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   2803篇
  免费   142篇
  国内免费   86篇
电工技术   55篇
技术理论   1篇
综合类   397篇
化学工业   252篇
金属工艺   70篇
机械仪表   250篇
建筑科学   351篇
矿业工程   46篇
能源动力   82篇
轻工业   65篇
水利工程   26篇
石油天然气   63篇
武器工业   7篇
无线电   171篇
一般工业技术   253篇
冶金工业   63篇
原子能技术   11篇
自动化技术   868篇
  2024年   1篇
  2023年   28篇
  2022年   27篇
  2021年   49篇
  2020年   43篇
  2019年   43篇
  2018年   44篇
  2017年   61篇
  2016年   102篇
  2015年   64篇
  2014年   159篇
  2013年   222篇
  2012年   145篇
  2011年   220篇
  2010年   164篇
  2009年   148篇
  2008年   168篇
  2007年   180篇
  2006年   172篇
  2005年   128篇
  2004年   127篇
  2003年   107篇
  2002年   95篇
  2001年   60篇
  2000年   74篇
  1999年   62篇
  1998年   52篇
  1997年   54篇
  1996年   44篇
  1995年   34篇
  1994年   37篇
  1993年   30篇
  1992年   12篇
  1991年   20篇
  1990年   9篇
  1989年   7篇
  1988年   7篇
  1987年   7篇
  1986年   4篇
  1984年   3篇
  1983年   5篇
  1982年   2篇
  1980年   4篇
  1978年   2篇
  1976年   1篇
  1975年   2篇
  1974年   1篇
  1971年   1篇
排序方式: 共有3031条查询结果,搜索用时 234 毫秒
1.
Heat transfer within ceramic feedstock powders is still unclear, which impedes optimization of the thermal and mechanical properties of the thermal sprayed coatings. The microspheres (yttria-stabilized zirconia YSZ and lanthanum zirconate LZO) were prepared via the electro-spraying assisted phase inversion method (ESP). The thermal properties of the two ESP microspheres and a commercial hollow spherical powder (HOSP) were investigated by using theoretical, experimental, and simulation methods. Thermal conductivity of the single microsphere was estimated via a novel nest model that was derived from the Maxwell-Eucken 1 and the EMT model. Thermal conductivity of a single YSZ/LZO-ESP microsphere prepared at 1100–1200 °C was within 0.36–0.75 W/m K, which was ~ 20 % lower than that of a single YSZ-HOSP microsphere with a similar porosity. Heat flux simulation showed that high tortuosity around the multi-scaled voids of the ESP microsphere led to a more efficient decrease in thermal conductivity compared with total porosity.  相似文献   
2.
Photocatalysts often show excellent performances on the basis of their surface state of exposed faces with high reactivity, but unfortunately surfaces of this type are usually concealed into the interior of crystals for their high surface energy. We report here a possibility that for fluorine-terminated surfaces of monoclinic ZrO2, these higher-energy surfaces could be retained and exposed. Urchin-like ZrO2 hollow microspheres (UZHS) composed of nanoribbons with exposed (010) facets are obtained through a fluoride mediately solvothermal method. We prove the stabilization effect of fluorine adsorption on (010) facets by density functional theory calculations. More interestingly, UZHS exhibit tunable photocatalytic selectivity in dye degradation. The fluorinated UZHS exhibit good performances both on decomposing Congo red (CR) and methylene blue, while the surface-modified UZHS by calcination only favor decomposition of CR.  相似文献   
3.
This research builds on the Theory of Planned Behavior (TPB) by proposing two additional constructs: warm glow and self-expressive benefits which could further drive consumer attitude and purchase intentions in the context of organic food consumption. We employed structural equation modelling (SEM) technique with Smart PLS 3.0 (Partial Least Squares) for the analysis of the hypothesised relationships between these psychological factors and the constructs of the Theory of Planned Behavior (TPB). The theoretical model was tested with samples from India (n = 471) and the USA (n = 440) collected using Amazon’s Mechanical Turk (M Turk). Results confirmed the importance of warm glow and self-expressive benefits in organic consumerism in both markets. The study makes an important contribution in adding these two constructs to the TPB and then suggests practical tips to policy makers.  相似文献   
4.
