全文获取类型
收费全文 | 52753篇 |
免费 | 5372篇 |
国内免费 | 2357篇 |
专业分类
电工技术 | 11165篇 |
技术理论 | 5篇 |
综合类 | 4832篇 |
化学工业 | 3977篇 |
金属工艺 | 1894篇 |
机械仪表 | 1418篇 |
建筑科学 | 10777篇 |
矿业工程 | 2686篇 |
能源动力 | 1303篇 |
轻工业 | 1842篇 |
水利工程 | 3291篇 |
石油天然气 | 2317篇 |
武器工业 | 362篇 |
无线电 | 3356篇 |
一般工业技术 | 2548篇 |
冶金工业 | 1926篇 |
原子能技术 | 527篇 |
自动化技术 | 6256篇 |
出版年
2024年 | 188篇 |
2023年 | 571篇 |
2022年 | 1280篇 |
2021年 | 1508篇 |
2020年 | 1448篇 |
2019年 | 1122篇 |
2018年 | 978篇 |
2017年 | 1338篇 |
2016年 | 1491篇 |
2015年 | 1776篇 |
2014年 | 3714篇 |
2013年 | 2686篇 |
2012年 | 3765篇 |
2011年 | 4327篇 |
2010年 | 3415篇 |
2009年 | 3555篇 |
2008年 | 3265篇 |
2007年 | 3926篇 |
2006年 | 3686篇 |
2005年 | 3019篇 |
2004年 | 2519篇 |
2003年 | 2328篇 |
2002年 | 1920篇 |
2001年 | 1582篇 |
2000年 | 1332篇 |
1999年 | 976篇 |
1998年 | 640篇 |
1997年 | 475篇 |
1996年 | 391篇 |
1995年 | 328篇 |
1994年 | 220篇 |
1993年 | 151篇 |
1992年 | 117篇 |
1991年 | 82篇 |
1990年 | 70篇 |
1989年 | 49篇 |
1988年 | 63篇 |
1987年 | 26篇 |
1986年 | 24篇 |
1985年 | 23篇 |
1984年 | 30篇 |
1983年 | 14篇 |
1982年 | 7篇 |
1981年 | 13篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1966年 | 3篇 |
1963年 | 3篇 |
1959年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
1.
卜寺沟水电站预可阶段正常蓄水位是考虑规划成果、地形、地质务件、梯级衔接、水库淹没、筑坝技术、水能资源利用等因素综合初选的.从理论角度分析,水库淹没时水库内寺庙的影响,按全部淹没进行经济补偿处理代价较小;其社会环境敏感因素对正常蓄水位的选择不应起决定性作用.但是,考虑到少数民族群众、僧侣和地方政府的要求,适当降低正常蓄水位,以减少对扎西日岗寺庙的影响,将带来较积极的社会影响. 相似文献
2.
Huai Wen-xin Wuhan University of Hydraulic & Electric Engineering Wuhan Hubei P.R.China Prof.Li Wei 《水动力学研究与进展(B辑)》1993,(3)
Turbulence represents an essential aspect in atmospheric and oceanic circulations.In particu-lar,it is a preponderant factor in the dispersion of pollutants of artificial or natural origin.Thevertical turbulent jets,plumes and buoyant jets discharging into static environment is one of themost important and basic flow patterns related with the environment pollution.These flows havenumerous important applications,for example,thrust augmentors,waste disposal plumes fromstacks and combustion systems,and significant problems of turbulent diffusion. 相似文献
3.
The authors highlight several possible ways in which the construction industry could lower present emissions of the greenhouse gas, carbon dioxide. It is an excellent discussion document and is recommended reading. 相似文献
4.
The causes of lightning outage are subdivided into direct lightning strokes and induced lightning strokes, which are identified by the characteristics of the lightning overvoltage. In the past, lightning protection devices were directed mainly toward the latter, and attention has been focused on the installation of lightning protection devices, ground wires, and reinforcement of insulators. However, lightning outages continue to occur. Thus it is extremely important to clarify the fault characteristics of lightning surges and to study the effectiveness of various lightning protection devices by considering both direct lightning stroke and induced lightning stroke in order to prevent lightning outage in the future. In this research, the electromagnetic transients program (EMTP) has been applied to the direct lightning stroke, and the induced lightning outage analysis program for multiple conductor systems has been applied to the induced lightning stroke to study the effectiveness of lightning protection devices provided by combination of various lightning protection devices. The most effective lightning protection schemes are analyzed and evaluated based on verification tests on the full scale models as well as economic considerations. 相似文献
5.
