbulators in a double pipe heat exchanger has been investigated. Cylindrical fin type of turbulators has been placed circumferentially separated by 90° on the outer side of an inner pipe at a regular pitch. Experimental studies were undertaken for different air flow rates in a turbulent regime whose Reynolds number range between 2500 and 10000. Heat transfer characteristics like Nu and friction factor have been experimentally determined. Parametric studies were conducted by changing the pitch and also the orientation of the turbulators. Nu and friction factor were found to increase as the pitch is reduced. A model with alternatively changed orientation outperformed others by exhibiting highest Nu and reduced friction factor.  相似文献   
99.
Journal of Sol-Gel Science and Technology - High temperature stable brookite rich titanium dioxide of average crystallite size 20&;nbsp;nm has been prepared by a novel aqueous sol–gel...  相似文献   
100.
The biomimetic sol—gel synthesis of silicon—chitosan-containing glycerohydrogels was carried out using silicon tetraglycerolate as a precursor. It was found that chitosan accelerates gel formation in weakly acidic media. In more acidic media, the kinetics of the process changes according to the curve with a maximum, which can be attributed to different mechanisms of silanol condensation before and after the isoelectric point. The investigated silicon—chitosan-containing glycerohydrogels exhibit antibacterial, anti-inflammatory, and wound healing activity. The synthesized hybrid glycerohydrogels are promising materials for biomedical applications.  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