全文获取类型
收费全文 | 36218篇 |
免费 | 2504篇 |
国内免费 | 2057篇 |
专业分类
电工技术 | 1244篇 |
综合类 | 1966篇 |
化学工业 | 12302篇 |
金属工艺 | 3590篇 |
机械仪表 | 961篇 |
建筑科学 | 2962篇 |
矿业工程 | 491篇 |
能源动力 | 1092篇 |
轻工业 | 1568篇 |
水利工程 | 96篇 |
石油天然气 | 1257篇 |
武器工业 | 293篇 |
无线电 | 3213篇 |
一般工业技术 | 5148篇 |
冶金工业 | 1440篇 |
原子能技术 | 662篇 |
自动化技术 | 2494篇 |
出版年
2024年 | 111篇 |
2023年 | 529篇 |
2022年 | 1183篇 |
2021年 | 1186篇 |
2020年 | 985篇 |
2019年 | 870篇 |
2018年 | 747篇 |
2017年 | 1016篇 |
2016年 | 1279篇 |
2015年 | 1242篇 |
2014年 | 1679篇 |
2013年 | 1883篇 |
2012年 | 2082篇 |
2011年 | 2734篇 |
2010年 | 1992篇 |
2009年 | 2461篇 |
2008年 | 1915篇 |
2007年 | 2377篇 |
2006年 | 2205篇 |
2005年 | 1763篇 |
2004年 | 1471篇 |
2003年 | 1479篇 |
2002年 | 1203篇 |
2001年 | 932篇 |
2000年 | 849篇 |
1999年 | 686篇 |
1998年 | 527篇 |
1997年 | 374篇 |
1996年 | 340篇 |
1995年 | 284篇 |
1994年 | 258篇 |
1993年 | 228篇 |
1992年 | 204篇 |
1991年 | 175篇 |
1990年 | 150篇 |
1989年 | 116篇 |
1988年 | 92篇 |
1987年 | 94篇 |
1986年 | 107篇 |
1985年 | 103篇 |
1984年 | 90篇 |
1983年 | 76篇 |
1982年 | 76篇 |
1981年 | 85篇 |
1980年 | 77篇 |
1978年 | 72篇 |
1977年 | 73篇 |
1976年 | 88篇 |
1975年 | 86篇 |
1974年 | 70篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Mitsuo Miyazawa Hideki Kawazoe Mitsuro Hyakumachi 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2003,78(6):620-625
The microbial transformation of l‐menthol ( 1 ) was investigated by using 12 isolates of soil‐borne plant pathogenic fungi, Rhizoctonia solani (AG‐1‐IA Rs24, Joichi‐2, RRG97‐1; AG‐1‐IB TR22, R147, 110.4; AG‐1‐IC F‐1, F‐4, P‐1; AG‐1‐ID RCP‐1, RCP‐3, and RCP‐7) as a biocatalyst. Rhizoctonia solani F‐1, F‐4 and P‐1 showed 89.7–99.9% yields of converted product from 1 , RCP‐1, RCP‐3, and RCP‐7 26.0–26.9% and the other isolates 0.1–12.0%. In the cases of F‐1, F‐4 and P‐1, substrate 1 was converted to (?)‐(1S,3R,4S,6S)‐6‐hydroxymenthol ( 2 ), (?)‐(1S,3R,4S)‐1‐hydroxymenthol ( 3 ) and (+)‐(1S,3R,4R,6S)‐6,8‐dihydroxymenthol ( 4 ), which was a new compound. Substrate 1 was converted to 2 and/or 3 by RRG97‐1, 110.4, RCP‐1, RCP‐3 and RCP‐7. The structures of the metabolic products were elucidated on the basis of their spectral data. In addition, metabolic pathways of the biotransformation of 1 by Rhizoctonia solani are discussed. Finally, from the main component analysis and the differences in the yields of converted product from 1 , the 12 isolates of Rhizoctonia solani were divided into three groups based on an analysis of the metabolites. Copyright © 2003 Society of Chemical Industry 相似文献
22.
