全文获取类型
收费全文 | 328667篇 |
免费 | 5684篇 |
国内免费 | 968篇 |
专业分类
电工技术 | 5566篇 |
综合类 | 415篇 |
化学工业 | 54094篇 |
金属工艺 | 12880篇 |
机械仪表 | 9433篇 |
建筑科学 | 8131篇 |
矿业工程 | 1980篇 |
能源动力 | 7834篇 |
轻工业 | 32484篇 |
水利工程 | 3505篇 |
石油天然气 | 7314篇 |
武器工业 | 28篇 |
无线电 | 33488篇 |
一般工业技术 | 63491篇 |
冶金工业 | 59783篇 |
原子能技术 | 7783篇 |
自动化技术 | 27110篇 |
出版年
2021年 | 3243篇 |
2019年 | 2779篇 |
2018年 | 4901篇 |
2017年 | 4731篇 |
2016年 | 5169篇 |
2015年 | 3607篇 |
2014年 | 5667篇 |
2013年 | 14624篇 |
2012年 | 8957篇 |
2011年 | 11656篇 |
2010年 | 9459篇 |
2009年 | 10551篇 |
2008年 | 10812篇 |
2007年 | 10518篇 |
2006年 | 9175篇 |
2005年 | 8416篇 |
2004年 | 7759篇 |
2003年 | 7385篇 |
2002年 | 7389篇 |
2001年 | 7070篇 |
2000年 | 6711篇 |
1999年 | 6883篇 |
1998年 | 17478篇 |
1997年 | 12736篇 |
1996年 | 9767篇 |
1995年 | 7251篇 |
1994年 | 6527篇 |
1993年 | 6377篇 |
1992年 | 4692篇 |
1991年 | 4657篇 |
1990年 | 4449篇 |
1989年 | 4502篇 |
1988年 | 4422篇 |
1987年 | 3770篇 |
1986年 | 3761篇 |
1985年 | 4395篇 |
1984年 | 4155篇 |
1983年 | 3785篇 |
1982年 | 3560篇 |
1981年 | 3737篇 |
1980年 | 3596篇 |
1979年 | 3485篇 |
1978年 | 3546篇 |
1977年 | 4173篇 |
1976年 | 5548篇 |
1975年 | 3241篇 |
1974年 | 3078篇 |
1973年 | 3127篇 |
1972年 | 2687篇 |
1971年 | 2512篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.
202.
203.
204.
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
205.
206.
207.
208.
Özge Seçmeler Özlem Güçlü Üstündağ 《International Journal of Food Science & Technology》2019,54(5):1609-1616
The partitioning of predominant lipophilic olive bioactives (squalene, β-sitosterol and α-tocopherol) in olive oil processing was studied for the first time using common integrated olive milling plant. 7% of the oil and 5% of the squalene present in the olives was lost in the last pomace. β-sitosterol and α-tocopherol, which are mainly concentrated in the seed of the olive fruit, was recovered in virgin olive oil to a lesser extent (66%, 67%) while 10% were lost in last pomace. Thus, the loss of β-sitosterol and α-tocopherol was higher than that of squalene and oil, due to nonrecovered bound forms. 19% of the α-tocopherol and 21% of the β-sitosterol loss was unaccounted for, which can be attributed to degradation of α-tocopherol and incomplete recovery of sterols from the olive and pomace matrices. This study provides a basis for process development studies. 相似文献
209.
Serdar Akbayrak Yalçın Tonbul Saim Özkar 《International Journal of Hydrogen Energy》2021,46(27):14259-14269
Herein, we report the use of tungsten(VI) oxide (WO3) as support for Rh0 nanoparticles. The resulting Rh0/WO3 nanoparticles are highly active and stable catalysts in H2 generation from the hydrolysis of ammonia borane (AB). We present the results of our investigation on the particle size distribution, catalytic activity and stability of Rh0/WO3 catalysts with 0.5%, 1.0%, 2.0% wt. Rh loadings in the hydrolysis reaction. The results reveal that Rh0/WO3 (0.5% wt. Rh) is very promising catalyst providing a turnover frequency of 749 min?1 in releasing 3.0 equivalent H2 per mole of AB from the hydrolysis at 25.0 °C. The high catalytic activity of Rh0/WO3 catalyst is attributed to the reducible nature of support. The report covers the results of kinetics study as well as comparative investigation of activity, recyclability, and reusability of colloidal(0) nanoparticles and Rh0/WO3 (0.5 % wt. Rh) catalyst in the hydrolysis reaction. 相似文献
210.
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