全文获取类型
收费全文 | 1327篇 |
免费 | 194篇 |
国内免费 | 74篇 |
专业分类
化学 | 37篇 |
晶体学 | 1篇 |
力学 | 523篇 |
综合类 | 36篇 |
数学 | 728篇 |
物理学 | 270篇 |
出版年
2024年 | 4篇 |
2023年 | 20篇 |
2022年 | 43篇 |
2021年 | 34篇 |
2020年 | 39篇 |
2019年 | 32篇 |
2018年 | 29篇 |
2017年 | 50篇 |
2016年 | 59篇 |
2015年 | 45篇 |
2014年 | 98篇 |
2013年 | 92篇 |
2012年 | 50篇 |
2011年 | 78篇 |
2010年 | 72篇 |
2009年 | 75篇 |
2008年 | 63篇 |
2007年 | 72篇 |
2006年 | 59篇 |
2005年 | 70篇 |
2004年 | 58篇 |
2003年 | 50篇 |
2002年 | 56篇 |
2001年 | 49篇 |
2000年 | 36篇 |
1999年 | 39篇 |
1998年 | 21篇 |
1997年 | 32篇 |
1996年 | 36篇 |
1995年 | 35篇 |
1994年 | 16篇 |
1993年 | 9篇 |
1992年 | 10篇 |
1991年 | 5篇 |
1990年 | 9篇 |
1989年 | 3篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1973年 | 1篇 |
排序方式: 共有1595条查询结果,搜索用时 26 毫秒
21.
Slowly time-varying delays are seldom, but do need to be, considered in the context of discrete-time systems. This paper addresses the exponential stability issue of discrete-time systems with slowly time-varying delays. The basic idea is to transform, by utilizing the switching transformation approach, the original system with slowly time-varying delays into an equivalent switched system with special switching signal. Different types of delays correspond to different types of switching signals, and the stability issue of the original system is converted into that of a switched system. It is the first time that the method of switched homogeneous polynomial Lyapunov function is applied to general delayed systems. Some sufficient exponential stability conditions for the original system are proposed in several situations. It is numerically shown that the conservativeness of the proposed conditions reduces as the degree of the switched homogeneous polynomial Lyapunov function increases. 相似文献
22.
H. L. Stalford 《Journal of Optimization Theory and Applications》1995,86(3):685-718
Using a class of linear static controllers, we stabilize the Petersen open-loop two-dimensional linear system (Ref. 1), which consists of one time-varying uncertainty in the state matrixA and one timevarying uncertainty in the input matrixB. We show that the worst-case uncertainty strategy for the closed-loop system is a piecewise constant strategy of the angular state with three switches on the half-turn, –/2/2; it is unique with respect to a set of measure zero. Formulas are derived for the worst-case half-turn radius gainr
HT
as a function of the parameters of the class of stabilizing linear static controllers. Using the class of scalar-quadratic Lyapunov functions, we show that a necessary and sufficient condition for the closed-loop system to be robustly stable against all time-varying admissible uncertainties is thatr
HT
be less than unity. The bound on the time-varying real parameter uncertainties for the closed-loop system to be robustly stable is derived for the class of linear static feedback controllers. We obtain stabilizing linear static controllers such that the bound is as close to infinity as desired. The derived results are compared with numerical results obtained using commerical robust-control software. 相似文献
23.
Reliability bounds in DFRA class with known mean and variance 总被引:1,自引:0,他引:1
RELIABILITYBOUNDSINDFRACLASSWITHKNOWNMEAN AND VARIANCECHENGKAN(程侃)(InstituteofAppliedMathematics,theChineseAcademyofScience,B... 相似文献
24.
Assume that the probability density function for the lifetime of a newly designed product has the form: [H(t)/Q()] exp{–H(t)/Q()}. The Exponential(), Rayleigh, WeibullW(, ) and Pareto pdf's are special cases.Q() will be assumed to have an inverse Gamma prior. Assume thatm independent products are to be tested with replacement. A Bayesian Sequential Reliability Demonstration Testing plan is used to eigher accept the product and start formal production, or reject the product for reengineering. The test criterion is the intersection of two goals, a minimal goal to begin production and a mature product goal. The exact values of various risks and the distribution of total number of failures are evaluated. Based on a result about a Poisson process, the expected stopping time for the exponential failure time is also found. Included in these risks and expected stopping times are frequentist versions, thereof, so that the results also provide frequentist answers for a class of interesting stopping rules.This research was supported by NSF grants DMS-8703620 and DMS-8923071, and forms part of the Ph.D. Thesis of the first author, the development of which was supported in part by a David Ross grant at Purdue University. The authors thank the editors and a referee for insightful comments and suggestions. 相似文献
25.
Karol Jankowski Danuta Rutkowska Andrzej Rutkowski 《Theoretical chemistry accounts》1978,48(2):119-125
It is shown that the Galerkin-Petrov method if applied in a controlled way yields reliable results for excited states of the
same symmetry classifications as the ground state. Computations are performed for the 21
S and 31
S states of He. The problem of optimizing nonlinear parameters of the basis functions by means of the GP method is discussed.
A special optimization scheme is suggested and numerically illustrated for someS states of He. 相似文献
26.
G. D. Manetto C. La Rosa D. M. Grasso D. Milardi 《Journal of Thermal Analysis and Calorimetry》2005,80(2):263-270
Summary We assessed the applicability of the extrapolation procedure at infinite scanning rate to differential scanning calorimetry (DSC) data related to irreversible protein unfolding. To this aim, an array of DSC curves have been simulated on the basis of the Lumry-Eyring model N↔U→F. The results obtained confirmed that when the apparent equilibrium constant Kapp (T=T1/2) is lower than 3, the application of the extrapolation procedure provides accurate thermodynamic parameters. Although this procedure applies only to monomeric proteins for which the Lumry-Eyring model is a reasonable approximation, it will hopefully contribute to increase the potential of DSC in obtaining reliable thermodynamic information regarding the folding/unfolding equilibrium. 相似文献
27.
28.
Carmen Luna Concepción Lloreda Juan F. Almagro Bello Jaime Botella Maria J. Orts Ana Gozalbo 《Mikrochimica acta》2004,145(1-4):121-127
Non-metallic inclusions in steel are formed due to interactions between liquid steel and its environment in the melting shop (refractories and slags). Particles not trapped in the slag remain in the cast steel, impairing steel properties in service. Inclusion composition varies and certified standards covering the whole compositional range are unavailable.The present study describes the preparation of a set of homogeneous, glassy and crystalline standards with a wide compositional range for use in analysing non-metallic steel inclusions. For this, materials were designed based on knowledge of the compositional range of interest in the Al2O3–SiO2–CaO–MgO–CaF2 system, which is the matrix of the most frequent steel inclusions. The composition and microstructural homogeneity of the reference materials was verified. 相似文献
29.
30.
Víctor Leiva 《商业与工业应用随机模型》2019,35(1):133-137
Sam C. Saunders, the son of Elizabeth Cundiff and Winston E. Saunders, was born in Richland, OR, on February 24, 1931. The family moved to La Grande, OR, in 1944, where Sam completed high school and two years at Eastern Oregon College. He then received the BSc degree in Mathematics from the University of Oregon, Eugene, OR, in 1952, and he attended the University of Washington, Seattle, WA, receiving a PhD degree under Z. W. Birnbaum. After graduating, he accepted employment at the Boeing Company in its Mathematical Services Unit and, in 1972, a position as a Full Professor at Washington State University, Pullman, WA, from which he retired in 1996. 相似文献