全文获取类型
收费全文 | 145752篇 |
免费 | 25513篇 |
国内免费 | 29146篇 |
专业分类
化学 | 105142篇 |
晶体学 | 3150篇 |
力学 | 9115篇 |
综合类 | 2424篇 |
数学 | 20160篇 |
物理学 | 60420篇 |
出版年
2024年 | 330篇 |
2023年 | 2389篇 |
2022年 | 4312篇 |
2021年 | 5110篇 |
2020年 | 5660篇 |
2019年 | 5426篇 |
2018年 | 4994篇 |
2017年 | 5488篇 |
2016年 | 6420篇 |
2015年 | 7013篇 |
2014年 | 8672篇 |
2013年 | 11222篇 |
2012年 | 12714篇 |
2011年 | 13394篇 |
2010年 | 10723篇 |
2009年 | 10634篇 |
2008年 | 11472篇 |
2007年 | 10379篇 |
2006年 | 9748篇 |
2005年 | 8257篇 |
2004年 | 6403篇 |
2003年 | 4807篇 |
2002年 | 4555篇 |
2001年 | 4194篇 |
2000年 | 4108篇 |
1999年 | 3216篇 |
1998年 | 2382篇 |
1997年 | 2023篇 |
1996年 | 1977篇 |
1995年 | 1812篇 |
1994年 | 1655篇 |
1993年 | 1427篇 |
1992年 | 1273篇 |
1991年 | 1040篇 |
1990年 | 931篇 |
1989年 | 790篇 |
1988年 | 563篇 |
1987年 | 524篇 |
1986年 | 474篇 |
1985年 | 379篇 |
1984年 | 320篇 |
1983年 | 243篇 |
1982年 | 204篇 |
1981年 | 167篇 |
1980年 | 116篇 |
1979年 | 100篇 |
1978年 | 48篇 |
1977年 | 38篇 |
1976年 | 38篇 |
1975年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
982.
The Randi? index R(G) of a (chemical) graph G is also called connectivity index. Hansen and Mélot [Variable neighborhood search for extremal graphs 6: analyzing bounds for the connectivity index, J. Chem. Inf. Comput. Sci. 43 (2003) 1-14] in their paper, characterized the chemical trees of given order and number of pendent vertices which have the minimum and maximum Randi? index, respectively. In this note, we point out the mistakes in the proofs of their results Theorems 8 and 10, while we still believe that the two theorems are true, and then we give their corrected proofs. 相似文献
983.
In this article,two uniqueness theorems of meromorphic mappings on moving targets with truncated multiplicities are proved. 相似文献
984.
985.
An economical magnetocardiogram (MCG) system is built in our laboratory. It mainly consists of a MCG data acquisition stage equipped with two high-To superconducting quantum interference device (SQUID) magnetometers, a data processing stage with digital filtering and a one-layer μ-metal magnetically shielded room in conjunction with a high-Tc SQUID based active compensation. Experimental results show that a noise level of pico-tesla in MCG profiles, which is necessary for clinical applications, may be achieved with the system. Moreover, stable and convenient operations of the system are demonstrated with simulating MCG measurements. 相似文献
986.
We consider in this paper the Lagrangian dual method for solving general integer programming. New properties of Lagrangian
duality are derived by a means of perturbation analysis. In particular, a necessary and sufficient condition for a primal
optimal solution to be generated by the Lagrangian relaxation is obtained. The solution properties of Lagrangian relaxation
problem are studied systematically. To overcome the difficulties caused by duality gap between the primal problem and the
dual problem, we introduce an equivalent reformulation for the primal problem via applying a pth power to the constraints. We prove that this reformulation possesses an asymptotic strong duality property. Primal feasibility
and primal optimality of the Lagrangian relaxation problems can be achieved in this reformulation when the parameter p is larger than a threshold value, thus ensuring the existence of an optimal primal-dual pair. We further show that duality
gap for this partial pth power reformulation is a strictly decreasing function of p in the case of a single constraint.
Dedicated to Professor Alex Rubinov on the occasion of his 65th birthday. Research supported by the Research Grants Council
of Hong Kong under Grant CUHK 4214/01E, and the National Natural Science Foundation of China under Grants 79970107 and 10571116. 相似文献
987.
Topological Properties of Urban Public Traffic Networks in Chinese Top-Ten Biggest Cities 总被引:2,自引:0,他引:2
下载免费PDF全文
![点击此处可从《中国物理快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We investigate the topological characteristics of complex networks as exemplified by the urban public traffic network (UPTN) in Chinese top-ten biggest cities. It is found that the UPTNs have small world behaviour, by the examination of their topological parameters. The quantitative analysis of the transport efficiency of the UPTNs reveals their higher local efficiency El and lower global efficiency Eg, which coincide well with the status quo of those Chinese cities still at their developing stage. Furthermore, the topological properties of efficiency in the UPTNs are also examined, and the findings indicate that, on the one hand, the UPTNs show robustness to random attacks and frangibility to malicious attacks on a global scale; on the other hand, the interrelation between UPTN efficiency and network motifs deserves our attention. The motifs which interrelate the UPTN efficiency are always triangular-formed patterns, e.g. motifs ID 238, ID 174 and ID 102, etc. 相似文献
988.
The effect of γ-ray irradiation on the magnetic properties of NdFeB and Fe–Cr–Co permanent magnets has been investigated. The magnetic flux loss of two kinds of magnets before and after irradiation was measured. Results show that the effect of γ-ray irradiation on the magnetic properties of sintered NdFeB is not so obvious as that on Fe–Cr–Co magnet. Irradiation-induced damage from γ-ray for the Fe–Cr–Co magnets was characterized for the first time. The decline of permanent magnetic properties of Fe–Cr–Co magnet induced by γ-ray irradiation is reversible except for the maximum energy product (BH)max. The difference of coercivity mechanism between these two kinds of permanent magnets is responsible for the different dependence of magnetic properties loss induced by γ-ray irradiation. 相似文献
989.
Polyphysa peniculus was grown in artificial seawater in the presence of arsenate, arsenite, monomethylarsonate and dimethylarsinic acid. The separation and identification of some of the arsenic species produced in the cells as well as in the growth medium were achieved by using hydride generation–gas chromatography–atomic absorption spectrometry methodology. Arsenite and dimethylarsinate were detected following incubation with arsenate. When the alga was treated with arsenite, dimethylarsinate was the major metabolite in the cells and in the growth medium; trace amounts of monomethylarsonate were also detected in the cells. With monomethylarsonate as a substrate, the metabolite is dimethylarsinate. Polyphysa peniculus did not metabolize dimethylarsinic acid when it was used as a substrate. Significant amounts of more complex arsenic species, such as arsenosungars, were not observed in the cells or medium on the evidence of flow injection–microwave digestion–hydride generation–atomic absorption spectrometry methodology. Transfer of the exposed cells to fresh medium caused release of most cell–associated arsenicals to the surrounding environment. 相似文献
990.
高抗冲聚丙烯序列结构的综合表征 总被引:3,自引:0,他引:3
用高分辨^13C NMR、FTIR等手段获得了高抗冲聚丙烯的组成和序列分布等链结构方面的信息。用DSC、WAXD等方法研究了它们的结晶行为、熔融转变及晶体结构,多种方法相结合有效地表征了高抗冲聚丙烯的序列结构。 相似文献