全文获取类型
收费全文 | 1510篇 |
免费 | 47篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 14篇 |
综合类 | 1篇 |
化学工业 | 228篇 |
金属工艺 | 26篇 |
机械仪表 | 40篇 |
建筑科学 | 78篇 |
矿业工程 | 4篇 |
能源动力 | 24篇 |
轻工业 | 164篇 |
水利工程 | 10篇 |
石油天然气 | 1篇 |
武器工业 | 2篇 |
无线电 | 98篇 |
一般工业技术 | 249篇 |
冶金工业 | 425篇 |
原子能技术 | 5篇 |
自动化技术 | 190篇 |
出版年
2022年 | 17篇 |
2021年 | 15篇 |
2020年 | 11篇 |
2019年 | 18篇 |
2018年 | 23篇 |
2017年 | 19篇 |
2016年 | 21篇 |
2015年 | 21篇 |
2014年 | 41篇 |
2013年 | 68篇 |
2012年 | 39篇 |
2011年 | 65篇 |
2010年 | 50篇 |
2009年 | 50篇 |
2008年 | 69篇 |
2007年 | 65篇 |
2006年 | 44篇 |
2005年 | 45篇 |
2004年 | 39篇 |
2003年 | 39篇 |
2002年 | 33篇 |
2001年 | 25篇 |
2000年 | 29篇 |
1999年 | 32篇 |
1998年 | 95篇 |
1997年 | 77篇 |
1996年 | 69篇 |
1995年 | 29篇 |
1994年 | 34篇 |
1993年 | 34篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1990年 | 14篇 |
1989年 | 11篇 |
1988年 | 15篇 |
1987年 | 16篇 |
1986年 | 18篇 |
1985年 | 15篇 |
1984年 | 16篇 |
1983年 | 17篇 |
1982年 | 9篇 |
1981年 | 15篇 |
1980年 | 15篇 |
1979年 | 18篇 |
1978年 | 10篇 |
1977年 | 20篇 |
1976年 | 26篇 |
1975年 | 9篇 |
1974年 | 13篇 |
1973年 | 14篇 |
排序方式: 共有1559条查询结果,搜索用时 15 毫秒
1.
2.
A case of arsenic intoxication associated with macrocytosis and neuropathy, without anemia, is presented. Evaluation of a 68-year-old man with a long history of peripheral neuropathy and persistent macrocytosis revealed exposure to an insecticide. Analysis of urine and hair revealed elevated levels of arsenic. A short course of d-penicillamine failed to promote urinary excretion of arsenic. Removal of the insecticide resulted in resolution of macrocytosis and slight improvement of neuropathy. This case emphasizes that arsenic intoxication should be considered in patients with macrocytosis with peripheral neuropathy, even in the absence of anemia. 相似文献
3.
Kizilyalli I.C. Rambaud M.M. Duncan A. Lytle S.A. Thoma M.J. 《Electron Device Letters, IEEE》1995,16(10):457-459
The trade-off between threshold voltage (Vth) and the minimum gate length (Lmin) is discussed for optimizing the performance of buried channel PMOS transistors for low voltage/low power high-speed digital CMOS circuits. In a low supply voltage CMOS technology it is desirable to scale Vth and Lmin for improved circuit performance. However, these two parameters cannot be scaled independently due to the channel punch-through effect. Statistical process/device modeling, split lot experiments, circuit simulations, and measurements are performed to optimize the PMOS transistor current drive and CMOS circuit speed. We show that trading PMOS transistor Vth for a smaller Lmin results in faster circuits for low supply voltage (3.3 to 1.8 V) n+-polysilicon gate CMOS technology, Circuit simulation and measurements are performed in this study. Approximate empirical expressions are given for the optimum buried channel PMOS transistor V th for minimizing CMOS circuit speed for cases involving: (1) constant capacitive load and (2) load capacitance proportional to MOS gate capacitance. The results of the numerical exercise are applied to the centering of device parameters of a 0.5 μm 3.3 V CMOS technology that (a) matches the speed of our 0.5 μm 5 V CMOS technology, and (b) achieves good performance down to 1.8 V power supply. For this process the optimum PMOS transistor Vth (absolute value) is approximately 0.85-0.90 V 相似文献
4.
On the detection of motion and the computation of optical flow 总被引:4,自引:0,他引:4
Duncan J.H. Chou T.-C. 《IEEE transactions on pattern analysis and machine intelligence》1992,14(3):346-352
A method for the detection of motion in image sequences is presented. In this method, the intensity history at each pixel is convolved with the second derivative in time of a temporal Gaussian smoothing function. The zero crossings in a single frame of the resulting function indicate the positions of moving edges. Intensity changes in time due to illumination effects do not produce zero crossings; thus, they are not interpreted as motion by the present method. It is also shown that the spatial and temporal derivatives of this function can be used to compute the component of the optical flow that is normal to the zero-crossing contours. This computation is also insensitive to nonconvective temporal and spatial variations in the image intensity that are caused by illumination effects 相似文献
5.
