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   341236篇
  免费   3415篇
  国内免费   346篇
化学   165351篇
晶体学   4043篇
力学   18349篇
综合类   3篇
数学   49220篇
物理学   108031篇
  2021年   3552篇
  2020年   4049篇
  2019年   4804篇
  2018年   7173篇
  2017年   7212篇
  2016年   9368篇
  2015年   4836篇
  2014年   8195篇
  2013年   14841篇
  2012年   13263篇
  2011年   15043篇
  2010年   11896篇
  2009年   11684篇
  2008年   14150篇
  2007年   13953篇
  2006年   12422篇
  2005年   10964篇
  2004年   10382篇
  2003年   9403篇
  2002年   9457篇
  2001年   8449篇
  2000年   6729篇
  1999年   4955篇
  1998年   4628篇
  1997年   4457篇
  1996年   4165篇
  1995年   3567篇
  1994年   3621篇
  1993年   3642篇
  1992年   3652篇
  1991年   4004篇
  1990年   3968篇
  1989年   3964篇
  1988年   3701篇
  1987年   3772篇
  1986年   3437篇
  1985年   4141篇
  1984年   4338篇
  1983年   3633篇
  1982年   3936篇
  1981年   3616篇
  1980年   3334篇
  1979年   3813篇
  1978年   3893篇
  1977年   4022篇
  1976年   4138篇
  1975年   3829篇
  1974年   3723篇
  1973年   3879篇
  1972年   3244篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
A temperature control unit was implemented to vary the temperature of samples studied on a commercial Mobile Universal Surface Explorer nuclear magnetic resonance (MOUSE-NMR) apparatus. The device was miniaturized to fit the maximum MOUSE sampling depth (25 mm). It was constituted by a sample holder sandwiched between two heat exchangers placed below and above the sample. Air was chosen as the fluid to control the temperature at the bottom of the sample, at the interface between the NMR probe and the sample holder, in order to gain space. The upper surface of the sample was regulated by the circulation of water inside a second heat exchanger placed above the sample holder. The feasibility of using such a device was demonstrated first on pure water and then on several samples of bread dough with different water contents. For this, T1 relaxation times were measured at various temperatures and depths and were then compared with those acquired with a conventional compact closed-magnet spectrometer. Discussion of results was based on biochemical transformations in bread dough (starch gelatinization and gluten heat denaturation). It was demonstrated that, within a certain water level range, and because of the low magnetic field strength of the MOUSE, a linear relationship could be established between T1 relaxation times and the local temperature in the dough sample.  相似文献   
52.
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   
53.
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   
54.
55.
Journal of Mathematical Chemistry - The analytical solutions of an asymmetric double well potential $$V(x)=a\, x^2-b\, x^3+c\, x^4$$ are found to be a triconfluent Heun function $$H_{T}(\alpha ,...  相似文献   
56.
57.
Physics of Particles and Nuclei Letters - When creating accelerators and storage-ring installations in a compact space, there is not always enough space for all the necessary magnet elements. In...  相似文献   
58.
Herein, we report the synthesis of specific silica-supported Co/Co3O4 core–shell based nanoparticles prepared by template synthesis of cobalt-pyromellitic acid on silica and subsequent pyrolysis. The optimal catalyst material allows for general and selective hydrogenation of pyridines, quinolines, and other heteroarenes including acridine, phenanthroline, naphthyridine, quinoxaline, imidazo[1,2-a]pyridine, and indole under comparably mild reaction conditions. In addition, recycling of these Co nanoparticles and their ability for dehydrogenation catalysis are showcased.  相似文献   
59.
Lanthanide dinitrogen complexes, Ln(N2) x (x = 1-8), were investigated by Density Functional Theory computations using the B3LYP exchange-correlation functional in conjunction with quasirelativistic pseudopotentials for Ln. After a recent study on the lanthanum complexes (A. Kovács, Structural Chemistry 2018 , 29, 1825), the present study aimed to probe the changes upon variously filled 4f subshells of Ln on the structures, stabilities, and bonding properties in related complexes of Nd, Ho, and Lu. The bonding properties were assessed on the basis of natural atomic charges, Ln valence orbital populations, and analysis of bonding molecular orbitals.  相似文献   
60.
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   
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