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   1234篇
  免费   31篇
  国内免费   1篇
电工技术   46篇
综合类   3篇
化学工业   183篇
金属工艺   57篇
机械仪表   21篇
建筑科学   76篇
矿业工程   9篇
能源动力   63篇
轻工业   92篇
水利工程   17篇
石油天然气   4篇
无线电   102篇
一般工业技术   181篇
冶金工业   185篇
原子能技术   10篇
自动化技术   217篇
  2024年   4篇
  2023年   6篇
  2022年   9篇
  2021年   13篇
  2020年   8篇
  2019年   22篇
  2018年   21篇
  2017年   24篇
  2016年   27篇
  2015年   23篇
  2014年   25篇
  2013年   71篇
  2012年   57篇
  2011年   76篇
  2010年   68篇
  2009年   63篇
  2008年   114篇
  2007年   90篇
  2006年   70篇
  2005年   84篇
  2004年   52篇
  2003年   37篇
  2002年   45篇
  2001年   25篇
  2000年   10篇
  1999年   18篇
  1998年   18篇
  1997年   24篇
  1996年   18篇
  1995年   20篇
  1994年   15篇
  1993年   8篇
  1992年   15篇
  1991年   5篇
  1990年   9篇
  1989年   6篇
  1988年   15篇
  1987年   4篇
  1986年   8篇
  1985年   5篇
  1984年   9篇
  1983年   5篇
  1982年   2篇
  1981年   3篇
  1980年   2篇
  1979年   3篇
  1977年   2篇
  1976年   2篇
  1975年   3篇
  1947年   1篇
排序方式: 共有1266条查询结果,搜索用时 15 毫秒
61.
Population-based data suggest that individuals who consume large dietary amounts of n-3 polyunsaturated fatty acids (PUFA) have lower odds of peripheral artery disease (PAD); however, clinical studies examining n-3 PUFA levels in patients with PAD are sparse. The objective of this study is to compare erythrocyte membrane fatty acid (FA) content between patients with PAD and controls. We conducted a cross-sectional study of 179 vascular surgery outpatients (controls, 34; PAD, 145). A blood sample was drawn and the erythrocyte FA content was assayed using capillary gas chromatography. We calculated the ratio of the n-3 PUFA eicosapentaenoic acid (EPA) to the n-6 PUFA arachidonic acid (ARA) as well as the omega-3 index (O3I), a measure of erythrocyte content of the n-3 PUFA, EPA, and docosahexaenoic acid (DHA), expressed as a percentage of total erythrocyte FA. Compared with controls, patients with PAD smoked more and were more likely to have hypertension and hyperlipidemia (p < 0.05). Patients with PAD had a lower mean O3I (5.0 ± 1.7% vs 6.0 ± 1.6%, p < 0.001) and EPA:ARA ratio (0.04 ± 0.02 vs 0.05 ± 0.05, p < 0.001), but greater mean total saturated fats (39.5 ± 2.5% vs 38.5 ± 2.6%, p = 0.01). After adjusting for several patient characteristics, comorbidities, and medications, an absolute decrease of 1% in the O3I was associated with 39% greater odds of PAD (odds ratio [OR] 1.39, 95% confidence interval [CI] 1.03–1.86, and p = 0.03). PAD was associated with a deficiency of erythrocyte n-3 PUFA, a lower EPA:ARA ratio, and greater mean total saturated fats. These alterations in FA content may be involved in the pathogenesis or development of poor outcomes in PAD.  相似文献   
62.
Synthesis of a polyfluorene/poly(p‐phenylene vinylene) derivative, the Poly [(9,9′‐di‐hexylfluorenediylvinylene‐alt‐1,4‐phenylenevinylene)‐co‐((9,9′‐(3‐t‐butylpropanoate) fluorene‐1,4‐phenylene)] (LaPPS 42) was performed following Wittig and Suzuki routes. Polyfluorenes and derivatives have been used in electroluminescent devices, and the synthesis described here has the advantage in pave the way to get distinct structures having different emission spectra. An extensive study of its electrochemical, thermomechanical, optical, and structural properties was carried out, as well as its application in electroluminescent devices. Polymer light‐emitting diodes (PLEDs) and polymer light‐emitting electrochemical cells (PLECs) were built using LaPPS 42 as active layer, and their electric and optical characterizations confirm they have a potential as active element in electroluminescent devices. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42579.  相似文献   
63.
Torrefied almond shells and wood chips were incorporated into polypropylene as fillers to produce torrefied biomass‐polymer composites. The composites were prepared by extrusion and injection molding. Response surface methodology was used to examine the effects of filler concentration, filler size, and lignin factor (relative lignin to cellulose concentration) on the material properties of the composites. The heat distortion temperatures, thermal properties, and tensile properties of the composites were characterized by thermomechanical analysis, differential scanning calorimetry, and tensile tests, respectively. The torrefied biomass composites had heat distortion temperatures of 8–24°C higher than that of neat polypropylene. This was due to the torrefied biomass restricting mobility of polypropylene chains, leading to higher temperatures for deformation. The incorporation of torrefied biomass generally resulted in an increase in glass transition temperature, but did not affect melting temperature. Also, the composites had lower tensile strength and elongation at break values than those of neat polypropylene, indicating weak adhesion between torrefied biomass and polypropylene. However, scanning electron microscopy results did indicate some adhesion between torrefied biomass and polypropylene. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41582.  相似文献   
64.
