全文获取类型
收费全文 | 353491篇 |
免费 | 28389篇 |
国内免费 | 15491篇 |
专业分类
电工技术 | 20772篇 |
技术理论 | 45篇 |
综合类 | 25354篇 |
化学工业 | 59014篇 |
金属工艺 | 20706篇 |
机械仪表 | 22495篇 |
建筑科学 | 27362篇 |
矿业工程 | 11550篇 |
能源动力 | 9687篇 |
轻工业 | 23707篇 |
水利工程 | 6707篇 |
石油天然气 | 23167篇 |
武器工业 | 2813篇 |
无线电 | 38491篇 |
一般工业技术 | 38982篇 |
冶金工业 | 18022篇 |
原子能技术 | 3646篇 |
自动化技术 | 44851篇 |
出版年
2024年 | 1154篇 |
2023年 | 5216篇 |
2022年 | 9115篇 |
2021年 | 13561篇 |
2020年 | 10154篇 |
2019年 | 8306篇 |
2018年 | 9655篇 |
2017年 | 10816篇 |
2016年 | 9895篇 |
2015年 | 13724篇 |
2014年 | 17323篇 |
2013年 | 20802篇 |
2012年 | 22700篇 |
2011年 | 25177篇 |
2010年 | 22253篇 |
2009年 | 21069篇 |
2008年 | 20661篇 |
2007年 | 19708篇 |
2006年 | 20080篇 |
2005年 | 17684篇 |
2004年 | 11976篇 |
2003年 | 10695篇 |
2002年 | 9906篇 |
2001年 | 8819篇 |
2000年 | 8775篇 |
1999年 | 9377篇 |
1998年 | 7155篇 |
1997年 | 6103篇 |
1996年 | 5783篇 |
1995年 | 4767篇 |
1994年 | 3847篇 |
1993年 | 2598篇 |
1992年 | 2051篇 |
1991年 | 1551篇 |
1990年 | 1218篇 |
1989年 | 980篇 |
1988年 | 807篇 |
1987年 | 484篇 |
1986年 | 386篇 |
1985年 | 237篇 |
1984年 | 186篇 |
1983年 | 139篇 |
1982年 | 124篇 |
1981年 | 71篇 |
1980年 | 95篇 |
1979年 | 43篇 |
1978年 | 17篇 |
1977年 | 23篇 |
1976年 | 28篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Ma Weidong Liu Wen Wenmin Wang Luo Yong Bu Qinlian Xiouli Zhao Jiang Shan Li Wei 《Photonics Technology Letters, IEEE》2007,19(15):1115-1117
An athermal 40-channel dense wavelength-division-multiplexing multi/demultiplexer using a novel combination technology is proposed. It consists of one 1times4 100- to 400-GHz spacing interleaver filter and four sub-arrayed-waveguide gratings (AWGs). The temperature-dependent wavelength shift of the combined device is successfully suppressed to 0.058 nm in the -20degC to 70degC temperature range. Moreover, the combined device's adjacent crosstalk (typically -35 dB) is much better than conventional AWGs (typically -25 dB). 相似文献
992.
Cheng Chen Zheng Guo Li Yeng Chai Soh 《Networking, IEEE/ACM Transactions on》2007,15(3):697-708
In this paper, we shall generalize the concepts of fairness, TCP-friendliness and TCP-compatibility such that more source adaptation schemes can be designed to support diverse applications over the Internet. A simple but efficient framework, in the form of a monotonic response function (MRF), is proposed for the analysis and the design of memoryless window-based source adaptation protocols by using these concepts. We first derive a necessary and sufficient condition for step-wise convergence to the weighted fairness. It is then used to construct increase-decrease policies. The requirements of our increase-decrease policy are less conservative than those of the CYRF (Choose Your Response Function) that was proposed in . Our MRF is suitable for transmission control protocol (TCP) and user datagram protocol (UDP), and can be used to design TCP-friendly and multimedia-friendly source adaptation schemes. Meanwhile, our MRF can be applied to provide bandwidth differentiation service without any change to the router of the existing Internet. 相似文献
993.
