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   717篇
  免费   53篇
  国内免费   2篇
电工技术   16篇
综合类   1篇
化学工业   144篇
金属工艺   25篇
机械仪表   22篇
建筑科学   29篇
矿业工程   1篇
能源动力   33篇
轻工业   28篇
水利工程   4篇
石油天然气   4篇
武器工业   1篇
无线电   118篇
一般工业技术   161篇
冶金工业   35篇
原子能技术   24篇
自动化技术   126篇
  2023年   16篇
  2022年   26篇
  2021年   31篇
  2020年   36篇
  2019年   25篇
  2018年   42篇
  2017年   37篇
  2016年   44篇
  2015年   24篇
  2014年   36篇
  2013年   41篇
  2012年   40篇
  2011年   63篇
  2010年   32篇
  2009年   42篇
  2008年   31篇
  2007年   22篇
  2006年   14篇
  2005年   13篇
  2004年   8篇
  2003年   8篇
  2002年   11篇
  2001年   11篇
  2000年   3篇
  1999年   7篇
  1998年   17篇
  1997年   8篇
  1996年   8篇
  1995年   11篇
  1994年   10篇
  1993年   9篇
  1992年   4篇
  1991年   3篇
  1990年   6篇
  1989年   4篇
  1988年   2篇
  1987年   1篇
  1986年   4篇
  1985年   2篇
  1984年   4篇
  1983年   2篇
  1982年   1篇
  1981年   1篇
  1980年   2篇
  1979年   2篇
  1978年   3篇
  1977年   2篇
  1976年   2篇
  1975年   1篇
排序方式: 共有772条查询结果,搜索用时 31 毫秒
761.
Many areas in the world face clean water scarcity problems and phosphorus reserves are likely to be depleted in the near future. Still, a large amount of clean water is used to transport excreta through sewer systems. Most of the wastewater generated worldwide is discharged untreated into aquatic systems and leads to water pollution and loss of valuable nutrients. In Hanoi, Vietnam's capital city, high population and economic growth as well as industrialisation have led to a decrease in groundwater level and to serious river and lake pollution. A probabilistic model, simulating the impact of measures on groundwater abstraction and nutrient recovery, was used to determine the impact of policy changes in Hanoi. The results obtained reveal that harmonising environmental sanitation and agricultural systems with one another will considerably increase nutrient recovery for food production, lower expenditure for artificial fertilisers and reduce the nutrient load into the environment. The model can be applied in urban areas of developing countries to assist in the design of environmental sanitation concepts.  相似文献   
762.
This paper presents a simple analytical approach to investigate the stability of functionally graded plates under in-plane compressive, thermal and combined loads. Material properties are assumed to be temperature-independent, and graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of constituents. Equilibrium and compatibility equations for functionally graded plates are derived by using the classical plate theory taking into account both geometrical nonlinearity in von Karman sense and initial geometrical imperfection. The resulting equations are solved by Galerkin procedure to obtain explicit expressions of postbuckling load–deflection curves. Stability analysis of a simply supported rectangular functionally graded plate shows the effects of the volume fraction index, plate geometry, in-plane boundary conditions, and imperfection on postbuckling behavior of the plate.  相似文献   
763.
The flavonoid rutin is present in significant amounts in the flower buds of Sophora japonica L. It offers numerous desired pharmacological effects. Under certain extraction conditions quercetin is found as a hydrolysis product which needs to be separated from rutin. This paper describes the application of liquid chromatography to solve this task. Based on the determination of adsorption equilibrium constants and column efficiencies, the productivity of the separation process is estimated, and scale-up considerations are presented. A comparison with alternatively directly crystallizing rutin from raw extracts is also reported.  相似文献   
764.
765.
Topics in Catalysis - Cobalt-doped cryptomelane material with different dopant amounts was prepared by a simple co-precipitation method. X-ray diffraction patterns and scanning electron microscope...  相似文献   
766.
