全文获取类型
收费全文 | 23903篇 |
免费 | 2244篇 |
国内免费 | 931篇 |
专业分类
电工技术 | 1214篇 |
综合类 | 1034篇 |
化学工业 | 4128篇 |
金属工艺 | 1516篇 |
机械仪表 | 1776篇 |
建筑科学 | 1308篇 |
矿业工程 | 608篇 |
能源动力 | 941篇 |
轻工业 | 1677篇 |
水利工程 | 314篇 |
石油天然气 | 973篇 |
武器工业 | 115篇 |
无线电 | 3265篇 |
一般工业技术 | 3954篇 |
冶金工业 | 1375篇 |
原子能技术 | 207篇 |
自动化技术 | 2673篇 |
出版年
2024年 | 108篇 |
2023年 | 483篇 |
2022年 | 800篇 |
2021年 | 1158篇 |
2020年 | 869篇 |
2019年 | 724篇 |
2018年 | 865篇 |
2017年 | 843篇 |
2016年 | 864篇 |
2015年 | 990篇 |
2014年 | 1204篇 |
2013年 | 1498篇 |
2012年 | 1596篇 |
2011年 | 1761篇 |
2010年 | 1472篇 |
2009年 | 1459篇 |
2008年 | 1314篇 |
2007年 | 1093篇 |
2006年 | 1024篇 |
2005年 | 894篇 |
2004年 | 701篇 |
2003年 | 682篇 |
2002年 | 643篇 |
2001年 | 528篇 |
2000年 | 501篇 |
1999年 | 494篇 |
1998年 | 502篇 |
1997年 | 380篇 |
1996年 | 346篇 |
1995年 | 278篇 |
1994年 | 224篇 |
1993年 | 143篇 |
1992年 | 119篇 |
1991年 | 85篇 |
1990年 | 80篇 |
1989年 | 68篇 |
1988年 | 44篇 |
1987年 | 36篇 |
1986年 | 38篇 |
1985年 | 28篇 |
1984年 | 24篇 |
1983年 | 13篇 |
1982年 | 9篇 |
1981年 | 18篇 |
1980年 | 13篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 11篇 |
1976年 | 13篇 |
1975年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
DNA and amphiphilic N,N,N‐trimethyl‐N‐hexadecylammonium bromide (THAB) were stoichiometrically mixed together to produce a DNA–lipid complex, which was dissolved in dimethyl sulfoxide (DMSO) at 65°C and then crosslinked with isophorone diisocyanate (IPDI). The obtained organogel swelled reversibly in DMSO, responding to the variation of temperature. Interestingly, we observed that the gel exhibited a temperature‐dependent shape‐memory behavior. Above 65°C, whatever the shape the gel was deformed to, it could retain the new shape as the temperature was decreased to room temperature, while, when the gel was heated to 65°C again, it could recover its initial shape. The shape‐memory characteristic is supposedly originated from the transition between the close‐packed and the destroyed DNA/lipid conformation. The elastic urethane crosslinking bonds between base‐pair sites act as a fixing phase. The gel holds promise in its application as a gentle actuator. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 259–263, 2002 相似文献
112.
Polyurethane acrylate anionomer (PUAA)/silica composite gels were prepared by the sol‐gel reaction of tetraethoxysilane (TEOS) and methacryloxypropyl trimethoxysilane (MPTS) incorporated to PUAA gels by using a swelling method. The formation and structure of composites were confirmed by FTIR, X‐ray diffraction, and SEM. As a result, we found that silica components in composites are located within the ionic domains of their gels and interacted with PUAA via hydrogen bonding. This drastically enhanced the mechanical properties of the composites. Mechanical properties are also improved by MPTS, because MPTS improves the dispersibility and adhesion of silica components in PUAA/silica composite gels. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2327–2334, 2002 相似文献
113.
114.
