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   824篇
  免费   57篇
  国内免费   1篇
电工技术   4篇
综合类   1篇
化学工业   178篇
金属工艺   5篇
机械仪表   13篇
建筑科学   36篇
矿业工程   1篇
能源动力   20篇
轻工业   94篇
水利工程   18篇
石油天然气   1篇
无线电   107篇
一般工业技术   139篇
冶金工业   132篇
原子能技术   14篇
自动化技术   119篇
  2023年   18篇
  2022年   24篇
  2021年   53篇
  2020年   29篇
  2019年   25篇
  2018年   37篇
  2017年   32篇
  2016年   25篇
  2015年   25篇
  2014年   24篇
  2013年   49篇
  2012年   47篇
  2011年   45篇
  2010年   32篇
  2009年   31篇
  2008年   34篇
  2007年   35篇
  2006年   20篇
  2005年   18篇
  2004年   19篇
  2003年   18篇
  2002年   5篇
  2001年   10篇
  2000年   6篇
  1999年   14篇
  1998年   30篇
  1997年   18篇
  1996年   12篇
  1995年   8篇
  1994年   14篇
  1993年   7篇
  1992年   8篇
  1991年   7篇
  1990年   8篇
  1989年   5篇
  1988年   4篇
  1987年   7篇
  1985年   4篇
  1983年   5篇
  1982年   5篇
  1980年   5篇
  1978年   6篇
  1977年   5篇
  1976年   11篇
  1975年   4篇
  1974年   4篇
  1973年   4篇
  1971年   3篇
  1969年   3篇
  1967年   3篇
排序方式: 共有882条查询结果,搜索用时 93 毫秒
41.
42.
43.
44.

Background  

Decreased bone mineral density and osteoporosis in postmenopausal women represents a growing source of physical limitations and financial concerns in our aging population. While appropriate medical treatments such as bisphosphonate drugs and hormone replacement therapy exist, they are associated with serious side effects such as osteonecrosis of the jaw or increased cardiovascular risk. In addition to calcium and vitamin D supplementation, previous studies have demonstrated a beneficial effect of dietary silicon on bone health. This study evaluated the absorption of silicon from bottled artesian aquifer water and its effect on markers of bone metabolism.  相似文献   
45.
This review identified fourteen reported illness outbreaks attributed to consumption of pathogen-contaminated spice during the period 1973–2010. Countries reporting outbreaks included Canada, Denmark, England and Wales, France, Germany, New Zealand, Norway, Serbia, and the United States. Together, these outbreaks resulted in 1946 reported human illnesses, 128 hospitalizations and two deaths. Infants/children were the primary population segments impacted by 36% (5/14) of spice-attributed outbreaks. Four outbreaks were associated with multiple organisms. Salmonella enterica subspecies enterica was identified as the causative agent in 71% (10/14) of outbreaks, accounting for 87% of reported illnesses. Bacillus spp. was identified as the causative agent in 29% (4/10) of outbreaks, accounting for 13% of illnesses. 71% (10/14) of outbreaks were associated with spices classified as fruits or seeds of the source plant. Consumption of ready-to-eat foods prepared with spices applied after the final food manufacturing pathogen reduction step accounted for 70% of illnesses. Pathogen growth in spiced food is suspected to have played a role in some outbreaks, but it was not likely a contributing factor in three of the larger Salmonella outbreaks, which involved low-moisture foods. Root causes of spice contamination included contributions from both early and late stages of the farm-to-table continuum.  相似文献   
46.
Monoculture farming systems have had serious environmental impacts such as loss of biodiversity and pollinator decline. The authors explain how temperate agroforestry systems show potential in being able to deliver multiple environmental benefits.  相似文献   
47.
The analysis of almost 200 Scottish Sphagnum moss samples collected over the past 170 years has revealed trends in the isotopic composition of lead similar to those previously established for dated Scottish lake sediments and peat bogs, lending credibility to these proxy records of atmospheric lead contamination and deposition. The effect of temporal variations in contributions from sources such as smelting of indigenous lead ores (206Pb/207Pb approximately 1.16-1.18), coal combustion (206Pb/207Pb approximately 1.17-1.19), and the use of imported Australian lead (206Pb/207Pb approximately 1.04) was clearly seen in the Scottish moss 206Pb/207Pb record. This showed some differences from the corresponding archival herbage record for the south of England, where the initial influence of Australian lead occurred earlier, at the end of the 19th century. A significant decline from a 206Pb/ 207Pb value of approximately 1.17 in the Scottish moss record began in the 1920s and continued until the 1980s (206Pb/207Pb approximately 1.12). The success of measures to reduce lead emissions to the atmosphere over the past 20 years in the U.K., in particular from petrol-engined vehicles using alkyl lead additives manufactured primarily from Australian lead, is evident in both the increasing 206Pb/207Pb ratio and falling lead concentration data for Scottish moss.  相似文献   
48.
The paper presents Bayesian information fusion theory in the context of neural-network model combination. It shows how confidence measures can be combined with individual model estimates to minimize risk through the fusion process. The theory is illustrated through application to the real task of quality prediction in the papermaking industry. Prediction uncertainty estimates are calculated using approximate Bayesian learning. These are incorporated into model combination as confidence measures. Cost functions in the fusion center are used to control the influence of the confidence measures and improve the performance of the resultant committee.  相似文献   
49.
This paper explores the economics of solar-plus-storage projects for commercial-scale, behind-the-meter applications. It provides insight into the near-term and future solar-plus-storage market opportunities across the U.S. We explore the impacts of location, building load profile, technology cost, utility rate structure, and policies on solar-plus-storage economic viability, and identify which factors are most significant to project economics. While savings from storage-only projects are largely derived from demand charge reductions, solar combined with storage also provides significant energy charge savings. A common assumption is that load profiles with peaks are likely candidates for savings from storage, due to the opportunity for demand charge reduction. Our results indicate that potential for savings from combining solar with storage is independent of building load variability, likely due to the energy cost reductions from the solar. Systems are more often economical under time of use and demand charge rates, particularly when demand charges are >$10 per kilowatt. Where systems were found to be economical, expected lifetime savings averaged between 7%–10%, with savings of 30% in numerous cases. Near term markets exist for solar-plus-storage in locations such as California and New York. As technology prices drop, the number of building types that can benefit increase, and additional markets appear in Colorado, New Mexico, and Alaska. All data from the study and interactive modeling results are available at: https://openei.org/wiki/Solar+Storage.  相似文献   
50.
The authors demonstrate an erbium-doped optical power limiting amplifier (OLA), study its noise characteristics, and discuss its application in the protection rings of a four-fiber, SONET self-healing interoffice ring network. System and network considerations are also presented. The feasibility of the network was tested by a system experiment using an OLA for up to 200-km conventional single-mode fiber transmission at a bit rate of 1.244 Gb/s (OC-24 line rate)  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