全文获取类型
收费全文 | 426325篇 |
免费 | 6637篇 |
国内免费 | 1394篇 |
专业分类
电工技术 | 7972篇 |
综合类 | 394篇 |
化学工业 | 65098篇 |
金属工艺 | 14672篇 |
机械仪表 | 12196篇 |
建筑科学 | 12275篇 |
矿业工程 | 967篇 |
能源动力 | 11370篇 |
轻工业 | 45777篇 |
水利工程 | 3415篇 |
石油天然气 | 1854篇 |
武器工业 | 13篇 |
无线电 | 56242篇 |
一般工业技术 | 80261篇 |
冶金工业 | 75269篇 |
原子能技术 | 5670篇 |
自动化技术 | 40911篇 |
出版年
2021年 | 2997篇 |
2020年 | 2088篇 |
2019年 | 2687篇 |
2018年 | 4351篇 |
2017年 | 4409篇 |
2016年 | 4692篇 |
2015年 | 3904篇 |
2014年 | 6263篇 |
2013年 | 20447篇 |
2012年 | 10864篇 |
2011年 | 15471篇 |
2010年 | 11982篇 |
2009年 | 13496篇 |
2008年 | 14586篇 |
2007年 | 14955篇 |
2006年 | 13255篇 |
2005年 | 12346篇 |
2004年 | 11870篇 |
2003年 | 11583篇 |
2002年 | 11247篇 |
2001年 | 11391篇 |
2000年 | 10487篇 |
1999年 | 10926篇 |
1998年 | 24153篇 |
1997年 | 17725篇 |
1996年 | 14020篇 |
1995年 | 11105篇 |
1994年 | 9881篇 |
1993年 | 9441篇 |
1992年 | 7200篇 |
1991年 | 6863篇 |
1990年 | 6465篇 |
1989年 | 6168篇 |
1988年 | 5917篇 |
1987年 | 4942篇 |
1986年 | 4875篇 |
1985年 | 6090篇 |
1984年 | 5719篇 |
1983年 | 4912篇 |
1982年 | 4586篇 |
1981年 | 4549篇 |
1980年 | 4283篇 |
1979年 | 4151篇 |
1978年 | 3850篇 |
1977年 | 4607篇 |
1976年 | 6156篇 |
1975年 | 3191篇 |
1974年 | 3062篇 |
1973年 | 2946篇 |
1972年 | 2349篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
261.
262.
MetaModel is a user-friendly program for calculating steady-state fluxes and metabolite concentrations of metabolic systems on the IBM PC and compatible computers. For any steady state that is obtained, one can then calculate a matrix of elasticity coefficients at that steady state, or a matrix of control and response coefficients. It thus offers a simple way to calculate the control structure of a pathway: it provides not only an educational tool that allows the student to verify empirically the classic summation relationships of metabolic control analysis but also a research tool for addressing 'what if?' questions about the behaviour of metabolic systems. Results can not only be printed or stored in a file, but can also be written to a special file that can be read by popular spreadsheet programs, thereby giving access to rapid, flexible and powerful methods for subsequent analysis and plotting of these results. 相似文献
263.
264.
A method for assessing health care technology that models the demand on the clinician's attention exerted by patients' data (diagnostic and therapeutic) can provide a means for simultaneously reducing the cost and improving the quality of health care. The attentional demand exerted by patients' data can be measured by the amount of uncertainty in the data. Uncertainty can be expressed mathematically by the concept of entropy in information theory. 相似文献
265.
Using a continuous, in-line, nondestructive technique based on the maximum bubble pressure method, the surface tension of
the wash water in a mechanical dishwashing machine has been monitored. This technique has enabled surface tension to be used
as a controlled variable, providing feedback to regulate the amount of surfactant added. Assuming the mechanical force of
the water spray is adequate to remove bound soil from the dish surface, the food soil may be titrated against surfactant,
providing an indirect indication as to when the dishes are clean. This technique also could be applied to a recirculated wash
solution for in-place cleaning. 相似文献
266.
