全文获取类型
收费全文 | 425416篇 |
免费 | 5819篇 |
国内免费 | 1319篇 |
专业分类
电工技术 | 7917篇 |
综合类 | 466篇 |
化学工业 | 61620篇 |
金属工艺 | 16827篇 |
机械仪表 | 13358篇 |
建筑科学 | 10258篇 |
矿业工程 | 2260篇 |
能源动力 | 10719篇 |
轻工业 | 36606篇 |
水利工程 | 4496篇 |
石油天然气 | 7353篇 |
武器工业 | 75篇 |
无线电 | 52815篇 |
一般工业技术 | 83060篇 |
冶金工业 | 78714篇 |
原子能技术 | 9389篇 |
自动化技术 | 36621篇 |
出版年
2021年 | 3359篇 |
2019年 | 3350篇 |
2018年 | 5554篇 |
2017年 | 5708篇 |
2016年 | 5999篇 |
2015年 | 3839篇 |
2014年 | 6559篇 |
2013年 | 18839篇 |
2012年 | 10732篇 |
2011年 | 14696篇 |
2010年 | 11690篇 |
2009年 | 13138篇 |
2008年 | 13909篇 |
2007年 | 13929篇 |
2006年 | 12319篇 |
2005年 | 11391篇 |
2004年 | 10971篇 |
2003年 | 10744篇 |
2002年 | 10081篇 |
2001年 | 10230篇 |
2000年 | 9863篇 |
1999年 | 10098篇 |
1998年 | 23758篇 |
1997年 | 17118篇 |
1996年 | 13478篇 |
1995年 | 10276篇 |
1994年 | 9232篇 |
1993年 | 9008篇 |
1992年 | 7100篇 |
1991年 | 6694篇 |
1990年 | 6387篇 |
1989年 | 6219篇 |
1988年 | 5945篇 |
1987年 | 5210篇 |
1986年 | 5025篇 |
1985年 | 5904篇 |
1984年 | 5490篇 |
1983年 | 5022篇 |
1982年 | 4623篇 |
1981年 | 4832篇 |
1980年 | 4445篇 |
1979年 | 4437篇 |
1978年 | 4262篇 |
1977年 | 4960篇 |
1976年 | 6382篇 |
1975年 | 3864篇 |
1974年 | 3815篇 |
1973年 | 3826篇 |
1972年 | 3056篇 |
1971年 | 2857篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Yu. A. Brodskii V. I. Bazikov I. V. Zubkov A. I. Krylov V. D. Stepanenko 《Chemical and Petroleum Engineering》2006,42(9-10):552-559
Modern designs are examined, and technical data presented for vibratory electric and convection driers, driers with infra-red sources, and steam driers. 相似文献
992.
Tian Yang Lipson S. O'Brien J.D. Deppe D.G. 《Photonics Technology Letters, IEEE》2005,17(11):2244-2246
We report on the demonstration of optically pumped photonic crystal lasers with InAs quantum dot active regions operating at room temperature near 1310 nm. Absorbed threshold pump powers as low as 25 /spl mu/W are observed. We also extract a characteristic temperature of 17 K, which is attributed to limitations caused by surface recombination. 相似文献
993.
Multicarrier spread spectrum (MC-SS) is an alternative to the conventional spread spectrum (SS) techniques that behave significantly better when the system is subject to narrow- or partial-band interference. However, successful implementation of the optimum detector requires knowledge of noise and interference variance in each subcarrier band. We propose a suboptimal detector for MC-SS that keeps the significant gain of MC-SS over the conventional SS, with a relatively low loss compared with the optimum MC-SS detector. Theoretical analysis and computer simulations that corroborate the theory are presented. 相似文献
994.
A. A. Kherani B. J. Prabhu K. E. Avrachenkov E. Altman 《Telecommunication Systems》2005,30(4):321-350
We study an Adaptive Window Protocol (AWP) with general increase and decrease profiles in the presence of window dependent
random losses. We derive a steady-state Kolmogorov equation, and then obtain its solution in analytic form for particular
TCP versions proposed for high speed networks, such as Scalable TCP and HighSpeed TCP. We also relate window evolution under
an AWP to workload process in queueing systems; this observation gives us a way to compare various AWP protocols. 相似文献
995.
