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   202083篇
  免费   1478篇
  国内免费   422篇
化学   104406篇
晶体学   2950篇
力学   10269篇
综合类   10篇
数学   21838篇
物理学   64510篇
  2021年   1966篇
  2020年   2013篇
  2019年   2571篇
  2018年   3658篇
  2017年   3668篇
  2016年   4817篇
  2015年   2349篇
  2014年   4303篇
  2013年   8591篇
  2012年   6847篇
  2011年   8060篇
  2010年   6469篇
  2009年   6641篇
  2008年   7640篇
  2007年   7608篇
  2006年   6704篇
  2005年   5933篇
  2004年   5650篇
  2003年   5170篇
  2002年   5162篇
  2001年   5607篇
  2000年   4142篇
  1999年   3138篇
  1998年   2706篇
  1997年   2765篇
  1996年   2544篇
  1995年   2210篇
  1994年   2328篇
  1993年   2231篇
  1992年   2527篇
  1991年   2602篇
  1990年   2505篇
  1989年   2567篇
  1988年   2503篇
  1987年   2504篇
  1986年   2365篇
  1985年   2994篇
  1984年   3068篇
  1983年   2569篇
  1982年   2527篇
  1981年   2503篇
  1980年   2304篇
  1979年   2687篇
  1978年   2646篇
  1977年   2854篇
  1976年   2856篇
  1975年   2646篇
  1974年   2584篇
  1973年   2691篇
  1972年   2073篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
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   
92.
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   
93.
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   
94.
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   
95.
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   
96.
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   
97.
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   
98.
99.
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   
100.
The random copolymerization of norbornene-functionalized macromonomers was explored as a method of synthesizing mixed-graft block copolymers (mGBCPs). The copolymerization kinetics of a model system of polystyrene (PS) and poly(lactic acid) (PLA) macromonomers was first analyzed, revealing a gradient composition of side chains along the mGBCP backbone. The phase separation behavior of mGBCPs with PS and PLA side chains of various backbone lengths and side chain molar ratios was investigated, and increasing the backbone length was found to stabilize the phase-separated nanostructures. The graft architecture was also demonstrated to improve the processability of the mGBCP, compared to a linear counterpart. Investigations of mGBCPs comprised of polydimethylsiloxane and poly(ethylene oxide) side chains exemplified the diverse self-assembled morphologies, including a Frank-Kasper A15 phase, that can be obtained with mGBCPs synthesized by random copolymerization of macromonomers. Lastly, a ternary mGBCP was synthesized by the copolymerization of three macromonomers.  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