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   18224篇
  免费   803篇
  国内免费   22篇
电工技术   224篇
综合类   18篇
化学工业   3819篇
金属工艺   322篇
机械仪表   404篇
建筑科学   1017篇
矿业工程   49篇
能源动力   503篇
轻工业   1716篇
水利工程   121篇
石油天然气   57篇
武器工业   1篇
无线电   1590篇
一般工业技术   3079篇
冶金工业   3078篇
原子能技术   188篇
自动化技术   2863篇
  2023年   159篇
  2022年   306篇
  2021年   468篇
  2020年   345篇
  2019年   373篇
  2018年   431篇
  2017年   394篇
  2016年   495篇
  2015年   430篇
  2014年   525篇
  2013年   1084篇
  2012年   869篇
  2011年   1136篇
  2010年   780篇
  2009年   831篇
  2008年   876篇
  2007年   765篇
  2006年   711篇
  2005年   599篇
  2004年   493篇
  2003年   444篇
  2002年   426篇
  2001年   301篇
  2000年   321篇
  1999年   349篇
  1998年   732篇
  1997年   478篇
  1996年   392篇
  1995年   288篇
  1994年   272篇
  1993年   268篇
  1992年   182篇
  1991年   154篇
  1990年   136篇
  1989年   136篇
  1988年   124篇
  1987年   116篇
  1986年   115篇
  1985年   139篇
  1984年   134篇
  1983年   115篇
  1982年   89篇
  1981年   101篇
  1980年   85篇
  1979年   98篇
  1978年   88篇
  1977年   115篇
  1976年   137篇
  1975年   79篇
  1974年   72篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
A common task for spoken dialog systems (SDS) is to help users select a suitable option (e.g., flight, hotel, and restaurant) from the set of options available. As the number of options increases, the system must have strategies for generating summaries that enable the user to browse the option space efficiently and successfully. In the user-model based summarize and refine approach (UMSR, Demberg and Moore, 2006), options are clustered to maximize utility with respect to a user model, and linguistic devices such as discourse cues and adverbials are used to highlight the trade-offs among the presented items. In a Wizard-of-Oz experiment, we show that the UMSR approach leads to improvements in task success, efficiency, and user satisfaction compared to an approach that clusters the available options to maximize coverage of the domain (Polifroni et al., 2003). In both a laboratory experiment and a web-based experimental paradigm employing the Amazon Mechanical Turk platform, we show that the discourse cues in UMSR summaries help users compare different options and choose between options, even though they do not improve verbatim recall. This effect was observed for both written and spoken stimuli.  相似文献   
992.
There is currently an international drive to build new nuclear power plants, bringing about what is being termed a “nuclear renaissance”. However, the public perception of nuclear energy has historically been, and continues to be, a key issue, particularly in light of the Fukushima nuclear incident. This paper discusses the disparity between perceived and calculated risks based on the last four decades of research into risk perception. The leading psychological and sociological theories, Psychometric Paradigm and Cultural Theory, respectively, are critically reviewed. The authors then argue that a new nuclear-build policy that promotes a broader approach to design incorporating a wider range of stakeholder inputs, including that of the lay public, may provide a means for reducing the perceived risk of a nuclear plant. Further research towards such a new approach to design is proposed, based on integrating expert and lay stakeholder inputs and taking into account broader socio-cultural factors whilst maintaining the necessary emphasis on safety, technological development, economics and environmental sustainability.  相似文献   
993.
Thermal and reduction-oxidation stability of substituted LaMn1−yCoyO3 perovskite-type oxides (0.0 ≤ yCo ≤ 1.0) prepared by the citrate route have been studied by means of surface area, X-ray diffraction, FTIR spectroscopy and magnetic properties. The perovskite orthorhombic structure is found for yCo ≤ 0.5, with the exception of yCo = 0.1, which corresponds better to rhombohedral LaMnO3.15. For yCo > 0.5 the diffraction profiles are quite similar to the cobaltite’s rhombohedral structure. Magnetic iso-field studies (ZFC-FC) reveal that, for yCo ≤ 0.50, the system presents an antiferromagnetic canted-like ordering of the Mn/Co sublattice, in which the presence of divalent Co ion creates Mn3+-Mn4+ pairs that interact ferromagnetically through the oxygen orbital. This interpretation is confirmed by the magnetization loops, in which the magnetic moment increases when substituting Mn for Co. Therefore, the general trend is: for yCo ≤ 0.5, the Co ions are inserted in the manganite structure and for yCo > 0.5, the Mn ions are inserted in cobaltite structure. The enhancement of the ferromagnetic properties and the thermal stability against reduction for yCo = 0.5 is attributed to optimized Co2+-Mn4+ interactions.  相似文献   
994.
