全文获取类型
收费全文 | 437111篇 |
免费 | 8373篇 |
国内免费 | 3326篇 |
专业分类
电工技术 | 7912篇 |
技术理论 | 3篇 |
综合类 | 4039篇 |
化学工业 | 59980篇 |
金属工艺 | 18077篇 |
机械仪表 | 14088篇 |
建筑科学 | 12113篇 |
矿业工程 | 2157篇 |
能源动力 | 11393篇 |
轻工业 | 38258篇 |
水利工程 | 4332篇 |
石油天然气 | 4197篇 |
武器工业 | 178篇 |
无线电 | 57041篇 |
一般工业技术 | 80852篇 |
冶金工业 | 73142篇 |
原子能技术 | 4911篇 |
自动化技术 | 56137篇 |
出版年
2022年 | 2054篇 |
2021年 | 3348篇 |
2020年 | 2489篇 |
2019年 | 2837篇 |
2018年 | 18077篇 |
2017年 | 17036篇 |
2016年 | 14031篇 |
2015年 | 4342篇 |
2014年 | 6173篇 |
2013年 | 17168篇 |
2012年 | 13060篇 |
2011年 | 22896篇 |
2010年 | 19020篇 |
2009年 | 17649篇 |
2008年 | 19487篇 |
2007年 | 20440篇 |
2006年 | 12318篇 |
2005年 | 12175篇 |
2004年 | 11405篇 |
2003年 | 11136篇 |
2002年 | 9843篇 |
2001年 | 9976篇 |
2000年 | 9124篇 |
1999年 | 9961篇 |
1998年 | 25266篇 |
1997年 | 17216篇 |
1996年 | 13154篇 |
1995年 | 9587篇 |
1994年 | 8393篇 |
1993年 | 8178篇 |
1992年 | 5511篇 |
1991年 | 5248篇 |
1990年 | 4858篇 |
1989年 | 4562篇 |
1988年 | 4341篇 |
1987年 | 3378篇 |
1986年 | 3281篇 |
1985年 | 3958篇 |
1984年 | 3498篇 |
1983年 | 3178篇 |
1982年 | 2947篇 |
1981年 | 2970篇 |
1980年 | 2690篇 |
1979年 | 2471篇 |
1978年 | 2234篇 |
1977年 | 2654篇 |
1976年 | 3613篇 |
1975年 | 1849篇 |
1974年 | 1731篇 |
1973年 | 1782篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Wastewater discharge from coal refining plants contains a number of biologically toxic compounds; 2000-2500 mg/l of COD of which 40% is composed of phenol, 100-400 mg/l of thiocyanate, 10-40 mg/l of cyanide, 100-250 mg/l of NH4+-N and 150-300 mg/l of total nitrogen. In order to treat this kind of high strength wastewater, we have developed a high performance biofilm process using fluidizing bio-carriers of the tube chip type. The fluidizing biofilm carriers are made of a composite of polyethylene and several inorganic materials, whose density is controlled at 0.97-0.98 g/ml. The fluidizing biofilm carriers show sound fluidization characteristics inside bioreactors. The wastewater is treated using three consecutive series reactors in oxic-anoxic-oxic arrangement. Each reactor is charged with the fluidizing biofilm carriers of 50 vol%. Furthermore, newly cultured active microorganisms for the thiocyanate biodegradation are added in the biofilm process. At total hydraulic retention time of 2.2 days, this process can achieve steady state removal efficiencies: COD, 99%; thiocyanate, 99%; NH4+-N, 99% and total nitrogen, 90%. 相似文献
972.
Weiming Shen S.Y.T. Lang Lihui Wang 《IEEE transactions on systems, man and cybernetics. Part C, Applications and reviews》2005,35(3):371-381
Global competition is driving manufacturing companies to change the way they do business. New kinds of shop floor control systems need to be implemented for these companies to respond quickly to changing shop floor environments and customer demands. This paper presents a new concept called iShopFloor-an intelligent shop floor based on the Internet, web, and agent technologies. It focuses on the implementation of distributed intelligence in the manufacturing shop floor. The proposed approach provides the framework for components of a complex control system to work together as a whole rather than as a disjoint set. It encompasses both information architecture and integration methodologies. The paper introduces the basic concept of iShopFloor, a generic system architecture, and system components. It also describes the implementation of eXtensible Markup Language message services in iShopFloor and the application of intelligent agents to distributed manufacturing scheduling. A prototype environment is presented, and some implementation issues are discussed. 相似文献
973.
