全文获取类型
收费全文 | 263334篇 |
免费 | 73933篇 |
国内免费 | 48422篇 |
专业分类
电工技术 | 31762篇 |
技术理论 | 9篇 |
综合类 | 24929篇 |
化学工业 | 37869篇 |
金属工艺 | 28752篇 |
机械仪表 | 11233篇 |
建筑科学 | 18536篇 |
矿业工程 | 14717篇 |
能源动力 | 10655篇 |
轻工业 | 24852篇 |
水利工程 | 8606篇 |
石油天然气 | 16578篇 |
武器工业 | 4060篇 |
无线电 | 39549篇 |
一般工业技术 | 40037篇 |
冶金工业 | 11022篇 |
原子能技术 | 2016篇 |
自动化技术 | 60507篇 |
出版年
2024年 | 2968篇 |
2023年 | 5528篇 |
2022年 | 6895篇 |
2021年 | 8274篇 |
2020年 | 10637篇 |
2019年 | 19806篇 |
2018年 | 21420篇 |
2017年 | 22906篇 |
2016年 | 22560篇 |
2015年 | 21989篇 |
2014年 | 21708篇 |
2013年 | 21863篇 |
2012年 | 21111篇 |
2011年 | 17849篇 |
2010年 | 16067篇 |
2009年 | 12846篇 |
2008年 | 10792篇 |
2007年 | 10135篇 |
2006年 | 9520篇 |
2005年 | 8735篇 |
2004年 | 10156篇 |
2003年 | 8546篇 |
2002年 | 7896篇 |
2001年 | 7048篇 |
2000年 | 6907篇 |
1999年 | 7005篇 |
1998年 | 6384篇 |
1997年 | 5485篇 |
1996年 | 5177篇 |
1995年 | 4913篇 |
1994年 | 4083篇 |
1993年 | 3503篇 |
1992年 | 3210篇 |
1991年 | 2391篇 |
1990年 | 1877篇 |
1989年 | 1726篇 |
1988年 | 1353篇 |
1987年 | 476篇 |
1986年 | 440篇 |
1985年 | 307篇 |
1984年 | 236篇 |
1983年 | 157篇 |
1982年 | 204篇 |
1981年 | 200篇 |
1980年 | 135篇 |
1976年 | 244篇 |
1975年 | 221篇 |
1972年 | 246篇 |
1971年 | 138篇 |
1960年 | 206篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
1960-1970年那段时间被称为立体声的黄金岁月 ,那时要调试并建立一套立体声系统是非常简单的,整个系统只包括一对音箱,一个功放(纯A/V功放或附带收音功能)或纯粹的无线电接收器以及诸如唱片机这类型的音源即可,而设置过程更是简单,只需要连接很少的几根线,再将扬声器放到一个合适的位置就可以了。[编者按] 相似文献
122.
Alexandre Szklo Giovani Machado Roberto Schaeffer Jacqueline Mariano Janaí na Sala Marina Tavares 《Catalysis Today》2005,106(1-4):123-128
This paper assesses the impacts of a GTL plant on the expansion of Brazil's oil refining segment. The GTL plant (50,000 bpd) was sized to start up operations in 2015, producing diesel and naphtha through the indirect route (FT-synthesis). This plant will consume the non-associated natural gas production from the recent discoveries at the Santos Basin (around 419 Bm3), and the associated gas production from the Campos Basin. Both basins are located in the Southeast of Brazil, the most populated, rich and industrialized region of the country. Two different criteria for refinery expansion were simulated in order to meet oil product demand scenarios. Findings show that depending on the refinery expansion criteria considered GTL will play a fundamental hole to meet the oil product demand forecast to Brazil in the next 10 years. 相似文献
123.
