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   4412篇
  免费   320篇
  国内免费   194篇
化学   2972篇
晶体学   74篇
力学   175篇
综合类   12篇
数学   647篇
物理学   1046篇
  2023年   54篇
  2022年   100篇
  2021年   118篇
  2020年   141篇
  2019年   162篇
  2018年   169篇
  2017年   134篇
  2016年   205篇
  2015年   167篇
  2014年   225篇
  2013年   413篇
  2012年   320篇
  2011年   337篇
  2010年   266篇
  2009年   198篇
  2008年   287篇
  2007年   252篇
  2006年   196篇
  2005年   162篇
  2004年   121篇
  2003年   98篇
  2002年   110篇
  2001年   77篇
  2000年   66篇
  1999年   43篇
  1998年   46篇
  1997年   46篇
  1996年   42篇
  1995年   37篇
  1994年   33篇
  1993年   27篇
  1992年   32篇
  1991年   17篇
  1990年   26篇
  1989年   22篇
  1988年   17篇
  1987年   17篇
  1986年   12篇
  1985年   18篇
  1984年   24篇
  1983年   13篇
  1982年   9篇
  1981年   9篇
  1980年   9篇
  1979年   10篇
  1978年   7篇
  1976年   4篇
  1975年   4篇
  1974年   4篇
  1970年   4篇
排序方式: 共有4926条查询结果,搜索用时 46 毫秒
11.
The relation of the isoelectric point (IEP) and the point of zero net charge (PZNC) of the hydrotalcite-like compounds was discussed. It was found that the IEP does not equal to the PZNC and the IEP is higher than the PZNC. The structural positive charges existing in the HTlc,which cause the difference between the IEP and the PZNC. The effects of the structural positive charges of the HTlc on its IEP and PZNC are the same as the specific adsorption of metal cations.  相似文献   
12.
Population balance equations combined with a three-dimensional two-fluid model are employed to predict subcooled boiling flow at low pressure in a vertical annular channel. The MUSIG (MUltiple-SIze-Group) model implemented in the computer code CFX4.4 is further developed to accommodate the wall nucleation at the heated wall and condensation in the subcooled boiling regime. Comparison of model predictions against local measurements is made for the void fraction, bubble Sauter mean diameter and gas and liquid velocities covering a range of different mass and heat fluxes and inlet subcooling temperatures. Additional comparison using empirical relationships for the active nucelation site density and local bubble diameter is also investigated. Good agreement is achieved with the local radial void fraction, bubble Sauter diameter and liquid velocity profiles against measurements. However, significant weakness of the model is evidenced in the prediction of the vapour velocity. Work is in progress to circumvent the deficiency through the consideration of additional momentum equations or developing an algebraic slip model to account for bubble separation.  相似文献   
13.
This article proves the existence of singular directions of value distribution theory for some transcendental holomorphic curves in the n-dimensional complex projective space Pn(C). An example is given to complement these results.  相似文献   
14.
The implementation of a nonzero-order joint transform correlator using the double port Mach-Zehnder interferometric technique is proposed and demonstrated. This approach provides on-line processing for directly removing the zero-order components of a joint power spectrum in one step and performs the nonzero-order optical correlation. Experimental results are presented and discussed.  相似文献   
15.
We define a multifunction F: XY to be upper (lower) D*-supercontinuous if F +(V) (F (V)) is d*-open in X for every open set V of Y. We obtain some characterizations and several properties concerning upper (lower) D*-supercontinuous multifunctions.   相似文献   
16.
This work proposes and demonstrates the feasibility of gray image encryption using multiple polarization encoding, in which the cascaded twisted nematic liquid crystal devices sandwiched between a crossed polarizer pair are used to implement exclusive OR (XOR) logical encryption and decryption. The polarization encoding scheme provides a multichannel XOR logic operation to secure bit-plane images derived from a gray image, according to the adiabatic following properties of twisted nematic liquid crystal devices. Experimental data reveal that the multiple polarization encoding schemes for gray image encryption and decryption are performed with acceptable image quality by selecting appropriate polarization orientation and modulation conditions. Both analytic and experimental results are presented and discussed.  相似文献   
17.
We extend the previously found accelerated Kerr-Schild metrics for Einstein-Maxwell-null dust and Einstein-Born-Infeld-null dust equations to the cases including the cosmological constant. This way we obtain the generalization of the charged de Sitter metrics in static space-times. We also give a generalization of the zero acceleration limit of our previous Einstein-Maxwell and Einstein-Born-Infeld solutions.  相似文献   
18.
We consider the problem of providing a minimum cost multi-service network subject to one link failure scenarios. We assume our network is fully meshed and demand is satisfied by using direct or two hop-paths. We provide a large scale linear programming formulation and propose and test two effective heuristics.  相似文献   
19.
20.
A dendritic macroinitiator having 16 TEMPO‐based alkoxyamines, Star‐16 , was prepared by the reaction of a dendritic macroinitiator having eight TEMPO‐based alkoxyamines, [G‐3]‐OH , with 4,4′‐bis(chlorocarbonyl)biphenyl. The nitroxide‐mediated radical polymerization (NMRP) of styrene (St) from Star‐16 gave 16‐arm star polymers with PDI of 1.19–1.47, and NMPR of 4‐vinylpyridine from the 16‐arm star polymer gave 16‐arm star diblock copolymers with PDI of 1.30–1.43. The ring‐opening polymerization of ε‐caprolactone from [G‐3]‐OH and the subsequent NMRP of St gave AB8 9‐miktoarm star copolymers with PDI of 1.30–1.38. The benzyl ether linkages of the 16‐arm star polymers and the AB8 9‐miktoarm star copolymers were cleaved by treating with Me3SiI, and the resultant poly(St) arms were investigated by size exclusion chromatography (SEC). The SEC results showed PDIs of 1.23–1.28 and 1.18–1.22 for the star polymers and miktoarm stars copolymers, respectively, showing that they have well‐controlled poly(St) arms. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1159–1169, 2007.  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