全文获取类型
收费全文 | 1727篇 |
免费 | 89篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 26篇 |
综合类 | 3篇 |
化学工业 | 360篇 |
金属工艺 | 37篇 |
机械仪表 | 47篇 |
建筑科学 | 44篇 |
矿业工程 | 2篇 |
能源动力 | 108篇 |
轻工业 | 162篇 |
水利工程 | 15篇 |
石油天然气 | 42篇 |
无线电 | 231篇 |
一般工业技术 | 348篇 |
冶金工业 | 88篇 |
原子能技术 | 14篇 |
自动化技术 | 296篇 |
出版年
2024年 | 5篇 |
2023年 | 48篇 |
2022年 | 79篇 |
2021年 | 115篇 |
2020年 | 76篇 |
2019年 | 66篇 |
2018年 | 88篇 |
2017年 | 80篇 |
2016年 | 79篇 |
2015年 | 46篇 |
2014年 | 68篇 |
2013年 | 143篇 |
2012年 | 103篇 |
2011年 | 113篇 |
2010年 | 72篇 |
2009年 | 88篇 |
2008年 | 67篇 |
2007年 | 79篇 |
2006年 | 55篇 |
2005年 | 42篇 |
2004年 | 33篇 |
2003年 | 33篇 |
2002年 | 16篇 |
2001年 | 8篇 |
2000年 | 13篇 |
1999年 | 14篇 |
1998年 | 12篇 |
1997年 | 17篇 |
1996年 | 13篇 |
1995年 | 16篇 |
1994年 | 10篇 |
1993年 | 16篇 |
1992年 | 9篇 |
1991年 | 12篇 |
1990年 | 9篇 |
1989年 | 10篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 5篇 |
1985年 | 9篇 |
1984年 | 6篇 |
1983年 | 9篇 |
1982年 | 4篇 |
1981年 | 8篇 |
1980年 | 3篇 |
1977年 | 4篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1970年 | 2篇 |
1966年 | 2篇 |
排序方式: 共有1823条查询结果,搜索用时 0 毫秒
991.
Climate change might have direct impacts on water quantity in Egypt and lead to indirect effects on Mediterranean saltwater intrusion to groundwater, which exposes agriculture to vulnerability. This study investigated impacts of climate change on agriculture, with particular regard to food security and socioeconomy, and quantified the effectiveness of cropping pattern adaptation measures by integrating three mathematical models. The Blue M model was used for hydrological simulations of Nasser Lake under flooding scenarios to predict the water supply from the High Aswan Dam. The water and salinity balance(WB-SAL) model was adopted to estimate the water salinity in the Nile Delta. The simulated results from the Blue M and WB-SAL models were integrated with the agricultural simulation model for Egypt(ASME) to project cropping patterns, food security, and socioeconomy throughout the country. The results showed that future climate change will directly affect the total crop area; crop areas for 13 crop types; the self-sufficiency of wheat, rice, cereal, and maize supplies; and socioeconomic indicators. The proposed cropping pattern adaptation measures focus on fixing the crop areas of rice and orchards and providing half of the population with lentils, maize, onion, vegetables, milk, and meat. The adaptation measures have the potential to promote food security without causing deterioration of the socioeconomic situation. However, water availability has much more significant effects on food security and socioeconomy than cropping pattern adaptation measures do. Accordingly, the country should rationalize water use efficiency and increase water supply. 相似文献
992.
Kersti Haahti Bassam A. Younis Leena Stenberg Harri Koivusalo 《Water Resources Management》2014,28(14):5175-5197
We developed and applied a computational model for simulating unsteady flow in a drainage network of a boreal forested peatland site. The input to the model was the hourly runoff produced by a hydrological model. The simulations of the flow in the ditch network were performed using an iterative procedure for solving the Saint-Venant equations that govern the flow in each of the network channels. These equations were solved separately for each ditch branch, and the flow depths at the junctions were corrected using the method of characteristics. The model was applied to the drainage network of a peatland catchment in Eastern Finland over a period of 15 months. Because flow resistance in the ditches depended strongly on flow conditions, flow resistance (Manning’s n) was introduced as a function of discharge. The model was calibrated and validated against field data and the simulation results were further applied to assess erosion risk. The highest risk of erosion occurred during long lasting flows induced by snowmelt at ditch sections with a steep slope and a large upstream area. These model results can aid in the design and siting of water protection measures within the drained area. 相似文献
993.