A feasibility analysis methodology adopted from reactive distillation is applied to membrane reactors. A model is formulated to depict the reactive liquid phase composition on the retentate side of a continuous type membrane reactor. The effects of both the chemical reaction kinetics and the membrane mass transfer kinetics on the feasible products are elucidated by means of retentate phase diagrams and bifurcation analysis. The proposed method can be applied to various membrane processes, independent of the specific structure of the membrane. Two quaternary reaction systems are considered to illustrate the methodology. In the first hypothetical system, it is shown how selective membranes can influence the sequence of effective volatilities which in turn affects the feasible products of the system. In the second example of practical importance, i.e. the heterogeneously catalysed synthesis of propyl acetate coupled with permeation through a porous polycarbonate membrane, the dusty gas model is applied to describe the component fluxes through the membrane. For the latter reaction system, the existence of reactive arheotrope is demonstrated. Arheotropes represent mass transfer controlled feasible products of membrane separation process. 相似文献
124.
在第一部分综合讨论的基础上对甘三酯立体专一分析方法作了初步探讨。以液体油(菜油)及固体脂(猪脂)为基质,系统地研究了这一分析方法,取得了经验并补充了一些具体验证方法。分析液体油的结果与文献数据相一致,分析猪脂的结果欠佳,还存在一些问题需待进一步研究。 相似文献
125.
126.
A model of the electronic structure of graphite-like carbon films, describing the semiconductor properties of this material, is presented. Spectra of optical constants of microcrystalline carbon films in the region λ = 0.4–8.0 μm were studied by the spectral ellipsometry and IR reflection methods. A number of distinctive features of the spectra, associated with both the appearance of C---C- and C---Hn-type bonds and direct energy gaps, were found. Analysis of the optical data using the proposed model makes possible a common interpretation of our results and literature data. Values of a parameter Θ, which is an averaged qualitative parameter of structural distortions within carbon microcrystallites as compared with crystalline graphite, are determined from comparison of theoretical results and experimental data. 相似文献
127.
C. Y. Liao S. N. Atluri 《International journal for numerical methods in engineering》1991,32(6):1339-1361
An efficient method, based on the Schwarz–Neumann alternating technique, is presented for computing weight functions of a general solid (3-D as well as 2-D), with embedded or surface-flaw configurations. The total rate of change of the crack-opening displacements, due to simple perturbations of crack-dimension characteristics, is conveniently decomposed into the infinite-domain and boundary-correction parts. The former is determined from available analytical solutions of ideal-shaped cracks, whereas the latter is computed numerically by imposing nil boundary-traction requirements for the displacement field corresponding to the weight functions. Numerical examples, with solutions for 3-D weighted-average and local stress intensity factors, indicate that the proposed method is very accurate and efficient. 相似文献
128.
129.
Ying Ding Chunqing Wang Yanhong Tian Binbin Zhang 《Metallurgical and Materials Transactions A》2006,37(12):1017-1025
in-situ transmission electron microscopy (TEM) tensile tests on as-cast and aged 63Sn37Pb solder alloys were conducted, and the fracture
behavior in nanometer scale ahead of the crack tip was inspected and discussed. Results show that the fracture was completed
by connecting the discontinuous cracks or voids. Dislocation behavior was concentrated along the grain boundaries for as-cast
samples, and displayed mainly as dislocation climb. The crack was intergranular dominated under the lower strain rate. While
remarkable mutual dislocation emission was detected in the aged solder. Transgranular cracks were dominant in the fractured
area, and they propagated by linking up with the nanometer scale cracks ahead of the crack tips under the effective promotion
of the inverse dislocation emission. At the same time, the partial interphase or intergranular cracks in the thinned area
were also found. Under this condition, a new critical stress intensity factor K
c
′ to define the mutual dislocation emission was proposed. 相似文献
130.
Wang Xuegang Yan Fengjie Yan Qian Li Xingeng 《Frontiers of Materials Science in China》2007,1(2):225-227
An iron-based amorphous foil (FeNiCrSiB) was used as an interlayer for the amorphous diffusion bonding of low carbon steel
pipes under argon flux. The microstructure and mechanical properties of the joint were analyzed using an electron probe micro-analyzer
(EPMA), tensile test, bending test and impact test. The results show that the joint microstructure resembles that of the base
metal and no precipitates form at the joint. Melting point depressants (B, Si) diffuse far away from the joint and the base
metal element is homogenous across the joint. The joint impact toughness is greater than the base metal toughness and the
mechanical properties of the joint are similar around the pipe. 相似文献