全文获取类型
收费全文 | 18675篇 |
免费 | 1784篇 |
国内免费 | 900篇 |
专业分类
电工技术 | 1150篇 |
综合类 | 1301篇 |
化学工业 | 3309篇 |
金属工艺 | 808篇 |
机械仪表 | 956篇 |
建筑科学 | 1096篇 |
矿业工程 | 426篇 |
能源动力 | 727篇 |
轻工业 | 1717篇 |
水利工程 | 370篇 |
石油天然气 | 484篇 |
武器工业 | 99篇 |
无线电 | 2369篇 |
一般工业技术 | 2189篇 |
冶金工业 | 1647篇 |
原子能技术 | 254篇 |
自动化技术 | 2457篇 |
出版年
2024年 | 46篇 |
2023年 | 174篇 |
2022年 | 392篇 |
2021年 | 527篇 |
2020年 | 391篇 |
2019年 | 401篇 |
2018年 | 436篇 |
2017年 | 455篇 |
2016年 | 467篇 |
2015年 | 654篇 |
2014年 | 817篇 |
2013年 | 1160篇 |
2012年 | 1127篇 |
2011年 | 1173篇 |
2010年 | 1083篇 |
2009年 | 1030篇 |
2008年 | 1041篇 |
2007年 | 1019篇 |
2006年 | 949篇 |
2005年 | 778篇 |
2004年 | 726篇 |
2003年 | 840篇 |
2002年 | 1085篇 |
2001年 | 905篇 |
2000年 | 521篇 |
1999年 | 400篇 |
1998年 | 417篇 |
1997年 | 345篇 |
1996年 | 249篇 |
1995年 | 200篇 |
1994年 | 139篇 |
1993年 | 155篇 |
1992年 | 100篇 |
1991年 | 98篇 |
1990年 | 82篇 |
1989年 | 72篇 |
1988年 | 65篇 |
1987年 | 41篇 |
1986年 | 41篇 |
1985年 | 42篇 |
1984年 | 37篇 |
1983年 | 46篇 |
1982年 | 52篇 |
1981年 | 50篇 |
1980年 | 43篇 |
1979年 | 36篇 |
1977年 | 61篇 |
1976年 | 54篇 |
1975年 | 40篇 |
1972年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
Chun Lin Ma Qing Feng Wang Rufen Zhang Jikun Li 《Journal of Inorganic and Organometallic Polymers and Materials》2008,18(2):229-235
Six triorganotin(IV) complexes of the type {(R3Sn)2[C3S3(COO)2]}n (R = C6H5 1; n-Bu 2; PhCH2 4; p-F-PhCH2 5; o-F-PhCH2 6) and {(R3Sn)2[C3S3(COO)2]}n·[EtOH] (R = Me 3) have been synthesized by the reaction of bis(carboxymethyl)trithiocarbonate with triorganotin(IV) chloride
in the presence of sodium ethoxide. All complexes were characterized by elemental analysis IR, 1H, 13C and 119Sn NMR spectroscopy. Except for 4–6, all complexes were also characterized by X-ray crystallography. The X-ray date revealed
that complexes 1–3 show two-dimensional network polymeric structure in which the geometries of tin atoms are trigonal bipyramid
with the axial positions occupied by carboxylic oxygen atoms. 相似文献
122.
Learning and memory of novel spatial configurations aids behaviors such as visual search through an implicit process called contextual cuing (M. M. Chun & Y. Jiang, 1998). The present study provides rigorous tests of the implicit nature of contextual cuing. Experiment 1 used a recognition test that closely matched the learning task, confirming that memory traces of predictive spatial context were not accessible to conscious retrieval. Experiment 2 gave explicit instructions to encode visual context during learning, but learning was not improved and conscious memory remained undetectable. Experiment 3 illustrates that memory traces for spatial context may persist for at least 1 week, suggesting a long-term component of contextual cuing. These experiments indicate that the learning and memory of spatial context in the contextual cuing task are indeed implicit. The results have implications for understanding the neural substrate of spatial contextual learning, which may depend on an intact medial temporal lobe system that includes the hippocampus (M. M. Chun & E. A. Phelps, 1999). (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
123.
