全文获取类型
收费全文 | 39581篇 |
免费 | 3884篇 |
国内免费 | 1880篇 |
专业分类
电工技术 | 2445篇 |
技术理论 | 3篇 |
综合类 | 2672篇 |
化学工业 | 6493篇 |
金属工艺 | 2180篇 |
机械仪表 | 2422篇 |
建筑科学 | 2952篇 |
矿业工程 | 1123篇 |
能源动力 | 1111篇 |
轻工业 | 2583篇 |
水利工程 | 765篇 |
石油天然气 | 2463篇 |
武器工业 | 379篇 |
无线电 | 4861篇 |
一般工业技术 | 4670篇 |
冶金工业 | 1725篇 |
原子能技术 | 406篇 |
自动化技术 | 6092篇 |
出版年
2024年 | 194篇 |
2023年 | 793篇 |
2022年 | 1426篇 |
2021年 | 2033篇 |
2020年 | 1484篇 |
2019年 | 1117篇 |
2018年 | 1325篇 |
2017年 | 1382篇 |
2016年 | 1157篇 |
2015年 | 1655篇 |
2014年 | 2134篇 |
2013年 | 2398篇 |
2012年 | 2720篇 |
2011年 | 2936篇 |
2010年 | 2609篇 |
2009年 | 2180篇 |
2008年 | 2315篇 |
2007年 | 2081篇 |
2006年 | 2006篇 |
2005年 | 1743篇 |
2004年 | 1135篇 |
2003年 | 959篇 |
2002年 | 926篇 |
2001年 | 804篇 |
2000年 | 797篇 |
1999年 | 964篇 |
1998年 | 752篇 |
1997年 | 590篇 |
1996年 | 559篇 |
1995年 | 467篇 |
1994年 | 388篇 |
1993年 | 258篇 |
1992年 | 234篇 |
1991年 | 171篇 |
1990年 | 127篇 |
1989年 | 97篇 |
1988年 | 82篇 |
1987年 | 49篇 |
1986年 | 47篇 |
1985年 | 36篇 |
1984年 | 29篇 |
1983年 | 28篇 |
1982年 | 23篇 |
1981年 | 21篇 |
1980年 | 21篇 |
1979年 | 12篇 |
1978年 | 12篇 |
1977年 | 11篇 |
1976年 | 8篇 |
1973年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
141.
Li Xi Zuoyan Peng Wei Fan Kui Guo Gu Jianmin Muyu Zhao Wu Guoqiang 《Materials Science and Engineering: B》1996,40(2-3):147-152
SrMgxTi1 - xO3 nanocrystals (x = 0.1–0.6) were synthesized by the stearic acid gel method. Powder samples were characterized by X-ray diffraction and X-ray photoelectron (XP) spectroscopy. The results showed that the lattice parameter a and the O 1s XP spectrum changed not only with the Mg content x but also with the grain size d of the samples. The conductivity of a thick film specimen fabricated on an aluminium oxide wafer was investigated in a nitrogen—oxygen atmosphere. 相似文献
142.
Experiments were conducted to investigate the fate of ethylbenzoate and soil microorganisms in shallow aquifers. Biodegradation and volatilization have been identified as the major mechanisms in attenuating ethylbenzoate in contaminated soils. The rate of volatilization was experimentally found to be limited by gas-phase diffusion. The parameters of an available model, i.e., the maximum specific growth rate and the saturation constant, have been estimated by fitting the model to the experimental data obtained with ethylbenzoate as the carbon source; the former was 0.49 h−1, and the latter was 62 mg L−1. Various facets of biodegradation, including the effects of mass-transfer resistance and initial distribution of microorganisms, have been numerically analyzed on the basis of the model. 相似文献
143.
介绍了液体通过核孔膜规律方面取得的新认识,包括:(1)纯净液体通过核孔膜的规律;(2)核孔膜测定液体粘滞系数的各种方法;(3)各种物质溶液浓度的核孔膜测定;(4)液相混合物快速分离和化学分离;(5)流体中固体微粒对核孔膜的堵塞及其公式;(6)用核孔膜滤除液中各各斩规律。 相似文献
144.
排列互比法用于超精测角的研究 总被引:3,自引:0,他引:3
作者分析了我互比法现行的两种数据处理方法的缺点,提出了应用最小二乘法原理推导出合理的数据处理方法。本文还首次从理论上阐明了排列互比法测量结果中出现一次谐波系统误差的原因,提出了减少和消除这一些系统误差的方法,并给实验验证。 相似文献
145.
146.
147.
An early step in the development of vertebrae, ribs, muscle, and dermis is the differentiation of the somitic mesoderm into dermomyotome dorsally and sclerotome ventrally. To analyze this process, we have developed an in vitro assay for somitic mesoderm differentiation. We show that sclerotomal markers can be induced by a diffusible factor secreted by notochord and floor plate and that heterologous cells expressing Sonic hedgehog (shh/vhh-1) mimic this effect. In contrast, expression of dermomyotomal markers can be caused by a contact-dependent signal from surface ectoderm and a diffusible signal from dorsal neural tube. Our results extend previous studies by suggesting that dorsoventral patterning of somites involves the coordinate action of multiple dorsalizing and ventralizing signals and that a diffusible form of Shh/Vhh-1 mediates sclerotome induction. 相似文献
148.
无源微波遥感用于地震预报的实验研究 总被引:4,自引:1,他引:3
对无源微波遥感用于地震预报在理论研究的基础上对不同岩性不同结构的岩石试件进行了加载实验,测量了岩石试件的微波辐射随载荷的变化.实验得出:岩石试件的微波辐射能量随岩石应力状态变化而显著变化;而且,不同的波段变化的幅度不同;同一波段不同极化方式的波随应力变化的变化量也不同;微波辐射能量的变化能够被卫星微波遥感探测器探测到.实验还发现,岩石试件临破裂前出现明显的微波辐射异常. 相似文献
149.
150.
Xiang Lu S. Sundar Kumar Iyer Jin Lee Brian Doyle Zhineng Fan Paul K. Chu Chenming Hu Nathan W. Cheung 《Journal of Electronic Materials》1998,27(9):1059-1066
We have demonstrated feasibility to form silicon-on-insulator (SOI) substrates using plasma immersion ion implantation (PIII)
for both separation by implantation of oxygen and ion-cut. This high throughput technique can substantially lower the high
cost of SOI substrates due to the simpler implanter design as well as ease of maintenance. For separation by plasma implantation
of oxygen wafers, secondary ion mass spectrometry analysis and cross-sectional transmission electron micrographs show continuous
buried oxide formation under a single-crystal silicon overlayer with sharp Si/SiO2 interfaces after oxygen plasma implantation and high-temperature (1300°C) annealing. Ion-cut SOI wafer fabrication technique
is implemented for the first time using PIII. The hydrogen plasma can be optimized so that only one ion species is dominant
in concentration and there are minimal effects by other residual ions on the ion-cut process. The physical mechanism of hydrogen
induced silicon surface layer cleavage has been investigated. An ideal gas law model of the microcavity internal pressure
combined with a two-dimensional finite element fracture mechanics model is used to approximate the fracture driving force
which is sufficient to overcome the silicon fracture resistance. 相似文献