全文获取类型
收费全文 | 164721篇 |
免费 | 16127篇 |
国内免费 | 11256篇 |
专业分类
化学 | 86946篇 |
晶体学 | 1745篇 |
力学 | 11850篇 |
综合类 | 591篇 |
数学 | 41214篇 |
物理学 | 49758篇 |
出版年
2024年 | 328篇 |
2023年 | 1871篇 |
2022年 | 3333篇 |
2021年 | 3408篇 |
2020年 | 3805篇 |
2019年 | 3643篇 |
2018年 | 12838篇 |
2017年 | 12564篇 |
2016年 | 10070篇 |
2015年 | 5242篇 |
2014年 | 5608篇 |
2013年 | 7123篇 |
2012年 | 12038篇 |
2011年 | 18476篇 |
2010年 | 11191篇 |
2009年 | 11232篇 |
2008年 | 12239篇 |
2007年 | 13795篇 |
2006年 | 5161篇 |
2005年 | 5301篇 |
2004年 | 4591篇 |
2003年 | 4356篇 |
2002年 | 3348篇 |
2001年 | 2267篇 |
2000年 | 2017篇 |
1999年 | 2065篇 |
1998年 | 1720篇 |
1997年 | 1622篇 |
1996年 | 1636篇 |
1995年 | 1297篇 |
1994年 | 1103篇 |
1993年 | 963篇 |
1992年 | 797篇 |
1991年 | 695篇 |
1990年 | 589篇 |
1989年 | 483篇 |
1988年 | 414篇 |
1987年 | 356篇 |
1986年 | 327篇 |
1985年 | 263篇 |
1984年 | 195篇 |
1983年 | 147篇 |
1982年 | 125篇 |
1981年 | 110篇 |
1980年 | 115篇 |
1979年 | 78篇 |
1978年 | 64篇 |
1977年 | 58篇 |
1976年 | 47篇 |
1973年 | 53篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
In previous work, we considered the representation of human decision-making processes in closed-form simulation models of conflict. An important element of this representation is the rapid planning process that embodies the processing of information for situation assessment to support a course of action decision (eg in a military headquarters). The application of this work is in support of operational analysis models for defence procurement and balance of investment. This paper describes the application of non-linear multi-attribute utility theory in conflict scenarios in order to extend the representation of the rapid planning process to account for a wider set of subjective attributes of the decision-maker. The results show, through examination of experimental data, that decision-making can be modelled through a particular class of utility functions. These utilities embody a geometry which allows us to classify the types of decision being made when there are conflicting objectives and when decision-makers adopt very different and subjective appraisals of constraints and beliefs in outcome. The experimental results help to demonstrate that the subjective nature of the situation assessment, and the personality, training, experience and history of the decision-maker are central to the functional representations. This paper presents a way to capture this deeper representation of human decision-making in a way that is potentially useful for quantitative modelling using the rapid planning process as a basis. 相似文献
992.
Xiangdong Xu Hockleong Kweh Zhengcao Zhang Zhihong Liu Wei Zhou Wei Zhang Peixin Qian 《Applied Surface Science》2006,252(20):7594-7598
Large-scale preparation of thin strain-relaxed SiGe is achieved by combining ion implantation and ultrahigh vacuum chemical vapor deposition. The resulting materials were analyzed by double crystal X-ray diffraction, micro-Raman spectroscopy, and tapping mode atomic force microscope. Results revealed that 100-nm-thick Si0.7Ge0.3 layers with the diameter of 125 mm and full strain relaxation are successfully prepared by pre-modifying the Si substrates using 50 keV Ar+ ions. The strain relaxation is also disclosed to change with both ion species and energy. However, post-modification of SiGe by ion implantation will cause serious damage to the crystal structures, and result in the formation of poly-crystal SiGe. 相似文献
993.
Rhyd Lewis 《Journal of Heuristics》2007,13(4):387-401
In this paper we present, to our knowledge, the first application of a metaheuristic technique to the very popular and NP-complete
puzzle known as ‘sudoku’. We see that this stochastic search-based algorithm, which uses simulated annealing, is able to complete
logic-solvable puzzle-instances that feature daily in many of the UK’s national newspapers. We also introduce a new method
for producing sudoku problem instances (that are not necessarily logic-solvable) and use this together with the proposed SA
algorithm to try and discover for what types of instances this algorithm is best suited. Consequently we notice the presence
of an ‘easy-hard-easy’ style phase-transition similar to other problems encountered in operational research. 相似文献
994.
This paper deals with the asymptotic analysis of the three-dimensional problem for a linearly elastic cantilever having an
open cross-section which is the union of rectangles with sides of order ε and ε
2, as ε goes to zero. Under suitable assumptions on the given loads and for homogeneous and isotropic material, we show that the
three-dimensional problem Γ-converges to the classical one-dimensional Vlassov model for thin-walled beams.
相似文献
995.
Denis V. Osin 《Archiv der Mathematik》2007,88(5):403-412
The aim of this paper is to show that free Burnside groups of sufficiently large odd exponent are non-amenable in a certain
strong sense. More precisely their left regular representations are isolated from the trivial representation uniformly on
finite generating sets. It follows that free Burnside groups are of uniform exponential growth. This answers a question of
de la Harpe.
This work has been partially supported by the NSF grant DMS-0605093 and by the RFBR Grant # 05-01-00892.
Received: 25 April 2006 相似文献
996.
Shuguan Ji Zhenxin Liu Shaoyun Shi 《Journal of Mathematical Analysis and Applications》2007,325(2):1306-1313
The method of equivalent variational methods, originally due to Carathéodory for free problems in the calculus of variations is extended to investigate boundary value problems for a class of second order differential equations on the half-line. Some applications are presented to illustrate the potential of this method. 相似文献
997.
Qin-long Wang Yi-rong Liu 《应用数学学报(英文版)》2007,23(3):451-466
In this paper, we study the appearance of limit cycles from the equator and isochronicity of infinity in polynomial vector fields with no singular points at infinity. We give a recursive formula to compute the singular point quantities of a class of cubic polynomial systems, which is used to calculate the first seven singular point quantities. Further, we prove that such a cubic vector field can have maximal seven limit cycles in the neighborhood of infinity. We actually and construct a system that has seven limit cycles. The positions of these limit cycles can be given exactly without constructing the Poincare cycle fields. The technique employed in this work is essentially different from the previously widely used ones. Finally, the isochronous center conditions at infinity are given. 相似文献
998.
999.
James Tanton 《Mathematical Intelligencer》2007,29(3):55-59
This column is a place for those bits of contagious mathematics that travel from person to person in the community, because
they are so elegant, suprising, or appealing that one has an urge to pass them on.
Contributions are most welcome. 相似文献
1000.