全文获取类型
收费全文 | 20686篇 |
免费 | 1922篇 |
国内免费 | 1214篇 |
专业分类
电工技术 | 1789篇 |
综合类 | 1762篇 |
化学工业 | 2033篇 |
金属工艺 | 1858篇 |
机械仪表 | 2022篇 |
建筑科学 | 1297篇 |
矿业工程 | 1362篇 |
能源动力 | 959篇 |
轻工业 | 1138篇 |
水利工程 | 640篇 |
石油天然气 | 771篇 |
武器工业 | 240篇 |
无线电 | 1484篇 |
一般工业技术 | 2242篇 |
冶金工业 | 595篇 |
原子能技术 | 207篇 |
自动化技术 | 3423篇 |
出版年
2024年 | 89篇 |
2023年 | 291篇 |
2022年 | 550篇 |
2021年 | 600篇 |
2020年 | 672篇 |
2019年 | 574篇 |
2018年 | 580篇 |
2017年 | 756篇 |
2016年 | 865篇 |
2015年 | 878篇 |
2014年 | 1318篇 |
2013年 | 1375篇 |
2012年 | 1419篇 |
2011年 | 1638篇 |
2010年 | 1193篇 |
2009年 | 1204篇 |
2008年 | 1049篇 |
2007年 | 1323篇 |
2006年 | 1193篇 |
2005年 | 1003篇 |
2004年 | 823篇 |
2003年 | 692篇 |
2002年 | 606篇 |
2001年 | 470篇 |
2000年 | 437篇 |
1999年 | 398篇 |
1998年 | 264篇 |
1997年 | 275篇 |
1996年 | 227篇 |
1995年 | 175篇 |
1994年 | 185篇 |
1993年 | 120篇 |
1992年 | 102篇 |
1991年 | 86篇 |
1990年 | 84篇 |
1989年 | 70篇 |
1988年 | 48篇 |
1987年 | 21篇 |
1986年 | 34篇 |
1985年 | 20篇 |
1984年 | 27篇 |
1983年 | 25篇 |
1982年 | 23篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1975年 | 2篇 |
1960年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Wassim Bahr 《国际自然能源杂志》2018,39(8):802-812
This paper assesses building integrated photovoltaic (BIPV) installation parameters based on the profit generated by a photovoltaic system. It takes into consideration a home building case study and it investigates its monthly energy demand based on a specific location and a typical occupancy. The capability of a photovoltaic (PV) system to generate more profit occurs when solar intensity is maximum while the electric energy price is at its highest rate. The paper traces a framework that encompasses different aspects such as energy demand, energy price, and solar intensity. This framework identifies profit alternatives according to different installation parameters. A tool that predicts a PV installation hourly electric energy production is developed. The profit generated is simulated for home buildings located in Beirut (Lebanon) and Xihua (China), both at 33.8° latitude north. The paper highlights a new approach for BIPV installations, taking into account weather conditions, energy demand, and electric energy utility rates. 相似文献
2.
The paper concerns an analysis of an equilibrium problem for 2D elastic body with two semirigid inclusions. It is assumed that inclusions have a joint point, and we investigate a junction problem for these inclusions. The existence of solutions is proved, and different equivalent formulations of the problem are proposed. We investigate a convergence to infinity of a rigidity parameter of the semirigid inclusion. It is proved that in the limit, we obtain an equilibrium problem for the elastic body with a rigid inclusion and a semirigid one. A parameter identification problem is investigated. In particular, the existence of a solution to a suitable optimal control problem is proved. 相似文献
3.
Cadmium Sulfide and Ferrous doped Cadmium Sulfide thin films have been prepared on different substrates using an electrodeposition technique. Linear sweep voltammetric analysis has been carried out to determine deposition potential of the prepared films. X-ray diffraction analysis showed that the prepared films possess polycrystalline nature with hexagonal structure. Surface morphology and film composition have been analyzed using Scanning electron microscopy and Energy dispersive analysis by X-rays. Optical absorption analysis showed that the prepared films are found to exhibit Band gap value in the range between 2.3, 2.8 eV for Cadmium Sulfide and Ferrous doped Cadmium Sulfide. 相似文献
4.