Cobo Molinos A Abriouel H Lucas López R Ben Omar N Valdivia E Gálvez A 《Food microbiology》2008,25(6):762-770
Enterocin AS-48 is a broad-spectrum cyclic antimicrobial peptide produced by Enterococcus faecalis. In the present study, the bacteriocin was tested alone and in combination with other antimicrobials for decontamination of Bacillus inoculated on alfalfa, soybean sprouts and green asparagus. Washing with enterocin AS-48 solutions reduced viable cell counts of Bacillus cereus and Bacillus weihenstephanensis by 1.0–1.5 and by 1.5–2.38 log units right after application of treatment, respectively. In both cases, the bacteriocin was effective in reducing the remaining viable population below detection levels during further storage of the samples at 6 °C, but failed to prevent regrowth in samples stored at 15 or 22 °C. Application of washing treatments containing enterocin AS-48 in combination with several other antimicrobials and sanitizers (cinnamic and hydrocinnamic acids, carvacrol, polyphosphoric acid, peracetic acid, hexadecylpyridinium chloride and sodium hypochlorite) greatly enhanced the bactericidal effects. The combinations of AS-48 and sodium hypochlorite, peracetic acid or hexadecylpyridinium chloride provided the best results. After application of the combined treatments on alfalfa sprouts contaminated with B. cereus or with B. weihenstephanensis, viable bacilli were not detected or remained at very low concentrations in the treated samples during a 1-week storage period at 15 °C. Inhibition of B. cereus by in situ produced bacteriocin was tested by cocultivation with the AS-48 producer strain E. faecalis A-48-32 inoculated on soybean sprouts. Strain A-48-32 was able to grow and produce bacteriocin on sprouts both at 15 and 22 °C. At 15 °C, growth of B. cereus was completely inhibited in the cocultures, while a much more limited effect was observed at 22 °C. The results obtained for washing treatments are very encouraging for the application of enterocin AS-48 in the decontamination of sprouts. Application of washing treatments containing AS-48 alone can serve to reduce viable cell counts of bacilli in samples stored under refrigeration, while application of combined treatments should be recommended to avoid proliferation of the surviving bacilli under temperature-abuse conditions. 相似文献
994.
Omar Mahfoud Abdelhafid Moummi Mahfoud Kadja Noureddine Moummi Ridha Mebrouk 《国际可持续能源杂志》2013,32(2):113-127
A dynamic and thermal simulation for two-dimensional model is developed on air flow and heat transfer control by chicanes in solar air collectors. New chicane form is adopted with two parts: the first is orthogonal to the air flow direction and the second is titled (α=60°). It is apparent that the turbulence created by introducing chicanes, resulting in greater increase in heat transfer inside the dynamic air vein with a rise of 23%. The effect of the variation of the Reynolds number in the range of 100<Re<4500, on the convective heat transfer coefficient, the pressure drop and Nusselt number are analysed and have shown good agreements with the literature results. Therefore, the mass flow rates effect on the velocity magnitude, temperature and the turbulent intensity is analysed. The Reynolds number variation showed a substantial effect on the mechanism of vortex development and separation phenomenon. 相似文献
995.
The preparation and characterisation of an inorganic blue-emitting alternate-current electrolumenescent (ACEL) cell based upon ZnS:Tm, Li phosphor powder are described. Electroluminescent and photoluminescent spectra clearly show a dominant blue-emission band peaking at 2.6 eV (477 nm) originated from 1G4→3H6 transition. Advantages and drawbacks of the powder-based ACEL cell have been discussed in comparison with a ACEL thin-film based upon a similar material. The near-infra-red band (801 nm, 1.55 eV, 3F4→3H6) seen in thin-film structure was significantly suppressed in these types of devices. 相似文献
996.
Software security is becoming an important concern as software applications are increasingly depending on the Internet, an untrustworthy computing environment. Vulnerabilities due to design errors, inconsistencies, incompleteness, and missing constraints in software design can be wrongly exploited by security attacks. Software functionality and security, however, are often handled separately in the development process. Software is designed
with the mindset of its functionalities and cost, where the focus is mainly on the operational behavior. Security concerns, on the other hand, are often described in an imprecise way and open to subjective interpretations. This paper presents a threat driven approach that improves on the quality of software through the realization of a more secure model. The approach introduces systematic transformation rules and integration steps for integrating attack tree representations into statechart-based functional models. Through the focus on the behavior of an attack from the perspective of the system behavior, software engineers can clearly define and understand security concerns as software is designed. Security analysis and threat identification are then applied to the integrated model in order to identify and mitigate vulnerabilities at the design level. 相似文献
997.
