全文获取类型
收费全文 | 17487篇 |
免费 | 1872篇 |
国内免费 | 1403篇 |
专业分类
化学 | 2486篇 |
晶体学 | 60篇 |
力学 | 1623篇 |
综合类 | 545篇 |
数学 | 11097篇 |
物理学 | 4951篇 |
出版年
2024年 | 21篇 |
2023年 | 129篇 |
2022年 | 227篇 |
2021年 | 289篇 |
2020年 | 338篇 |
2019年 | 342篇 |
2018年 | 393篇 |
2017年 | 479篇 |
2016年 | 532篇 |
2015年 | 367篇 |
2014年 | 668篇 |
2013年 | 1191篇 |
2012年 | 765篇 |
2011年 | 1031篇 |
2010年 | 1012篇 |
2009年 | 1235篇 |
2008年 | 1252篇 |
2007年 | 1230篇 |
2006年 | 1180篇 |
2005年 | 932篇 |
2004年 | 831篇 |
2003年 | 770篇 |
2002年 | 732篇 |
2001年 | 610篇 |
2000年 | 568篇 |
1999年 | 500篇 |
1998年 | 433篇 |
1997年 | 375篇 |
1996年 | 334篇 |
1995年 | 287篇 |
1994年 | 213篇 |
1993年 | 189篇 |
1992年 | 181篇 |
1991年 | 122篇 |
1990年 | 130篇 |
1989年 | 103篇 |
1988年 | 81篇 |
1987年 | 73篇 |
1986年 | 49篇 |
1985年 | 70篇 |
1984年 | 64篇 |
1983年 | 36篇 |
1982年 | 70篇 |
1981年 | 42篇 |
1980年 | 44篇 |
1979年 | 63篇 |
1978年 | 43篇 |
1977年 | 40篇 |
1974年 | 26篇 |
1973年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
E.B.Manoukian 《理论物理通讯》2013,(12):677-686
The paper represents a rigorous treatment of the underlying quantum theory, not just in words but providing the underlying technical details, as to why matter occupies so large a volume and its intimate connection with the Pauli exclusion principle, as more and more matter is put together, as well as of the contraction or shrinkage of "bosonic matter", upon collapse, for which the Panli exclusion is abolished. From the derived explicit bounds of integrals of powers of the particle number densities, explicit bounds on probabilities of the occurrences of the events just described are extracted. These probabilities lead one to infer the change of the "size" or extension of such matter, upon expansion or contraction, respectively, as their content is increased. 相似文献
962.
A new mathematical algorithm is proposed to address the essential details of vertical distributions of horizontal velocity for one‐dimensional steady open‐channel flow. This new algorithm comprises a system of weighted averaged equations developed from corresponding Reynolds equations by performing weighted average operations instead of conventional depth average operations. It is the system of weighted averaged equations, instead of the vertical grids, that allows for more hydraulic coefficients identifiable. It can be thought of as an extension of the St. Venant equations to address the vertical distributions of horizontal velocities, as well as the water surface profiles. To avoid the difficult expansion of governing partial differential equations in high order, an indirect scheme is proposed to solve hydraulic variables through their weighted average values. The governing partial differential equations are generated by using a variety of weight functions, and the weighted averages of relevant hydraulic variables are taken as the unknown independent variables to be solved first. Then, on the basis of the values and polynomial expansions of these weighted averaged velocities, a system of linear algebraic equations is generated and the unknown hydraulic variables or their coefficients are easily solved. Note that the new model is not proposed to compete with any three‐dimensional models in modeling accuracy or accommodation ability to all conditions. It just provides a valuable option to study the vertical structure of flow in open channels where only essential detail and reasonable accuracy of vertical distributions are required, and the data availability and other conditions limit the application of fully three‐dimensional models. The performance of the model is evaluated with experimental data of flows in two different flumes. It is shown that the model well predicted the velocity profiles of sections along the centerlines of these flumes with reasonable accuracy and essential details of vertical distributions of horizontal velocity. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
963.
Lack of homogeneity in the product (LHP) appears in some production processes which incorporate raw materials that originate directly from nature and/or production processes with operations that confer heterogeneity to the characteristics of the outputs obtained, even when the inputs used are homogeneous. Poor LHP management may have a very negative impact on the customer service level and on the supply chains’ operation costs, especially when the customer needs to be served with homogeneous units of one same product. One of the key processes for suitable LHP management is the order-promising process. This work presents a mathematical programming order-promising model for make-to-stock environments with LHP. The model considers two objectives placed within a single objective by the weighted sum method. For the purpose of testing the validity of the proposed model and to evaluate the characteristics of the solutions obtained in different scenarios, numerical experiments based on realistic data from a ceramic tile company have been conducted. The results show that better results are obtained for the defined performance measures if multiple objectives are considered when promising orders than the single objective of maximizing profits. Furthermore, the superiority of the results obtained from the proposed model, if compared with current company practice, proves the model’s utility. 相似文献
964.
In this paper we have completely determined: (1) all almost simple groups which act 2-transitively on one of their sets of
Sylow p-subgroups. (2) all non-abelian simple groups T whose automorphism group acts 2-transitively on one of the sets of Sylow p-subgroups of T. (3) all finite groups which are 2-transitive on all their sets of Sylow subgroups.
The first author acknowledges the support of OPR Scholarship of Australia
The second author is supported by the National Natural Science Foundation of China. Thanks are also due to the Department
of Mathematics, the University of Western Australia, where he did his part of this work for its hospitality 相似文献
965.
966.
根据我国现行的税法,个人所得税纳税采用九级累进税率.年工资和年终奖在速算扣除数个数上存在不同,使得对于相同的税前年收入,如果采用不同的年工资和年终奖分配方案会产生不同的税后实际所得.通过简化变量和缩小有效解区域,以及一系列严格的数学推导,得到了任意年收入下,月工资和年终奖的最优分配方案,使得在现有税制下,纳税额最小,税后收入最大.这个最优方案避免了税金负效应现象,保证了纳税公平性,有利于国家税务监管,企业员工薪金分配和个人纳税筹划;具有广阔的应用前景. 相似文献
967.
通过对一道积分不等式提供多种不同的证法,希望能对学生创造性思维及发散性思维的培养、开阔解题思路、提高综合应用数学知识的能力等有所帮助,并使学生对证明不等式的常用方法有所了解. 相似文献
968.
969.
970.
We give some multidimensional Tauberian theorems for generalized functions and show examples of their application in mathematical physics. In particular, we consider the problems of stabilizing the solutions of the Cauchy problem for the heat kernel equation, multicomponent gas diffusion, and the asymptotic Cauchy problem for a free Schrödinger equation in the norms of different Banach spaces among others. 相似文献