全文获取类型
收费全文 | 753篇 |
免费 | 29篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 7篇 |
化学工业 | 176篇 |
金属工艺 | 22篇 |
机械仪表 | 11篇 |
建筑科学 | 50篇 |
矿业工程 | 1篇 |
能源动力 | 46篇 |
轻工业 | 51篇 |
水利工程 | 3篇 |
石油天然气 | 1篇 |
无线电 | 59篇 |
一般工业技术 | 146篇 |
冶金工业 | 83篇 |
原子能技术 | 14篇 |
自动化技术 | 114篇 |
出版年
2022年 | 4篇 |
2021年 | 9篇 |
2020年 | 6篇 |
2019年 | 15篇 |
2018年 | 12篇 |
2017年 | 21篇 |
2016年 | 10篇 |
2015年 | 18篇 |
2014年 | 30篇 |
2013年 | 27篇 |
2012年 | 33篇 |
2011年 | 57篇 |
2010年 | 44篇 |
2009年 | 46篇 |
2008年 | 43篇 |
2007年 | 38篇 |
2006年 | 43篇 |
2005年 | 35篇 |
2004年 | 28篇 |
2003年 | 20篇 |
2002年 | 23篇 |
2001年 | 15篇 |
2000年 | 17篇 |
1999年 | 19篇 |
1998年 | 16篇 |
1997年 | 10篇 |
1996年 | 18篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 8篇 |
1992年 | 12篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1986年 | 4篇 |
1985年 | 8篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 2篇 |
1975年 | 7篇 |
1973年 | 3篇 |
1972年 | 3篇 |
1906年 | 2篇 |
排序方式: 共有784条查询结果,搜索用时 15 毫秒
101.
Hansson J Båth M Håkansson M Grundin H Bjurklint E Orvestad P Kjellström A Boström H Jönsson M Jonsson K Månsson LG 《Radiation protection dosimetry》2005,114(1-3):278-285
The aim of this study was to find the optimum tube voltage for neonatal chest imaging in computed radiography. The study was designed to take full advantage of the benefits of digital imaging, for example, by comparing the tube voltages at constant effective dose. A phantom study using a living rabbit was first conducted. Images were collected at tube voltages ranging from 40 to 90 kV(p). The reproduction of four structures (central vessels, peripheral vessels, carina and thoracic vertebrae) was rated by 10 radiologists. The reproduction of both central and peripheral vessels was relatively independent of tube voltage. The carina was better reproduced at higher tube voltages whereas the opposite was true for the thoracic vertebrae. Based on the higher importance of the reproduction of the carina it was decided that 90 kV(p) was the optimal tube voltage. To validate the result from the phantom study, a follow-up study was conducted in which images of neonates collected at the tube voltage regularly used at Sahlgrenska University Hospital (70 kV(p)) were compared with images collected at the tube voltage proposed by the phantom study. The follow-up study confirmed the results from the phantom study that the reproduction of the carina was better at 90 than at 70 kV(p). In conclusion, for neonatal chest imaging-given the same effective dose-90 kVp gives better reproduction of important structures than the regularly used 70 kV(p). 相似文献
102.
103.
Wadman MW van Zadelhoff G Hamberg M Visser T Veldink GA Vliegenthart JF 《Lipids》2005,40(11):1163-1170
Oxylipins are associated with important processes of the fungal life cycle, such as spore formation. Here, we report the formation
of FA metabolites in Agaricus bisporus. Incubation of a crude extract of lamellae with linoleic acid (18∶2) led to the extensive formation of two oxylipins. They
were identified as 8(R)-hydroxy-9Z,12Z-octadecadienoic acid (8-HOD) and 8(R),11(S)-dihydroxy-9Z,12Z-octadecadienoic acid (8,11-diHOD) by using RP-HPLC, GC-MS, IR, GC-MS analysis of diastereomeric derivatives, and 1H NMR and 13C NMR spectroscopy. Neither compound has been reported before in A. bisporus. Oleic (18∶1), α-linolenic (18∶3n−3), and γ-linolenic (18∶3n−6) acids were converted into their 8-hydroxy derivatives as
well, and 18∶3n−3 was further metabolized to its 8,11-diol derivative. Reactions with [U-13C]18∶2 demonstrated that the compounds 8-HOD and 8,11-diHOD were formed from exogenously supplied 18∶2. When [U-13C]8-HOD was supplied, it was not converted into 8,11-diHOD, indicating that it was not an intermediate in the formation of
8,11-diHOD. When a crude extract of A. bisporus was incubated under an atmosphere of 16O2/18O2, the two hydroxyl groups of 8,11-diHOD contained either two 18O atoms or two 16O atoms. Species that contained one of each isotope could not be detected. We propose that the formation of the 8,11-dihydroxy
compounds occurs through either an 8,11-endoperoxy, an 8-peroxo free radical, or an 8-hydroperoxy intermediate. In the latter
case, the reaction should be catalyzed by dioxygenase with novel specificity. 相似文献
104.
