全文获取类型
收费全文 | 34796篇 |
免费 | 2339篇 |
国内免费 | 1481篇 |
专业分类
电工技术 | 512篇 |
技术理论 | 1篇 |
综合类 | 2347篇 |
化学工业 | 19191篇 |
金属工艺 | 1385篇 |
机械仪表 | 751篇 |
建筑科学 | 226篇 |
矿业工程 | 309篇 |
能源动力 | 668篇 |
轻工业 | 1313篇 |
水利工程 | 41篇 |
石油天然气 | 1856篇 |
武器工业 | 393篇 |
无线电 | 1791篇 |
一般工业技术 | 5009篇 |
冶金工业 | 668篇 |
原子能技术 | 157篇 |
自动化技术 | 1998篇 |
出版年
2024年 | 64篇 |
2023年 | 363篇 |
2022年 | 544篇 |
2021年 | 773篇 |
2020年 | 712篇 |
2019年 | 659篇 |
2018年 | 695篇 |
2017年 | 816篇 |
2016年 | 1014篇 |
2015年 | 1027篇 |
2014年 | 1670篇 |
2013年 | 1691篇 |
2012年 | 2151篇 |
2011年 | 2680篇 |
2010年 | 2023篇 |
2009年 | 2236篇 |
2008年 | 1927篇 |
2007年 | 2492篇 |
2006年 | 2262篇 |
2005年 | 2080篇 |
2004年 | 1700篇 |
2003年 | 1567篇 |
2002年 | 1420篇 |
2001年 | 1170篇 |
2000年 | 1015篇 |
1999年 | 810篇 |
1998年 | 666篇 |
1997年 | 464篇 |
1996年 | 398篇 |
1995年 | 329篇 |
1994年 | 299篇 |
1993年 | 229篇 |
1992年 | 169篇 |
1991年 | 117篇 |
1990年 | 105篇 |
1989年 | 56篇 |
1988年 | 45篇 |
1987年 | 31篇 |
1986年 | 20篇 |
1985年 | 19篇 |
1984年 | 24篇 |
1983年 | 13篇 |
1982年 | 13篇 |
1981年 | 12篇 |
1980年 | 7篇 |
1979年 | 15篇 |
1978年 | 9篇 |
1977年 | 5篇 |
1975年 | 2篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
以溴和苯基取代的对苯二甲酰氯及2,2′-二甲基联苯-4,4′-二甲酰氯作为单体,分别与甲基、叔丁基、苯基取代的对苯二酚经熔融缩聚反应,合成一类具有刚性棒状结构的全芳香液晶聚酯。聚酯的热性质以TGA、DSC,热台偏光显微镜研究。所有的聚酯均为热致性液晶,它们具有相对较低的转变温度,在普通的有机溶剂中具有较好的溶解性质。 相似文献
104.
Preparation of nanocrystalline ZSM-5 has been proven possible with carbon matrix by using confined space synthesis. In combination with the hydrothermal method, by the use of a mesoporous carbon nanotube as the inert support material, ZSM-5 with SiO2/Al2O3 ratios of 100 was successfully synthesized with an average crystal size of 27 nm. Their structures were preliminarily characterized by x-ray power diffraction (XRPD) and infrared spectroscopy (IR), and scanning electron microscopy (SEM), respectively. At the same time, we put forward the mechanism about the confined space synthesis in terms of the results. 相似文献
105.
Fresh niobium hydroxide was first precipitated from NbF5 solution using an aqueous ammonium hydroxide under basic conditions. Then a simple procedure of mixing lithium and niobium hydroxides together and heating at a low temperature (400 °C) produced pure ultrafine single phase LiNbO3 (LN). In the literature, this is the lowest temperature so far reported on the formation of LN. The phase content and lattice parameters are determined by X-ray diffraction (XRD). The average particle size and morphology were studied by transmission electron microscopy (TEM). 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.
Mushroom-like ZnO microcrystals have been prepared via a solution calcination route, using Zn(NO3)2 as Zn source in the absence of any surfactants, templates or catalysts. This is the first example to prepare mushroom-like crystals as semiconductors, which are expected to show particular physical properties. The ZnO products were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy and photoluminescence (PL) spectrum measurements. A suitable concentration of Zn(NO3)2 solution was important for the growth of the mushroom-like products. The reported synthetic procedure is straightforward and inexpensive, and thus can be readily adopted to produce large quantities of mushroom-like ZnO microcrystals. 相似文献
110.
Two-phase (B2+L12) nickel aluminide intermetallic compounds were synthesized by the pressure-assisted volume combustion synthesis (CS). The production and characterization of the samples containing NiAl+Ni3Al were investigated. Aluminum (99% pure, 15 μm) and carbonyl nickel (99.8 pure, 4-7 μm) powders were used. The production of intermetallic compound was carried out at 1050 °C under 150 MPa uniaxial pressure in open air atmosphere in an electrical resistance furnace for 60 min. The formation temperature of intermetallic compound was determined by differential scanning calorimeter (DSC) analysis, and exothermic temperature of powder mixture was determined as 653 °C. The characterization of samples was confirmed by optical microscope, SEM and XRD analysis. It was observed that the structure of compound has very low porosity and the formation of NiAl was completed successfully. The relative density of test materials measured according to Archimedes’ principle was 98.04%. The microhardness of test materials was about 351 HVN1. 相似文献