124.
125.
126.
概述了设计话带MODEM时所要考虑的基本问题。介绍了一种用通用DSP设计的MODEM,并讨论了相应的控制程序和调制,解调程序的设计方法和结构框图,而且设计了一个简单实用的握手协议。最后,进一步分析了这种MODEM的特点和它的应用前景。 相似文献
127.
H King MC McCulloch JA Barrie E Kyriakides CV Beechey BM Cattanach IR Griffiths 《Canadian Metallurgical Quarterly》1997,26(8):557-566
Animals with spontaneous mutations affecting myelin formation have provided useful information about the genetic and cellular mechanisms regulating normal and abnormal myelination. In this paper we describe a novel murine mutation termed hindshaker (hsh), which is inherited in an autosomal recessive manner. Affected mice are characterised by a variable tremor of the hind end which commences at about 2 weeks of age and largely disappears in animals older than 6 weeks. There is hypomyelination affecting predominantly the spinal cord, although the optic nerves and brain are involved to a much lesser degree. The defect of thinly myelinated and naked axons is maximal at 20 days of age and largely resolves with time so that in the adult most axons are myelinated. The myelin structure appears normal and immunostains for the major proteins. Although the distribution of oligodendrocytes in the spinal cord is similar to normal during the period of hypomyelination, there are fewer mature cells. The hsh mutation appears to delay the maturation of oligodendrocytes, particularly in the spinal cord. Additionally, there is a considerable variation in phenotypic expression and in penetrance when the mutation is expressed on different genetic backgrounds, suggesting the hsh locus is subject to the influence of modifying gene(s). Identification of the hsh gene should identify a factor important in the development of oligodendrocytes, particularly those in the spinal cord. 相似文献
128.
H Wakasaki D Koya FJ Schoen MR Jirousek DK Ways BD Hoit RA Walsh GL King 《Canadian Metallurgical Quarterly》1997,94(17):9320-9325
Increased cardiovascular mortality occurs in diabetic patients with or without coronary artery disease and is attributed to the presence of diabetic cardiomyopathy. One potential mechanism is hyperglycemia that has been reported to activate protein kinase C (PKC), preferentially the beta isoform, which has been associated with the development of micro- and macrovascular pathologies in diabetes mellitus. To establish that the activation of the PKCbeta isoform can cause cardiac dysfunctions, we have established lines of transgenic mice with the specific overexpression of PKCbeta2 isoform in the myocardium. These mice overexpressed the PKCbeta2 isoform transgene by 2- to 10-fold as measured by mRNA, and proteins exhibited left ventricular hypertrophy, cardiac myocyte necrosis, multifocal fibrosis, and decreased left ventricular performance without vascular lesions. The severity of the phenotypes exhibited gene dose-dependence. Up-regulation of mRNAs for fetal type myosin heavy chain, atrial natriuretic factor, c-fos, transforming growth factor, and collagens was also observed. Moreover, treatment with a PKCbeta-specific inhibitor resulted in functional and histological improvement. These findings have firmly established that the activation of the PKCbeta2 isoform can cause specific cardiac cellular and functional changes leading to cardiomyopathy of diabetic or nondiabetic etiology. 相似文献
129.
130.
The factors leading to the success or failure of IT implementations by accountants are investigated in a health service situation. Tbe case study adopts the participant observation methodology and the factors observed are classified as motivators and demotivators. Using a project dependent definition of success, a catastrophe theory framework is used to describe the outcome of the combined influence of these factors. Four particular IT projects are discussed and the factors observed include: the influence of higher levels in the organizational hierarchy, some systems characteristics, the seduction of technology, external pressures, the 'rate of change', skills shortage and reliability. By comparing the examples described with features mentioned by other authors, it is noted that some factors appear to be generally applicable, whereas others may be context dependent. 相似文献