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   279854篇
  免费   1798篇
  国内免费   801篇
化学   128560篇
晶体学   4150篇
力学   16927篇
综合类   11篇
数学   53501篇
物理学   79304篇
  2021年   1988篇
  2020年   2023篇
  2019年   2600篇
  2018年   13935篇
  2017年   13749篇
  2016年   10798篇
  2015年   3168篇
  2014年   4614篇
  2013年   8921篇
  2012年   10529篇
  2011年   18307篇
  2010年   11999篇
  2009年   12573篇
  2008年   14083篇
  2007年   16137篇
  2006年   6925篇
  2005年   7171篇
  2004年   7134篇
  2003年   7105篇
  2002年   6158篇
  2001年   5860篇
  2000年   4433篇
  1999年   3286篇
  1998年   2896篇
  1997年   2909篇
  1996年   2745篇
  1995年   2338篇
  1994年   2416篇
  1993年   2333篇
  1992年   2588篇
  1991年   2716篇
  1990年   2619篇
  1989年   2700篇
  1988年   2608篇
  1987年   2623篇
  1986年   2491篇
  1985年   3088篇
  1984年   3165篇
  1983年   2654篇
  1982年   2617篇
  1981年   2578篇
  1980年   2402篇
  1979年   2776篇
  1978年   2720篇
  1977年   2909篇
  1976年   2905篇
  1975年   2707篇
  1974年   2629篇
  1973年   2753篇
  1972年   2123篇
排序方式: 共有10000条查询结果,搜索用时 625 毫秒
91.
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   
92.
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   
93.
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   
94.
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   
95.
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   
96.
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   
97.
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   
98.
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   
99.
100.
Journal of Solid State Electrochemistry - Oxygen transport in ceramic oxide materials has been actively explored over the past decades. This is due to the desire to design high-temperature...  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