Within cells, the close spatial arrangement of cascade enzymes facilitates the channeling of intermediates and enhances cascade reaction efficiency. Reconfigurable DNA nanostructures, owing to their structural controllability and precise spatial addressability, are promising tools for mimicking such processes. In this study, a 3D DNA origami scaffold, with a dynamic shape transformation from its open boat form to a closed hexagonal prism induced by toehold-mediated strand displacement, is designed to investigate the enzyme cascade reaction of xylose reductase and xylitol dehydrogenase from D-xylose metabolic pathway. Enzymes are assembled on the DNA scaffold in its open state, which is subsequently closed by the assistance of DNA sequence-specific closing keys. The enzyme cascade efficiency is much higher in the static encapsulated closed state than in the open state due not only to the enzyme proximity but also the environmental factors of 3D DNA structure. These results provide novel insights into controlling enzyme cascade reactions by inducing the shape transformation of DNA nanostructures and how environmental factors affect the action of multi-enzyme complexes in the cell.  相似文献   
767.
Bitumen-derived asphaltenes are rich in carbon but of low value and contain other elements such as nitrogen, sulphur, oxygen, vanadium, and nickel. Their use as a feedstock for producing carbon fibre (CF) is largely under-investigated. In this study, electrospinning was used to create asphaltene fibres (AFs), which is a pre-carbon fibre material, from asphaltenes. Various operational parameters were investigated in order to improve the spinning abilities, such as the concentration of asphaltenes in toluene, pumping rate, voltage, and distance between the tip of the needle to the collector. Results indicated that asphaltenes concentrations had the greatest effect on the quality of the produced AFs, with the range of asphaltenes concentrations from 45 to 50 wt.% being suitable for producing the AFs, while voltage, pumping rate, and tip distance had less of an effect on electrospun AF production.  相似文献   
768.
In this paper, we design dynamic event-triggered interval functional observers (FOs) for interconnected systems comprising M $$ M $$ ( M 2 ) $$ \left(M\ge 2\right) $$ subsystems where each subsystem is subject to nonlinearities and output disturbances. Our design method consists of two main steps. First, we design decentralized dynamic event-triggered mechanisms (ETMs) which use only locally measured output information. We then consider the design of distributed interval FOs by using the newly proposed ETMs. Their existence conditions are established and formulated in terms of linear programming. We also derive a bound on the estimated error vector and show that this bound is the smallest. Thus, this ensures that the unknown linear functional state vector can be estimated within an upper and lower bound of its true value by the designed interval observers. Finally, we apply the obtained results to design dynamic event-triggered interval observers for linear functions of the state vectors of an N $$ N $$ -machine power system.  相似文献   
769.
Due to the nonlinearities and dynamical properties of multisection web machines, it is essential to accomplish an appropriate mathematical model as well as design a compatible control scheme. A generalized fully driven web winding model is constructed taking unpredictable changes of moment of inertia and radius of rolls into consideration. In this article, a fractional-order sliding surface algorithm-based hierarchical control frame is applied to multisection web machines to deal with matched and mismatched uncertainties and disturbances. In addition, the Radius Basis Function neural network is deployed to estimate necessary system dynamics and the proposed control scheme taking advantage of first-order low-pass filters to produce virtual control signals without complicated calculation and attenuate the explosion of terms phenomenon. Finally, the semi-global stability of the entire system is determined using Lyapunov's stability theory. The simulation results are presented to clarify the superior performance of robust control algorithm and approximation law in the presence of nonideal elements.  相似文献   
770.

The effects of the substitution of V5+ with Ni2+ at the corresponding sites in BiVO4 on the crystal structures, optical properties, and photocatalytic efficiency of BiVO4 was investigated. Ni2+ cations doped at the V5+ sites in BiVO4 was confirmed by X-ray diffraction, Raman, X-ray photoelectron spectroscopy, ultraviolet–visible diffuse reflectance spectra, and photoluminescence spectra. Ni-doped BiVO4 exhibited excellent degradation of crystal violet (CV) compared with the bare BiVO4. For optimal Ni2+ doping of 5%, the degradation rate of CV, which reached about 95% within 180 min of LED light irradiation, was obtained. Ni doping can introduce advantageous defect states that significantly increase the separation and diffusion efficiency of the photo-induced charge carriers, thereby boosting the photocatalytic activity of crystal structures.

  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