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   476292篇
  免费   4502篇
  国内免费   1499篇
电工技术   8121篇
综合类   607篇
化学工业   72184篇
金属工艺   23338篇
机械仪表   16353篇
建筑科学   9991篇
矿业工程   4617篇
能源动力   10120篇
轻工业   30210篇
水利工程   6490篇
石油天然气   16025篇
武器工业   68篇
无线电   49231篇
一般工业技术   106021篇
冶金工业   76069篇
原子能技术   15625篇
自动化技术   37223篇
  2021年   4495篇
  2019年   4216篇
  2018年   7814篇
  2017年   8150篇
  2016年   8625篇
  2015年   4944篇
  2014年   8497篇
  2013年   20069篇
  2012年   12823篇
  2011年   16860篇
  2010年   13412篇
  2009年   15239篇
  2008年   15605篇
  2007年   15319篇
  2006年   12865篇
  2005年   11676篇
  2004年   11544篇
  2003年   11250篇
  2002年   10877篇
  2001年   10818篇
  2000年   10413篇
  1999年   10162篇
  1998年   22042篇
  1997年   16256篇
  1996年   12452篇
  1995年   9800篇
  1994年   8797篇
  1993年   8955篇
  1992年   6963篇
  1991年   6895篇
  1990年   6807篇
  1989年   6704篇
  1988年   6338篇
  1987年   5917篇
  1986年   5839篇
  1985年   6345篇
  1984年   5961篇
  1983年   5669篇
  1982年   5272篇
  1981年   5423篇
  1980年   5408篇
  1979年   5353篇
  1978年   5554篇
  1977年   5879篇
  1976年   7168篇
  1975年   4912篇
  1974年   4968篇
  1973年   5014篇
  1972年   4350篇
  1971年   3945篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
Institute of Mining, Siberian Branch, Academy of Sciences of the USSR, Novosibirsk. Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 1, pp. 114–118, January–February, 1989.  相似文献   
44.
An analysis is performed for the existing hypotheses and theories used for calculating the technological parameters of operations on methane extraction from coal seams. The priority of geodynamic processes in methane collector formation, as well as the methods applied for the morphometry and processing of the remote probing data are substantiated. The urgency is shown for the investigation into the autooxidation and other exothermic reactions proceeding in coal seams and leading to methane transition to the free state.  相似文献   
45.
The relevance of particle mass, surface area or number concentration as risk indicators for health effects in non-industrial buildings has been assessed by a European interdisciplinary group of researchers (called EUROPART) by reviewing papers identified in Medline, Toxline, and OSH. Studies dealing with dermal effects or cancer or specifically addressing environmental tobacco smoke, house dust-mite, cockroach or animal allergens, microorganisms and pesticides were excluded. A total of 70 papers were reviewed, and eight were identified for the final review: Five experimental studies involving mainly healthy subjects, two cross-sectional office studies and one longitudinal study among elderly on cardiovascular effects. From most studies, no definite conclusions could be drawn. Overall, the group concluded that there is inadequate scientific evidence that airborne, indoor particulate mass or number concentrations can be used as generally applicable risk indicators of health effects in non-industrial buildings and consequently that there is inadequate scientific evidence for establishing limit values or guidelines for particulate mass or number concentrations.  相似文献   
46.
We report the results of experiments designed to improve the efficacy of the solar disinfection of drinking water, inactivation process. The effects of periodic agitation, covering the rear surface of the container with aluminium foil, container volume and turbidity on the solar inactivation kinetics of Escherichia coli (starting population = 10(6) CFU ml(-1)) were investigated. It was shown that agitation promoted the release of dissolved oxygen from water with subsequent decrease in the inactivation rates of E. coli. In contrast, covering the rear surface of the solar disinfection container with aluminium foil improved the inactivation efficiency of the system. The mean decay constant for bacterial populations in foil-backed bottles was found to be a factor of 1.85 (std. dev. = 0.43) higher than that of non-foil-backed bottles. Inactivation rates decrease as turbidity increases. However, total inactivation was achievable in 300 NTU samples within 8 h exposure to strong sunshine. Inactivation kinetics was not dependent on the volume of the water container for volumes in the range 500-1500 ml.  相似文献   
47.
Elimination of beta-blockers in sewage treatment plants   总被引:2,自引:0,他引:2  
beta-Blockers are used to treat high blood pressure as well as patients recovering from heart attacks. In several studies, they were detected in surface water, thus indicating incomplete degradability of these substances in sewage treatment plants (STPs). In this study, we determined the sorption coefficients (K(D)) and degradation rates of the four beta-blockers sotalol, atenolol, metoprolol and propranolol in sludge from an STP operating with municipal wastewater. The sorption coefficients (K(D), standard deviations in brackets) were determined as 0.04(+/-0.035), 0.04(+/-0.033), 0.00(+/-0.023) and 0.32(+/-0.058) Lg(-1)(COD), and the pseudo-first-order degradation rate constants were estimated to be 0.29(+/-0.02), 0.69(+/-0.05), 0.58(+/-0.05) and 0.39(+/-0.07) Ld(-1)g(-1)(COD) for sotalol, atenolol, metoprolol and propranolol, respectively. These values translate into a typical elimination in STPs (sludge concentrations of 4g(COD)L(-1) and a hydraulic retention time of 6h) of 25%, 37%, 44% and 50% for sotalol, propranolol, metoprolol and atenolol, respectively. These results are also confirmed by measurements in two municipal STPs for atenolol, sotalol and propranolol. The estimated eliminations are slightly too high for metoprolol.  相似文献   
48.
Walk through questionnaires may be feasible tools to obtain data on the indoor environment in community studies. However, limited information is available regarding the reproducibility of the data obtained through these questionnaires. In this pilot study, two construction engineering students inspected ten dwellings twice by means of a standardized walk through questionnaire. The two engineering students inspected the dwellings independent of each other within two months. Time between the two visits varied between 14 and 40 days. The variables presented were based on information from the residents and inspection. The continuous variables recorded included number of rooms in the dwellings, room volume, length of filled shelves and textile area. The inter- and intra-observed variabilities were poorer for number of rooms and shelf factor than for the other variables. For the 3 of the 9 categorical variables based on inspection, the inter-observer comparison showed complete agreement with a kappa statistics of 1.0, these variables being condition of the window frames and construction of outside walls and roof. One of the categorical variables showed a kappa statistics of < 0.5, these variables being presence of basement and presence of condensation at windows. This study indicates a wide variation in observer variability between various items of a walk through questionnaire. Clear definitions of all the parts of the questionnaire are needed, as well as thorough training of observers.  相似文献   
49.
In this paper the migration routes of British Asian women living in London are examined. It is shown that British Asians connect with a myriad of landscapes abroad, including East Africa, India and Pakistan. These connections to past landscapes are mapped and considered here as valued environments of British Asian women in Britain. Through the mapping of their biographies, it is apparent that memories of other landscapes are embedded in environmental practices in Britain, therefore contributing to making the landscape in Britain inclusive and meaningful in the context of the South Asian migration. The maps of migration show the heterogeneity of landscapes experienced by the British Asian women. Memories of other lands manifest themselves in the UK. The effect of these memories on the South Asian home itself in the process of shaping diasporic geographies of belonging and being within the UK is illustrated.  相似文献   
50.
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