全文获取类型
收费全文 | 5321篇 |
免费 | 223篇 |
国内免费 | 13篇 |
专业分类
电工技术 | 90篇 |
综合类 | 30篇 |
化学工业 | 1523篇 |
金属工艺 | 111篇 |
机械仪表 | 99篇 |
建筑科学 | 323篇 |
矿业工程 | 23篇 |
能源动力 | 106篇 |
轻工业 | 421篇 |
水利工程 | 35篇 |
石油天然气 | 2篇 |
无线电 | 342篇 |
一般工业技术 | 1122篇 |
冶金工业 | 531篇 |
原子能技术 | 41篇 |
自动化技术 | 758篇 |
出版年
2023年 | 38篇 |
2022年 | 51篇 |
2021年 | 87篇 |
2020年 | 74篇 |
2019年 | 70篇 |
2018年 | 86篇 |
2017年 | 99篇 |
2016年 | 144篇 |
2015年 | 103篇 |
2014年 | 168篇 |
2013年 | 252篇 |
2012年 | 228篇 |
2011年 | 333篇 |
2010年 | 251篇 |
2009年 | 262篇 |
2008年 | 254篇 |
2007年 | 241篇 |
2006年 | 243篇 |
2005年 | 210篇 |
2004年 | 179篇 |
2003年 | 141篇 |
2002年 | 112篇 |
2001年 | 87篇 |
2000年 | 90篇 |
1999年 | 102篇 |
1998年 | 131篇 |
1997年 | 90篇 |
1996年 | 100篇 |
1995年 | 73篇 |
1994年 | 75篇 |
1993年 | 78篇 |
1992年 | 76篇 |
1991年 | 64篇 |
1990年 | 61篇 |
1989年 | 57篇 |
1988年 | 65篇 |
1987年 | 59篇 |
1986年 | 48篇 |
1985年 | 46篇 |
1984年 | 55篇 |
1983年 | 41篇 |
1982年 | 49篇 |
1981年 | 48篇 |
1980年 | 32篇 |
1979年 | 29篇 |
1978年 | 34篇 |
1977年 | 33篇 |
1976年 | 37篇 |
1975年 | 40篇 |
1973年 | 31篇 |
排序方式: 共有5557条查询结果,搜索用时 15 毫秒
71.
M. P. Murari R. Murari S. Parthasarathy C. A. Guy V. V. Kumar B. Malewicz Wolfgang J. Baumann 《Lipids》1990,25(10):606-612
Described is a reaction sequence for the total synthesis of lyso platelet activating factor (lysoPAF; 1-O-alkyl-sn-glycero-3-phosphocholine) and its enantiomer. The procedure is versatile and yields optically pure isomers of defined chain
length. The synthesis is equally suited for the preparation of lysoPAF analogues and its enantiomers with unsaturation in
the long aliphatic chain. First,rac-1(3)-O-alkylglycerol is prepared by alkylation ofrac-isopropylideneglycerol with alkyl methanesulfonate followed by acid-catalyzed removal of the ketal group. The primary hydroxy
group of alkylglycerol is then protected by tritylation, the secondary hydroxy group is acylated, and the protective trityl
group is removed under mild acidic conditions with boric acid on silicic acid, essentially without acyl migration. Condensation
of the diradylglycerol with bromoethyl dichlorophosphate in diethyl ether, hydrolysis of the resulting chloride, and nucleophilic
displacement of the bromine with trimethylamine givesrac-1-O-alkyl-2-acylglycero-3-phosphocholine in good overall yield. The racemic alkylacylglycerophosphocholine is finally treated
with snake venom phospholipase A2 (Ophiophagus hannah) which affords 1-O-alkyl-sn-glycero-3-phosphocholine (lysoPAF) of natural configuration in optically pure form. The “unnatural” 3-O-alkyl-2-O-acyl-sn-glycerol-1-phosphocholine enantiomer, which is not susceptible to phospholipase A2 cleavage, gives 3-O-alkyl-sn-glycero-1-phosphocholine upon deacylation with methanolic sodium hydroxide. Homogeneity and structure of the intermediates
and final products were ascertained by carbon-13 nuclear magnetic resonance spectroscopy on monomeric solutions. 相似文献
72.
Johannes Konnerth Andreas Jger Josef Eberhardsteiner Ulrich Müller Wolfgang Gindl 《应用聚合物科学杂志》2006,102(2):1234-1239
Seven different polymers used frequently as adhesives and/or matrix polymers in wood, wood composites, and natural fiber‐reinforced composites were studied by uniaxial tensile tests and nanoindentation. It was shown that the elastic modulus, the hardness, the creep factor, and the elastic‐, plastic‐, and viscoelastic work of indentation of the seven different polymers is essentially the same regardless whether the polymers were tested in the form of pure films or in situ, i.e., in an adhesive bond line with spruce wood. An excellent correlation was found between the elastic modulus measured by tensile tests and the elastic modulus measured by nanoindentation. In spite of the good correlation, the elastic modulus measured by nanoindentation is significantly higher than the elastic modulus measured by tensile tests. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:1234–1239, 2006 相似文献
73.
74.
