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   513篇
  免费   29篇
  国内免费   1篇
电工技术   5篇
综合类   1篇
化学工业   105篇
金属工艺   5篇
机械仪表   15篇
建筑科学   56篇
矿业工程   4篇
能源动力   28篇
轻工业   30篇
水利工程   6篇
石油天然气   1篇
无线电   26篇
一般工业技术   105篇
冶金工业   65篇
原子能技术   7篇
自动化技术   84篇
  2023年   7篇
  2022年   13篇
  2021年   8篇
  2020年   7篇
  2019年   9篇
  2018年   19篇
  2017年   22篇
  2016年   9篇
  2015年   7篇
  2014年   16篇
  2013年   32篇
  2012年   21篇
  2011年   34篇
  2010年   26篇
  2009年   28篇
  2008年   36篇
  2007年   24篇
  2006年   27篇
  2005年   21篇
  2004年   14篇
  2003年   13篇
  2002年   16篇
  2001年   13篇
  2000年   7篇
  1999年   5篇
  1998年   10篇
  1997年   4篇
  1996年   11篇
  1995年   6篇
  1994年   7篇
  1993年   2篇
  1992年   3篇
  1991年   4篇
  1990年   3篇
  1989年   4篇
  1988年   2篇
  1986年   3篇
  1985年   2篇
  1984年   2篇
  1983年   6篇
  1982年   5篇
  1981年   5篇
  1980年   3篇
  1979年   2篇
  1978年   3篇
  1977年   5篇
  1975年   3篇
  1974年   4篇
  1973年   2篇
  1959年   2篇
排序方式: 共有543条查询结果,搜索用时 15 毫秒
41.
Spatial analysis of annual air pollution exposure and mortality   总被引:1,自引:0,他引:1  
The aim of this study was to relate ambient air pollution levels to mortality in Auckland, New Zealand. We used urban airshed modelling and GIS-based techniques to quantify long-term exposure to ambient air pollution levels and associated mortality. After adjusting for age, sex, ethnicity, socio-economic status, and urban/rural domicile there was a 1.3% (95%CI: 1-1.5%) increase in non-external cause mortality, and 1.8% (95%CI: 1.5-2.1%) increase in circulatory and respiratory causes per 1 microg/m(3) increase in annual average NO(2). Based on these exposure-response relationships and applying an annual average threshold of 13 microg/m(3), the average annual (for 1996-1999) number of people estimated to die from non-external causes and circulatory and respiratory causes attributable to air pollution in Auckland is 268 (95% range: 227-310) (3.9% of total all cause deaths) and 203 (95% range: 169-237) (5.9% of total circulatory and respiratory deaths) per year, respectively. The number of attributable deaths found in this study are consistent with a previous New Zealand risk assessment using a different methodology, and is approximately twice the number of people dying from motor vehicle accidents in the region, which is on average (1996-1999) 103 per year. The GIS-based exposure maps identify high exposure areas for policy developers and planners in a simple and realistic manner. Taken together with overseas studies the study provides additional evidence that long-term exposure to poor air quality, even at levels below current standards, is a hazard to the public health.  相似文献   
42.
The reaction of equivalent quantities of sec-butyllithium with m-diisopropenylbenzene in cyclohexane and benzene solution in the presence and absence of catalytic amounts of triethylamine, does not yield the diadduct quantitatively. Oligomer formation occurs to varying extents depending on the reaction conditions, and, contrary to claims in the literature, this may not be a good route to a difunctional initiator for anionic polymerization.  相似文献   
43.
An overview of methods being used at the University of Missouri-Rolla to measure differential ionisation for positron impact is presented. Examples of triply differential electron emission and doubly differential positron scattering and energy loss data are given and contributions to each due to binary and recoil events are discussed. In addition, angular distribution data for electron emission due to double and triple ionisation are presented.  相似文献   
44.
Base Resistance of Jacked Pipe Piles in Sand   总被引:1,自引:0,他引:1  
The paper presents the results from an experimental program carried out at Trinity College Dublin, in which instrumented model piles were jacked into loose dry sand in a large testing chamber. A number of pile installations were carried out to study the effects of in situ stress, diameter, and wall thickness on the behavior of open-ended piles in sand. These indicated that plug stiffness and capacity may be expressed as simple functions of the cone penetration test end resistance and the incremental filling ratio prior to loading. The magnitude and distribution of shear stresses measured on the inner wall are shown to be compatible with existing experimental data and can be related directly to the stress level, interface friction angle, and dilation of the sand at the pile wall. The data are shown to facilitate a better understanding of the factors controlling plug resistance.  相似文献   
45.
