全文获取类型
收费全文 | 49195篇 |
免费 | 5485篇 |
国内免费 | 2487篇 |
专业分类
电工技术 | 2938篇 |
技术理论 | 2篇 |
综合类 | 3550篇 |
化学工业 | 11019篇 |
金属工艺 | 1353篇 |
机械仪表 | 2022篇 |
建筑科学 | 3319篇 |
矿业工程 | 4204篇 |
能源动力 | 4523篇 |
轻工业 | 2944篇 |
水利工程 | 896篇 |
石油天然气 | 2994篇 |
武器工业 | 433篇 |
无线电 | 4890篇 |
一般工业技术 | 4955篇 |
冶金工业 | 2751篇 |
原子能技术 | 1063篇 |
自动化技术 | 3311篇 |
出版年
2024年 | 224篇 |
2023年 | 844篇 |
2022年 | 1407篇 |
2021年 | 1799篇 |
2020年 | 1858篇 |
2019年 | 1619篇 |
2018年 | 1517篇 |
2017年 | 1818篇 |
2016年 | 2056篇 |
2015年 | 2120篇 |
2014年 | 3240篇 |
2013年 | 3348篇 |
2012年 | 3806篇 |
2011年 | 3784篇 |
2010年 | 2858篇 |
2009年 | 2897篇 |
2008年 | 2606篇 |
2007年 | 2896篇 |
2006年 | 2689篇 |
2005年 | 2212篇 |
2004年 | 1786篇 |
2003年 | 1708篇 |
2002年 | 1375篇 |
2001年 | 1162篇 |
2000年 | 1007篇 |
1999年 | 834篇 |
1998年 | 651篇 |
1997年 | 555篇 |
1996年 | 510篇 |
1995年 | 404篇 |
1994年 | 349篇 |
1993年 | 233篇 |
1992年 | 183篇 |
1991年 | 170篇 |
1990年 | 122篇 |
1989年 | 97篇 |
1988年 | 81篇 |
1987年 | 64篇 |
1986年 | 54篇 |
1985年 | 41篇 |
1984年 | 38篇 |
1983年 | 27篇 |
1982年 | 28篇 |
1981年 | 18篇 |
1980年 | 9篇 |
1979年 | 8篇 |
1978年 | 4篇 |
1959年 | 6篇 |
1955年 | 4篇 |
1951年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Joo H. Kang Eujin Um Alexander Diaz Harry Driscoll Melissa J. Rodas Karel Domansky Alexander L. Watters Michael Super Howard A. Stone Donald E. Ingber 《Small (Weinheim an der Bergstrasse, Germany)》2015,11(42):5657-5666
Magnetic nanoparticles have been employed to capture pathogens for many biological applications; however, optimal particle sizes have been determined empirically in specific capturing protocols. Here, a theoretical model that simulates capture of bacteria is described and used to calculate bacterial collision frequencies and magnetophoretic properties for a range of particle sizes. The model predicts that particles with a diameter of 460 nm should produce optimal separation of bacteria in buffer flowing at 1 L h−1. Validating the predictive power of the model, Staphylococcus aureus is separated from buffer and blood flowing through magnetic capture devices using six different sizes of magnetic particles. Experimental magnetic separation in buffer conditions confirms that particles with a diameter closest to the predicted optimal particle size provide the most effective capture. Modeling the capturing process in plasma and blood by introducing empirical constants (ce), which integrate the interfering effects of biological components on the binding kinetics of magnetic beads to bacteria, smaller beads with 50 nm diameters are predicted that exhibit maximum magnetic separation of bacteria from blood and experimentally validated this trend. The predictive power of the model suggests its utility for the future design of magnetic separation for diagnostic and therapeutic applications. 相似文献
42.
