全文获取类型
收费全文 | 32149篇 |
免费 | 860篇 |
国内免费 | 816篇 |
专业分类
电工技术 | 634篇 |
综合类 | 137篇 |
化学工业 | 4176篇 |
金属工艺 | 2464篇 |
机械仪表 | 1241篇 |
建筑科学 | 812篇 |
矿业工程 | 59篇 |
能源动力 | 1136篇 |
轻工业 | 1605篇 |
水利工程 | 190篇 |
石油天然气 | 412篇 |
武器工业 | 7篇 |
无线电 | 4482篇 |
一般工业技术 | 8197篇 |
冶金工业 | 5068篇 |
原子能技术 | 398篇 |
自动化技术 | 2807篇 |
出版年
2023年 | 143篇 |
2022年 | 263篇 |
2021年 | 379篇 |
2020年 | 285篇 |
2019年 | 381篇 |
2018年 | 604篇 |
2017年 | 583篇 |
2016年 | 642篇 |
2015年 | 548篇 |
2014年 | 850篇 |
2013年 | 2066篇 |
2012年 | 1343篇 |
2011年 | 1872篇 |
2010年 | 1468篇 |
2009年 | 1717篇 |
2008年 | 1728篇 |
2007年 | 1690篇 |
2006年 | 1489篇 |
2005年 | 1341篇 |
2004年 | 1145篇 |
2003年 | 1089篇 |
2002年 | 1006篇 |
2001年 | 952篇 |
2000年 | 906篇 |
1999年 | 929篇 |
1998年 | 1936篇 |
1997年 | 1355篇 |
1996年 | 1124篇 |
1995年 | 705篇 |
1994年 | 579篇 |
1993年 | 517篇 |
1992年 | 320篇 |
1991年 | 324篇 |
1990年 | 226篇 |
1989年 | 219篇 |
1988年 | 173篇 |
1987年 | 140篇 |
1986年 | 117篇 |
1985年 | 91篇 |
1984年 | 69篇 |
1983年 | 51篇 |
1982年 | 36篇 |
1981年 | 69篇 |
1980年 | 38篇 |
1979年 | 29篇 |
1978年 | 34篇 |
1977年 | 48篇 |
1976年 | 62篇 |
1975年 | 23篇 |
1973年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
In this paper, a novel approach of automated multirobot nanoassembly planning is presented. This approach uses an improved self-organizing map to coordinate assembly tasks of nanorobots while generating optimized motion paths at run time with a modified shunting neural network. It is capable of synchronizing multiple nanorobots working simultaneously and efficiently on the assembly of swarms of objects in the presence of obstacles and environmental uncertainty. Operation of the presented approach is demonstrated with experiments at the end of the paper. 相似文献
102.
La doping effects on intergrowth Bi2WO6–Bi3TiNbO9 ferroelectric ceramics were studied by X-ray diffraction, electron probe microanalysis and dielectric spectroscopy. It was found that the La3+ distribution, ferroelectric phase transition and dielectric relaxation behavior are apparently affected by La doping. With increasing La3+ content, the site of dopant ion varies, the grain growth of Bi5TiNbWO15 is restrained, the Curie temperature is reduced and broadened. Furthermore, two dielectric relaxation loss peaks were observed both in temperature and frequency spectra. The calculated relaxation parameters revealed the oxygen vacancy related to the relaxation process. 相似文献
103.
M.-F. Foulon T. Crepin X. Melique D. Lippens 《Microwaves, Antennas & Propagation, IET》2007,1(1):23-28
Co-planar strip (CPS) transmission lines, aimed at operating up to sub-millimetre wavelengths, were periodically loaded by lumped capacitances and inductances in series and shunt configuration, respectively. Under this condition, propagation on the line is backward with group and phase velocities of opposite signs. The transmission lines were fabricated onto a quartz substrate by e-beam patterning and thin film deposition, silicon nitride and gold layers, on a deep sub-micron scale (~200 nm). A direct evidence of left-handedness between 160 and 380 GHz was achieved via the tracking of phase advance in a differential phase experiment using electro-optic sampling. The comparison between modelling results by electromagnetic full wave circuit analysis and experiment was performed in the time and frequency domains. It shows a good agreement in the dispersion characteristics and ultra-fast variations in the transmitted signals. At last, we took benefit of a lumped element fitting approach in order to discuss of the frequency capability of this non-resonant approach 相似文献
104.
