全文获取类型
收费全文 | 290174篇 |
免费 | 1975篇 |
国内免费 | 847篇 |
专业分类
化学 | 122864篇 |
晶体学 | 3583篇 |
力学 | 17151篇 |
综合类 | 5篇 |
数学 | 63643篇 |
物理学 | 85750篇 |
出版年
2018年 | 18086篇 |
2017年 | 18716篇 |
2016年 | 10297篇 |
2015年 | 2658篇 |
2014年 | 1810篇 |
2013年 | 5363篇 |
2012年 | 10852篇 |
2011年 | 25349篇 |
2010年 | 14657篇 |
2009年 | 14863篇 |
2008年 | 20142篇 |
2007年 | 25495篇 |
2006年 | 4676篇 |
2005年 | 12552篇 |
2004年 | 8540篇 |
2003年 | 8502篇 |
2002年 | 5543篇 |
2001年 | 4003篇 |
2000年 | 3295篇 |
1999年 | 2394篇 |
1998年 | 2142篇 |
1997年 | 2061篇 |
1996年 | 2175篇 |
1995年 | 1999篇 |
1994年 | 1734篇 |
1993年 | 1725篇 |
1992年 | 1877篇 |
1991年 | 1817篇 |
1990年 | 1747篇 |
1989年 | 1765篇 |
1988年 | 1783篇 |
1987年 | 1763篇 |
1986年 | 1667篇 |
1985年 | 2259篇 |
1984年 | 2405篇 |
1983年 | 1995篇 |
1982年 | 2331篇 |
1981年 | 2148篇 |
1980年 | 2188篇 |
1979年 | 2201篇 |
1978年 | 2328篇 |
1977年 | 2134篇 |
1976年 | 2181篇 |
1975年 | 2117篇 |
1974年 | 1941篇 |
1973年 | 2222篇 |
1972年 | 1335篇 |
1971年 | 1003篇 |
1968年 | 1166篇 |
1967年 | 1141篇 |
排序方式: 共有10000条查询结果,搜索用时 796 毫秒
991.
The logarithmic decrement and shear modulus of a bulk amorphous Zr52.5Ti5Cu17.9Ni14.6Al10 alloy were studied with an inverse torsion pendulum in the range from room temperature to the crystallization temperature and in the frequency range 5–40 Hz. The activation energy spectra of reversible and irreversible structural relaxation were estimated. The results obtained are discussed in the context of a two-energy-level model. 相似文献
992.
In this paper a tripartite qualitative design combining abservation, stimulated recall and interview is presented and discussed. This three-step-design makes it possible to get insight into the interaction of internal and external processes when solving mathematical tasks. The data analysis depends on the research question and the methodological approach. In the light of two research projects in mathematics education two different methods of data analysis are presented and methodologically reflected. 相似文献
993.
We draw upon the concepts of knowledge market, organizational tacit knowledge, credit assignment, and single-loop learning in proposing a market-based conceptual model for collaborative organizational learning. Our proposed model is characterized by the local competition among seller agents and the global collaboration among winner agents in forming a plan, through a chain of ‘upstream–downstream’ working relationship, for task accomplishment. This feature is achieved through three closely coupled processes: the expert selection process, the capital reallocation process, and the plan formation process. Our model is intended for multiple-step learning environment in which each task consists of a sequence of single-step learning tasks. Learning at the global level is the result of a sequence of nested single-loop learning at the local level. 相似文献
994.
In this paper, we investigate the exact distribution of the waiting time for ther-th ℓ-overlapping occurrence of success-runs of a specified length in a sequence of two state Markov dependent trials. The
probability generating functions are derived explicitly, and as asymptotic results, relationships of a negative binomial distribution
of orderk and an extended Poisson distribution of orderk are discussed. We provide further insights into the run-related problems from the viewpoint of the ℓ-overlapping enumeration
scheme. We also study the exact distribution of the number of ℓ-overlapping occurrences of success-runs in a fixed number
of trials and derive the probability generating functions. The present work extends several properties of distributions of
orderk and leads us a new type of geneses of the discrete distributions. 相似文献
995.
996.
V. A. Reznikov 《Technical Physics》2003,48(9):1216-1218
A shell model that describes the formation of molecular complexes around a C60 molecule upon the solid-phase interaction of the powders is considered. From the absorption spectra, it follows that a reacting
particle is a fullerene dimer. 相似文献
997.
T. M. Shneidman G. G. Adamian N. V. Antonenko S. P. Ivanova R. V. Jolos W. Scheid 《Physics of Atomic Nuclei》2003,66(2):206-217
Based on the dinuclear system concept, the role of bending vibrations in creation of the angular momentum of primary fission fragments is investigated. For 252Cf spontaneous fission, the angular momenta of the fragments are calculated as a function of the neutron multiplicity and compared with available experimental data. Different cluster compositions of the 252Cf fission modes at the scission point are considered. 相似文献
998.
R. Weidmann 《Archiv der Mathematik》2003,81(5):589-595
We describe a family of graph manifolds that have 2-generated
fundamental group but do not admit a Heegaard splitting of genus 2. They are
closely related to the examples provided by Boileau and Zieschang if these are
considered as (non-proper) graph manifolds.Received: 14 August 2002 相似文献
999.
1000.
Lasing and discharge in mixtures of SF6 with hydrogen and hydrocarbons are investigated. If the chemical reaction is initiated by a self-sustained discharge (a generator
with both an inductive and capacitive energy storage can be used), the maximum lasing efficiency is attained at high values
of the ratio E/p (where E is the electric field intensity and p is the pressure in the mixture) if shaped electrodes and preionization of the discharge gap are employed. For the first time,
the lasing efficiency obtained in a nonchain HF laser is as high as 10% of the energy deposit and 4.5% of the stored energy
for a specific radiation energy of ≈140 J/(l atm). At high efficiencies, the emission spectrum of the nonchain HF laser significantly
broadens and cascade lasing at P(3-2) → P(2-1) → P(1-0) vibrational transitions for several rotational lines is realized. 相似文献