全文获取类型
收费全文 | 277971篇 |
免费 | 30725篇 |
国内免费 | 9916篇 |
专业分类
电工技术 | 14108篇 |
技术理论 | 24篇 |
综合类 | 15621篇 |
化学工业 | 56390篇 |
金属工艺 | 14272篇 |
机械仪表 | 15998篇 |
建筑科学 | 20364篇 |
矿业工程 | 7924篇 |
能源动力 | 7634篇 |
轻工业 | 20972篇 |
水利工程 | 4246篇 |
石油天然气 | 17335篇 |
武器工业 | 1744篇 |
无线电 | 32746篇 |
一般工业技术 | 38783篇 |
冶金工业 | 13889篇 |
原子能技术 | 2387篇 |
自动化技术 | 34175篇 |
出版年
2024年 | 1053篇 |
2023年 | 3965篇 |
2022年 | 6769篇 |
2021年 | 9696篇 |
2020年 | 8647篇 |
2019年 | 9026篇 |
2018年 | 9745篇 |
2017年 | 10895篇 |
2016年 | 10532篇 |
2015年 | 12879篇 |
2014年 | 15364篇 |
2013年 | 18447篇 |
2012年 | 17378篇 |
2011年 | 18295篇 |
2010年 | 16549篇 |
2009年 | 15679篇 |
2008年 | 14996篇 |
2007年 | 14356篇 |
2006年 | 14543篇 |
2005年 | 12594篇 |
2004年 | 9078篇 |
2003年 | 8412篇 |
2002年 | 8114篇 |
2001年 | 7187篇 |
2000年 | 7046篇 |
1999年 | 7237篇 |
1998年 | 5662篇 |
1997年 | 4652篇 |
1996年 | 4318篇 |
1995年 | 3642篇 |
1994年 | 2953篇 |
1993年 | 2052篇 |
1992年 | 1614篇 |
1991年 | 1283篇 |
1990年 | 966篇 |
1989年 | 765篇 |
1988年 | 574篇 |
1987年 | 351篇 |
1986年 | 297篇 |
1985年 | 209篇 |
1984年 | 147篇 |
1983年 | 123篇 |
1982年 | 129篇 |
1981年 | 103篇 |
1980年 | 80篇 |
1979年 | 45篇 |
1978年 | 27篇 |
1977年 | 22篇 |
1976年 | 36篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
72.
针对国外变频器价格昂贵、调试周期和维修周期长等特点,我公司自主研发了可替代进口机的高性能钻机国产专用变频器。该变频器能够从零开始调速。当钻井卡钻时,能及时断开电动机,在低速提升时,能最大限度地发挥电动机的动力特性,提供220%的转矩输出。变频器具有易安装、调试、维护,性能稳定。应用中据实测数据显示,采用变频改造后,打1口井可节省柴油15t。 相似文献
73.
A locomotive cabin adsorption air‐conditioner has been equipped in #DF4B‐2369 locomotive; and has been successfully run for 2 years. It is powered by waste heat from the exhaust of the diesel engine. The influence on heat transfer is described by the equivalent heat transfer coefficient or thermal resistance of components inside the adsorber. The variation of adsorption capacity is expressed by a non‐equilibrium adsorption function. The dynamic heat transfer process of adsorption air‐conditioning system is treated with the lumped parameter method. Some typical running experimental results are present. The diesel engine rotating speed and locomotive speed influenced on the refrigeration system are discussed. The maximum mean refrigeration power is regarded as an objective function. Based on experiments and theoretical analysis, the running characteristics of the air‐conditioning system are optimized. Some techniques of performance improvement are suggested as well. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
74.
75.
L. Vu‐Quoc V. Srinivas Y. Zhai 《International journal for numerical methods in engineering》2003,58(3):397-461
We establish a systematic methodology to design and analyse electromagnetic components such as advanced multilayer ceramic capacitors (MLCCs) using the finite element (FE) method. We employ a coupled formulation to compute the interaction between the electric and magnetic fields. Unlike a linear distribution of current assumed in the circuit model, an accurate electrostatic solution to model the entire advanced MLCCs (4 × 4 × 27 = 432 cells) is presented. The FE solution is used to compute the lumped parameters for a range of frequencies. These lumped parameters are then used to compute the parasitic elements of the MLCCs. We introduce two algorithms to efficiently analyse the behaviour of a capacitor with changing frequency. The lower frequency (much below the self‐resonant frequency of the capacitor) algorithm separates the effect of the electric and magnetic fields and reduces the computational effort required to solve the FE problem, whereas, the high‐frequency algorithm couples the effect between the electric and the magnetic fields. We use these algorithms in conjunction with a new multiple scale technique to effectively determine the small values of R, L and C in MLCCs. The formulation, the implementation, and the numerical results demonstrate the efficacy of the present FE formulation and establish a systematic methodology to design and analyse advanced electromagnetic components. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
76.
Gas/liquid mass transfer has been investigated using a stirred vessel gas/liquid contactor using non‐Newtonian media and carbon dioxide as absorbent and gas phase, respectively. The volumetric mass transfer coefficients at different operational variables have been determined. Non‐Newtonian media (liquid phase) were prepared as aqueous solutions of sodium carboxymethyl cellulose salt. The influence of the rheological properties, polymer concentration, stirring rate, and gas flow rate on mass transfer was studied for these liquid phases. Kinematic viscosity and density experimental data were used to calculate the average molecular weight corresponding to the polymer employed. The Ostwald model has been used to fit the rheological behavior of aqueous solutions of the polymer employed as absorbent phase. Reasonably good agreement was found between the predictions of the proposed models and the experimental data of mass transfer coefficients. 相似文献
77.
78.
In this paper, we propose a routing algorithm called minimum fusion Steiner tree (MFST) for energy efficient data gathering with aggregation (fusion) in wireless sensor networks. Different from existing schemes, MFST not only optimizes over the data transmission cost, but also incorporates the cost for data fusion, which can be significant for emerging sensor networks with vectorial data and/or security requirements. By employing a randomized algorithm that allows fusion points to be chosen according to the nodes' data amounts, MFST achieves an approximation ratio of 5/4log(k + 1), where k denotes the number of source nodes, to the optimal solution for extremely general system setups, provided that fusion cost and data aggregation are nondecreasing against the total input data. Consequently, in contrast to algorithms that only excel in full or nonaggregation scenarios without considering fusion cost, MFST can thrive in a wide range of applications 相似文献
79.
In advancement of Pyrosil®‐technology a new kind of precursor delivery was developed, build and tested on real substrates. A Lab‐demonstrator was build to demonstrate the resources of the technology. 相似文献
80.
Commercial purity aluminum (99.5%) was fabricated by equal channel angular pressing (ECAP) up to total accumulated strains of approx. 10. The annealing behavior of material deformed to total strains of approx. 1 and 10 was investigated, using heat treatments of 2 h at various temperatures from 100 to 500 °C. The microstructure of the annealed materials was characterized using the electron back-scatter pattern technique. A number of parameters were determined including the distribution and average values of both the boundary spacings and misorientations. For samples deformed to a total strain of 1, annealing resulted in discontinuous recrystallization. For samples deformed to a total strain of 10, annealing resulted in microstructures exhibiting characteristics of both uniform coarsening and, in a number of places, of discontinuous recrystallization. An attempt was made, based on the boundary spacing distributions, to separate these two components. The grain size after annealing was still however small, being just 6.4 μm after 2 h at 300 °C. 相似文献