全文获取类型
收费全文 | 173531篇 |
免费 | 15146篇 |
国内免费 | 7854篇 |
专业分类
电工技术 | 11021篇 |
技术理论 | 12篇 |
综合类 | 11593篇 |
化学工业 | 28808篇 |
金属工艺 | 9803篇 |
机械仪表 | 10612篇 |
建筑科学 | 14593篇 |
矿业工程 | 4891篇 |
能源动力 | 5142篇 |
轻工业 | 11185篇 |
水利工程 | 3115篇 |
石油天然气 | 10229篇 |
武器工业 | 1364篇 |
无线电 | 20234篇 |
一般工业技术 | 20917篇 |
冶金工业 | 7920篇 |
原子能技术 | 1997篇 |
自动化技术 | 23095篇 |
出版年
2024年 | 830篇 |
2023年 | 2984篇 |
2022年 | 5116篇 |
2021年 | 7200篇 |
2020年 | 5389篇 |
2019年 | 4503篇 |
2018年 | 4928篇 |
2017年 | 5645篇 |
2016年 | 4870篇 |
2015年 | 6829篇 |
2014年 | 8320篇 |
2013年 | 10015篇 |
2012年 | 10948篇 |
2011年 | 11694篇 |
2010年 | 10352篇 |
2009年 | 9793篇 |
2008年 | 9718篇 |
2007年 | 9229篇 |
2006年 | 9511篇 |
2005年 | 8186篇 |
2004年 | 5662篇 |
2003年 | 5014篇 |
2002年 | 4898篇 |
2001年 | 4410篇 |
2000年 | 4346篇 |
1999年 | 4643篇 |
1998年 | 3772篇 |
1997年 | 3247篇 |
1996年 | 3039篇 |
1995年 | 2591篇 |
1994年 | 2109篇 |
1993年 | 1522篇 |
1992年 | 1275篇 |
1991年 | 990篇 |
1990年 | 702篇 |
1989年 | 614篇 |
1988年 | 504篇 |
1987年 | 341篇 |
1986年 | 232篇 |
1985年 | 151篇 |
1984年 | 99篇 |
1983年 | 69篇 |
1982年 | 92篇 |
1981年 | 57篇 |
1980年 | 53篇 |
1979年 | 18篇 |
1978年 | 5篇 |
1965年 | 3篇 |
1959年 | 6篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
5.
Xian Suo Xili Cui Lifeng Yang Nan Xu Yuqi Huang Yi He Sheng Dai Huabin Xing 《Advanced materials (Deerfield Beach, Fla.)》2020,32(29):1907601
The design of highly stable and efficient porous materials is essential for developing breakthrough hydrocarbon separation methods based on physisorption to replace currently used energy-intensive distillation/absorption technologies. Efforts to develop advanced porous materials such as zeolites, coordination frameworks, and organic polymers have met with limited success. Here, a new class of ionic ultramicroporous polymers (IUPs) with high-density inorganic anions and narrowly distributed ultramicroporosity is reported, which are synthesized by a facile free-radical polymerization using branched and amphiphilic ionic compounds as reactive monomers. A covalent and ionic dual-crosslinking strategy is proposed to manipulate the pore structure of amorphous polymers at the ultramicroporous scale. The IUPs exhibit exceptional selectivity (286.1–474.4) for separating acetylene from ethylene along with high thermal and water stability, collaboratively demonstrated by gas adsorption isotherms and experimental breakthrough curves. Modeling studies unveil the specific binding sites for acetylene capture as well as the interconnected ultramicroporosity for size sieving. The porosity-engineering protocol used in this work can also be extended to the design of other ultramicroporous materials for the challenging separation of other key gas constituents. 相似文献
6.
The existing analytical average bit error rate (ABER) expression of conventional generalised spatial modulation (CGSM) does not agree well with the Monte Carlo simulation results in the low signal‐to‐noise ratio (SNR) region. Hence, the first contribution of this paper is to derive a new and easy way to evaluate analytical ABER expression that improves the validation of the simulation results at low SNRs. Secondly, a novel system termed CGSM with enhanced spectral efficiency (CGSM‐ESE) is presented. This system is realised by applying a rotation angle to one of the two active transmit antennas. As a result, the overall spectral efficiency is increased by 1 bit/s/Hz when compared with the equivalent CGSM system. In order to validate the simulation results of CGSM‐ESE, the third contribution is to derive an analytical ABER expression. Finally, to improve the ABER performance of CGSM‐ESE, three link adaptation algorithms are developed. By assuming full knowledge of the channel at the receiver, the proposed algorithms select a subset of channel gain vector (CGV) pairs based on the Euclidean distance between all CGV pairs, CGV splitting, CGV amplitudes, or a combination of these. 相似文献
7.
8.
9.
10.