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   19313篇
  免费   501篇
  国内免费   17篇
电工技术   231篇
综合类   14篇
化学工业   2699篇
金属工艺   234篇
机械仪表   345篇
建筑科学   902篇
矿业工程   43篇
能源动力   470篇
轻工业   2000篇
水利工程   267篇
石油天然气   30篇
无线电   1727篇
一般工业技术   2485篇
冶金工业   5542篇
原子能技术   153篇
自动化技术   2689篇
  2023年   68篇
  2022年   164篇
  2021年   280篇
  2020年   137篇
  2019年   202篇
  2018年   272篇
  2017年   253篇
  2016年   282篇
  2015年   256篇
  2014年   397篇
  2013年   683篇
  2012年   702篇
  2011年   954篇
  2010年   655篇
  2009年   691篇
  2008年   725篇
  2007年   693篇
  2006年   582篇
  2005年   575篇
  2004年   517篇
  2003年   478篇
  2002年   436篇
  2001年   361篇
  2000年   329篇
  1999年   447篇
  1998年   1978篇
  1997年   1212篇
  1996年   823篇
  1995年   491篇
  1994年   478篇
  1993年   470篇
  1992年   205篇
  1991年   206篇
  1990年   196篇
  1989年   202篇
  1988年   197篇
  1987年   133篇
  1986年   133篇
  1985年   185篇
  1984年   139篇
  1983年   100篇
  1982年   111篇
  1981年   117篇
  1980年   86篇
  1979年   94篇
  1978年   81篇
  1977年   137篇
  1976年   151篇
  1975年   78篇
  1974年   71篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
In the Netherlands both nursing homes and homes for the aged serve as a residence for demented elderly. Although these institutions differ considerably regarding financing and care facilities, specific functions of each institute concerning demented elderly have not been clearly defined. In order to know to what extent residential facilities serve demented elderly, the prevalence and severity of dementia among residents aged 65 and over was studied as part of a prevalence study among elderly people in a rural area of the Netherlands. The target population existed of all persons aged 65 and over who were registered in eight general practices. Patients who had to leave the practice on account of ill-health and were admitted to nursing homes were included in the study. In a two stage study the MMSE was applied as a screening instrument. Based on MMSE-score a non-proportional stratified random sample was drawn for the second, diagnostic stage, which existed of the CAMDEX. Prevalence estimates for DSM-III-R-dementia were 21% among residents of homes for the aged, 48% among residents of somatic wards of nursing homes and 100% among those admitted to psychogeriatric wards of nursing homes. Severity of dementia was highest among residents of psychogeriatric wards of nursing homes and lowest among those living in homes for the aged. Prevalence of dementia among residents of homes for the aged can be fully attributed to the age-distribution. The high frequency of dementia among residents of somatic nursing home wards can be explained in several ways: First, admission can be necessary due to a combination of dementia and somatic illness.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
102.
An 8-b 650-MHz folding analog-to-digital converter (ADC) with analog error correction in the comparators is presented. With an input frequency of 150 MHz, 7.8 effective bits are obtained. The ADC is implemented in a 1-μm 13-GHz triple-level interconnect bipolar process, requiring 850 mW from a single -4.5 V supply. The die size is 4.2 mm2  相似文献   
103.
Porphyromonas endodontalis (formerly Bacteroides endodontalis) is a black-pigmented anaerobic Gram-negative rod which is associated with endodontal infections. It has been isolated from infected dental root canals and submucous abscesses of endodontal origin. The presence of P. endodontalis in infected dental root canals has been correlated with symptoms of an acute infection. It is occasionally found on oral mucous membranes and periodontal pockets. P. endodontalis has shown relatively low virulence in experimental monoinfections. In anaerobic mixed infections it can play an essential role. Differences in virulence between strains have been related to capsular material. On the basis of different types of capsules, three serotypes have been described. P. endodontalis is sensitive to a wide range of antibiotics, including the penicillins, the tetracyclines, and metronidazole.  相似文献   
104.
An efficient iterative method for solving quasi-static electromagnetic field problems is presented. The electromagnetic field is generated by an inductive applicator and is represented as a superposition of two constituents, viz. a primary field in absence of the tissue configuration and a secondary field generated by the presence of the tissue. Then, for the secondary field a quasi-static approximation is employed. In the quasi-static field equations a relaxation function is introduced, such that the resulting equations can be solved iteratively. For a realistic three-dimensional model of a human hand numerical results are presented.  相似文献   
105.
106.
107.
108.
A learning event can be dissociated into 3 components: acquisition, storage, and recall. When the laboratory wild-type strain of Caenorhabditis elegans (N2 strain) is exposed to benzaldehyde in the absence of food, the worms display a reduction of their attractive response to this volatile odorant. This results from the association between benzaldehyde and a nutrient-deficient environment. Another wild-type isolate, the CB4856 strain, fails to display this decreased response to benzaldehyde after exposure to benzaldehyde in the absence of food. However, like the N2 strain, when tested to isoamyl alcohol after benzaldehyde conditioning, the CB4856 strain displays a decreased isoamyl alcohol response. Therefore, the CB4856 strain does not have an acquisition deficit, but it suffers from a recall deficit specific to benzaldehyde. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
109.
New climate change scenarios for the Netherlands.   总被引:4,自引:0,他引:4  
A new set of climate change scenarios for 2050 for the Netherlands was produced recently. The scenarios span a wide range of possible future climate conditions, and include climate variables that are of interest to a broad user community. The scenario values are constructed by combining output from an ensemble of recent General Climate Model (GCM) simulations, Regional Climate Model (RCM) output, meteorological observations and a touch of expert judgment. For temperature, precipitation, potential evaporation and wind four scenarios are constructed, encompassing ranges of both global mean temperature rise in 2050 and the strength of the response of the dominant atmospheric circulation in the area of interest to global warming. For this particular area, wintertime precipitation is seen to increase between 3.5 and 7% per degree global warming, but mean summertime precipitation shows opposite signs depending on the assumed response of the circulation regime. Annual maximum daily mean wind speed shows small changes compared to the observed (natural) variability of this variable. Sea level rise in the North Sea in 2100 ranges between 35 and 85 cm. Preliminary assessment of the impact of the new scenarios on water management and coastal defence policies indicate that particularly dry summer scenarios and increased intensity of extreme daily precipitation deserves additional attention in the near future.  相似文献   
110.
Models and methods are presented for determining practical limits of the packing density of TRISO particles in fuel pebbles for a pebble-bed reactor (PBR). These models are devised for designing and interpreting fuel testing experiments. Two processes for particle failure are accounted for: failure of touching particles at the pressing stage in the pebble manufacturing process and failure due to inner pressure buildup during irradiation. The second process gains importance with increasing fuel temperature, which limits the particle packing density and the corresponding fuel enrichment. Suggestions for improvements to the models are presented.  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