全文获取类型
收费全文 | 66820篇 |
免费 | 5364篇 |
国内免费 | 8431篇 |
专业分类
化学 | 50022篇 |
晶体学 | 1424篇 |
力学 | 1643篇 |
综合类 | 459篇 |
数学 | 11480篇 |
物理学 | 15587篇 |
出版年
2024年 | 84篇 |
2023年 | 508篇 |
2022年 | 1082篇 |
2021年 | 1068篇 |
2020年 | 1501篇 |
2019年 | 1474篇 |
2018年 | 1322篇 |
2017年 | 1851篇 |
2016年 | 1994篇 |
2015年 | 1866篇 |
2014年 | 2454篇 |
2013年 | 5338篇 |
2012年 | 4507篇 |
2011年 | 3709篇 |
2010年 | 3098篇 |
2009年 | 4108篇 |
2008年 | 4316篇 |
2007年 | 4449篇 |
2006年 | 4059篇 |
2005年 | 3579篇 |
2004年 | 3365篇 |
2003年 | 2795篇 |
2002年 | 3786篇 |
2001年 | 2397篇 |
2000年 | 2171篇 |
1999年 | 2075篇 |
1998年 | 1746篇 |
1997年 | 1401篇 |
1996年 | 1078篇 |
1995年 | 1054篇 |
1994年 | 966篇 |
1993年 | 744篇 |
1992年 | 786篇 |
1991年 | 491篇 |
1990年 | 429篇 |
1989年 | 423篇 |
1988年 | 314篇 |
1987年 | 245篇 |
1986年 | 241篇 |
1985年 | 212篇 |
1984年 | 210篇 |
1983年 | 123篇 |
1982年 | 181篇 |
1981年 | 150篇 |
1980年 | 178篇 |
1979年 | 157篇 |
1978年 | 143篇 |
1977年 | 102篇 |
1976年 | 87篇 |
1973年 | 52篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
贝克曼Allegra^TM 21R型超高速离心机开机后,操作面板上出现错误代码“28”,离心机不旋转。离心机的电机采用无刷感应驱动,由电机驱动电源模块BSMl0GD60DN2驱动离心机的电机。故障是由于电源模块BSMl0GD60DN2损坏引起的。采用东芝三相桥式IGBT电源模块MG25Q6ES42代替BSMl0GD60DN2,并更换已烧毁的栅极电阻后。开机试验,仪器恢复正常。 相似文献
102.
[Na(18-C-6)]2[Cu(i-mnt)2]的合成与结构分析 总被引:2,自引:2,他引:0
研究了18-冠-6与Na2[Cu(i-mnt)2][i-mnt=异丁二腈烯二硫醇阴离子,S2CC(CN)2-2]的反应,得到的配合物[Na(18-C-6)]2[Cu(i-mnt)2](1)通过元素分析、红外光谱、X射线单晶衍射进行了结构分析.配合物为单斜晶系,空间群P2(1)/c.晶体学结构数据a=1.2819(11),b=1.1793(10),c=1.4928(13)nm,β=99.121(16)°,V=2.228(3)nm3,Z=2,Dcaled.=1.369g/cm3,F(000)=958,R1=0.0521,wR2=0.1003.1中的[Cu(i-mnt)2]基团通过配体i-mnt的氮原子与两个[Na(18-C-6)]基团中的钠原子成键,形成稳定的中性配合物. 相似文献
103.
104.
105.
P. R. Latthe P. S. Shinge Bharati V. Badami P. B. Patil S. N. Holihosur 《Journal of Chemical Sciences》2006,118(3):249-256
3-[4-(Azidocarbonyl)]phenylsydnone (2) obtained from 3-(4-hydrazinocarbonyl) phenylsydnone (1) on Curtius rearrangement with alcohols, water and amines afforded the corresponding carbamates (3a-h), 4,4′-(sydnone-3-yl) diphenyl urea (4) and 4-(heterocyclyl)phenyl ureas (5a-l). Compounds (5a-l) on one-pot ring conversion yielded the 1,3,4-oxadiazolin-2-one derivatives (6a-l), which on reaction with N2H4 gave the 4-amino-1,2,4-triazolin-3-ones (7a-l). All these compounds exhibited moderate antimicrobial activity against the few microbes tested. The carbamates have been
found to be more toxic against fourth instar larvae ofAedes aegypti, in particular, then-butyl derivative (3e). 相似文献
106.
Admissible slopes for monotone and convex interpolation 总被引:1,自引:0,他引:1
Summary In many applications, interpolation of experimental data exhibiting some geometric property such as nonnegativity, monotonicity or convexity is unacceptable unless the interpolant reflects these characteristics. This paper identifies admissible slopes at data points of variousC
1 interpolants which ensure a desirable shape. We discuss this question, in turn for the following function classes commonly used for shape preserving interpolations: monotone polynomials,C
1 monotone piecewise polynomials, convex polynomials, parametric cubic curves and rational functions. 相似文献
107.
A graph G is N2‐locally connected if for every vertex ν in G, the edges not incident with ν but having at least one end adjacent to ν in G induce a connected graph. In 1990, Ryjá?ek conjectured that every 3‐connected N2‐locally connected claw‐free graph is Hamiltonian. This conjecture is proved in this note. © 2004 Wiley Periodicals, Inc. J Graph Theory 48: 142–146, 2005 相似文献
108.
In this paper we show that for a given 3-manifold and a given Heegaard splitting there are finitely many preferred decomposing systems of 3g−3 disjoint essential disks. These are characterized by a combinatorial criterion which is a slight strengthening of Casson-Gordon's rectangle condition. This is in contrast to fact that in general there can exist infinitely many such systems of disks which satisfy just the Casson-Gordon rectangle condition. 相似文献
109.
ZHU Yabin ZHOU Yueliang LIU Zhen WANG Shufang CHEN Zhenghao U Huibin YANG Guozhen XlAO Ling Ren Hongtao JIAO Yulei Zheng Minghui 《中国科学G辑(英文版)》2004,47(2):165-172
The irreversibility field (Hirr) of Y-based superconductor is much higher than that of Bi-based superconductor. Y-based superconductor is capable of maintaining stable electrical currents in high magnetic field and electric field, so it is a better suited mate-rial for electric-current applications. Commonly, the Y-based tapes comprise a YBCO thick film deposited on a flexible substrate, typically with an intermediate buffer layer, and an overcoat of noble metal. In this process, the interm… 相似文献
110.