全文获取类型
收费全文 | 47500篇 |
免费 | 1235篇 |
国内免费 | 1722篇 |
专业分类
化学 | 25427篇 |
晶体学 | 412篇 |
力学 | 1743篇 |
综合类 | 22篇 |
数学 | 11371篇 |
物理学 | 11482篇 |
出版年
2023年 | 176篇 |
2022年 | 443篇 |
2021年 | 562篇 |
2020年 | 467篇 |
2019年 | 517篇 |
2018年 | 1505篇 |
2017年 | 1743篇 |
2016年 | 1486篇 |
2015年 | 1172篇 |
2014年 | 1174篇 |
2013年 | 2039篇 |
2012年 | 4578篇 |
2011年 | 3890篇 |
2010年 | 2696篇 |
2009年 | 2635篇 |
2008年 | 1723篇 |
2007年 | 1703篇 |
2006年 | 1545篇 |
2005年 | 5340篇 |
2004年 | 5058篇 |
2003年 | 3082篇 |
2002年 | 1236篇 |
2001年 | 665篇 |
2000年 | 407篇 |
1999年 | 408篇 |
1998年 | 328篇 |
1997年 | 256篇 |
1996年 | 241篇 |
1995年 | 203篇 |
1994年 | 164篇 |
1993年 | 164篇 |
1992年 | 288篇 |
1991年 | 236篇 |
1990年 | 211篇 |
1989年 | 171篇 |
1988年 | 166篇 |
1987年 | 119篇 |
1986年 | 111篇 |
1985年 | 126篇 |
1984年 | 120篇 |
1983年 | 96篇 |
1982年 | 77篇 |
1981年 | 81篇 |
1980年 | 66篇 |
1979年 | 64篇 |
1978年 | 57篇 |
1976年 | 105篇 |
1975年 | 64篇 |
1974年 | 69篇 |
1973年 | 65篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
We analyze the critical length for design purposes of six-dimensional spaces invariant under translations and reflections
containing the functions 1, cos t and sin t. These spaces also contain the first degree polynomials as well as trigonometric and/or hyperbolic functions. We identify
the spaces whose critical length for design purposes is greater than 2π and find its maximum 4π. By a change of variables,
two biparametric families of spaces arise. We call shape preservation region to the set of admissible parameters in order
that the space has shape preserving representations for curves. We describe the shape preserving regions for both families.
To our friend Mariano Gasca on occasion of his 60th birthday
Research partially supported by the Spanish Research Grant MTM2006-03388, by Gobierno de Aragón and Fondo Social Europeo. 相似文献
112.
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
113.
We study linear dynamical systems with multidimensional time in Banach spaces. Using Taylor functional calculus we prove that under additional assumptions hyperbolic systems have shadowing property. 相似文献
114.
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
115.
It is shown that the presence of mixed-culture growth in batch fermentation processes can be very accurately inferred from total biomass data by means of the wavelet analysis for singularity detection. This is accomplished by considering simple phenomenological models for the mixed growth and the more complicated case of mixed growth on a mixture of substrates. The main quantity provided by the wavelet analysis is the Hölder exponent of the singularity that we determine for our illustrative examples. The numerical results point to the possibility that Hölder exponents can be used to characterize the nature of the mixed-culture growth in batch fermentation processes with potential industrial applications. Moreover, the analysis of the same data affected by the common additive Gaussian noise still lead to the wavelet detection of the singularities although the Hölder exponent is no longer a useful parameter. 相似文献
116.
117.
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
118.
J. Gañán J.F. González C.M. González-García A. Ramiro E. Sabio S. Román 《Applied Surface Science》2006,252(17):5988-5992
In this work the results obtained in the preparation and characterization of carbons made from almond tree pruning by non-catalytic and catalytic gasification (using K and Co) with air are analyzed and discussed. The main aim was to obtain high quality activated carbons at the lowest possible cost. The variables studied have been the temperature (190-260 °C) and the time (1-10 h) in non-catalytic gasification and the influence of the catalyst type (K and Co, 1 wt.% referred to cation, at 190 °C and 1 h) and the time (1-4 h) in catalytic gasification with Co at 190 °C. The air flow rate used in all the series was 167 cm3 min−1. In non-catalytic gasification the reaction normalized rate versus the conversion degree was maintained until a conversion value of 10% for the experiment made at 260 °C since, at lower temperatures, this rate drops quickly for low conversion values. The N2 adsorption isotherms for the carbons of this series resemble type I, although there is an increase of N2 adsorbed volume at relatively high pressures. A temperature rise produced an increase of the carbon porosity and BET specific surface (116-469 m2 g−1). The activation time has a positive effect on the N2 volume adsorbed by the carbons. The isotherms shapes were similar to those previously commented. A concentration equal to 1 wt.% was used to study the influence of the catalyst type. Under the studied experimental conditions, Co drives to a bigger porosity development than K, although with both catalysts a very similar pore size distribution is obtained. The activation time, in the gasifications catalyzed with Co, gives rise to a very important porosity development in the carbons. This produces a strong increase of the carbon specific surface area with very high values in the 4 h experiment, in which a BET specific surface of 959 m2 g−1 was obtained. 相似文献
119.
We continue the studies on the so–called genuine Bernstein–Durrmeyer operators U
n
by establishing a recurrence formula for the moments and by investigating the semigroup T(t) approximated by U
n
. Moreover, for sufficiently smooth functions the degree of this convergence is estimated. We also determine the eigenstructure
of U
n
, compute the moments of T(t) and establish asymptotic formulas.
Received: January 26, 2007. 相似文献
120.
Wei-nan E Ping-bing Ming 《应用数学学报(英文版)》2007,23(4):529-550
We study continuum and atomistic models for the elastodynamics of crystalline solids at zerotemperature.We establish sharp criterion for the regime of validity of the nonlinear elastic wave equationsderived from the well-known Cauchy-Born rule. 相似文献