Collaboration has been found in previous studies on the design of assembly lines to be a useful mechanism. In this study, the focus is on a collaborative assembly (CA) framework, inspired by the design principles of CCT, the Collaborative Control Theory, to improve balanceability and flexibility of assembly lines through tool sharing (TS) among idle and bottleneck workstations. TS is widely practiced in advanced assembly facilities to reduce cost and improve consistency and standardization in assembly and in assembly-and-test utilities, relying often on real time control. The framework developed here addresses the systems design aspect of Mechatronics, covering the planning, execution, and control mechanisms. Planning includes assembly line balancing (ALB) and initial TS decisions, made continually by solving a bi-objective mixed-integer program (BOMIP). A collaborative multi-agent system (CMAS) enhanced with a TS-best matching (BM) protocol is developed to execute the plan, control the process, and modify the TS decisions, considering dynamic changes in the system’s operations. Experiments show that the new CA framework significantly outperforms classic approaches (i.e., ALB without TS-BM) in terms of cycle time, utilization of tools, and balanceability. In addition, the control mechanism is proven to augment the line’s flexibility against the inherent uncertainties of assembly processes, compared to the previously developed static CA frameworks.  相似文献   
5.
Obtaining strong interfacial interaction between filler and polymer matrix is very crucial for the fabrication of polymer nanocomposites with superior performance. Present study is aimed to fabricate high performance styrene butadiene rubber (SBR) nanocomposites with imidazolium type ionic liquid modified multiwalled carbon nanotube (MWCNT). Ionic liquid facilitates the dispersion of MWCNT in rubber matrix and it is obvious from transmission electron microscopy images. Diffusion of toluene through SBR nanocomposite membranes has been investigated as a function of surface modified MWCNT (f-MWCNT) content to analyze the chain dynamics and filler-polymer interactions. O2 gas barrier effect of nanocomposites with special reference to the filler loading is explored. The substantial improvement in the barrier effect in presence of filler interpreted on the grounds of a theoretical model describing permeability of heterogeneous systems. Finally solvent sensing characteristics of prepared nanocomposites are also analyzed and it is observed that prepared nanocomposites can be used as a flexible solvent sensor.  相似文献   
6.
《云南化工》2020,(2):197-198
对石油化工文本的英译汉研究,有利于将国外最新技术成果带回国内,以供国内学者学习与借鉴。基于卡特福德的翻译转换理论,通过典型案例研究,提出适合该类文本的翻译方法,以期为从事该类的译者提供借鉴,提高该类文本翻译准确性,并为技术交流提供语言服务。  相似文献   
7.
Information systems, like biological systems, are susceptible to external perturbations. Similar to flora and fauna in a biome, species of data can be classified within a dataphora. While entropic properties and data geometries can be used to describe local species of data within a dataphora, they are not designed to describe the global properties of an information system or evaluate its stability. Ecologists have used Information Theories to describe macro-level properties of biological ecosystems and statistical tools to evaluate biological systems. This research leverages an ecological perspective to model information systems as a living system. Our findings support the theory of dataphoric ascendancy with Wikipedia having a Diversity Index value of 0.68, within the range of 0.65 and 0.80 that indicates a balanced state. We further support our findings with additional evaluations of other ecosystems including the predicted collapse of the information service known as the Digital Universe. This research allows for an information system’s stability to be (a) characterized and (b) predicted using ecological measures specific to the diversity of data within the ecosystem.  相似文献   
8.
The synergistic effects of using several supplementary cementitious materials (SCMs), such as Blast Furnace Slags plus Limestone Filler or Fly Ashes, depend on the OPC composition. When using an OPC which is poor in C3A and alkalis in ternary formulations, a similar initial strength gain to that of a plain OPC is detected and at longer hydration ages, the formation of monocarboaluminate, hemicarbonate and hydrotalcite instead of monosulphate can be seen. If an OPC with a higher C3A content and alkalis is used with SCMs, the higher availability of Al causes the early formation of monocarboaluminate and a lower initial strength gain. At longer hydration times, in ternary blends with both OPCs, the mechanical strengths are higher and the C-S-H gels formed are richer in Al and poorer in C/S ratio with a subsequent lowering of the alkali content in the pore solution when compared to that in plain OPC.  相似文献   
9.
地质环境合理开发利用集对论准则   总被引:2,自引:0,他引:2  
龚士良 《西部探矿工程》2003,15(11):164-166
资源与环境是当今社会面临的两大问题,是影响可持续发展的重要因素。地质环境具有资源与灾害的双重属性,不合理的开发利用将引发环境负效应,其影响具有扩散性与延滞性。借鉴集对论基本原理与方法,对城市化进程中地质环境的合理开发利用提出总体思路及其具体途径。  相似文献   
10.
成本管理是涉及煤炭企业各部门的一项综合性管理工作,是整个企业管理的重要组成部分。介绍了成本的概念及内容,成本管理的内容及要求,提高降低的办法和途径。  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