全文获取类型
收费全文 | 518811篇 |
免费 | 7213篇 |
国内免费 | 1402篇 |
专业分类
电工技术 | 10132篇 |
综合类 | 872篇 |
化学工业 | 76730篇 |
金属工艺 | 18679篇 |
机械仪表 | 15593篇 |
建筑科学 | 13162篇 |
矿业工程 | 1852篇 |
能源动力 | 13802篇 |
轻工业 | 47647篇 |
水利工程 | 4718篇 |
石油天然气 | 7042篇 |
武器工业 | 76篇 |
无线电 | 66282篇 |
一般工业技术 | 98348篇 |
冶金工业 | 96165篇 |
原子能技术 | 9655篇 |
自动化技术 | 46671篇 |
出版年
2021年 | 3978篇 |
2019年 | 3857篇 |
2018年 | 6495篇 |
2017年 | 6420篇 |
2016年 | 6761篇 |
2015年 | 4538篇 |
2014年 | 7819篇 |
2013年 | 23676篇 |
2012年 | 12722篇 |
2011年 | 17551篇 |
2010年 | 13735篇 |
2009年 | 15706篇 |
2008年 | 16714篇 |
2007年 | 16516篇 |
2006年 | 14906篇 |
2005年 | 13627篇 |
2004年 | 13217篇 |
2003年 | 12922篇 |
2002年 | 12448篇 |
2001年 | 12527篇 |
2000年 | 12025篇 |
1999年 | 12494篇 |
1998年 | 29127篇 |
1997年 | 21105篇 |
1996年 | 16685篇 |
1995年 | 12997篇 |
1994年 | 11663篇 |
1993年 | 11319篇 |
1992年 | 8781篇 |
1991年 | 8302篇 |
1990年 | 8104篇 |
1989年 | 7679篇 |
1988年 | 7457篇 |
1987年 | 6399篇 |
1986年 | 6389篇 |
1985年 | 7560篇 |
1984年 | 6956篇 |
1983年 | 6419篇 |
1982年 | 5865篇 |
1981年 | 6122篇 |
1980年 | 5658篇 |
1979年 | 5502篇 |
1978年 | 5234篇 |
1977年 | 6171篇 |
1976年 | 7831篇 |
1975年 | 4684篇 |
1974年 | 4499篇 |
1973年 | 4555篇 |
1972年 | 3689篇 |
1971年 | 3369篇 |
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
211.
212.
213.
C. Busuioc C.D. Ghitulica A. Stoica M. Stroescu G. Voicu V. Ionita L. Averous S.I. Jinga 《Ceramics International》2018,44(8):9433-9441
Bacterial cellulose membranes were employed as templates for calcium phosphates deposition by successive immersion in solutions of Ca(NO3)2·4H2O and (NH4)2HPO4, under ultrasonication. During the wet chemical reaction, mineral phases were loaded on bacterial cellulose fibrils, leading to precursor hybrid composites. These were subjected to a lyophilisation procedure in order to preserve the 3D porous aspect and afterwards to a thermal treatment with the aim of removing the polymeric phase and generating well crystallized structures. Different types of morphologies were achieved by varying the heating rate, as well as the calcination temperature and period. The as-prepared samples and the final ones were investigated from compositional and structural point of view through X-ray diffraction and Fourier-transform infrared spectroscopy and morphologically concerning by scanning electron microscopy. The magnetic properties were also evaluated in order to demonstrate the suitability of the obtained materials for the development of magnetic scaffolds dedicated to hard tissue applications. 相似文献
214.
ABSTRACTThis paper proposes the multiple-hypotheses image segmentation and feed-forward neural network classifier for food recognition to improve the performance. Initially, the food or meal image is given as input. Then, the segmentation is applied to identify the regions, where a particular food item is located using salient region detection, multi-scale segmentation, and fast rejection. Then, the features of every food item are extracted by the global feature and local feature extraction. After the features are obtained, the classification is performed for each segmented region using a feed-forward neural network model. Finally, the calorie value is computed with the aid of (i) food volume and (ii) calorie and nutrition measure based on mass value. The experimental results and performance evaluation are validated. The outcome of the proposed method attains 0.947 for Macro Average Accuracy (MAA) and 0.959 for Standard Accuracy (SA), which provides better classification performance. 相似文献
215.