Cho Younghee; Luce R. Duncan; von Winterfeldt Detlof 《Canadian Metallurgical Quarterly》1994,20(5):931
A rank- and sign-dependent utility theory is based on an operation of joint receipt of 2 independent gambles and 3 assumptions regarding the operation (R. D. Luce, 1992). The authors tested these 3 assumptions (i.e., segregation, duplex decomposition, and the additivity of certainty equivalents over joint receipt) using both judged and choice certainty equivalents (CEs). Median choice CEs provided support for both segregation and duplex decomposition but little support for additivity in gains or in losses, whereas median judged CEs also failed to support segregation. The latter failure appears to result from some Ss misunderstanding the instructions. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
6.
Determinants of off-road vehicle transmission 'shift quality' 总被引:2,自引:0,他引:2
This study was conducted to determine the relationship between factors associated with a tractor transmission shift and the tractor operator's judgement of the quality of the shift. The specific objective was to measure experienced tractor operators' ratings of shift 'acceptability' as peak acceleration, peak jerk and direction of initial acceleration were varied at two levels of background vibration. A six-degree-of-freedom vehicle motion simulator in the Deere & Company Technical Center's human factors laboratory was used to simulate the background vibration and to control the experimental variables. The key results are: (1) The most important factor influencing 'shift quality' is the peak acceleration experienced during the shift. (2) Background vehicle vibration experienced by the tractor operator affects his perception of 'shift quality'. Higher background vibration masks the acceleration experienced during a shift and makes the shift more acceptable than when experienced at a low level of background vibration. (3) Peak jerk experienced during a shift has a negligible effect on 'shift quality'. (4) Upshifts and downshifts of the same peak acceleration, peak jerk, and background vibration receive the same general rating of 'shift quality'. 相似文献
7.
Characterization of branched chain fatty acids from subcutaneous triacyglycerols of barley-fed lambs 总被引:1,自引:0,他引:1
The fatty acids of subcutaneous triacylglycerols (containing ca. 11% of branched chain components) from lambs fed on barley-rich diets were fractionated by treatment with mercuric acetate and by urea adduct formation to yield concentrates rich in the branched chain components, all of which were saturated. The concentrates were subjected to analysis by high resolution gas liquid chromatography in conjunction with mass spectrometry. The branched chain fatty acids consisted of a complex mixture of mono-, di-, and trimethyl substituted components. The greater part of the mixture comprised monomethyl substituted acids of chain length 10–17 carbon atoms. Within each of these molecular species, a number of positional isomers was identified, notably in respect of methyltetradecanoic acid (methyl substituent on carbon 2, 4, 6, 8, 10, and 12) and methylhexadecanoic acid (methyl substituent on carbon 2, 4, 6, 8, 12, and 14). Homologous series also could be recognized of one of which all eight members from 4-methyldecanoic acid to 4-methylheptadecanoic acid were identified; together they accounted for ca. 39% of the branched chain fatty acids which were sampled for mass spectrometry. The dibranched acids identified consisted of five members of a homologous series, ranging in chain length from 11–15 carbon atoms and with substituent methyl groups at positions 4 and 8. Though the identity of only one tribranched acid (2,6,10-trimethyltetradecanoic acid) was established, others also apparently were present in the mixture. The probable involvement of methylmalonate in the biosynthesis of these branched chain acids is discussed briefly, with particular reference to the availability of vitamin B12 in relation to the activity of methylmalonyl coenzyme A mutase. 相似文献
8.
C. C. Duncan D. M. Yermanos J. Kumamoto C. S. Levesque 《Journal of the American Oil Chemists' Society》1974,51(12):534-536
A rapid ethanolysis procedure for preparing jojoba wax for gas liquid chromatographic analysis is described. The wax esters
are hydrolyzed by refluxing 4 drops of jojoba wax in 5% HCl in anhydrous ethanol in a test tube. The resulting fatty acid
ethyl esters and fatty alcohols are separated and quantitated by a single gas liquid chromatographic run. Analysis of duplicate
samples by this procedure gives essentially the same results as a procedure which requires 10 times more sample and reagents
and considerably more time. 相似文献
9.
Kathleen Menzies Duncan Birrell Gordon Dunsire 《New Review of Information Networking》2013,18(2):92-140
This article reports on the key findings and implications of the Joint Information Systems Committee (JISC)-funded Online Catalogue and Repository Interoperability Study (OCRIS), a 3-month project which investigated the interoperability of Online Public Access Catalogues (OPACs) and Institutional Repositories (IRs) within UK universities. A series of detailed recommendations enumerate some of the ways in which they might begin to develop and support an interoperable systems landscape to the benefit of all key stakeholders. The project combined quantitative and qualitative research methods including an online questionnaire distributed to staff within 85 universities, desk research, and two case studies conducted at the Universities of Cambridge and Glasgow. 相似文献
10.
Sharon Christensen William J. Caelli William D. Duncan 《Information & Communications Technology Law》2010,19(1):61-85
Critical, or national, information infrastructure protection, referred to as either CIIP or NIIP, has been highlighted as a critical factor in overall national security by the United States, the United Kingdom, India and the European Community. As nations move inexorably towards so-called ‘digital economies’, critical infrastructure depends on information systems to process, transfer, store and exchange information through the Internet. Electronic attacks such as denial of service attacks on critical information infrastructures challenge the law and raise concerns. A myriad of issues potentially plague the protection of critical information infrastructures owing to the lack of legal regulation aimed at ensuring the protection of critical information infrastructures. This paper will highlight the legal concerns that relate to the denial of service attacks on critical information infrastructures and provide an introductory overview of the law as it relates to CIIP in Australia. 相似文献