全文获取类型
收费全文 | 286139篇 |
免费 | 40403篇 |
国内免费 | 28171篇 |
专业分类
化学 | 143747篇 |
晶体学 | 2240篇 |
力学 | 15271篇 |
综合类 | 1459篇 |
数学 | 28386篇 |
物理学 | 84700篇 |
无线电 | 78910篇 |
出版年
2024年 | 992篇 |
2023年 | 5799篇 |
2022年 | 7851篇 |
2021年 | 10009篇 |
2020年 | 9880篇 |
2019年 | 9136篇 |
2018年 | 8301篇 |
2017年 | 8057篇 |
2016年 | 11598篇 |
2015年 | 12251篇 |
2014年 | 14968篇 |
2013年 | 19587篇 |
2012年 | 23080篇 |
2011年 | 23568篇 |
2010年 | 16918篇 |
2009年 | 16950篇 |
2008年 | 18092篇 |
2007年 | 16465篇 |
2006年 | 15724篇 |
2005年 | 13627篇 |
2004年 | 9783篇 |
2003年 | 8230篇 |
2002年 | 7414篇 |
2001年 | 6403篇 |
2000年 | 6079篇 |
1999年 | 6815篇 |
1998年 | 6060篇 |
1997年 | 5355篇 |
1996年 | 5538篇 |
1995年 | 4723篇 |
1994年 | 4360篇 |
1993年 | 3649篇 |
1992年 | 3323篇 |
1991年 | 2818篇 |
1990年 | 2205篇 |
1989年 | 1682篇 |
1988年 | 1347篇 |
1987年 | 1055篇 |
1986年 | 994篇 |
1985年 | 882篇 |
1984年 | 612篇 |
1983年 | 480篇 |
1982年 | 406篇 |
1981年 | 291篇 |
1980年 | 209篇 |
1979年 | 131篇 |
1978年 | 100篇 |
1976年 | 100篇 |
1974年 | 102篇 |
1973年 | 100篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
The 57Fe Mössbauer effect study at 5.0 K and in an external magnetic field of 9.0 T on a high-quality stable decagonal quasicrystal Al65Co15Cu19.9Fe0.1 is presented. It is shown that the iron atoms are located in two distinct classes of sites. The values of the principal component of the electric field gradient tensor and the asymmetry parameter at these sites are, respectively, ?1.90(10)?×?1021 V/m2, 0.97(15) and ?3.95(12)?×?1021 V/m2, 0.00(17). 相似文献
972.
Jing Ping YANG Shi Hong CHENG Xiao Qian WANG 《数学学报(英文版)》2007,23(3):467-478
This paper investigates bivariate recursive equations on excess-of-loss reinsurance. For an insurance portfolio, under the assumptions that the individual claim severity distribution has bounded continuous density and the number of claims belongs to R1 (a, b) family, bivariate recursive equations for the joint distribution of the cedent's aggregate claims and the reinsurer's aggregate claims are obtained. 相似文献
973.
Stadia are popular models of chaotic billiards introduced by Bunimovich in 1974. They are analogous to dispersing billiards
due to Sinai, but their fundamental technical characteristics are quite different. Recently many new results were obtained
for various chaotic billiards, including sharp bounds on correlations and probabilistic limit theorems, and these results
require new, more powerful technical apparatus. We present that apparatus here, in the context of stadia, and prove “regularity”
properties.
相似文献
974.
A mistake concerning the ultra LI-ideal of a lattice implication algebra is pointed out, and some new sufficient and necessary conditions for an LI-ideal to be an ultra LI-ideal are given. Moreover, the notion of an LI-ideal is extended to MTL-algebras, the notions of a (prime, ultra, obstinate, Boolean) LI-ideal and an ILI-ideal of an MTL-algebra are introduced, some important examples are given, and the following notions are proved to be equivalent in MTL-algebra: (1) prime proper LI-ideal and Boolean LI-ideal, (2) prime proper LI-ideal and ILI-ideal, (3) proper obstinate LI-ideal, (4) ultra LI-ideal.
This work was supported by the Zhejiang Provincial Natural Science Foundation of China (Grant No. Y605389) and K. C. Wong
Magna Fund in Ningbo University. 相似文献
975.
In this article,the Hausdorff dimension and exact Hausdorff measure function of any random sub-self-similar set are obtained under some reasonable conditions.Several examples are given at the end. 相似文献
976.
The stagnation slip flow on an axially moving cylinder is studied.The NavierStokes and energy equations reduce to nonlinearordinary differential equations under a similarity transform.For large slip, the flow field decays exponentially into potentialflow. The heat transfer can be expressed as an incomplete gammafunction. In general, the heat transfer increases with slip,Prandtl number and Reynolds number. 相似文献
977.
978.
The basic structural units of the genome are nucleotides. A single nucleotide polymorphism (SNP) is a mutation at a single nucleotide position. This paper discusses several major problems in SNP data analysis and review some existing solutions in this work. Generally speaking, a rich set of SNP analysis problems are cast in the signal processing framework. Our objective is to offer a state-of-the art review on this topic from a signal processing viewpoint so that researchers in the signal processing field can grasp the important domain knowledge to overcome the barrier between the two fields 相似文献
979.
A route to the total synthesis of koumine has been suggested. Five 4-substituted 1, 2-d hydropyridine derivatives, which are supposed to be a conjugated diene of Diels-Alder reaction to produce the isoquinuclidine ring of koumine, have been synthesized. Only two of them were found to be able to undergo the Diels-Alder reaction. The stereochemistry of the reaction product has also been examined. 相似文献
980.
J. Mass M. Avella J. Jimnez M. Callahan E. Grant K. Rakes D. Bliss B. Wang 《Superlattices and Microstructures》2007,42(1-6):306
Understanding the luminescence of ZnO is very important for some applications. In spite of the many studies carried out, there are still some points concerning the origin of some of the luminescence emissions in ZnO crystals that require additional study; in particular, the role of extended defects remains to be a matter of controversy. We present here a cathodoluminescence analysis of the defects generated by Vickers indentation in hydrothermal HTT crystals. Special emphasis was paid to the luminescence band peaking around 3.3 eV. The origin of this band is a matter of controversy, since it has been related to different causes, extended defects being one of the candidates for this emission. The CL images were acquired around crystal defects. It is observed that the 3.3 eV emission is enhanced around the crystal defects; though it is also observed, but weaker, out of the defect regions, which suggests that there exist two luminescence emissions peaking very close to 3.3 eV. The two emissions, one related to structural defects and the other to the LO phonon replica of the free excitonic band, appear very close each other and their relative intensity should determine the shape of the spectrum. 相似文献