全文获取类型
收费全文 | 19502篇 |
免费 | 494篇 |
国内免费 | 17篇 |
专业分类
电工技术 | 225篇 |
综合类 | 14篇 |
化学工业 | 2527篇 |
金属工艺 | 231篇 |
机械仪表 | 335篇 |
建筑科学 | 893篇 |
矿业工程 | 42篇 |
能源动力 | 452篇 |
轻工业 | 1938篇 |
水利工程 | 261篇 |
石油天然气 | 28篇 |
无线电 | 1703篇 |
一般工业技术 | 2372篇 |
冶金工业 | 6228篇 |
原子能技术 | 142篇 |
自动化技术 | 2622篇 |
出版年
2023年 | 65篇 |
2022年 | 84篇 |
2021年 | 262篇 |
2020年 | 135篇 |
2019年 | 199篇 |
2018年 | 266篇 |
2017年 | 246篇 |
2016年 | 271篇 |
2015年 | 252篇 |
2014年 | 387篇 |
2013年 | 658篇 |
2012年 | 676篇 |
2011年 | 916篇 |
2010年 | 636篇 |
2009年 | 663篇 |
2008年 | 697篇 |
2007年 | 672篇 |
2006年 | 566篇 |
2005年 | 552篇 |
2004年 | 505篇 |
2003年 | 469篇 |
2002年 | 427篇 |
2001年 | 343篇 |
2000年 | 319篇 |
1999年 | 464篇 |
1998年 | 2223篇 |
1997年 | 1330篇 |
1996年 | 891篇 |
1995年 | 520篇 |
1994年 | 507篇 |
1993年 | 504篇 |
1992年 | 208篇 |
1991年 | 206篇 |
1990年 | 203篇 |
1989年 | 197篇 |
1988年 | 200篇 |
1987年 | 137篇 |
1986年 | 135篇 |
1985年 | 188篇 |
1984年 | 140篇 |
1983年 | 100篇 |
1982年 | 112篇 |
1981年 | 115篇 |
1980年 | 92篇 |
1979年 | 92篇 |
1978年 | 80篇 |
1977年 | 157篇 |
1976年 | 206篇 |
1975年 | 78篇 |
1974年 | 70篇 |
排序方式: 共有10000条查询结果,搜索用时 546 毫秒
111.
A semi-empirical mathematical model for the acid-oxygen pressure leaching of Ni–Cu matte is presented, based on data from batch leaching experiments. The primary controlling factor in the leaching process is found to be galvanic inhibition of the more highly oxidized copper and nickel sulfide species by less oxidized species, particularly Ni alloy and Ni3S2. The leaching rate of many species is greatly reduced by the presence of one or both of these phases, and others will not commence leaching until neither is present. The mathematical model is based on first-order chemical reaction controlled rate expressions, as the reactions occurring are electrochemical in nature. Mass transfer effects are included only empirically. Some possibly diffusion-related phenomena are noted, although the model is not extended to incorporate these effects on a fundamental level. The model is verified and extended by the inclusion of several different factors that were tested experimentally. The effects of variations in O2 flow rate and partial pressure, initial particle size, reaction pulp density and initial acid concentration were all studied, and included in the model. Variations in O2 flow rate and partial pressure are found to affect the reaction rates via the dissolved oxygen concentration in the solution phase. 相似文献
112.
We introduce optical local-area network (LAN) architectures based on multimode optical fiber and components, short wavelength lasers and detectors, and the widely used fast Ethernet protocol. These architectures are designed to lower the costs associated with passive optical LAN implementation. Further reduction in overall cost is achieved through decreased network downtime, lower maintenance cost, extended geometrical spans, and larger headroom for future capacity increase. These optically transparent networks represent a novel approach for implementing fiber-to-the-desk. 相似文献
113.
The crystal structure of CaMgGeO4 is described. CaMgGeO4, Mr = 200.9, orthorhombic, Pnam, A = 11.285(5) Å, B = 5.016(2) Å, C = 6.435(2) Å, V = 364.36 Å3, Dx = 3.664 Mg/m3.λ(MoKa = 0.71069 Å, F(000) = 384, room temperature, final R = 0.045 for 1752 observed reflections. The structure is isomorphous with CaMgSiO4 (monticellite). 相似文献
114.
Bushman Brad J.; Bonacci Angelicca M.; van Dijk Mirjam; Baumeister Roy F. 《Canadian Metallurgical Quarterly》2003,84(5):1027
Laboratory analog studies investigated the theory that narcissism and reactance contribute to causing rape. In Study 1, narcissism correlated positively with rape-supportive beliefs and negatively with empathy for rape victims. In Study 2, narcissists reported more enjoyment than other men of film depictions that presented consensual, affectionate activity followed by rape (but not in response to either affection or rape alone). In Study 3, narcissists were more punitive than other men toward a female confederate who refused to read a sexually arousing passage aloud to them. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
115.
116.
117.
118.
S Delorme A Dietz V Rudat I Zuna ML Bahner G van Kaick 《Canadian Metallurgical Quarterly》1997,23(9):1311-1317
This summary of the practice parameters describes the assessment, differential diagnosis, and treatment of children, adolescents, and adults who present with symptoms of attention-deficit/hyperactivity disorder. The rationales for specific recommendations are based on a review of the scientific literature and clinical consensus which is contained in the complete document. Assessment includes clinical interviews with the child and parents and standardized rating scales from parent and teachers. Testing of intelligence and academic achievement is usually required. Comorbidity is common. The cornerstones of treatment are support and education of parents, appropriate school placement, and psychopharmacology. The primary medications are psychostimulants, but antidepressants and alpha-adrenergic agonists are used in special circumstances. Other treatments such as behavior modification, school consultation, family therapy, and group therapy address remaining symptoms. 相似文献
119.
One hundred years ago, on 1 May 1898, the Netherlands Orthopaedic Association was founded. This was prompted by the view that general surgeons paid insufficient attention to the treatment of the locomotor system; they were permitted to join the new association, however, at any rate until 1947. It was especially in the last 30 years that orthopaedic surgery underwent major changes. The most striking novelty was arthroplastic surgery. There have also been developments in the treatment of spinal abnormalities, rheumatological surgery, sports medicine, oncology and traumatology. 相似文献
120.
Fundus reflection densitometry or retinal densitometry is a non-invasive technique to examine the visual photopigment kinetics in living eyes. The technique is based on the comparison of the reflected light from the fundus in a fully light adapted eye (when all visual photopigment has been bleached) with the reflected light following complete dark adaptation (when the retina contains its maximum amount of visual photopigment). The technique provides a measure of the density of visual photopigment, its time constant of regeneration, its distribution and spectral characteristics if measured at a series of wavelengths. Fundus reflection densitometry in the human eye was introduced 40 years ago. Presently, it is the only available technique from which direct and objective insight can be obtained into visual photopigment. This knowledge is particularly relevant in eyes where abnormalities of photoreceptor function are suspected. This paper summarizes the current knowledge of fundus reflection densitometry in the diseased and in the aging human retina, gathered over the last 30 years. Considerable improvements of the instrument for clinical purposes have been obtained, and are also discussed. 相似文献