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   1591篇
  免费   109篇
  国内免费   3篇
电工技术   17篇
综合类   1篇
化学工业   257篇
金属工艺   27篇
机械仪表   16篇
建筑科学   120篇
矿业工程   7篇
能源动力   29篇
轻工业   157篇
水利工程   15篇
石油天然气   1篇
无线电   69篇
一般工业技术   285篇
冶金工业   412篇
自动化技术   290篇
  2023年   19篇
  2022年   13篇
  2021年   23篇
  2020年   25篇
  2019年   37篇
  2018年   51篇
  2017年   55篇
  2016年   54篇
  2015年   57篇
  2014年   62篇
  2013年   121篇
  2012年   92篇
  2011年   115篇
  2010年   71篇
  2009年   53篇
  2008年   77篇
  2007年   69篇
  2006年   64篇
  2005年   44篇
  2004年   35篇
  2003年   33篇
  2002年   29篇
  2001年   25篇
  2000年   15篇
  1999年   24篇
  1998年   113篇
  1997年   64篇
  1996年   47篇
  1995年   26篇
  1994年   19篇
  1993年   22篇
  1992年   9篇
  1991年   12篇
  1990年   4篇
  1989年   9篇
  1988年   6篇
  1987年   5篇
  1986年   5篇
  1985年   9篇
  1984年   12篇
  1983年   5篇
  1982年   3篇
  1981年   10篇
  1980年   7篇
  1979年   6篇
  1978年   3篇
  1977年   13篇
  1976年   16篇
  1975年   5篇
  1973年   3篇
排序方式: 共有1703条查询结果,搜索用时 15 毫秒
81.
82.
83.
Electrical transport properties of molecular junctions are fundamentally affected by the energy alignment between molecular frontier orbitals (highest occupied molecular orbital (HOMO) or lowest unoccupied molecular orbital (LUMO)) and Fermi level (or work function) of electrode metals. Dithiafulvene (DTF) is used as substituent group to the oligo(phenylene ethynylene) (OPE) molecular wires and different molecular structures based on OPE3 backbone (with linear to cruciform framework) are achieved, with viable molecular orbitals and HOMO–LUMO energy gaps. OPE3, OPE3–DTF, and OPE3–tetrathiafulvalene (TTF) can form good self‐assembled monolayers (SAMs) on Au substrates. Molecular heterojunctions based on these SAMs are investigated using conducting probe–atomic force microscopy with different tips (Ag, Au, and Pt) and Fermi levels. The calibrated conductance values follow the sequence OPE3–TTF > OPE3–DTF > OPE3 irrespective of the tip metal. Rectification properties (or diode behavior) are observed in case of the Ag tip for which the work function is furthest from the HOMO levels of the OPE3s. Quantum chemical calculations of the transmission qualitatively agree with the experimental data and reproduce the substituent effect of DTF. Zero‐bias conductance, and symmetric or asymmetric couplings to the electrodes are investigated. The results indicate that improved fidelity of molecular transport measurements may be achieved by systematic studies of homologues series of molecular wires applying several different metal electrodes.  相似文献   
84.
85.
Private investment subsidies are a key instrument for regional policy making to foster the economic development in lagging regions. In this paper, we analyze their effect on labor productivity growth for German labor market regions for the period from 1994 to 2006. A spatially augmented multiplicative interaction model based on neoclassical growth theory is used, which allows us to assess the marginal effect of regional policy proxied by overall payments of the main German regional development program on the region’s convergence speed conditional on its initial income position as well as policy-related spillovers from its spatial neighborhood. Our results show a statistically significant positive effect of regional policy on labor productivity growth, which increases, the further away the supported region is from its steady-state income level, and the more grants are provided to its geographical neighborhood. The latter effect highlights the existence of positive spatial spillover effects from regional policy in Germany, which enhance the attractiveness of the whole macro region for private sector investments. The additional growth stimulus provided by a 1 % increase in the region’s funding volume is thereby related to an up to 0.3 % gain in terms of labor productivity growth. For regions with the highest initial gaps to steady-state income in the sample distribution, the regional policy stimulus accounts for almost 8 % of the regions’ productivity growth performance.  相似文献   
86.
