全文获取类型
收费全文 | 88756篇 |
免费 | 1380篇 |
国内免费 | 459篇 |
专业分类
电工技术 | 833篇 |
综合类 | 2339篇 |
化学工业 | 12559篇 |
金属工艺 | 4844篇 |
机械仪表 | 3271篇 |
建筑科学 | 2257篇 |
矿业工程 | 571篇 |
能源动力 | 1431篇 |
轻工业 | 4351篇 |
水利工程 | 1308篇 |
石油天然气 | 367篇 |
武器工业 | 1篇 |
无线电 | 9846篇 |
一般工业技术 | 17447篇 |
冶金工业 | 2699篇 |
原子能技术 | 306篇 |
自动化技术 | 26165篇 |
出版年
2024年 | 117篇 |
2023年 | 259篇 |
2022年 | 490篇 |
2021年 | 818篇 |
2020年 | 510篇 |
2019年 | 518篇 |
2018年 | 14781篇 |
2017年 | 13660篇 |
2016年 | 10271篇 |
2015年 | 827篇 |
2014年 | 503篇 |
2013年 | 562篇 |
2012年 | 3346篇 |
2011年 | 9640篇 |
2010年 | 8402篇 |
2009年 | 5662篇 |
2008年 | 6843篇 |
2007年 | 7842篇 |
2006年 | 147篇 |
2005年 | 1225篇 |
2004年 | 1158篇 |
2003年 | 1194篇 |
2002年 | 548篇 |
2001年 | 100篇 |
2000年 | 184篇 |
1999年 | 67篇 |
1998年 | 67篇 |
1997年 | 39篇 |
1996年 | 54篇 |
1995年 | 26篇 |
1994年 | 18篇 |
1993年 | 19篇 |
1992年 | 19篇 |
1991年 | 29篇 |
1988年 | 13篇 |
1969年 | 24篇 |
1968年 | 43篇 |
1967年 | 33篇 |
1966年 | 42篇 |
1965年 | 44篇 |
1963年 | 28篇 |
1962年 | 22篇 |
1961年 | 19篇 |
1960年 | 30篇 |
1959年 | 35篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1956年 | 34篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
Muhammad Kaleem Yves Farizon Francis Enjalbert Annabelle Troegeler‐Meynadier 《European Journal of Lipid Science and Technology》2013,115(2):161-169
Heating oilseeds has been shown to improve the milk fatty acid profile when given to dairy cows, compared to raw oilseeds. However, results from published studies are conflicting. The conditions of heating and storage of the oilseeds could be responsible for these differences, probably partly through their effects on lipid oxidation, the products of which could act on ruminal biohydrogenation (BH). Thus, 15 different treatments were applied to ground soybeans: three levels of heating (no heating, 30 min at 110 or 150°C) × 5 ambient storage durations (0, 1, 2, 4, or 6 months). Soybeans were incubated in vitro with ruminal fluid for 6 h. Triacylglycerol (TAG) polymers, hydroperoxides and hydroxyacids (HOA), aldehydes, and fatty acids were assayed in soybeans and ruminal culture. No TAG polymer was detected in any treatment. Soybeans stored for a long time had a high content of HOA, whereas those heated at 150°C, whatever the storage duration, had high aldehyde contents. The percentage disappearance of cis‐9,cis‐12 18:2 and cis‐9,cis‐12,cis‐15 18:3 in incubates decreased significantly in cultures with heated soybeans, especially at 150°C, suggesting that this partial protection of polyunsaturated fatty acids (PUFA) from BH was at least in part linked to the aldehyde content of the heated soybeans. Practical applications: Oilseeds given to ruminants are often heated, and heat treatment is known to generate oxidation products. Knowing what oxidation products influence ruminal biohydrogenation of unsaturated fatty acids could result in technological processes allowing a better transfer of unsaturated fatty acids from oilseeds to ruminant products. 相似文献
104.
Object detection is a wide area problem domain in the field of computer and machine vision. Complex background adds challenge and error margin as well to the problem significantly lot algorithms for object detection are hard to comply with occlusion and pixel bending moment affect. In this paper a highly robust algorithm ORBTRIAN for a less resolution image has been proposed and implemented using ORB detection with gradient boosting machine learning algorithm. The work has been compared with Adaboost and Surf based technology. The analysis shows 3.8% increase in performance of earlier model. The feature points extracted from ORB method are further processed to reduce the processing further. Only those points are selected which are triangularly farthest from centroid of it and only 1 point of feature selected. Thus the result is around 28%, much faster than earlier computation. The tree based GB has been implemented in this algorithm. With more number of feature points more classes need to be recognized and hence the computations performed is required an unreasonable amount of effort and time. So some nearby classes are assigned at same level using our algorithm to reduce the number of tree nodes. Overall performance of the proposed algorithm shows a significant increase in efficiency in computation time. 相似文献
105.
