全文获取类型
收费全文 | 7647篇 |
免费 | 890篇 |
国内免费 | 402篇 |
专业分类
电工技术 | 180篇 |
综合类 | 537篇 |
化学工业 | 1215篇 |
金属工艺 | 169篇 |
机械仪表 | 363篇 |
建筑科学 | 149篇 |
矿业工程 | 49篇 |
能源动力 | 135篇 |
轻工业 | 280篇 |
水利工程 | 47篇 |
石油天然气 | 101篇 |
武器工业 | 120篇 |
无线电 | 2622篇 |
一般工业技术 | 1633篇 |
冶金工业 | 117篇 |
原子能技术 | 412篇 |
自动化技术 | 810篇 |
出版年
2024年 | 16篇 |
2023年 | 92篇 |
2022年 | 123篇 |
2021年 | 203篇 |
2020年 | 199篇 |
2019年 | 180篇 |
2018年 | 157篇 |
2017年 | 239篇 |
2016年 | 278篇 |
2015年 | 251篇 |
2014年 | 388篇 |
2013年 | 502篇 |
2012年 | 447篇 |
2011年 | 564篇 |
2010年 | 430篇 |
2009年 | 478篇 |
2008年 | 388篇 |
2007年 | 429篇 |
2006年 | 416篇 |
2005年 | 390篇 |
2004年 | 323篇 |
2003年 | 333篇 |
2002年 | 256篇 |
2001年 | 226篇 |
2000年 | 209篇 |
1999年 | 182篇 |
1998年 | 153篇 |
1997年 | 150篇 |
1996年 | 129篇 |
1995年 | 131篇 |
1994年 | 106篇 |
1993年 | 97篇 |
1992年 | 73篇 |
1991年 | 71篇 |
1990年 | 51篇 |
1989年 | 53篇 |
1988年 | 31篇 |
1987年 | 16篇 |
1986年 | 21篇 |
1985年 | 38篇 |
1984年 | 35篇 |
1983年 | 23篇 |
1982年 | 39篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1976年 | 5篇 |
1974年 | 3篇 |
1973年 | 1篇 |
1959年 | 3篇 |
排序方式: 共有8939条查询结果,搜索用时 125 毫秒
91.
Computing scattering rates of electrons and phonons stands at the core of studies of electron transport properties. In the high field regime, the interactions between all electron bands with all phonon bands need to be considered. This full band interaction implies a huge computational burden in calculating scattering rates. In this study, a new accelerated algorithm is presented for this task, which speeds up the computation by two orders of magnitude (100 times) and dramatically simplifies the coding. At the same time, it visually demonstrates the physical process of scattering more clearly. 相似文献
92.
The autocorrelation functions and corresponding relaxation times obtained from the forward depolarized quasi-elastic light scattering experiment are exhibited for two quite similar models of flexible polymer chains in solution. A very small change in the chain dynamics is found to be sufficient to change the relaxation time from a relatively short time independent of chain length, with an autocorrelation function suggestive of an unweighted sum of contributions from all the relaxation times in the spectrum of chain motion, to a long time with an autocorrelation function identical with that for the end-to-end vector, strongly dependent upon chain length and dominated by the longest relaxation time in the spectrum. These results raise the question whether widely-used models in which information about short-range chain structure and motion is deliberately omitted can be expected to be appropriate for the interpretation of depolarized scattering experiments. 相似文献
93.
A. Grüneis M.H. Rümmeli C. Kramberger A. Barreiro T. Pichler R. Pfeiffer H. Kuzmany T. Gemming B. Büchner 《Carbon》2006,44(15):3177-3182
We have synthesized double wall carbon nanotubes (DWNTs) with few defects and little amorphous carbon by hot wall chemical vapor deposition (CVD) of alcohol. Catalysts for the DWNT growth were made from cobalt and molybdenum acetates. Scanning electron microscopy, transmission electron microscopy, multi frequency resonance Raman spectroscopy and optical absorption spectroscopy were used for characterization of the product with regard to DWNT yield, the nanotube diameter distribution, defect concentration and amorphous carbon content. Base pressures lower than 1 × 10−5 mbar in the CVD reactor considerably suppress defects in the DWNTs. Optimized growth conditions for DWNT formation are presented. 相似文献
94.
95.