Two different cooling rates have been imposed during the early solidification of two multi-crystalline silicon ingots with 250mm diameter and 100mm height in a pilot scale directional solidification furnace. This has been done by opening a variable heat leak system below the crucible in order to achieve a high initial cooling rate in one of the ingots. The grain-structure and -orientation of these two ingots have been investigated by light microscopy (LM) and electron backscattered diffraction (EBSD), and their electrical properties by quasi-steady state photo-conductance (QSSPC) and surface photovoltage (SPV) method. The ingot with the high initial cooling rate shows predominantly grains which are significantly larger than what is usually found in mc-Si. The minority carrier diffusion lengths measured on the large grains in the ingot with high cooling rate show higher values than those measured on the ingot with smaller grains. These results indicate that principles of grain size and -orientation control in mc-Si ingots can be applied to a pilot scale furnace, and the potential for up-scaling to industrial ingots with improved electrical properties and, thus, higher solar cell conversion efficiency.  相似文献   
995.
Many soft food materials, including vegetable shortening, exhibit complex rheological behavior. For shortening, a precise determination of rheological behavior is necessary to understand its functionality as a food ingredient. Commercial vegetable shortening was subjected to monotonic and cyclic uniaxial compression tests at a wide range of loading rates. The elastic modulus determined from unloading was a function of strain, varying between 740 kPa in the shortening’s strain hardening region to 220 kPa at large strain where perfect plasticity had developed. Visual analysis of shortening specimens during the compression process showed that a rate-dependent stress overshoot was attributable to the development of a shear band following strain hardening. An elastoviscoplastic constitutive model was developed to define the complex rate-dependent compression response of vegetable shortening. Using the fundamental parameters obtained from the different types of compression tests, the proposed model accurately predicted the uniaxial compression response of vegetable shortening over a wide range (three decades) of compression rates. A model with predictive capabilities of large strain properties is desirable because shortening is subject to large strain in essentially all applications.  相似文献   
996.
997.
The sea provides a large variety of seaweeds that, because of their chemical composition, are fantastic precursors of nanotextured carbons. The carbons are obtained by the simple pyrolysis of the seaweeds under a nitrogen atmosphere between 600 and 900 °C, followed by rinsing the product in slightly acidic water. Depending on the origin of the seaweed and on the pyrolysis conditions, the synthesis may be oriented to give an oxygen‐enriched carbon or to give a tuned micro/mesoporous carbon. The samples with a rich oxygenated surface functionality are excellent as supercapacitor electrodes in an aqueous medium whereas the perfectly tuned porous carbons are directly applicable for organic media. In both cases, the specific surface area of the attained carbons does not exceed 1300 m2 g−1, which results in high‐density materials. As a consequence, the volumetric capacitance is very high, making these materials more interesting than activated carbons from the point of view of developing small and compact electric power sources. Such versatile carbons, obtained by a simple, ecological, and cheap process, could be well used for environment remediation such as water and air treatment.  相似文献   
998.
Objective: The aim of this study is to investigate whether individual personality or temperamental qualities that emerge early and persist over the life course, predict adult midlife health. Specific childhood personality attributes considered include distress proneness, behavioral inhibition, and ability to stay focused on a task. Design: Prospective data are from 569 individuals followed from birth into adulthood. Main Outcome Measures: Outcomes include two different measures of adult health: self-rated general health, and number of illnesses in adulthood. Results: Childhood personality attributes related to attention and distress were significantly associated with adult health, with stronger effects evident among women. Children with high attention reported better self-rated health (b = 0.12, p  相似文献   
999.
1000.
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