全文获取类型
收费全文 | 74416篇 |
免费 | 5191篇 |
国内免费 | 3234篇 |
专业分类
电工技术 | 2530篇 |
技术理论 | 4篇 |
综合类 | 6998篇 |
化学工业 | 24370篇 |
金属工艺 | 2927篇 |
机械仪表 | 2270篇 |
建筑科学 | 6607篇 |
矿业工程 | 2547篇 |
能源动力 | 1879篇 |
轻工业 | 4443篇 |
水利工程 | 2001篇 |
石油天然气 | 3914篇 |
武器工业 | 567篇 |
无线电 | 3981篇 |
一般工业技术 | 8465篇 |
冶金工业 | 3233篇 |
原子能技术 | 522篇 |
自动化技术 | 5583篇 |
出版年
2024年 | 223篇 |
2023年 | 919篇 |
2022年 | 1466篇 |
2021年 | 1863篇 |
2020年 | 1699篇 |
2019年 | 1567篇 |
2018年 | 1500篇 |
2017年 | 1734篇 |
2016年 | 2067篇 |
2015年 | 2184篇 |
2014年 | 3718篇 |
2013年 | 3665篇 |
2012年 | 4576篇 |
2011年 | 5348篇 |
2010年 | 4105篇 |
2009年 | 4551篇 |
2008年 | 4062篇 |
2007年 | 5247篇 |
2006年 | 4765篇 |
2005年 | 4345篇 |
2004年 | 3635篇 |
2003年 | 3362篇 |
2002年 | 2941篇 |
2001年 | 2429篇 |
2000年 | 2081篇 |
1999年 | 1686篇 |
1998年 | 1289篇 |
1997年 | 1005篇 |
1996年 | 866篇 |
1995年 | 764篇 |
1994年 | 629篇 |
1993年 | 516篇 |
1992年 | 397篇 |
1991年 | 266篇 |
1990年 | 262篇 |
1989年 | 200篇 |
1988年 | 163篇 |
1987年 | 126篇 |
1986年 | 84篇 |
1985年 | 79篇 |
1984年 | 74篇 |
1983年 | 37篇 |
1982年 | 36篇 |
1981年 | 44篇 |
1980年 | 35篇 |
1979年 | 46篇 |
1978年 | 25篇 |
1977年 | 23篇 |
1976年 | 20篇 |
1975年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
By mans of a chemical synthesis technique stoichiometric CdTe-nanocrystals thin films were prepared on glass substrates at 70 °C. First, Cd(OH)2 films were deposited on glass substrates, then these films were immersed in a growing solution prepared by dissolution of Te in hydroxymethane sulfinic acid to obtain CdTe. The structural analysis indicates that CdTe thin films have a zinc-blende structure. The average nanocrystal size was 19.4 nm and the thickness of the films 170 nm. The Raman characterization shows the presence of the longitudinal optical mode and their second order mode, which indicates a good crystalline quality. The optical transmittance was less than 5% in the visible region (400–700 nm). The compositional characterization indicates that CdTe films grew with Te excess. 相似文献
2.
The supervision of a hybrid power plant, including solar panels, a gas microturbine and a storage unit operating under varying solar power profiles is considered. The Economic Supervisory Predictive controller assigns the power references to the controlled subsystems of the hybrid cell using a financial criterion. A prediction of the renewable sources power is embedded into the supervisor. Results deteriorate when the solar power is unsteady, owing to the inaccuracy of the predictions for a long-range horizon of 10 s. The receding horizon is switched between an upper and a lower value according to the amplitude of the solar power trend. Theoretical results show the relevance of horizon switching, according to a tradeoff between performance and prediction accuracy. Experimental results, obtained in a Hardware In the Loop (HIL) framework, show the relevance of the variable horizon approach. Power amplifiers allow us to simulate virtual components, such as a gas microturbine, and to blend their powers with that of real devices (storage unit, real solar panels). In this case, fuel savings, reaching 15%, obtained under unsteady operating conditions lead to a better overall performance of the hybrid cell. The overall savings obtained in the experiments amount to 12%. 相似文献
3.