On the complexity of sphere decoding in digital communications 总被引:14,自引:0,他引:14
Sphere decoding has been suggested by a number of authors as an efficient algorithm to solve various detection problems in digital communications. In some cases, the algorithm is referred to as an algorithm of polynomial complexity without clearly specifying what assumptions are made about the problem structure. Another claim is that although worst-case complexity is exponential, the expected complexity of the algorithm is polynomial. Herein, we study the expected complexity where the problem size is defined to be the number of symbols jointly detected, and our main result is that the expected complexity is exponential for fixed signal-to-noise ratio (SNR), contrary to previous claims. The sphere radius, which is a parameter of the algorithm, must be chosen to ensure a nonvanishing probability of solving the detection problem. This causes the exponential complexity since the squared radius must grow linearly with problem size. The rate of linear increase is, however, dependent on the noise variance, and thus, the rate of the exponential function is strongly dependent on the SNR. Therefore sphere decoding can be efficient for some SNR and problems of moderate size, even though the number of operations required by the algorithm strictly speaking always grows as an exponential function of the problem size. 相似文献
996.
Zogas D.A. Karagiannidis G.K. Kotsopoulos S.A. 《Wireless Communications, IEEE Transactions on》2005,4(2):374-379
Motivated by the importance of Nakagami-n (Rice) and Nakagami-q (Hoyt) statistical models to describe channel fading in land, mobile, terrestrial, and satellite telecommunications, we present an alternative moments-based approach to the performance analysis of equal-gain combining (EGC) receivers over independent, not necessarily identically distributed Rice- and Hoyt-fading channels. Exact closed-form expressions for the moments of the signal-to-noise ratio (SNR) at the output of the combiner are derived and significant performance criteria such as, the average output SNR, the amount of fading and the spectral efficiency at the low power regime, are studied. Moreover, using Pade rational approximation to the moment-generating function of the output SNR, the average symbol error probability and the outage probability are evaluated. We also study the suitability of modeling a Hoyt-fading environment by a properly chosen Nakagami-m model, as far as the error performance of the EGC is concerned. 相似文献
997.
Towards real-time business intelligence 总被引:1,自引:0,他引:1
Analysing data to predict market trends of products and services and to improve performances of enterprise business systems has always been part of running a competitive business. But it is becoming essential nowadays that not only is the analysis done on real-time data, but also actions in response to analysis results can be performed in real time and instantaneously change parameters of business processes. This paper discusses issues and problems of current business intelligence systems, and then outlines our vision of future real-time business intelligence. We present a list of emerging technologies which could contribute to the realisation of real-time business intelligence and some examples of applying them to improve BT’s systems and services. 相似文献
998.
Turner S.E. Elder R.B. Jr. Jansen D.S. Kotecki D.E. 《Microwave and Wireless Components Letters, IEEE》2005,15(3):144-146
A 41-GHz 4-b adder-accumulator test circuit implemented in InP double heterojunction bipolar transistor (DHBT) technology using 624 transistors is reported. High clock rates are obtained by combining the logic functions into pipelined latches. The adder-accumulator contains a single-level parallel-gated carry circuit that is used as a step toward reduced power consumption. The carry circuit has a maximum clock frequency of 55 GHz. The accumulator architecture employs modular, pipelined 2-b adders and is cascadable to 2 N-bits. The test circuit includes a 4-b digital to analog converter (DAC) that facilitates demonstration of high-speed operation. 相似文献
999.
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
1000.
A high PAPR is a main drawback of OFDM. There are many methods for reducing the PAPR with an ultimate goal of reducing the PAPR as much as possible. It is shown that if, among other factors, the power efficiency-PAPR relationship of the power amplifier is also taken into account, then there exists a PAPR level for which the BER reaches a minimal value. This PAPR may be used as a definition of an efficient PAPR. The efficient PAPR is not necessary the lowest possible value of PAPR. 相似文献