Francis Leonard Deepak Rodrigo Esparza Belsay Borges Xóchitl López-Lozano Miguel Jose-Yacaman 《Catalysis Letters》2011,141(4):518-524
Abstract
Aberration corrected (Cs) scanning transmission electron microscopy (STEM) has been used for the first time to characterize MoS2 catalysts (supported on Al2O3 substrates) to provide detailed information of its shape and structure. The high-resolution imaging reveals unprecedented morphologies present in the MoS2 catalyst that have never been observed before with other experimental techniques because of the insufficient image contrast and/or resolution. High angle annular dark field (HAADF)-STEM images shows very clearly that the catalyst is formed by elongated chains with a twisted and helical structure. Based on the HAADF-STEM images, we built three atomic models to illustrate the different morphologies found in the MoS2 catalyst. The existence of these nanostructures opens the posibility for novel catalyticaly active edge morphologies in MoS2-based nanocatalysts. 相似文献106.
Pei Lin Baolin Li Jiangtao Li Huichun Wang Xiaobing Bian Xiaomei Wang 《Catalysis Letters》2011,141(3):459-466
Abstract
A carbon nanocage material (CKT) was first successfully sulfonated by introducing sulfophenyl groups on the surface of pore channels through benzenesulfonic acid-containing aryl radical in situ generated from the reaction of 4-aminobenzenesulfonic acid and isoamyl nitrite in water. The sulfonated carbon nanocage material (S-CKT) was characterized by Fourier transform infrared spectroscopy, transmission electron microscopy, powder small-angle X-ray diffraction and nitrogen sorption measurements. The results showed that the S-CKT still possess the high specific surface area (787 m2/g) and uniform mesoporous (pore diameter 4.7 nm) structures, although the structure of S-CKT is slightly disorder, compared with its unsulfonated precursor. S-CKT, as a carbon-based solid acid catalyst, showed good catalytic performance and reusability in the cross-Aldol condensation of ketones with aromatic aldehydes under solvent-free condition. 相似文献107.
Abstract
Silica functionalized Mn(acac)3 was prepared and employed for the one-pot oxidative synthesis of 2-arylbenzimidazoles, 2-arylbenzothiazoles; and oxidation of benzoins to benzils under air atmosphere using water as the reaction medium. Environmentally friendly procedure, chemoselectivity and excellent yields are main advantages of this procedure. In all the cases, the catalyst was found to be highly active and selective; passes hot filtration test successfully; and could be recycled several times with a slight loss of activity. 相似文献108.
Elodie G. Rodrigues Sónia A. C. Carabineiro Xiaowei Chen Juan J. Delgado José L. Figueiredo Manuel F. R. Pereira José J. M. Órfão 《Catalysis Letters》2011,141(3):420-431
Abstract
Noble metal catalysts (Pt, Ir, Pd, Rh, Au) supported on activated carbon were assessed for glycerol oxidation. Rhodium is a highly efficient catalyst when the support has neutral or basic properties. The surface chemistry of activated carbon plays a key role in the performance. 相似文献109.
Abstract
The gaseous products of photocatalytic oxidation (PCO) of acrylonitrile on sulphated P25 in concentrations from 10 to 100 ppm at 60 to 130 °C were CO2, HCN and HNCO. This photocatalyst showed disproportionally improved performance at higher temperature and longer retention times. The temperature-programmed oxidation (TPO) after PCO disclosed possible reaction routes. 相似文献110.
Yan Wu Tiewei Wang Mingjun Li Tengfei Fan Hongxia Gao Xuemin Wu 《Journal of Polymer Research》2011,18(5):1147-1158
A new amphiphilic hyperbranched poly (amine-ester)-poly(ε-caprolactone) copolymer (HPAE-co-PCL) was synthesized by ring-opening polymerization of ε-caprolactone and branched poly (amine-ester) (HPAE-OHs) with Sn(Oct)2 as catalyst. The chemical structures of copolymers were determined by FT-IR, 1H-NMR (13C-NMR), thermo gravimetric analysis apparatus (TGA) and differential scanning calorimetry (DSC). Camptothecin (CPT)-loaded copolymer nanoparticles were prepared by the oil-in water (o/w) emulsion technique method. Their physicochemical characteristics, e.g. morphology and nanoparticles size distribution were then evaluated by means of fluorescence spectroscopy, environmental scanning electron microscopy (ESEM), and dynamic light scattering (DLS). CPT-loaded nanoparticles assumed a spherical shape and have unimodal size distribution. It was found that the chemical composition of the nanoparticles was a key factor in controlling nanoparticles size, drug-loading content, and drug release behavior. As the molar ratio of ε-caprolactone to HPAE increased, the nanoparticles size and drug-loading content increased, and the drug release rate decreased. The antitumor activity of the CPT-loaded HPAE-co-PCL nanoparticles against human hepatoma HEPG2 cells was evaluated by 3-(4, 5-Dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) method. The CPT-loaded HPAE-co-PCL nanoparticles showed comparable anticancer efficacy with the free drug. 相似文献