全文获取类型
收费全文 | 2833篇 |
免费 | 96篇 |
国内免费 | 69篇 |
专业分类
化学 | 197篇 |
晶体学 | 2篇 |
力学 | 169篇 |
综合类 | 26篇 |
数学 | 2273篇 |
物理学 | 331篇 |
出版年
2024年 | 2篇 |
2023年 | 25篇 |
2022年 | 45篇 |
2021年 | 42篇 |
2020年 | 34篇 |
2019年 | 33篇 |
2018年 | 30篇 |
2017年 | 31篇 |
2016年 | 51篇 |
2015年 | 40篇 |
2014年 | 83篇 |
2013年 | 128篇 |
2012年 | 106篇 |
2011年 | 107篇 |
2010年 | 123篇 |
2009年 | 187篇 |
2008年 | 209篇 |
2007年 | 235篇 |
2006年 | 169篇 |
2005年 | 135篇 |
2004年 | 117篇 |
2003年 | 110篇 |
2002年 | 110篇 |
2001年 | 83篇 |
2000年 | 79篇 |
1999年 | 72篇 |
1998年 | 84篇 |
1997年 | 61篇 |
1996年 | 60篇 |
1995年 | 40篇 |
1994年 | 44篇 |
1993年 | 42篇 |
1992年 | 28篇 |
1991年 | 25篇 |
1990年 | 22篇 |
1989年 | 20篇 |
1988年 | 29篇 |
1987年 | 16篇 |
1986年 | 18篇 |
1985年 | 20篇 |
1984年 | 24篇 |
1983年 | 5篇 |
1982年 | 17篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1978年 | 10篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1975年 | 2篇 |
排序方式: 共有2998条查询结果,搜索用时 15 毫秒
91.
《Optimization》2012,61(4):335-350
We provide a theoretical basis for approximating the sensitivity of a perturbed solution and the local optimalvalue function, using information generated by a sequential unconstrained minimization technique in the normal course of solving a mathematical program. We show that various algorithmic sensitivity results can be obtained without other assumptions than those needed for the corresponding nonalgorithmic results. Our results extend the algorithmic calculation of sensitivity information introduced by Fiacco, utilizing the logarithmic barrier function and quadratic penalty function 相似文献
92.
Abstract In this article, two static routing algorithms have been proposed and compared to some of the existing algorithms on the basis of blocking probability. The two proposed static routing and wavelength assignment algorithms reduce the blocking probability to maximize the utilization of the network. All of these algorithms are analyzed and compared with four wavelength assignment schemes, which are first-fit, random, most used, and least used. It is shown that our proposed static algorithms give the best performance for first-fit wavelength assignment and most used wavelength assignment strategies with reduced complexity. For least used wavelength assignment and random wavelength assignment, 1 fixed and 2 alternate routing algorithm gives the lowest blocking probability. 相似文献
93.
94.
Monika Cichocka 《光谱学快报》2018,51(2):118-121
The intracellular brain pH in phosphorus magnetic resonance spectroscopy is calculated using the chemical shift between the inorganic phosphate and phosphocreatine with the Henderson–Hasselbalch equations. Researchers use various mathematical formulas that have different parameters and get various results for the same input data as a consequence. Thus, the aim of this article was to determine the mathematical formulas that allow the conversion of the pH values obtained by the most popular analysis methods to each other. To determine the relationships between pH results and the applied mathematical formula, the pH values were calculated using two algorithms for the theoretical chemical shift values. The pH results were compared with each other using the appropriate t-tests. Mathematical formulas were designed to simplify the conversion of pH values obtained by two data analysis methods to each other. The pH values with were obtained this way did not differ significantly from the pH values calculated directly from the given formula. The computed mathematical formulas will make it possible to simplify pH conversions without knowing the chemical shift between inorganic phosphate and phosphocreatine but only basing on the final pH values obtained by one of the formulas. 相似文献
95.
96.
Michael A. TrickHakan Yildiz 《European Journal of Operational Research》2012,216(2):286-292
This paper presents a genetic algorithm (GA) to solve the Traveling Umpire Problem, which is a recently introduced sports scheduling problem that is based on the most important features of the real Major League Baseball umpire scheduling problem. In our GA, contrary to the traditional way of randomly obtaining new solutions from parent solutions, we obtain partially optimized solutions with a Locally Optimized Crossover operator. This operator also presents a link between the evolutionary mechanism on a population of solutions and the local search on a single solution. We present improved results over other methods on benchmark instances. 相似文献
97.
Truemper configurations (thetas, pyramids, prisms, and wheels) have played an important role in the study of complex hereditary graph classes (eg, the class of perfect graphs and the class of even-hole-free graphs), appearing both as excluded configurations, and as configurations around which graphs can be decomposed. In this paper, we study the structure of graphs that contain (as induced subgraphs) no Truemper configurations other than (possibly) universal wheels and twin wheels. We also study several subclasses of this class. We use our structural results to analyze the complexity of the recognition, maximum weight clique, maximum weight stable set, and optimal vertex coloring problems for these classes. Furthermore, we obtain polynomial -bounding functions for these classes. 相似文献
98.
This paper deals with the minimum cost automatic design of precast bridge decks made of U-beams and an upper slab. It uses a hybrid memetic algorithm that combines the population search of solutions by genetic algorithms and a search by variable neighborhood. This algorithm is applied to a bridge made of two isostatic U-beams of 20-40 m of span and a width of 12 m. This example has 40 discrete variables. The evaluation module takes into account the service and ultimate limit states usually considered for these structures, i.e. flexure, shear, torsion, cracking, deflections, etc. The use of the memetic algorithm requires its previous calibration. Each of the heuristics is run 12 times, obtaining information about the minimum and average values, as well as the scatter. The parametric study showed a good correlation for the cost, the number of strands and the steel and concrete quantities with the span length. Savings have been found between 8 and 50% compared to other structures really executed. The presented procedure allows the practical application to the real design and its adaptation to the precast process. 相似文献
99.
Magdy H. Metry Allan R. Sampson 《Journal of computational and graphical statistics》2013,22(2):209-223
Abstract This article introduces an approach for characterizing the classes of empirical distributions that satisfy certain positive dependence notions. Mathematically, this can be expressed as studying certain subsets of the class SN of permutations of 1, …, N, where each subset corresponds to some positive dependence notions. Explicit techniques for it-eratively characterizing subsets of SN that satisfy certain positive dependence concepts are obtained and various counting formulas are given. Based on these techniques, graph-theoretic methods are used to introduce new and more efficient algorithms for constructively generating and enumerating the elements of various of these subsets of SN. For example, the class of positively quadrant dependent permutations in SN is characterized in this fashion. 相似文献
100.
绿色建筑凭借其诸多优点,已然成为我国未来建筑发展的新方向,而对绿色建筑的工期、成本和功能进行全面系统研究并进行综合均衡优化,对于促进绿色建筑的发展具有深远影响.在描述各工程活动的成本和持续时间之间、功能和持续时间之间的非线性关系基础上,运用多属性效用函数理论构建了绿色建筑项目的功能一工期一成本综合均衡优化模型,并用遗传算法进行求解,可以得到最佳均衡解.最后通过一个实例验证了优化模型具有良好的科学性和实用性. 相似文献