全文获取类型
收费全文 | 147959篇 |
免费 | 2634篇 |
国内免费 | 1608篇 |
专业分类
电工技术 | 2611篇 |
综合类 | 1012篇 |
化学工业 | 15543篇 |
金属工艺 | 6261篇 |
机械仪表 | 4200篇 |
建筑科学 | 3072篇 |
矿业工程 | 675篇 |
能源动力 | 3464篇 |
轻工业 | 8384篇 |
水利工程 | 1379篇 |
石油天然气 | 922篇 |
武器工业 | 32篇 |
无线电 | 18052篇 |
一般工业技术 | 25405篇 |
冶金工业 | 46264篇 |
原子能技术 | 1603篇 |
自动化技术 | 13322篇 |
出版年
2023年 | 459篇 |
2022年 | 683篇 |
2021年 | 915篇 |
2020年 | 661篇 |
2019年 | 823篇 |
2018年 | 1673篇 |
2017年 | 1925篇 |
2016年 | 2348篇 |
2015年 | 1816篇 |
2014年 | 2113篇 |
2013年 | 5345篇 |
2012年 | 4908篇 |
2011年 | 6398篇 |
2010年 | 3880篇 |
2009年 | 4567篇 |
2008年 | 4571篇 |
2007年 | 4766篇 |
2006年 | 4299篇 |
2005年 | 6669篇 |
2004年 | 5815篇 |
2003年 | 5249篇 |
2002年 | 3810篇 |
2001年 | 3962篇 |
2000年 | 3100篇 |
1999年 | 3737篇 |
1998年 | 15457篇 |
1997年 | 9879篇 |
1996年 | 7214篇 |
1995年 | 4596篇 |
1994年 | 3839篇 |
1993年 | 3806篇 |
1992年 | 1880篇 |
1991年 | 1898篇 |
1990年 | 1811篇 |
1989年 | 1592篇 |
1988年 | 1454篇 |
1987年 | 1075篇 |
1986年 | 1086篇 |
1985年 | 1083篇 |
1984年 | 874篇 |
1983年 | 783篇 |
1982年 | 827篇 |
1981年 | 857篇 |
1980年 | 762篇 |
1979年 | 539篇 |
1978年 | 515篇 |
1977年 | 1143篇 |
1976年 | 2277篇 |
1975年 | 398篇 |
1974年 | 319篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
H H T?nnesen J Karlsen 《Zeitschrift für Lebensmittel-Untersuchung und -Forschung》1985,180(5):402-404
The kinetics of the pH-dependent degradation of curcumin has been investigated. A plot of the rate constant against pH indicates the pKa values of the acid protons. The graph also indicates the complexity of the curcumin degradation. 相似文献
952.
953.
954.
The design of controlled-resistance loads for domestic induction heating applications using thin non-magnetic conductive layers is described. Thin metallic layers are fabricated using the phase vapour deposition technique. Such layers would enable vessels, the inductive behaviour of which was similar to those fabricated with conventional ferromagnetic bulk materials, to be manufactured. Optimum layer thickness is investigated using an analytical impedance model of the complete induction system 相似文献
955.
956.
Yadin Y. Nazarathy M. Bilenca A. Orenstein M. 《Lightwave Technology, Journal of》2007,25(6):1431-1440
The recently introduced multichip differential phase-shift keying (MC-DPSK) optical transmission format, entailing the modulation of relative phases over a moving transmission window of successive chip intervals, is analytically and numerically analyzed. The maximum-likelihood optimal MC-DPSK receiver is derived and synthesized using integrated-optic Mach-Zehnder delay interferometers, whose electrical outputs are interpreted as generalized Stokes' parameters. The MC-DPSK performance over a nonlinear fiber channel, limited by the combination of amplified spontaneous emission noise and self-phase modulation, is further derived and simulated, demonstrating that the lowest complexity three-chip binary-phase MC-DPSK receiver provides an ~1-dB Q-factor advantage over conventional DPSK. 相似文献
957.
Strategy for olive mill wastewater treatment and reuse with a sewage plant in an arid region. 总被引:1,自引:0,他引:1
This study was conducted to evaluate the treatability of OMW (olive mill wastewater) with sewage and sewage sludge, which could supplement nutrients and microbes required for OMW treatment and reduce its possible toxicity. The amount of OMW added to an aeration tank was based on the loading difference between the designed and actual COD loads, while the amount added to anaerobic digestion for energy recovery was determined by CH4 production. The COD removal efficiencies were 70-85% for both systems. Compost of OMW with dried sewage sludge also showed a similar temperature profile without OMW addition. This strongly suggested that OMW can be treated at a sewage plant without pretreatment and the treated effluent can be reused in irrigation for an arid region. 相似文献
958.
Domestic wastewater is a significant source of nitrogen and phosphorus, which cause lake eutrophication. Among the wastewater treatment technologies, constructed wetlands are a promising low-cost means of treating point and diffuse sources of domestic wastewater in rural areas. However, the sustainable operation of constructed wetland treatment systems depends upon a high rate conversion of organic and nitrogenous loading into their metabolic gaseous end products, such as N2O and CH4. In this study, we examined and compared the performance of three typical types of constructed wetlands: Free Water Surface (FWS), Subsurface Flow (SF) and Vertical Flow (VF) wetlands. Pollutant removal efficiency and N2O and CH4 emissions were assessed as measures of performance. We found that the pollutant removal rates and gas emissions measured in the wetlands exhibited clear seasonal changes, and these changes were closely associated with plant growth. VF wetlands exhibited stable removal of organic pollutants and NH3-N throughout the experiment regardless of season and showed great potential for CH4 adsorption. SF wetlands showed preferable T-N removal performance and a lower risk of greenhouse gas emissions than FWS wetlands. Soil oxidation reduction potential (ORP) analysis revealed that water flow structure and plant growth influenced constructed wetland oxygen transfer, and these variations resulted in seasonal changes of ORP distribution inside wetlands that were accompanied by fluctuations in pollutant removal and greenhouse gas emissions. 相似文献
959.
A method for predicting the long-term performance of solar energy systems, based on the analysis of system performance for one particular day—the typical meteorological day (TMD)—is presented. The TMD is constructed from the cumulative time distribution of insolation values on the collector aperture. The TMD method requires little calculational effort and a small data base relative to standard yearly computer simulations. Good agreement is found between the predictions of the new method and the corresponding results of the
-f-chart method. The TMD method is of particular value for cases that may often be treated inaccurately by simple calculational methods: (1) high threshold problems; (2) systems with short response times (e.g., due to small storage); and (3) systems in which collectors other than flat plates are used (the method is applicable to all solar collector types). 相似文献
960.
Presented is an eigen filter to remove autogenic electrical stimulation artefacts and M-waves while preserving the volitional electromyographic signal. The optimality of the eigen filter is shown, along with simulated and measured data to indicate its superior performance over conventional prediction error filters. 相似文献