全文获取类型
收费全文 | 1337篇 |
免费 | 12篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 6篇 |
化学工业 | 50篇 |
金属工艺 | 4篇 |
机械仪表 | 25篇 |
建筑科学 | 19篇 |
矿业工程 | 2篇 |
能源动力 | 8篇 |
轻工业 | 29篇 |
水利工程 | 7篇 |
石油天然气 | 1篇 |
无线电 | 61篇 |
一般工业技术 | 98篇 |
冶金工业 | 977篇 |
自动化技术 | 64篇 |
出版年
2020年 | 6篇 |
2019年 | 4篇 |
2018年 | 8篇 |
2017年 | 7篇 |
2016年 | 7篇 |
2015年 | 5篇 |
2014年 | 6篇 |
2013年 | 23篇 |
2012年 | 21篇 |
2011年 | 27篇 |
2010年 | 12篇 |
2009年 | 13篇 |
2008年 | 18篇 |
2007年 | 16篇 |
2006年 | 9篇 |
2005年 | 10篇 |
2004年 | 11篇 |
2003年 | 14篇 |
2002年 | 7篇 |
2001年 | 17篇 |
2000年 | 9篇 |
1999年 | 34篇 |
1998年 | 285篇 |
1997年 | 178篇 |
1996年 | 105篇 |
1995年 | 71篇 |
1994年 | 68篇 |
1993年 | 67篇 |
1992年 | 10篇 |
1991年 | 12篇 |
1990年 | 12篇 |
1989年 | 9篇 |
1988年 | 11篇 |
1987年 | 21篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 29篇 |
1976年 | 87篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1968年 | 2篇 |
1965年 | 2篇 |
1926年 | 3篇 |
排序方式: 共有1351条查询结果,搜索用时 46 毫秒
71.
Lawrence K. Forbes 《Journal of Engineering Mathematics》2011,70(1-3):205-224
The classical Rayleigh?CTaylor instability refers to a situation in which two inviscid fluids lie in horizontal layers, with a sharp interface separating them. The upper fluid is heavier, and so disturbances to the interface are unstable and grow with time. The present paper considers the analogous planar flow in cylindrical geometry. A light fluid is being produced by a line source at the origin, and is separated by a sharp interface from a surrounding more dense fluid. As the interface is forced outward, small disturbances to the flow grow with time. There is a finite critical time at which the curvature at the interface evidently becomes infinite, as in the planar case, and inviscid theory fails to be valid beyond this time. By introducing viscosity, it is argued that the high interfacial curvatures in the inviscid model are associated with formation of regions of large vorticity at the interface, and these serve as triggers for the interface to roll up into plume structures. A linearized inviscid theory is presented, and methods for computing nonlinear solutions in the inviscid and viscous models are outlined. Different solution modes exist, in which integer numbers of plumes are formed on the cylindrical outflow, and these are presented and discussed. The second mode, representing bi-polar symmetry, may be of particular relevance in astrophysical applications. 相似文献
72.
73.
Michael Forbes Jim Lawrence Yu Lei Raghu N. Kacker D. Richard Kuhn 《Journal of research of the National Institute of Standards and Technology》2008,113(5):287-297
Covering arrays are structures for well-representing extremely large input spaces and are used to efficiently implement blackbox testing for software and hardware. This paper proposes refinements over the In-Parameter-Order strategy (for arbitrary t). When constructing homogeneous-alphabet covering arrays, these refinements reduce runtime in nearly all cases by a factor of more than 5 and in some cases by factors as large as 280. This trend is increasing with the number of columns in the covering array. Moreover, the resulting covering arrays are about 5 % smaller. Consequently, this new algorithm has constructed many covering arrays that are the smallest in the literature. A heuristic variant of the algorithm sometimes produces comparably sized covering arrays while running significantly faster. 相似文献
74.
A survey over a 3-year period, which commenced in 1987, of the plant and bird communities along 1200 km of river in Lincolnshire and South Humberside, Eastern England, is described. Analysis of data from 247 km of river recorded a great diversity of wildlife, comprising 570 species of plant and 80 species of breeding birds. The management value of such surveys is discussed and these include the preparation of detailed maps of each 500m section of river, which illustrate the habitat structure, and plant and bird communities. A maintenance procedure for each 500 m section of river is then agreed between conservation and operations personnel, preventing areas of wildlife importance from being accidentally destroyed. An index which combines both the diversity and rarity of the plant and bird communities is proposed as a measure of conservation importance. This index allows sections of river to be graded according to their conservation value into one of five groups. The surveys also enable predictions to be made of the effects of management actions on the wildlife and provide information by which fundamental reviews of operational activities can be carried out. 相似文献
75.
