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   317篇
  免费   14篇
电工技术   2篇
化学工业   79篇
金属工艺   4篇
机械仪表   4篇
建筑科学   16篇
能源动力   1篇
轻工业   64篇
无线电   10篇
一般工业技术   45篇
冶金工业   60篇
自动化技术   46篇
  2023年   6篇
  2022年   11篇
  2021年   23篇
  2020年   13篇
  2019年   5篇
  2018年   21篇
  2017年   10篇
  2016年   3篇
  2015年   6篇
  2014年   10篇
  2013年   25篇
  2012年   10篇
  2011年   26篇
  2010年   10篇
  2009年   14篇
  2008年   18篇
  2007年   13篇
  2006年   12篇
  2005年   8篇
  2004年   6篇
  2003年   7篇
  2002年   4篇
  2001年   5篇
  2000年   4篇
  1999年   6篇
  1998年   4篇
  1997年   3篇
  1996年   5篇
  1995年   3篇
  1994年   4篇
  1993年   3篇
  1992年   5篇
  1991年   1篇
  1989年   3篇
  1988年   1篇
  1987年   4篇
  1986年   1篇
  1983年   1篇
  1982年   1篇
  1981年   1篇
  1980年   4篇
  1979年   1篇
  1978年   1篇
  1977年   2篇
  1973年   1篇
  1970年   1篇
  1966年   1篇
  1960年   1篇
  1959年   1篇
  1958年   1篇
排序方式: 共有331条查询结果,搜索用时 15 毫秒
51.
Three methods of assessing the non‐pecuniary benefits of good quality water are suggested. One depends on calculating the implicit valuation accorded them by the existing expenditure on pollution control and from the amount of “damage” caused. A second method consists in calculating all the costs imposed on users of water before and after a control programme is put into operation. Both these methods require more information about expenditure than is at present usually available. A third proposal uses biological assessment of water quality as a representative of the other “intangibles”. Since high biological quality indicates a water suitable for any other use this could be a useful approximation. When information on expenditure is also available, it is possible to calculate a cost for achieving a given quality in a particular situation, which could be used in cost‐effectiveness comparisons of different programmes or different situations.  相似文献   
52.
This paper defines stock transfer organisations and argues that they have a pivotal role in accessing funding for the social and economic regeneration of their communities. It places housing and regeneration policy within the changing policy context of ‘new localism’, which, at least rhetorically, emphasises improvement in public services, multi-level governance structures and devolution of decision making. For stock transfer housing organisations this means an increasing need to engage in a wide range of partnerships and policy forums. Bourdieu's notion of habitus, i.e. social, economic and cultural capital, is used to explore the possible reasons for the differential approach of stock transfer organisations to regeneration and the variable success at engaging in a wide range of regeneration activity and attracting additional resources.  相似文献   
53.
Previous studies have shown the worldwide presence of six congeners of polybrominated diphenyl ethers (PBDEs) in marine biota (BDE-28, -47, -99, -100, -153 and -154). The objective of the present study was to document their presence, their level and their transfer in the food web of two major estuaries in France, the Loire and the Seine. PBDEs were quantified in eight principal species from the Loire, representing primary consumers (the bivalve Scrobicularia plana), omnivores (the worm Nereis diversicolor, the shrimps Crangon crangon, Palaemon elegans and Palaemon serratus, the flatfish Platichthys flesus and Solea solea) and supercarnivores (the eel Anguilla anguilla). In the Seine, only worms, bivalves, sole and eels have been studied. Parameters, which can interfere with the interpretation of contamination data (organ distribution, influence of weight or size of specimens, lipid richness, intrinsic variability), have been examined. BDE-47 was the predominant congener in all biota. Higher contamination was observed in most of the species collected from the Seine, in agreement with the higher human presence and economic activity in the Seine than in the Loire basin. PBDEs have been shown to biomagnify in both of the studied estuarine food webs. However, assessment of PBDE transfer from seafood products exposed to contaminants in the Seine estuary showed that human daily intake is far below the no observed adverse effect levels.  相似文献   
54.
An automatic method is established for layer‐by‐layer (LbL) assembly of biomimetic coatings in cell culture microplates using a commercial liquid‐handling robot. Highly homogeneous thin films are formed at the bottom of each microwell. The LbL film‐coated microplates are compatible with common cellular assays, using microplate readers and automated microscopes. Cellular adhesion is screened on crosslinked and peptide‐functionalized LbL films and stem cell differentiation in response to increasing doses of bone morphogenetic proteins (2, 4, 7, 9). This method paves the way for future applications of LbL films in cell‐based assays for regenerative medicine and high‐throughput drug screening.  相似文献   
55.
56.
57.

