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   339816篇
  免费   2003篇
  国内免费   558篇
化学   157943篇
晶体学   5220篇
力学   19212篇
综合类   11篇
数学   50915篇
物理学   109076篇
  2021年   2554篇
  2020年   2677篇
  2019年   3278篇
  2018年   11513篇
  2017年   12109篇
  2016年   9520篇
  2015年   3687篇
  2014年   5613篇
  2013年   11157篇
  2012年   12498篇
  2011年   20595篇
  2010年   13941篇
  2009年   14320篇
  2008年   18496篇
  2007年   21321篇
  2006年   8919篇
  2005年   12725篇
  2004年   9880篇
  2003年   9602篇
  2002年   7952篇
  2001年   7417篇
  2000年   5697篇
  1999年   4153篇
  1998年   3646篇
  1997年   3591篇
  1996年   3431篇
  1995年   2962篇
  1994年   3024篇
  1993年   2951篇
  1992年   3251篇
  1991年   3428篇
  1990年   3261篇
  1989年   3397篇
  1988年   3238篇
  1987年   3197篇
  1986年   3052篇
  1985年   3782篇
  1984年   3969篇
  1983年   3320篇
  1982年   3335篇
  1981年   3211篇
  1980年   2988篇
  1979年   3400篇
  1978年   3520篇
  1977年   3611篇
  1976年   3545篇
  1975年   3287篇
  1974年   3267篇
  1973年   3398篇
  1972年   2550篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
The results of investigation of optical image detectors designed for the largest problem, near-VUV, range of the spectrum are presented. The possibility of using a dual-stage image detection system to appreciably lower the sensitivity threshold and make computer data processing feasible is considered. The integration of a UV module into a wideband image detector is studied.  相似文献   
62.
63.
Russian Chemical Bulletin - Quantum chemical calculations and a comparative analysis of Raman spectra of 3,4,5-triphenyl-1-propyl-1,2-diphosphole (1),...  相似文献   
64.
65.
Two new compounds of fluorine: (C2H5)4N[I2F] and (C2H5)4N[Br2F], have been easily synthesized in a nearly quantitative by a direct reaction of (C2H5)4NF, I2 and Br2. The products were isolated and characterized by elemental analysis and spectroscopic methods such as: Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible spectroscopy (UV-Vis). These compounds have been studied computationally with the Scalar ZORA relativistic level of theory using the ADF program package. The molecular parameters, and vibrational spectra were calculated. The excitation energies were found by timedependent perturbation density functional theory (TD-DFT). Molecule optimization, frequencies and excitation energies were calculated with standard Slatertype-orbital (STO) basis sets with triple-zeta quality double plus polarization functions (TZ2P) for all atoms. The FTIR, UV-Vis spectra and assignment of principal transitions and total density of state (TDOS) were extracted using the GaussSum 2.2 program. The comparison between experimental and calculated values showes that the experimental results correlate well with the predicted data.  相似文献   
66.
Journal of Experimental and Theoretical Physics - We suggest that the principle of holographic duality be extended beyond conformal invariance and AdS isometry. Such an extension is based on a...  相似文献   
67.
68.
69.
Journal of Applied and Industrial Mathematics - We consider the optimization of the short wave phased antenna arrays as a quadratic programming problem. The penalty function method and the gradient...  相似文献   
70.
Injection-moulding is one of the most common manufacturing processes used for polymers. In many applications, the mechanical properties of the product is of great importance. Injection-moulding of thin-walled polymer products tends to leave the polymer structure in a state where the mechanical properties are anisotropic, due to alignment of polymer chains along the melt flow direction. The anisotropic elastic-viscoplastic properties of low-density polyethylene, that has undergone an injection-moulding process, are therefore examined in the present work. Test specimens were punched out from injection-moulded plates and tested in uniaxial tension. Three in-plane material directions were investigated. Because of the small thickness of the plates, only the in-plane properties could be determined. Tensile tests with both monotonic and cyclic loading were performed, and the local strains on the surface of the test specimens were measured using image analysis. True stress vs. true strain diagrams were constructed, and the material response was evaluated using an elastic-viscoplasticity law. The components of the anisotropic compliance matrix were determined together with the direction-specific plastic hardening parameters.  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