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   1439篇
  免费   3篇
电工技术   16篇
化学工业   60篇
金属工艺   7篇
机械仪表   6篇
建筑科学   6篇
矿业工程   1篇
能源动力   5篇
轻工业   90篇
水利工程   1篇
无线电   85篇
一般工业技术   62篇
冶金工业   1055篇
原子能技术   7篇
自动化技术   41篇
  2021年   5篇
  2019年   3篇
  2018年   3篇
  2015年   3篇
  2014年   8篇
  2013年   26篇
  2012年   6篇
  2011年   11篇
  2010年   8篇
  2009年   10篇
  2008年   13篇
  2007年   19篇
  2006年   14篇
  2005年   12篇
  2004年   7篇
  2003年   16篇
  2002年   9篇
  2001年   16篇
  2000年   15篇
  1999年   42篇
  1998年   284篇
  1997年   172篇
  1996年   122篇
  1995年   73篇
  1994年   65篇
  1993年   70篇
  1992年   26篇
  1991年   17篇
  1990年   28篇
  1989年   27篇
  1988年   30篇
  1987年   25篇
  1986年   18篇
  1985年   22篇
  1984年   5篇
  1983年   11篇
  1982年   4篇
  1981年   9篇
  1980年   15篇
  1979年   10篇
  1978年   11篇
  1977年   31篇
  1976年   68篇
  1975年   11篇
  1974年   5篇
  1973年   7篇
  1971年   3篇
  1970年   3篇
  1969年   4篇
  1965年   3篇
排序方式: 共有1442条查询结果,搜索用时 15 毫秒
1.
California is the leading state for the production of almonds, with more than 400,000 bearing hectares of orchards that produced approximately 1 billion kilograms of shelled nuts in 2017. Almond hulls (AH) are a regional by-product feedstuff fed predominantly to dairy cattle in California. A 2012 study surveyed 40 dairy farms in California and found that 39 out of 104 total mixed rations contained AH, with a mean daily feeding rate of 1.45 kg/cow. In 2017, approximately 2 billion kilograms of AH was produced. At a feeding rate of 1.45 kg/cow daily, even if all 1.7 million lactating cows in California are consuming AH, there will be a surplus of AH on the market as the approximately 130,000 nonbearing hectares come into nut production. Therefore, the potential of feeding varying amounts of AH to lactating dairy cows was investigated using 12 Holstein cows with 4 primiparous and 8 multiparous cows. The dietary treatments were 4 total mixed rations containing 0, 7, 13, or 20% AH. The AH used contained 12.8% crude fiber (as-is basis), which was below the 15% legal limit set by state feed regulations. Diets were formulated so that as the inclusion rate of AH increased, the amount of steam-flaked corn and soyhull pellets decreased and soybean meal inclusion increased. Experimental design was a replicated 4 × 4 Latin square. Diet had a cubic effect on actual milk yield, energy-corrected milk yield, and dry matter intake, with the 7% AH diet having the highest values and the 13% AH diet having the lowest. The percent and yield of total solids and the yields of lactose and fat did not differ with diet, but percent and yield of protein declined linearly with increased AH inclusion, and fat percent increased linearly. Apparent total-tract digestibilities of dry matter and organic matter were higher with the inclusion of AH in the diet. Total percentage of the day spent ruminating increased linearly with higher amounts of AH. Overall, this work demonstrated that AH can be fed at varying amounts, up to 20% of the diet, to lactating dairy cows to support high levels of milk production and that increasing amounts of AH (up to 20%) in the diet could lead to improved digestibility and milk fat percentage but decreased milk protein production.  相似文献   
2.
3.