Objective

The aim of this study was to determine whether pre-licence driving experiences, that is driving before beginning the licensing process, increased or decreased crash risk as a car driver, during the learner or the restricted licence stages of the graduated driver licensing system (GDLS).

Method

Study participants were 15–24 year old members of the New Zealand Drivers Study (NZDS) – a prospective cohort study of newly licensed car drivers. The interview stages of the NZDS are linked to, the three licensing stages of the GDLS: learner, restricted and full. Baseline demographic (age, ethnicity, residential location, deprivation), personality (impulsivity, sensation seeking, aggression) and, behavioural data, (including pre-licensed driving behaviour), were obtained at the learner licence interview. Data on distance driven and crashes that occurred at the learner licence and restricted licence stages, were reported at the restricted and full licence interviews, respectively. Crash data were also obtained from police traffic crash report files and this was combined with the self-reported crash data. The analysis of the learner licence stage crashes, when only supervised driving is allowed, was based on the participants who had passed the restricted licence test and undertaken the NZDS, restricted licence interview (n = 2358). The analysis of the restricted licence stage crashes, when unsupervised driving is first allowed, was based on those who had passed the full licence test and completed the full licence interview (n = 1428).

Results

After controlling for a range of demographic, personality, behavioural variables and distance driven, Poisson regression showed that the only pre-licence driving behaviour that showed a consistent relationship with subsequent crashes was on-road car driving which was associated with an increased risk of being the driver in a car crash during the learner licence period.

Conclusion

This research showed that pre-licensed driving did not reduce crash risk among learner or restricted licensed drivers, and in some cases (such as on-road car driving) may have increased risk. Young people should be discouraged from the illegal behaviour of driving a car on-road before licensing.  相似文献   
58.
The oxidation resistance of β-Sialon processed with Y2O3 sintering additive and β-Sialon/TiN composites containing 1–10 wt% TiN was studied using ion beam analysis (IBA) techniques, augmented by XRD and SEM measurements. Rutherford backscattering spectrometry was used to monitor the diffusion of Y and Ti in the oxidised samples, and the diffusion of oxygen and nitrogen was observed by particle-induced gamma emission and nuclear reaction analysis. These techniques showed that in the Sialon control sample without TiN, oxygen was the first element to migrate at 1000 °C, followed by Y and N at 1100 °C. At 1200 °C, a N-poor, Y- and O-rich oxidised layer was formed, containing crystalline Y2Si2O7. In the TiN-containing samples, Si, Al, Y and Ti were very mobile even at 1000 °C and the surface nitrogen was depleted by 1250 °C. The combined presence of yttrium aluminium garnet (YAG) and TiN protects the β-Sialon phase by forming an oxygen-rich crystalline barrier layer. The oxidation products of TiN in these composites are TiO2 and Y2Ti2O7. The details of the oxidation mechanism of the β-Sialon/TiN composites provided by these IBA studies (movement of yttrium and titanium, replacement of nitrogen by oxygen in the glassy yttrium phase and major crystalline and chemical changes in an outer oxidised layer) could not readily have been obtained by any other techniques, and illustrate the value of IBA for oxidation studies of non-oxide ceramics.  相似文献   
59.
Abstract

Samuel Bourne was one of the great pioneers of travel photography, and the photographs which he took in India during the 1860s have become familiar to a wide audience through their inclusion in exhibitions, their use as book illustrations and also through television coverage. Although acknowledging the merit of that aspect of his work, this paper discusses the hitherto comparatively little-known role which he played in the arena of photography during the period immediately before he went to India, and also his activities in the latter part of the 19th and early 20th centuries.  相似文献   
60.
The durability of an organic color and its resistance against external chemical agents and exposure to light can be significantly enhanced by hybridizing the natural dye with a mineral. In search for stable natural pigments, the present work focuses on the association of indigo blue with several zeolitic matrices (LTA zeolite, mordenite, MFI zeolite). The manufacturing of the hybrid pigment is tested under varying oxidizing conditions, using Raman and ultraviolet-visible (UV-Vis) spectrometric techniques. Blending indigo with MFI is shown to yield the most stable composite in all of our artificial indigo pigments. In the absence of defects and substituted cations such as aluminum in the framework of the MFI zeolite matrix, we show that matching the pore size with the dimensions of the guest indigo molecule is the key factor. The evidence for the high color stability of indigo@MFI opens a new path for modeling the stability of indigo in various alumino-silicate substrates such as in the historical Maya Blue pigment.  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