全文获取类型
收费全文 | 22195篇 |
免费 | 1639篇 |
国内免费 | 1265篇 |
专业分类
化学 | 2595篇 |
晶体学 | 104篇 |
力学 | 2593篇 |
综合类 | 214篇 |
数学 | 14738篇 |
物理学 | 4855篇 |
出版年
2024年 | 37篇 |
2023年 | 206篇 |
2022年 | 346篇 |
2021年 | 387篇 |
2020年 | 532篇 |
2019年 | 496篇 |
2018年 | 564篇 |
2017年 | 581篇 |
2016年 | 554篇 |
2015年 | 469篇 |
2014年 | 884篇 |
2013年 | 1831篇 |
2012年 | 1010篇 |
2011年 | 1255篇 |
2010年 | 1041篇 |
2009年 | 1393篇 |
2008年 | 1399篇 |
2007年 | 1477篇 |
2006年 | 1320篇 |
2005年 | 1060篇 |
2004年 | 973篇 |
2003年 | 989篇 |
2002年 | 859篇 |
2001年 | 652篇 |
2000年 | 677篇 |
1999年 | 558篇 |
1998年 | 566篇 |
1997年 | 500篇 |
1996年 | 395篇 |
1995年 | 335篇 |
1994年 | 247篇 |
1993年 | 212篇 |
1992年 | 215篇 |
1991年 | 158篇 |
1990年 | 136篇 |
1989年 | 79篇 |
1988年 | 81篇 |
1987年 | 71篇 |
1986年 | 75篇 |
1985年 | 96篇 |
1984年 | 82篇 |
1983年 | 38篇 |
1982年 | 56篇 |
1981年 | 39篇 |
1980年 | 29篇 |
1979年 | 33篇 |
1978年 | 29篇 |
1977年 | 23篇 |
1976年 | 19篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
51.
Li Jiayu 《偏微分方程(英文版)》1990,3(3)
Let M be a n-dimensional simply connected, complete Riemannian manifold with constant negative curvature. The heat kernel on M is denoted by H^M_t(x, y) = H^M_t(r(x, y)), where r(x, y) = dist(x, y). We have the explicit formula of H^M_t(x, y) for n=2, 3, and the induction formula of H^M_t(x, y) for n ≥ 4^{[-1]}. But the explicit formula is very complicated for n ≥ 4. ln this paper we give some simple and useful global estimates of H^M_t(x, y), and apply these estimates to the problem of eigenvalue. 相似文献
52.
53.
This paper investigates the existence of positive solutions of a singular boundary value problem with negative exponent similar
to standard Emden-Fowler equation. A necessary and sufficient condition for the existence of C[0, 1] positive solutions as
well as C1[0, 1] positive solutions is given by means of the method of lower and upper solutions with the Schauder fixed point theorem. 相似文献
54.
This paper describes an optimization technique based on an heuristic procedure which is applied to analyse and improve the efficiency of the design of Global Positioning System (GPS) surveying networks. GPS is a valuable survey tool because of its ability to increase the accuracy, speed and flexibility of a survey. A GPS network can be defined as a number of stations, which are co-ordinated by a series of sessions, formed by placing receivers on stations. The goal is to select the best order in which these sessions can be organised to give the best possible schedule. Generally, solving large networks to optimality requires impractical computational time. This paper proposes a Tabu Search technique which provides optimal or near-optimal solutions for large networks with an acceptable amount of computational effort. Computational results for several case studies with known and unknown optimal schedules have been presented to assess the performance of the proposed technique. 相似文献
55.
56.
The Euclidean distance matrix (EDM) completion problem and the positive semidefinite (PSD) matrix completion problem are considered in this paper. Approaches to determine the location of a point in a linear manifold are studied, which are based on a referential coordinate set and a distance vector whose components indicate the distances from the point to other points in the set. For a given referential coordinate set and a corresponding distance vector, sufficient and necessary conditions are presented for the existence of such a point that the distance vector can be realized. The location of the point (if it exists) given by the approaches in a linear manifold is independent of the coordinate system, and is only related to the referential coordinate set and the corresponding distance vector. An interesting phenomenon about the complexity of the EDM completion problem is described. Some properties about the uniqueness and the rigidity of the conformation for solutions to the EDM and PSD completion problems are presented. 相似文献
57.
In this paper, we continue extending the theory of boundary-value problems to ordinary differential equations and inclusions with discontinuous right-hand side. To this end, we construct a new version of the method of shifts along trajectories. We compare the results obtained by the new approach and those obtained by the method of Fuik spectra. 相似文献
58.
W. Brüggemann K. Fischer H. Jahnke 《Journal of Mathematical Modelling and Algorithms》2003,2(2):153-169
In Part I of this study, we suggest to identify an operations research (OR) problem with the equivalence class of models describing the problem and enhance the standard computer-science theory of computational complexity to be applicable to this situation of an often model-based OR context. The Discrete Lot-sizing and Scheduling Problem (DLSP) is analysed here in detail to demonstrate the difficulties which can arise if these aspects are neglected and to illustrate the new theoretical concept. In addition, a new minimal model is introduced for the DLSP which makes this problem eventually amenable to a rigorous analysis of its computational complexity. 相似文献
59.
Mathematical Notes - 相似文献
60.
Éric D. Taillard 《Journal of Heuristics》2003,9(1):51-73
This article presents new heuristic methods for solving a class of hard centroid clustering problems including the p-median, the sum-of-squares clustering and the multi-source Weber problems. Centroid clustering is to partition a set of entities into a given number of subsets and to find the location of a centre for each subset in such a way that a dissimilarity measure between the entities and the centres is minimized. The first method proposed is a candidate list search that produces good solutions in a short amount of time if the number of centres in the problem is not too large. The second method is a general local optimization approach that finds very good solutions. The third method is designed for problems with a large number of centres; it decomposes the problem into subproblems that are solved independently. Numerical results show that these methods are efficient—dozens of best solutions known to problem instances of the literature have been improved—and fast, handling problem instances with more than 85,000 entities and 15,000 centres—much larger than those solved in the literature. The expected complexity of these new procedures is discussed and shown to be comparable to that of an existing method which is known to be very fast. 相似文献