全文获取类型
收费全文 | 528684篇 |
免费 | 8096篇 |
国内免费 | 1466篇 |
专业分类
电工技术 | 9599篇 |
综合类 | 527篇 |
化学工业 | 79135篇 |
金属工艺 | 20013篇 |
机械仪表 | 15254篇 |
建筑科学 | 12811篇 |
矿业工程 | 2285篇 |
能源动力 | 14585篇 |
轻工业 | 47337篇 |
水利工程 | 5253篇 |
石油天然气 | 9349篇 |
武器工业 | 37篇 |
无线电 | 60360篇 |
一般工业技术 | 102266篇 |
冶金工业 | 105161篇 |
原子能技术 | 10583篇 |
自动化技术 | 43691篇 |
出版年
2022年 | 3178篇 |
2021年 | 4924篇 |
2020年 | 3504篇 |
2019年 | 4602篇 |
2018年 | 7858篇 |
2017年 | 7640篇 |
2016年 | 7967篇 |
2015年 | 5589篇 |
2014年 | 9292篇 |
2013年 | 24233篇 |
2012年 | 14701篇 |
2011年 | 20270篇 |
2010年 | 15897篇 |
2009年 | 17782篇 |
2008年 | 18223篇 |
2007年 | 17906篇 |
2006年 | 15612篇 |
2005年 | 14301篇 |
2004年 | 13679篇 |
2003年 | 13473篇 |
2002年 | 12711篇 |
2001年 | 12921篇 |
2000年 | 11933篇 |
1999年 | 12688篇 |
1998年 | 33210篇 |
1997年 | 23150篇 |
1996年 | 17613篇 |
1995年 | 13177篇 |
1994年 | 11421篇 |
1993年 | 11104篇 |
1992年 | 7979篇 |
1991年 | 7465篇 |
1990年 | 7325篇 |
1989年 | 7090篇 |
1988年 | 6524篇 |
1987年 | 5826篇 |
1986年 | 5710篇 |
1985年 | 6334篇 |
1984年 | 5955篇 |
1983年 | 5219篇 |
1982年 | 4943篇 |
1981年 | 5002篇 |
1980年 | 4755篇 |
1979年 | 4652篇 |
1978年 | 4444篇 |
1977年 | 5400篇 |
1976年 | 7116篇 |
1975年 | 3833篇 |
1974年 | 3579篇 |
1973年 | 3695篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
291.
292.
N. Bartsch M. Girard A. Wilde T. Bruhn O. Kappenstein B. Vieth C. Hutzler A. Luch 《乙烯基与添加剂工艺杂志》2019,25(Z2):E12-E27
The thermo‐oxidative stability of widely used polymer additives has been investigated. A comparative analytical approach with classic and innovative decomposition models for polymer additives was conducted and the results supported using quantum‐chemical calculations. Unique pyrolysis products of the analytes were compiled utilizing pyrolysis online coupled to gas chromatography followed by mass spectrometric detection (Pyr‐GC–MS). The pyrolysis was either performed under inert conditions or in an oxygen‐containing atmosphere. Squalane was applied as polymer‐mimicking liquid next to low density polyethylene (LDPE) and polyamide 6 (PA 6) as matrices for 10 selected additives. The additives included in this study range from antioxidants and plasticizers to processing aids. These were selected to address a range of application in consumer products and to cover different chemical classes. The toxicological relevance of additives and potential breakdown products was considered. Consequently, degradation of sterically hindered antioxidants, diarylamines, and a trimellitic acid derivative was investigated. The findings were used to predict the behavior of consumer products made of polymeric materials entailing additives. The level of Antioxidant 2246 [2‐tert‐butyl‐6‐[(3‐tert‐butyl‐2‐hydroxy‐5‐methylphenyl)methyl]‐4‐methylphenol] and one of its predicted decomposition products was determined in baby bottle nipples made of natural rubber [2‐tert‐butyl‐4‐methylphenol] utilizing the complementary technique of gas chromatography coupled to tandem mass spectrometry (GC–MS/MS). This study provides a comprehensive characterization of important polymer additives and enables the prioritization of degradation products for further risk assessment. J. VINYL ADDIT. TECHNOL., 25:E12–E27, 2019. © 2018 The Authors. Journal of Vinyl and Additive Technology published by Wiley Periodicals, Inc. on behalf of Society of Plastics Engineers 相似文献
293.
