全文获取类型
收费全文 | 3073篇 |
免费 | 43篇 |
国内免费 | 33篇 |
专业分类
化学 | 1761篇 |
晶体学 | 60篇 |
力学 | 68篇 |
数学 | 668篇 |
物理学 | 592篇 |
出版年
2022年 | 49篇 |
2021年 | 64篇 |
2020年 | 30篇 |
2019年 | 36篇 |
2018年 | 38篇 |
2017年 | 56篇 |
2016年 | 79篇 |
2015年 | 76篇 |
2014年 | 86篇 |
2013年 | 210篇 |
2012年 | 134篇 |
2011年 | 179篇 |
2010年 | 115篇 |
2009年 | 125篇 |
2008年 | 171篇 |
2007年 | 160篇 |
2006年 | 148篇 |
2005年 | 124篇 |
2004年 | 142篇 |
2003年 | 99篇 |
2002年 | 106篇 |
2001年 | 50篇 |
2000年 | 44篇 |
1999年 | 43篇 |
1998年 | 41篇 |
1997年 | 51篇 |
1996年 | 55篇 |
1995年 | 31篇 |
1994年 | 34篇 |
1993年 | 42篇 |
1992年 | 27篇 |
1991年 | 30篇 |
1990年 | 33篇 |
1989年 | 32篇 |
1988年 | 20篇 |
1987年 | 26篇 |
1986年 | 18篇 |
1985年 | 30篇 |
1984年 | 42篇 |
1983年 | 25篇 |
1982年 | 24篇 |
1981年 | 31篇 |
1980年 | 23篇 |
1979年 | 22篇 |
1978年 | 20篇 |
1977年 | 29篇 |
1976年 | 12篇 |
1975年 | 13篇 |
1974年 | 10篇 |
1972年 | 11篇 |
排序方式: 共有3149条查询结果,搜索用时 15 毫秒
21.
Andrzej Małecki Jalees A.K. Tareen Jean Pierre Doumerc Louis Rabardel Jean Claude Launay 《Journal of solid state chemistry》1985,56(1):49-57
Kinetics of thermal decomposition in vacuum of Co3O4 powder as well as single crystals has been investigated. Discrepancies with the results of previous authors have been discussed. Decomposition of Co3O4 proceeds through formation of a compact layer of CoO and hence diffusion is the rate-limiting factor. The experimental curves α(t) be described for 0.05 < α < 0.85 using a modified Ginstling-Brounshtein equation: 1 ? 2α/3 ? (1 ? α)2/3 = ktn where the activation energy varies with the degree of decomposition. 相似文献
22.
A master equation is used to study transitions between the stable limit cycle and stable focus in the two-variable bistable system. The distribution function of the mean first passage time between these attractors and the relative dispersion of the mean first return time from the stable focus to itself as a function of the intensity of fluctuations are calculated and discussed. A coherence resonance is observed for the return time from the focus to itself. 相似文献
23.
Andrzej Smajdor 《Results in Mathematics》1994,26(3-4):385-389
A set-valued function F defined on a convex cone S in a real vector space X into the set n(Y) of all non-empty subsets of a real vector space Y is said to be the Jensen function iff $${1\over 2}\lbrack F(x)+F(x)\rbrack=F\lbrack{1\over 2}(x+y)\rbrack$$ for all x, y ∈ S. This note deals with iteration semigroups of Jensen set-valued functions on S. 相似文献
24.
25.
Andrzej Machocki Tadeusz Borowiecki Andrezej Denis 《Reaction Kinetics and Catalysis Letters》1993,51(2):541-545
The studies of the influence of the kind of natural calcium mineral and the kind and amount of sodium promoter on the conversion degree of methane and oxygen, selectivity and yield of the oxidative conversion of methane have shown the usability of limestone as a basic component of the catalyst for this process. 相似文献
26.
A planar ordered set has a triangle-free, planar covering graph; on the other hand, there are nonplanar ordered sets whose covering graphs are planar. We show thatevery triangle-free planar graph has a planar upward drawing. This planar upward drawing can be constructed in time, polynomial in the number of vertices.Our results shed light on the apparently difficult problem, of long-standing, whether there is aneffective planarity-testing procedure for an ordered set.Supported in part by the Alexander von Humboldt Stiftung.Supported in part by the Deutsche Forschungsgemeinschaft. 相似文献
27.
The palladium catalysed cross-coupling reaction of aryl iodides and bromides with pinacolborane in 1,3-dialkylimidazolium tetrafluoroborates and hexafluorophosphates producing arylboronates is described. 相似文献
28.
Many-body perturbation theory is used for the calculation of the quadrupole polarizability of the Be atom within the finite-field perturbation scheme. The correlation corrections exhibit a considerable dependence on the f-type orbital exponents and the final results are in the range 287–294 au. The convergence of the correlation perturbation series is discussed. 相似文献
29.
Zenon Lukaszewski Andrzej Szymanski Bogdan Wyrwas 《Trends in analytical chemistry : TRAC》1996,15(10):1239-531
The evolution of the BiAS procedure is reviewed and its standard recommended version was compared with the modified version combined with the indirect tensammetric method (BiAS-ITM). New applications of the use of BiAS-ITM for the determination of nonionic surfactants (in the presence of hydrocarbons or adsorbed on particles) and polyethylene glycols were discussed. 相似文献
30.
Sánchez-Moreno MJ Gómez-Coca RB Fernández-Botello A Ochocki J Kotynski A Griesser R Sigel H 《Organic & biomolecular chemistry》2003,1(10):1819-1826
The synthesis of (1H-benzimidazol-2-yl-methyl)phosphonic acid, H2(Bimp)+/-, is described: 2-chloromethylbenzimidazole was reacted with ethylchloroformate to give 1-carboethoxy-2-chloromethylbenzimidazole which was treated with trimethyl phosphite and after hydrolysis with aqueous HBr H2(Bimp)+/- was obtained. In H2(Bimp)+/- one proton is at the N-3 site and the other at the phosphonate group; both acidity constants were determined in aqueous solution by potentiometric pH titrations (25 degrees C; I = 0.1 M, NaNO3) and this furnished the pKa values of 5.37 +/- 0.02 and 7.41 +/- 0.02, respectively. The acidity constant for the release of the primary proton from the P(O)(OH)2 group of H3(Bimp)+ was estimated: pKa = 1.5 +/- 0.2. Moreover, Bimp2- can be further deprotonated at its neutral (N-1/N-3)H site to give the benzimidazolate residue, but this reaction occurs only in strongly alkaline solution (KOH); application of the H_ scale developed by G. Yagil (J. Phys. Chem., 1967, 71, 1034) together with UV spectrophotometric measurements gave pKa = 14.65 +/- 0.12. Comparisons with acidity constants taken from the literature show that this latter pKa value is far too large and this allows the conclusion that an intramolecular hydrogen bond is formed between the (N-1/N-3)H site and the phosphonate group of Bimp2-; the formation degree of this hydrogen-bonded isomer is estimated to be 98 +/- 2%. The general relevance of this and the other results are shortly discussed and the species distribution for the Bimp system in dependence on pH is provided. 相似文献