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   1376篇
  免费   97篇
  国内免费   2篇
电工技术   20篇
化学工业   362篇
金属工艺   23篇
机械仪表   41篇
建筑科学   50篇
矿业工程   1篇
能源动力   69篇
轻工业   149篇
水利工程   8篇
石油天然气   3篇
无线电   103篇
一般工业技术   235篇
冶金工业   141篇
原子能技术   16篇
自动化技术   254篇
  2023年   19篇
  2022年   81篇
  2021年   81篇
  2020年   38篇
  2019年   65篇
  2018年   58篇
  2017年   59篇
  2016年   61篇
  2015年   50篇
  2014年   45篇
  2013年   90篇
  2012年   95篇
  2011年   113篇
  2010年   79篇
  2009年   82篇
  2008年   64篇
  2007年   69篇
  2006年   27篇
  2005年   31篇
  2004年   35篇
  2003年   16篇
  2002年   18篇
  2001年   8篇
  2000年   9篇
  1999年   10篇
  1998年   30篇
  1997年   15篇
  1996年   20篇
  1995年   10篇
  1994年   12篇
  1993年   9篇
  1992年   8篇
  1991年   2篇
  1990年   6篇
  1989年   5篇
  1987年   4篇
  1986年   6篇
  1985年   3篇
  1984年   6篇
  1983年   3篇
  1982年   4篇
  1981年   5篇
  1980年   3篇
  1979年   2篇
  1978年   4篇
  1977年   2篇
  1975年   2篇
  1973年   3篇
  1972年   2篇
  1957年   1篇
排序方式: 共有1475条查询结果,搜索用时 9 毫秒
81.
In Europe, a common framework for renewable energy sources (RES) is aspired. Tradable green certificates (TGCs) are a market-based cost-efficient means to stimulate electricity production from RES. Since TGCs are the most widespread support scheme in Europe together with feed-in tariffs, chances are that a common European framework could well be based on TGCs. However, while integrating currently existing different national TGC systems, any remaining differences should be carefully considered. Just how difficult the creation of an international TGC market would be is illustrated in this paper by the case of Belgium, where no less than 4 different TGC systems exist nowadays. The example of Belgium illustrates that harmonizing different TGC systems is easier said than done and represents a serious challenge. This clearly illustrates that a single European support scheme for RES, however desirable, is still far in the future.  相似文献   
82.
Although moisture significantly affects the performance and durability of building envelope systems, effective methods to quantify the relative drying capacity of these systems are yet to be developed. A new testing method and an evaluation approach for comparing the drying capacity of wood-frame wall systems in evacuating water due to rain penetration in the stud cavities are presented in this paper. A controllable and consistent moisture loading is created by placing a water tray on a load cell at the bottom of the stud cavity of the wall assembly which is then subjected to lab generated indoor/outdoor conditions. The data on water evaporation from water trays and the monitored moisture accumulations in the materials surrounding the stud cavities are used to establish load–response relations. Using these relations the relative performance of various building envelope systems in preventing biodeterioration caused by rainwater penetration into the stud cavities can be compared. The concept of in-cavity evaporation allowance (ICEA) has been proposed and it is based on the limit of 20% moisture content (MC) being reached at any location of the building envelope.  相似文献   
83.
A Fabry-Perot resonator filled with second-order nonlinear optical material is investigated. Attention is devoted to making the resonator act as a nonlinear mirror for ultralow-intensity light signals that can be switched by a control beam at the second-harmonic frequency. The interaction process is an input-phase-independent parametric downconversion. The theoretical problem is solved through implementation of a dummy variable method optimized for a parametric process. Efficient amplification and bistability of low-intensity signals have been found.  相似文献   
84.
System reliability analysis and optimization are important to efficiently utilize available resources and to develop an optimal system design architecture. System reliability optimization has been solved by using optimization techniques including meta-heuristics. Meanwhile, the development of meta-heuristics has been an active research field of the reliability optimization wherein the redundancy, the component reliability, or both are to be determined. In recent years, a broad class of stochastic meta-heuristics, such as simulated annealing, genetic algorithm, tabu search, ant colony, and particle swarm optimization paradigms, has been developed for reliability-redundancy optimization of systems. Recently, a new kind of evolutionary algorithm called Imperialist Competitive Algorithm (ICA) was proposed. The ICA is based on imperialistic competition where the populations are represented by countries, which are classified as imperialists or colonies. However, the trade-off between the exploration (i.e. the global search) and the exploitation (i.e. the local search) of the search space is critical to the success of the classical ICA approach. An improvement in the ICA by implementing an attraction and repulsion concept during the search for better solutions, the AR-ICA approach, is proposed in this paper. Simulations results demonstrates the AR-ICA is an efficient optimization technique, since it obtained promising solutions for the reliability redundancy allocation problem when compared with the previously best-known results of four different benchmarks for the reliability-redundancy allocation problem presented in the literature.  相似文献   
85.
