全文获取类型
收费全文 | 26473篇 |
免费 | 751篇 |
国内免费 | 158篇 |
专业分类
化学 | 17396篇 |
晶体学 | 241篇 |
力学 | 440篇 |
综合类 | 4篇 |
数学 | 4453篇 |
物理学 | 4848篇 |
出版年
2023年 | 171篇 |
2022年 | 418篇 |
2021年 | 518篇 |
2020年 | 452篇 |
2019年 | 511篇 |
2018年 | 515篇 |
2017年 | 490篇 |
2016年 | 907篇 |
2015年 | 758篇 |
2014年 | 841篇 |
2013年 | 1637篇 |
2012年 | 1606篇 |
2011年 | 1846篇 |
2010年 | 1190篇 |
2009年 | 1124篇 |
2008年 | 1608篇 |
2007年 | 1517篇 |
2006年 | 1369篇 |
2005年 | 1248篇 |
2004年 | 998篇 |
2003年 | 855篇 |
2002年 | 732篇 |
2001年 | 523篇 |
2000年 | 453篇 |
1999年 | 370篇 |
1998年 | 289篇 |
1997年 | 288篇 |
1996年 | 343篇 |
1995年 | 243篇 |
1994年 | 257篇 |
1993年 | 243篇 |
1992年 | 232篇 |
1991年 | 190篇 |
1990年 | 181篇 |
1989年 | 139篇 |
1988年 | 131篇 |
1987年 | 148篇 |
1986年 | 139篇 |
1985年 | 167篇 |
1984年 | 175篇 |
1983年 | 118篇 |
1982年 | 135篇 |
1981年 | 113篇 |
1980年 | 117篇 |
1979年 | 89篇 |
1978年 | 75篇 |
1977年 | 76篇 |
1976年 | 68篇 |
1975年 | 52篇 |
1973年 | 63篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
Fe–Al alloys around the concentration of 30 at. % Al present re-entrant spin-glass behaviour at low temperatures. This behaviour is not completely understood and Mössbauer spectroscopy, combined with other experimental techniques, is useful to describe and explain this behaviour. Results show that the Mössbauer spectra coincide with the magnetic behaviour showed in literature and they can be explained as a magnetic cluster system whose magnetic clusters are getting smaller when the temperature is decreasing. When the temperature is reaching to the spin-glass transition at 92 K the spins in the paramagnetic matrix are moving slower and below this transition the spins are completely frozen. 相似文献
33.
34.
Parking Capacity and Pricing in Park'n Ride Trips: A Continuous Equilibrium Network Design Problem 总被引:2,自引:0,他引:2
In this paper we consider the problem of designing parking facilities for park'n ride trips. We present a new continuous equilibrium network design problem to decide the capacity and fare of these parking lots at a tactical level. We assume that the parking facilities have already been located and other topological decisions have already been taken.The modeling approach proposed is mathematical programming with equilibrium constraints. In the outer optimization problem, a central Authority evaluates the performance of the transport network for each network design decision. In the inner problem a multimodal traffic assignment with combined modes, formulated as a variational inequality problem, generates the share demand for modes of transportation, and for parking facilities as a function of the design variables of the parking lots. The objective is to make optimal parking investment and pricing decisions in order to minimize the total travel cost in a subnetwork of the multimodal transportation system.We present a new development in model formulation based on the use of generalized parking link cost as a design variable.The bilevel model is solved by a simulated annealing algorithm applied to the continuous and non-negative design decision variables. Numerical tests are reported in order to illustrate the use of the model, and the ability of the approach to solve applications of moderate size. 相似文献
35.
36.
R. Euler B. Fricke T. Morović W. -D. Sepp A. Rosén 《Zeitschrift für Physik A Hadrons and Nuclei》1980,297(2):101-104
Total energy SCF calculations were performed for noble gas difluorides in a relativistic procedure and compared with analogous non-relativistic calculations. The discrete variational method with numerical basis functions was used. Rather smooth potential energy curves could be obtained. The theoretical Kr-F and Xe-F bond distances were calculated to be 3.5 a.u. and 3.6 a.u. which should be compared with the experimental values of 3.54 a.u. and 3.7 a.u. Although the dissociation energies are off by a factor of about five it was found that ArF2 may be a stable molecule. Theoretical ionization energies for the outer levels reproduce the experimental values for KrF2 and XeF2 to within 2 eV. 相似文献
37.
On a recursive method for the estimation of unknown parameters of partially observed chaotic systems
We investigate a recently proposed method for on-line parameter estimation and synchronization in chaotic systems. This novel technique has been shown effective to estimate a single unknown parameter of a primary chaotic system with known functional form that is only partially observed through a scalar time series. It works by periodically updating the parameter of interest in a secondary system, with the same functional form as the primary one but no explicit coupling between their dynamic variables, in order to minimize a suitably defined cost function. In this paper, we review the basics of the method, and investigate its robustness and new extensions. In particular, we study the performance of the novel technique in the presence of noise (either observational, i.e., an additive contamination of the observed time series, or dynamical, i.e., a random perturbation of the system dynamics) and when there is a mismatch between the primary and secondary systems. Numerical results, including comparisons with other techniques, are presented. Finally, we investigate the extension of the original method to perform the estimation of two unknown parameters and illustrate its effectiveness by means of computer simulations. 相似文献
38.
The aim of this article is to derive stable generalized sampling in a shift-invariant space by using some special dual frames in L2(0,1). These sampling formulas involve samples of filtered versions of the functions in the shift-invariant space. The involved samples are expressed as the frame coefficients of an appropriate function in L2(0,1) with respect to some particular frame in L2(0,1). Since any shift-invariant space with stable generator is the image of L2(0,1) by means of a bounded invertible operator, our generalized sampling is derived from some dual frame expansions in L2(0,1). 相似文献
39.
M. Olivares-Marín C. Fernández-González V. Gómez-Serrano 《Applied Surface Science》2006,252(17):5980-5983
Using cherry stones, the preparation of activated carbon has been undertaken in the present study by chemical activation with potassium hydroxide. A series of KOH-activated products was prepared by varying the carbonisation temperature in the 400-900 °C range. Such products were characterised texturally by gas adsorption (N2, −196 °C), mercury porosimetry, and helium and mercury density measurements. FT-IR spectroscopy was also applied. The carbons prepared as a rule are microporous and macroporous solids. The degree of development of surface area and porosity increases with increasing carbonisation temperature. For the carbon heated at 900 °C the specific surface area (BET) is 1624 m2 g−1, the micropore volume is 0.67 cm3 g−1, the mesopore volume is 0.28 cm3 g−1, and the macropore volume is 1.84 cm3 g−1. 相似文献
40.
We give a concise review and extension of S-procedure that is an instrumental tool in control theory and robust optimization analysis. We also discuss the approximate S-Lemma as well as its applications in robust optimization.The many suggestions and detailed corrections of an anonymous referee are gratefully acknowledged. 相似文献