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   844篇
  免费   16篇
化学   654篇
晶体学   1篇
力学   5篇
数学   55篇
物理学   145篇
  2023年   3篇
  2022年   7篇
  2021年   6篇
  2020年   11篇
  2019年   5篇
  2018年   15篇
  2017年   14篇
  2016年   38篇
  2015年   43篇
  2014年   33篇
  2013年   72篇
  2012年   46篇
  2011年   86篇
  2010年   70篇
  2009年   57篇
  2008年   44篇
  2007年   15篇
  2006年   44篇
  2005年   20篇
  2004年   13篇
  2003年   15篇
  2002年   21篇
  2001年   9篇
  2000年   8篇
  1999年   19篇
  1998年   7篇
  1997年   10篇
  1996年   11篇
  1994年   6篇
  1992年   7篇
  1991年   6篇
  1990年   4篇
  1989年   4篇
  1988年   6篇
  1987年   8篇
  1986年   8篇
  1985年   4篇
  1984年   8篇
  1983年   3篇
  1981年   3篇
  1979年   3篇
  1978年   4篇
  1977年   5篇
  1976年   5篇
  1975年   4篇
  1974年   3篇
  1973年   5篇
  1968年   4篇
  1962年   2篇
  1956年   2篇
排序方式: 共有860条查询结果,搜索用时 46 毫秒
1.
A tree T is arbitrarily vertex decomposable if for any sequence τ of positive integers adding up to the order of T there is a sequence of vertex-disjoint subtrees of T whose orders are given by τ. An on-line version of the problem of characterizing arbitrarily vertex decomposable trees is completely solved here.  相似文献   
2.
We present a solution to the moment problem for effect algebras, concerning mean values of all powers of an observable concentrated on the interval [0, 1] for states from a convex set. We give a solution for particular examples, e.g., for the set of all effect operators. We examine how this problem is related to a socalled E-property. Finally, we give a solution for observables studied in the operational approach to physical theories.  相似文献   
3.
This paper discusses the influence of chemical composition on the final electromagnetic properties in higher permeability material. Furthermore, the effect of the hot rolling practice and the end of austenite transformation temperature range on the hot band microstructure is described. The magnetic polarization J5000 better than 1.7 T, using hot rolling conditions 40 mm transfer bar thickness, finish mill entry temperature 1000 °C, and finishing temperature 800–840 °C and after decarburization heat treatment and grain growth treatment, was obtained.  相似文献   
4.
The paper presents the classification of the electronic empty lattice eigenvalues and the classification of the Bloch sums for the garnet structureIa3d (O h 10 ) at the symmetry points, H, P, andN of the Brillouin zone. This provides a starting point for the energy band studies of these technologically important materials.The author thanks Dr. V. Frei for useful comments.  相似文献   
5.
Summary From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Pb2+(aq)+SrL2+ (nb)↔PbL2+ (nb)+Sr2+ (aq) taking place in the two-phase water-nitrobenzene system (L=PEG 400; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as logKex(Pb2+, SrL2+)=2.0±0.1. Further, the stability constant of the PEG 400 - lead complex in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log βnb(PbL2+)=12.9±0.1.  相似文献   
6.
The related parameters of cation size and valence that control the crystallization of Sr(3)CaRu(2)O(9) into a 1:2 B-site-ordered perovskite structure were explored by cationic substitution at the strontium and calcium sites and by the application of high pressure. At ambient pressures, Sr(3)MRu(2)O(9) stoichiometries yield multiphasic mixtures for M = Ni(2+), Mg(2+), and Y(3+), whereas pseudocubic perovskites result for M = Cu(2+) and Zn(2+). For A-site substitutions, an ordered perovskite structure results for Sr(3-x)Ca(x)CaRu(2)O(9), with 0 相似文献   
7.
Summary Extraction of microamounts of calcium by a nitrobenzene solution of hydrogen dicarbollylcobaltate (H+B-) in the presence of 18-crown-6 (18C6, L) has been investigated. The equilibrium data have been explained assuming that the complexes HL+, CaL2+and CaL are extracted into the organic phase. The values of extraction and stability constants of the complex species in nitrobenzene saturated with water have been determined.  相似文献   
8.
The number of chromosomal and chromatid breaks, deletions, as well as fragments, have been followed in correlation to the physical dose as assessed by the specific radioactivity of DNA. Human lymphocytes from adult donors were incubated for 44 hours in media supplemented with tritiated thymidine. An uneven distribution of labelling in the cell population has been found and about 50% of the population of cells remained unlabelled. The dose-response curve was flat reflecting loss of damaged cells and/or repair of damage. The dose-response curve showed that at the experimental conditions used the dose of 100 mGy absorbed from incorporated tritium caused about 0.1 deletions per. cell. Doubling the number of deletions to about 0.2 per cell required approximately a five times higher absorbed dose.  相似文献   
9.
Extraction of85Sr by a nitrobenzene solution of bis-1,2-dicarbollylcobaltate in the presence of 15-crown-5 (15C5, L) has been investigated. The equilibrium data and the typical maxima concerning the dependencies of the Sr distribution ratios on the analytical concentration of 15C5 in the system under study can be explained assuming that the HL+, HL2 + and SrL2 2+ species are extracted into the nitrobenzene phase. The values of the corresponding extraction and stability constants of the extracted species in nitrobenzene saturated with water have been determined.  相似文献   
10.
Summary Extraction of microamounts of yttrium by a nitrobenzene solution of hydrogen dicarbollylcobaltate (H+B-) in the presence of 15-crown-5 (15C5,L) has been investigated. The equilibrium data have been explained assuming that the complexes HL+, HL2,+, YL3+, YL2,3+and YH-1L2,2+are extracted into the organic phase. The values of extraction and stability constants of the species in nitrobenzene saturated with water have been determined.  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