Hadjem A. Lautru D. Dale C. Man Fai Wong Hanna V.F. Wiart J. 《Microwave Theory and Techniques》2005,53(1):4-11
This paper gives a first comparison of specific absorption rate (SAR) induced in a child-sized (CS) head and an adult head using a dual-band mobile phone. In the second study, the visible human head is considered and comparison of SAR induced in a CS or child-like (CL) head and an adult head using a dual-band mobile phone is given. All the peaks of average SAR over a mass of 10 and 1 g in the head and the power budget are determined in the two comparisons using the finite-difference time-domain method. The differences between the results for adult and CS or CL heads are given at 900 and 1800 MHz. No important differences are noted for the peak SAR averaged over 10 g (SAR10 g), between the two adult head models, as well as between the two child head models. The peak SAR10 g in the brain of the CS or CL head is slightly more significant than that for the adult one. 相似文献
974.
J.-P. Han S.M. Koo E.M. Vogel E.P. Gusev C. DEmic C.A. Richter J.S. Suehle 《Microelectronics Reliability》2005,45(5-6):783
Anomalous threshold voltage roll-up behavior, commonly referred as reverse short channel effect (RSCE), has been observed in high-k (HfO2 on SiON buffer, Al2O3 on SiON buffer) gated submicron nMOSFETs, while the SiO2 or SiON control samples show normal short channel effect (SCE) behavior. The possible causes such as inhomogeneous channel doping profile and gate oxide thickness variation near S/D ends have been ruled out. The results indicate that interface trap density that dependents on channel length is the main cause of the RSCE observed here. In addition, oxide charge also plays a role. 相似文献
975.
Dielectric reliability in Al2O3(2–3.1nm)–HfO2(3nm) stack capacitor with Metal–Insulator–Si(MIS) structure is investigated in this paper. We propose an optimized capacitor process through the Time–Dependent Dielectric Breakdown (TDDB) data under various process conditions. Furthermore, due to asymmetric current at both negative and positive voltage stress polarities, we show different lifetime extrapolation by a fluence–driven model. As a result, the maximum allowed operating voltage is projected to be 1.7V (failure rate 10ppm during 10year @ 85°C) for Data “0” retention lifetime. 相似文献
976.
This letter extends a low-density parity-check code construction using maximum-length linear congruential sequences by Prabhakar and Narayanan. The corresponding bipartite graphs of their construction were guaranteed to have a girth larger than four by a sufficient condition. However, their sufficient condition was limited to regular codes and data-node degree equal to three. The extension in this letter allows arbitrary data-node degrees and is applicable to irregular codes. Further, simpler sufficient conditions are derived and larger girths are addressed. 相似文献
977.
Peak-to-average power reduction in space division multiplexing based OFDM systems through spatial shifting 总被引:2,自引:0,他引:2
A new method to reduce the peak-to-average power ratio (PAPR) in space division multiplexing systems applying orthogonal frequency division multiplexing is proposed. The method applies spatial shifting to partial transmit sequences to achieve a decreased PAPR on all transmit branches. 相似文献
978.
A new frequency notched ultra-wideband microstrip slot antenna with a parasitic tuning stub is proposed. The antenna is similar in configuration to a conventional microstrip slot antenna; by introducing a parasitic open-circuit tuning stub, flexible frequency notched function is achieved. Several properties of the antenna, such as frequency notched function, antenna transfer function and gain, have been investigated. As is reported, the operation bandwidth of the antenna is 2.91-11.16 GHz, in which a frequency notched band of 5.10-5.85 GHz has been achieved. Furthermore, good ultra-wideband linear transmission performance over the entire operation frequency range has also been achieved. 相似文献
979.
A simple and successful design method that yields a wideband and compact antenna without a ground plane is proposed. The antenna, referred to as the folded loop antenna, can, with the right parameters, achieve wideband characteristics. Calculated and measured results agree well and more than 50% bandwidth (return loss /spl les/-10 dB) is obtained. 相似文献
980.
J. Chen J. B. Xu K. Xue J. An N. Ke W. Cao H. B. Xia J. Shi D. C. Tian 《Microelectronics Reliability》2005,45(1):137-142
Transition-metal compound TiC60 thin films were grown by co-deposition from two separated sources of fullerene C60 powder and titanium. Study of structural properties of the films, by Raman spectroscopy, atomic force microscopy, and scanning tunneling spectroscopy reveals that the films have a deformed C60 structure with certain amount of sp3 bonds and a rough surface with a large number of nanoclusters. z–V tunnelling spectroscopic measurements suggest that several charge transport mechanisms are involved in as the tip penetrates into the thin film. Conventional field electron emission (FEE) measurements show a high emission current density of 10 mA/cm2 and a low turn-on field less than 8 V/μm, with the field enhancement factors being 659 and 1947 for low-field region and high-field region, respectively. By exploiting STM tunneling spectroscopy, local FEE on nanometer scale has also been characterized in comparison with the conventional FEE. The respective field enhancement factors are estimated to be 99–355 for a gap varying from 36 to 6 nm. The enhanced FEE of TiC60 thin films can be ascribed to structural variation of C60 in the films and the electrical conducting paths formed by titanium nanocrystallites embedded in C60 matrix. 相似文献