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   311037篇
  免费   2755篇
  国内免费   1199篇
化学   142234篇
晶体学   4755篇
力学   17404篇
综合类   1篇
数学   57071篇
物理学   93526篇
  2020年   1880篇
  2019年   2135篇
  2018年   12878篇
  2017年   12638篇
  2016年   9912篇
  2015年   3306篇
  2014年   4374篇
  2013年   10549篇
  2012年   11389篇
  2011年   19758篇
  2010年   12252篇
  2009年   12576篇
  2008年   15270篇
  2007年   17399篇
  2006年   8705篇
  2005年   8926篇
  2004年   8547篇
  2003年   8170篇
  2002年   7148篇
  2001年   7336篇
  2000年   5660篇
  1999年   4400篇
  1998年   3766篇
  1997年   3637篇
  1996年   3531篇
  1995年   3149篇
  1994年   3048篇
  1993年   3151篇
  1992年   3223篇
  1991年   3414篇
  1990年   3154篇
  1989年   3095篇
  1988年   3135篇
  1987年   3023篇
  1986年   2863篇
  1985年   3874篇
  1984年   4072篇
  1983年   3244篇
  1982年   3464篇
  1981年   3385篇
  1980年   3291篇
  1979年   3387篇
  1978年   3472篇
  1977年   3379篇
  1976年   3475篇
  1975年   3163篇
  1974年   3171篇
  1973年   3219篇
  1972年   2252篇
  1971年   1860篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Crystallography Reports - Some questions related to the establishment, development, and prospects of physical studies using inelastic thermal-neutron scattering are briefly reviewed. The directions...  相似文献   
22.
Theoretical and Mathematical Physics - The fractional derivative method is used to take wave dispersion into account in the wave equation when describing the propagation of gravitational soliton...  相似文献   
23.
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   
24.
Crystallography Reports - Methods of coherent X-ray diffraction imaging of the spatial structure of noncrystalline objects and nanocrystals (nanostructures) are considered. Particular attention is...  相似文献   
25.
Secondary structures tend to be recognizable because they have repeating structural motifs, but mimicry of these does not have to follow such well-defined patterns. Bioinformatics studies to match side-chain orientations of a novel hydantoin triazole chemotype ( 1 ) to protein-protein interfaces revealed it tends to align well across parallel and antiparallel sheets, like rungs on a ladder. One set of these overlays was observed for the protein-protein interaction uPA⋅uPAR. Consequently, chemotype 1 was made with appropriate side-chains to mimic uPA at this interface. Biophysical assays indicate these compounds did in fact bind uPAR, and elicit cellular responses that affected invasion, migration, and wound healing.  相似文献   
26.
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   
27.
28.
29.
A two‐step synthesis of structurally diverse pyrrole‐containing bicyclic systems is reported. ortho‐Nitro‐haloarenes coupled with vinylic N‐methyliminodiacetic acid (MIDA) boronates generate ortho‐vinyl‐nitroarenes, which undergo a “metal‐free” nitrene insertion, resulting in a new pyrrole ring. This novel synthetic approach has a wide substrate tolerance and it is applicable in the preparation of more complex “drug‐like” molecules. Interestingly, an ortho‐nitro‐allylarene derivative furnished a cyclic β‐aminophosphonate motif.  相似文献   
30.
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