X. Biquard O. Proux J. Cibert D. Ferrand H. Mariette R. Giraud B. Barbara 《Journal of Superconductivity and Novel Magnetism》2003,16(1):127-129
Mn has been incorporated in epilayers of the large-gap semiconductor GaN grown by molecular beam epitaxy using a nitrogen plasma cell. Detailed extended X-ray absorption fine structure (EXAFS) studies of a Ga0.98Mn0.02N epilayer confirm that the Mn atoms substitute the Ga atoms, with an increase by 2.7% of the distance to the nearest nitrogen atoms. Near-edge spectroscopy results tend to indicate that the valence state of Mn is slightly higher than 3+, while EXAFS analysis suggests an electron transfer to the N neighbors. 相似文献
105.
In recent years, the Asia-Pacific region has experienced several financial setbacks, including speculative attacks in 1998 and the SARS outbreak in 2003. Financial stresses of this nature are unanticipated, and not all of the dangers can be predicted by the examination of market information and macroeconomic indicators. The Early Warning System (EWS) that has been adopted by the International Monetary Fund may not be able to predict future financial crises for all possible scenarios, because shocks come in many different forms. To supplement the EWS, this paper proposes a data mining framework to measure the resilience of an economy. The resilience framework does not predict a crisis, but rather assesses the current state of health of an economy and its ability to withstand a financial shock should one occur. The framework is based on a feedback system consisting of two stages. The first stage assigns a resilience score to each economy based on a fuzzy logic scoring scheme that is built on the ambiguous reasoning of experts. The second stage uses the classification tree approach to estimate thresholds for each economic indicator, and examines the quality of the fuzzy score. The result from the second stage is then passed back to the first stage as feedback. The final result is obtained when the feedback system reaches its equilibrium state. The proposed resilience framework is applied to the external-sector and the public-sector economies of several countries to illustrate its applicability. 相似文献
106.
107.
108.
Y.X. Li 《Materials Letters》2007,61(22):4366-4369
TiC/Al composite was successfully synthesized utilizing laser ignited self-propagating high-temperature synthesis (SHS) of Al-C-Ti system with the different C/Ti molar ratio. When the molar ratio of C to Ti is below 1:1 in the starting materials, in addition to fine TiC particulates, a large amount of Al3Ti phase was found in the composites; however, when the molar ratio of C to Ti is 1:1 in the starting materials, the Al3Ti phase was almost completely eliminated and the distribution of TiC particulates generally appeared to be more homogeneous throughout the products synthesized. 相似文献
109.
The Karlsruhe Tritium Neutrino experiment (KATRIN) is going to use a very large electro-static tandem spectrometer to measure the electron spectrum from the tritium beta decay, where several kilometers of non-evaporable getter (NEG) strips (type ST707) are to be used to achieve the UHV requirements. Different geometrical configurations of the NEG strips have been studied by Monte Carlo simulations. It is shown that the resulting pumping speed of the getter pumps will allow to get a pressure below 10−11 mbar in the huge vessel with a volume of 1400 m3. By systematic assessment of the statistics of the pumping surfaces, it could be demonstrated that the design is sound. 相似文献
110.
There is a growing trend of research in neuropsychological assessment in Asia: The mean number of published studies increased from 1.8 in the 1980s to 16.0 in 2 recent years. About 40% of the studies reviewed concerned test development or adaptation, with the latter greatly outnumbering the former. To facilitate the test selection for clinical use, 36 clinical measures were evaluated based on some statistical criteria. The results showed that only 8 neuropsychological tests (5 Chinese. 2 Korean, and 1 Japanese) met the criteria. Given that Asian and Western populations differ on certain cognitive processes, future development of neuropsychological assessment measures in Asia should move from the adaptation of Western tests toward the construction of original tests with better ecological validity. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献