全文获取类型
收费全文 | 93103篇 |
免费 | 18645篇 |
国内免费 | 31378篇 |
专业分类
化学 | 68468篇 |
晶体学 | 3649篇 |
力学 | 7050篇 |
综合类 | 3408篇 |
数学 | 15456篇 |
物理学 | 45095篇 |
出版年
2024年 | 247篇 |
2023年 | 960篇 |
2022年 | 3119篇 |
2021年 | 3105篇 |
2020年 | 3161篇 |
2019年 | 3139篇 |
2018年 | 2934篇 |
2017年 | 4082篇 |
2016年 | 3427篇 |
2015年 | 4717篇 |
2014年 | 5767篇 |
2013年 | 7462篇 |
2012年 | 7612篇 |
2011年 | 8334篇 |
2010年 | 8075篇 |
2009年 | 8454篇 |
2008年 | 9257篇 |
2007年 | 8499篇 |
2006年 | 8225篇 |
2005年 | 6990篇 |
2004年 | 5438篇 |
2003年 | 4080篇 |
2002年 | 4106篇 |
2001年 | 4101篇 |
2000年 | 4088篇 |
1999年 | 2494篇 |
1998年 | 1341篇 |
1997年 | 1066篇 |
1996年 | 1032篇 |
1995年 | 899篇 |
1994年 | 938篇 |
1993年 | 879篇 |
1992年 | 805篇 |
1991年 | 538篇 |
1990年 | 503篇 |
1989年 | 517篇 |
1988年 | 456篇 |
1987年 | 385篇 |
1986年 | 330篇 |
1985年 | 251篇 |
1984年 | 239篇 |
1983年 | 207篇 |
1982年 | 160篇 |
1981年 | 142篇 |
1980年 | 109篇 |
1979年 | 123篇 |
1978年 | 46篇 |
1977年 | 27篇 |
1965年 | 44篇 |
1959年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
1 INTRODUCTION Carbon nanotubes have many potential applica- tions due to their unique structures and properties[1~4]. Physicists have been studying their electrical, me- chanical and other properties since their discove- ries[5, 6]. Recently, chemists are interested in carbon nanotubes because their properties can be altered by chemical functionalization[7~14], and these functiona- lized nanotubes can undergo further chemical trea- tment. So the potential application range of such na- … 相似文献
104.
基于自适应差分量化理论,提出了在不增加转换位数的情况下提高模数转换器(ADC)动态范围的一种设计方法。该方法通过量化输入与预测的差值来获得预测增益,从而扩大ADC的动态范围;通过差分量化值与预测值相加得到输出信号,并将该分别采用LMS和RLS算法进行处理.得到输入信号的预测值.计算机模拟结果证实,上述两种算法均能使模数转换器的动态范围提高约25dB.比较而言,RLS算法收敛速度更快,收敛性更好,但计算量较大. 相似文献
105.
This paper undertakes a systematic treatment of the low regularity local wellposedness and ill-posedness theory in Hs andHs for semilinear wave equations with polynomial nonlinearity in u and (e)u. This ill-posed result concerns the focusing type equations with nonlinearity on u and (e)tu. 相似文献
106.
马歇尔-勒纳条件的实证研究 总被引:6,自引:0,他引:6
本文从人民币实际汇率变动是否会对我国贸易收支产生影响出发,基于马歇尔.勒纳条件,对计算贸易弹性常用的OLS回归模型进行了改进,建立了向量自回归误差修正模型来估算我国的国际贸易弹性。实证研究表明:我国进出口需求的价格弹性之和大于1。因此人民币贬值可改善贸易收支;反之升值将使贸易收支恶化。 相似文献
107.
GAO Xiaoyan CAI Xiao CAO Zeng CUI Chenghe 《核工业西南物理研究院年报(英文版)》2004,(1):54-56
HL-2A is the first divertor tokamak in China. The vacuum system is one of the important parts of the HL-2A tokamak, which has to be work well during the physics campaign in 2004. As the tokamak machine is separated from the operation staff during discharges, to guarantee the safe and reliable operation of the vacuum system, it is necessary to watch the vacuum system outside the machine hall with an automatic monitoring system. The paper describes the design and manufacture of the monitoring system. 相似文献
108.
In the ever fusion experiments in SWIP, pellet forming process was carried out through adjusting relative devices by staff member in site, which will make every pellet-forming process slight distinction and will result in pellet difference in shape, size and intensity. In the intervals of HL-2A discharges, staff member have to go site to accomplish the pellet-forming process, this wastes human power and increase the potential danger. So it is necessary to develop a remote control system to perform the pellet-forming process. The control system needs have the features of real-time, reliability and be easy to operate and maintain. 相似文献
109.
The vacuum system of today's tokamak devices is designed to meet the operational requirements of the experiments. The operation can be divided into five modes, (1) pumping down and leak detecting of the vacuum vessel, (2) baking, (3) plasma-facing component (PFC) conditioning, (4)evacuating and controlling of the particles at plasma edge, (5) plasma discharge experiments. 相似文献
110.
YBa2Cu3O7-x (YBCO) bulk is one of the most important high temperature superconducting materials for magnetic levitation applications, because it has a high magnetic irreversibility field Hirr at liquid nitrogen temperature, and can grow into large grains. The levitation force of YBCO bulk is proportional to the critical current density (Jc) and grain radius (r)[1], so higher Jc and r are appreciated for YBCO bulks to achieve higher levitation force. Now single-domain YBCO bulks up to s… 相似文献