全文获取类型
收费全文 | 16014篇 |
免费 | 212篇 |
国内免费 | 26篇 |
专业分类
电工技术 | 188篇 |
综合类 | 3篇 |
化学工业 | 2008篇 |
金属工艺 | 363篇 |
机械仪表 | 338篇 |
建筑科学 | 512篇 |
矿业工程 | 60篇 |
能源动力 | 306篇 |
轻工业 | 1214篇 |
水利工程 | 89篇 |
石油天然气 | 118篇 |
无线电 | 1509篇 |
一般工业技术 | 2334篇 |
冶金工业 | 5655篇 |
原子能技术 | 160篇 |
自动化技术 | 1395篇 |
出版年
2021年 | 101篇 |
2019年 | 102篇 |
2018年 | 135篇 |
2017年 | 101篇 |
2016年 | 94篇 |
2015年 | 107篇 |
2014年 | 224篇 |
2013年 | 569篇 |
2012年 | 306篇 |
2011年 | 406篇 |
2010年 | 332篇 |
2009年 | 336篇 |
2008年 | 450篇 |
2007年 | 439篇 |
2006年 | 433篇 |
2005年 | 385篇 |
2004年 | 323篇 |
2003年 | 363篇 |
2002年 | 309篇 |
2001年 | 321篇 |
2000年 | 314篇 |
1999年 | 412篇 |
1998年 | 1617篇 |
1997年 | 999篇 |
1996年 | 699篇 |
1995年 | 497篇 |
1994年 | 419篇 |
1993年 | 446篇 |
1992年 | 280篇 |
1991年 | 253篇 |
1990年 | 262篇 |
1989年 | 223篇 |
1988年 | 227篇 |
1987年 | 212篇 |
1986年 | 195篇 |
1985年 | 256篇 |
1984年 | 208篇 |
1983年 | 207篇 |
1982年 | 203篇 |
1981年 | 185篇 |
1980年 | 194篇 |
1979年 | 128篇 |
1978年 | 139篇 |
1977年 | 267篇 |
1976年 | 381篇 |
1975年 | 137篇 |
1974年 | 125篇 |
1973年 | 107篇 |
1972年 | 78篇 |
1970年 | 83篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
R. Smith 《Journal of Engineering Mathematics》1995,29(6):497-516
A two-dimensional horizontal dispersion equation is derived for the many ways that buoyancy modifies the spreading of a mono-disperse discharge of particles in a shallow-water flow. The particle-induced lateral density gradient gives rise to a secondary transverse flow which tends to carry particles outwards. Stratification with the consequent reduced mixing, changes the local vertical profile of the original flow and gives rise to a Burgers nonlinearity (slowing down of sinking particles or a speeding up of buoyant particles). Stratification also modifies the non-local horizontal distribution of the current, with an inflow towards particle-laden regions where the drag is reduced. A simple eddy-diffusivity turbulence model is used which permits explicit evaluation of most of the linear and nonlinear coefficients. Nonlinear effects are shown to be significant for particle volume concentrations of only 10 parts per million. 相似文献
62.
63.
S. H. Smith 《Journal of Engineering Mathematics》1995,29(2):195-202
The second order boundary layer effects are considered for the classical problem of the impulsive motion past a flat plate. Although Stewartson [1], [2] showed clearly how the effect of the leading edge requires a finite time to enter the boundary layer when only first order effects are included, we see here how this second order contribution is noticed immediately throughout the layer, and so becomes the dominant contribution after the Rayleigh behaviour during this time. 相似文献
64.
We propose a composite multivariate quality control (CMQC) system to control simultaneously measured variables. This system is designed to detect unacceptable trends and systematic error in one or more variables, unacceptable random error in one or more variables, and unacceptable changes in the correlation structure in any pair of variables. It is also designed to be tolerant of missing data, to be capable of rejecting as few as one or as many as all variables in a run, and to provide the analyst with control statistics and graphics that logically relate to sources of analytical error. Quality control rules for univariate, multivariate, and correlation conditions are incorporated in the system, as are plots displaying CMQC statistic values and control limits for univariate, multivariate, and correlation parameters. We also discuss advantages of the CMQC over the T2 and principal component multivariate quality control methods. We demonstrate the CMQC procedure using data from a laboratory process in which 40 variables were measured during 40 characterization runs and 23 runs analyzing unknowns. 相似文献
65.
