全文获取类型
收费全文 | 21451篇 |
免费 | 3568篇 |
国内免费 | 1849篇 |
专业分类
化学 | 4910篇 |
晶体学 | 56篇 |
力学 | 2775篇 |
综合类 | 554篇 |
数学 | 9726篇 |
物理学 | 8847篇 |
出版年
2024年 | 36篇 |
2023年 | 224篇 |
2022年 | 483篇 |
2021年 | 563篇 |
2020年 | 578篇 |
2019年 | 521篇 |
2018年 | 517篇 |
2017年 | 779篇 |
2016年 | 886篇 |
2015年 | 731篇 |
2014年 | 1184篇 |
2013年 | 1469篇 |
2012年 | 1182篇 |
2011年 | 1353篇 |
2010年 | 1202篇 |
2009年 | 1355篇 |
2008年 | 1511篇 |
2007年 | 1584篇 |
2006年 | 1295篇 |
2005年 | 1169篇 |
2004年 | 1159篇 |
2003年 | 936篇 |
2002年 | 888篇 |
2001年 | 718篇 |
2000年 | 625篇 |
1999年 | 589篇 |
1998年 | 506篇 |
1997年 | 441篇 |
1996年 | 388篇 |
1995年 | 381篇 |
1994年 | 243篇 |
1993年 | 222篇 |
1992年 | 163篇 |
1991年 | 197篇 |
1990年 | 126篇 |
1989年 | 83篇 |
1988年 | 111篇 |
1987年 | 74篇 |
1986年 | 61篇 |
1985年 | 65篇 |
1984年 | 46篇 |
1983年 | 31篇 |
1982年 | 33篇 |
1981年 | 38篇 |
1980年 | 27篇 |
1979年 | 27篇 |
1978年 | 16篇 |
1977年 | 11篇 |
1976年 | 8篇 |
1974年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
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
92.
The propagation properties of decentered twisted Gaussian Schell-model (DTGSM) beams passing through a misaligned first-order optical system are studied. The explicit expressions for the cross-spectral density function and Wigner distribution function of the output beam are derived, which retain their form unchanged. It is shown that the DTGSM beams preserve their closed property. The second-order moments matrix and the Wigner distribution function evolve with the usual laws, whereas the first-order moments matrix varies, as if a ray passes through such system. The propagation of DTGSM beams through an aligned first-order optical system is treated as the limiting case that corresponds to the vanishing misalignment parameters. 相似文献
93.
We study elliptic systems of strongly nonlinear first-order differential equations in complex form on the plane. For such systems we develop the theory of Hilbert boundary value problems which is very much similar to the well-known theory for a holomorphic vector. Systems of nonlinear elliptic equations describe problems of interaction of several nonlinear stationary processes in the diffusive and convective mass and heat transport by hydrodynamic fluid flows. 相似文献
94.
V. Sree Krishna Chaitanya 《Nonlinear Analysis: Real World Applications》2005,6(5):845-857
In this paper, a structurally unstable man–machine system is considered and a rigorous mathematical analysis is performed to study the influence of time delays in the control force on stability of the equilibrium solution of this system. Results on stability, instability and conditions for the preservation of stability (instability), besides the existence of bifurcation are presented. 相似文献
95.
区域技术创新系统评估体系的研究 总被引:5,自引:0,他引:5
技术创新对提升企业竞争力、提高综合国力、促进经济增长和国家持续发展非常重要。本在研究了区域经济发展和国家创新系统的相关献基础上,建立了系统、量化的区域技术创新系统评估指标体系,提出了决定区域创新系统技术创新能力的主要因素,并用TOPSIS方法对指标的量化进行了尝试。 相似文献
96.
97.
98.
Peter J. Cameron 《组合设计杂志》2005,13(6):466-470
It is shown that there is a function g on the natural numbers such that a partial Steiner triple system U on u points can be embedded in a Steiner triple system V on ν points, in such a way that all automorphisms of U can be extended to V, for every admissible ν satisfying ν > g(u). We find exponential upper and lower bounds for g. © 2005 Wiley Periodicals, Inc. J Combin Designs. 相似文献
99.
We find a minimal system of generators and a homogeneous system of parameters for the algebra of invariants of three matrices of third order over a field of an arbitrary characteristic. 相似文献
100.
Strong limit-point criteria for singular Hamiltonian differential expressions with complex coefficients are obtained. The main results are extensions of the previous results due to Everitt, Giertz, and Weidmann for scalar differential expressions.