全文获取类型
收费全文 | 6569篇 |
免费 | 168篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 80篇 |
综合类 | 2篇 |
化学工业 | 1354篇 |
金属工艺 | 154篇 |
机械仪表 | 132篇 |
建筑科学 | 372篇 |
矿业工程 | 6篇 |
能源动力 | 153篇 |
轻工业 | 509篇 |
水利工程 | 52篇 |
石油天然气 | 13篇 |
武器工业 | 2篇 |
无线电 | 391篇 |
一般工业技术 | 1014篇 |
冶金工业 | 1370篇 |
原子能技术 | 46篇 |
自动化技术 | 1094篇 |
出版年
2022年 | 57篇 |
2021年 | 77篇 |
2020年 | 62篇 |
2019年 | 98篇 |
2018年 | 98篇 |
2017年 | 81篇 |
2016年 | 101篇 |
2015年 | 105篇 |
2014年 | 150篇 |
2013年 | 369篇 |
2012年 | 240篇 |
2011年 | 346篇 |
2010年 | 278篇 |
2009年 | 252篇 |
2008年 | 331篇 |
2007年 | 286篇 |
2006年 | 267篇 |
2005年 | 209篇 |
2004年 | 201篇 |
2003年 | 179篇 |
2002年 | 192篇 |
2001年 | 103篇 |
2000年 | 92篇 |
1999年 | 103篇 |
1998年 | 143篇 |
1997年 | 116篇 |
1996年 | 120篇 |
1995年 | 112篇 |
1994年 | 117篇 |
1993年 | 107篇 |
1992年 | 99篇 |
1991年 | 72篇 |
1990年 | 87篇 |
1989年 | 98篇 |
1988年 | 64篇 |
1987年 | 62篇 |
1986年 | 87篇 |
1985年 | 106篇 |
1984年 | 84篇 |
1983年 | 96篇 |
1982年 | 88篇 |
1981年 | 89篇 |
1980年 | 80篇 |
1979年 | 83篇 |
1978年 | 64篇 |
1977年 | 71篇 |
1976年 | 65篇 |
1975年 | 67篇 |
1974年 | 47篇 |
1973年 | 54篇 |
排序方式: 共有6744条查询结果,搜索用时 15 毫秒
1.
Good requirements practices are neither necessary nor sufficient 总被引:2,自引:2,他引:0
2.
3.
4.
Diane M. Hopkins Alan D. Jackson Kenneth Oates 《Microscopy research and technique》1991,18(2):176-182
The standardisation of frozen hydrated bulk biological specimens using gelatin standards is described. The relationship between corrected elemental X-ray counts and ionic concentration was found to be linear, and minimum detectable limits for each element are stated. Variations in uncorrected standard curves were found to be due to changes in aluminium coating thickness. There was an inverse relationship between coating thickness and elemental X-ray counts. The factors causing this are discussed. To avoid errors arising from inconsistent aluminium thickness, experimental material should only be compared with standards of similar aluminium net counts. This can be achieved most easily by mounting and analysing specimen and standard together. 相似文献
5.
A systems approach is introduced and applied to the development of expressive and communicative action of infants in the first year of life. In this approach, expressive and communicative actions are organized, as part of cooperative systems with other elements of the infants' physiology, cognition, behavior, and social environment. A systems approach presumes that order arises dynamically as a result of the interaction between the cooperating elements that are changing asynchronously, rather than as the result of centrally coordinated developmental change that is synchronous across domains. The systems approach further assumes that the control parameter responsible for eliciting developmental change may be different depending on age, context, and task. It offers a means to understand previously unexplained developmental phenomena: the appearance of mature forms of expression before mature functon has been achieved, the asynchronous rates of development of communicative-action components, discontinuous developmental shifts arising from continuous processes, and the process by which adults influence communicative development. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
6.
