全文获取类型
收费全文 | 292篇 |
免费 | 11篇 |
专业分类
化学 | 127篇 |
晶体学 | 8篇 |
力学 | 7篇 |
数学 | 24篇 |
物理学 | 100篇 |
无线电 | 37篇 |
出版年
2022年 | 4篇 |
2020年 | 2篇 |
2019年 | 5篇 |
2018年 | 5篇 |
2017年 | 3篇 |
2016年 | 5篇 |
2015年 | 7篇 |
2014年 | 7篇 |
2013年 | 19篇 |
2012年 | 16篇 |
2011年 | 22篇 |
2010年 | 21篇 |
2009年 | 11篇 |
2008年 | 16篇 |
2007年 | 13篇 |
2006年 | 9篇 |
2005年 | 12篇 |
2004年 | 8篇 |
2003年 | 5篇 |
2002年 | 3篇 |
2001年 | 2篇 |
2000年 | 7篇 |
1998年 | 3篇 |
1997年 | 6篇 |
1996年 | 6篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1981年 | 3篇 |
1980年 | 9篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1963年 | 1篇 |
1960年 | 1篇 |
1959年 | 3篇 |
1958年 | 1篇 |
排序方式: 共有303条查询结果,搜索用时 15 毫秒
31.
A non-interacting s-d band model is used to evaluate ?2(ω) in copper. The free electron approximation is used for electrons in s-band, while a simplified tight-binding scheme is used for the d-electrons. It is found that only d-bands with m = 0 contribute to optical transitions. The transition matrix elements are explicitly calculated. The calculated ?2(ω) gives reasonable agreement with measured optical conductivity. 相似文献
32.
In this paper the concepts of strictly convex and uniformly convex normed linear spaces are extended to metric linear spaces. A relationship between strict convexity and uniform convexity is established. Some existence and uniqueness theorems on best approximation in metric linear spaces under different conditions are proved. 相似文献
33.
The results of a Compton profile study on polycrystallineα-Mn are reported. Our measurement are compared with theoretical results computed for different 3d-4s electron configurations within the RFA model. Best agreement between the measured and calculated values is found for 3d
5·44s
1·6 configuration. Theoretical Compton profile ofγ-Mn calculated using the same procedure is close to that for bcc phase with similar electron configurations. 相似文献
34.
A method is described for measuring the acoustic properties of an absorbent material and a duct/nozzle system (with or without airflow) in which a high voltage spark discharge is used as an impulse source of sound. The cross-spectra of the incident, reflected and transmitted acoustic pressure transients are analyzed by way of a FFT digital processor in the form of complex transfer functions. These transfer functions have a direct relationship to the termination impedance and radiation directivity. The impulse method has been justified by comparisons that show excellent agreement with data obtained from existing methods (both experimental and theoretical). 相似文献
35.
A recently formulated transformation for implementing 1-dimensional variable-cutoff filters is extended to the design of 2-dimensional variable-cutoff lowpass filters, and it is shown that the cutoff frequencies along the two frequency axes can be independently controlled, each by one parameter. The filters designed with the 1st-order transformation have certain drawbacks, which are shown to be overcome with the 2nd-order transformation with proper constraints on the variable parameters. 相似文献
36.
Grigoriev A Skorodumova NV Simak SI Wendin G Johansson B Ahuja R 《Physical review letters》2006,97(23):236807
The conductance of monoatomic gold wires containing 3-7 gold atoms has been obtained from ab initio calculations. The transmission is found to vary significantly depending on the wire stretching and the number of incorporated atoms. Such oscillations are determined by the electronic structure of the one-dimensional (1D) part of the wire between the contacts. Our results indicate that the conductivity of 1D wires can be suppressed without breaking the contact. 相似文献
37.
L. Huang L. Vitos B. Johansson R. Ahuja 《Journal of Physics and Chemistry of Solids》2010,71(8):1065-1068
The anomalous temperature dependence of elastic constant c44 for elements V, Nb, Ta, Pd, and Pt, has been calculated using first-principles theory. It is shown that the variation of elastic constant for simple elements can be approximated as the sum of thermal expansion and electronic components. The thermal expansion contributes the normal linearly decreasing effect to the elastic constant with temperature, while electronic contribution is determined by the unique character of electronic structure of elements and leads to the anomalous effect to the elastic constant with temperature. 相似文献
38.
39.
Actinide dioxides (ThO 2 , UO 2 , Pu 2 etc.) compounds have the CaF 2 -type structure at ambient pressure and temperature. Under high pressure, they exist in the PbCl 2 -type structure, belonging to space group Pnma [1]. We have studied crystal structures under high pressure in actinide dioxides by means of first-principles self-consistent total-energy calculations with the non-local Perdew, Burke and Ernzerhof (PBE) exchange correlation using the full-potential linear-muffin-tin-orbital (FPLMTO) method. The atomic equilibrium volume, bulk modulus and transition pressure for actinide dioxides were calculated, covering the full pressure range for which the mentioned experiments have been done [2]. 相似文献
40.
Ethernet-over-SONET/SDH (EoS) is a popular approach for interconnecting geographically distant Ethernet segments using a SONET/SDH
transport infrastructure. It typically uses virtual concatenation (VC) for dynamic bandwidth management. The aggregate SONET/SDH
bandwidth for a given EoS connection is obtained by “concatenating” a number of equal-capacity virtual channels. Together,
these virtual channels form a virtually concatenated group (VCG). In this article, we introduce a new concatenation technique,
referred to as cross-virtual concatenation (CVC), which involves the concatenation of virtual channels of heterogeneous capacities. We show that CVC can be implemented through a simple upgrade at the end node, thus utilizing the existing legacy
SDH infrastructure. By employing CVC for EoS systems, we show that the SDH bandwidth can be harvested more efficiently than
in conventional VC. We consider two problems associated with routing CVC connections: the connection establishment problem
and the connection upgrade problem. The goal of the first problem is to compute a set of paths between two EoS end systems
such that a total bandwidth demand and a constraint on the differential delay between the paths are satisfied. Among all feasible sets, the one that consumes the least amount of network bandwidth is selected. For this problem, we develop an integer linear
program (ILP) and an efficient algorithm based on the sliding-window approach. For the connection upgrade problem, the goal
is to augment an existing set of paths so as to increase the aggregate bandwidth, while continue to meet the differential-delay
constraint. We model this problem as a flow-maximization problem with a constraint on the delay of the virtual channels with
positive flow. We then consider the problem of path selection under imprecise network state information. Simulations are conducted
to demonstrate the advantages of employing CVC and to evaluate the performance of the proposed algorithms.
相似文献
Marwan Krunz (Corresponding author)Email: |