全文获取类型
收费全文 | 357216篇 |
免费 | 27919篇 |
国内免费 | 15710篇 |
专业分类
电工技术 | 20877篇 |
技术理论 | 45篇 |
综合类 | 25380篇 |
化学工业 | 59628篇 |
金属工艺 | 20784篇 |
机械仪表 | 22456篇 |
建筑科学 | 27632篇 |
矿业工程 | 11680篇 |
能源动力 | 9699篇 |
轻工业 | 23998篇 |
水利工程 | 6746篇 |
石油天然气 | 23424篇 |
武器工业 | 2796篇 |
无线电 | 38777篇 |
一般工业技术 | 39357篇 |
冶金工业 | 18522篇 |
原子能技术 | 3626篇 |
自动化技术 | 45418篇 |
出版年
2024年 | 1456篇 |
2023年 | 5565篇 |
2022年 | 9866篇 |
2021年 | 13858篇 |
2020年 | 10437篇 |
2019年 | 8543篇 |
2018年 | 9851篇 |
2017年 | 11061篇 |
2016年 | 10134篇 |
2015年 | 13868篇 |
2014年 | 17453篇 |
2013年 | 20901篇 |
2012年 | 22695篇 |
2011年 | 25167篇 |
2010年 | 22250篇 |
2009年 | 21057篇 |
2008年 | 20639篇 |
2007年 | 19688篇 |
2006年 | 20052篇 |
2005年 | 17652篇 |
2004年 | 11960篇 |
2003年 | 10690篇 |
2002年 | 9892篇 |
2001年 | 8807篇 |
2000年 | 8754篇 |
1999年 | 9386篇 |
1998年 | 7175篇 |
1997年 | 6134篇 |
1996年 | 5812篇 |
1995年 | 4785篇 |
1994年 | 3886篇 |
1993年 | 2622篇 |
1992年 | 2072篇 |
1991年 | 1569篇 |
1990年 | 1233篇 |
1989年 | 996篇 |
1988年 | 830篇 |
1987年 | 524篇 |
1986年 | 410篇 |
1985年 | 258篇 |
1984年 | 206篇 |
1983年 | 164篇 |
1982年 | 128篇 |
1981年 | 76篇 |
1980年 | 96篇 |
1979年 | 43篇 |
1978年 | 17篇 |
1977年 | 23篇 |
1976年 | 28篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
81.
82.
Qing Li 《Computer Standards & Interfaces》1991,13(1-3):99-103
The term ‘object-oriented database’ has been used to refer to different characteristics and mechanisms supported by semantic databases and (behaviorally) object-oriented ones. While this indicates the current confusion due to the lack of a common model, it also suggests the potential desirability of combining these two kinds of modeling facilities into the same nutshell. This paper summarizes from these two paradigms the features common to both, the features influenced/adopted by each other, and the features which are presented in one paradigm but missing from the other. After a brief analysis and discussion of these features, we conclude this paper by proposing our major theme: a complete object data model should take the union of the facilities offered by these two kinds of models. 相似文献
83.
A 78-year-old Chinese woman presented with recurrent postprandial abdominal pain. Computerised tomography revealed a small bowel tumour causing volvulus of a segment of the small bowel. Laparotomy confirmed an extraluminal ileal tumour with partial volvulus of the involved small bowel segment. Small bowel resection was done. Histological and ultrastructural studies confirmed a gastrointestinal autonomic nerve tumour. We review the medical literature on this rare tumour. 相似文献
84.
Extracellular single-unit discharges were obtained from 165 spontaneously active neurons within the region of the rostral ventrolateral medulla (RVLM) by glass microelectrode from 89 brain slices of the Sprague-Dawley rats. The units could be divided into three types: regular (61.8%), irregular (24.2%) and silent (14%). Acetylcholine (ACh, 0.1, 0.3 mumol/L) showed four kinds of effects on spontaneous discharges of RVLM neurons: excitatory, inhibitory, biphasic and non-responsive, counting respectively 41.8%, 20%, 3% and 35.2% of the neurons tested. The excitatory effect of ACh was dose-dependent. The effects, either excitatory or inhibitory, of ACh (n = 49) were mostly blocked by atropine (0.3 mumol/L, n = 42). The excitatory effect of ACh (n = 14) could be blocked mainly by selective antagonist of M1 receptor, pirenzepine (PZ, 30 nmol/L, n = 9), but not by selective antagonist of M2 receptor, methoctramine (MT) and AFDX-116. The inhibitory effect of ACh (n = 10) could be blocked mostly by M2 receptor antagonist MT (30 nmol/L, n = 7); and this inhibitory effect (n = 9) could be blocked mostly by another M2 receptor antagonist AFDX-116 (30 nmol/L, n = 6), but not by M1 receptor antagonist PZ. 相似文献
85.
86.
烧成及热处理工艺对钛酸锶铅基热敏材料性能及显微结构的影响 总被引:3,自引:0,他引:3
研究了烧成及热处理工艺对钛酸锶铅基热敏材料的阻温特性及显微结构的影响。通过扫描电镜(SEM)和能量分散仪(EDAX)分析了材料的显微结构及不同形貌晶粒的成份。通过对组成、烧成及热处理工艺的控制,可得到具有V型PTCR特性的热敏材料。 相似文献
87.
Huai Wen-xin Wuhan University of Hydraulic & Electric Engineering Wuhan Hubei P.R.China Prof.Li Wei 《水动力学研究与进展(B辑)》1993,(3)
Turbulence represents an essential aspect in atmospheric and oceanic circulations.In particu-lar,it is a preponderant factor in the dispersion of pollutants of artificial or natural origin.Thevertical turbulent jets,plumes and buoyant jets discharging into static environment is one of themost important and basic flow patterns related with the environment pollution.These flows havenumerous important applications,for example,thrust augmentors,waste disposal plumes fromstacks and combustion systems,and significant problems of turbulent diffusion. 相似文献
88.
89.
报道了4,4′-硫代双[2-(1,1-二甲基乙基)-5一甲基苯酚]的合成方法及结构鉴定。 相似文献
90.