全文获取类型
收费全文 | 532055篇 |
免费 | 5444篇 |
国内免费 | 1488篇 |
专业分类
化学 | 273291篇 |
晶体学 | 8382篇 |
力学 | 25273篇 |
综合类 | 16篇 |
数学 | 64620篇 |
物理学 | 167405篇 |
出版年
2021年 | 4262篇 |
2020年 | 4722篇 |
2019年 | 5312篇 |
2018年 | 7269篇 |
2017年 | 7401篇 |
2016年 | 10458篇 |
2015年 | 6063篇 |
2014年 | 10008篇 |
2013年 | 23858篇 |
2012年 | 18179篇 |
2011年 | 22001篇 |
2010年 | 16024篇 |
2009年 | 15875篇 |
2008年 | 20054篇 |
2007年 | 20079篇 |
2006年 | 18609篇 |
2005年 | 16429篇 |
2004年 | 15195篇 |
2003年 | 13616篇 |
2002年 | 13542篇 |
2001年 | 15498篇 |
2000年 | 11767篇 |
1999年 | 9179篇 |
1998年 | 7832篇 |
1997年 | 7729篇 |
1996年 | 7231篇 |
1995年 | 6486篇 |
1994年 | 6571篇 |
1993年 | 6219篇 |
1992年 | 6937篇 |
1991年 | 7110篇 |
1990年 | 6880篇 |
1989年 | 6667篇 |
1988年 | 6542篇 |
1987年 | 6615篇 |
1986年 | 6276篇 |
1985年 | 8080篇 |
1984年 | 8372篇 |
1983年 | 6992篇 |
1982年 | 7162篇 |
1981年 | 6849篇 |
1980年 | 6800篇 |
1979年 | 7021篇 |
1978年 | 7356篇 |
1977年 | 7233篇 |
1976年 | 7267篇 |
1975年 | 6725篇 |
1974年 | 6788篇 |
1973年 | 6985篇 |
1972年 | 4956篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
821.
822.
M C Testik J K Cochran G C Runger 《The Journal of the Operational Research Society》2004,55(3):233-239
We study the short-term staffing problem of systems that experience random, non-stationary demand. The typical method to accommodate changes in arrival rate is to use historical data to identify peak periods and associated forecasting for upcoming time windows. In this paper, we develop a method that instead detects change as it happens. Motivated by an automatic call distributor system in a call centre with time-varying arrivals, we propose a change detection algorithm based upon non-homogeneous Poisson processes. The proposed method is general and may be thought of as a feed-forward strategy, in which we detect a change in the arrival process, estimate the new magnitude of the arrival rate, and assign an appropriate number of servers to the tasks. The generalized likelihood ratio statistic is used and a recommendation for its decision limit is developed. Simulation results are used to evaluate the performance of the detector in the context of a telephone call centre. 相似文献
823.
This paper considers a receiver set partitioning and sequencing problem in a wavelength division multiplexing single-hop lightwave network for multicasting traffic. The problem is analysed in the approach of uncapacitated single batch-processing machine scheduling. In the analysis, several solution properties are characterized with respect to a mean flow time measure, based upon which two heuristic algorithms are developed, along with a dynamic programming algorithm. Several numerical experiments show that the heuristic algorithms generate good schedules. The problem is extended to consider two measures simultaneously including the mean flow time and the number of transmissions, for which the proposed algorithms also perform well. 相似文献
824.
Influence of the Type of a Ligand on the Intensity of Luminescence of Ln3+ Ions in Aqueous Solutions
I. V. Barsukov E. N. Kabaeva V. V. Syt'ko S. D. Umreiko 《Journal of Applied Spectroscopy》2003,70(3):470-473
The luminescence characteristics of hydrated Ln3+ ions and their complexes with some acidic ligands have been investigated. The possibility of determining the stability of the complexes of lanthanides in solutions from the intensity of luminescence bands is shown. The influence of the characteristic features of the f-electron shell of Ln3+ on the formation of the spectrochemical series is discussed. 相似文献
825.
M. R. McEwen J. P. Sephton P. H. G. Sharpe D. R. Shipley 《Radiation Physics and Chemistry》2003,68(6):1017-1022
A phantom composed of alanine dosimeter material has been constructed and depth–dose measurements made in a 10 MeV electron beam. The results have demonstrated the feasibility of using relative depth–dose measurements to determine stopping power ratios in materials of dosimetric interest. Experimental stopping power ratios for alanine dosimeter material and water agreed with the data of ICRU Report 37 within the uncertainty of the experiment (±1.2% at a 95% confidence level). 相似文献
826.
We study conditions on the matrix mask of a vector subdivision scheme ensuring that certain polynomial input vectors yield polynomial output again. The conditions are in terms of a recurrence formula for the vectors which determine the structure of polynomial input with this property. From this recurrence, we obtain an algorithm to determine polynomial input of maximal degree. The algorithm can be used in the design of masks to achieve a high order of polynomial reproduction. 相似文献
827.
S. Tavazzi A. Borghesi M. Campione A. Papagni A. Sassella P. Spearman 《Journal of luminescence》2004,110(4):212-216
We examine absorption of light in quaterthiophene crystals for different directions of the ray and wave-normal vector after refraction on the vacuum/crystal interface. Experimental non-normal incidence spectra are reported where different absorption bands show different behaviour as a function of the angle of incidence. This allows to identify those originating from the bu Frenkel exciton state. 相似文献
828.
The mechanism of transition of a Bose gas to the superfluid state via thermal fluctuations under the condition of external cooling at a temperature above the transition point is considered. The probability of formation of such critical fluctuations (instantons) is calculated; it is found that this probability increases as the system approaches the transition temperature. It is shown that the evolution of an individual instanton is impossible without the formation of vortices in its superfluid part. 相似文献
829.
830.
S.V.N Bhaskara Rao T.K. Balasubramanian 《Journal of Quantitative Spectroscopy & Radiative Transfer》2004,87(2):203-210
Fresh computations of rovibrational matrix elements of the polarizability α[=(α||+2α⊥)/3] and the polarizability anisotropy γ(=α||−α⊥) of the heteronuclear isotopomers, HD, HT, and DT, of the hydrogen molecule are presented. The computations combine the most accurate polarizability functions α(R) and γ(R) (R being the bond distance) on the one hand and the most accurate adiabatic potential on the other. The calculations are extended to the product operators xα and xγ where x is the centre of mass to centre of charge separation in the heteronuclear species. The latter matrix elements are needed, additionally, for elucidating the absorption intensities of some of the zero-phonon rovibrational transitions peculiar to the heteronuclear species in the crystalline phase. 相似文献