全文获取类型
收费全文 | 36799篇 |
免费 | 1370篇 |
国内免费 | 254篇 |
专业分类
化学 | 23658篇 |
晶体学 | 254篇 |
力学 | 833篇 |
数学 | 5681篇 |
物理学 | 5235篇 |
无线电 | 2762篇 |
出版年
2022年 | 231篇 |
2021年 | 493篇 |
2020年 | 573篇 |
2019年 | 535篇 |
2018年 | 434篇 |
2017年 | 433篇 |
2016年 | 949篇 |
2015年 | 853篇 |
2014年 | 932篇 |
2013年 | 1912篇 |
2012年 | 2060篇 |
2011年 | 2585篇 |
2010年 | 1266篇 |
2009年 | 1137篇 |
2008年 | 2217篇 |
2007年 | 2255篇 |
2006年 | 2216篇 |
2005年 | 2084篇 |
2004年 | 1735篇 |
2003年 | 1550篇 |
2002年 | 1419篇 |
2001年 | 501篇 |
2000年 | 470篇 |
1999年 | 416篇 |
1998年 | 396篇 |
1997年 | 408篇 |
1996年 | 552篇 |
1995年 | 401篇 |
1994年 | 355篇 |
1993年 | 315篇 |
1992年 | 323篇 |
1991年 | 304篇 |
1990年 | 253篇 |
1989年 | 242篇 |
1988年 | 263篇 |
1987年 | 235篇 |
1986年 | 228篇 |
1985年 | 393篇 |
1984年 | 391篇 |
1983年 | 283篇 |
1982年 | 363篇 |
1981年 | 378篇 |
1980年 | 342篇 |
1979年 | 321篇 |
1978年 | 291篇 |
1977年 | 269篇 |
1976年 | 231篇 |
1975年 | 242篇 |
1974年 | 232篇 |
1973年 | 237篇 |
排序方式: 共有10000条查询结果,搜索用时 757 毫秒
151.
David P. Williamson 《Mathematical Programming》2002,91(3):447-478
In this survey, we give an overview of a technique used to design and analyze algorithms that provide approximate solutions
to NP-hard problems in combinatorial optimization. Because of parallels with the primal-dual method commonly used in combinatorial
optimization, we call it the primal-dual method for approximation algorithms. We show how this technique can be used to derive
approximation algorithms for a number of different problems, including network design problems, feedback vertex set problems,
and facility location problems.
Received: June 19, 2000 / Accepted: February 7, 2001?Published online October 2, 2001 相似文献
152.
David Swanson William P. Ziemer 《Calculus of Variations and Partial Differential Equations》2002,14(1):69-84
Let be a connected open set, . We give a sufficient condition for a mapping , , to have the property that sgn is almost everywhere of one sign. Following the work of Müller, Spector, and Tang [MST], we give an application of our results
to the theory of non-linear elasticity.
Received: 13 October 2000 / Accepted: 23 January 2001 / Published online: 4 May 2001 相似文献
153.
Tamal Bose M. -Q. Chen David A. Trautman 《Circuits, Systems, and Signal Processing》1994,13(5):601-614
A special class of complex biquad digital filters called orthogonal filters are investigated for stability under two's complement
quantization. A sufficient condition is derived for the asymptotic stability of the nonlinear filter. Bounds on the possible
limit cycles are also obtained. Using these bounds, any given filter can be tested for stability. The stability triangle is
then scanned using a dense grid, and each point on the grid is tested for stability/limit cycles. By this method, the stability
region given by the sufficient condition is extended. Regions within the linear stability triangle where various types of
limit cycles are possible are also identified. 相似文献
154.
155.
156.
157.
Summary. We examine the convergence characteristics of iterative methods based on a new preconditioning operator for solving the linear
systems arising from discretization and linearization of the steady-state Navier-Stokes equations. With a combination of analytic
and empirical results, we study the effects of fundamental parameters on convergence. We demonstrate that the preconditioned
problem has an eigenvalue distribution consisting of a tightly clustered set together with a small number of outliers. The
structure of these distributions is independent of the discretization mesh size, but the cardinality of the set of outliers
increases slowly as the viscosity becomes smaller. These characteristics are directly correlated with the convergence properties
of iterative solvers.
Received August 5, 2000 / Published online June 20, 2001 相似文献
158.
Lisa Higham David Kirkpatrick Karl Abrahamson Andrew Adler 《Journal of Algorithms in Cognition, Informatics and Logic》1997,23(2):291-328
Probabilistic algorithms are developed for a basic problem in distributed computation, assuming anonymous, asynchronous, unidirectional rings of processors. The problem, known as Solitude Detection, requires that a nonempty subset of the processors, calledcontenders, determine whether or not there is exactly one contender. Monte Carlo algorithms are developed that err with probability bounded by a specified parameter and exhibit either message or processor termination. The algorithms transmit an optimal expected number of bits, to within a constant factor. Their bit complexities display a surprisingly rich dependence on the kind of termination exhibited and on the processors' knowledge of the size of the ring. Two probabilistic tools are isolated and then combined in various ways to achieve all our algorithms. 相似文献
159.
DavidKatz TomaszLukasiak RickGentile 《世界电子元器件》2003,(6):27-30
如今的数字信号处理器(DSP)在性能、外围设备集成、功耗和成本方面都具备很多优势,很多系统设计人员希望在原有系统设计中利用DSP获得比传统处理器更好的效益。但其中一个 相似文献
160.
Ng J.S. Tan C.H. David J.P.R. Hill G. Rees G.J. 《Electron Devices, IEEE Transactions on》2003,50(4):901-905
Electron and hole ionization coefficients in In/sub 0.53/Ga/sub 0.47/As are deduced from mixed carrier avalanche photomultiplication measurements on a series of p-i-n diode layers, eliminating other effects that can lead to an increase in photocurrent with reverse bias. Low field ionization is observed for electrons but not for holes, resulting in a larger ratio of ionization coefficients, even at moderately high electric fields than previously reported. The measured ionization coefficients are marginally lower than those of GaAs for fields above 250 kVcm/sup -1/, supporting reports of slightly higher avalanche breakdown voltages in In/sub 0.53/Ga/sub 0.47/As than in GaAs p-i-n diodes. 相似文献