全文获取类型
收费全文 | 603902篇 |
免费 | 5656篇 |
国内免费 | 1688篇 |
专业分类
化学 | 293955篇 |
晶体学 | 9282篇 |
力学 | 29569篇 |
综合类 | 9篇 |
数学 | 87116篇 |
物理学 | 191315篇 |
出版年
2021年 | 4542篇 |
2020年 | 5063篇 |
2019年 | 5641篇 |
2018年 | 13397篇 |
2017年 | 13907篇 |
2016年 | 13916篇 |
2015年 | 7482篇 |
2014年 | 10816篇 |
2013年 | 25748篇 |
2012年 | 22625篇 |
2011年 | 31879篇 |
2010年 | 21917篇 |
2009年 | 21624篇 |
2008年 | 28357篇 |
2007年 | 30437篇 |
2006年 | 19587篇 |
2005年 | 21898篇 |
2004年 | 18260篇 |
2003年 | 16509篇 |
2002年 | 14990篇 |
2001年 | 16030篇 |
2000年 | 12421篇 |
1999年 | 9560篇 |
1998年 | 7994篇 |
1997年 | 7675篇 |
1996年 | 7554篇 |
1995年 | 6617篇 |
1994年 | 6561篇 |
1993年 | 6486篇 |
1992年 | 6976篇 |
1991年 | 7198篇 |
1990年 | 6895篇 |
1989年 | 6684篇 |
1988年 | 6525篇 |
1987年 | 6508篇 |
1986年 | 6118篇 |
1985年 | 8042篇 |
1984年 | 8283篇 |
1983年 | 6744篇 |
1982年 | 7002篇 |
1981年 | 6700篇 |
1980年 | 6485篇 |
1979年 | 6860篇 |
1978年 | 6916篇 |
1977年 | 6808篇 |
1976年 | 6935篇 |
1975年 | 6415篇 |
1974年 | 6399篇 |
1973年 | 6533篇 |
1972年 | 4574篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
A Monte Carlo simulation method is used to study thermal desorption of gas molecules from mixed adlayers containing two species. The effects of lateral interactions among adatoms and initial surface coverage on the desorption spectra are examined. It is shown that attractive lateral interactions lead to sharper peaks and that desorption occurs at high temperatures, whereas repulsive interactions lead to multiple peak spectra. It is found that interactions between unlike molecules affect the spectra for species with lower desorption energy only, and that the two species desorb together only in certain cases. Lateral interactions also affect the desorption kinetics significantly and very different behavior for the two species may be obtained. 相似文献
993.
S. F. Karpenko 《Ukrainian Mathematical Journal》1989,41(4):487-492
Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 41, No. 4, pp. 559–565, April, 1989. 相似文献
994.
995.
996.
This paper provides a quantitative and comparative economic and risk approach to strategic quality control in a supply chain, consisting of one supplier and one producer, using a random payoff game. Such a game is first solved in a risk-neutral framework by assuming that both parties are competing with each other. We show in this case that there may be an interior solution to the inspection game. A similar analysis under a collaborative framework is shown to be trivial and not practical, with a solution to the inspection game being an ‘all or nothing’ solution to one or both the parties involved. For these reasons, the sampling random payoff game is transformed into a Neyman–Pearson risk constraints game, where the parties minimize the expected costs subject to a set of Neyman–Pearson risk (type I and type II) constraints. In this case, the number of potential equilibria can be large. A number of such solutions are developed and a practical (convex) approach is suggested by providing an interior (partial sampling) solution for the collaborative case. Numerical examples are developed to demonstrate the procedure used. Thus, unlike theoretical approaches to the solution of strategic quality control random payoff games, the approach we construct is both practical and consistent with the statistical risk Neyman–Pearson approach. 相似文献
997.
Eliza P. de Jager 《Topology and its Applications》2007,154(10):2117-2126
We show that the infimum of any family of proximally symmetric quasi-uniformities is proximally symmetric, while the supremum of two proximally symmetric quasi-uniformities need not be proximally symmetric. On the other hand, the supremum of any family of transitive quasi-uniformities is transitive, while there are transitive quasi-uniformities whose infimum with their conjugate quasi-uniformity is not transitive. Moreover we present two examples that show that neither the supremum topology nor the infimum topology of two transitive topologies need be transitive. Finally, we prove that several operations one can perform on and between quasi-uniformities preserve the property of having a complement. 相似文献
998.
We study the spectral properties of a large class of compact flat Riemannian manifolds of dimension 4, namely, those whose
corresponding Bieberbach groups have the canonical lattice as translation lattice. By using the explicit expression of the
heat trace of the Laplacian acting on p-forms, we determine all p-isospectral and L-isospectral pairs and we show that in this class of manifolds, isospectrality on functions and isospectrality on p-forms for all values of p are equivalent to each other. The list shows for any p, 1 ≤ p ≤ 3, many p-isospectral pairs that are not isospectral on functions and have different lengths of closed geodesics. We also determine
all length isospectral pairs (i.e. with the same length multiplicities), showing that there are two weak length isospectral
pairs that are not length isospectral, and many pairs, p-isospectral for all p and not length isospectral.
Mathematics Subject Classifications (2000): 58J53, 58C22, 20H15. 相似文献
999.
1000.
O.G. Kosareva N.A. Panov N. Akozbek V.P. Kandidov Q. Luo S.A. Hosseini W. Liu J.-F. Gravel G. Roy S.L. Chin 《Applied physics. B, Lasers and optics》2006,82(1):111-122
We demonstrate a three orders of magnitude increase and stability in the backscattered fluorescence signal from nitrogen molecules
by terawatt femtosecond laser pulse induced air filaments using a new method. The method is based on squeezing the initial
beam diameter using a telescope. The effect of laser shot-to-shot fluctuations was included in numerical simulations by a
random distribution of the initial intensity in both squeezed and non-squeezed beams. Statistical processing of the simulation
results shows that the average diameter of plasma channels as well as the total amount of free electrons generated in a bunch
of multiple filaments in air is larger in the squeezed beam. Shot-to-shot stability of the simulated plasma density increases
in the squeezed beam. The change of this plasma density with propagation distance is in good qualitative agreement with the
change of the range-corrected nitrogen fluorescence signal with distance.
PACS 42.65.Jx; 42.60.Jf; 42.68.Ay; 42.68.Wt 相似文献