全文获取类型
收费全文 | 19751篇 |
免费 | 1794篇 |
国内免费 | 924篇 |
专业分类
化学 | 4474篇 |
晶体学 | 59篇 |
力学 | 2201篇 |
综合类 | 300篇 |
数学 | 11563篇 |
物理学 | 3872篇 |
出版年
2024年 | 33篇 |
2023年 | 197篇 |
2022年 | 470篇 |
2021年 | 524篇 |
2020年 | 448篇 |
2019年 | 450篇 |
2018年 | 469篇 |
2017年 | 651篇 |
2016年 | 617篇 |
2015年 | 497篇 |
2014年 | 884篇 |
2013年 | 1203篇 |
2012年 | 1025篇 |
2011年 | 942篇 |
2010年 | 926篇 |
2009年 | 1075篇 |
2008年 | 1190篇 |
2007年 | 1258篇 |
2006年 | 1067篇 |
2005年 | 917篇 |
2004年 | 721篇 |
2003年 | 734篇 |
2002年 | 784篇 |
2001年 | 625篇 |
2000年 | 562篇 |
1999年 | 468篇 |
1998年 | 498篇 |
1997年 | 405篇 |
1996年 | 366篇 |
1995年 | 354篇 |
1994年 | 283篇 |
1993年 | 255篇 |
1992年 | 224篇 |
1991年 | 179篇 |
1990年 | 139篇 |
1989年 | 112篇 |
1988年 | 100篇 |
1987年 | 82篇 |
1986年 | 88篇 |
1985年 | 118篇 |
1984年 | 88篇 |
1983年 | 42篇 |
1982年 | 61篇 |
1981年 | 66篇 |
1980年 | 44篇 |
1979年 | 59篇 |
1978年 | 42篇 |
1977年 | 45篇 |
1976年 | 33篇 |
1974年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
P.A. Ramachandran 《Numerical Methods for Partial Differential Equations》2006,22(4):831-846
Time‐dependent differential equations can be solved using the concept of method of lines (MOL) together with the boundary element (BE) representation for the spatial linear part of the equation. The BE method alleviates the need for spatial discretization and casts the problem in an integral format. Hence errors associated with the numerical approximation of the spatial derivatives are totally eliminated. An element level local cubic approximation is used for the variable at each time step to facilitate the time marching and the nonlinear terms are represented in a semi‐implicit manner by a local linearization at each time step. The accuracy of the method has been illustrated on a number of test problems of engineering significance. © 2005 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2006 相似文献
22.
超尺寸物品装箱问题及其算法 总被引:3,自引:0,他引:3
本文探讨一类新装箱问题-超尺寸物品装箱问题。针对实际解决该问题的两涉法,我们提出了一个评价效率更高的目标函数,证明了在此目标函数下两步法的渐近最坏比不小于2,并给出了渐近量坏比与拆分次数的关系。最后本文提出了一种不同于两步法的新在线算法MA,证明了在新目标函数下其渐近最坏比不超过7/4。 相似文献
23.
Mikhail Andramonov 《Journal of Global Optimization》2002,24(2):115-132
We consider applications of disjunctive programming to global optimization and problems with equilibrium constraints. We propose a modification of the algorithm of F. Beaumont for disjunctive programming problems and show its numerical efficiency. 相似文献
24.
Y. Wardi 《Journal of Optimization Theory and Applications》1989,61(3):473-485
A stochastic algorithm for finding stationary points of real-valued functions defined on a Euclidean space is analyzed. It is based on the Robbins-Monro stochastic approximation procedure. Gradient evaluations are done by means of Monte Carlo simulations. At each iteratex
i
, one sample point is drawn from an underlying probability space, based on which the gradient is approximated. The descent direction is against the approximation of the gradient, and the stepsize is 1/i. It is shown that, under broad conditions, w.p.1 if the sequence of iteratesx
1,x
2,...generated by the algorithm is bounded, then all of its accumulation points are stationary. 相似文献
25.
26.
We consider the problem of maximizing a linear fractional function on the Pareto efficient frontier of two other linear fractional functions. We present a finite pivoting-type algorithm that solves the maximization problem while computing simultaneously the efficient frontier. Application to multistage efficiency analysis is discussed. An example demonstrating the computational procedure is included. 相似文献
27.
Most of the novel highly potent drugs, developed on the basis of modern molecular medicine, taking into account cell surface recognition techniques, show poor water solubility. A chemical modification of the drug substance enhancing the solubility often decreases the pharmacological activity. Thus, as an alternative an increase of the solubility can be obtained by the reduction of the size of the drug particles. Unfortunately, it is often difficult to obtain micro or nanosized drug particles by classical or more advanced crystallization using supercritical gases or by milling techniques. In addition, nanosized particles are often not physically stable and need to be stabilized in an appropriate matrix. Thus, it may be of interest to manufacture directly nanosized drug particles stabilized in an inert hydrophilic matrix, i.e. nanostructured and nanocomposite systems. Solid solutions and solid dispersions represent nanostructured and nanocomposite systems. In this context, the use of the vacuum-fluidized-bed technique for the spray-drying of a low water soluble drug cosolubilized with a hydrophilic excipient in a polar organic solvent is discussed. In order to avoid the use of organic solvents, a special spray-freeze-drying technique working at atmospheric pressure is presented. This process is very suitable for temperature and otherwise sensitive drugs such as pharmaproteins. 相似文献
28.
We describe a new algorithm which uses the trajectories of a discrete dynamical system to sample the domain of an unconstrained objective function in search of global minima. The algorithm is unusually adept at avoiding nonoptimal local minima and successfully converging to a global minimum. Trajectories generated by the algorithm for objective functions with many local minima exhibit chaotic behavior, in the sense that they are extremely sensitive to changes in initial conditions and system parameters. In this context, chaos seems to have a beneficial effect: failure to converge to a global minimum from a given initial point can often be rectified by making arbitrarily small changes in the system parameters. 相似文献
29.
The annealing algorithm (Ref. 1) is modified to allow for noisy or imprecise measurements of the energy cost function. This is important when the energy cannot be measured exactly or when it is computationally expensive to do so. Under suitable conditions on the noise/imprecision, it is shown that the modified algorithm exhibits the same convergence in probability to the globally minimum energy states as the annealing algorithm (Ref. 2). Since the annealing algorithm will typically enter and exit the minimum energy states infinitely often with probability one, the minimum energy state visited by the annealing algorithm is usually tracked. The effect of using noisy or imprecise energy measurements on tracking the minimum energy state visited by the modified algorithms is examined.The research reported here has been supported under Contracts AFOSR-85-0227, DAAG-29-84-K-0005, and DAAL-03-86-K-0171 and a Purdue Research Initiation Grant. 相似文献
30.
带干扰的多险种风险模型 总被引:2,自引:0,他引:2
由于保险公司风险经营规模不断扩大,用单一险种的模型来描述风险过程存在局限性,本文讨论了带干扰多险种风险模型,应用鞅论方法,得出伦德伯格不等式和最终破产概率公式。 相似文献