Understanding longitudinal trends in the processing of carbon in rivers represents a much conceptualised, but infrequently tested, issue in aquatic ecology. In this study, we conducted concurrent longitudinal examinations of three very different rivers in eastern Australia to determine whether general principles in river functioning exist across broad geographic and hydrologic scales. Specifically, we examined trends in ambient basic water chemistry, nutrient concentrations, dissolved organic carbon (DOC), extracellular enzymes and food web structure and functioning and conducted bioassays to examine the degree to which DOC and nutrients limit heterotrophic bacterial respiration. These parameters revealed striking similarities across all sites. For metazoan communities, stable isotope analysis showed that algal carbon was the dominant basal resource utilised by consumers in all three rivers, suggesting that in‐stream primary producers strongly underpin trophic pathways regardless of the position within a catchment or catchment condition. Analyses of extracellular enzymes revealed that microbial communities are actively utilising DOC at all sites. In fact, heterotrophic microbial respiration was strongly limited by DOC at all sites, with nutrient additions resulting in only relatively minor increases in respiration. Ultimately, this study demonstrates that DOC and algal carbon are critically important drivers of ecosystem processes in Australian riverine ecosystems. Furthermore, across all of our sites and rivers, ambient nutrient concentrations did not influence carbon processing. The consistent longitudinal trends in river function identified in this study provide useful insights for catchment managers and modellers with respect to identifiying key principles that underpin ecosystem functioning in Australian rivers. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   
46.
Refinement-closed security properties allow the verification of systems for all possible implementations. Some systems, however, have refinements that do not represent possible implementations. In particular, real instantiations of abstract systems comprising security-critical components surrounded by maximally hostile unrefined components are often characterised only by compositions of refinements of the abstract system's components, rather than all refinements of the abstract system. In this case, refinement-closed security properties that examine multiple behaviours of a system at once can be falsely violated by the presence of inconsistent pairs of behaviour arising from different, incompatible refinements of the system's components.We show how to weaken a class of such properties, which includes both information flow and causation properties, to allow them to be applied to these sorts of abstract systems. The weakened properties ignore all pairs of inconsistent behaviour that would have violated the original property from which they are derived. We also show how to adapt existing automated tests for these properties to allow them to be used to test for their weakened counterparts instead. This enables greater flexibility in the application of these sorts of properties to compositions of nondeterministic components.  相似文献   
47.
48.
This paper presents a preliminary compilation and analysis of the water reported to have been consumed by a range of various mineral commodities and compares it to mine production data. This has been undertaken to assess and quantify the ‘embodied water’ of mineral products—a key aspect of sustainability (embodied water is the total water required to produce a good or service). At present, although the use of formal reporting protocols such as the global reporting initiative (GRI) is increasing, there are still critical weaknesses. Some key aspects to facilitate proper water accounting are not listed in sustainability reports, including the extent of recycled water used, mine site water inventories, the quality of various waters, and impacts on water resources. Based on the data compiled, there is wide variation in the water used for different mineral commodities as well as for the same commodity. There is little evidence for ‘economies of scale’ in base metals and bulk minerals, though for precious metals (gold, platinum), greater throughput does tend to lead to greater efficiency. For many mines, there is little evidence of improving efficiency over time, although some mines have made substantive improvements in reducing water consumed. The grade of ore being processed is clearly critical in understanding the embodied water of minerals, with declining ore grades leading to an increased chance of higher embodied water in the future. Given that many metals are declining in average ore grade, the sensitivity of embodied water to ore grade provides a major sustainability challenge for mining generally. In summary, the embodied water of minerals is clearly significant, and will likely gradually increase in the future, and so must be more completely accounted for to understand a fundamental aspect of sustainability and mining—that of water resources.  相似文献   
49.
This paper presents some crystalline structures which can be taken as the approximants of the corresponding metallic glassy phases. Such phases have a clustered structure and preferably (but not strictly necessarily) a large unit cell. Peak intensities of their radial distribution functions (RDFs) must be integrated at a step of about 0.01 nm in order to obtain RDFs similar to those of the corresponding glassy alloys owing to a degree of disorder related to the corresponding glassy structures.  相似文献   
50.
Bioabsorbable polyglycolide-co-lactide microtubes have been developed for the continuous delivery of fluid medications directly to an operative site. Studies conducted with radio-opaque solution using porcine models indicated that infusion of fluids in the wound site was rapid and complete. The tissue reaction to the microtube was generally characterized as minimal to mild with complete absorption occurring within 56 days postimplantation. Processing–microstructure-property relationships and bio-degradation characteristics of the microtubes 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