This study is to evaluate the potential for development of a cellulosic ethanol facility in Vietnam. Rice straw is abundant in Vietnam and highly concentrated in the Mekong Delta, where about 26 Mt year−1 of rice straw has been yearly produced. To minimize the overall production cost (PC) of ethanol from rice straw, it is crucial to choose the optimal facility size. The delivered cost of rice straw varied from 20.5 to 65.4 $ dry t−1 depending on transportation distance. The Mekong Delta has much lower rice straw prices compared with other regions in Vietnam because of high density and quantity of rice straw supply. Thus, this region has been considered as the most suitable location for deploying ethanol production in Vietnam. The optimal plant size of ethanol production in the region was estimated up to 200 ML year−1. The improvement in solid concentration of material in the hydrothermal pre-treatment step and using residues for power generation could substantially reduce the PC in Vietnam, where energy costs account for the second largest contribution to the PC, following only enzyme costs. The potential for building larger ethanol plants with low rice straw costs can reduce ethanol production costs in Vietnam. The current estimated production cost for an optimal plant size of 200 ML year−1 was 1.19 $ L−1. For the future scenario, considering improvements in pre-treatment, enzyme hydrolysis steps, specific enzyme activity, and applying residues for energy generation, the ethanol production cost could reduce to 0.45 $ L−1 for a plant size of 200 ML year−1 in Vietnam. These data indicated that the cost-competitiveness of ethanol production could be realized in Vietnam with future improvements in production technologies. 相似文献
5.
高频结构仿真器(HFSS)是一种微波器件设计软件,该软件界面友好,通过仿真计算减小了调试工作量,使得微波器件的设计变得简单易行。本文利用HFSS对波导魔T进行了仿真分析,得到了该器件的S参数和动、静态场的分布情况,并对该器件进行了优化设计。 相似文献
6.
7.
A method of measuring and identifying the static parameters of a bipolar transistor is considered. The characteristic of the transistor, from which the parameters of the model are determined, is chosen depending on what group the calculated parameters belong to. The characteristics are measured in such a way that the equations of the model describing them can be reduced to the simplest form. 相似文献
8.
基于模式理论光栅椭偏参数反演的数值模拟 总被引:5,自引:2,他引:3
将一种广泛用于求解系统优化问题的方法——正单纯形法,求解光栅的椭偏方程。首先,利用求解光栅的傅立叶模式理论对TE和TM波的复反射系数进行求解。然后计算出其相应的椭偏参数(△,Ψ),并在该值的基础上加入不同偏差的随机高斯噪声,将加入噪声后的值(△m,Ψm)作为模拟测量值。最后使用优化算法进行反演。通过对几种常用面形光栅椭偏参数的数值模拟,一方面表明傅立叶模式理论计算光栅的椭偏参数不仅精度高。而且速度快;另一方面表明利用正单纯形法得到的光栅参数值很接近于正演时假设的参数值,从而从理论上证明了利用椭偏法测量光栅各种光学参数的可行性。 相似文献
9.
10.
The problem of operating freeze drying of pharmaceutical products in vials placed in trays of a freeze dryer to remove free water (in frozen state) at a minimum time was formulated as an optimal control problem. Two different types of freeze dryer designs were considered. In type I freeze dryer design, upper and lower plate temperatures were controlled together, while in type II freeze dryer design, upper and lower plate temperatures were controlled independently. The heat input to the material being dried and the drying chamber pressure were considered as control variables. Constraints were placed on the system state variables by the melting and scorch temperatures during primary drying stage. Necessary conditions of optimality for the primary drying stage of freeze drying process in vials are derived and presented. Furthermore, an approach for constructing the optimal control policies that would minimize the drying time for the primary drying stage was given. In order to analyze optimal control policy for the primary drying stage of the freeze-drying process in vials, a rigorous multi-dimensional unsteady state mathematical model was used. The theoretical approach presented in this work was applied in the freeze drying of skim milk. Significant reductions in the drying times of primary drying stage of freeze drying process in vials were obtained, as compared to the drying times obtained from conventional operational policies. 相似文献