Albert Lamperti Alan Conger Leslie Delaney Marvin Sodicoff 《Drug development and industrial pharmacy》1994,20(12):1971-1989
ABSTRACT
Our transdermal permeation studies of radioprotectors in permeation-enhancing vehicles led us to hypothesize that radiation-induced hair loss could be reduced by topical application of radioprotectors. In the present study we used a hair regrowth assay in “plucked” mice to measure the radioprotective effectiveness of WR-1065, cysteine and TEMPOL when they were dissolved in a variety of vehicles, i.e., saline, dimethyl formamide (DMF), propylene glycol (PG), dimethyl sulfoxide (DMSO), ethanol. Protector effectiveness varied with radiation dose and vehicles. At 600 R, WR-1065 or cysteine, in any vehicle, reduced radiation-induced baldness scores; at 800 R, only WR-1065 in DMF and cysteine in saline, produced some protection. TEMPOL in ethanol produced protection at both the 600 and 800 R. Results suggest that suitably chosen topical application of protector/vehicle combinations can reduce radiation-induced hair loss. 相似文献
Our transdermal permeation studies of radioprotectors in permeation-enhancing vehicles led us to hypothesize that radiation-induced hair loss could be reduced by topical application of radioprotectors. In the present study we used a hair regrowth assay in “plucked” mice to measure the radioprotective effectiveness of WR-1065, cysteine and TEMPOL when they were dissolved in a variety of vehicles, i.e., saline, dimethyl formamide (DMF), propylene glycol (PG), dimethyl sulfoxide (DMSO), ethanol. Protector effectiveness varied with radiation dose and vehicles. At 600 R, WR-1065 or cysteine, in any vehicle, reduced radiation-induced baldness scores; at 800 R, only WR-1065 in DMF and cysteine in saline, produced some protection. TEMPOL in ethanol produced protection at both the 600 and 800 R. Results suggest that suitably chosen topical application of protector/vehicle combinations can reduce radiation-induced hair loss. 相似文献
7.
Blind MPEG-2 video watermarking robust against geometric attacks: a set of approaches in DCT domain.
A set of robust MPEG-2 video watermarking techniques is proposed, focusing on commonly used typical geometric processing for bit-rate reduction, cropping, removal of any rows, arbitrary-ratio downscaling, and frame dropping. Both the embedding and the extraction of watermarks are done in the compressed domain, so the computational cost is low. Moreover, the watermark extraction is blind, i.e., no original unwatermarked MPEG-2 video is needed for watermark extraction. The presented technique is applicable not only to MPEG-2 video, but also to other DCT-based coding videos. Selected experimental results validate our techniques. 相似文献
8.
David N. Johnson Alan A. Johnson 《Fatigue & Fracture of Engineering Materials & Structures》1985,8(3):287-294
The results of Stan ton and Bairstow (1908) have been reanalyzed to yield information on the composition dependence of the low cycle impact fatigue properties of pearlitic plain carbon steels. It has been found that the energy absorbed per impact, Ei, and the number of impacts are failure, Nf, are related by the equation: In this equation q is determined by the carbon, manganese and silicon contents of the steel; Eo is the impact endurance limit; and C and D are constants. The curve represented by this equation intersects that representing the Johnson-Keller high cycle impact fatigue equation at a value of logeNf equal to 1/C. Thus, the transition from low to high cycle impact fatigue occurs at this value of logeNf. 相似文献
9.
Martin E. Valdez H. Shibata Alan W. Cramb 《Metallurgical and Materials Transactions B》2006,37(6):959-965
The objective of this study is to determine the conditions under which the inclusions present in liquid steel can act as heterogeneous
nucleants for solidification. In order to study the factors that define the undercooling of a given metal/oxide couple, the
undercooling of a pure iron sessile droplet in contact with Al2O3, ZrO2, and MgO substrates was measured under controlled oxygen partial pressures by observing droplet recalescence. The results
showed that the undercooling of iron, in contact with a particular substrate, did not have a unique value, but was significantly
affected by the oxygen content on the gas phase. For oxygen partial pressures between 10−21 and 10−19, the undercooling of iron on ZrO2 substrates was stable and around 290 °C. In the same range of oxygen partial pressure, the undercooling of iron on MgO substrates
remained below 100 °C due to the low stability of this oxide. At lower oxygen contents, substrate decomposition might be the
cause for the observed drop in the undercooling of iron on ZrO2 substrates to below 100 °C. The undercooling also decreased for increasing oxygen content as verified when the gas was changed
from gettered Ar/Ar-H2 to CO/CO2 mixtures. The variation in undercooling was related to the wetting of the substrate by the liquid metal, where the deep undercooling
observed in the ZrO2 experiments occurred when the highest contact angle between the liquid metal and the substrate was achieved. 相似文献
10.
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