This paper reports further progress in understanding the theory of emission-area extraction from Fowler-Nordheim plots, and reports some useful interim results derived by modelling field electron emission from hemi-ellipsoidal emitters. The mathematical nature of the relationship between a new approach to emission-area extraction, recently proposed, and older approaches is demonstrated. The new approach is extended to cover field dependence in emission area. Preliminary results are reported from an investigation into the effects of making erroneous assumptions about the tunnelling barrier seen by the electron and the absence of field dependence in emission area. If wrong theoretical assumptions are made, then emission area can be overpredicted by a factor of as much as 10 or 20. On the other hand, if correct theoretical assumptions are made, then the extracted emission area is close to an emission area derived directly from the model calculations. The problematical nature of the concept of emission area, when emission area is a function of field, is pointed out. 相似文献
76.
Long-term inhalable particles and other air pollutants related to mortality in nonsmokers 总被引:5,自引:0,他引:5
DE Abbey N Nishino WF McDonnell RJ Burchette SF Knutsen W Lawrence Beeson JX Yang 《Canadian Metallurgical Quarterly》1999,159(2):373-382
Long-term ambient concentrations of inhalable particles less than 10 microm in diameter (PM10) (1973- 1992) and other air pollutants-total suspended sulfates, sulfur dioxide, ozone (O3), and nitrogen dioxide-were related to 1977-1992 mortality in a cohort of 6,338 nonsmoking California Seventh-day Adventists. In both sexes, PM10 showed a strong association with mortality for any mention of nonmalignant respiratory disease on the death certificate, adjusting for a wide range of potentially confounding factors, including occupational and indoor sources of air pollutants. The adjusted relative risk (RR) for this cause of death as associated with an interquartile range (IQR) difference of 43 d/yr when PM10 exceeded 100 microg/m3 was 1.18 (95% confidence interval [CI]: 1.02, 1.36). In males, PM10 showed a strong association with lung cancer deaths-RR for an IQR was 2.38 (95% CI: 1.42, 3.97). Ozone showed an even stronger association with lung cancer mortality for males with an RR of 4.19 (95% CI: 1.81, 9.69) for the IQR difference of 551 h/yr when O3 exceeded 100 parts per billion. Sulfur dioxide showed strong associations with lung cancer mortality for both sexes. Other pollutants showed weak or no association with mortality. 相似文献
77.
Noise is an important consideration in the reliability of microelectronic circuits determining the sensitivity of the circuits and placing a lower limit on the regions of operation. Proper modeling of noise in integrated circuits is essential for reliable operation. A derivation is given for the channel noise coefficient of FET’s operating in the saturation region. Some simple approximations are made for hot electron effects which can be incorporated into the derivation and accounted for by a numerical integration technique. Experimental results of measured and calculated noise coefficients are compared for depletion mode MESFETs of different gate lengths. This model gives a much more realistic representation of the channel noise coefficients for short gate length devices rather than the simple 2/3 value currently used in circuit simulations. 相似文献
78.
79.
A detailed literature survey has shown that considerable controversy exists on the mode of action of organic sulfur compounds as load-carrying additives. Previous work by the authors, using four ball extreme-pressure and wear tests, has suggested that under mixed lubrication (antiwear) conditions, organic disulfides are adsorbed on to the metal surface with cleavage of the sulfur-sulfur bond to form an iron mercaptide layer. However, under more severe conditions such as exist in the extreme-pressure region, cleavage of the carbon-sulfur bond occurs to give an inorganic sulfur-containing layer. Thus the different relative performances of disulfides in the mixed lubrication and extreme-pressure regions are readily explained. This paper now presents the results of a detailed examination of the wear scars obtained with certain disulfides using an electron probe microanalyser. The results illustrate the use of this new technique for studying the nature of worn surfaces but, even more important, lend strong support to the suggested mechanism of action of organic disulfides. The results of this study also offer an explanation for the apparently conflicting rig test results often reported in the literature. 相似文献
80.
Homoacetogenic bacteria are strict anaerobes capable of autotrophic growth on H(2)/CO(2) or CO, and of heterotrophic growth on a wide range of sugars, alcohols, methoxylated aromatic compounds and one carbon compounds, yielding acetate as their sole metabolic end-product. Batch activity tests on anaerobic granular sludge, using H(2)/CO(2) as a substrate and 2-bromoethanesulfonate (BES) as a specific methanogenic inhibitor revealed that H(2)/CO(2) conversion and concomitant acetate production commenced only after a lag period of 60-100 h. This finding suggests that the homoacetogenic population of digester sludge could be maintained by heterotrophic growth on sugars or other organic compounds, rather than by autotrophic growth on H(2)/CO(2). In the present study, two upflow anaerobic sludge bed (UASB) reactors were operated at 37 degrees C and 55 degrees C for two distinct trial periods, each characterised by the application of influents designed to enrich for homoacetogenic bacteria. Specific primers designed for the amplification of the functional gene encoding formyltetrahydrofolate synthetase (FTHFS), a key enzyme in the acetyl-CoA pathway of acetogenesis, were used as a specific probe for acetogenic bacteria. The diversity of acetogens in the granular sludge cultivated in each reactor was revealed by application of FTHFS targeted PCR. Results show that biomass acetogenic composition was dependent upon the operational temperature of the reactor and the substrate supplied as influent. 相似文献