全文获取类型
收费全文 | 6217篇 |
免费 | 695篇 |
国内免费 | 435篇 |
专业分类
电工技术 | 96篇 |
综合类 | 520篇 |
化学工业 | 1520篇 |
金属工艺 | 928篇 |
机械仪表 | 119篇 |
建筑科学 | 302篇 |
矿业工程 | 231篇 |
能源动力 | 228篇 |
轻工业 | 416篇 |
水利工程 | 793篇 |
石油天然气 | 247篇 |
武器工业 | 25篇 |
无线电 | 122篇 |
一般工业技术 | 673篇 |
冶金工业 | 975篇 |
原子能技术 | 83篇 |
自动化技术 | 69篇 |
出版年
2024年 | 37篇 |
2023年 | 103篇 |
2022年 | 209篇 |
2021年 | 221篇 |
2020年 | 251篇 |
2019年 | 242篇 |
2018年 | 235篇 |
2017年 | 268篇 |
2016年 | 276篇 |
2015年 | 225篇 |
2014年 | 393篇 |
2013年 | 438篇 |
2012年 | 482篇 |
2011年 | 495篇 |
2010年 | 363篇 |
2009年 | 333篇 |
2008年 | 266篇 |
2007年 | 370篇 |
2006年 | 360篇 |
2005年 | 307篇 |
2004年 | 258篇 |
2003年 | 202篇 |
2002年 | 191篇 |
2001年 | 140篇 |
2000年 | 129篇 |
1999年 | 92篇 |
1998年 | 67篇 |
1997年 | 57篇 |
1996年 | 46篇 |
1995年 | 46篇 |
1994年 | 36篇 |
1993年 | 46篇 |
1992年 | 29篇 |
1991年 | 23篇 |
1990年 | 23篇 |
1989年 | 18篇 |
1988年 | 15篇 |
1987年 | 10篇 |
1986年 | 12篇 |
1985年 | 2篇 |
1984年 | 9篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1977年 | 1篇 |
1951年 | 4篇 |
排序方式: 共有7347条查询结果,搜索用时 31 毫秒
101.
Christine Baatz Nadine Thielecke Ulf Prüße 《Applied catalysis. B, Environmental》2007,70(1-4):653-660
In this work, two deposition–precipitation methods for the preparation of gold catalysts for glucose oxidation were investigated. Thus far, gold colloids immobilized on carbon have been used for catalytic glucose oxidation, but the long-term stability of these systems was not sufficient. To improve the long-term stability we used the deposition–precipitation methods using NaOH (DP NaOH) or urea (DP urea) as precipitation agents as they were described by Haruta and Dekkers, respectively, using alumina as a support material. With these methods, it was possible to prepare highly active and selective catalysts which showed an excellent long-term stability. DP urea was found to be the preferred method, because in contrast to DP NaOH, no losses of gold occurred during the preparation, and it was possible to adjust various gold contents up to 10 wt% Au. 相似文献
102.
103.
定性分析有机同相沉积对储层的影响,定量研究有机固相沉积后储层的损伤情况.利用岩石-毛细管模型描述地层孔隙空间,并用孔隙度、渗透率与比面等的相互关系推导出有机同相沉积量与储地层参数的变化关系式. 相似文献
104.
借鉴自回归模型,采取添加随机项的方法对加权马尔可夫链预测模型进行优化,并把优化后的模型应用于郑州市年降雨量的预测,通过与原模型和自回归模型预测结果的对比分析发现,优化后的模型弥补了原模型预测结果缺乏波动性的不足,同时使预测结果不仅在精度上有一定的提高,而且在趋势上更接近于实测值. 相似文献
105.
A new method was used to analyze the factors affecting the precipitation of reversed austenite during tempering. The samples were kept at various tempering temperatures for 10 min and their length changes were recorded. Then, the precipitation of reversed austenite which led to the length reduction was shown by thermal expansion curves. The results show that the effects of process parameters on the precipitation of reversed austenite can be determined more accurately by this method than by X-ray diffraction... 相似文献
106.
The time-temperature-transformation (TTT) curve of the 00Cr25Ni7Mo4N duplex stainless steel was obtained with a Formastot-digital thermal dilatometer,and the influence of isothermal aging on σ precipitation was studied by metallographic observation,X-ray diffraction (XRD),and transmission electron microscopy (TEM).The results show that the decomposition of ferrite phase is accompanied by the formation of σ phase at 750-1000℃,especially in the range of 800-900℃.The longer the aging time,the higher the amount of σ precipitation.The area fraction of various phases remains at a certain value upon the completion of ferrite deformation.The temperature of 850℃ is the most sensitive transaction temperature,the incubation time for the formation of o precipitation is less than 1 min,and aging for 20 min leads to the complete transformation of ferrite.The o phase is formed preferentially at the α/α/γ junction,and then grows along the α/α boundary in the matrix. 相似文献
107.
Fe/Si3N4 composite powder was synthesized by the heterogeneous precipitation-thermal reduction process, and then pressed into flakes
under a pressure of 10 MPa. Flakes were sintered by pressureless and hot-pressing at 1 600 °C under 0.1 MPa N2. The chemical composition, phases and microstructure of composite powder and sintered flakes were investigated by energy
dispersive spectroscopy (EDS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy
(TEM). The results show that the structure of composite powders is Si3N4 coated by nano Fe. The crystal phases of sintered flakes by pressureless are Fe(Si) compound, SiC and Si3N4. The crystal phases of the sintered samples by hot-pressing are Fe, Fe(Si) compound and Si3N4. It is found that crystal phases flakes obtained by pressureless and hot-pressing are very different.
Foundation item: Project(50804016) supported by the National Natural Science Foundation of China 相似文献
108.
对1951—2000年的ENSO事件对松花江流域夏季(6—8月)降水的影响进行了分析,结果显示:赤道中东太平洋海温异常与松花江流域夏季降水有很好的相关性,特别是ENSO事件出现后,El Nino事件影响年通常对应于松花江流域夏季降水偏多,La Nina事件影响年松花江流域夏季降水则较常年偏少,且二者通过了置信度α=0.05的显著性检验.这种相关性可用于进行松花江流域夏季降水的预测. 相似文献
109.
The Ytterbium doped gadolinium gallium garnet [Yb3+:Gd3Ga5O12, Yb:GGG] precursor powders were synthesized via homogeneous precipitation method using Yb2O3, Ga2O3, Gd2O3 and ammonium bicarbonate [NH4HCO3] as precipitator, and ammonium sulfate [(NH4)2SO4] as additive. The evolution of phase composition and micro-structure of the powders were characterized by TG- DTA, XRD, IR, and TEM. The results indicate that all precursor powders completely transform to Yb:GGG phase by calcining at 900 ℃ for 8 h, the resultant powders are well dispersed and have smaller particle size approximately 80 nm owing to the electrostatic effect. 相似文献
110.
Yongjun He 《Powder Technology》2005,155(1):1-4
Nanostructured CeO2 microspheres with an average diameter of 11 μm were prepared by a novel surfactant-free emulsion for the first time. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Brunauer-Emmet-Teller (BET) measurements were used to characterize the products. The images of SEM showed that the CeO2 microspheres consisted of petal-like nanostructures with petal thickness in a range of 60 nm to 100 nm. The BET measurements showed the specific surface area of the CeO2 microspheres exceeded 43 m2/g. The XRD analysis indicated the nanostructured CeO2 microspheres were of cubic lattice. A possible mechanism of an interfacial precipitation reaction with the droplets of solid-stabilized emulsion as templates was proposed. 相似文献