全文获取类型
收费全文 | 42173篇 |
免费 | 541篇 |
国内免费 | 790篇 |
专业分类
电工技术 | 724篇 |
综合类 | 52篇 |
化学工业 | 6378篇 |
金属工艺 | 3094篇 |
机械仪表 | 1386篇 |
建筑科学 | 863篇 |
矿业工程 | 151篇 |
能源动力 | 1429篇 |
轻工业 | 2265篇 |
水利工程 | 356篇 |
石油天然气 | 1386篇 |
无线电 | 3976篇 |
一般工业技术 | 10667篇 |
冶金工业 | 7218篇 |
原子能技术 | 788篇 |
自动化技术 | 2771篇 |
出版年
2021年 | 342篇 |
2020年 | 276篇 |
2019年 | 373篇 |
2018年 | 665篇 |
2017年 | 657篇 |
2016年 | 743篇 |
2015年 | 539篇 |
2014年 | 807篇 |
2013年 | 2388篇 |
2012年 | 1405篇 |
2011年 | 1884篇 |
2010年 | 1489篇 |
2009年 | 1781篇 |
2008年 | 1624篇 |
2007年 | 1768篇 |
2006年 | 1400篇 |
2005年 | 1226篇 |
2004年 | 1178篇 |
2003年 | 1078篇 |
2002年 | 1066篇 |
2001年 | 1119篇 |
2000年 | 964篇 |
1999年 | 999篇 |
1998年 | 2115篇 |
1997年 | 1657篇 |
1996年 | 1440篇 |
1995年 | 983篇 |
1994年 | 757篇 |
1993年 | 774篇 |
1992年 | 597篇 |
1991年 | 572篇 |
1990年 | 524篇 |
1989年 | 485篇 |
1988年 | 369篇 |
1987年 | 402篇 |
1986年 | 364篇 |
1985年 | 381篇 |
1984年 | 305篇 |
1983年 | 300篇 |
1982年 | 301篇 |
1981年 | 296篇 |
1980年 | 349篇 |
1979年 | 341篇 |
1978年 | 294篇 |
1977年 | 415篇 |
1976年 | 629篇 |
1975年 | 308篇 |
1974年 | 292篇 |
1973年 | 311篇 |
1972年 | 272篇 |
排序方式: 共有10000条查询结果,搜索用时 13 毫秒
141.
142.
143.
A simple electrical network is used to represent the five differential equations describing basic phenomena in one-dimensional semiconductor devices. Both standard and integrated approaches for solving transport equations are developed. Also, an electrical network equivalent for the nonlinear Poisson equation was derived. It allows students to better understand the physical phenomena and the process of computer simulation of such semiconductor devices 相似文献
144.
The effects of epithelial removal and cyclooxygenase inhibition on contractions induced by exogenous acetylcholine (ACh) and electrical field stimulation (EFS) were evaluated in horse tracheal strips and bronchial rings. Epithelial removal potentiated the response to ACh but had no influence on the response to EFS. The effect of epithelial removal was not altered by pretreating the tissues with meclofenamate, a cyclooxygenase inhibitor. In trachealis strips, meclofenamate augmented contractions induced by EFS but not by ACh. In bronchial rings, meclofenamate augmented EFS-induced contraction to a greater extent than ACh-induced contraction. These effects of meclofenamate were epithelium-independent. We conclude that horse airway epithelium produces a relaxant factor that is not a prostanoid. Endogenous prostanoids originating from non-epithelial sites inhibit only cholinergic nerves in the trachea but both parasympathetic nerves and smooth muscle in the bronchi. 相似文献
145.
Z Bujas-Petkovi? 《Canadian Metallurgical Quarterly》1993,115(1-2):60-62
This paper describes Asperger's syndrome, a disease similar to the autistic disorder, delineated for the first time by Asperger in 1944, just a few months after L. Kanner described infantile autism. Although, according to the epidemiological data, it occurs far more frequently than infantile autism, in practice this diagnosis is rarely established. Asperger's syndrome is defined as autistic syndrome among children with relatively high degree of intellectual functions, with marked disorder of speech and motoricity and interest confined to a very specified area. Learning is mechanical and routine and games uninventive. Children lack the need for age peer company. Boys are affected ten times more frequently than girls. 相似文献
146.
147.
148.
The purpose of this study was to evaluate the changes in condylar position following bilateral sagittal split ramus osteotomy with 5- and 10-mm setback in 1 symmetric human cadaver mandibles. A Plexiglas device was constructed to determine the mandibular morphology and the movements of the condyle and the proximal segments before and after surgery. There was no statistically significant relationship between mandibular morphology or the magnitude of setback and changes in condylar position postsurgery. All condyles and rami tipped in a highly variable fashion in the coronal plane. In the axial plane, the lateral pole of the condyles rotated predominantly anteriorly; the left side rotated significantly more than did the right. In the sample studied, the position of the condylar and proximal segments was altered in a highly variable and unpredictable manner, regardless of the magnitude of setback or the morphology of the mandible. 相似文献
149.
The main maturation stages of Norway rat megakaryocytic series, megakaryoblasts and mature megakaryocytes, stained by silver for demonstration of argyrophil nucleolus organizer regions (AgNORs) were investigated to provide basic information on the number of nucleoli and interphasic AgNORs in these cells. The results showed that megakaryoblasts as well as mature megakaryocytes possess numerous nucleoli; their number and also the number of AgNORs is significantly higher in less mature than in more mature cells. The number of AgNORs in megakaryocytes of the Norway rat and man are virtually the same, although the numbers of nucleolar organizers per haploid chromosome set differ markedly. This fact leads to the conclusion that the number of interphasic AgNORs depends on the function and metabolic state of the cell rather than on the number of nucleolar organizers. 相似文献
150.