Chemoresistance is a hallmark of malignant pleural mesothelioma (MPM) management and the expression of ALDH1A3 is responsible for the survival and activity of MPM chemoresistant cell subpopulations (ALDHbright cells). We enriched mesothelioma ALDHbright cells to near homogeneity by FACS sorting and an Aldefluor assay and performed unbiased Affymetrix gene expression profiling. Viability and ELISA assays were used to rule out significant apoptosis in the sorted cell subpopulations and to assess target engagement by butein. Statistical analysis of the results, pathway enrichment and promoter enrichment were employed for the generation of the data. Q-RTPCR was used to validate a subset of the identified, modulated mRNAs In this work, we started from the observation that the mRNA levels of the ALDH1A3 isoform could prognostically stratify MPM patients. Thus, we purified MPM ALDHbright cells from NCI-H2595 cells and interrogated their gene expression (GES) profile. We analyzed the GES of the purified cells at both a steady state and upon treatment with butein (a multifunctional tetrahydroxy-chalcone), which abates the ALDHbright cell number, thereby exerting chemo-sensitizing effects in vitro and in vivo. We identified 924 genes modulated in a statistically significant manner as a function of ALDH status and of the response to the inhibitor. Pathway and promoter enrichment identified the molecular determinant of high ALDH status and how butein treatment altered the molecular portrait of those chemoresistant cell subpopulations. Further, we unraveled an eighteen-gene signature with high prognostic significance for MPM patients, and showed that most of the identified prognostic contributors escaped the analysis of unfractionated samples. This work proves that digging into the unexplored field of intra-tumor heterogeneity (ITH) by working at the cell subpopulation level may provide findings of prognostic relevance, in addition to mechanistic insights into tumor resistance to therapy.  相似文献   
86.
87.
88.
Xu P  Brissaud F  Fazio A 《Water research》2002,36(12):3074-3082
In Noirmoutier, a French island off the Atlantic coast, secondary effluents flow into a series of four lagoons, 1.4-2.8 m deep, and are reused for agricultural irrigation. The excess water is disposed of to the sea. The aim of this study was to provide a model capable of predicting the microbiological quality of the water pumped for irrigation or discharged to the sea. Meteorological variables, flow rates, physical-chemical characteristics and faecal coliform (FC) contents were monitored for a year and a half. The hydraulic pattern of each lagoon was assumed to be that of completely mixed reactor because of the calculated dispersion numbers and the wind mixing effect. Coliform decay was assumed to follow first order kinetics in each lagoon. Die-off coefficients were calculated in each lagoon using a non-steady-state model. The main bacterial removal mechanism was shown to be solar irradiation. Empirical equations were established to calculate die-off coefficients as a function of received solar energy and temperature. FC die-off rates were higher in the first lagoon and then decreased successively in those following. FC numbers in the different lagoons were predicted with reasonable accuracy in spite of high variation in inlet water quality. The model will facilitate the prediction of water quality under various climatic conditions and different water reuse scenarios and will help to optimise reclamation and storage facilities.  相似文献   
89.
Silver, gold, copper and platinum nanoparticles (NPs) were grown on surfaces in the form of patterns by the exposure of laser radiation onto droplets of metal ion solutions and the aid of a reducing agent. The generation of patterns from metallic NPs was achieved by combining induced growth of NPs and nanostructures by laser incidence directly on surfaces and optical image formation techniques for transferring the patterns. Near-UV (363.8 nm) and visible (532 nm) laser wavelengths were used for the laser-induced growth of NPs into microstructures on glass, quartz, stainless steel, silicon, and gold-on-silicon substrates. The sizes of the patterns formed were on the micrometer scale and the sizes of the transferred patterns were on the millimeter scale. The patterns formed were generated by optical transference of image and interference of laser beams. Ag and Au substrates were highly active in surface enhanced Raman spectroscopy (SERS). The enhanced Raman activity was measured for SERS probe molecules: 9H-purin-6-amine (adenine) and 1,2-bis (4-pyridyl)-ethane analytes on Ag and Au substrates, respectively. The enhancement factors obtained were 1.8×10(5) and 6.2×10(6), respectively.  相似文献   
90.
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