全文获取类型
收费全文 | 256629篇 |
免费 | 20975篇 |
国内免费 | 11111篇 |
专业分类
电工技术 | 14840篇 |
技术理论 | 24篇 |
综合类 | 16731篇 |
化学工业 | 42876篇 |
金属工艺 | 14780篇 |
机械仪表 | 16242篇 |
建筑科学 | 19823篇 |
矿业工程 | 8356篇 |
能源动力 | 7261篇 |
轻工业 | 16471篇 |
水利工程 | 4299篇 |
石油天然气 | 17639篇 |
武器工业 | 2088篇 |
无线电 | 28305篇 |
一般工业技术 | 30179篇 |
冶金工业 | 13618篇 |
原子能技术 | 2738篇 |
自动化技术 | 32445篇 |
出版年
2024年 | 1197篇 |
2023年 | 4417篇 |
2022年 | 7854篇 |
2021年 | 10981篇 |
2020年 | 8378篇 |
2019年 | 7026篇 |
2018年 | 7762篇 |
2017年 | 8678篇 |
2016年 | 7700篇 |
2015年 | 10370篇 |
2014年 | 12973篇 |
2013年 | 15198篇 |
2012年 | 16410篇 |
2011年 | 17773篇 |
2010年 | 15520篇 |
2009年 | 14662篇 |
2008年 | 14207篇 |
2007年 | 13436篇 |
2006年 | 13694篇 |
2005年 | 11912篇 |
2004年 | 8080篇 |
2003年 | 6895篇 |
2002年 | 6181篇 |
2001年 | 5522篇 |
2000年 | 5787篇 |
1999年 | 6663篇 |
1998年 | 5552篇 |
1997年 | 4545篇 |
1996年 | 4269篇 |
1995年 | 3556篇 |
1994年 | 2865篇 |
1993年 | 1995篇 |
1992年 | 1551篇 |
1991年 | 1249篇 |
1990年 | 946篇 |
1989年 | 754篇 |
1988年 | 545篇 |
1987年 | 345篇 |
1986年 | 288篇 |
1985年 | 199篇 |
1984年 | 142篇 |
1983年 | 116篇 |
1982年 | 127篇 |
1981年 | 101篇 |
1980年 | 81篇 |
1979年 | 42篇 |
1978年 | 26篇 |
1977年 | 20篇 |
1976年 | 35篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Sutomo W. Xuefeng Wang Bullen D. Braden S.K. Chang Liu 《Journal of microelectromechanical systems》2003,12(1):64-69
Parylene is an emerging material for MEMS. It is an organic material that is grown by using the chemical vapor deposition method at room temperature. The deposition thickness is commonly controlled by the amount of solid-phase dimer loaded in a sublimation chamber. In a conventional deposition machine, the end point of the process is designated by the moment the dimer is exhausted. However, this end-of-process criterion does not offer precise, repeatable control of film thickness. We present the results of the development of an in situ end-point detector for a Parylene chemical vapor deposition process. The detector is based on the thermal transfer principle and can be implemented on commercial parylene deposition systems with minimal system modification. Such a sensor enables a user to stop the deposition when a targeted thickness is reached. The end point detector is very simple to implement on existing parylene deposition systems. A series of such sensors with different target deposition thickness would allow extraction of the actual deposition rate within a deposition run. 相似文献
102.
103.
Piezoelectric Nanogenerators for Self-Powered Nanodevices 总被引:1,自引:0,他引:1
A novel approach converts nanoscale mechanical energy into electric energy for self-powering nanodevices.In our own work, we've used piezoelectric zinc-oxide nanowire (ZnO NW) arrays to demonstrate a novel approach for converting nanoscale mechanical energy into electric energy. Here, we review the fundamental principle behind the nanogenerator, present an approach for improving its performance, and discuss some of the challenges we face in pushing this technology to reach its potential. 相似文献
104.
