全文获取类型
收费全文 | 134260篇 |
免费 | 12525篇 |
国内免费 | 14031篇 |
专业分类
化学 | 71159篇 |
晶体学 | 1205篇 |
力学 | 3189篇 |
综合类 | 1024篇 |
数学 | 14875篇 |
物理学 | 25061篇 |
无线电 | 44303篇 |
出版年
2024年 | 300篇 |
2023年 | 1254篇 |
2022年 | 2399篇 |
2021年 | 2768篇 |
2020年 | 3329篇 |
2019年 | 3093篇 |
2018年 | 2888篇 |
2017年 | 4352篇 |
2016年 | 4592篇 |
2015年 | 4521篇 |
2014年 | 6196篇 |
2013年 | 9504篇 |
2012年 | 9542篇 |
2011年 | 8797篇 |
2010年 | 6931篇 |
2009年 | 8499篇 |
2008年 | 8984篇 |
2007年 | 9480篇 |
2006年 | 8743篇 |
2005年 | 7383篇 |
2004年 | 6663篇 |
2003年 | 5617篇 |
2002年 | 6322篇 |
2001年 | 3983篇 |
2000年 | 3614篇 |
1999年 | 3187篇 |
1998年 | 2747篇 |
1997年 | 2252篇 |
1996年 | 1891篇 |
1995年 | 1801篇 |
1994年 | 1500篇 |
1993年 | 1253篇 |
1992年 | 1147篇 |
1991年 | 792篇 |
1990年 | 644篇 |
1989年 | 604篇 |
1988年 | 433篇 |
1987年 | 328篇 |
1986年 | 303篇 |
1985年 | 262篇 |
1984年 | 266篇 |
1983年 | 148篇 |
1982年 | 233篇 |
1981年 | 194篇 |
1980年 | 204篇 |
1979年 | 194篇 |
1978年 | 177篇 |
1977年 | 128篇 |
1976年 | 117篇 |
1973年 | 69篇 |
排序方式: 共有10000条查询结果,搜索用时 671 毫秒
991.
K. Yasuda Y. Tomita Y. Masuda T. Ishiguro Y. Kawauchi H. Morishita Y. Agata 《Journal of Electronic Materials》2002,31(7):785-790
Iodine doping of CdTe layers grown on (100) GaAs by metal-organic vapor phase epitaxy (MOVPE) was studied using diethyltelluride
(DETe) and diisopropyltelluride (DiPTe) as tellurium precursors and ethyliodine (EI) as a dopant. Electron densities of doped
layers increased gradually with decreasing the growth temperature from 425°C to 325°C. Doped layers grown with DETe had higher
electron densities than those grown with DiPTe. When the hot-wall temperature was increased from 200°C to 250°C at the growth
temperature of 325°C, doped layers grown with DETe showed an increase of the electron density from 3.7×1016 cm−3 to 2.6×1018 cm−3. On the other hand, such an increase of the electron density was not observed for layers grown with DiPTe. The mechanisms
for different doping properties for DETe and DiPTe were studied on the basis of the growth characteristics for these precursors.
Higher thermal stability of DETe than that of DiPTe was considered to cause the difference of doping properties. With increasing
the hot-wall temperature from 200°C to 250°C, the effective ratio of Cd to Te species on the growth surface became larger
for layers grown with DETe than those grown with DiPTe. This was considered to decrease the compensation of doped iodine and
to increase the electron density of layers grown with DETe. The effective ratio of Cd to Te species on the growth surface
also increased with decreasing growth temperature. This was considered to increase the electron density with decreasing growth
temperature. 相似文献
992.
993.
NGN问题及其发展策略考虑 总被引:1,自引:0,他引:1
本文在分析讨论NGN的背景,目前存在的争议基础上,结合中国国情,重点对NGN框架目标进行了展望并提出了发展策略考虑。 相似文献
994.
995.
996.
用小波变换抑制SAR图像中的斑点噪声 总被引:3,自引:0,他引:3
抑制合成孔径雷达图像中的斑点噪声一直是处理图像并得到准确图像信息的难点,提出了一种基于小波变换抑制合成孔径雷达(SAR)图像中的斑点噪声的方法,对原有的小波变换方法作了改进,能更好地保留图像的边缘信息,并能简化计算量。在仿真实验中使用了合成的模拟图像和真实的合成孔径雷图像,并与以往的小波去噪滤波方法以及一些经典的斑点噪声滤波方法(包括中值滤波,Lee滤波,Frost滤波)进行比较,在综合考虑了滤波算法在均匀区域对斑点噪声的抑制能力以及保留边缘信息能力的情况下,提出的算法有更好的效果。 相似文献
997.
David Swanson William P. Ziemer 《Calculus of Variations and Partial Differential Equations》2002,14(1):69-84
Let be a connected open set, . We give a sufficient condition for a mapping , , to have the property that sgn is almost everywhere of one sign. Following the work of Müller, Spector, and Tang [MST], we give an application of our results
to the theory of non-linear elasticity.
Received: 13 October 2000 / Accepted: 23 January 2001 / Published online: 4 May 2001 相似文献
998.
Backlund transformation and variable separation solutions for the generalized Nozhnik—Novikov—Veselov equation
下载免费PDF全文
![点击此处可从《中国物理》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Using the extended homogeneous balance method, the B?cklund transformation for a (2+1)-dimensional integrable model, the generalized Nizhnik-Novikov-Veselov (GNNV) equation, is first obtained. Also, making use of the B?cklund transformation, the GNNV equation is changed into three equations: linear, bilinear and trilinear form equations. Starting from these three equations, a rather general variable separation solution of the model is constructed. The abundant localized coherent structures of the model can be induced by the entrance of two variable-separated arbitrary functions. 相似文献
999.
低相噪,低杂波数字锁相环路滤波器的设计 总被引:11,自引:0,他引:11
较详细地分析数字锁相频率合成器的相位噪声,着重用控制论方法对低相噪、低杂波锁相环的环路滤波器进行设计,并用某S波段频率合成器的实验结果进行了验证。 相似文献
1000.
Pd-Ge based ohmic contact to n-GaAs with a TiW diffusion barrier was investigated. Electrical analysis as well as Auger electron
spectroscopy and the scanning electron microscopy were used to study the contact after it was subjected to different furnace
and rapid thermal annealing and different aging steps. All analyses show that TiW can act as a good barrier metal for the
Au/Ge/Pd/n-GaAs contact system. A value of 1.45 × 10−6 Ω-cm2 for the specific contact resistance was obtained for the Au/TiW/Ge/Pd/n-GaAs contact after it was rapid thermally annealed
at 425°C for 90 s. It can withstand a thermal aging at 350°C for 40 h with its ρc increasing to 2.94 × 10−6Ω-cm2 and for an aging at 410°C for 40 h with its ρc increasing to 1.38 × 10−5 Ω-cm2. 相似文献