全文获取类型
收费全文 | 2157篇 |
免费 | 19篇 |
国内免费 | 42篇 |
专业分类
电工技术 | 56篇 |
综合类 | 33篇 |
化学工业 | 584篇 |
金属工艺 | 135篇 |
机械仪表 | 357篇 |
建筑科学 | 30篇 |
矿业工程 | 9篇 |
能源动力 | 74篇 |
轻工业 | 170篇 |
水利工程 | 3篇 |
石油天然气 | 20篇 |
武器工业 | 2篇 |
无线电 | 272篇 |
一般工业技术 | 368篇 |
冶金工业 | 20篇 |
原子能技术 | 26篇 |
自动化技术 | 59篇 |
出版年
2023年 | 8篇 |
2022年 | 21篇 |
2021年 | 29篇 |
2020年 | 31篇 |
2019年 | 16篇 |
2018年 | 17篇 |
2017年 | 18篇 |
2016年 | 26篇 |
2015年 | 46篇 |
2014年 | 74篇 |
2013年 | 237篇 |
2012年 | 86篇 |
2011年 | 133篇 |
2010年 | 95篇 |
2009年 | 105篇 |
2008年 | 97篇 |
2007年 | 97篇 |
2006年 | 114篇 |
2005年 | 97篇 |
2004年 | 85篇 |
2003年 | 95篇 |
2002年 | 62篇 |
2001年 | 74篇 |
2000年 | 85篇 |
1999年 | 83篇 |
1998年 | 94篇 |
1997年 | 55篇 |
1996年 | 47篇 |
1995年 | 53篇 |
1994年 | 32篇 |
1993年 | 27篇 |
1992年 | 22篇 |
1991年 | 15篇 |
1990年 | 7篇 |
1989年 | 11篇 |
1988年 | 3篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有2218条查询结果,搜索用时 15 毫秒
1.
《Ceramics International》2020,46(4):4148-4153
The ferroelectric photovoltaic (FPV) effect obtained in inorganic perovskite ferroelectric materials has received much attention because of its large potential in preparing FPV devices with superior stability, high open-circuit voltage (Voc) and large short-circuit current density (Jsc). In order to obtain suitable thickness for the ferroelectric thin film as light absorption layer, in which, the sunlight can be fully absorbed and the photo-generated electrons and holes are recombined as few as possible, we prepare Pb0.93La0.07(Zr0.6Ti0.4)0.9825O3 (PLZT) ferroelectric thin films with different layer numbers by the sol-gel method and based on these thin films, obtain FPV devices with FTO/PLZT/Au structure. By measuring photovoltaic properties, it is found that the device with 4 layer-PLZT thin film (~300 nm thickness) exhibits the largest Voc and Jsc and the photovoltaic effect obviously depends on the value and direction of the poling electric field. When the device is applied a negative poling electric field, both the Voc and Jsc are significantly higher than those of the device applied the positive poling electric field, due to the depolarization field resulting from the remnant polarization in the same direction with the built-in electric field induced by the Schottky barrier, and the higher the negative poling electric field, the larger the Voc and Jsc. At a -333 kV/cm poling electric field, the FPV device exhibits the most superior photovoltaic properties with a Voc of as high as 0.73 V and Jsc of as large as 2.11 μA/cm2. This work opens a new way for developing ferroelectric photovoltaic devices with good properties. 相似文献
2.
A mathematical model of evaporation process from a laminar falling liquid film on a vertical plate of constant temperature is presented. The model is developed with and without interfacial shear stress due to the vapor flow at the liquid film surface. The vapor pressure drop, vapor exit velocity and cooling rate are calculated for different liquid mass flow values. It is shown that lower liquid mass flow produces higher cooling rate. The results also show that the interfacial shear stress has a considerable negative effect on the cooling rate. It is proved that there exists an optimum distance between the plates, which gives the maximum volumetric cooling rate. 相似文献
3.
ChenluSONG WenjianWENG KuiCHENG HaiboQU PiyiDU GeSHEN GaorongHAN JuanYANC JoseM.F.Ferreira 《材料科学技术学报》2003,19(5):495-499
Fluorapatite/hydroxyapatite solid solution has better biological properties than other apatites, especially used as films or coatings. In this work, sol-gel preparation and in vitro behavior of fluorapatite/hydroxyapatite solid solution films on titanium alloy were investigated. Ca(NO3)2-4H20 and PO(OH)x(OEt)3-x were selected as precursors, and hexafluorophosphoric acid (HPFo) was used as a fluorine containing reagent. The Ca and P precursors were mixed with HPFo to keep the Ca/P molar ratio 1.67. The mixtures refluxed for 12 h were used as dipping sols for the preparation of the films. The phase of the films obtained at 600℃ was apatite. The F contents in the films increased with the concentrations of HPF6 in the dipping sols. The solid solution films were shown to have better stability than hydroxyapatite films, and a reasonably good bioactivity in the in vitro evaluation. 相似文献
5.
