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   36405篇
  免费   2560篇
  国内免费   1114篇
化学   24396篇
晶体学   296篇
力学   1319篇
综合类   86篇
数学   5597篇
物理学   8385篇
  2023年   327篇
  2022年   454篇
  2021年   568篇
  2020年   631篇
  2019年   698篇
  2018年   579篇
  2017年   539篇
  2016年   951篇
  2015年   820篇
  2014年   999篇
  2013年   2066篇
  2012年   2100篇
  2011年   2521篇
  2010年   1414篇
  2009年   1288篇
  2008年   2026篇
  2007年   1986篇
  2006年   1930篇
  2005年   1846篇
  2004年   1579篇
  2003年   1322篇
  2002年   1271篇
  2001年   575篇
  2000年   513篇
  1999年   448篇
  1998年   497篇
  1997年   503篇
  1996年   541篇
  1995年   493篇
  1994年   447篇
  1993年   411篇
  1992年   374篇
  1991年   322篇
  1990年   313篇
  1989年   304篇
  1988年   311篇
  1987年   283篇
  1986年   280篇
  1985年   407篇
  1984年   454篇
  1983年   343篇
  1982年   439篇
  1981年   408篇
  1980年   350篇
  1979年   333篇
  1978年   351篇
  1977年   332篇
  1976年   275篇
  1975年   273篇
  1974年   262篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Following detoxification of the liquid hydrolysate produced in a corn stover pretreatment process, inhibitor levels are seen to increase with the re-addition of solids for the ensuing hydrolysis and fermentation processes. The solids that were separated from the slurry before detoxification of the liquor contain approx 60% (w/w) moisture, and contamination occurs owing to the diffusion of inhibitors from the moisture entrained in the porous structure of the corn stover solids into the bulk fluid. This evidence suggests the need for additional separation and detoxification steps to purge residual inhibitors entrained in the moisture in the solids. An overliming process to remove furans from the hydrolysate failed to reduce total organic acids concentration, so acids were removed by treatment with an activated carbon powder. Smaller carbon doses proved more efficient in removing organic acids in terms of grams of acid removed per gram of carbon powder. Sugar adsorption by the activated carbon powder was minimal.  相似文献   
92.
The hot bimodal fission of 252Cf is reexamined with new high-statistics data. We constructed a γ-γ-γ coincidence cube for binary fission and LCP-gated γ-γ matrix for ternary fission. By identifying the secondary fission fragments from their γ-ray transitions, we measured the yields for various fission splits. The normal neutron yield distribution is found to be Gaussian for Xe-Ru. However, the binary fission split of Ba-Mo is found to exhibit a bimodal neutron distribution with the “hot mode” corresponding to ≈3.1% of the total yield. In α ternary fission, the first measurements of yields for specific fission splits are presented. The Te-α-Ru and Xe-α-Mo neutron yields fit well with a single mode, but the Ba-α-Zr split shows evidence for an enhanced hot mode with an intensity of ≈13.8% of the normal mode. The text was submitted by the authors in English.  相似文献   
93.
We demonstrate a three orders of magnitude increase and stability in the backscattered fluorescence signal from nitrogen molecules by terawatt femtosecond laser pulse induced air filaments using a new method. The method is based on squeezing the initial beam diameter using a telescope. The effect of laser shot-to-shot fluctuations was included in numerical simulations by a random distribution of the initial intensity in both squeezed and non-squeezed beams. Statistical processing of the simulation results shows that the average diameter of plasma channels as well as the total amount of free electrons generated in a bunch of multiple filaments in air is larger in the squeezed beam. Shot-to-shot stability of the simulated plasma density increases in the squeezed beam. The change of this plasma density with propagation distance is in good qualitative agreement with the change of the range-corrected nitrogen fluorescence signal with distance. PACS 42.65.Jx; 42.60.Jf; 42.68.Ay; 42.68.Wt  相似文献   
94.
95.
96.
The enthalpies of formation of simple nonmetal or metalloid oxyanions in aqueous solution are discussed. Archival values are cited and estimates are made. Trends prove evasive.  相似文献   
97.
98.
The spin polarized β-emitting nuclei12B (I π=1+,T 1/2=20.18 ms) were produced by the nuclear reaction11B(d, p)12B and by the selection technique of the incident deuteron energy and the12B recoil angle following the nuclear reaction. The nuclear magnetic moment of the short-lived nuclei12B was measured by β-NMR with the β-NMR and β-NQR setup established for the first time in China. The nuclear magnetic moment of12B was determined to be μ=0.99993±0.00048 nm org=0.99993±0.00048 after the precise correction of the Knight shift.  相似文献   
99.
There are few techniques available to numerically solve sixth-order boundary-value problems with two-point boundary conditions. In this paper we show that the Sinc-Galerkin method is a very effective tool in numerically solving such problems. The method is then tested on examples with homogeneous and nonhomogeneous boundary conditions and a comparison with the modified decomposition method is made. It is shown that the Sinc-Galerkin method yields better results.

  相似文献   

100.
Fractalmania     
  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