全文获取类型
收费全文 | 285154篇 |
免费 | 5984篇 |
国内免费 | 1885篇 |
专业分类
电工技术 | 5845篇 |
技术理论 | 5篇 |
综合类 | 1321篇 |
化学工业 | 46177篇 |
金属工艺 | 11671篇 |
机械仪表 | 8292篇 |
建筑科学 | 7266篇 |
矿业工程 | 1796篇 |
能源动力 | 6002篇 |
轻工业 | 29173篇 |
水利工程 | 3093篇 |
石油天然气 | 6108篇 |
武器工业 | 255篇 |
无线电 | 29051篇 |
一般工业技术 | 53755篇 |
冶金工业 | 53421篇 |
原子能技术 | 5754篇 |
自动化技术 | 24038篇 |
出版年
2021年 | 2967篇 |
2020年 | 2065篇 |
2019年 | 2454篇 |
2018年 | 4135篇 |
2017年 | 4063篇 |
2016年 | 4473篇 |
2015年 | 3498篇 |
2014年 | 5381篇 |
2013年 | 12895篇 |
2012年 | 8868篇 |
2011年 | 11351篇 |
2010年 | 9128篇 |
2009年 | 9643篇 |
2008年 | 10533篇 |
2007年 | 10602篇 |
2006年 | 9130篇 |
2005年 | 7983篇 |
2004年 | 7103篇 |
2003年 | 6608篇 |
2002年 | 6586篇 |
2001年 | 6608篇 |
2000年 | 6186篇 |
1999年 | 6252篇 |
1998年 | 14808篇 |
1997年 | 10715篇 |
1996年 | 8088篇 |
1995年 | 6036篇 |
1994年 | 5481篇 |
1993年 | 5312篇 |
1992年 | 4086篇 |
1991年 | 3897篇 |
1990年 | 3946篇 |
1989年 | 3909篇 |
1988年 | 3655篇 |
1987年 | 3156篇 |
1986年 | 3165篇 |
1985年 | 3595篇 |
1984年 | 3483篇 |
1983年 | 3220篇 |
1982年 | 2809篇 |
1981年 | 3057篇 |
1980年 | 2793篇 |
1979年 | 2942篇 |
1978年 | 2830篇 |
1977年 | 3037篇 |
1976年 | 4116篇 |
1975年 | 2532篇 |
1974年 | 2360篇 |
1973年 | 2419篇 |
1972年 | 2015篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
Y.K. Yang F.L. Liu Y.W. Zhang M.F. Li F. Ling H.T. Wu 《Ceramics International》2018,44(11):12238-12244
In this work, ultra-low loss Li2MgTi0.7(Mg1/3Nb2/3)0.3O4 ceramics were successfully prepared via the conventional solid-state method. X-ray photoelectron spectroscopy (XPS), thermally stimulated depolarization current (TSDC) and bond energy were used to determine the distinction between intrinsic and extrinsic dielectric loss in (Mg1/3Nb2/3)4+ ions substituted ceramics. The addition of (Mg1/3Nb2/3)4+ ions enhances the bond energy in unit cell without changing the crystal structure of Li2MgTiO4, which results in high Q·f value as an intrinsic factor. The extrinsic factors such as porosity and grain size influence the dielectric loss at lower sintering temperature, while the oxygen vacancies play dominant role when the ceramics densified at 1400?°C. The Li2MgTi0.7(Mg1/3Nb2/3)0.3O4 ceramics sintered at 1400?°C can achieve an excellent combination of microwave dielectric properties: εr =?16.19, Q·f?=?160,000?GHz and τf =??3.14?ppm/°C. In addition, a certain amount of LiF can effectively lower the sintering temperature of the matrix, and the Li2MgTi0.7(Mg1/3Nb2/3)0.3O4-3?wt% LiF ceramics sintered at 1100?°C possess balanced properties with εr?=?16.32, Q·f?=?145,384?GHz and τf =??16.33?ppm/°C. 相似文献
142.
143.
Freddy A. Bernal Dr. Marcel Kaiser Prof. Dr. Bernhard Wünsch Prof. Dr. Thomas J. Schmidt 《ChemMedChem》2020,15(1):68-78
Protozoal infections are still a global health problem, threatening the lives of millions of people around the world, mainly in impoverished tropical and sub-tropical regions. Thus, in view of the lack of efficient therapies and increasing resistances against existing drugs, this study describes the antiprotozoal potential of synthetic cinnamate ester analogues and their structure-activity relationships. In general, Leishmania donovani and Trypanosoma brucei were quite susceptible to the compounds in a structure-dependent manner. Detailed analysis revealed a key role of the substitution pattern on the aromatic ring and a marked effect of the side chain on the activity against these two parasites. The high antileishmanial potency and remarkable selectivity of the nitro-aromatic derivatives suggested them as promising candidates for further studies. On the other hand, the high in vitro potency of catechol-type compounds against T. brucei could not be extrapolated to an in vivo mouse model. 相似文献
144.
145.
146.
A new constitutive equation of thermoelasticity for crystals is presented based on the interatomic potential and solid mechanics at finite temperature. Using the new constitutive equation, the calculations for crystal copper and graphene are carried out under different loading paths at different temperatures. The calculated results are in good agreement with those of the previous thermoelasticity constitutive equation based on quantum mechanics, which clearly indicates that our new constitutive equation of thermoelasticity is correct. A lot of comparisons also show that the present theory is more concise and efficient than the previous thermal stress theory in the practical application. 相似文献
147.
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
148.
149.
150.
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