Y. G. Wang H. Q. Ye K. H. Kuo X. J. Feng S. Z. Long G. L. Lao 《Journal of Materials Science》1991,26(23):6325-6330
The microstructures of unhydrated calcium aluminosulphate Ca4Al6SO16 and Ca3SrAl6SO16 have been studied by high-resolution electron microscopy (HREM). The results showed that twinning and twinned slabs could be introduced taking the [1 1 2] direction as the twin axis so that it seems to be coincident with the law of twinning formed in body-centred cubic structures. A previously reported superlattice with a repeat period twice that of the fundamental structure along the 〈1 1 0〉 direction has also been found in both matrix and twin variants. The close intergrowth of Ca3SrAl6SO16 and another phase, possibly Sr3Al2O6 existing as an inclusion between these two twin variants, was determined and clearly revealed by electron diffraction and HREM images. The coherent interphase boundaries and orientation relationship between them can also be deduced. 相似文献
267.
Abstract— The paper addresses some aspects of the differences in fatigue crack growth rate behaviour and threshold values obtained for long through-cracks, short through-cracks and surface cracks. Attention is focused on plasticity induced closure in the wake behind the growing crack tip. For long cracks at high K max , closure is found to depend in a linear manner on K max , i.e. K op , increases with the size of the monotonic plastic zone. Closure increases at low δ K and this is primarily a consequence of the load shedding procedure. If short through-cracks are prepared by machining specimens containing long cracks, a substantial part of the plastic wake is removed and this can produce marked effects on the closure contribution during subsequent growth. The length of crack "closed" in a long crack threshold test was found to be of the order of 1 mm. Cracks less than this length exhibited "short crack" behaviour: greater than this length, they behaved as "long cracks", with plastic wake effects apparently fully operative. Small surface cracks exhibit "long crack" behaviour at lengths as short as 0.2 mm and reasons for this are discussed. 相似文献
268.
269.
Ploennigs J. Neugebauer M. Kabitzsch K. 《Industrial Informatics, IEEE Transactions on》2008,4(2):71-79
Network performance engineering can verify the design and dimensioning of large-scale control networks like CSMA-based building automation networks. It combines performance analysis with diagnosis methods to evaluate the network utilization and to detect design errors before installation and can therewith save the expenses of overdimensioning and redesign. This paper will develop a diagnosis model based on fault trees that is able to use the huge amount of performance analysis results to identify design errors and analyze their coherences. This enables not only a fast tracing back of fault causes and the derivation of solutions; it can also visualize the fault coherence to the user and help him to understand his design. Additional consulting tools implement best practice strategies, to support the user in parameterization. 相似文献
270.
J.P. MacDonald B. GualtieriN. Runga E. TelizC.F. Zinola 《International Journal of Hydrogen Energy》2008
The presence of a second metal on platinum surfaces affects the performance of methanol oxidation. However, most of the electrocatalytic reactions are studied by using electrochemically deposited platinum alloys, but in the case of spontaneous deposition the situation is not so clear since the surface distribution, stability and morphology are usually not well documented. The formation of surface decorated samples on mono- and poly-crystalline platinum is followed by electrochemical and spectroscopic techniques and analysis of their performance towards methanol adsorption and oxidation compared with that on pure platinum. Pt/Sn and Pt/Ru are of special interest because of their well-known performance in methanol fuel cells. Methanol oxidation on Pt(111)/Ru, Pt(111)/Sn and Pt(111) shows that ruthenium is the only one able to promote the reaction since the simultaneous dissolution of tin occurs and competes with the process of interest. The in situ infrared spectroscopy is used to compare methanol oxidation on Pt(111)/Ru and Pt(111) in acid media using p-polarized light. The formation of bridge bound carbon monoxide is inhibited in the presence of ruthenium ad-species, whereas on Pt(111) the three adsorption configurations are observed. Linear sweep polarization curves and Tafel slopes (calculated from steady state potentiostatic plots) for methanol oxidation are compared on polycrystalline surfaces modified by tin or ruthenium at different coverages. There is almost no change in the Tafel slopes due to the presence of the foreign metal except for Pt/Ru, where a 0.09 V decade−1 slope was calculated below 0.55 V due to hydroxyl adsorbates on ruthenium islands. The anodic stripping of methanol residues on the three surfaces indicates a lower amount of carbon monoxide-type adsorbates on Pt/Ru, and the simultaneous tin dissolution process leading to residues oxidation on Pt/Sn electrodes. 相似文献