The industrial revolution demonstrated the limitations of a pure mechanistic approach towards work design. Human work is now seen as a complex entity that involves different scientific branches and blurs the line between mental and physical activities. Job design has been a traditional concern of applied psychology, which has provided insight into the interaction between the individual and the work environment. The goal of this paper is to introduce the human-at-work system as a holistic approach to organizational design. It postulates that the well-being of workers and work outcomes are issues that need to be addressed jointly, moving beyond traditional concepts of job satisfaction and work stress. The work compatibility model (WCM) is introduced as an engineering approach that seeks to integrate previous constructs of job and organizational design. The WCM seeks a balance between energy expenditure and replenishment. The implementation of the WCM in industrial settings is described within the context of the Work Compatibility Improvement Framework. A sample review of six models (motivation-hygiene theory; job characteristics theory; person-environment fit; demand-control model; and balance theory) provides the foundation for the interaction between the individual and the work environment. A review of three workload assessment methods (position analysis questionnaire, job task analysis and NASA task load index) gives an example of the foundation for the taxonomy of work environment domains. Previous models have sought to identify a balance state for the human-at-work system. They differentiated between the objective and subjective effects of the environment and the worker. An imbalance between the person and the environment has been proven to increase health risks. The WCM works with a taxonomy of 12 work domains classified in terms of the direct (acting) or indirect (experienced) effect on the worker. In terms of measurement, two quantitative methods are proposed to measure the state of the system. The first method introduced by Abdallah et al. (2004) identifies operating zones. The second method introduced by Salem et al. (2006) identifies the distribution of the work elements on the x/y coordinate plane. While previous efforts have identified some relevant elements of the systems, they failed to provide a holistic, quantitative approach combining organizational and human factors into a common framework. It is postulated that improving the well-being of workers will simultaneously improve organizational outcomes. The WCM moves beyond previous models by providing a hierarchical structure of work domains and a combination of methods to diagnose any organizational setting. The WCM is an attempt to achieve organizational excellence in human resource management, moving beyond job design to an integrated improvement strategy. A joint approach to organizational and job design will not only result in decreased prevalence of health risks, but in enhanced organizational effectiveness as well. The implementation of the WCM, that is, the Work Compatibility Improvement Framework, provides the basis for integrating different elements of the work environment into a single reliable construct. An improvement framework is essential to ensure that the measures of the WCM result in a system that is adaptive and self-regulated. 相似文献
998.
High velocity SAW using aluminum nitride film on unpolished nucleation side of free-standing CVD diamond 总被引:1,自引:0,他引:1
Elmazria O Mortet V El Hakiki M Nesladek M Alnot P 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2003,50(6):710-715
High performances surface acoustic wave (SAW) filters based on aluminium nitride (AlN)/diamond layered structure have been fabricated. The C-axis oriented aluminum nitride films with various thicknesses were sputtered on unpolished nucleation side of free-standing polycrystalline chemical vapor deposition (CVD) diamond obtained by silicon substrate etching. Experimental results show that high order modes as well as Rayleigh waves are excited. Experimental results are in good agreement with the theoretical dispersion curves determined by software simulation with Green's function formalism. We demonstrate that high phase velocity first mode wave (so-called Sezawa wave) with high electromechanical coupling coefficient are obtained on AlN/diamond structure. This structure also has a low temperature coefficient of frequency (TCF), and preliminary results suggest that a zero TCF could be expected. 相似文献
999.
A. Younis A. Hussain M. Asghar A. Manzoor S. Javed 《Journal of Superconductivity and Novel Magnetism》2011,24(4):1327-1332
The dielectric properties of Cu0.5Tl0.5Ba2Ca2−q
Mg
q
Cu3O10−δ
(q=0, 0.5, 1.0 1.5) superconductor samples were studied at two temperatures of 80 and 290 K by capacitance (C) and conductance (G) measurements with the test frequency (f) in the range of 10 KHz to 10 MHz. We have presented the measurements of the dielectric constants (ε′ and ε″), dielectric loss factor (tan δ) and ac-conductivity (σ
ac) as a function of frequency and temperature. A negative capacitance (NC) experience has been observed, which is most likely
due to different contact electrodes and superconductor samples’ Fermi levels. Since metals have their Fermi levels higher
than ceramics, there is a flow of the carriers from the ceramic samples towards the metal electrodes. The dielectric polarization
phenomenon is observed, which is due to dislodgment of mobile charges from their equilibrium position relative to fixed charges
of the reservoir layer. The improved inter plane coupling promoted by Mg substitution at Ca site would change the dielectric
response of Cu0.5Tl0.5Ba2Ca2−q
Mg
q
Cu3O10−δ
superconductors. To observe such effects in Mg doped Cu0.5Tl0.5Ba2Ca2−q
Mg
q
Cu3O10−δ
superconductors, di- electric measurements were carried out both at room temperature (290 K) and in the superconducting state
closer to the boiling point of liquid nitrogen (80 K). The excess conductivity arising due to superconducting state of material
has been determined, and its role in the mechanism of superconductivity is suggested. The negative dielectric constant (ε′) and dielectric loss factor (tan δ) show strong dispersion at low frequencies. The lower thermal agitation at 80 K may enhance the polarizability and hence
the dielectric constants (ε′ and ε″). 相似文献
1000.
Omar A.S. Jostingmeier A. Rieckmann C. Lutgert S. 《Microwave Theory and Techniques》1994,42(11):2139-2148
The generalized spectral domain (GSD) technique is applied to the analysis of waveguide coupling by axially uniform slots. For a slotted-circular waveguide, cut off wavenumbers of TE and TM modes as well as the corresponding field distributions in the composite waveguide are determined and compared to that obtained by other methods. Plots of the field lines corresponding to the dominant as well as a number of higher order modes are presented. It is shown that considering the H00 modes in the comprising waveguides is necessary. Furthermore, it is demonstrated how the efficiency of the method regarding accuracy and CPU time requirements can considerably be enhanced if infinite sums over eigenmodes which have to be evaluated are replaced by closed-form expressions 相似文献