C. Busuioc C.D. Ghitulica A. Stoica M. Stroescu G. Voicu V. Ionita L. Averous S.I. Jinga 《Ceramics International》2018,44(8):9433-9441
Bacterial cellulose membranes were employed as templates for calcium phosphates deposition by successive immersion in solutions of Ca(NO3)2·4H2O and (NH4)2HPO4, under ultrasonication. During the wet chemical reaction, mineral phases were loaded on bacterial cellulose fibrils, leading to precursor hybrid composites. These were subjected to a lyophilisation procedure in order to preserve the 3D porous aspect and afterwards to a thermal treatment with the aim of removing the polymeric phase and generating well crystallized structures. Different types of morphologies were achieved by varying the heating rate, as well as the calcination temperature and period. The as-prepared samples and the final ones were investigated from compositional and structural point of view through X-ray diffraction and Fourier-transform infrared spectroscopy and morphologically concerning by scanning electron microscopy. The magnetic properties were also evaluated in order to demonstrate the suitability of the obtained materials for the development of magnetic scaffolds dedicated to hard tissue applications. 相似文献
294.
Silicon - Thin film nanocomposites of sodium silicate (80 SiO2 –20 Na2O)/ tartrazine dye (E102) prepared using sol gel process in acidic system. The change in the physicochemical properties... 相似文献
295.
Radiochemistry - The study deals with separation of uranium, thorium, and yttrium with highest possible purity from El-Garaa El-Hamara sulfate leach liquor. From the latter, almost complete... 相似文献
296.
297.
298.
Wyatt L. Brown Douglas A. Day Harald Stark Demetrios Pagonis Jordan E. Krechmer Xiaoxi Liu Derek J. Price Erin F. Katz Peter F. DeCarlo Catherine G. Masoud Dongyu S. Wang Lea Hildebrandt Ruiz Caleb Arata David M. Lunderberg Allen H. Goldstein Delphine K. Farmer Marina E. Vance Jose L. Jimenez 《Indoor air》2021,31(1):141-155
Understanding the sources and composition of organic aerosol (OA) in indoor environments requires rapid measurements, since many emissions and processes have short timescales. However, real-time molecular-level OA measurements have not been reported indoors. Here, we present quantitative measurements, at a time resolution of five seconds, of molecular ions corresponding to diverse aerosol-phase species, by applying extractive electrospray ionization mass spectrometry (EESI-MS) to indoor air analysis for the first time, as part of the highly instrumented HOMEChem field study. We demonstrate how the complex spectra of EESI-MS are screened in order to extract chemical information and investigate the possibility of interference from gas-phase semivolatile species. During experiments that simulated the Thanksgiving US holiday meal preparation, EESI-MS quantified multiple species, including fatty acids, carbohydrates, siloxanes, and phthalates. Intercomparisons with Aerosol Mass Spectrometer (AMS) and Scanning Mobility Particle Sizer suggest that EESI-MS quantified a large fraction of OA. Comparisons with FIGAERO-CIMS shows similar signal levels and good correlation, with a range of 100 for the relative sensitivities. Comparisons with SV-TAG for phthalates and with SV-TAG and AMS for total siloxanes also show strong correlation. EESI-MS observations can be used with gas-phase measurements to identify co-emitted gas- and aerosol-phase species, and this is demonstrated using complementary gas-phase PTR-MS observations. 相似文献
299.
Technical Physics Letters - Possible designs of a terahertz laser that use the effect of Bloch oscillations in SiC natural superlattices have been considered. It has been proposed to use as a... 相似文献
300.
V. A. Grechishnikov Yu. E. Petukhov P. M. Pivkin A. V. Isaev V. B. Romanov V. A. Kosarev A. S. Babaev A. A. Ershov 《Russian Engineering Research》2020,40(1):70-72
The shaping of the toroidal cutting section of end mills is considered. Methods are devised for selecting the positional parameters in shaping the helical rake surface on the toroidal section. Relations are established between the geometric parameters of the end mill in the toroidal section. 相似文献