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   283741篇
  免费   2594篇
  国内免费   1044篇
化学   132077篇
晶体学   4022篇
力学   15107篇
综合类   32篇
数学   43268篇
物理学   92873篇
  2020年   1559篇
  2019年   1584篇
  2018年   10775篇
  2017年   11616篇
  2016年   7240篇
  2015年   2927篇
  2014年   3353篇
  2013年   8063篇
  2012年   10708篇
  2011年   20224篇
  2010年   12620篇
  2009年   12792篇
  2008年   17634篇
  2007年   21073篇
  2006年   6983篇
  2005年   12945篇
  2004年   8856篇
  2003年   8154篇
  2002年   6185篇
  2001年   5711篇
  2000年   4513篇
  1999年   3373篇
  1998年   2863篇
  1997年   2761篇
  1996年   2652篇
  1995年   2452篇
  1994年   2409篇
  1993年   2186篇
  1992年   2508篇
  1991年   2637篇
  1990年   2409篇
  1989年   2370篇
  1988年   2353篇
  1987年   2251篇
  1986年   2107篇
  1985年   2679篇
  1984年   2861篇
  1983年   2307篇
  1982年   2509篇
  1981年   2407篇
  1980年   2265篇
  1979年   2491篇
  1978年   2652篇
  1977年   2455篇
  1976年   2527篇
  1975年   2362篇
  1974年   2389篇
  1973年   2440篇
  1972年   1629篇
  1971年   1438篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
33.
34.
Su  X. F.  Zhang  Y. L.  Maximov  A. L.  Zhang  K.  Xin  Q.  Feng  C. Q.  Bai  X. F.  Wu  W. 《Russian Journal of Applied Chemistry》2020,93(1):127-136
Russian Journal of Applied Chemistry - Nanoscale ZSM-5 (AlZ5-D) and Ga-substituted ZSM-5 zeolites ((Al,Ga)Z5-D and GaZ5-D) were synthesized by a green dry-gel conversion strategy. For comparison,...  相似文献   
35.
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   
36.
37.
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   
38.
Development of biocompatible porous supports is a promising strategy in the field of tissue engineering for the repair and regeneration of bone tissues with severe damage. Graphene oxide aerogels (GOAs) are excellent candidates for the manufacture of these systems due to their porosity, ability to imitate bone structure, and mechanical resistance, and according to their surface chemical reactivity, they can facilitate osseointegration, osteogenesis, osteoinduction and osteoconduction. In this review, synthesis of GOAs from the most primary source is described, and recent studies on the use of these functionalized carbonaceous foams as scaffolding for bone tissue regeneration are presented.  相似文献   
39.
Journal of Thermal Analysis and Calorimetry - In the present work, pyrolysis kinetic mechanism was studied for regenerated cellulosic fiber (RCF) and composite RCF containing silicon/nitrogen flame...  相似文献   
40.
The research progress of a novel traffic solution,a submerged floating tunnel(SFT),is reviewed in terms of a study approach and loading scenario.Among existing publications,the buoyancy-weight ratio(BWR) is usually predefined.However,BWR is a critical structural parameter that tremendously affects the dynamic behaviour of not only the tunnel tube itself but also the cable system.In the context of a SFT prototype(SFTP) project in Qiandao Lake(Zhejiang Province,China),the importance of BWR is illustrated by finite element analysis and subsequently,an optimized BWR is proposed within a reasonable range in the present study.In the numerical model,structural damping is identified to be of importance.Rayleigh damping and the corresponding Rayleigh coefficients are attained through a sensitivity study,which shows that the adopted damping ratios are fairly suitable for SFTP.Lastly,the human sense of security is considered by quantifying the comfort index,which helps further optimize BWR in the SFTP structural parameter design.  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