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   537015篇
  免费   6629篇
  国内免费   3046篇
化学   263514篇
晶体学   7585篇
力学   28233篇
综合类   148篇
数学   84490篇
物理学   162720篇
  2021年   4049篇
  2020年   4454篇
  2019年   4912篇
  2018年   15954篇
  2017年   15931篇
  2016年   15068篇
  2015年   6670篇
  2014年   9561篇
  2013年   22583篇
  2012年   20890篇
  2011年   30791篇
  2010年   20277篇
  2009年   20557篇
  2008年   25137篇
  2007年   27118篇
  2006年   17924篇
  2005年   16894篇
  2004年   15917篇
  2003年   14468篇
  2002年   13566篇
  2001年   14923篇
  2000年   11344篇
  1999年   8755篇
  1998年   7130篇
  1997年   7012篇
  1996年   6738篇
  1995年   5819篇
  1994年   5607篇
  1993年   5442篇
  1992年   6016篇
  1991年   6195篇
  1990年   5762篇
  1989年   5663篇
  1988年   5472篇
  1987年   5505篇
  1986年   5210篇
  1985年   6950篇
  1984年   6945篇
  1983年   5730篇
  1982年   5910篇
  1981年   5577篇
  1980年   5458篇
  1979年   5689篇
  1978年   5762篇
  1977年   5744篇
  1976年   5646篇
  1975年   5415篇
  1974年   5290篇
  1973年   5386篇
  1972年   3625篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Crystallography Reports - The specific features of the formation of crystallites in gallium arsenide crystals grown by the Czochralski method have been investigated. The crystallites are found to...  相似文献   
62.
Herein, we successfully construct the 3D biocompatible graphene through crosslinking 2D graphene nanosheet onto carbon fiber paper with poly(diallyldimethylammonium chloride) (PDDA) as anode of the alcohol biofuel cell. Compared with the bioanode without 3D graphene, the current density and output power of PDDA-graphene-ADH bioanode is increased by 23 % and 41 % at a high concentration of ethanol at pH 8.9, suggesting the stabilization role of graphene in enzyme loading. The study provides us a deep analysis on structures and performances of the bioanode incl. electrochemistry, X-ray photoelectron spectra, and atomic force microscopy images, which is significant to develop the new methods to construct 3D porous electrodes in energy conversion device.  相似文献   
63.
A facile biosynthesis route was followed to prepare zinc oxide nanoparticles (ZnO NPs) using Euphorbia milii (E. milii) leaf constituents. The SEM images exhibited presence of spherical ZnO NPs and the corresponding TEM images disclosed monodisperse nature of the ZnO NPs with diameter ranges between 12 and 20 nm. The Brunauer–Emmett–Teller (BET) analysis revealed that the ZnO NPs have specific surface area of 20.46 m2/g with pore diameter of 2 nm–10 nm and pore volume of 0.908 cm3/g. The EDAX spectrum exemplified the existence of Zn and O elements and non-appearance of impurities that confirmed pristine nature of the ZnO NPs. The XRD pattern indicated crystalline peaks corresponding to hexagonal wurtzite structured ZnO with an average crystallite size of 16.11 nm. The FTIR spectrum displayed strong absorption bands at 512 and 534 cm?1 related to ZnO. The photocatalytic action of ZnO NPs exhibited noteworthy degradation of methylene blue dye under natural sunlight illumination. The maximum degradation efficiency achieved was 98.17% at an illumination period of 50 min. The reusability study proved considerable photostability of the ZnO NPs during photocatalytic experiments. These findings suggest that the E. milii leaf constituents can be utilized as suitable biological source to synthesis ZnO NPs for photocatalytic applications.  相似文献   
64.
65.
Russian Physics Journal - The paper shows that the values of zero-point energy and vibrations of atoms in a crystal determined by the uncertainty principle, depend on the dynamic response of atoms....  相似文献   
66.
67.
68.
69.
The design of new solid-state proton-conducting materials is a great challenge for chemistry and materials science. Herein, a new anionic porphyrinylphosphonate-based MOF ( IPCE-1Ni ), which involves dimethylammonium (DMA) cations for charge compensation, is reported. As a result of its unique structure, IPCE-1Ni exhibits one of the highest value of the proton conductivity among reported proton-conducting MOF materials based on porphyrins (1.55×10−3 S cm−1 at 75 °C and 80 % relative humidity).  相似文献   
70.
In the paper, the authors establish several integral representations for the generating functions of the large and little Schröder numbers and for the large and little Schröder numbers.  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