首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   4394篇
  免费   114篇
  国内免费   1篇
电工技术   25篇
综合类   3篇
化学工业   638篇
金属工艺   26篇
机械仪表   37篇
建筑科学   223篇
矿业工程   85篇
能源动力   60篇
轻工业   459篇
水利工程   27篇
石油天然气   6篇
无线电   142篇
一般工业技术   458篇
冶金工业   1828篇
原子能技术   17篇
自动化技术   475篇
  2022年   36篇
  2021年   67篇
  2020年   34篇
  2019年   51篇
  2018年   56篇
  2017年   62篇
  2016年   76篇
  2015年   53篇
  2014年   64篇
  2013年   227篇
  2012年   150篇
  2011年   197篇
  2010年   177篇
  2009年   158篇
  2008年   214篇
  2007年   210篇
  2006年   157篇
  2005年   175篇
  2004年   141篇
  2003年   160篇
  2002年   128篇
  2001年   102篇
  2000年   87篇
  1999年   104篇
  1998年   113篇
  1997年   110篇
  1996年   115篇
  1995年   80篇
  1994年   94篇
  1993年   113篇
  1992年   101篇
  1991年   37篇
  1990年   86篇
  1989年   68篇
  1988年   73篇
  1987年   73篇
  1986年   76篇
  1985年   65篇
  1984年   56篇
  1983年   49篇
  1982年   47篇
  1981年   37篇
  1980年   21篇
  1979年   38篇
  1978年   32篇
  1977年   15篇
  1976年   21篇
  1975年   18篇
  1974年   14篇
  1973年   20篇
排序方式: 共有4509条查询结果,搜索用时 15 毫秒
81.
The paper discusses a series of driving trials that were conducted to investigate postural stability of disabled drivers and to assess the effectiveness of a representative sample of support aids. Twenty-three disabled drivers with varying levels of physical disability and seven non disabled drivers participated in the study. The test car was equipped with transducers to measure vehicle velocity and acceleration (longitudinal and lateral), steering wheel movement and torque, and the bracing forces exerted by the driver on the steering wheel. Video cameras were installed to record postural support strategies and displacement of the driver and to record deviation of the car from the specified path. Subjective data regarding driver attitudes and acceptance were also collected through the administration of questionnaires. Findings from the study showed that support aids significantly improved driving performance and reduced physical exertion to maintain an upright driving position for disabled drivers. However, ergonomics design aspects regarding the ease of use and acceptance of the support aids by the end users were identified as obstacles to their sustained use in everyday driving.  相似文献   
82.
The interaction of water molecules with apolar amino acids isan important aspect of the hydrophobic effect and hence of proteinfolding. Our distributed multipole electrostatic model for waterinteracting with phenylalanine dipeptides shows that minimumenergy sites exist above the aromatic ring such that a solventmolecule can interact with the electrons, but only when thissite is not blocked by mainchain atoms or disturbed by main-chainpolar atoms. This is consistent with the experimental evidenceof others that water can hydrogen bond to aromatic n electrons.In contrast, our analysis of solvent interactions with phenylalanineresidues based on 48 high-resolution, well-refined protein structuresshows that the dominant interaction of solvent molecules iswith the edge of the ring and not with the 7i electrons. Asthe faces of phenylalanine rings tend to be buried, and solventinteractions with neighbouring polar atoms are more favourable,the interaction of water molecules with the faces of aromatic rings appears not to occur frequently in proteins  相似文献   
83.
84.
This study examined the perceived motivations and consequences of voluntary disclosure of Facebook active users using a survey administered to college students in a public‐speaking course. College‐age students who took the survey were motivated to use Facebook because they perceived their relationships improved with friends and family, although using Facebook could become negatively habit forming. The research suggests that users of Facebook use it more for disclosing to distant friends rather than to close friends, which is divergent from most early disclosure research that equates disclosure with intimacy. This research utilizes Communication Privacy Management Theory for the theoretical framework.  相似文献   
85.
This study presents two extensions to the two‐stage expectation‐confirmation theory of information systems (IS) continuance. First, we expand the belief set from perceived usefulness in the original IS continuance model to include three additional predictors identified in the unified theory of acceptance and use of technology, namely effort expectancy, social influence and facilitating conditions. Second, we ground the IS continuance model in the context of transactional systems that involve transmission of personal and sensitive information and include trust as a key contextual belief in the model. To test the expanded IS continuance model, we conducted a longitudinal field study of 3159 Hong Kong citizens across two electronic government (e‐government) technologies that enable citizens' access to government services. In general, the results support the expanded model that provides a rich understanding of the changes in the pre‐usage beliefs and attitudes through the emergent constructs of disconfirmation and satisfaction, ultimately influencing IS continuance intention. Finally, we discuss the theoretical and practical implications of the expanded model.  相似文献   
86.
