全文获取类型
收费全文 | 22057篇 |
免费 | 3775篇 |
国内免费 | 3104篇 |
专业分类
化学 | 16894篇 |
晶体学 | 265篇 |
力学 | 1195篇 |
综合类 | 220篇 |
数学 | 2660篇 |
物理学 | 7702篇 |
出版年
2024年 | 50篇 |
2023年 | 471篇 |
2022年 | 586篇 |
2021年 | 765篇 |
2020年 | 955篇 |
2019年 | 993篇 |
2018年 | 785篇 |
2017年 | 674篇 |
2016年 | 1066篇 |
2015年 | 1075篇 |
2014年 | 1281篇 |
2013年 | 1663篇 |
2012年 | 2018篇 |
2011年 | 1985篇 |
2010年 | 1385篇 |
2009年 | 1238篇 |
2008年 | 1400篇 |
2007年 | 1269篇 |
2006年 | 1186篇 |
2005年 | 1068篇 |
2004年 | 818篇 |
2003年 | 735篇 |
2002年 | 833篇 |
2001年 | 700篇 |
2000年 | 480篇 |
1999年 | 458篇 |
1998年 | 411篇 |
1997年 | 332篇 |
1996年 | 352篇 |
1995年 | 278篇 |
1994年 | 269篇 |
1993年 | 231篇 |
1992年 | 225篇 |
1991年 | 180篇 |
1990年 | 144篇 |
1989年 | 130篇 |
1988年 | 87篇 |
1987年 | 70篇 |
1986年 | 57篇 |
1985年 | 56篇 |
1984年 | 52篇 |
1983年 | 33篇 |
1982年 | 23篇 |
1981年 | 17篇 |
1980年 | 16篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1957年 | 5篇 |
1936年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
81.
Based on solving the couple mode equation numerically, the characterization of the signal power on the gate power was analyzed. And the relationship of the tolerance of the grating period and the bulk temperature on the interaction length was analyzed. 相似文献
82.
Low-loss and rugged distal tips for CO2 laser have been proposed and fabricated based on a commercially available stainless steel (St) pipe. A method of smoothening the inner surface of the St pipe with a rough inner surface is put forward. Fabrication parameters, transmission properties, and mechanical strength of the cyclic olefin polymer-coated silver hollow St distal tip are experimentally discussed. 相似文献
83.
This paper is to investigate the approximate confidence limits of the reliability performances (such as failure rate, reliability function and average life) for a cold standby series system. The Bayesian approximate upper confidence limit of failure rate is obtained firstly, and next Bayesian approximate lower confidence limits for reliability function and average life are presented. The expressions for calculating Bayesian lower confidence limits of the reliability function and average life are also obtained, and an illustrative example is examined numerically by means of the Monte-Carlo simulation. Finally, the accuracy of confidence limits is discussed. 相似文献
84.
ChunXiaLI YingXiaLI LingBoYU HuaZHANG SiftDongCHU HuaShiGUAN 《中国化学快报》2003,14(8):776-778
A convenient synthetic route was developed for the synthesis of the novel glycolipids: 1,2-di-O-acyl-3-O-(2‘-acylamide-2‘-denxy-ct-D-glucopyranosyl)-sn-glycerols. 10 new compounds of glycolipids with different acyl groups were obtained. 相似文献
85.
5‐Methylene‐2‐oxazolidinone (1) and 5‐methylene‐1,3‐thiazolidine‐2‐thione (4) react with various isocyanates to give the corresponding urethanes 3 and 5 in high yields in the presence of palladium(0) or palladium(II) catalyst under mild reaction conditions. A mechanism is proposed. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
86.
87.
对不同的本底真空条件下,采用甚高频等离子体增强化学气相沉积技术沉积的氢化微晶硅(μc_Si∶H)薄膜中的氧污染问题进行了比较研究.对不同氧污染条件下制备的薄膜样品的x射线光电子能谱与傅里叶变换红外吸收光谱测量结果表明:μc_Si∶H薄膜中,氧以Si—O,O—O和O—H三种不同的键合模式存在,不同的键合模式源自不同的物理机理.μc_Si∶H薄膜的Raman光谱、电导率与激活能的测量结果进一步显示:沉积过程中氧污染程度的不同,对μc_Si∶H薄膜的结构特性与电学特性产生显著影响;而不同氧污染对μc_Si∶H薄膜电学特性的影响不同于氢化非晶硅(a_Si:H)薄膜.
关键词:
氢化微晶硅薄膜
甚高频等离子体增强化学气相沉积
氧污染 相似文献
88.
YunFei Liu ShengCai Shi ShengLin Yu 《International Journal of Infrared and Millimeter Waves》2003,24(12):2069-2077
When electromagnetic waves propagate through a wire grid, there will be some evanescent space harmonics generated around the wire grid. In this paper, we mainly investigate their effects on the transmission characteristics of a Gaussian beam by cylindrical wire grids. The results are compared with those without taking account of evanescent space-harmonics. 相似文献
89.
90.
The properties of pulsed laser vapor doping on p-Si(1 0 0) with a KrF (248 nm) excimer pulsed laser (248 nm) and BCl3 gas are reported in this paper. The doped samples are characterized by the resistance measured using a four-probe method, since the sheet resistance changes with the carrier concentration of the sample. The doping effects with the variation of laser energy density, pulse number, and the pressure of BCl3 were investigated in terms of the sheet resistance. In this way, the optimized parameters were obtained and used for the positive heavy doping on p-Si(1 0 0) and p-Si(1 1 1). Then, using a square mesh under the above conditions, an image doping was completed. Finally, the metal–semiconductor Ohmic contacts were realized by plating Ag and Cu films on the doped surface. 相似文献