Li Yonghua Wang Chunbo Chen Hongwei 《Frontiers of Energy and Power Engineering in China》2007,1(1):96-100
Power plants in China have to burn blended coal instead of one specific coal for a variety of reasons. So it is of great necessity
to investigate the combustion of blended coals. Using a test rig with a capacity of 640 MJ/h with an absolute milling system
and flue gas online analysis system, characteristics such as burnout, slag, and pollution of some blended coals were investigated.
The ratio of coke and slag as a method of distinguishing coal slagging characteristic was introduced. The results show that
the blending of coal has some effect on NO
x
but there is no obvious rule. SO
x
emission can be reduced by blending low sulfur coal.
Translated from Proceedings of the CSEE, 2005, 25(18): 97–103 [译自: 中国电机工程学报] 相似文献
994.
On the basis of Odum's ecological economic measure of emergy as embodied solar energy, a system account of biomass resource exploitation by agriculture in China 2004 is developed in this paper, which supplements a former study on corresponding long-term historical trends during 1978 to 2000 (Chen et al., 2006. Emergy-based analysis of the Chinese agriculture. Agriculture, Ecosystems and Environment 115, 161–173). The aggregate fluxes and indicators for biomass resource exploitation in China 2004 are calculated and illustrated when compared with those for 2000 to elucidate the latest status of the Chinese agriculture as the exploitation sector for biomass resource. Data sources and algorithm are presented in detail as basic references for related analysis involving the ecological economy of biomass exploitation in agriculture. 相似文献
995.
Fanggao Chang Tao Li Yongxia Ge Zhenping Chen Zhongshi Liu Xiping Jing 《Journal of Materials Science》2007,42(17):7109-7115
DC resistivity, dielectric constant, dielectric loss and positron annihilation spectra of (Ba1−x
Ho
x
)TiO3 ceramics have been measured as a function of holmium concentration x. It has been found that the DC resistivity of (Ba1−x
Ho
x
)TiO3 is strongly dependent on the Ho content: it decreases three orders of magnitude and reaches a minimum at x = 0.4%. Doping with 0.6% holmium increases the permittivity of BaTiO3 by approximately three times (from ∼1,300 to ∼4,000), with only a slight increase in the corresponding dielectric loss. The
local electron density and defect concentration estimated using positron annihilation technique conforms well to the features
found in the dielectric and resistivity measurements. The results have been discussed in terms of a mixed compensation model. 相似文献
996.
Zehui Li Peng Zhao 《Reliability, IEEE Transactions on》2007,56(2):340-348
We investigate the delta-shock model of complex systems consisting of n i.i.d. components. We first obtain a general lifetime distribution for the delta-shock model of a general complex system by reducing the system to a linear combination of parallel systems. We then consider coherent system structures including series, parallel, and k-out-of-n, then derive some useful results including reliability bounds, bounds on the mean lifetime, limiting distributions, and Laplace-Stieltes transforms 相似文献
997.
998.
在建的南渡江河口段防洪工程具有海岸堤防工程的特点。本文对原堤防存在的问题、设计洪(潮)水面线的确定、不同条件下的堤防断面的设计、水土保持的设计以及环境保护设计等关键的技术问题,进行阐述,以供与一般江河堤防比较和类似海岸堤防工程参考。 相似文献
999.
引言
随着近年来数字处理电路电压的不断降低,电源功率密度的不断提高,对于电源次级整流的要求越来越高。整流器件已从最初的肖特基二极管整流,发展到用同步整流开关管替代二极管,以降低功耗。目前,控制同步整流开关管的方法主要有分立式和基于锁相环的控制芯片两种。用分立元件实现同步整流的缺点是响应过慢,系统可靠性相对差。单芯片同步整流是基于锁相环技术的,从初级取信号同步控制次级整流开关管,这种方法的缺点是不能保证在间隔模式(轻载或空载时发生)下可靠操作。 相似文献
1000.