6.
Aboubakar Sako Kenneth G. MacLeod Catherine M. O’Reilly 《Journal of Great Lakes research》2007,33(4):806-815
In this study, we measured growth trends in oxygen and carbon isotopic ratios in whole sagittal otoliths from three adult centropomid fish (Lates stappersii) from each of three sub-basins of Lake Tanganyika, East Africa. Sampling density was 20 to 50 samples per otolith. Both δ18O and δ13C values increase with age. The δ18O data suggest that otoliths were precipitated near the expected equilibrium with the ambient environment (ca. +3.5‰) and support a migration pattern from surface waters during larval stages to deeper waters (40 to 80 m) for mature fish. Relatively high δ18O values in the southern sub-basin are consistent with cooler temperatures in the region during seasonal upwelling. The δ13C increase from otolith core to edge is large (up to 4‰) and is interpreted as due to ontogenetic changes in diet and contributions from a decrease in the proportion of respired CO2 incorporated into otolith carbonate as metabolic rates of the fish dropped with maturity. The data seem to successfully reveal life strategy and migration patterns of L. stappersii, document regional differences in lake conditions, and provide a record of temperature within the water column during which the fish lived. Higher resolution studies and analyses of historical samples could be used to constrain modern and past growth patterns, and to reconstruct past temperature gradients and productivity patterns in the lake. 相似文献
7.
Sanghoon Lee Chris Podilchuk Vidhya Krishnan Alan C. Bovik 《The Journal of VLSI Signal Processing》2003,34(1-2):149-166
By exploiting new human-machine interface techniques, such as visual eyetrackers, it should be possible to develop more efficient visual multimedia services associated with low bandwidth, dynamic channel adaptation and robust visual data transmission. In this paper, we introduce foveation-based error resilience and unequal error protection techniques over highly error-prone mobile networks. Each frame is spatially divided into foveated and background layers according to perceptual importance. Perceptual importance is determined either through an eye tracker or by manually selecting a region of interest. We attempt to improve reconstructed visual quality by maintaining the high visual source throughput of the foveated layer using foveation-based error resilience and error correction using a combination of turbo codes and ARQ (automatic reQuest). In order to alleviate the degradation of visual quality, a foveation based bitstream partitioning is developed. In an effort to increase the source throughput of the foveated layer, we develop unequal delay-constrained ARQ (automatic reQuest) and rate compatible punctured turbo codes where the punctual pattern of RCPC (rate compatible punctured convolutional) codes in H.223 Annex C is used. In the simulation, the visual quality is significantly increased in the area of interest using foveation-based error resilience and unequal error protection; (as much as 3 dB FPSNR (foveal peak signal to noise ratio) improvement) at 40% packet error rate. Over real-fading statistics measured in the downtown area of Austin, Texas, the visual quality is increased up to 1.5 dB in PSNR and 1.8 dB in FPSNR at a channel SNR of 5 dB. 相似文献
8.
9.
Ken Smith 《Color research and application》2007,32(4):249-255
This study describes a process of relating the perceptual analysis of the colors of the terrestrial atmosphere to currently available pigments used in artists' painting systems. This process sought to discover how the colors of the sky could be defined and simulated by these pigments. The author also describes how confusion over the bewildering choice of suitable pigments on offer in the market place can be clarified. © 2006 Wiley Periodicals, Inc. Col Res Appl, 32, 249–255, 2007 相似文献
10.
We have assessed the antimicrobial, vapor-phase activity of the following natural essential oils (EOs) when used in paraffin-based “active coatings” for paper packaging materials intended to come into contact with foods: clove (Sygzium aromaticum), cinnamon (Cinnamomum zeylanicum), and oregano (Origanum vulgare) EOs, and cinnamaldehyde-enriched cinnamon EO. To our knowledge, this is the first time that such an approach has been presented for consideration by the scientific community. 相似文献