全文获取类型
收费全文 | 1355388篇 |
免费 | 25851篇 |
国内免费 | 7757篇 |
专业分类
化学 | 680642篇 |
晶体学 | 20109篇 |
力学 | 74723篇 |
综合类 | 105篇 |
数学 | 241110篇 |
物理学 | 372307篇 |
出版年
2021年 | 13532篇 |
2020年 | 15919篇 |
2019年 | 16063篇 |
2016年 | 27593篇 |
2015年 | 20656篇 |
2014年 | 30447篇 |
2013年 | 74413篇 |
2012年 | 38560篇 |
2011年 | 35291篇 |
2010年 | 36528篇 |
2009年 | 38820篇 |
2008年 | 34652篇 |
2007年 | 30263篇 |
2006年 | 37455篇 |
2005年 | 29031篇 |
2004年 | 30643篇 |
2003年 | 28850篇 |
2002年 | 30033篇 |
2001年 | 30397篇 |
2000年 | 26028篇 |
1999年 | 23053篇 |
1998年 | 21240篇 |
1997年 | 21186篇 |
1996年 | 21161篇 |
1995年 | 19220篇 |
1994年 | 18660篇 |
1993年 | 18216篇 |
1992年 | 18533篇 |
1991年 | 18730篇 |
1990年 | 17977篇 |
1989年 | 18009篇 |
1988年 | 17540篇 |
1987年 | 17523篇 |
1986年 | 16479篇 |
1985年 | 22849篇 |
1984年 | 23975篇 |
1983年 | 20090篇 |
1982年 | 21715篇 |
1981年 | 20959篇 |
1980年 | 20277篇 |
1979年 | 20603篇 |
1978年 | 21824篇 |
1977年 | 21494篇 |
1976年 | 21200篇 |
1975年 | 19953篇 |
1974年 | 19571篇 |
1973年 | 20076篇 |
1972年 | 14551篇 |
1968年 | 12409篇 |
1967年 | 12768篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
The alternative: equivalence-singularity on the conic sigma-field is established for a pair of centered Gaussian distributions and a corresponding criterion is given. The behavior of the logarithmic variation is established for the Radon–Nikodym derivative on the conic sigma-subfield. Bibliography: 6 titles. 相似文献
942.
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
943.
Christopher E. Stuart Paul Abraham 《Journal of Mathematical Analysis and Applications》2004,300(2):224-361
Generalizations of the Nikodym boundedness and Vitali–Hahn–Saks theorems for scalar-valued measures on rings of sets that are in general not σ-rings are presented. As a consequence, the rings of subsets of N with density zero and uniform density zero are shown to have the Nikodym property. In addition, vector measure generalizations of the Vitali–Hahn–Saks theorem are given. 相似文献
944.
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
945.
946.
ABSTRACT. We consider autonomous population models under periodic harvesting and population models in periodic environments and seek conditions under which there is an asymptotically stable periodic solution. 相似文献
947.
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
948.
In this work, the melting-point depression and molecular dynamics of hexamethyldisilane confined within five controlled pore
glasses, with mean diameters ranging from 7.9 to 23.9 nm, are studied by high-field (9.4 T) nuclear magnetic resonance (NMR),
and the results are discussed with reference to the bulk substance. The melting-point depression in pores with radiusR follows the simplified Gibbs-Thompson equation ΔT=k
p/(R−s) with ak
p value of 74 K · nm and ans value of 1 nm. To our knowledge, this is the first time thek
p value of hexamethyldisilane is reported. Proton spin-lattice relaxation times (T
1), spin-spin relaxation times (T
2), and diffusivities (D) are reported as a function of temperature. The confinement in the pores gives rise to substantial changes in the molecular
dynamics and the phase behavior. The line-shape measurements reveal a two-phase system assigned to a relatively mobile component
at the pore walls and a crystalline solid at the center of the pores. However, theT
2 measurements show that the mobile phase also embraces a minor component attributed to nonfrozen liquid in pockets or micropores.
The diffusivity of the major narrow-line component is approximately three orders of magnitude larger than that in the plastic
bulk phase, reflecting fast diffusion of mobile molecules. Below the melting region,T
1 of the narrow line is significantly shorter thanT
1 of the broad line, suggesting that the molecular reorientation is more hindered close to the surface than at the center of
the pore. 相似文献
949.
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
950.
The pumiceous products of the large-scale explosive eruptions at Santorini show a high grade of similarity in their optical
appearance as well as in their chemical composition. The demand for a clear classification of these eruption products was
raised from archaeological research, where pumice can be interpreted as a “post-eruption” time marker. The aim of this work
was to find elements that underwent significant changes because of geochemical processes and that could be indicative for
a distinction of pumice produced by the five major explosive eruptions. INAA of 25 elements allows a clear classification
and contributes new information to the chemical evolution of Santorini volcano.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献