Si3N4 ceramic was jointed to itself using a filler alloy of Cu76.5Pd8.5Ti15, and the mechanical properties of the jointwere measured and analyzed. By using a filler alloy of Cu76.5Pd8.5Ti15, the SisN4/SisN4 joints were obtained bybrazing at 1373~1473 K f 相似文献
23.
利用硫酸软骨素(chondroitin sulfate,CS)在云母基底上通过浇铸法制备的自组装膜为基底,诱导草酸钙在其上的凝集生长。发现当硫酸软骨素的浓度为1.Omg/ml时在该膜体系中可形成规整的周期性草酸钙环状沉淀。这种有序的环状结构可能是耗散结构的一种具体表现形式。利用原子力显微镜(atomic forcemicroscope,AFM)和傅立叶红外光谱仪对这种结构进行了表征,实验结果显示合适浓度下形成的CS膜在一定程度上可以抑制草酸钙的凝集结晶,表明高分子基质与无机离子间强烈的相互作用对无机盐的成核结晶有显著影响,为探讨结石的形成与抑制提供了一定的实验依据。 相似文献
24.
M. Kaiarov E. Rudnayov J. Koval
ík J. Dusza M. Hnatko P. ajgalík A. Merstallinger 《Materialwissenschaft und Werkstofftechnik》2003,34(4):338-342
In the presented work some properties of a recently developed Si3N4/SiC micro/nanocomposite have been investigated. The material was tested using a pin on disc configuration. Under unlubricated sliding conditions using Si3N4 pin at 50 % humidity, the friction coefficient was in the range of 0,6 ‐ 0,7. The reduction of humidity resulted in a lower coefficient of friction, in vacuum the coefficient of friction had a value of about 0,6. The wear resistance in vacuum was significantly lower then that in air. The wear patterns on the Si3N4+SiC disc revealed that mechanical fracture was the wear controlling mechanism. Creep tests were realized in four point bending configuration in the temperature interval 1200‐1400 °C at stresses 50,100 and 150 MPa and the minimal creep deformation rate was established for each stress level. The activation energy, established from the minimal creep deformation had a value of about 360 kJ/mol and the stress exponent values were in the range of 0.8‐1.28. From the achieved stress exponents it can be assumed that under the studied load/temperature conditions the diffusion creep was the most probable creep controlling mechanism. 相似文献
25.
26.
Fe3O4/PSt/TiO2多层包覆电磁响应微球的制备 总被引:7,自引:0,他引:7
首先采用分散聚合法将自制的Fe3O4磁流体和苯乙烯反应合成有磁核的Fe3O4/PSt磁性聚合物微球,然后,用非均匀成核水解反应在Fe3O4/PSt微球外包覆无定形二氧化钛,获得Fe3O4/PSt/TiO2复合微粒。用红外光谱、扫描电镜和热分析对粒子的形貌和结构进行了表征。并测试了微粒的介电性能和磁性,结果表明,所制得复合微粒有良好的电、磁响应性。 相似文献
27.
V S R Murthy 《Bulletin of Materials Science》1993,16(2):87-108
Research and development efforts on high-temperature, oxidation-resistant fibres have increased over the past decade due to
the demand for light-weight, stiff and strong composite materials in aerospace applications. Varieties of ‘high-performance’,
continuous, non-oxide fibres with low-density, high tensile strength and tensile modulus have been developed either from organic
precursors or via chemical vapour deposition for fabrication of ceramic matrix composites. Fibres derived from polymer precursors
(e.g. Nicalon, Tyranno, HPZ) are small in diameter (compared to CVD monofilaments) and are ideally suited for ceramic composites.
Processing, microstructural stability and mechanical properties of these newly developed SiC and Si3N4 base fibres are briefly reviewed in this paper. 相似文献
28.
超细Fe3O4粒子表面包覆酞菁钴性质研究 总被引:3,自引:1,他引:2
本文研究了合成载氧体的金属有机化学液相淀积法制造工艺,所得产物经TEM、XPS、Moss-bauer谱和B-H仪等手段,研究了它的结构和磁性能。实验表明,酞青钴以薄层形式包覆在Fe_3O_4的表面,封闭了Fe_3O_4的表面孔洞,稳定了Fe_3O_4的物相,增强了磁性能。 相似文献
29.
30.