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   26249篇
  免费   1421篇
  国内免费   1103篇
化学   25391篇
晶体学   42篇
力学   625篇
综合类   168篇
数学   1674篇
物理学   873篇
  2024年   17篇
  2023年   241篇
  2022年   440篇
  2021年   349篇
  2020年   485篇
  2019年   530篇
  2018年   542篇
  2017年   794篇
  2016年   857篇
  2015年   846篇
  2014年   818篇
  2013年   1169篇
  2012年   1557篇
  2011年   1431篇
  2010年   1192篇
  2009年   1427篇
  2008年   986篇
  2007年   1264篇
  2006年   1126篇
  2005年   1146篇
  2004年   1033篇
  2003年   818篇
  2002年   765篇
  2001年   593篇
  2000年   697篇
  1999年   642篇
  1998年   565篇
  1997年   626篇
  1996年   512篇
  1995年   564篇
  1994年   479篇
  1993年   383篇
  1992年   289篇
  1991年   361篇
  1990年   332篇
  1989年   285篇
  1988年   386篇
  1987年   376篇
  1986年   298篇
  1985年   275篇
  1984年   284篇
  1983年   146篇
  1982年   251篇
  1981年   193篇
  1980年   165篇
  1979年   164篇
  1978年   36篇
  1977年   9篇
  1976年   6篇
  1975年   6篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
In this paper, we first introduce a concept of L p -dual Quermassintegral sum function of convex bodies and establish the polar projection Minkowski inequality and the polar projection Aleksandrov-Fenchel inequality for L p -dual Quermassintegral sums. Moreover, by using Lutwak’s width-integral of index i, we establish the L p -Brunn-Minkowski inequality for the polar mixed projection bodies. As applications, we prove some interrelated results. This work was partially supported by the National Natural Science Foundation of China (Grant No. 10271071), Zhejiang Provincial Natural Science Foundation of China (Grant No. Y605065) and Foundation of the Education Department of Zhejiang Province of China (Grant No. 20050392)  相似文献   
73.
74.
Summary Furocoumarins from extracts ofHeracleum genus fruits were separated using normal and reversed phase TLC and HPLC and isolated in the milligram scale using overloaded systems of column chromatography. Binary or ternary solvents containing a polar modifier (methanol, diisopropyl ether or acetonitrile) were used as the mobile phases. Preliminary report on this work was presented at the 47th International Congress of Pharmaceutical Sciences of F.I.P. in Amsterdam. The Netherlands, 30 August–5 September 1987.  相似文献   
75.
用核磁共振对非晶态中B3+离子的微观结构进行了测定,结合Raman光谱的研究,对Li2O-B2O3-P2O5系统非晶态的性能(电导率、密度等)在P2O5/B2O3比约等于1时产生极值的原因从理论上作了阐明。  相似文献   
76.
Analytical approach is presented to the isoperimetric type problems of finding convex figures separated by current hyperplanes.  相似文献   
77.
We have investigated the low-lying collective states and electromagnetic transitions in 94Mo within the framework of the interacting boson model. The influence of model parameters on the energy levels and electromagnetic properties has been investigated. The analysis of the obtained results and the parameter values predict that the 23+state is the lowest mixed symmetry state with pure F = Fmax - 1 in this nucleus. The calculated results predicate that the 25+ (two-Q-phonon) mixed symmetry state is closed to the J = 2+ at 2.870 MeV in the experimental data, and the 2.965 MeV state is the lowest mixed symmetry with J = 3+.  相似文献   
78.
Two methods for sampling and concentration of volatile organic compounds are reported. In the first method, traps coated with a very thick film (ca. 100 μm) of cross-linked silicone stationary phase are employed. Such thick films can be prepared with a modified dynamic coating procedure, which is briefly described. The low phase ratio traps can be utilized for enrichment of volatiles from gaseous as well as aqueous matrices. The second technique is based on chromatographic evaporation of a solvent in a capillary tube, where the process is sustained by a repeated sample injection and a cyclic flow reversal. In this way, large solvent volumes can be handled by a small volume system. Under optimal conditions, when using a solvent barrier, quantitative recovery is possible even for compounds of comparatively high volatility. Another important application of the technique is extraction of trace components from gases such as headspace samples, polluted air, etc.  相似文献   
79.
Technical cellulose-2.5-acetates (CA 2.5) were characterized regarding their carbohydrate composition in comparison to the raw material. The association of the CA 2.5 samples in acetone was studied by size exclusion chromatography (SEC) using various acetone grades and styrene divinylbenzene copolymer columns. In HPLC grade acetone with and without addition of 1% water up to three different pre-humps eluted in front of the main fraction of the polymer. The evaluation of the main peak by light scattering measurements resulted in high molar masses indicating that for these technical CA 2.5 samples even the main fraction is not dissolved without association. No pre-humps or association phenomena were observed after addition of 1 ppm LiBr to HPLC grade acetone or with p.a. grade acetone. In addition pre-hump enriched and pre-hump free fractions were isolated by fractionated precipitation. The carbohydrate composition of these fractions was determined and correlated with their association pattern in SEC investigations.  相似文献   
80.
In this article we prove uniform convergence estimates for the recently developed Galerkin‐multigrid methods for nonconforming finite elements for second‐order problems with less than full elliptic regularity. These multigrid methods are defined in terms of the “Galerkin approach,” where quadratic forms over coarse grids are constructed using the quadratic form on the finest grid and iterated coarse‐to‐fine intergrid transfer operators. Previously, uniform estimates were obtained for problems with full elliptic regularity, whereas these estimates are derived with less than full elliptic regularity here. Applications to the nonconforming P1, rotated Q1, and Wilson finite elements are analyzed. The result applies to the mixed method based on finite elements that are equivalent to these nonconforming elements. © 2002 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 18: 203–217, 2002; DOI 10.1002/num.10004  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