全文获取类型
收费全文 | 3441篇 |
免费 | 74篇 |
国内免费 | 128篇 |
专业分类
化学 | 484篇 |
晶体学 | 5篇 |
力学 | 603篇 |
综合类 | 15篇 |
数学 | 1635篇 |
物理学 | 901篇 |
出版年
2024年 | 5篇 |
2023年 | 64篇 |
2022年 | 42篇 |
2021年 | 35篇 |
2020年 | 61篇 |
2019年 | 73篇 |
2018年 | 53篇 |
2017年 | 73篇 |
2016年 | 69篇 |
2015年 | 77篇 |
2014年 | 183篇 |
2013年 | 312篇 |
2012年 | 206篇 |
2011年 | 245篇 |
2010年 | 208篇 |
2009年 | 251篇 |
2008年 | 185篇 |
2007年 | 228篇 |
2006年 | 156篇 |
2005年 | 124篇 |
2004年 | 108篇 |
2003年 | 89篇 |
2002年 | 81篇 |
2001年 | 67篇 |
2000年 | 49篇 |
1999年 | 54篇 |
1998年 | 55篇 |
1997年 | 56篇 |
1996年 | 56篇 |
1995年 | 32篇 |
1994年 | 42篇 |
1993年 | 34篇 |
1992年 | 34篇 |
1991年 | 24篇 |
1990年 | 13篇 |
1989年 | 11篇 |
1988年 | 17篇 |
1987年 | 25篇 |
1986年 | 9篇 |
1985年 | 34篇 |
1984年 | 31篇 |
1983年 | 13篇 |
1982年 | 14篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1978年 | 10篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1971年 | 1篇 |
排序方式: 共有3643条查询结果,搜索用时 31 毫秒
1.
Boban Marinković 《Mathematical Methods of Operations Research》2006,63(3):513-524
We present local sensitivity analysis for discrete optimal control problems with varying endpoints in the case when the customary regularity of boundary conditions can be violated. We study the behavior of the optimal solutions subject to parametric perturbations of the problem. 相似文献
2.
In this work we study nonnegativity and positivity of a discrete quadratic functional with separately varying endpoints. We introduce a notion of an interval coupled with 0, and hence, extend the notion of conjugate interval to 0 from the case of fixed to variable endpoint(s). We show that the nonnegativity of the discrete quadratic functional is equivalent to each of the following conditions: The nonexistence of intervals coupled with 0, the existence of a solution to Riccati matrix equation and its boundary conditions. Natural strengthening of each of these conditions yields a characterization of the positivity of the discrete quadratic functional. Since the quadratic functional under consideration could be a second variation of a discrete calculus of variations problem with varying endpoints, we apply our results to obtain necessary and sufficient optimality conditions for such problems. This paper generalizes our recent work in [R. Hilscher, V. Zeidan, Comput. Math. Appl., to appear], where the right endpoint is fixed. 相似文献
3.
4.
The modification of the number field sieve which Joux and Lercier recently used to compute logarithms in a prime field of a record 120 decimal digits makes use of the notion of a virtual logarithm of a prime ideal in a number ring. We provide necessary and sufficient conditions for their method to succeed and give an explicit formula for the virtual logarithm of an ideal. 相似文献
5.
The lattice profile analyzes the intrinsic structure of pseudorandom number sequences with applications in Monte Carlo methods and cryptology. In this paper, using the discrete Fourier transform for periodic sequences and the relation between the lattice profile and the linear complexity, we give general formulas for the expected value, variance, and counting function of the lattice profile of periodic sequences with fixed period. Moreover, we determine in a more explicit form the expected value, variance, and counting function of the lattice profile of periodic sequences for special values of the period. 相似文献
6.
Haibo Peng Boyu Wu Qiong Song Fei Lu Shuyun Luo 《International Journal of Infrared and Millimeter Waves》2003,24(9):1587-1596
Hybrid electrode combined coplanar waveguide (CPW) and microstrip lines in ultra-broadband electro-optic modulators. The characteristics of the modulators with hybrid electrode is like that of the modulator with the microstrip lines, in which the microstrip electrode is loaded above only one arm of Mach-Zehnder (M-Z) optical waveguide, besides the problem of microstrip line to coaxial transition and corona polarization in polymer modulators have been best solved at the same time. By using finite element method (FEM), the characteristic parameters such as half-wave voltage, modulation bandwidth characteristic impedance, effective microwave refractive index of polymer modulators with microstrip line and hybrid electrode are analysed and compared in this paper. The results present that velocity match, impendence match and lower microwave propagating loss is easily realized in modulators with hybrid electrode. 相似文献
7.
Semra Harmandar 《Journal of Quantitative Spectroscopy & Radiative Transfer》2004,84(4):395-407
A radiation code based on method of lines solution of discrete ordinates method for radiative heat transfer in axisymmetric cylindrical enclosures containing absorbing-emitting medium was developed and tested for predictive accuracy by applying it to (i) test problems with black and grey walls (ii) a gas turbine combustor simulator enclosing a non-homogeneous absorbing-emitting medium and benchmarking its steady-state predictions against exact solutions and measurements. Comparisons show that it provides accurate solutions for radiative heat fluxes and can be used with confidence in conjunction with CFD codes based on the same approach. 相似文献
8.
研究了m-维离散Lotka-Volterra竞争系统,并获得了该系统周期解的存在性及其全局吸引性. 相似文献
9.
10.
Jrg Winkelmann 《Mathematische Nachrichten》1997,186(1):285-302
We investigate under which conditions an algebraic group G defined over a locally compact field k admitr a subgroup Γ? G(k) which is dense in the Zariski topology, but discerte in the topology induced by the locally compact topology on k. For non—solvable groups we provide a complete answer. 相似文献