Fei Li Xin-Gang Wang Xiao Huang Ji-Xuan Liu Weichao Bao Guo-Jun Zhang Hongzhi Wang 《Journal of the European Ceramic Society》2018,38(14):4806-4813
We present a straightforward method via sol-gel process using polyethylene glycol (PEG) as phase separation inducer to prepare zirconium carbide/silicon carbide (ZrC/SiC) porous monoliths. Organic/inorganic hybrid gels are prepared using zirconium oxychloride, furfuryl alcohol, and tetraethyl orthosilicate as major starting materials. In the presence of PEG, crack-free hybrid monoliths are obtained by drying the wet gels under ambient pressure, whereas in the absence of PEG, the wet gels break into pieces as expected. PEG plays a key role in maintaining the macroscopic shape of the monoliths. After ceramization at 1300–1500?°C, ZrC/SiC porous monoliths are obtained. SEM and mercury intrusion porosimetry data show that PEG also has strong influence on the microstructures of the monoliths. The compressive strengths of the ceramic monoliths are in the range of 0.3 to 0.7?MPa. And their compressive behavior starts to differ due to the changes in their microstructures, especially the pore structure. 相似文献
43.
The present study was aimed to utilize low‐cost alumina (Al2O3) nanoparticles for improving the heat transfer behavior in an intercooler of two‐stage air compressor. Experimental investigation was carried out with three different volume concentrations of 0.5%, 0.75%, and 1.0% Al2O3/water nanofluids to assess the performance of the intercooler, that is, counterflow heat exchanger at different loads. Thermal properties such as thermal conductivity and overall heat transfer coefficient of nanofluid increased substantially with increasing concentration of Al2O3 nanoparticles. Specific heat capacity of nanofluids were lower than base water. The intercooler performance parameters such as effectiveness and efficiency improved appreciably with the employment of nanofluid. The efficiency increased by about 6.1% with maximum concentration of nanofluid, that is, 1% at 3‐bar compressor load. It is concluded from the study that high concentration of Al2O3 nanoparticles dispersion in water would offer better heat transfer performance of the intercooler. 相似文献
44.
Md. Abdur Rahim Shamim Mahbub Md. Kamrul Islam Sk. Md. Ali Ahsan Shahed Rana Malik Abdul Rub Anish Khan Md. Anamul Hoque 《Journal of surfactants and detergents》2020,23(2):457-470
Conductometric and cloud point (CP) measurement studies have been performed to investigate the interaction of tetradecyltrimethylammonium bromide (TTAB) and Triton® X-100 (TX-100) with ciprofloxacin hydrochloride (CFH) in different solvents over the temperature range of 295.15–315.15 K. CFH is used for the treatment of various bacterial infections. The observed critical micelle concentration (CMC) values of TTAB were found to be reduced in the presence of electrolytes (Na2SO4/Na3PO4), and this reduction proceeds with the elevation of salt concentration. The order of the CMC of TTAB follows the trend: > >. The observed CMC values of TTAB were found to increase with increasing temperature and decrease with increasing concentration of CFH in aqueous medium. The values of Gibbs free energy of micellization () for the TTAB/TTAB + CFH mixture were found to be negative, implying spontaneous micellization. The estimated CP of TX-100 decreases with increasing concentration of TX-100 in aqueous medium. The CP values first decrease with increasing concentration of CFH and then increase at higher concentration of CFH almost in all cases investigated. The values of free energy of clouding were found to be positive in all cases studied implying that phase separation of TX-100 was nonspontaneous. The other thermodynamic parameters associated with the micellization of TTAB and the phase separation of TX-100 were estimated and explained. 相似文献
45.
This paper addresses the multi-objective optimization problem arising in the operation of heat integrated batch plants, where makespan and utility consumption are the two conflicting objectives. A new continuous-time MILP formulation with general precedence variables is proposed to simultaneously handle decisions related to timing, product sequencing, heat exchanger matches (selected from a two-stage superstructure) and their heat loads. It features a complex set of timing constraints to synchronize heating and cooling tasks, derived from Generalized Disjunctive Programming. Through the solution of an industrial case study from a vegetable oil refinery, we show that major savings in utilities can be achieved while generating the set of Pareto optimal solutions through the ɛ-constraint method. 相似文献
46.
