全文获取类型
收费全文 | 96565篇 |
免费 | 9880篇 |
国内免费 | 8053篇 |
专业分类
化学 | 28394篇 |
晶体学 | 445篇 |
力学 | 7389篇 |
综合类 | 1361篇 |
数学 | 26771篇 |
物理学 | 28860篇 |
无线电 | 21278篇 |
出版年
2024年 | 129篇 |
2023年 | 896篇 |
2022年 | 1494篇 |
2021年 | 1853篇 |
2020年 | 2100篇 |
2019年 | 2116篇 |
2018年 | 1876篇 |
2017年 | 2407篇 |
2016年 | 2798篇 |
2015年 | 2756篇 |
2014年 | 4227篇 |
2013年 | 6181篇 |
2012年 | 4749篇 |
2011年 | 5074篇 |
2010年 | 4319篇 |
2009年 | 5366篇 |
2008年 | 5870篇 |
2007年 | 6159篇 |
2006年 | 5850篇 |
2005年 | 4999篇 |
2004年 | 4695篇 |
2003年 | 4592篇 |
2002年 | 4051篇 |
2001年 | 3402篇 |
2000年 | 3270篇 |
1999年 | 2863篇 |
1998年 | 2592篇 |
1997年 | 2162篇 |
1996年 | 1984篇 |
1995年 | 1732篇 |
1994年 | 1582篇 |
1993年 | 1355篇 |
1992年 | 1274篇 |
1991年 | 1008篇 |
1990年 | 855篇 |
1989年 | 735篇 |
1988年 | 631篇 |
1987年 | 472篇 |
1986年 | 413篇 |
1985年 | 470篇 |
1984年 | 459篇 |
1983年 | 228篇 |
1982年 | 364篇 |
1981年 | 421篇 |
1980年 | 319篇 |
1979年 | 303篇 |
1978年 | 232篇 |
1977年 | 213篇 |
1976年 | 161篇 |
1974年 | 113篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
891.
本文介绍了兰州重离子加速器(HIRFL)的注入器(SFC)所用PIG离子源的研制和改进工作,使用新研制的PIG源,已在注人器SFC上获得了5μA的O_(16)~(5+)及10μA的C_(16)~(4+)的离子束。 相似文献
892.
Shoaib Ahmad 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(3):309-318
The mechanisms and processes of the formation of the regenerative soot in a graphite hollow cathode discharge that produces
and emits carbon clusters are presented. Mass spectrometry with a specially designed E×B velocity filter analyzes the entire range of the charged clusters from C
1 to ∼C
4300. The state of the carbon vapour within the source is evaluated by using the characteristic line emissions from the carbonaceous
discharge whose formative mechanisms depend upon the kinetic and potential sputtering of the sooted cathode. The carbonaceous
discharge generates atomic and ionic C and its clusters C
m (m≥ 2), noble gas metastable atoms and ions, energetic electrons and photons in the cavity of the graphite hollow cathode. The
parameters of soot formation and its recycling depend critically on the discharge parameters, the geometry of the hollow cathode
and 3D profile of the cusp magnetic field contours.
Received 2nd July 2001 and Received in final form 10 September 2001 相似文献
893.
Thomas Andreae 《Journal of Graph Theory》2002,39(4):222-229
For a graph A and a positive integer n, let nA denote the union of n disjoint copies of A; similarly, the union of ?0 disjoint copies of A is referred to as ?0A. It is shown that there exist (connected) graphs A and G such that nA is a minor of G for all n??, but ?0A is not a minor of G. This supplements previous examples showing that analogous statements are true if, instead of minors, isomorphic embeddings or topological minors are considered. The construction of A and G is based on the fact that there exist (infinite) graphs G1, G2,… such that Gi is not a minor of Gj for all i ≠ j. In contrast to previous examples concerning isomorphic embeddings and topological minors, the graphs A and G presented here are not locally finite. The following conjecture is suggested: for each locally finite connected graph A and each graph G, if nA is a minor of G for all n ? ?, then ?0A is a minor of G, too. If true, this would be a far‐reaching generalization of a classical result of R. Halin on families of disjoint one‐way infinite paths in graphs. © 2002 Wiley Periodicals, Inc. J Graph Theory 39: 222–229, 2002; DOI 10.1002/jgt.10016 相似文献
894.
895.
散斑条纹的快速高精度处理技术 总被引:3,自引:1,他引:2
本文提出一种快速高精度散斑杨氏条纹(斑纹)场处理方法——同态阀值滤波法。用它实现了散斑场条纹的快速、逐点连续高精度处理。 相似文献
896.
897.
Wieczorek-Ciurowa K. Gamrat K. Paryło M. Shirokov Ju. G. 《Journal of Thermal Analysis and Calorimetry》2002,70(1):165-172
The physical mixtures of hydroxocarbonates of Cu and Ni with aluminium were activated using a laboratory planetary mill. The
chemical reactions and alloy formations as the effects of grinding were followed by the phase analysis of solid products based
on the thermogravimetry and X-ray diffractometry. Experimental evidence indicates that the nature of reactions and products
of mechanical activation was dependent on the amount of aluminium and time of grinding.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
898.
提出了WDM环形网络的几种保护方案,分析了利用1:1环路配置方式进行WDM光环形网络保护的实现方法,简单介绍APS在环保护中的应用。 相似文献
899.
900.
M. A. Macrì C. Del Gratta L. Di Donato S. Di Luzio G. L. Romani S. Della Penna A. Pasquarelli 《Il Nuovo Cimento D》1994,16(5):425-432
Summary A preliminary study is here reported on a new potential marker for biomagnetic measurements. The marker consists of superparamagnetic
polymer microspheres which were detected in the presence of external steady magnetic fields by means of an r.f.-SQUID magnetometer.
The particles were prepared in samples differing in the concentration value and immersed in a homogeneous magnetic field of
variable intensity. A simple model was taken into account for the distribution of the microspheres in the samples, so that
the theoretical values were compared to the marker field values measured by the biomagnetic sensor. The overall sensitivity
of the experimental apparatus and the minimum concentration value of the marker were then estimated. 相似文献