全文获取类型
收费全文 | 107687篇 |
免费 | 8219篇 |
国内免费 | 9999篇 |
专业分类
化学 | 48505篇 |
晶体学 | 575篇 |
力学 | 7191篇 |
综合类 | 1865篇 |
数学 | 33054篇 |
物理学 | 34715篇 |
出版年
2023年 | 990篇 |
2022年 | 1376篇 |
2021年 | 2790篇 |
2020年 | 2143篇 |
2019年 | 2272篇 |
2018年 | 1968篇 |
2017年 | 2391篇 |
2016年 | 2792篇 |
2015年 | 2731篇 |
2014年 | 3804篇 |
2013年 | 6947篇 |
2012年 | 4424篇 |
2011年 | 5024篇 |
2010年 | 4491篇 |
2009年 | 6082篇 |
2008年 | 6592篇 |
2007年 | 6954篇 |
2006年 | 6132篇 |
2005年 | 4918篇 |
2004年 | 4531篇 |
2003年 | 4504篇 |
2002年 | 6537篇 |
2001年 | 3823篇 |
2000年 | 3395篇 |
1999年 | 3015篇 |
1998年 | 2820篇 |
1997年 | 2356篇 |
1996年 | 2022篇 |
1995年 | 1860篇 |
1994年 | 1733篇 |
1993年 | 1541篇 |
1992年 | 1459篇 |
1991年 | 1122篇 |
1990年 | 942篇 |
1989年 | 831篇 |
1988年 | 788篇 |
1987年 | 607篇 |
1986年 | 560篇 |
1985年 | 708篇 |
1984年 | 616篇 |
1983年 | 324篇 |
1982年 | 591篇 |
1981年 | 810篇 |
1980年 | 679篇 |
1979年 | 664篇 |
1978年 | 529篇 |
1977年 | 440篇 |
1976年 | 371篇 |
1974年 | 177篇 |
1973年 | 249篇 |
排序方式: 共有10000条查询结果,搜索用时 172 毫秒
991.
“Optimization of aircraft maintenance/support infrastructure using genetic algorithms—level of repair analysis” 总被引:4,自引:0,他引:4
Level of repair analysis (LORA) is an approach used during the design stage of complex equipment for analysis of the cost
effectiveness of competing maintenance strategies. LORA is carried as a part of the life cycle cost and cost of ownership
analysis and plays a significant role in minimizing the life cycle cost and cost of ownership of the capital equipment. Since
many purchasing decisions of complex equipment are based on cost of ownership, it has become essential to carry out LORA to
compete in the market. In this paper, we develop a mathematical model for LORA and propose a solution methodology based on
genetic algorithms. The concept is illustrated using a hypothetical aircraft engine. 相似文献
992.
Given a constant of motion for the one-dimensional harmonic oscillator with linear dissipation in the velocity, the problem to get the Hamiltonian for this system is pointed out, and the quantization up to second order in the perturbation approach is used to determine the modification on the eigenvalues when dissipation is taken into consideration. This quantization is realized using the constant of motion instead of the Hamiltonian.
PACS: 03.20.+i, 03.30.+p, 03.65.−w,03.65.Ca 相似文献
993.
Alexandra Shlapentokh 《Compositio Mathematica》2002,132(1):99-120
Let F be a function field of characteristic p > 2, finitely generated over a field C algebraic over a finite field C
p
and such that it has an extension of degree p. Then Hilbert's Tenth Problem is not decidable over F. 相似文献
994.
995.
In a secret sharing scheme, some participants can lie about the value of their shares when reconstructing the secret in order to obtain some illicit benefit. We present in this paper two methods to modify any linear secret sharing scheme in order to obtain schemes that are unconditionally secure against that kind of attack. The schemes obtained by the first method are robust, that is, cheaters are detected with high probability even if they know the value of the secret. The second method provides secure schemes, in which cheaters that do not know the secret are detected with high probability. When applied to ideal linear secret sharing schemes, our methods provide robust and secure schemes whose relation between the probability of cheating and the information rate is almost optimal. Besides, those methods make it possible to construct robust and secure schemes for any access structure. 相似文献
996.
A. S. Belenky 《Mathematical and Computer Modelling》2002,36(11-13)
Two games of interacting between a coalition of players in a marketplace and the residual players acting there are discussed, along with two approaches to fair imputation of gains of coalitions in cooperative games that are based on the concepts of the Shapley vector and core of a cooperative game. In the first game, which is an antagonistic one, the residual players try to minimize the coalition's gain, whereas in the second game, which is a noncooperative one, they try to maximize their own gain as a coalition. A meaningful interpretation of possible relations between gains and Nash equilibrium strategies in both games considered as those played between a coalition of firms and its surrounding in a particular marketplace in the framework of two classes of n-person games is presented. A particular class of games of choosing partners and forming coalitions in which models of firms operating in the marketplace are those with linear constraints and utility functions being sums of linear and bilinear functions of two corresponding vector arguments is analyzed, and a set of maximin problems on polyhedral sets of connected strategies which the problem of choosing a coalition for a particular firm is reducible to are formulated based on the firm models of the considered kind. 相似文献
997.
998.
A posteriori error estimators for the Stokes equations 总被引:5,自引:0,他引:5
Summary We present two a posteriori error estimators for the mini-element discretization of the Stokes equations. One is based on a suitable evaluation of the residual of the finite element solution. The other one is based on the solution of suitable local Stokes problems involving the residual of the finite element solution. Both estimators are globally upper and locally lower bounds for the error of the finite element discretization. Numerical examples show their efficiency both in estimating the error and in controlling an automatic, self-adaptive mesh-refinement process. The methods presented here can easily be generalized to the Navier-Stokes equations and to other discretization schemes.This work was accomplished at the Universität Heidelberg with the support of the Deutsche Forschungsgemeinschaft 相似文献
999.
研究了混合稀土储氢合金中氧和氮的测定方法。针对稀土金属高温易挥发、分解的特点,选择适宜的加热温度,使用镍浴,选择高温座坩埚进行试验:选择出了合适的助熔剂的预处理方法。方法已用于实际样品。对含氧0.43%、含氮0.018%的试样,分析精密度为氧4.3%,氮5.9%,加标回收率氧为93%~104%,氮为92%~110%。 相似文献
1000.
Bin Han 《Advances in Computational Mathematics》2006,24(1-4):375-403
In this paper, we present a necessary and sufficient condition for the existence of solutions in a Sobolev space Wpk(ℝs) (1≤p≤∞) to a vector refinement equation with a general dilation matrix. The criterion is constructive and can be implemented.
Rate of convergence of vector cascade algorithms in a Sobolev space Wpk(ℝs) will be investigated. When the dilation matrix is isotropic, a characterization will be given for the Lp (1≤p≤∞) critical smoothness exponent of a refinable function vector without the assumption of stability on the refinable function
vector. As a consequence, we show that if a compactly supported function vector φ∈Lp(ℝs) (φ∈C(ℝs) when p=∞) satisfies a refinement equation with a finitely supported matrix mask, then all the components of φ must belong to a Lipschitz
space Lip(ν,Lp(ℝs)) for some ν>0. This paper generalizes the results in R.Q. Jia, K.S. Lau and D.X. Zhou (J. Fourier Anal. Appl. 7 (2001) 143–167)
in the univariate setting to the multivariate setting.
Dedicated to Professor Charles A. Micchelli on the occasion of his 60th birthday
Mathematics subject classifications (2000) 42C20, 41A25, 39B12.
Research was supported in part by the Natural Sciences and Engineering Research Council of Canada (NSERC Canada) under Grant
G121210654. 相似文献