Wei Fen Zhang Xi Guang Chen Pi Wu Li Cheng Sheng Liu Qiang Zhi He 《Drying Technology》2008,26(1):108-115
Three kinds of carboxymethyl chitosan/β-cyclodextrin microspheres loaded with theophylline were prepared by spray drying intended for pulmonary delivery. Mucociliotoxicity, permeation rate, and drug release characteristics of the product were investigated. The microspheres obtained by spray drying were found to be spherical with smooth or wrinkled surfaces. The mean particle size was between 3.39 and 6.06 µm. The microspheres demonstrated high product yield (43.7-50.2%), high drug loading (13.7-38.1%), and high encapsulation efficiency (86.9-92.8%). FT-IR indicated that there were interactions of theophylline with carboxymethyl chitosan matrix. Further studies on mucociliotoxicity and permeation confirmed that microspheres had better adaptability and high permeation rate. In vitro drug release from the microspheres was not related to the drug/polymer ratios. 相似文献
105.
Flammability ranking of foliage species by factor analysis of physical and chemical pyric properties
In this paper, factor analysis is introduced to evaluate the flammability of 55 foliage species that may be used in China for construction of the fuel break network of forest strips with lower flammability. Six pyric parameters, i.e. air dry moisture content, absolute dry moisture content, ignition point, ash content, caloric value and extractive content, are measured and used as variables for factor analysis. The covariance analysis shows that four principal factors can be extracted to reflect the flammability in different physical and chemical senses. In terms of the contributions of the four factors to the variances and the physical significance of the relevant parameters, the four factors are, respectively, termed as ‘flaming factor,’ ‘air dry factor,’ ‘ash factor’ and ‘absolute dry factor.’ The stability of the factor analysis method is examined by a different number of samples considered, and the variation degrees of the orderings indicate that the method has high reliability to measure the total flammability of foliage species. The results of the flammability evaluation are verified by comparison with the recommended tree species in the Chinese technology standard. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
106.
Hydrothermal Synthesis of Magnesium Aluminate Platelets 总被引:1,自引:0,他引:1
Zhi-Zhan Chen Er-Wei Shi Hua-Wei Zhang Yong Zhang Xiang-Biao Li Xue-Chao Liu Bing Xiao 《Journal of the American Ceramic Society》2006,89(12):3635-3637
Magnesium aluminate (MgAl2 O4 ) platelets were first synthesized by hydrothermal treatment of γ-AlO(OH) in a magnesium nitrate aqueous solution at 400°C. The platelets are 100–200 nm in width and 25 nm in thickness. The influence of temperature, the anions of the magnesium salt, the amount of magnesium salt, and precursor pH on the formation of such structure was investigated. The experimental results indicated that the anions of the magnesium salt and precursor pH could have a significant influence on the growth of MgAl2 O4 . MgAl2 O4 formation followed the in situ transformation mechanism, which was the reason why the MgAl2 O4 crystallites had a platelet morphology. 相似文献
107.
以三聚磷酸钠生产过程为例,论述了在以纯碱为原料的非强酸性水溶液体系中,由于反应不完全导致反应物中存在少量的碳酸盐,这部分碳酸盐干扰了用酸碱滴定法测量的中和度,并据此提出中和度分析改进方法.由此可以推广到其它以纯碱为原料的非强酸性水溶液体系中. 相似文献
108.
Summary Well-defined water-soluble poly(styrenesulfonate)-b-poly(ethylene glycol)-b- poly(styrenesulfonate) (PSS-b-PEG-b-PSS) triblock
copolymers with narrow molecular weight distribution (1.29 < Mw/Mn < 1.36) were synthesized in aqueous solution at 70 oC via reversible addition-fragmentation chain transfer (RAFT) polymerization. The complex formed by the PSS-b-PEG-b-PSS triblock
copolymer coordinated with aluminum ion was investigated with turbidimetry, dynamic light scattering (DSL), zeta-potential,
and transmission electron microscopy (TEM). The aggregation formation was based on the neutralization of the SO3- groups in the PSS blocks with Al3+ ions. The appearance, size and stability of the PSS-b-PEG-b-PSS/Al3+ aggregates were controlled by varying the PSS block length and degree of neutralization (DN). At DN = 0.33, where the PSS-b-PEG-b-PSS
copolymer was completely neutralized with Al3+, the aggregate size increased with increasing PSS block length. The transition from the shrinking coil of small size to the
interchain aggregates of large size was found at DN of about 0.33. 相似文献
109.
刘建平 《电信工程技术与标准化》2008,21(6):32-38
本文研究了ROADM的技术优势,主要结构类型,涉及的关键技术以及存在的问题,并分析了当前ROADM标准化进展情况与发展趋势,还介绍了当前设备现状和现网应用情况。 相似文献
110.