全文获取类型
收费全文 | 31600篇 |
免费 | 144篇 |
国内免费 | 282篇 |
专业分类
化学 | 11947篇 |
晶体学 | 283篇 |
力学 | 1452篇 |
综合类 | 12篇 |
数学 | 9390篇 |
物理学 | 8942篇 |
出版年
2021年 | 56篇 |
2019年 | 48篇 |
2018年 | 1215篇 |
2017年 | 1467篇 |
2016年 | 759篇 |
2015年 | 593篇 |
2014年 | 504篇 |
2013年 | 742篇 |
2012年 | 3191篇 |
2011年 | 2395篇 |
2010年 | 1868篇 |
2009年 | 1612篇 |
2008年 | 643篇 |
2007年 | 687篇 |
2006年 | 678篇 |
2005年 | 4522篇 |
2004年 | 3974篇 |
2003年 | 2363篇 |
2002年 | 553篇 |
2001年 | 350篇 |
2000年 | 143篇 |
1999年 | 208篇 |
1998年 | 140篇 |
1997年 | 103篇 |
1996年 | 87篇 |
1995年 | 95篇 |
1994年 | 95篇 |
1993年 | 86篇 |
1992年 | 229篇 |
1991年 | 192篇 |
1990年 | 174篇 |
1989年 | 144篇 |
1988年 | 136篇 |
1987年 | 97篇 |
1986年 | 82篇 |
1985年 | 76篇 |
1984年 | 73篇 |
1983年 | 63篇 |
1982年 | 55篇 |
1981年 | 63篇 |
1980年 | 54篇 |
1979年 | 65篇 |
1978年 | 61篇 |
1977年 | 56篇 |
1976年 | 123篇 |
1975年 | 57篇 |
1974年 | 64篇 |
1973年 | 89篇 |
1972年 | 50篇 |
1970年 | 56篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
M. Abel 《Journal of Mathematical Sciences》2007,140(3):346-353
Bounded representations of bornological algebras are considered. The left and right bornological radicals in bornological
algebras are introduced. It is shown that the left (right) bornological radical of a bornological algebra A is equal to the
intersection of all bornologically closed maximal regular left (respectively, right) ideals of A, and both these radicals
of A and the Jacobson radical of A coincide if A is an advertive and simplicial bornological algebra (in particular, a bornological
Q-algebra). Bibliography: 16 titles.
Published in Zapiski Nauchnykh Seminarov POMI, Vol. 326, 2005, pp. 9–22. 相似文献
32.
P E S?rensen R A McClelland R D Gandour 《Acta chemica Scandinavica (Copenhagen, Denmark : 1989)》1991,45(6):558-566
The ring-chain tautomerism in aqueous solution of some aryl-substituted morpholinium salts (bromides), has been studied and equilibrium constants are reported. In the crystals the substrates exist entirely in their cyclic forms as hemiacetals, but in aqueous solution NMR measurements reveal that an equilibrium is established between the cyclic (hemiacetal) and the noncyclic (ketone) form, the degree of ring-opening being more pronounced with electron-donating aryl substituents at the carbonyl carbon. The kinetics of the ring-chain interconversion in water has been investigated spectrophotometrically by a 'pH jump' stopped-flow technique. General base catalysis is observed with a Br?nsted beta value apparently independent of substituent and equal to 0.60. The Hammett rho values for various base catalysts are close to those for very similar intermolecular reactions involving hemiacetal breakdown, leading to the suggestion of a 'normal' class n mechanism for base catalysis. For acid catalysis, however, a quite different situation is encountered, since no general acid but only (weak) catalysis by the hydronium ion can be detected. We believe this deviation from 'normal' general acid catalysis is caused by an electrostatic interaction, and we suggest that it might result from a change in the usual class e mechanism for general acid catalysis by a situation in which rate-limiting concerted proton transfer is replaced by rate-limiting preprotonation. This is supported by the observed drastic change in Hammett rho value for catalysis by the hydronium ion, compared with the 'normal' case. An interesting case is encountered for the 4-aminophenyl-substituted substrate, in which the amino group becomes protonated in acid solution, thus representing a new substituent. Despite this complication, the various equilibrium and rate constants may also be evaluated experimentally for this substrate. 相似文献
33.
34.
F. Cannata J. P. Dedonder L. Le?niak 《Zeitschrift für Physik A Hadrons and Nuclei》1992,343(4):451-460
We investigate the origin of the attraction in theK¯K channel around the threshold by introducing an additional channel to theππ andK¯K channels in a separable potential formalism assuming, in general, no direct interaction in theK¯K channel. To reproduce the features of the data, we find that the threshold of the additional channel is much above thef 0(975) meson position. We show that this three-channel problem can be reduced to an effective two-channel problem where thef 0(975) behaves as if it were aK¯K molecule bound by the coupling to the exotic channel. This picture is also supported by the fact that a single pole only, in the complexK¯K momentum plane, is associated to thef 0(975) meson. Various physical observables, like the decay branching ratio and theK¯K scattering length, are then discussed in an effective two-channel framework. 相似文献
35.
Dorota G?azowska Janusz Matkowski 《Journal of Mathematical Analysis and Applications》2007,331(2):1187-1199
The invariance of the geometric mean G with respect to the Lagrangian mean-type mapping (Lf,Lg), i.e. the equation G○(Lf,Lg)=G, is considered. We show that the functions f and g must be of high class regularity. This fact allows to reduce the problem to a differential equation and determine the second derivatives of the generators f and g. 相似文献
36.
In the paper we indicate an error made in the proof of the main result of the paper [M.A. Darwish, On quadratic integral equation of fractional orders, J. Math. Anal. Appl. 311 (2005) 112-119]. Moreover, we provide correct proof of a slightly modified version of the mentioned result. The main tool used in our proof is the technique associated with the Hausdorff measure of noncompactness. 相似文献
37.
In this paper we deal with nonlinear second-order boundary value problems with impulses. The impulsive functions depend implicitly on the different considered variables and the boundary value conditions are nonlinear. In both cases functional dependence on the solution is allowed. The existence results follow from the existence of a pair of well-ordered lower and upper solutions. 相似文献
38.
S?awomir Solecki 《Topology and its Applications》2007,154(12):2462-2464
Let I0 be the σ-ideal of subsets of a Polish group generated by Borel sets which have perfectly many pairwise disjoint translates. We prove that a Fubini-type theorem holds between I0 and the σ-ideals of Haar measure zero sets and of meager sets. We use this result to give a simple proof of a generalization of a theorem of Balcerzak-Ros?anowski-Shelah stating that I0 on N2 strongly violates the countable chain condition. 相似文献
39.
40.
R. Knizikevi?ius 《Applied Surface Science》2006,253(3):1581-1583
The ion-beam-assisted etching of silicon in Cl2 environment is considered. The theoretically calculated dependences of silicon etching rate on the flux of Cl2 molecules at different ion current densities are compared with experimentally measured. The composition of the adsorbed layer is determined. It is found that SiCl2 molecules prevail in the adsorbed layer. The reciprocal of relative concentration of SiCl2 molecules in the adsorbed layer linearly depends on the ion-to-neutral flux ratio. 相似文献