全文获取类型
收费全文 | 10118篇 |
免费 | 334篇 |
国内免费 | 13篇 |
专业分类
电工技术 | 140篇 |
综合类 | 8篇 |
化学工业 | 2212篇 |
金属工艺 | 242篇 |
机械仪表 | 188篇 |
建筑科学 | 457篇 |
矿业工程 | 53篇 |
能源动力 | 309篇 |
轻工业 | 668篇 |
水利工程 | 104篇 |
石油天然气 | 99篇 |
无线电 | 665篇 |
一般工业技术 | 1763篇 |
冶金工业 | 1851篇 |
原子能技术 | 104篇 |
自动化技术 | 1602篇 |
出版年
2021年 | 133篇 |
2020年 | 122篇 |
2019年 | 117篇 |
2018年 | 160篇 |
2017年 | 161篇 |
2016年 | 203篇 |
2015年 | 173篇 |
2014年 | 256篇 |
2013年 | 717篇 |
2012年 | 393篇 |
2011年 | 500篇 |
2010年 | 370篇 |
2009年 | 413篇 |
2008年 | 457篇 |
2007年 | 404篇 |
2006年 | 396篇 |
2005年 | 333篇 |
2004年 | 306篇 |
2003年 | 260篇 |
2002年 | 254篇 |
2001年 | 177篇 |
2000年 | 148篇 |
1999年 | 138篇 |
1998年 | 217篇 |
1997年 | 183篇 |
1996年 | 155篇 |
1995年 | 143篇 |
1994年 | 150篇 |
1993年 | 141篇 |
1992年 | 130篇 |
1991年 | 109篇 |
1990年 | 111篇 |
1989年 | 143篇 |
1988年 | 100篇 |
1987年 | 117篇 |
1986年 | 121篇 |
1985年 | 134篇 |
1984年 | 158篇 |
1983年 | 116篇 |
1982年 | 115篇 |
1981年 | 95篇 |
1980年 | 91篇 |
1979年 | 99篇 |
1978年 | 82篇 |
1977年 | 100篇 |
1976年 | 97篇 |
1975年 | 87篇 |
1974年 | 93篇 |
1973年 | 73篇 |
1972年 | 61篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
41.
Home ownership and access to opportunity are foundations of the American ethos. While little research has explicitly examined a relationship between home ownership and opportunity, considerable empirical work has examined how home ownership impacts important elements of local opportunity structures as well as individual subjective perceptions of those structures. Available evidence suggests that home ownership may affect the opportunity structure by enhancing neighbourhood stability and civic involvement in local voluntary and political affairs. Home ownership may also impact perceptions of opportunity by increasing financial resources, enhancing psychological and physical health, and influencing the behaviour of youth. There is a great need for additional research that directly assesses the impacts of home ownership on local objective opportunity structures and the perception of those structures. 相似文献
42.
George Villanueva 《Journal of Urban Design》2021,26(1):14-37
ABSTRACT This paper illustrates a design activism project that led to a co-designed ‘anti-displacement map’ and ‘walking tour’ in Chicago’s Chinatown. The work argues that one way to deploy urban design projects that consider the fears of displacement in gentrifying neighbourhoods is to integrate what aspects of the neighbourhood existing community actors value and promote advocacy for a future that these participants envision. The project accomplished these goals through ‘communication asset mapping’, an application centring on communicative spaces that are of value to existing communities and help to create the capacity for positive social change in the built environment. 相似文献
43.
Global human population and urban development are increasing at unprecedented rates and creating tremendous stress on local, regional, and global air and water quality. However, little is known about how urban areas vary in their capacity to address effectively air and water quality impacts associated to urban development. There exists a need to better understanding the factors that mediate the interactions between urbanisation and variations of environmental quality. By synthesizing literatures on the relationship between urban development and air and water quality, we assess the amount of scholarship for each of these cities, characterize population growth rates in one hundred of the largest global cities, and link growth trends to changes in air and water quality. Our results suggest that, while there is a growing literature linking urbanisation and environmental quality, some regions of the globe are better represented than others, and that these trends are consistent with our characterization of population growth rates. In addition, the comparison between population growth rates and air and water quality suggest that multiple factors affect the environmental quality, and that approaching rates of urbanisation through the lens of ‘resiliency’ can be an effective integrative concept for studying the capacity of urban areas to respond to rapid rates of change. Based on these results we offer a framework for systematically assessing changes in air and water quality in megacities. 相似文献
44.
