全文获取类型
收费全文 | 41199篇 |
免费 | 1773篇 |
国内免费 | 158篇 |
专业分类
电工技术 | 509篇 |
综合类 | 250篇 |
化学工业 | 7527篇 |
金属工艺 | 859篇 |
机械仪表 | 810篇 |
建筑科学 | 1818篇 |
矿业工程 | 140篇 |
能源动力 | 1277篇 |
轻工业 | 4846篇 |
水利工程 | 401篇 |
石油天然气 | 202篇 |
武器工业 | 7篇 |
无线电 | 3114篇 |
一般工业技术 | 6442篇 |
冶金工业 | 8765篇 |
原子能技术 | 294篇 |
自动化技术 | 5869篇 |
出版年
2023年 | 218篇 |
2022年 | 626篇 |
2021年 | 1010篇 |
2020年 | 693篇 |
2019年 | 776篇 |
2018年 | 943篇 |
2017年 | 978篇 |
2016年 | 1036篇 |
2015年 | 796篇 |
2014年 | 1242篇 |
2013年 | 2223篇 |
2012年 | 1890篇 |
2011年 | 2454篇 |
2010年 | 1830篇 |
2009年 | 1828篇 |
2008年 | 1842篇 |
2007年 | 1698篇 |
2006年 | 1371篇 |
2005年 | 1409篇 |
2004年 | 1397篇 |
2003年 | 1199篇 |
2002年 | 1253篇 |
2001年 | 974篇 |
2000年 | 810篇 |
1999年 | 758篇 |
1998年 | 2269篇 |
1997年 | 1531篇 |
1996年 | 1100篇 |
1995年 | 824篇 |
1994年 | 659篇 |
1993年 | 723篇 |
1992年 | 376篇 |
1991年 | 358篇 |
1990年 | 362篇 |
1989年 | 310篇 |
1988年 | 316篇 |
1987年 | 273篇 |
1986年 | 247篇 |
1985年 | 316篇 |
1984年 | 256篇 |
1983年 | 172篇 |
1982年 | 182篇 |
1981年 | 184篇 |
1980年 | 159篇 |
1979年 | 143篇 |
1978年 | 116篇 |
1977年 | 165篇 |
1976年 | 259篇 |
1975年 | 104篇 |
1973年 | 71篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Mark Parsons Tony Allen 《今日电子》2006,(4):44-45
对于绝大多数微控制器时钟电路而言,硅振荡器是一种简单且有效的解决方案。与晶体和陶瓷谐振器不同,基于硅材料的定时器具有抗振动、抗撞击和抗电磁干扰的优点。同时,硅振荡器不需要严格匹配的定时元件和线路板走线。 相似文献
62.
Shanchieh Jay Yang Gustavo de Veciana 《Networking, IEEE/ACM Transactions on》2004,12(2):349-360
With a view on improving user-perceived performance on networks supporting best effort flows, e.g., multimedia/data file transfers, we propose a family of bandwidth allocation criteria that depends on the residual work of on-going transfers. Analysis and simulations show that allocating bandwidth in this fashion can significantly improve the user-perceived delay, bit transmission delay, and throughput over traditional approaches, e.g., by 58% on an 80% loaded linear network. A simple implementation based on TCP Reno, exemplifies how one might approach practically realizing such gains. We discuss several other advantages of incorporating such differentiation at the transport level. In particular we make the case that favoring small transfers combined with user impatience or peak rate constraints, both of which are natural mechanisms for users to express the utility of completing transfers, offers a lightweight approach to achieving good overall network goodput and/or utility for best effort networks. 相似文献
63.
A General Role for Early Onset Cues and Intra-Event Learning; Comment on McDonald and Siegel (2004).
