全文获取类型
收费全文 | 30087篇 |
免费 | 2328篇 |
国内免费 | 1104篇 |
专业分类
电工技术 | 1467篇 |
技术理论 | 2篇 |
综合类 | 1715篇 |
化学工业 | 5168篇 |
金属工艺 | 1838篇 |
机械仪表 | 1990篇 |
建筑科学 | 2367篇 |
矿业工程 | 1001篇 |
能源动力 | 791篇 |
轻工业 | 1718篇 |
水利工程 | 529篇 |
石油天然气 | 2064篇 |
武器工业 | 213篇 |
无线电 | 3214篇 |
一般工业技术 | 3703篇 |
冶金工业 | 1614篇 |
原子能技术 | 353篇 |
自动化技术 | 3772篇 |
出版年
2024年 | 118篇 |
2023年 | 550篇 |
2022年 | 890篇 |
2021年 | 1239篇 |
2020年 | 1033篇 |
2019年 | 784篇 |
2018年 | 958篇 |
2017年 | 972篇 |
2016年 | 927篇 |
2015年 | 1142篇 |
2014年 | 1435篇 |
2013年 | 1778篇 |
2012年 | 1880篇 |
2011年 | 1907篇 |
2010年 | 1717篇 |
2009年 | 1682篇 |
2008年 | 1566篇 |
2007年 | 1549篇 |
2006年 | 1654篇 |
2005年 | 1368篇 |
2004年 | 882篇 |
2003年 | 839篇 |
2002年 | 746篇 |
2001年 | 625篇 |
2000年 | 670篇 |
1999年 | 806篇 |
1998年 | 692篇 |
1997年 | 624篇 |
1996年 | 553篇 |
1995年 | 460篇 |
1994年 | 355篇 |
1993年 | 265篇 |
1992年 | 196篇 |
1991年 | 159篇 |
1990年 | 116篇 |
1989年 | 100篇 |
1988年 | 80篇 |
1987年 | 51篇 |
1986年 | 50篇 |
1985年 | 24篇 |
1984年 | 23篇 |
1983年 | 16篇 |
1982年 | 18篇 |
1981年 | 11篇 |
1980年 | 7篇 |
1979年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
982.
983.
Iron was recovered from blast furnace dust and high-phosphorus oolitic hematite in the presence of Na2CO3 and CaCO3 additives. The functions of Na2CO3 and CaCO3 during the coreduction roasting process were investigated by XRD and SEM-EDS analyses. Results indicate that these additives not only hinder the reduction of fluorapatite, CaCO3 also decreases the P content of direct reduced iron (DRI) by increasing the reduction alkalinity. P remains as fluorapatite in the slag, which can be removed by grinding and magnetic separation under optimal conditions. The Na2CO3 promotes hematite reduction and improves the iron recovery (εFe) by replacing the FeO from fayalite, which results in quick growth and aggregation of metallic iron and improvement of εFe in DRI. A DRI with 91.88 mass% Fe, and 0.065 mass% P can be achieved at a recovery of 87.86 mass% under the optimal condition. 相似文献
984.
1概况
新洛公司山西煤矿主采煤层23#、21#、13#煤层,其中23#煤层为厚煤层,平均厚度5.0 m ,煤层结构复杂,含多层薄层夹矸,普氏硬度3~4,煤层倾角8°~22°,煤层赋存相对稳定。23#煤层伪顶为粉砂岩夹煤线,厚度0.8 m ,含炭质较高;直接顶为粗粉砂岩,厚度2.0m,致密坚硬;老顶为灰色细砂岩,厚度15 m ,坚硬。直接底为粉砂岩,厚度2.0m ,较坚硬,不易底鼓;老底为灰色细砂岩,厚度5m ,致密坚硬。该矿为瓦斯矿井,23#煤层瓦斯绝对涌出量为3.17 m3/min ,相对涌出量6.28 m3/t ,煤层不易自燃,煤尘无爆炸性。 相似文献
新洛公司山西煤矿主采煤层23#、21#、13#煤层,其中23#煤层为厚煤层,平均厚度5.0 m ,煤层结构复杂,含多层薄层夹矸,普氏硬度3~4,煤层倾角8°~22°,煤层赋存相对稳定。23#煤层伪顶为粉砂岩夹煤线,厚度0.8 m ,含炭质较高;直接顶为粗粉砂岩,厚度2.0m,致密坚硬;老顶为灰色细砂岩,厚度15 m ,坚硬。直接底为粉砂岩,厚度2.0m ,较坚硬,不易底鼓;老底为灰色细砂岩,厚度5m ,致密坚硬。该矿为瓦斯矿井,23#煤层瓦斯绝对涌出量为3.17 m3/min ,相对涌出量6.28 m3/t ,煤层不易自燃,煤尘无爆炸性。 相似文献
985.