The response of polycrystalline TiB2 to neutron irradiation was investigated. The material was fabricated using isotopically enriched 11B powders to minimize helium production via the 10B(n, α)7Li reaction. Neutron irradiation was conducted at temperatures of ~200°C and ~600°C to a fast fluence of 2.4 × 1025 n/m2 (>0.1 MeV). The material exhibited some swelling, but less swelling at the higher irradiation temperature. No macroscopic damage was observed in the irradiated material, although moderate irradiation-induced micro-cracking was found in the irradiated TiB2. This study demonstrated improved radiation resistance of isotopically tailored TiB2 compared with natural boron TiB2, which exhibited macroscopic fracture by irradiation.  相似文献   
65.
To study the dynamic mechanical behavior of C60 concrete at high temperatures, impact tests under different steady-state temperature fields (100, 200, 300, 400 and 500.℃) were conducted under a variety of durations at the corresponding constant high temperature, namely 0, 30, 60, 90 and 120.min, employing split Hopkinson pressure bar (SHPB) system. In addition, the impact tests were also conducted on the specimens cooled from the high temperature to the room temperature and the specimen under room temperature. From the analysis, it is found that C60 concrete has a time-dependent behavior under high-temperature environment. Under 100, 200, 300, 400 and 500.℃ steady-state temperature fields respectively, as the duration at the corresponding constant high temperature increases, the dynamic compressive strength and the elastic modulus decrease but the peak strain generally ascends. After cooling to the room temperature, the dynamic compressive strength and the elastic modulus descend as well, but the peak strain increases first and then decreases slightly, when the duration increases. For specimens under and cooled from the high-temperature, as the temperature increases, the dynamic compressive strength and the peak strain raise first and then reduce gradually,and the dynamic compressive strength of specimen under high temperature is higher than that of the specimen cooled from the same high temperature.  相似文献   
66.
The nanostructure of stretched and nonstretched PVDF samples was studied by small-angle X-ray scattering (SAXS). The crystallinity of the samples was determined by wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC), and crystalline phases by Fourier transform infrared spectroscopy (FTIR). The nanostructure can be described by a lamellar stacking of crystalline and amorphous layers, with a fairly well defined long period D and a diffuse-boundary in the interface between the crystalline and amorphous phases. The crystallinity of the stretched sample was found to be greater than that of the nonstretched sample. The long period D and the thicknesses of the crystalline lamellae Tc were found to be greater in the stretched sample than those in the nonstretched sample. The thickness of the diffuse-boundary was evaluated as being ∼ 1.4 nm in the nonstretched sample and 1.1 nm in the stretched sample. It was concluded that the growth of the thickness of the crystalline layer induced by the stretching process (stretch-induced crystallization) occurs partially at expense of the diffuse boundary and also by the coarsening of the structure with the stretching process, because of the diminution in the surface area to volume ratio observed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012  相似文献   
67.
An enhanced genetic algorithm for automated assembly planning   总被引:15,自引:0,他引:15  
Automated assembly planning reduces manufacturing manpower requirements and helps simplify product assembly planning, by clearly defining input data, and input data format, needed to complete an assembly plan. In addition, automation provides the computational power needed to find optimal or near-optimal assembly plans, even for complex mechanical products. As a result, modern manufacturing systems use, to an ever greater extent, automated assembly planning rather than technician-scheduled assembly planning. Thus, many current research reports describe efforts to develop more efficient automated assembly planning algorithms. Genetic algorithms show particular promise for automated assembly planning. As a result, several recent research reports present assembly planners based upon traditional genetic algorithms. Although prior genetic assembly planners find improved assembly plans with some success, they also tend to converge prematurely at local-optimal solutions. Thus, we present an assembly planner, based upon an enhanced genetic algorithm, that demonstrates improved searching characteristics over an assembly planner based upon a traditional genetic algorithm. In particular, our planner finds optimal or near-optimal solutions more reliably and more quickly than an assembly planner that uses a traditional genetic algorithm.  相似文献   
68.
In a buyer-supplier game, a special type of assignment game, a distinguished player, called the buyer, wishes to purchase some combinatorial structure. A set of players, called suppliers, offer various components of the structure for sale. Any combinatorial minimization problem can be transformed into a buyer-supplier game. While most previous work has been concerned with characterizing the core of buyer-supplier games, in this paper we study optimization over the set of core vectors. We give a polynomial time algorithm for optimizing over the core of any buyer-supplier game for which the underlying minimization problem is solvable in polynomial time. In addition, we show that it is hard to determine whether a given vector belongs to the core if the base minimization problem is not solvable in polynomial time. Finally, we introduce and study the concept of focus point price, which answers the question: If we are constrained to play in equilibrium, how much can we lose by playing the wrong equilibrium?  相似文献   
69.
Concept browsing interfaces can help educators and learners to locate and use learning resources that are aligned with recognized learning goals. The Strand Map Service enables users to navigate interactive visualizations of related learning goals and to request digital library resources aligned with learning goals. These interfaces are created using a programmatic Web service interface that dynamically generates interactive visual components. Preliminary findings suggest that these library interfaces appear to help users stay focused on the scientific content of their information discovery task, as opposed to focusing on the mechanics of searching.  相似文献   
70.
In this article, we propose the application of a control-theoretic framework to human-automation interaction. The framework consists of a set of conceptual distinctions that should be respected in automation research and design. We demonstrate how existing automation interface designs in some nuclear plants fail to recognize these distinctions. We further show the value of the approach by applying it to modes of automation. The design guidelines that have been proposed in the automation literature are evaluated from the perspective of the framework. This comparison shows that the framework reveals insights that are frequently overlooked in this literature. A new set of design guidelines is introduced that builds upon the contributions of previous research and draws complementary insights from the control-theoretic framework. The result is a coherent and systematic approach to the design of human-automation-plant interfaces that will yield more concrete design criteria and a broader set of design tools. Applications of this research include improving the effectiveness of human-automation interaction design and the relevance of human-automation interaction research.  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