David J. Lawrence Brianna L. Smith Cameron D. Collard Keyton A. Elliott Kyle L. Fakhoury Jeffery D. Mangold Anna N. Soyka 《International Journal of Hydrogen Energy》2021,46(2):1642-1655
Monolithically-integrated tandem photoanodes were fabricated on substrates consisting of epitaxial n-GaAs1-xPx (x ? 0.32) grown on n+-GaAs wafers. A p+-n junction photovoltaic (PV) cell was first formed by zinc diffusion into the n-GaAs0.68P0.32 from a deposited ZnO coating. After diffusion the ZnO serves as a transparent electrical contact to the resulting p+-GaAs0.68P0.32 surface layer. Transparent, conducting SnO2:F provides chemical and mechanical protection for the ZnO and the underlying PV cell, and it electrically connects this cell to a top BiVO4 photocatalyst layer. In some photoanodes, a WO3 thin film was interposed between the SnO2:F and BiVO4. All oxide coatings were produced by ultrasonic spray pyrolysis except WO3, which was spin coated. Unassisted (unbiased) solar water splitting was achieved, with a solar-to-hydrogen efficiency approaching 2%, without addition of any co-catalyst to the BiVO4 surface. This work can provide insights to other researchers regarding scalable, low cost approaches for the planar monolithic integration of oxide photoanode materials with PV cells to create new tandem devices. 相似文献
216.
Ci̇velekler Ebru Okur Volkan D. Afacan Kamil B. 《Bulletin of Engineering Geology and the Environment》2021,80(7):5589-5607
Bulletin of Engineering Geology and the Environment - Local soil characteristics play a key role in determining soil-structure interaction and reliability of the superstructure behavior under... 相似文献
217.
In this paper, implementation of the Benchmark Simulation Model No 2 (BSM2) within Matlab-Simulink is presented. The BSM2 is developed for plant-wide WWTP control strategy evaluation on a long-term basis. It consists of a pre-treatment process, an activated sludge process and sludge treatment processes. Extended evaluation criteria are proposed for plant-wide control strategy assessment. Default open-loop and closed-loop strategies are also proposed to be used as references with which to compare other control strategies. Simulations indicate that the BM2 is an appropriate tool for plant-wide control strategy evaluation. 相似文献
218.
Enhanced sludge conditioning by enzyme pre-treatment: comparison of laboratory and pilot scale dewatering results. 总被引:2,自引:0,他引:2
The effect of enzyme pre-treatment on dewaterability of anaerobically digested sludge was investigated at both laboratory and pilot scale. Our results revealed a significant increase in cake solid content (27% cake solids compared to 18% without enzyme pre-treatment), using an enzyme dose of only 20 mg/L. In order to assess practical application, enzyme pre-treatment was applied at the Wilmington, Delaware (U.S.) wastewater treatment plant, using a pilot-scale centrifuge. However, the efficiency reached in laboratory scale could not be obtained in pilot scale, where the final cake solids content did not exceed 20%. Centrifuge and belt filter press (simulated by Crown Press) dewatering were compared in terms of the process efficiencies in the absence and presence of enzyme pre-treatment. Possible factors that might cause the differences were tested by experimental and statistical comparisons. Results indicated that the higher shear applied in centrifugation is responsible for the lack of improved cake solids. The network strength of sludge determined by rheological measurements revealed that enzymatic treatment weakens the gel structure of the sludge floc through the hydrolysis of extracellular polymeric substances; this allows improved dewatering by filtration processes, but leads to floc deterioration when subjected to high shear during centrifugation. 相似文献
219.
Electrodewatering is a technique in which pressure dewatering is combined with electrokinetic effects to realize an improved solid/liquid separation and hence increased filter cake dry matter contents. In order to be energy efficient, it is shown that sludge should be dewatered by pressure dewatering to a high extent prior to electric field application, and a sufficient contact time for the electric field must be guaranteed. In order to realize these goals, a bench- and pilot-scale diaphragm filter press suited for electrodewatering were constructed for treatment of sewage and other types of sludges. It was shown that electrodewatering of sludge is a feasible technique, especially for biological sludge types. Other types of sludge are less suited for electrodewatering because of the restricted improvements that can be realized in cake dry matter content and the high electric energy consumption. Furthermore, it was shown in pilot-scale tests that the use of a diaphragm filter press with electrodewatering facilities was very well suited to deliver dry filter cakes of sewage sludge at a moderate energy consumption. Depending on local market prices for investment, operating and sludge disposal costs, this technology may therefore lead to important savings in the sludge management process. 相似文献
220.
Alum sludge refers to the by-product from the processing of drinking water in water treatment works. In this study, groups of batch experiments were designed to identify the characteristics of dewatered alum sludge for phosphorus adsorption. Air-dried alum sludge (moisture content 10.2%), which was collected from a water treatment works in Dublin, was subjected to artificial P-rich wastewater adsorption tests using KH2PO4 as a model P source. Adsorption behaviours were investigated as a function of amount and particle size of alum sludge, pH of solution and adsorption time. The results have shown that pH plays a major role not only in the adsorption process but also in the adsorption capacity. With regard to adsorption capacity, this study reveals the Langmuir adsorption isotherm being the best fit with experimental data (R2 = 0.98-0.99). The maximum adsorption capacities range from 0.7 to 3.5 mg-P/g when the pH of the synthetic P solution was varied from 9.0 to 4.3, accordingly. The outcome of this study indicated that alum sludge is suitable for use as an adsorbent for removal of phosphate from wastewater. 相似文献