Musculoskeletal disorders are among the most costly health care problems facing society today. The scientific literature has indicated that psychosocial factors, individual factors, workplace physical requirements, and workplace organizational factors have been associated with risk. Since musculoskeletal risk is multi-dimensional, the magnitude of risk attributable to various factors can be of importance to scientists and policy makers in designing countermeasures to reduce injury incidence. Traditionally, the disciplines of biomechanics, physiology, and psychophysics have dominated the body of knowledge that has defined exposure limitations to work. However, recent research has explored the association of psychosocial and work organization factors with musculoskeletal problems. Advances have been made to better quantify the levels of occupational exposure by improved exposure metrics, quantification of three-dimensional loads experienced by certain joints (e.g. the spine), identification of tissue tolerance limits and tissue response to mechanical stresses, and the impact of psychosocial stresses. However, efforts to quantitatively link epidemiological, biomechanical loading, soft tissue tolerance, and psychosocial studies should be pursued to establish a better understanding of the pathways of injury and resultant preventive strategies. Although we are beginning to understand how the major risk factors influence the load-tolerance relationship of human tissue, how these risk factors interact is virtually unexplored. Since the impact of the interactions may be far greater than that of any individual factor, the impact of the interactions between risk factors must be delineated so that work-related risk can be better quantified. Efforts to quantitatively link epidemiological, biomechanical loading, soft tissue tolerance, and psychosocial studies should be pursued to establish a better understanding of the pathways of injury and resultant preventive strategies.  相似文献   
87.
Telecenters take on a prominent role within the current information and communications technology (ICT) ecosystem in Brazil. They are seen by a great many as a key means to foster the digital inclusion of the older population in the country. This paper draws upon a rapid ethnographic study conducted with 78 older people in a center that teaches computer classes to seniors in Brazil. The results show that providing older people with technological infrastructures is not enough to strengthen their digital inclusion if their basic and non-instrumental needs are not taken into consideration in defining educational activities to be carried out in public centers. Participants’ basic needs when it comes to interacting with ICT, such as coping with accessibility issues, were dynamic, whilst non-instrumental needs, fulfilled by using these technologies, such as interacting with relevant others, remained fairly constant throughout the study. Drawing on the results of the study, strategies for fostering the digital inclusion and well-being of older people in Brazil that go beyond telecenters are suggested.  相似文献   
88.
This report provides an overview of physical ergonomic exposures in highway construction work across trades and major operations. For each operation, the observational method “PATH” (Posture, Activity, Tools and Handling) was used to estimate the percentage of time that workers spent in specific tasks and with exposure to awkward postures and load handling. The observations were carried out on 73 different days, typically for about 4 h per day, covering 120 construction workers in 5 different trades: laborers, carpenters, ironworkers, plasterers, and tilers. Non-neutral trunk postures (forward or sideways flexion or twisting) were frequently observed, representing over 40% of observations for all trades except laborers (28%). Kneeling and squatting were common in all operations, especially tiling and underground utility relocation work. Handling loads was frequent, especially for plasterers and tilers, with a range of load weights but most often under 15 pounds. The results of this study provide quantitative evidence that workers in highway tunnel construction operations are exposed to ergonomic factors known to present significant health hazards. Numerous opportunities exist for the development and implementation of ergonomic interventions to protect the health and safety of construction workers.  相似文献   
89.
90.
Two piezoresistive (n-polysilicon) strain sensors on a thin Si3N4/SiO2 membrane with improved sensitivity were successfully fabricated by using MEMS technology. The primary difference between the two designs was the number of strips of the polysilicon patterns. For each design, a doped n-polysilicon sensing element was patterned over a thin 3 μm Si3N4/SiO2 membrane. A 1000×1000 μm2 window in the silicon wafer was etched to free the thin membrane from the silicon wafer. The intent of this design was to fabricate a flexible MEMS strain sensor similar in function to a commercial metal foil strain gage. A finite element model of this geometry indicates that strains in the membrane will be higher than strains in the surrounding silicon. The values of nominal resistance of the single strip sensor and the multi-strip sensor were 4.6 and 8.6 kΩ, respectively. To evaluate thermal stability and sensing characteristics, the temperature coefficient of resistance [TCR=(ΔR/R0)/ΔT] and the gage factor [GF=(ΔR/R0)/] for each design were evaluated. The sensors were heated on a hot plate to measure the TCR. The sensors were embedded in a vinyl ester epoxy plate to determine the sensor sensitivity. The TCR was 7.5×10−4 and 9.5×10−4/°C for the single strip and the multi-strip pattern sensors. The gage factor was as high as 15 (bending) and 13 (tension) for the single strip sensor, and 4 (bending) and 21 (tension) for the multi-strip sensor. The sensitivity of these MEMS sensors is much higher than the sensitivity of commercial metal foil strain gages and strain gage alloys.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号