G. S. Xeidakis I. S. Samaras 《Bulletin of Engineering Geology and the Environment》1996,53(1):121-129
The use of marble in Architecture began on the 7th century B.C. and continued to be used without stop untill today. Greece and especially the East Macedonia region is an extremely privileged area on marble deposits both in quantities and qualities and colours. In the present work the main physical and engineering properties of some varieties of greek marbles are given and a comparison with the international standards is made. The experimental material (marbles) was from East Macedonia, Argolida-Arcadia and Magnessia, three of the biggest marble deposit areas in Greece. From the results obtained, it is concluded that the marbles examined satisfy all the international standard codes and thus they can be used as building stones and decoration materials. 相似文献
45.
朱剑飞在他令人深思的文章“批评的演化——中国与西方的交流”中,谈到了我2004年在《哈佛设计杂志》(Harvard Design)上发表的论文“批评性及其不满”。我在那篇文章里提出,雷姆·库哈斯在最近出现的关于批评性的讨论中所扮演的核心角色。我实际提出这样一个现象,即企图摈弃“批评性”,在理论和职业上为建 相似文献
46.
A series of full-scale explosion suppression experiments were conducted in a compartment. The suppression performance of three
extinguishing systems with two suppressants for the deflagration-type explosion was studied. The impact of agent discharge
direction, the presence of an obstacle and the use of additives on suppression performance were investigated with extensive
data collection and analysis. The negative aspects and toxicity issues associated with the protection systems are also addressed
in the paper. The three extinguishing systems evaluated in this project were a high pressure HFC-227ea (FM-200) extinguisher,
a hybrid gas generator with FM-200, and a hybrid gas generator with water, with full-system hardware including optical flame
sensors and electronic controllers. The experimental results showed that the explosion in a compartment originating from a
fuel spray was a serious threat to any occupant in the compartment and could cause major damage to equipment, but, the explosion
generated in the experiments was controlled or extinguished by appropriate extinguishing systems. 相似文献
47.
A mass-transfer model analogous to one used to describe the volatilization of organics from natural waters was used to describe the dissolution of constituent organics from a floating oil film into the underlying water. The mass flux of a material across the oil-water interface was depicted using an oil-phase mass-transfer coefficient, ko a water-phase mass-transfer coefficient, kw, a partition coefficient, P, describing the equilibrium partitioning of a substance between oil and water, and the concentrations of the substance in the oil and water, Co and Cw, in the following expression: Rates of dissoltion were observed to vary with properties of the solute, P, the oil (viscosity, P, oil depth) and the environment (oil and water mixing, water depth). The observed rates of dissolution of chemicals from a low-viscosity oil (heptane) varied by a factor of 104 between the most rapidly and most slowly dissolving materials. 相似文献
48.
Generation and Transport of Smoke Components 总被引:2,自引:1,他引:2
Smoke is a mixture of gases, vapors, and suspended particulate matter, or aerosols. The nature of the aerosol component of smoke can play a significant role in its deposition in the fire environment and in its lethal and sublethal effects on people. This paper presents the current state of knowledge about smoke aerosol phenomena that affects smoke toxicity: soot generation, fractal structure of soot, agglomerate transport via thermophoresis, sedimentation, and diffusion, agglomerate growth through coagulation and condensation, and the potential for the aerosols to transport adsorbed or absorbed toxic gases or vapors into the lungs. Tables are included for measured smoke yields and aerodynamic particle sizes, equations and references are provided for the smoke agglomerate transport properties and wall loss, and key literature references are provided for adsorption of irritant gases on soot particles and water droplets and the toxicity of nanosize particles. 相似文献
49.
Abstract: Object-oriented programming characteristics of abstraction, inheritance, and encapsulation of data and operations support three desirable features in the development of complicated engineering software systems: modularity, reusability, and ease of maintenance. This paper presents computer-aided design (CAD) of structures using the object-oriented programming paradigm and a blackboard architecture for management of input/output data as well as intermediate data created during a consultation with the CAD system. 相似文献
50.
Fecal coliform removal in wastewater treatment plants studied by plate counts and enzymatic methods 总被引:1,自引:0,他引:1
Twelve wastewater treatment plants (WWTPs) were sampled in France and Belgium in 1999 and 2000 in order to estimate the fecal coliform (FC) removal efficiency of various types of treatment. Only one of these WWTPs was equipped with a specific step to eliminate microorganisms (UV disinfection preceded by sand filtration). FC abundance was measured in raw and treated sewage by plate counts on selective medium and rapid beta-D-glucuronidase (GLUase)-based assays. Removal of culturable FC was the most efficient in treatments with high retention time (activated sludge process with nitrification and denitrification, lagooning), in biofiltration and in the treatment with a tertiary disinfection step. GLUase activity measurements showed the same removal pattern as plate counts except for UV disinfection, where no reduction of GLUase activity was measured. Specific loads of culturable FC and GLUase activity, i.e. daily amounts of culturable FC or GLUase activity in sewage per inhabitant-equivalent, were calculated in raw and treated wastewater for the different WWTPs. 相似文献