全文获取类型
收费全文 | 40039篇 |
免费 | 3978篇 |
国内免费 | 1914篇 |
专业分类
电工技术 | 2497篇 |
技术理论 | 3篇 |
综合类 | 2689篇 |
化学工业 | 6560篇 |
金属工艺 | 2207篇 |
机械仪表 | 2420篇 |
建筑科学 | 2972篇 |
矿业工程 | 1135篇 |
能源动力 | 1122篇 |
轻工业 | 2624篇 |
水利工程 | 778篇 |
石油天然气 | 2511篇 |
武器工业 | 379篇 |
无线电 | 4903篇 |
一般工业技术 | 4764篇 |
冶金工业 | 1786篇 |
原子能技术 | 404篇 |
自动化技术 | 6177篇 |
出版年
2024年 | 239篇 |
2023年 | 830篇 |
2022年 | 1519篇 |
2021年 | 2061篇 |
2020年 | 1527篇 |
2019年 | 1149篇 |
2018年 | 1366篇 |
2017年 | 1427篇 |
2016年 | 1180篇 |
2015年 | 1679篇 |
2014年 | 2158篇 |
2013年 | 2417篇 |
2012年 | 2734篇 |
2011年 | 2952篇 |
2010年 | 2618篇 |
2009年 | 2189篇 |
2008年 | 2325篇 |
2007年 | 2078篇 |
2006年 | 2019篇 |
2005年 | 1748篇 |
2004年 | 1137篇 |
2003年 | 960篇 |
2002年 | 932篇 |
2001年 | 806篇 |
2000年 | 798篇 |
1999年 | 964篇 |
1998年 | 759篇 |
1997年 | 594篇 |
1996年 | 565篇 |
1995年 | 470篇 |
1994年 | 390篇 |
1993年 | 259篇 |
1992年 | 238篇 |
1991年 | 174篇 |
1990年 | 129篇 |
1989年 | 99篇 |
1988年 | 86篇 |
1987年 | 52篇 |
1986年 | 47篇 |
1985年 | 37篇 |
1984年 | 31篇 |
1983年 | 28篇 |
1982年 | 23篇 |
1981年 | 22篇 |
1980年 | 23篇 |
1979年 | 12篇 |
1978年 | 12篇 |
1977年 | 11篇 |
1976年 | 8篇 |
1973年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
A novel milk-like Cu-thiourea colloid has been synthesized. Nanocrystalline quaternary copper sulfide Cu2FeSnS4 was obtained through the Cu-thiourea colloidal precursor cooperative conversion route at low temperature. The samples were characterized by means of X-ray powder diffraction, transmission electron microscopy, scanning electron microscopy, inductively coupled plasma atomic emission spectroscopy, and X-ray energy dispersive spectroscopy techniques. The reaction details and features were described and discussed. 相似文献
73.
移动代理计算模式较传统的分布式计算模式有明显的优势,而伴随它有诸多安全问题出现,这使得它没有得到十分广泛的应用。本文针对代理自身的安全问题,分析了代理可能受到的攻击,并提出了一个安全方案。 相似文献
74.
如何利用循环体诸如初值、终值、步长和下标式等数学对象的诸如恒等、正负、单调性一类的数学特征,按照严格推导出来的简单规则,绕过各种复杂的数据依赖关系图及其上诸如拓扑排序或等价变换等复杂的操作,直接从事向量化处理,这是极富实用价值的研究方向.文献[2,3,5]给出的可原形/准原形算法,以及本文的可反原形与拟离散性,正是这样的捷径.它们能使相当部分的常见循环,直接向量化. 相似文献
75.
Hinshaw Stephen P.; Carte Estol T.; Fan Catherine; Jassy Jonathan S.; Owens Elizabeth B. 《Canadian Metallurgical Quarterly》2007,21(2):263
The current study prospectively followed girls with attention-deficit/hyperactivity disorder (ADHD), along with a matched comparison sample, 5 years after childhood neuropsychological assessments. Follow-up neuropsychological measures emphasized attentional skills, executive functions, and language abilities. Paralleling childhood findings, the childhood-diagnosed ADHD group displayed moderate to large deficits in executive/attentional performance as well as in rapid naming relative to the comparison group at follow up (Mage 14.2 years). ADHD-inattentive versus ADHD-combined contrasts were nonsignificant and of negligible effect size, even when a refined, sluggish cognitive tempo subgroup of the inattentive type was examined. Although ADHD versus comparison group differences largely withstood statistical control of baseline demographics and comorbidities, control of childhood IQ reduced executive function differences to nonsignificance. Yet when the subset of girls meeting diagnostic criteria for ADHD in adolescence was compared with the remainder of the participants, neuropsychological deficits emerged even with full statistical control. Overall, childhood ADHD in girls portends neuropsychological and executive deficits that persist for at least 5 years. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
76.
77.
Ring‐opening polymerization of D,L ‐lactide (LA) has been successfully carried out by using rare earth 2,6‐dimethylaryloxide (Ln(ODMP)3) as single component catalyst or initiator for the first time. The effects of different rare earth elements, solvents, monomers and catalyst concentration as well as polymerization temperature and time on the polymerization were investigated. The results show that La(ODMP)3 exhibits higher activity to prepare poly(D,L ‐lactide) (PLA) with a viscosity molecular weight of 4.5 × 104 g mol?1 and the conversion of 97 % at 100 °C in 45 min. The catalytic activity of Ln(ODMP)3 has following sequence: La > Nd > Sm > Gd > Er > Y. A kinetic study has indicated that the polymerization is first order with respect to both monomer and catalyst concentration. The apparent activation energy of the polymerization of LA with La(ODMP)3 is 69.6 kJ mol?1. The analyses of polymer ends indicate that the LA polymerization proceeds according to ‘coordination–insertion’ mechanism with selective cleavage of the acyl–oxygen bond of the monomer. Copyright © 2004 Society of Chemical Industry 相似文献
78.
Hydrate formation rate plays an important role in making hydrates for the storage and transport of natural gas. Micellar surfactant solutions were found to increase gas hydrate formation rate and storage capacity. With the presence of surfactant, hydrate could form quickly in a quiescent system and the energy costs of hydrate formation reduced. Surfactants (an anionic surfactant, a non‐ionic surfactant and their mixtures) and liquid hydrocarbons (cyclopentane and methylcyclohexane) were used to improve hydrate formation. The experiments of hydrate formation were carried out in the pressure range 3.69–6.82 MPa and the temperature range 274.05–277.55 K. The experimental pressures were kept constant during hydrate formation in each experimental run. The effect of anionic surfactant (sodium dodecyl sulphate (SDS)) on natural gas storage in hydrates is more pronounced compared to a non‐ionic surfactant (dodecyl polysaccharide glycoside (DPG)). The induction time of hydrate formation was reduced with the presence of cyclopentane (CP). Cyclopentane and methylcyclohexane (MCH) could increase hydrate formation rate, but reduced hydrate storage capacity The higher methylcyclohexane concentration, the lower the hydrate storage capacity. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
79.
范锦忠 《墙材革新与建筑节能》2005,(9):22-24
本文结合国内外生产实践,介绍了陶粒混凝土复合保温板的构造、基本配方、物理力学性能、生产方法与工艺流程以及应用情况。 相似文献