全文获取类型
收费全文 | 5027篇 |
免费 | 134篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 29篇 |
综合类 | 2篇 |
化学工业 | 798篇 |
金属工艺 | 62篇 |
机械仪表 | 65篇 |
建筑科学 | 92篇 |
矿业工程 | 4篇 |
能源动力 | 93篇 |
轻工业 | 171篇 |
水利工程 | 15篇 |
石油天然气 | 9篇 |
无线电 | 271篇 |
一般工业技术 | 586篇 |
冶金工业 | 2564篇 |
原子能技术 | 13篇 |
自动化技术 | 389篇 |
出版年
2023年 | 23篇 |
2022年 | 51篇 |
2021年 | 85篇 |
2020年 | 61篇 |
2019年 | 65篇 |
2018年 | 73篇 |
2017年 | 57篇 |
2016年 | 87篇 |
2015年 | 57篇 |
2014年 | 72篇 |
2013年 | 156篇 |
2012年 | 143篇 |
2011年 | 159篇 |
2010年 | 132篇 |
2009年 | 107篇 |
2008年 | 145篇 |
2007年 | 131篇 |
2006年 | 106篇 |
2005年 | 96篇 |
2004年 | 93篇 |
2003年 | 69篇 |
2002年 | 73篇 |
2001年 | 57篇 |
2000年 | 57篇 |
1999年 | 96篇 |
1998年 | 693篇 |
1997年 | 424篇 |
1996年 | 269篇 |
1995年 | 161篇 |
1994年 | 152篇 |
1993年 | 172篇 |
1992年 | 50篇 |
1991年 | 45篇 |
1990年 | 47篇 |
1989年 | 56篇 |
1988年 | 52篇 |
1987年 | 60篇 |
1986年 | 48篇 |
1985年 | 41篇 |
1984年 | 22篇 |
1983年 | 32篇 |
1982年 | 32篇 |
1981年 | 37篇 |
1980年 | 38篇 |
1978年 | 28篇 |
1977年 | 106篇 |
1976年 | 211篇 |
1975年 | 21篇 |
1974年 | 17篇 |
1973年 | 15篇 |
排序方式: 共有5163条查询结果,搜索用时 15 毫秒
1.
2.
Renal cell carcinoma may metastasize to the head and neck region at different stages of its evolution. We present a case of an undiagnosed renal cell carcinoma presenting as an ear polyp, and discuss the difficulties of the diagnosis and the management of these tumours. 相似文献
3.
The purpose of this study was to determine whether retention of fetal lung liquid is more prevalent in polyalveolar congenital lobar emphysema than in conventional congenital lobar emphysema. Two patients with congenital lobar emphysema were prospectively identified in a 3-year period. Twenty-five such patients were identified in a retrospective study covering 39 years. Medical records were available for 22 patients who had 23 emphysematous lobes. Both babies from the prospective study and six subjects from the retrospective group had respiratory symptoms and underwent chest X-ray in the first day of life. Six of the eight babies with respiratory symptoms and chest imaging in the first day of life had retention of fetal lung liquid in an emphysematous lobe. All six of these lobes were polyalveolar. The lobe in one child was a polyalveolar lobe but without retained fetal lung liquid, and one child exhibited conventional lobar emphysema also without retained fetal lung liquid. One polyalveolar lobe caused no neonatal symptoms and was not imaged until the child was 3 months old. No baby with conventional lobar emphysema was shown to have retained fetal lung liquid. There seems to be a correlation between polyalveolar lobe and onset of respiratory symptoms in the first day of life. Retention of fetal lung liquid within the affected lobe was documented only in cases of polyalveolar lobe. 相似文献
4.
5.
6.
A micromechanics analysis is performed for the determination of the five independent elastic moduli of unidirectional fiber composites. By considering viscoelastic phases and by using the correspondence principle and the inversion of the Laplace transform, the five time-dependent functions which characterize the effective behavior of viscoelastic composites are established. The predicted time-dependent behavior is applied for the analysis of viscoelastic laminated plates. The resulting viscoelastic effects are shown, and comparison between the results obtained within the classical laminated plate theory and the first-order shear deformation theory is discussed. 相似文献
7.
Jacob Hooker David Hinks Gerardo Montero Christopher Conlee 《Coloration Technology》2002,118(6):273-276
The synthesis of azo dyes via a conventional aqueous-based diazotisation and coupling reaction requires the use of relatively high concentrations of mineral acids, which leads to high electrolyte concentrations in wastewater. Reported in this paper is an environmentally benign one-pot method for the synthesis of a nonionic azo dye, N,N -diethyl- N -{4-[( E )-(4-nitrophenyl)diazenyl]phenyl}amine, in supercritical carbon dioxide without using a mineral acid. The product yield increased significantly with temperature, with 91% theoretical yield afforded at 80 °C. The pressure of the system had little influence on product yield. 相似文献
8.
Gibbs energies of formation of CoF2 and MnF2 have been measured in the temperature range from 700 to 1100 K using Al2O3-dispersed CaF2 solid electrolyte and Ni+NiF2 as the reference electrode. The dispersed solid electrolyte has higher conductivity than pure CaF2 thus permitting accurate measurements at lower temperatures. However, to prevent reaction between Al2O3 in the solid electrolyte and NiF2 (or CoF2) at the electrode, the dispersed solid electrolyte was coated with pure CaF2, thus creating a composite structure. The free energies of formation of CoF2 and MnF2 are (± 1700) J mol−1; {fx37-1} The third law analysis gives the enthalpy of formation of solid CoF2 as ΔH° (298·15 K) = −672·69 (± 0·1) kJ mol−1, which compares with a value of −671·5 (± 4) kJ mol−1 given in Janaf tables. For solid MnF2, ΔH°(298·15 K) = − 854·97 (± 0·13) kJ mol−1, which is significantly different from a value of −803·3 kJ mol−1 given in the compilation by Barinet al. 相似文献
9.
10.