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   411610篇
  免费   4298篇
  国内免费   1965篇
化学   214170篇
晶体学   6114篇
力学   19430篇
综合类   73篇
数学   53062篇
物理学   125024篇
  2020年   3449篇
  2019年   4021篇
  2018年   6623篇
  2017年   6889篇
  2016年   8277篇
  2015年   4837篇
  2014年   7571篇
  2013年   16715篇
  2012年   16062篇
  2011年   18068篇
  2010年   13413篇
  2009年   13182篇
  2008年   15502篇
  2007年   15541篇
  2006年   14262篇
  2005年   16494篇
  2004年   15036篇
  2003年   12303篇
  2002年   10522篇
  2001年   11418篇
  2000年   8524篇
  1999年   6406篇
  1998年   5380篇
  1997年   5379篇
  1996年   5151篇
  1995年   4493篇
  1994年   4665篇
  1993年   4480篇
  1992年   5031篇
  1991年   5179篇
  1990年   4926篇
  1989年   4863篇
  1988年   4714篇
  1987年   4615篇
  1986年   4531篇
  1985年   5825篇
  1984年   5922篇
  1983年   4973篇
  1982年   5150篇
  1981年   4915篇
  1980年   4512篇
  1979年   5037篇
  1978年   5201篇
  1977年   5353篇
  1976年   5479篇
  1975年   4983篇
  1974年   5017篇
  1973年   5169篇
  1972年   3935篇
  1971年   3417篇
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
131.
Doklady Mathematics - An Erratum to this paper has been published: https://doi.org/10.1134/S1064562421330012  相似文献   
132.
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   
133.
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   
134.
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   
135.
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   
136.
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   
137.
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   
138.
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   
139.
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   
140.
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