Glioblastoma multiforme (GBM) is a highly invasive primary brain tumour that has poor prognosis despite aggressive treatment. A hallmark of these tumours is diffuse invasion into the surrounding brain, necessitating a multi-modal treatment approach, including surgery, radiation and chemotherapy. We have previously demonstrated the ability of our model to predict radiographic response immediately following radiation therapy in individual GBM patients using a simplified geometry of the brain and theoretical radiation dose. Using only two pre-treatment magnetic resonance imaging scans, we calculate net rates of proliferation and invasion as well as radiation sensitivity for a patient''s disease. Here, we present the application of our clinically targeted modelling approach to a single glioblastoma patient as a demonstration of our method. We apply our model in the full three-dimensional architecture of the brain to quantify the effects of regional resistance to radiation owing to hypoxia in vivo determined by [18F]-fluoromisonidazole positron emission tomography (FMISO-PET) and the patient-specific three-dimensional radiation treatment plan. Incorporation of hypoxia into our model with FMISO-PET increases the model–data agreement by an order of magnitude. This improvement was robust to our definition of hypoxia or the degree of radiation resistance quantified with the FMISO-PET image and our computational model, respectively. This work demonstrates a useful application of patient-specific modelling in personalized medicine and how mathematical modelling has the potential to unify multi-modality imaging and radiation treatment planning.  相似文献   
4.
Dan Swanson 《EDPACS》2019,59(2):1-5
As I have discussed in past articles, internal audit efforts must be risk-based and contribute to the long-term assurance needs of the organization and its board. A formal risk-assessment audit must be completed at least annually and the results of that assessment should direct audit priorities. Periodic updates throughout the year are also highly recommended. Over time, a focus on short-term results (quarterly financial results, meeting current regulatory requirements, etc.) has driven the priorities of management and consequently the organization toward a short-term perspective. Similarly, internal auditing’s efforts has commonly moved toward this short-term focus, boiling down priorities to whichever audits the company needs to complete in the immediate quarter or two. During the challenging business environment period some would say it is not a good time to refocus sights on the long-term horizon. I disagree. For example, knowing what the organization want to achieve in the next two to five years, and what does it need to do to get there, is critical to success! Certainly, each organization will have different goals, objectives, issues, and challenges, and no single “standard” long-term internal audit plan will work; but I took a shot at it anyway, and present the results in this article.  相似文献   
5.
6.
7.
8.
Aircraft emissions of black carbon (BC) contribute to anthropogenic climate forcing and degrade air quality. The smoke number (SN) is the current regulatory measure of aircraft particulate matter emissions and quantifies exhaust plume visibility. Several correlations between SN and the exhaust mass concentration of BC (C BC) have been developed, based on measurements relevant to older aircraft engines. These form the basis of the current standard method used to estimate aircraft BC emissions (First Order Approximation version 3 [FOA3]) for the purposes of environmental impact analyses. In this study, BC with a geometric mean diameter (GMD) of 20, 30, and 60 nm and filter diameters of 19 and 35 mm are used to investigate the effect of particle size and sampling variability on SN measurements. For BC with 20 and 30 nm GMD, corresponding to BC emitted by modern aircraft engines, a smaller SN results from a given C BC than is the case for BC with 60 nm GMD, which is more typical of older engines. An updated correlation between C BC and SN that accounts for typical size of BC emitted by modern aircraft is proposed. An uncertainty of ±25% accounts for variation in GMD in the range 20–30 nm and for the range of filter diameters. The SN–C BC correlation currently used in FOA3 underestimates by a factor of 2.5–3 for SN ≤15, implying that current estimates of aircraft BC emissions derived from SN are underestimated by the same factor.

Copyright 2013 American Association for Aerosol Research  相似文献   
9.
Nitrate layered double hydroxide (LDH) phase Zn2Al(OH)6(NO3)·2H2O is successfully exfoliated in the presence of polyester under mild conditions using water as essential solvent and at room temperature under air. From small angle X‐ray scattering spectroscopy a total exfoliation is found to be achieved using up to 10 wt % LDH, while intercalated polymer nanocomposite structures largely extended up to 14 nm are observed for loading ranging from 10 to 20 wt %. The process is found to be explained by the diffusion of the polymer chain into the interlayer host structure. Starting from an initial value of 0.89 nm, ≈3, 7, 10, 14, and 20 nm transient interleaved nanostructures are formed without any carbonate uptake. The collective gap distance is certainly due to a defined number of polymer chains diffusing into the LDH interstices. Similarly, starting from an aqueous polyester solution highly concentrated in LDH nitrate phase up to 50% w.w, successive dilutions yield platelet exfoliation, thus rendering a smooth chemistry process attractive for potential applications. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013  相似文献   
10.
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