全文获取类型
收费全文 | 313384篇 |
免费 | 25199篇 |
国内免费 | 14507篇 |
专业分类
电工技术 | 20323篇 |
技术理论 | 12篇 |
综合类 | 21192篇 |
化学工业 | 43790篇 |
金属工艺 | 18832篇 |
机械仪表 | 18425篇 |
建筑科学 | 21672篇 |
矿业工程 | 8464篇 |
能源动力 | 8112篇 |
轻工业 | 20493篇 |
水利工程 | 7006篇 |
石油天然气 | 11796篇 |
武器工业 | 2763篇 |
无线电 | 36902篇 |
一般工业技术 | 39398篇 |
冶金工业 | 11942篇 |
原子能技术 | 3024篇 |
自动化技术 | 58944篇 |
出版年
2024年 | 1204篇 |
2023年 | 3967篇 |
2022年 | 8149篇 |
2021年 | 11011篇 |
2020年 | 8242篇 |
2019年 | 6354篇 |
2018年 | 20936篇 |
2017年 | 21079篇 |
2016年 | 16819篇 |
2015年 | 11357篇 |
2014年 | 13552篇 |
2013年 | 15902篇 |
2012年 | 21206篇 |
2011年 | 28118篇 |
2010年 | 25231篇 |
2009年 | 21589篇 |
2008年 | 22483篇 |
2007年 | 22504篇 |
2006年 | 13719篇 |
2005年 | 12013篇 |
2004年 | 8549篇 |
2003年 | 7232篇 |
2002年 | 6301篇 |
2001年 | 5072篇 |
2000年 | 4325篇 |
1999年 | 3462篇 |
1998年 | 2313篇 |
1997年 | 1876篇 |
1996年 | 1812篇 |
1995年 | 1446篇 |
1994年 | 1183篇 |
1993年 | 770篇 |
1992年 | 641篇 |
1991年 | 448篇 |
1990年 | 349篇 |
1989年 | 288篇 |
1988年 | 228篇 |
1987年 | 142篇 |
1986年 | 121篇 |
1985年 | 67篇 |
1984年 | 51篇 |
1982年 | 45篇 |
1981年 | 50篇 |
1980年 | 51篇 |
1968年 | 50篇 |
1966年 | 46篇 |
1965年 | 46篇 |
1959年 | 54篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
In this paper we investigated the BER performance of DS-CDMA using various chip-waveforms, which include three time-limited chip-waveforms and two band-limited chip-waveforms. Closed-form formulae were derived for evaluating the achievable bit-error rate performance with the aid of the standard Gaussian approximation, when communicating over a Nakagami-m channel. The time-limited waveforms impose a low implementational complexity, since they maybe over sampled and read from a look-up table. However, they are outperformed by the frequency-domain raised-cosine waveform as well as the optimum waveform specifically designed by Cho and Lehnert for achieving the lowest possible bit error rate 相似文献
2.
设计并实现了一种DVB—T调制器的外码编码器,着重介绍了码流自适应接口、能量扩散、RS编码器及卷积交织器的设计方法,该设计方案最终在Altera的FPGA上进行验证。 相似文献
3.
Introduction
The IEC central office informed in 7/543/AC that the secretariat of TC 7 would be taken over by the Chinese National Committee on January 10, 2003 and affirmed subsequently in 7/544/AC that the secretariat of TC 7 has been taken over by the Chinese National Committee which appointing secretary in Shanghai Electric Cable Research Institute as no objection has been raised by the Standardization Management Board members. It's the first IEC secretariat that assumed by China, with great significance, just as commented by the media that the commitment indicate undoubtedly China is to play a much more active and important role in the world especially after its entry into world trade organization as well as the trend of global economic integration. 相似文献
4.
5.
6.
Ferrite particles coated with biocompatible phases can be used for hyperthermia treatment of cancer. We have synthesized substituted
calcium hexaferrite, which is not stable on its own but is stabilized with small substitution of La. Hexaferrite of chemical
composition (CaO)0.75(La203)0.20(Fe2O3)6 was prepared using citrate gel method. Hydroxyapatite was prepared by precipitating it from aqueous solution of Ca(NO3)2 and (NH4)2HPO4 maintaining pH above 11. Four different methods were used for coating of hydroxyapatite on ferrite particles. SEM with EDX
and X-ray diffraction analysis shows clear evidence of coating of hydroxyapatite on ferrite particles. These coated ferrite
particles exhibited coercive field up to 2 kOe, which could be made useful for hysteresis heating in hyperthermia. Studies
by culturing BHK-21 cells and WBC over the samples show evidence of biocompatibility. SEM micrographs and cell counts give
clear indication of cell growth on the surface of the sample. Finally coated ferrite particle was implanted in Kasaulli mouse
to test its biocompatibility. The magnetic properties and biocompatibility studies show that these hydroxyapatite coated ferrites
could be useful for hyperthermia. 相似文献
7.
Xue‐Yong Liu Xiao‐Bin Ding Zhao‐Hui Zheng Yu‐Xing Peng Albert S
C Chan C
W Yip Xin‐Ping Long 《Polymer International》2003,52(2):235-240
Amphiphilic magnetic microspheres ranging in diameter from 5 to 100 µm were prepared by dispersion copolymerization of styrene and poly(ethylene oxide) vinylbenzyl (PEO‐VB) macromonomer (MPEO) in the presence of Fe3O4 magnetic fluid. The effects of various polymerization parameters on the average particle size were systematically investigated. The average particle size was found to increase with increasing styrene concentration and initiator concentration. It also increased with decreasing stabilizer concentration and molecular weight of MPEO. The content of the hydroxyl groups localized in the microspheres ranged from 0.01 to 0.2 mmol g?1. © 2003 Society of Chemical Industry 相似文献
8.
Chloride doped polyaniline conducting polymer films have been prepared in a protic acid medium (HCl) by potentiodynamic method
in an electrochemical cell and studied by cyclic voltammetry and FTIR techniques. The FTIR spectra confirmed Cl- ion doping in the polymers. The polymerization rate was found to increase with increasing concentration of aniline monomer.
But the films obtained at high monomer concentration were rough having a nonuniform flaky polyaniline distribution. Results
showed that the polymerization rate did not increase beyond a critical HCl concentration. Cyclic voltammetry suggested that,
the oxidation-reduction current increased with an increase in scan rate and that the undoped polyaniline films were not hygroscopic
whereas chloride doped polyaniline films were found to be highly hygroscopic. 相似文献
9.
川合137井大修井工艺技术浅析 总被引:2,自引:0,他引:2
在川合137井的修井作业中,运用了多种修井工具和工艺技术。通过内捞、外捞、强提、倒扣、磨铣、套铣、开钻新井眼和铣锥通井的方法,充分解放了油气层,达到了修井目的。其独特的想法、施工和自制工具的成功应用对今后大修井作业具有很高的参考价值。 相似文献
10.