Mass spectrometry in metabolome analysis 总被引:12,自引:0,他引:12
105.
106.
107.
Passive chilled beams are often used to provide cooling or additional cooling when the ventilation system cannot cope with the whole cooling load. The advantage of passive cooling is that it is a silent cooling. Often the chilled beams are installed above a false ceiling and thereby the room is subdivided into two compartments. From the chilled beam a plume is generated. Make-up air (return air) needs to flow into the upper compartment to substitute the airflow generated by the chilled beam. Therefore openings for this purpose are installed in the false ceiling. Small openings constitute a resistance to the flow and the locations of the openings affect the flow pattern. The overall performance was studied in a mock-up of a real office by changing both the size and position of the openings for the make-up air. A uniform heating source was arranged by covering the floor with a heating foil. The best location and size of the openings were explored by both recording the heat absorbed by the beam and the temperature in the room. Minimum temperature attained in the room is the signature of the most efficient cooling. To achieve efficient cooling with a uniform floor-based heating source, two conditions must be fulfilled: a) the return opening area must be at least equal to the horizontal area of the chilled beam; b) the return air openings must be located at the perimeter of the room. 相似文献
108.
Fusarium oxysporum f. sp. tulipae (FOT) secretes (+)-7-iso-jasmonoyl-(S)-isoleucine ((+)-JA-Ile) to the growth medium together with about 10 times less 9,10-dihydro-(+)-7-iso-JA-Ile. Plants and fungi form (+)-JA-Ile from 18:3n-3 via 12-oxophytodienoic acid (12-OPDA), which is formed sequentially by 13S-lipoxygenase, allene oxide synthase (AOS), and allene oxide cyclase (AOC). Plant AOC does not accept linoleic acid (18:2n-6)-derived allene oxides and dihydrojasmonates are not commonly found in plants. This raises the question whether 18:2n-6 serves as the precursor of 9,10-dihydro-JA-Ile in Fusarium, or whether the latter arises by a putative reductase activity operating on the n-3 double bond of (+)-JA-Ile or one of its precursors. Incubation of pentadeuterated (d5) 18:3n-3 with mycelia led to the formation of d5-(+)-JA-Ile whereas d5-9,10-dihydro-JA-Ile was not detectable. In contrast, d5-9,10-dihydro-(+)-JA-Ile was produced following incubation of [17,17,18,18,18-2H5]linoleic acid (d5-18:2n-6). Furthermore, 9(S),13(S)-12-oxophytoenoic acid, the 15,16-dihydro analog of 12-OPDA, was formed upon incubation of unlabeled or d5-18:2n-6. Appearance of the α-ketol, 12-oxo-13-hydroxy-9-octadecenoic acid following incubation of unlabeled or [13C18]-labeled 13(S)-hydroperoxy-9(Z),11(E)-octadecadienoic acid confirmed the involvement of AOS and the biosynthesis of the allene oxide 12,13(S)-epoxy-9,11-octadecadienoic acid. The lack of conversion of this allene oxide by AOC in higher plants necessitates the conclusion that the fungal AOC is distinct from the corresponding plant enzyme. 相似文献
109.
110.
Kim Bini Desta Gedefaw Caroline Pan Jonas M. Bjuggren Anirudh Sharma Ergang Wang Mats R. Andersson 《应用聚合物科学杂志》2019,136(27):47729
An easily accessible anthraquinone-benzodithiophene-based high bandgap polymer (PTAq) was synthesized by Stille coupling reactions in remarkably high yield (96.5%). The highest occupied molecular orbital energy level of the polymer was estimated from the onset of oxidation in a cyclic voltammetry study to be −5.7 eV. PTAq showed an orange-to-green color switching with the application of a 1.0-V external potential to the polymer film, which was visible to the naked eye. The optical behavior change was also monitored using ultraviolet–visible absorption spectroscopy and revealed a respectable 75% transmittance change when the polymer film was subjected to a 1.0-V external potential. The high color contrast observed makes PTAq one of the most promising materials for electrochromic device applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47729. 相似文献