Kyeong Joong Kim Jong-Yeul Suh Moon Gi Kang Kyu Tae Park 《Electronics letters》1998,34(13):1302-1303
The boundary is approximated by a polygon which can be encoded with the smallest number of bits for maximum distortion. The temporal redundancy between two successive frames is efficiently removed with the proposed scheme, resulting in a lower bit rate than the conventional algorithms 相似文献
115.
Simultaneous polymerization and doping of pyrrole have been carried out in the presence of a halogenic electron acceptor, bromine (Br2) or iodine (I2), in aqueous dispersion or in a two-phase solvent system. The morphology of the polypyrrole (PPY) so produced is granular and porous. The electrical conductivity of the PPY-I2 charge transfer (CT) complex is of the order of 101 ohm−1 cm−1 while that of the PPY-Br2 complex is about one order of magnitude less. Both complexes are stable in the atmosphere. The physicochemical properties of the PPY-I2 and PPY-Br2 CT complexes prepared under various experimental conditions are examined in detail. 相似文献
116.
掺杂对低压ZnO压敏陶瓷材料显微结构及性能的影响 总被引:1,自引:0,他引:1
本文探讨了多种金属氧化物对ZnO-Bi_2O_3-TiO_2系材料的改性作用和对其微结构的影响,为得到预定性能的材料提供了掺杂方面的实验依据。 相似文献
117.
Keon Woo Kang Jaemin Ann Hwang Soo Lee 《Electronics letters》1994,30(25):2153-2154
The authors propose a method to estimate the synchronisation offset for orthogonal frequency division multiplexing (OFDM) frame alignment without resort to pilot tones. A decision-directed maximum-likelihood estimation of frame synchronisation offset is derived, and the performance of the proposed scheme is confirmed by computer simulation for QAM systems 相似文献
118.
钒冶炼焙烧添加剂选择研究 总被引:1,自引:0,他引:1
对小型钒冶炼厂焙烧工艺所用添加剂进行改进的可能性进行了探讨,研究了几种常用添加剂的焙烧条件,分析比较了其性能,提出用NaCl-Na2CO3作焙烧添加剂替代NaCl可大幅度减少大气污染,提高冶钒转化率;且不改变工艺流程,无需设备投资,具有较好的经济效益和环境效益。 相似文献
119.
Suk Lee Kyung Chang Lee Man Hyung Lee Harashima F. 《Industrial Electronics, IEEE Transactions on》2002,49(3):693-701
This paper focuses on a method to integrate mobile devices such as a mobile robot, automated guided vehicle, and unmanned container transporter to form an automated material handling system. In this paper, the stationary devices are connected via a Profibus network while the mobile devices are communicating via an IEEE 802.11 wireless LAN. In order to integrate these two networks, a protocol converter is developed on a PC platform that runs two interacting processes with shared internal buffers. The protocol converter performs a role of translator between two different protocols by converting the format of a data frame. In addition to this basic conversion function, the protocol converter has a virtual polling algorithm to reduce the uncertainty involved in accessing the wireless network. Finally, the integrated network. of Profibus and IEEE 802.11 is experimentally evaluated for its data latency and throughput, which shows the feasibility of the Profibus-IEEE 802.11 network for industrial applications involving mobile devices 相似文献
120.
Analysis and characterization of traveling-wave electrode in electroabsorption modulator for radio-on-fiber application 总被引:1,自引:0,他引:1
Jiyoun Lim Young-Shik Kang Kwang-Seong Choi Jong-Hyun Lee Sung-Bock Kim Jeha Kim 《Lightwave Technology, Journal of》2003,21(12):3004-3010
Comparing with a lumped electroabsorption modulator (EAM), we show the merits of a long EAM with traveling-wave electrode with high radio-frequency (RF) gain that could be used in high-frequency analog application. By terminating the RF output port with the characteristic impedance of 30 /spl Omega/, the device exhibited a large enhancement of 6 dB above 10 GHz in the electrical-to-optical response and a wide fractional bandwidth as estimated from simulation. In addition, an input impedance matching circuit of stub embedded on the device chip was found to be very effective for improving RF characteristics in the narrow band of frequency. 相似文献