全文获取类型
收费全文 | 32960篇 |
免费 | 3385篇 |
国内免费 | 1526篇 |
专业分类
电工技术 | 2396篇 |
技术理论 | 1篇 |
综合类 | 2063篇 |
化学工业 | 5593篇 |
金属工艺 | 1841篇 |
机械仪表 | 2086篇 |
建筑科学 | 2655篇 |
矿业工程 | 1013篇 |
能源动力 | 920篇 |
轻工业 | 2475篇 |
水利工程 | 611篇 |
石油天然气 | 1709篇 |
武器工业 | 299篇 |
无线电 | 4109篇 |
一般工业技术 | 4191篇 |
冶金工业 | 1388篇 |
原子能技术 | 421篇 |
自动化技术 | 4100篇 |
出版年
2024年 | 189篇 |
2023年 | 691篇 |
2022年 | 1346篇 |
2021年 | 1624篇 |
2020年 | 1255篇 |
2019年 | 1019篇 |
2018年 | 1122篇 |
2017年 | 1263篇 |
2016年 | 1039篇 |
2015年 | 1420篇 |
2014年 | 1782篇 |
2013年 | 1943篇 |
2012年 | 2132篇 |
2011年 | 2189篇 |
2010年 | 1879篇 |
2009年 | 1878篇 |
2008年 | 1828篇 |
2007年 | 1608篇 |
2006年 | 1675篇 |
2005年 | 1368篇 |
2004年 | 891篇 |
2003年 | 903篇 |
2002年 | 837篇 |
2001年 | 743篇 |
2000年 | 764篇 |
1999年 | 808篇 |
1998年 | 659篇 |
1997年 | 568篇 |
1996年 | 489篇 |
1995年 | 441篇 |
1994年 | 330篇 |
1993年 | 251篇 |
1992年 | 229篇 |
1991年 | 146篇 |
1990年 | 128篇 |
1989年 | 115篇 |
1988年 | 84篇 |
1987年 | 52篇 |
1986年 | 31篇 |
1985年 | 35篇 |
1984年 | 18篇 |
1983年 | 21篇 |
1982年 | 23篇 |
1981年 | 7篇 |
1980年 | 11篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1975年 | 3篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
Dianjun Yao 《Polymer》2005,46(12):4390-4396
The crystalline conformations of perylene polyimides (PPIs), with alkyl spacers varying in length from C3 to C12 are discussed. Although modeling of single chains would suggest the possibility that those with odd number of CH2 groups adopt a flat helical shape, X-ray diffraction suggests that the chains with odd and even spacers have the same conformation, due to the necessity to pack the perylene units. Upon annealing, the UV-vis absorption maximum red-shifts by about 10 nm, indicating enhanced π-stacking between the perylenes. Several changes in the spectra are seen with an increase in annealing time, at a given temperature. With an increase in annealing time, X-ray diffraction patterns show changes in the number of reflections, indicative of a crystal to mesogenic transition. The time required for this transition increases with a decrease in the spacer length, and annealing temperature, suggesting that the dynamics of this transition is very slow. 相似文献
63.
Qingzhao Yao Yuming Zhou Yanqing Sun Xiaoyun Ye 《Journal of Inorganic and Organometallic Polymers and Materials》2008,18(4):477-484
TiO2 hybrid molecular imprinted polymer (MIP) for ethofumesate using methacrylic acid (MAA) as the functional monomer and silane
coupling agent 3-(trimethoxysilyl) propylmethacrylate (KH570) as organic–inorganic connective bridge was synthesized via photo-excitation
method. Hydrogen bond was proved to act between MAA and ethofumesate for pre- and post-polymerization binding properties as
testified by UV spectrometric method. KH570 modified TiO2 nanoparticles were prepared via sonochemical reaction, which can accelerate hydrolysis, increase collision chance for the
reactive system and improve the dispersion of the nanoparticles. Scanning electron microscope (SEM), transmission electron
microscope (TEM), binding and the adsorption kinetics experiments as well as thermogravimetric analysis (TGA) were employed
for characterization. The results indicated that the hybrid MIP revealed a larger surface area and more ordered imprinting
cavities with improved thermal stability compared to organic-only MIP. Furthermore, faster adsorption kinetics and enhancive
adsorption capacity were achieved, which made it promising in chemical sensor applications. 相似文献
64.
The present study is an investigation on the behaviors of concrete-filled thin-walled steel tubular members subjected to combined loading, such as compression and torsion, bending and torsion, compression, bending and torsion. ABAQUS software is used in this paper for the finite element analysis (FEA). A comparison of results calculated using this modeling shows generally good agreement with test results. The FEA modeling is then used to investigate the influence of important parameters that determine the ultimate strength of the composite members under combined loading, such as compression and torsion, bending and torsion, compression, bending and torsion. The parametric studies provide information for the development of formulae for calculating the ultimate strength of the composite members subjected to combined loading. 相似文献
65.
66.
Wei Li Zhang Wei Pan Bin Luo Xi Hua Zou Meng Yao Wang 《Photonics Technology Letters, IEEE》2008,20(9):712-714
A theoretical construction of one-to-many (OTM) and many-to-one (MTO) chaos synchronization communications using semiconductor lasers is presented. One center laser provides strong injections (strong link) to other side lasers, and the side lasers also provide weak injections (weak link) to the center one. Simulation results show that the side lasers synchronize with the center laser through injection-locking. In addition, messages transmitted via the strong links or the weak links experience strong chaos pass filtering, enabling us to realize OTM and MTO communications. 相似文献
67.
68.
Evolving artificial neural network ensembles 总被引:3,自引:0,他引:3
Using a coordinated group of simple solvers to tackle a complex problem is not an entirely new idea. Its root could be traced back hundreds of years ago when ancient Chinese suggested a team approach to problem solving. For a long time, engineers have used the divide-and-conquer strategy to decompose a complex problem into simpler sub-problems and then solve them by a group of solvers. However, knowing the best way to divide a complex problem into simpler ones relies heavily on the available domain knowledge. It is often a manual process by an experienced engineer. There have been few automatic divide-and-conquer methods reported in the literature. Fortunately, evolutionary computation provides some of the interesting avenues to automatic divide-and-conquer methods. An in-depth study of such methods reveals that there is a deep underlying connection between evolutionary computation and ANN ensembles. Ideas in one area can be usefully transferred into another in producing effective algorithms. For example, using speciation to create and maintain diversity had inspired the development of negative correlation learning for ANN ensembles, and an in-depth study of diversity in ensembles. This paper will review some of the recent work in evolutionary approaches to designing ANN ensembles. 相似文献
69.
基于DSP的电力数据采集平台的设计与研究 总被引:1,自引:0,他引:1
介绍了一种用于电力系统的数据采集系统.该系统采用数字信号处理器(DSP)和复杂可编程逻辑器件(CPLD)作为核心芯片,给出了主要部分的电路及其原理、功能,系统中使用CPLD实现基本逻辑,使系统有足够的冗余和灵活性,具有可靠性高、可升级等优点. 相似文献
70.
Analyzing the performance and fairness of BitTorrent-like networks using a general fluid model 总被引:2,自引:0,他引:2
In this paper, a general fluid model is developed to study the performance and fairness of BitTorrent-like networks. The fluid model incorporates two important features previously isolated from system performance models, user settings with multiple groups and inter-group data exchange induced by the choking algorithm. Our numerical results point out some key parameters of performance, such as the staying time of seeders. Generally, selfish behavior does not receive equal performance degradation, and in some scenarios users have strong incentives of free-riding. We also find content delivery can be greatly deterred when malicious free-riders are overwhelming. 相似文献