Thomas Fehn Felix Kugler Beatrice Tübke Rainer Schweppe Phillip Mebert Wolfgang Krcmar Ulrich Teipel 《化学,工程师,技术》2021,93(5):771-780
Due to the growing energy requirements, the proportion of external thermal insulation composite systems (ETICS) installed has increased significantly during the past 50 years. Due to the longevity of these systems, ETICS waste is currently accumulating. Owing to the complex construction as well as a multitude of differently installed materials and substances of the past generations, there are many uncertainties and problems with the clean and low-pollutant processing of such systems. In the frame of this work, the ETICS were processed and sorted before being screened for ingredients or pollutants as well as for the purity of the recovered material fractions. 相似文献
75.
Silica gel or zeolites AlPO-5 and SAPO-34 are recommended as adsorbents in water-driven heat pumps because of their selective water uptake. Secondary energy, like solar energy, can be used for regeneration of loaded adsorbers. In case of the availability of only low energy levels, the use of dealuminated Y zeolite (DAY) is the better choice because of the infinitely variation of its hydrophilic properties by tailoring of the framework Si/Al ratio. Actual data on the hydrothermal stability of DAY are lacking. Thus, we report on the long-term behavior of DAY zeolites with different Si/Al ratios. 相似文献
76.
Chaudry Oliver Friedberger Andreas Grimm Alexandra Uder Michael Nagel Armin Michael Kemmler Wolfgang Engelke Klaus 《Magma (New York, N.Y.)》2021,34(3):367-376
Magnetic Resonance Materials in Physics, Biology and Medicine - To develop a precise semi-automated segmentation of the fascia lata (FL) of the thigh to quantify IMAT volume in T1w MR images and... 相似文献
77.
Wolfgang Tillmann Matthias Manka Lukas Wojarski Michael Holewa 《Science & Technology of Welding & Joining》2020,25(4):290-296
ABSTRACTTools for machining are exposed to high loads, wear, and elevated temperatures. Commonly, such tools consist of cemented carbides and tool steel. To combine the advantages of both materials, high-quality-joints with high strengths are desired. When brazing these materials, the main challenge is the mismatch of the Coefficient of Thermal Expansion (CTE) and the poor wettability of cemented carbides by molten filler alloys. In this regard, the feasibility of two custom-made alloys (CuNi12Si5, CuNi12Si5B0.4) was analysed. Besides being a cost-efficient alternative, these alloys offer the possibility to modify their mechanical properties by precipitation hardening to reduce stresses within the final joints. Thus, this paper shows that a temperature of 1060°C is suitable for wetting and brazing tests on different substrates. 相似文献
78.
Erika Leitel Wolfgang Hübner Karsten P. Thiessen Ju. B. Makari
ev A. G. Akimov 《工业材料与腐蚀》1988,39(1):1-7
Investigation into the passivation mechanism of iron in phosphate electrolytes on surfaces exposed to erosive attack On iron electrodes in neutral phosphate electrolytes by continuous solid particle impingement a reaction layer is formed within the transition potential region under anodic polarization. XPS and AES investigations show that the reaction layer formed under impingement will be replaced by an oxide layer during the transition into the passive state under simultaneous decrease of the layer thickness. The active/passive transition in phosphate electrolytes may be attached to the equilibrium potential of the reaction . According to this thermodynamic interpretation of both the active/passive transition and the passive/active transition, respectively on iron in presence of phosphate ions may be described as the Fe(II)/Fe(III)-redox reaction with two solid phases, the iron(II)-phosphate phase and the iron(III)-oxide phase. The increase of the interfacial dynamic processes at the solid/liquid interface causes in consequence of the solid particle impingement that thermodynamic laws govern the course of reactions. 相似文献
79.
Jan Behmann Kathrin Hendriksen Ute Müller Wolfgang Büscher Lutz Plümer 《GeoInformatica》2016,20(4):693-714
Tracking the spatio-temporal activity is highly relevant for domains like security, health, and quality management. Since animal welfare became a topic in politics and legislation locomotion patterns of livestock have received increasing interest. In contrast to the monitoring of pedestrians cattle activity tracking poses special challenges to both sensors and data analysis. Interesting states are not directly observable by a single sensor. In addition, sensors must be accepted by cattle and need to be robust enough to cope with a rough environment. In this article, we introduce the novel combination of heart rate and positioning sensors. Attached to neck and chest they are less interfering than accelerometers at the ankles. Exploiting the potential of such combined sensor system that records locomotion and non-spatial information from the heart rate sensor however is challenging. We introduce a novel two level method for the activity tracking focused on the duration and sequence of activity states. We combine Support Vector Machine (SVM) with Conditional Random Field (CRF) and extend Conditional Random fields by an explicit representation of duration. The SVM characterizes local activity states, whereas the CRF addresses sequences of local states to sequences incorporating spatial and non-spatial contextual knowledge. This combination provides a reliable and comprehensive identification of defined activity patterns, as well as their chronology and durations, suitable for the integration in an activity data base. This data base is used to extract physiological parameters and promises insights into internal states such as fitness, well-being and stress. Interestingly we were able to demonstrate a significant correlation between resting pulse rate and the day of pregnancy. 相似文献
80.