A novel liquid crystalline epoxy resin (LCER) derived from asymmetric mesogen unit was synthesized. Its structure and liquid crystalline behavior were characterized by hydrogen nuclear magnetic resonance (H‐NMR), differential scanning calorimetry (DSC), polarized optical microscopy (POM). The results indicated that the LCER converted to a nematic phase at 85°C during heating and finally became isotropic at 145°C. The curing behavior and phase behavior of the LCER with 4,4′‐diaminodiphenyl methane and methyl hexahydrophthalic anhydride were also studied by DSC and POM, respectively. Their apparent activation energy (Ea) was evaluated according to the Ozawa's isoconversional method. The results suggested that autocatalytic reaction had occurred in these two systems. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 相似文献
986.
987.
To address the problems of the present Tera Hertz medium access control(MAC) protocols such as not updating the time slot requests numbers in time, unreasonable superframe structures and not merging time slot requests from the same pair of nodes, high throughput low delay medium access control(HLMAC), a novel MAC protocol for Tera Hertz ultra-high data-rate wireless networks is proposed. It reduces the data access delay largely with a new superframe structure, from which nodes can get time slot allocation information immediately. The network throughput is also improved with the help of updating time slot requests number and merging time slot requests from the same pair of nodes. The theoretical analysis verifies the effectiveness of HLMAC, and the simulation results show that HLMAC improves the network throughput by 65.7% and decreases the access delay by 30%, as compared to energy and spectrum-aware medium access control(ES-MAC). 相似文献
988.
Poly-crystalline In(OH) 3 nanorods have been successfully prepared via a urea-based precipitation using the colloidal carbon spheres as the templates. After calcinations, the resulted In 2 O 3 nanorods with poly-crystalline structure were fabricated. Structure and morphology of the product were characterized by X-ray diffraction (XRD), and transmission electron microscopy (TEM). The possible formation process was schemed. The sensor gas properties towards C 2 H 5 OH and CO were examined. 相似文献
989.
Graphene as a well-known electron cocatalyst can enhance the hydrogen-production performance of photocatalysts due to its excellent conductivity. For highly efficient graphene-modified TiO2 photocatalyst, besides the speedy electron transfer via graphene, it is significant to raise the interfacial hydrogen-generation reaction rate on the graphene surface. In this paper, thiourea (TU) can covalently functionalize graphene and act as effective H+-adsorbed active sites to improve the hydrogen-production efficiency of graphene-modified TiO2 (TiO2/rGO-TU). The TiO2/rGO-TU sample was successfully prepared by a facile nucleophilic substitution reaction between the thiol (-SH) of thiourea and carboxyl (-COOH) of graphene. The TiO2/rGO-TU could possess the maximum H2-generation rate of 241.83 μmol h?1 g?1, which was 2.33 and 6.60 times greater than that of TiO2/rGO and TiO2, respectively. The enhanced photocatalytic activity of TiO2/rGO-TU can be ascribed to the synergistic effect of graphene and thiourea, namely, the graphene functions as a cocatalyst to capture the photoexcited electrons of TiO2 and the thiourea acts as effectual H+-adsorbed active sites to promote interfacial hydrogen generation. This study presents a feasible strategy for developing grephene-based photocatalysts for prospective applications in the hydrogen-production field. 相似文献
990.
Cognition, Technology & Work - In existing studies about analogical reasoning during idea generation in design, there is lack in quantitative and objective evidences showing the relationship... 相似文献