G. William Chase Jr. Casimir C. Akoh Ronald R. Eitenmiller 《Journal of the American Oil Chemists' Society》1994,71(11):1273-1276
A high-performance liquid chromatographic method is described to determine the sucrose polyester (SPE) content in seven blends
of cooking oils. Four gel-permeation chromatography (GPC) columns were used in series with an evaporative light scattering
mass detector to separate the SPE from the acylglycerols in the final chromatogram. The SPE fraction was collected off the
GPC column and injected onto a reverse-phase C-18 column for quantitation with sucrose octaacetate as an internal standard
and a gradient of nonaqueous solvents as mobile phase. The chromatograms were interference-free, with only two sharp peaks
appearing. The standards were linear from 500 to 5000 μg/mL with a correlation coefficient of r=0.999. The mean percent recovery
(n=9) and standard deviation were 102±6.7. The detector could detect amounts as low as 5 μg SPE. 相似文献
96.
97.
Aqueous heterophase polymerization of styrene—a study by means of multi-angle laser light scattering
An online multi-angle laser light scattering study of ab initio surfactant-free styrene emulsion polymerization reveals unexpected results regarding the development of the dispersity during the whole reaction starting from mixing styrene and water at reaction temperature. The experimentally observed change in the dispersity, which is an indirect measure of the average characteristic size of the colloidal objects, allows the identification of three characteristic intervals. During interval A the equilibration of styrene in water is characterized by the formation of styrene domains, which increase in number and size until an equilibrium state is reached. This means that there is virtually no homogeneous/molecular styrene in water solution but rather nanodroplets of about 200 nm in diameter (assuming spherical shape) are formed. During interval B, after initiation of the polymerization and particle formation, the dispersity increases again as the average size decreases and the number of scattering objects increases. The polymer particles suck up the monomer from the monomer nanodroplets, which leads to the disappearance of the nanodroplets and to a decrease in the average size. During interval C the average size increases again due to the predominantly growth of the polystyrene particles. 相似文献
98.
在含氟表面活性剂存在下,将聚偏氟乙烯超声分散于甲基丙烯酸甲酯和丙烯酸丁酯的混合单体中进行乳液聚合,制备了聚偏氟乙烯/聚丙烯酸酯复合乳液。采用动态光散射DLS、透射电镜TEM和红外光谱FT—IR对乳液组成及乳胶粒子的形态进行了表征,并对聚合物胶膜的性能进行了测试分析。结果表明:聚偏氟乙烯的加入,使复合乳液膜的拉伸强度显著增大,吸水率减小。 相似文献
99.
Strain-induced ordering of microdomain structures in cross-linked polystyrene-block-polybutadiene-block-polystyrene (SBS) triblock copolymers was examined by the small-angle X-ray scattering technique. To stretch the SBS samples at elevated temperature above the glass transition temperature of polystyrene, polybutadiene blocks were chemically cross-linked in the disordered state. The initial morphology was disorder-like or bicontinuous due to incompletion of microphase separation in the presence of the chemical cross-links. When the cross-linked SBS samples were mechanically stretched at 130 °C and were further annealed for 24 h under a stretched state, the random domain structures ordered gradually and lamellar-like regularity was finally attained. It was found that the ordering proceeded more for the case of the higher strain. 相似文献
100.
Huifen Nie Minghai Li Rama Bansil estmír Kok Martin Helmstedt Jyotsana Lal 《Polymer》2004,45(26):8791-8799
We have examined solutions of a polystyrene-polybutadiene pentablock copolymer in n-heptane, a strongly selective solvent for polybutadiene. Small angle neutron scattering from 7 to 15% samples reveals domains about 10 nm in radius formed by the association of 200 polystyrene blocks. Dynamic light scattering measurements on 8 and 9% samples showed three modes: a fast diffusive mode related to the collective diffusion in semidilute solutions/gels; a relaxational mode related to the local dynamics of polystyrene domains trapped in the gel formed by bridging the domains with the polybutadiene chains; and a very slow diffusive mode. The relaxational dynamics persisted over the entire temperature range, becoming faster with increasing temperature, indicating a decreased microviscosity at higher temperatures. The slow dynamics seems to be connected with heterogeneities in the physical gel due to microsyneresis and almost disappeared above 50 °C. Macroscopic phase separation into two liquid phases was observed in a dilute solution of the un-associated copolymer, and into a liquid and gel phase at higher concentrations. The absence of flower-like micelles in dilute solutions and the macroscopic phase seperation suggest that the gels in the pentablock are formed by random association of multiplet domains and not by bridging of micellar domains. 相似文献