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   231572篇
  免费   2263篇
  国内免费   801篇
化学   116332篇
晶体学   3169篇
力学   10773篇
综合类   1篇
数学   25602篇
物理学   78759篇
  2020年   1797篇
  2019年   2048篇
  2018年   2725篇
  2017年   2657篇
  2016年   3934篇
  2015年   2401篇
  2014年   3990篇
  2013年   10100篇
  2012年   7558篇
  2011年   9434篇
  2010年   6716篇
  2009年   6648篇
  2008年   8723篇
  2007年   8755篇
  2006年   8293篇
  2005年   7510篇
  2004年   6936篇
  2003年   6120篇
  2002年   6075篇
  2001年   7095篇
  2000年   5374篇
  1999年   4239篇
  1998年   3565篇
  1997年   3475篇
  1996年   3297篇
  1995年   3009篇
  1994年   2954篇
  1993年   3045篇
  1992年   3153篇
  1991年   3232篇
  1990年   2984篇
  1989年   2937篇
  1988年   2973篇
  1987年   2877篇
  1986年   2721篇
  1985年   3740篇
  1984年   3929篇
  1983年   3112篇
  1982年   3341篇
  1981年   3277篇
  1980年   3170篇
  1979年   3291篇
  1978年   3383篇
  1977年   3318篇
  1976年   3427篇
  1975年   3108篇
  1974年   3122篇
  1973年   3168篇
  1972年   2214篇
  1971年   1837篇
排序方式: 共有10000条查询结果,搜索用时 281 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.
Russian Physics Journal - A relationship between the structural-morphological and physical-mechanical properties of macro-porous calcium phosphate (CaP) coatings on the surface of titanium implants...  相似文献   
26.

A complex study of a spearhead dated back to IV mill. BC from burial mound no. 1 near Novosvobodnaya village (collection of the State Historical Museum) and, in particular, the material of spearhead superficial crust has been performed. The elemental and phase composition of the metal of spearhead and the superficial crust on its surface have been determined by scanning electron microscopy, jointly with energydispersive X-ray microanalysis and X-ray phase analysis. A comparative analysis of the results of studying the spearhead superficial crust and similar crusts on other artifacts from the mounds near Novosvobodnaya village suggest natural origin of the crust on copper?arsenic artifacts.

  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