在有壁垒膜存在的表面,多孔膜的生长在氧化初期受到延迟阻碍,这一现象在直流恒压多孔阳极氧化电流一时间曲线上反映出来。电流达到稳态氧化的时间愈长,壁垒膜愈厚。文中应用此法判断了0.5MH_3BO_3介质的pH值、温度对壁垒阳极氧化膜厚的影响,并应用记录同一介质环境壁垒恒流阳极氧化的槽压一时间曲线得到验证。 相似文献
6.
Ti1−xVxO2 solid solution film photoelectrodes were prepared by the dip-coating sol–gel method. X-ray diffraction and X-ray photoelectron spectroscopy were employed to ensure the formation of the solid solution and their composition. Obvious photoresponses were observed in the visible region for the solid solution film electrodes with x0.05 and the red shift of the photoresponse was enhanced with increasing x. Moreover, the solid solution film electrodes were found to be photoelectrochemically stable. However, the onset potential of photocurrent shifted positively with increasing x. Band model of the solid solution was suggested to explain the effects of the vanadium incorporation on the photoelectrochemical properties. 相似文献
7.
8.
Ingo Alig Dirk Lellinger Harald Oehler Sergey A. Adamovsky Christoph Schick 《Progress in Organic Coatings》2008,61(2-4):166-175
A new microcalorimeter with eight parallel channels using robust, low cost sensors for characterization of coatings and adhesives is described and first experiments on coatings and adhesives are presented. The calorimetric sensors are based on thin glass plates (20 mm × 20 mm, thickness 150 μm) with heater and thermocouple sputtered on the surfaces (calorimetric active area of about 9 mm2). The setup allows heating and cooling experiments as well as isothermal measurements in the temperature-modulated mode with up to eight sensors in parallel. The measured quantities are the real (C′p) and imaginary part (C″p) of the complex heat capacity (), the related absolute value of the heat capacity () and the heat flow . An industrial computer (NI PXI system) with specific software for calibration and data recording controls the electronic components. Sensors can be embedded in a temperature controlled oven (heating and cooling by Peltier elements) or alternatively in a climatic cabinet with controlled temperature and humidity.
The method has been applied successfully to monitoring of film formation of aqueous polymer dispersions (styrene-acrylate copolymer) and curing of coatings. 相似文献
9.
S. Sarkar P. K. Singha S. Dey M. Mohanty B. Adhikari 《Materials and Manufacturing Processes》2006,21(3):291-296
A polyester urethane was synthesized for use in a biodegradable scaffold. The polyurethane was synthesized in a two-step process: first, ester diol was synthesized from lactic acid and polyethylene glycol 400 (PEG 400), then it was polymerized with toluene diisocyanate using dibutyl tin dilaurate (DBTDL) as a catalyst to form a polyester urethane. Polyester urethane has tensile strength of 51-59 MPa and elongation at fracture of 369-439%. FTIR and XRD were used to confirm the formation and structure of the polymer. Hydrolytic degradation was studied in different alkali solutions and in saline water. In order to assess the cellular response of this material, cytotoxicity analysis was carried out against the cell line. 相似文献
10.
Per Axel Clausen 《Indoor air》1993,3(4):269-275
A waterborne paint was applied to tin plated steel sheets with three different film thicknesses. The emission of volatile and semivolaile organic compounds ((S) VOCs) from the samples was measured in small climatic chambers under standard conditions over a two-week period. The purpose of the study was to evaluate the effect of the film thickness on the emission rate decay. First order decay models, including sink effects for the high boiling (S) VOCs, were fitted to the concentration versus time data. The results showed that the first order rate constants decrease with increasing film thickness. In uddition, the results indicated that the emissions of the (S)VOCs in the waterborne paint film seemed to be controlled by evaporation. The thicknesses of paint films used in climatic chamber tests to estimate emission rates for product compurison or emission prediction must be known in order to prevent erroneous conclusions 相似文献