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
66.
Becker D. Vaughn; Kenrick Douglas T.; Neuberg Steven L.; Blackwell K. C.; Smith Dylan M. 《Canadian Metallurgical Quarterly》2007,92(2):179
Findings of 7 studies suggested that decisions about the sex of a face and the emotional expressions of anger or happiness are not independent: Participants were faster and more accurate at detecting angry expressions on male faces and at detecting happy expressions on female faces. These findings were robust across different stimulus sets and judgment tasks and indicated bottom-up perceptual processes rather than just top-down conceptually driven ones. Results from additional studies in which neutrally expressive faces were used suggested that the connections between masculine features and angry expressions and between feminine features and happy expressions might be a property of the sexual dimorphism of the face itself and not merely a result of gender stereotypes biasing the perception. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
67.
Enteric viral infections of calves and passive immunity 总被引:6,自引:0,他引:6
At least eight viruses have been identified, four within the last 5 yr, that produce diarrhea and pathological intestinal lesions in experimentally inoculated calves. Coronavirus and rotavirus frequently are associated with the neonatal calf diarrhea syndrome, but the etiologic role of the newly identified viruses is undefined. All diarrheal viruses replicate within small intestinal epithelial cells, resulting in variable degrees of villous atrophy. Immunity against these viral infections, therefore, must be directed toward protection of the susceptible intestinal epithelial cells. Because most of these viral infections occur in calves less than 3 wk of age, passive lactogenic immunity within the gut lumen plays an important role in protection. This report reviews methods of boosting rotavirus antibody responses in bovine mammary secretions and analyses of passive and active immunity in calves supplemented with colostrum and challenged by rotavirus. Results indicate rotavirus immunoglobulin G1 antibodies in colostrum and milk were elevated after intramuscular and intramammary vaccination of pregnant cows with an Ohio Agricultural Research and Development Center rotavirus vaccine but not after intramuscular immunization with a commercial rota-coronavirus vaccine. Feeding colostrum from intramuscular plus intramammary immunized cows to newborn calves challenged by rotavirus prevented diarrhea and shedding of rotavirus. 相似文献
68.
To improve a company's 'chopping' power it is necessary to apply systems engineering principles to 'project systems' and take the time to plan effectively, to reflect upon what it is that is being done and thereby improve the way things are done. This article takes a systems view of the project and applies systems engineering principles to project management. Projects (complex systems) are needed to create deliverables (which are also complex systems) and investing in the former will be more than paid back in the latter. It is our aim here to clear up some misunderstandings about systems engineering and its role within a complex project and to highlight the need for businesses to take time to improve their processes in the context of good systems engineering practice. 相似文献
69.
70.
Carl A. Soderstrom Patricia C. Dischinger Gordon S. Smith J.Richard Hebel David R. McDuff David A. Gorelick Timothy J. Kerns Shiu M. Ho Kathleen M. Read 《Accident; analysis and prevention》1997,29(6):715-721
A structured in-depth interview employing standardized criteria was used to determine the prevalence of lifetime and current alcohol dependence (alcoholism) in unselected consecutive patients admitted to a regional Level I trauma center. Of 629 patients, 157 (25.0%) were current alcoholics at the time of injury. An additional 87 (13.8%) were diagnosed as lifetime non-current alcoholics. There was no significant difference in the rates of current alcohol dependence among patients injured in vehicular crashes (23.5%), other unintentional trauma victims (29.3%), and those injured as a result of violence (24.6%). Of BAC + (blood alcohol concentration positive) patients, 54.5% were current alcoholics. However, 14.4% of alcohol-negative patients were also diagnosed as alcohol dependent. 相似文献