Research on classical conditioning with drug unconditional stimuli has had a profound effect on the understanding of general conditioning processes. The experiment reported by R. V. McDonald and S. Siegel (see record 2004-10475-001) demonstrates that cues coincident with the onset of an event can become associated with the rest of the event. This sort of learning is probably ubiquitous and has been proposed as a mechanism behind the development of panic disorder, in which interoceptive cues coincident with the start of a panic attack can be associated with the rest of the attack and can eventually come to elicit full-blown panic on their own. Evidence that extinction exposure to early onset cues can reduce their power is especially important. Drug conditioning research continues to provide a powerful testing ground for important general principles of learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
64.
65.
66.
67.
MA Molina MJ Romero E Abril I Delgado RM Cano F Garrido JM de Pablos ML Garrido 《Canadian Metallurgical Quarterly》1994,39(4):253-256
INTRODUCTION: Heterozygous beta-thalassemia manifests hematologically with microcytosis, reduced red blood cell hemoglobin concentration and high hemoglobin A2 levels. Almost all molecular alterations are due to point mutations. We attempt to determinate the frequency of that mutations in the Oriental Andalusia Area, and its relationship with the hematological phenotype. PATIENTS AND METHODS: We have studied 45 heterozygous patients. DNA samples were amplified by PCR, using the printers CD7 and HI1. A 16 Kb fragment corresponding to beta globin gene was obtained and analyzed by Dot Blot assay and hybridized with allelic specific oligonucleotide (ASO) probes to detect the 6 more frequent mutations found in the South of Spain. RESULTS: Codon 39 nonsense mutation (31.1%) was the most frequent finding followed by IVS-1 NT 110 (26.7%). The relationship between hematological parameters and molecular mutations concluded that IVS-I NT 6 mutation developed a minimal anemia. DISCUSSION: From the practical point of view, this study indicates that we were able to detect more than 90% of heterozygous beta-tal. with 5 out of 6 ASO probes used in this work. Thus, our data also provides a further implication in prenatal diagnosis. 相似文献
68.
JJ Jiménez-Nácher N de Alonso B Vega A del Río JL Moya V Barrios A Hurtado 《Canadian Metallurgical Quarterly》1993,193(6):290-292
Pericardial effusion (PE) as a hypothyroidism associated sign, is something that can be found with relative frequency; nevertheless, cardiac tamponade (CT) as the first sign of this disease may be considered exceptional especially in young patients. We report a 31 years old woman with clinical symptoms and signs of CT that in the forward workshop was diagnosed of primary hypothyroidism as cause of the CT. We shortly describe the case and review the literature, emphasizing the importance of the knowledge of CT trigger factors in myxedematous PE, as well as its usual benign evolution with hormonal treatment, without recurrences of the CT after pericardiocentesis is performed. This justify a conservative approach, in spite of the slow resolution of the PE what can take as long as 1.5 years. 相似文献
69.
Daniela M. Nevskaia Maria Luisa Rojas Cervantes Antonio Guerrero Ruíz Juan de Dios Lpez Gonzlez 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1995,63(3):249-256
Adsorption of Triton X-100 on various silica substrates has been investigated. A number of solids, including a natural quartz, this quartz washed with HCl acid and subsequently heated at 1273 K; two aerosils and one Kieselgel silicas were studied. These solids exhibit surface areas in the range of 5 to 430 m2 g?1. All the Triton adsorption isotherms display an S-shape at the adsorption temperatures studied (298 and 308 K). It has been found that the pretreatments of natural quartz (by water washing, impurities removed by acid and/or high temperature calcination) affect considerably the amounts of TX-100 adsorbed. Measurements of surface composition have been made by X-ray photoelectron spectroscopy (XPS) with particular emphasis on the presence of impurities and on the number of OH groups at the surface of the samples. The nature of the surface hydroxyl has also been studied by infrared spectroscopy. Furthermore, the specific number of hydroxyl groups on the surface of the silica samples has been determined by thermogravimetric analysis. Finally an attempt to correlate solid surface characteristics with adsorption isotherms has been developed. 相似文献
70.