This study assessed the collection efficiency (CE) of two popularly used sampling devices (BioSampler and Coriolis sampler) for fungal aerosols. Phosphate‐buffered saline (PBS) supplemented with or without surfactant (Tween‐20, Tween‐80, or Triton X‐100) and antifoam agent was prepared and used as collection liquids. The agar impactor (BioStage) was simultaneously operated with liquid‐based samplers to collect fungi from seven sites located at a university building, public library, and animal farming. Fungal concentrations determined by liquid samplers were divided by those by BioStage, and the ratio values represented CE. Results indicate that the CE of BioSampler was superior to that of Coriolis (P = 0.0001) and the PBS containing surfactant collected fungi better than that without surfactant (P < 0.0001), whereas antifoam agent showed no influence (P = 0.8). Moreover, fungal concentrations determined by BioSampler with surfactant‐added PBS were statistically indifferent from those by BioStage (P > 0.05) with a Spearman correlation coefficient of 0.81‐0.83 (P < 0.01). In addition to sampler and collection liquid, sampling location was also identified as a significant CE factor (P = 0.006), implying potential influences by fungal genera in the studied fields. Overall, BioSampler with surfactant‐supplemented PBS (eg, Triton X‐100) is recommended considering the great CE and compatibility with a variety of analytical assays. 相似文献
47.
《International Journal of Hydrogen Energy》2020,45(27):13975-13984
An intervening barrier for photocatalytic water decomposition and pollutant degradation is the frustratingly quick recombination of e− - h+ pairs. Delicate design of heterojunction photocatalysts by coupling the semiconductors at nanoscale with well-matched geometrical and electronic alignments is an effective strategy to ameliorate the charge separation. Here a facile and environment-friendly l-cysteine-assisted hydrothermal process under weakly alkaline conditions is demonstrated for the first time to fabricate ZnIn2S4/In(OH)3 hollow microspheres with intimate contact, which are verified by XRD, SEM, (HR)TEM, XPS, N2 adsorption-desorption, UV–Vis DRS and photoluminescence spectra. ZnIn2S4/In(OH)3 heterostructure (L-cys/Zn2+ = 4, molar ratio) with a band-gap of 2.50 eV, demonstrates the best photocatalytic performance for water reduction and MB degradation under visible light, outperforming its counterparts (In(OH)3 and ZnIn2S4). The excellent activity of ZnIn2S4/In(OH)3 heterostructure arises from the intercrossed band-edge positions as well as the unique hollow structure with large surface area and wide pore-size distribution, which are beneficial for the efficient charge migration from bulk to surface as well as at the interface between ZnIn2S4 and In(OH)3. This work provides an efficient and eco-friendly strategy for one-pot synthesis of heterostructured composites with intimate contact for photocatalytic application. 相似文献
48.
Siqi Yu Qin Wang Jianwei Wang Yong Xiang Xiaobin Niu Tingshuai Li 《International Journal of Hydrogen Energy》2021,46(27):14331-14337
Artificial nitrogen fixation is emerging as a promising approach for synthesis of ammonia at mild conditions. Inspired by biological nitrogen fixation based on bacteria containing iron, zinc doped Fe2O3 nanoparticles are proposed as an efficient and earth abundant electrocatalyst for converting N2 to NH3. In neutral media, it achieves a maximum Faradaic efficiency (FE) of 10.4% and a large NH3 yield rate of 15.1 μg h?1 mg?1cat. at ?0.5 V vs. reversible hydrogen electrode. This catalyst also exhibits excellent selectivity and stability. Theoretical calculations suggest the reaction follows the associative enzymatic mechanism and it has a barrier of as low as 0.68 eV. 相似文献
49.
50.
垦71井区三维VSP资料波场分离方法应用研究 总被引:8,自引:5,他引:3
三维VSP资料是多偏移距VSP资料,资料中多种类型的波叠合在一起形成复杂波场。从复杂波场中分离出单一的保幅反射波波场是三维VSP波场分离的重要工作。常规二维VSP波场处理方法单一,难以适用于复杂的三维波场处理。针对三维VSP资料的波场特点,以分离上行反射P波为例,将单一波场分离方法加以适当组合,对垦71井区三维VSP实际资料进行了应用研究。结果表明,波场分离处理中叠加消去法和中值滤波相结合以及F—K滤波和中值滤波相结合的方法克服了单一方法的缺陷,波场处理后获得了波组特征明显、波场清晰单一的上行反射P波保幅波场,取得了较好的波场分离效果。 相似文献