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   95977篇
  免费   3681篇
  国内免费   2196篇
化学   37035篇
晶体学   960篇
力学   7734篇
综合类   76篇
数学   33865篇
物理学   22184篇
  2023年   409篇
  2022年   594篇
  2021年   687篇
  2020年   764篇
  2019年   762篇
  2018年   10979篇
  2017年   10680篇
  2016年   6943篇
  2015年   1673篇
  2014年   1358篇
  2013年   1736篇
  2012年   5473篇
  2011年   12172篇
  2010年   6744篇
  2009年   7080篇
  2008年   7743篇
  2007年   9742篇
  2006年   1232篇
  2005年   2094篇
  2004年   2126篇
  2003年   2383篇
  2002年   1445篇
  2001年   587篇
  2000年   572篇
  1999年   566篇
  1998年   502篇
  1997年   448篇
  1996年   495篇
  1995年   377篇
  1994年   298篇
  1993年   323篇
  1992年   212篇
  1991年   230篇
  1990年   188篇
  1989年   161篇
  1988年   147篇
  1987年   133篇
  1986年   129篇
  1985年   102篇
  1984年   100篇
  1983年   68篇
  1982年   73篇
  1981年   62篇
  1980年   72篇
  1979年   54篇
  1978年   47篇
  1914年   45篇
  1912年   40篇
  1909年   41篇
  1908年   40篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
181.
182.
Vasily L. Morgunov 《Pramana》2007,69(6):1097-1100
A new calorimeter energy calibration method was developed for the proposed ILC detectors. The method uses the center-of-mass energy of the accelerator as the reference. It has been shown that using the energy conservation law it is possible to make ECAL and HCAL cross calibration to reach a good energy resolution for the simple calorimeter energy sum.   相似文献   
183.
184.
In a conventional diffractometer having single monochromator, only one position, parallel position, is used for the diffraction experiment (i.e. detection) because the resolution property of the other one, anti-parallel position, is very poor. However, a bent perfect crystal (BPC) monochromator at monochromatic focusing condition can provide a quite flat and equal resolution property at both parallel and anti-parallel positions and thus one can have a chance to use both sides for the diffraction experiment. From the data of the FWHM and the Δd/d measured on three diffraction geometries (symmetric, asymmetric compression and asymmetric expansion), we can conclude that the simultaneous diffraction measurement in both parallel and anti-parallel positions can be achieved.  相似文献   
185.
A novel type of corner reflector for the reflection of surface plasmon polariton (SPP) is proposed. The reflector consists of two layers of compensatory media whose permittivity and permeability take opposite signs to that of the corresponding layer of the SP waveguide. By rigorously solving Maxwell's equations, the reflected SPP is proved to exist. The transverse wave vector of the reflected SPP is always antiparallel to that of the incident SPP and no phase retardation is introduced.  相似文献   
186.
Forecasting electricity prices in presentday competitive electricity markets is a must for both producers and consumers because both need price estimates to develop their respective market bidding strategies. This paper proposes a transfer function model to predict electricity prices based on both past electricity prices and demands, and discuss the rationale to build it. The importance of electricity demand information is assessed. Appropriate metrics to appraise prediction quality are identified and used. Realistic and extensive simulations based on data from the PJM Interconnection for year 2003 are conducted. The proposed model is compared with naïve and other techniques.  相似文献   
187.
In this paper, we found that boron deposited on the surface of support when sodium borohydride used as reducing agent during the preparation of Pt/C catalyst. The deposition of boron markedly reduces particle size of Pt, raises electrochemical active surface (EAS) area of catalyst and electrochemical activity for hydrogen evolution or oxygen reduction reaction (ORR) compared with which prepared using other reducing agents (hydrogen and formaldehyde).  相似文献   
188.
A planar optical waveguide has been formed in a LiB3O5 crystal using 6.0 MeV Cu+-ions with a dose of 1 × 1015 ions/cm2 at room temperature. Possible propagating modes were measured at a wavelength of 633 nm using the prism-coupling method. The refractive index profiles of the waveguide were reconstructed by an effective refractive index method and the beam propagation method was used to investigate the properties of the propagation modes in the formed waveguide. The results suggest that the fundamental TE0 and TM0 modes may be well-confined and propagate a longer distance inside the waveguide. The implantation process was also simulated using the transport of ions in matter code (TRIM), which indicates that the nuclear energy deposition may be the main factor for the refractive index change.  相似文献   
189.
In this paper we generalize to coisotropic actions of compact Lie groups a theorem of Guillemin on deformations of Hamiltonian structures on compact symplectic manifolds. We show how one can reconstruct from the moment polytope the symplectic form on the manifold. Received: 21 March 2006  相似文献   
190.
We investigate the variety of residuated lattices with a commutative and idempotent monoid reduct.  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