全文获取类型
收费全文 | 2160篇 |
免费 | 73篇 |
国内免费 | 72篇 |
专业分类
化学 | 1042篇 |
晶体学 | 12篇 |
力学 | 57篇 |
综合类 | 2篇 |
数学 | 499篇 |
物理学 | 693篇 |
出版年
2023年 | 9篇 |
2022年 | 48篇 |
2021年 | 55篇 |
2020年 | 54篇 |
2019年 | 47篇 |
2018年 | 70篇 |
2017年 | 56篇 |
2016年 | 93篇 |
2015年 | 41篇 |
2014年 | 69篇 |
2013年 | 97篇 |
2012年 | 103篇 |
2011年 | 126篇 |
2010年 | 87篇 |
2009年 | 79篇 |
2008年 | 93篇 |
2007年 | 65篇 |
2006年 | 96篇 |
2005年 | 89篇 |
2004年 | 155篇 |
2003年 | 141篇 |
2002年 | 86篇 |
2001年 | 89篇 |
2000年 | 24篇 |
1999年 | 20篇 |
1998年 | 31篇 |
1997年 | 18篇 |
1996年 | 14篇 |
1995年 | 19篇 |
1994年 | 25篇 |
1993年 | 34篇 |
1992年 | 31篇 |
1991年 | 23篇 |
1990年 | 19篇 |
1989年 | 18篇 |
1988年 | 22篇 |
1987年 | 11篇 |
1986年 | 10篇 |
1985年 | 17篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1980年 | 5篇 |
1977年 | 4篇 |
1976年 | 8篇 |
1974年 | 5篇 |
1973年 | 7篇 |
1972年 | 4篇 |
1911年 | 4篇 |
排序方式: 共有2305条查询结果,搜索用时 31 毫秒
1.
Software failures have become the major factor that brings the system down or causes a degradation in the quality of service. For many applications, estimating the software failure rate from a user's perspective helps the development team evaluate the reliability of the software and determine the release time properly. Traditionally, software reliability growth models are applied to system test data with the hope of estimating the software failure rate in the field. Given the aggressive nature by which the software is exercised during system test, as well as unavoidable differences between the test environment and the field environment, the resulting estimate of the failure rate will not typically reflect the user‐perceived failure rate in the field. The goal of this work is to quantify the mismatch between the system test environment and the field environment. A calibration factor is proposed to map the failure rate estimated from the system test data to the failure rate that will be observed in the field. Non‐homogeneous Poisson process models are utilized to estimate the software failure rate in both the system test phase and the field. For projects that have only system test data, use of the calibration factor provides an estimate of the field failure rate that would otherwise be unavailable. For projects that have both system test data and previous field data, the calibration factor can be explicitly evaluated and used to estimate the field failure rate of future releases as their system test data becomes available. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
2.
The OPAL Collaboration G. Abbiendi et al. 《The European Physical Journal C - Particles and Fields》2003,27(3):311-329
This paper describes topological searches for neutral scalar bosons S0 produced in association with a Z0 boson via the Bjorken process at centre-of-mass energies of 91 GeV and 183-209 GeV. These searches are based on studies of the recoil mass spectrum of
and events and on a search for with and S or photons. They cover the decays of the S0 into an arbitrary combination of hadrons, leptons, photons and invisible particles as well as the possibility that it might
be stable.
No indication for a signal is found in the data and upper limits on the cross section of the Bjorken process are calculated.
Cross-section limits are given in terms of a scale factor k with respect to the Standart Model cross section for the Higgs-strahlung process .
These results can be interpreted in general scenarios independently of the decay modes of the S0. The examples considered here are the production of a single new scalar particle with a decay width smaller than the detector
mass resolution, and for the first time, two scenarios with continuous mass distributions, due to a single very broad state
or several states close in mass.
Received: 13 March 2002 / Published online: 19 February 2003 相似文献
3.
Andr Luciani Christopher J. G. Plummer Tuan Nguyen Lszl Garamszegi Jan‐Anders E. Mnson 《Journal of Polymer Science.Polymer Physics》2004,42(7):1218-1225
The effects of the size (pseudo‐generation number) and nature of end groups on physical and rheological properties were investigated for a series of hyperbranched polyesters based on an ethoxylated pentaerythritol core and 2,2‐bis‐(hydroxymethyl)propionic acid repeat units. The observed linear dependence of the melt viscosity on the molar mass in the high pseudo‐generation‐number limit indicated that entanglement effects were substantially absent. Moreover, the marked influence of end capping of the end groups on the physical and rheological properties suggested that intermolecular interactions were dominated by contacts between the outer shells of the molecules, in which the end groups were assumed to be concentrated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1218–1225, 2004 相似文献
4.
5.
6.
7.
8.
9.
全固态多波长飞秒脉冲激光系统 总被引:1,自引:1,他引:0
利用棱镜对引进频谱空间啁啾来补偿飞秒脉冲激光二次谐波产生中的相位失配,提高了倍频效率建立了一套全固态、多波长(1065nm, 532nm,823.1nm, 402nm)飞秒脉冲激光系统自制的Nd:YVO4激光器输出532nm绿光激光,最高平均功率可达5.6W当用2.5W绿光激光泵浦时,从自制的钛宝石激光器及经BBO倍频可分别输出中心波长为823.1nm和402nm,平均功率300mW和73mW,谱宽32.3nm和5.1nm,脉宽22fs和33.3fs、重复率108MHz的近红外和蓝光激光整个系统具有结构紧凑、倍频效率高、运行稳定的特点. 相似文献
10.
N.D. Tho N. Chau S.C. Yu H.B. Lee N.D. The L.A. Tuan 《Journal of magnetism and magnetic materials》2006
Effect of annealing on the soft magnetic properties of Fe73.5Si13.5B9Nb3Au1 amorphous ribbon has been investigated by means of structure examination, magnetoimpedance ratio (MIR) and incremental permeability ratio (PR) spectra measured in the frequency range of 1–10 MHz at a fixed current of 10 mA X-ray diffraction analysis showed that the as-cast sample was amorphous and it became nanocrystalline under a proper heat treatment. When annealing amorphous alloy at 530 °C for 30, 60, 90 min, soft magnetic properties have been improved drastically. Among the samples investigated, the sample annealed at 530 °C for 90 min showed the softest magnetic behavior. The MIR and PR curves revealed the desirable changes in anisotropy field depending upon annealing. 相似文献