《Intermetallics》2015
The structural changes induced in a CoCrCuFeNi multicomponent nano-crystalline high-entropy alloy (HEA) under fast electron irradiation were investigated by in-situ transmission electron microscopy (TEM) using a high voltage electron microscope (HVEM). A fine-grained face centered cubic (fcc) single phase was obtained in the sputtered specimens. The fcc solid solution showed high phase stability against irradiation over a wide temperature range from 298 to 773 K, and remained as the main constituent phase even when the samples were irradiated up to 40 displacement per atom (dpa). Moreover, the irradiation did not seem to induce grain coarsening. This is the first report on the irradiation damage in 5-component HEA under MeV electron irradiation. 相似文献
4.
Measuring nonlinear optical response of a specific material in a mixture, not only leads to investigate the behavior of a particular component in various circumstances, but also can be a way to select suitable combination and optimum concentration of additives and therefore obtaining the maximum nonlinear optical signals. In this work, by using dual-arm Z-scan technique, the nonlinear refractive index of Disperse Red1 (DR1) organic dye molecules inside the core of prepared polymeric nanocapsules was measured among various materials which prepared nanocapsules were made of them. Then the measured value was compared with nonlinear refractive index of DR1 solved in dichloromethane. 相似文献
5.
A novel synthetic route has been proposed to prepare hausmannite nanoparticles. The synthetic route comprises an iron mediated constant current cathodic electrodeposition of manganite and heat treatment of the latter to obtain hausmannite. The obtained nanostructures have been characterized using X-ray Diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX) and Fourier transform Infrared Spectrometry (FTIR). The role of iron in the formation of manganite precursor has been studied by cyclic voltammetry (CV) and differential thermal analysis (DTA). A formation mechanism based on iron mediated formation of Mn3+ and subsequent cathodic reduction of the disproportionated products has been proposed accordingly. The prepared nanoparticles exhibited specific capacitance of 143 F g−1 in 0.5 M Na2SO4 solution. The retained specific capacity was 87% after 2000 cycles. 相似文献
6.
文章中主要采用有机溶剂萃取法(OSE)对高浓度石油污染土壤进行修复,经过精馏操作,有效回收原油,建立脱附等温曲线,研究了石油污染物在土壤-有机溶剂两相间的迁移规律。 相似文献
7.
The synthesis of BaMgAl10O17∶ Eu2 (BAM) phosphors using the sol-gel method and their luminescence properties were reported. The blue-light emitting BAM was synthesized using citric acid and ethylene glycol as chelating materials. Emission of blue-light was obtained from these phosphors. The luminescent intensity increases as the temperature of heat treatment is increased. This study investigated the effects of the molar ratio of ethylene glycol to citric acid (Φ value), with respect to the phase formation and luminescence properties of BAM. The variation of the Φ value resulted in the change of the sol-gel reaction mechanism and the microstructures of the resultant powders. An increase in Φ value leads to an increase in the rate of BAM phase formation. The photoluminescent intensity of the prepared phosphors increases with heating temperatures because of enhanced crystallization. 相似文献
8.
9.
Chloride doped polyaniline conducting polymer films have been prepared in a protic acid medium (HCl) by potentiodynamic method
in an electrochemical cell and studied by cyclic voltammetry and FTIR techniques. The FTIR spectra confirmed Cl- ion doping in the polymers. The polymerization rate was found to increase with increasing concentration of aniline monomer.
But the films obtained at high monomer concentration were rough having a nonuniform flaky polyaniline distribution. Results
showed that the polymerization rate did not increase beyond a critical HCl concentration. Cyclic voltammetry suggested that,
the oxidation-reduction current increased with an increase in scan rate and that the undoped polyaniline films were not hygroscopic
whereas chloride doped polyaniline films were found to be highly hygroscopic. 相似文献
10.
针对辽河油区超稠油采油污水的特点,采用Fenton试剂催化氧化,对采油污水处理进行研究。实验研究及现场应用结果表明,此方法对污水的CODCr具有良好的去除效果。处理后污水经过简单生化,进一步降解污染物,能够实现稳定迭标排放,且具有能耗低、运行成本低和操作简单等特点。 相似文献