全文获取类型
收费全文 | 112087篇 |
免费 | 7823篇 |
国内免费 | 6490篇 |
专业分类
电工技术 | 8065篇 |
技术理论 | 3篇 |
综合类 | 7253篇 |
化学工业 | 29220篇 |
金属工艺 | 6276篇 |
机械仪表 | 7692篇 |
建筑科学 | 3781篇 |
矿业工程 | 1447篇 |
能源动力 | 3630篇 |
轻工业 | 7075篇 |
水利工程 | 647篇 |
石油天然气 | 6421篇 |
武器工业 | 908篇 |
无线电 | 12186篇 |
一般工业技术 | 11817篇 |
冶金工业 | 2515篇 |
原子能技术 | 1189篇 |
自动化技术 | 16275篇 |
出版年
2024年 | 305篇 |
2023年 | 1377篇 |
2022年 | 2399篇 |
2021年 | 2853篇 |
2020年 | 2559篇 |
2019年 | 2551篇 |
2018年 | 2391篇 |
2017年 | 3137篇 |
2016年 | 3400篇 |
2015年 | 3542篇 |
2014年 | 5166篇 |
2013年 | 5995篇 |
2012年 | 6496篇 |
2011年 | 7621篇 |
2010年 | 6330篇 |
2009年 | 7198篇 |
2008年 | 6926篇 |
2007年 | 7729篇 |
2006年 | 7474篇 |
2005年 | 6220篇 |
2004年 | 5434篇 |
2003年 | 5241篇 |
2002年 | 4312篇 |
2001年 | 3480篇 |
2000年 | 3034篇 |
1999年 | 2490篇 |
1998年 | 1841篇 |
1997年 | 1448篇 |
1996年 | 1297篇 |
1995年 | 1267篇 |
1994年 | 1126篇 |
1993年 | 923篇 |
1992年 | 725篇 |
1991年 | 459篇 |
1990年 | 288篇 |
1989年 | 290篇 |
1988年 | 193篇 |
1987年 | 124篇 |
1986年 | 124篇 |
1985年 | 113篇 |
1984年 | 99篇 |
1983年 | 72篇 |
1982年 | 86篇 |
1981年 | 57篇 |
1980年 | 30篇 |
1979年 | 24篇 |
1978年 | 24篇 |
1977年 | 21篇 |
1976年 | 26篇 |
1975年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Identification of organochlorines and organobromines in coals 总被引:1,自引:0,他引:1
Xian-Yong Wei Xiao-Hua Wang Zhi-Min Zong Zhong-Hai Ni Li-Fang Zhang Ya-Fei Ji Ke-Chang Xie Chul Wee Lee Zhen-Xue Liu Nai-Bo Chu Jiao-Ying Cui 《Fuel》2004,83(17-18):2435-2438
Four Chinese bituminous coals were extracted with CS2, n-hexane, benzene, methanol, acetone, tetrahydrofuran (THF) and THF/methanol (1: 3 vol/vol) mixed solvent sequentially. The resulting 28 extracts were analyzed with GC/MS. Six organochlorines (OCs) and two organobromines (OBs) were identified in eight extracts from the coals. Our experiments provide, for the first time, the information on the molecular structure of OCs and OBs in coals. 相似文献
992.
993.
994.
The subsequent melting behaviour of poly(butylene succinate) (PBSU) and poly(ethylene succinate) (PES) was investigated using DSC and temperature modulated DSC (TMDSC) after they finished nonisothermal crystallization from the melt. PBSU exhibited two melting endotherms in the DSC traces upon heating to the melt, which was ascribed to the melting and recrystallization mechanism. However, one melting endotherm with one shoulder and one crystallization exotherm just prior to the melting endotherm were found for PES. The crystallization exotherm was ascribed to the recrystallization of the melt of the crystallites with low thermal stability, and the shoulder was considered to be the melting endotherm of the crystallites with high thermal stability. The final melting endotherm was ascribed to the melting of the crystallites formed through the reorganization of the crystallites with high thermal stability during the DSC heating process. TMDSC experiments gave the direct evidences to support the proposed models to explain the melting behaviour of PBSU and PES crystallized nonisothermally from the melt. 相似文献
995.
Isotactic polypropylene and ethylene-1-hexene copolymers containing 32 and 57 mol% of 1-hexene copolymers blends (i-PP/EH32 and i-PP/EH57) were prepared by solution blending, precipitating followed by drying and hot pressing. The two blends were subject to investigation on structure and mechanical properties of these blends under uniaxial drawing. The i-PP/EH32 and i-PP/EH57 represented the immiscible and miscible blends, respectively. The tensile stresses and strains at breaking point of i-PP/EH57 were remarkably higher than those of i-PP/EH32 at room temperature. From wide-angle X-ray diffraction (WAXD) measurement, it was observed that the orientation of crystallites occurred early and then propagated gradually up to about drawing ratio 8 because chains of EH57 copolymer were incorporated into the amorphous regions between lamellae of i-PP. In the WAXD patterns of i-PP/EH57, the oriented spot reflections coexsisted with unoriented ring reflections up to draw ratio higher than in pure i-PP. On the other hand, the two-phase structure was observed from TEM and AFM in i-PP/EH32, and on the drawing, separation at the interface between two-phase was observed in i-PP/EH32 even at the low strain. 相似文献
996.
997.
998.
999.
Shim JH Kim YW Kim TJ Chae HY Park JH Cha H Kim JW Kim YR Schaefer T Spendler T Moon TW Park KH 《Protein engineering, design & selection : PEDS》2004,17(3):205-211
In an effort to improve the properties of cyclodextrin glucanotransferase (CGTase) as an antistaling enzyme, error-prone PCR was used to introduce random mutations into a CGTase cloned from alkalophilic Bacillus sp. I-5 (CGTase I-5). A mutant CGTase[3-18] with the three mutations M234T, F259I and V591A was selected by agar plate assay. Sequence alignment of various CGTases indicated that M234 and F259 are located in the vicinity of the catalytic sites of the enzyme and V591 in the starch binding domain E. The cyclization activity of CGTase[3-18] was dramatically decreased by 10-fold, while the hydrolyzing activity was increased by up to 15-fold. These mutations near subsite +1 (M234T) and at subsite +2 (F259I) are likely to alter the enzyme activity in a concerted manner, promoting hydrolysis of substrate while retarding cyclization. The addition of CGTase[3-18] reduced the retrogradation rate of bread by as much as did the commercial antistaling enzyme Novamyl during 7-day storage at 4 degrees C. No cyclodextrin (CD) was detected in bread treated with CGTase[3-18], whereas 21 mg of CD per 10 g of bread was produced in bread treated with wild-type CGTase. 相似文献
1000.
Nianxue Song Colin Rhodes David W. Johnson Graham J. Hutchings 《Catalysis Letters》2005,102(3-4):271-279
Temperature programmed reduction (TPR) and oxidation (TPO) are used extensively in catalyst characterisation. In this paper, we examine the use of TPR/TPO cycles for the characterisation of a range of molybdates and single oxides. In particular we observe that the first cycle differs from that of subsequent analyses, even when the maximum temperature is limited to that used in the catalytic reaction. The effect is independent of heating rates and cooling atmospheres and has been demonstrated using different bed configurations. This observation has significance when these oxides are used in periodic flow reactors that involve many cyclical reduction/oxidation. 相似文献