Although the selective excitatory amino acid transporter subtype 1 (EAAT1) inhibitor UCPH‐101 has become a standard pharmacological tool compound for in vitro and ex vivo studies in the EAAT research field, its inability to penetrate the blood–brain barrier makes it unsuitable for in vivo studies. In the present study, per os (p.o.) administration (40 mg kg?1) of the closely related analogue UCPH‐102 in rats yielded respective plasma and brain concentrations of 10.5 and 6.67 μm after 1 h. Three analogue series were designed and synthesized to improve the bioavailability profile of UCPH‐102, but none displayed substantially improved properties in this respect. In vitro profiling of UCPH‐102 (10 μm ) at 51 central nervous system targets in radioligand binding assays strongly suggests that the compound is completely selective for EAAT1. Finally, in a rodent locomotor model, p.o. administration of UCPH‐102 (20 mg kg?1) did not induce acute effects or any visible changes in behavior.  相似文献   
87.
Routine bridge inspections usually consist of visual observations. These inspections are time-consuming and subjective. There is a need to identify new inspection techniques for infrastructure that reduce traffic disturbance, and improve the efficiency and reliability of the acquired data. This study compared the performance of three different imaging technologies for the three-dimensional (3D) geometric modeling of existing structures: terrestrial laser scanning, close-range photogrammetry, and infrared scanning. Each technology was used to assess six existing concrete railway bridges. The technologies were compared in terms of geometric deviations, visualization capabilities, the level of the inspector’s experience, and degree of automation. The results suggest that all methods investigated can be used to create 3D models, however, with different level of completeness. Measurements such as span length, deck widths, etc. can be extracted with good accuracy. Although promising, a full off-site inspection is currently not feasible as some areas of the bridges were difficult to capture mainly due to restricted access and narrow spaces. Measurements based on terrestrial laser scanning were closer to the reality compared to photogrammetry and infrared scanning. The study indicates the no special training is needed for photogrammetry and infrared scanning to generate a 3D geometric model.  相似文献   
88.
The intelligent recycling of plastics waste is a major concern. Because of the widespread use of polyethylene terephtalate, considerable amounts of PET waste are generated that are ideally re‐introduced into the material cycle by generating second generation products without loss of materials performance. Chemical recycling methods are often expensive and entail environmentally hazardous by‐products. Established mechanical methods generally provide materials of reduced quality, leading to products of lower quality. These drawbacks can be avoided by the development of new recycling methods that provide materials of high quality in every step of the production cycle. In the present work, oligomeric ethylene terephthalate with defined degrees of polymerization and defined molecular weight is produced by melt‐mixing PET with different quantities of adipic acid as an alternative pathway of recycling PET with respect to conventional methods, offering ecofriendly and economical aspects. Additionally, block‐copolyesters of defined block length are designed from the oligomeric products. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39786.  相似文献   
89.
Thermal pest control requires long treatment times due to the low thermal conductivity of wood and may lead to the formation of cracks. Here, the thermal treatment with radio waves as well as microwaves has been studied. The direct dielectric heating has the advantage of a good homogeneity. The obtained temperature profiles for radio waves were more homogeneous compared to microwaves. Detailed studies showed that elimination of pests was not related to the application of the electromagnetic field itself, but due to the temperature increase.  相似文献   
90.
Shredder residue materials are produced after the removal of ferrous and non-ferrous fractions from end-of-life electronic equipment. Despite the high plastic content and metal value in the ash, high percentages of these materials are currently sent to landfills. In this study, the potential of utilising shredder residue material and other plastic-containing materials as reducing agents was studied. Plastic-containing materials were co-injected with coal into a zinc-fuming furnace in Boliden-Rönnskär smelter. The data obtained from the trial, such as the data from the chemical analysis of the slag and the steam production, are discussed. The observations indicate that plastic-containing material can replace up to 1?ton?h?1 of coal without a significant decrease in the zinc reduction 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