全文获取类型
收费全文 | 477153篇 |
免费 | 12163篇 |
国内免费 | 4262篇 |
专业分类
电工技术 | 11520篇 |
技术理论 | 10篇 |
综合类 | 4855篇 |
化学工业 | 72706篇 |
金属工艺 | 17676篇 |
机械仪表 | 15681篇 |
建筑科学 | 16898篇 |
矿业工程 | 2660篇 |
能源动力 | 12947篇 |
轻工业 | 48875篇 |
水利工程 | 4580篇 |
石油天然气 | 5413篇 |
武器工业 | 539篇 |
无线电 | 63101篇 |
一般工业技术 | 84407篇 |
冶金工业 | 78003篇 |
原子能技术 | 6262篇 |
自动化技术 | 47445篇 |
出版年
2022年 | 3014篇 |
2021年 | 5411篇 |
2020年 | 3952篇 |
2019年 | 4141篇 |
2018年 | 5777篇 |
2017年 | 5919篇 |
2016年 | 6103篇 |
2015年 | 6000篇 |
2014年 | 8957篇 |
2013年 | 23053篇 |
2012年 | 14414篇 |
2011年 | 19254篇 |
2010年 | 15070篇 |
2009年 | 16475篇 |
2008年 | 17468篇 |
2007年 | 17573篇 |
2006年 | 15953篇 |
2005年 | 14738篇 |
2004年 | 13622篇 |
2003年 | 13092篇 |
2002年 | 12585篇 |
2001年 | 12622篇 |
2000年 | 11896篇 |
1999年 | 12698篇 |
1998年 | 25630篇 |
1997年 | 18901篇 |
1996年 | 15213篇 |
1995年 | 12064篇 |
1994年 | 10725篇 |
1993年 | 10004篇 |
1992年 | 7641篇 |
1991年 | 7159篇 |
1990年 | 6703篇 |
1989年 | 6387篇 |
1988年 | 6067篇 |
1987年 | 5025篇 |
1986年 | 4933篇 |
1985年 | 6046篇 |
1984年 | 5650篇 |
1983年 | 4868篇 |
1982年 | 4543篇 |
1981年 | 4478篇 |
1980年 | 4239篇 |
1979年 | 4093篇 |
1978年 | 3776篇 |
1977年 | 4556篇 |
1976年 | 6106篇 |
1975年 | 3117篇 |
1974年 | 3020篇 |
1973年 | 2897篇 |
排序方式: 共有10000条查询结果,搜索用时 17 毫秒
961.
The hydrolysis and condensation reactions of γ-APS have been studied in different acid content aqueous solution by using Fourier
Transform infrared (FT-IR) spectroscopy. The hydrolysis of γ-APS under the studied conditions can be followed by the increase
of the ethanol band located at 882 cm−1 and the decrease of the band due to the ρ(CH3) of γ-APS molecules located at 959 cm−1. Hydrolysis reaction is faster by increasing both H2O and acid concentrations, and it is completed when 3 moles of H2O per mole of γ-APS are used. The increase of the vibrational band located at 1146 cm−1 shows that condensation of the hydrolysed γ-APS molecules take place forming linear chains in poorly cross-linked structures.
Besides, both 8-membered cyclic siloxane formations and poorly cross-linked structures are formed and increase as the water
and acid content are increased. On the other hand, highly connected cross-linked structures do not appear due to the steric
hindrance of the non-hydrolysable aminopropyl group. The silanol band shows that hydrolysis is faster than condensation except
for samples with the lowest H2O content. 相似文献
962.
Alexander Chroneos Nicholas J. Ashley Kaajal H. Desai John F. Maguire R. W. Grimes 《Journal of Materials Science》2007,42(6):2024-2029
The structures of a number of hydroxide and oxyhydroxide minerals have previously been reported without the hydrogen positions
explicitly defined. Here we use two atomic scale computer simulation techniques, one based on classical ionic potentials,
the other on density functional theory (DFT), to predict these positions. The aim is not only to provide data that can be
used as the basis for future experimental structure optimizations but also model parameters that can be used to predict complex
hydroxide structures. The efficacy of the approach is demonstrated through the comparison of predicted and experimental data
for minerals whose hydrogen positions are known. 相似文献
963.
Daniel X. Gouveia Odair P. Ferreira Antonio G. Souza Filho M. G. da Silva J. A. C. de Paiva Oswaldo L. Alves Josué Mendes Filho 《Journal of Materials Science》2007,42(2):534-538
The thermal decomposition properties of Mg–Fe hydrotalcites were studied through in situ 57Fe Mössbauer spectroscopy and in situ X-ray diffraction. Abrupt changes in the quadrupolar splitting measured in the Mössbauer spectra revealed a phase transition from the starting lamellar structure to a new crystalline arrangement. By analyzing the Mössbauer parameters we show that the material is highly disordered in the 300–400 °C temperature range. This hypothesis is confirmed by the X-ray results whose diffractograms indicated the collapse of the lamellar structure and the formation of a solid solution. 相似文献
964.
Christian P. Romero Jonathan I. Avila Edgardo Cisternas Guerau B. Cabrera Alejandro L. Cabrera Kristiaan Temst Margriet J. Van Bael 《Journal of Materials Science》2007,42(18):7667-7672
Hydrogen desorption curves were obtained from a sample composed of a square arrangement of Co dots with average diameter of
4.4 μm, separated by a distance of 11.6 μm. A macroscopic sample of Co dots grown on a 2.5 × 2.5 cm Si substrate was made
by standard lithographic techniques and used in these experiments. Thermal programmed desorption (TPD) was performed under
ultra-high vacuum conditions. Hydrogen TPD curves were obtained from a 1 × 1 cm Co dots samples displaying a maximum of intensity
at 425 K. Hydrogen TPD curve was also obtained from 1 cm× 1 cm samples of Co films and Co foils for comparison. The hydrogen
TPD curves have decreasing intensity from the Co foils to the Co dots and finally to the Co films. This indicates that there
are more sites for hydrogen adsorption on the Co dots than in the Co films. This is a surprising result because there is approximately
8.7 times less Co atoms exposed in the Co dots that in the Co film sample. A desorption energy of 27 kcal/mol was obtained
for the Co dots suggesting that hydrogen is adsorbed on an hcp hollow site of the Co dot crystalline structure. 相似文献
965.
966.
967.
The solid solutions of Ba-doped SrBi2Ta2O9 layered perovskite ceramic powders have been successfully prepared via a two-step process using BiTaO4 as a precursor. The lattice constants of the solid solutions monotonically increase with increasing barium-ion content. The sinterability of (Sr1–xBax)Bi2Ta2O9 powders is significantly improved by increasing the barium-ion content. When the specimens with high barium-ion contents are sintered at 1100°C, they thermally decompose to form rod-like grains and the matrix expands, leading to a lower density. The addition of barium ions to SrBi2Ta2O9 also results in significant variation in the morphology of the sintered specimens and the occurrence of c-axis preferred orientation which is ascribed to the anisotropic growth of plate-like grains. The precise control of the barium-ion content as well as the sintering conditions is critical for obtaining densified barium-ion doped SrBi2Ta2O9 ceramics with a pure, layered perovskite structure. 相似文献
968.
969.
970.
Damage detection of CFRP using fiber Bragg gratings 总被引:1,自引:0,他引:1