全文获取类型
收费全文 | 864869篇 |
免费 | 11830篇 |
国内免费 | 2212篇 |
专业分类
电工技术 | 15978篇 |
综合类 | 769篇 |
化学工业 | 133786篇 |
金属工艺 | 33939篇 |
机械仪表 | 26873篇 |
建筑科学 | 21327篇 |
矿业工程 | 4981篇 |
能源动力 | 22332篇 |
轻工业 | 75027篇 |
水利工程 | 9245篇 |
石油天然气 | 16385篇 |
武器工业 | 52篇 |
无线电 | 99031篇 |
一般工业技术 | 170313篇 |
冶金工业 | 154919篇 |
原子能技术 | 18473篇 |
自动化技术 | 75481篇 |
出版年
2021年 | 7284篇 |
2019年 | 6984篇 |
2018年 | 11867篇 |
2017年 | 12119篇 |
2016年 | 12806篇 |
2015年 | 8528篇 |
2014年 | 14187篇 |
2013年 | 40333篇 |
2012年 | 22687篇 |
2011年 | 31245篇 |
2010年 | 24885篇 |
2009年 | 27807篇 |
2008年 | 28784篇 |
2007年 | 28676篇 |
2006年 | 25190篇 |
2005年 | 22935篇 |
2004年 | 22170篇 |
2003年 | 21625篇 |
2002年 | 20908篇 |
2001年 | 20568篇 |
2000年 | 19421篇 |
1999年 | 19706篇 |
1998年 | 45582篇 |
1997年 | 33205篇 |
1996年 | 25980篇 |
1995年 | 20155篇 |
1994年 | 18116篇 |
1993年 | 17624篇 |
1992年 | 13515篇 |
1991年 | 12956篇 |
1990年 | 12727篇 |
1989年 | 12300篇 |
1988年 | 11811篇 |
1987年 | 10411篇 |
1986年 | 10169篇 |
1985年 | 11941篇 |
1984年 | 11025篇 |
1983年 | 10085篇 |
1982年 | 9259篇 |
1981年 | 9298篇 |
1980年 | 8883篇 |
1979年 | 8930篇 |
1978年 | 8627篇 |
1977年 | 9824篇 |
1976年 | 12700篇 |
1975年 | 7578篇 |
1974年 | 7248篇 |
1973年 | 7208篇 |
1972年 | 6116篇 |
1971年 | 5599篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
991.
992.
Auld B.A. Chimenti D.E. Shull P.J. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1996,43(2):319-325
The transverse resonance approach to guided wave analysis is applied to shear horizontal (SH) wave propagation in periodically layered composites. It is found for SH waves that at high values of the guided wavevector β, the wave energy is trapped in the slower of the two media and propagates accordingly at the slower wavespeed. At low values of β, however, the modes demonstrate a clustering behavior, indicative of the underlying Floquet wave structure. The number of modes in a cluster is observed to correlate with the number of unit cells in the layered plate. New physical insights into the behavior of these systems are obtained by analyzing the partial waves of the guided SH modes in terms of Floquet waves. We show that the fast and slow shear waves in the periodically layered composite play an analogous role to the longitudinal and shear partial waves comprising Lamb waves in a homogeneous plate 相似文献
993.
994.
995.
A 3-wave longitudinal design was used to examine the relationships among emotional restraint, peer drug associations, and gateway drug use in a sample of 1,256 middle school students. Structural equation modeling was used to compare 3 models: (1) One model viewed drug use as a consequence of emotional restraint and peer variables; (2) 1 viewed drug use as a cause of restraint and peer variables; and (3) 1 included reciprocal effects. All 3 models fit the data fairly well. However, the reciprocal model fit the data significantly better than either of the others. Within this model, low emotional restraint was significantly related to subsequent increases in gateway drug use among boys. In contrast, peer drug models and peer pressure were not related to subsequent changes in gateway drug use. Changes in peer drug models were, however, predicted by previous levels of gateway drug use. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
996.
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
997.
998.
Data from the past few years have shown that as caffeine metabolizes solely in the liver, caffeine elimination can serve as a liver function test. We have collected data by monitoring 40 persons with liver diseases (11 chronic alcoholic hepatitis, 24 liver cirrhosis, 5 non-cirrhotic liver disease). Eight subjects served as controls. The patients with liver cirrhosis were classified according to the Child--Pugh scoring system. To determine caffeine elimination blood samples were collected before and at 3, 6, 9 and 12 hours after oral administration of 0.2 g caffeine. Fasting serum caffeine concentration and concentration 12 hours after administration, serum clearance, half life, peak concentration and volume of distribution have been compared. The respective values measured in patients with non-cirrhotic liver diseases did not differ significantly from the controls. The disappearance of caffeine was significantly decreased in cirrhotics. Our results demonstrated a good correlation between impairment of caffeine elimination and assessment of severity of liver disease by the Child--Pugh classification. Measuring serum levels in samples taken 12 hours after caffeine administration is a simple and useful method in the diagnosis of liver diseases at cirrhotic stage. 相似文献
999.
J Valls-Solé A Cruz Martinez F Graus A Saiz J Arpa JM Grau 《Canadian Metallurgical Quarterly》1995,45(11):2024-2028
Two patients exhibited chronic, slightly asymmetric weakness and wasting with fasciculations of the upper limb and hand muscles. Motor nerve conduction studies showed features of multifocal conduction block in nerve segments other than those usually involved in entrapment syndromes. The F wave was markedly delayed in the median and ulnar nerves. Transcranial cortical and cervical root magnetic stimulation showed bilaterally delayed thenar responses with normal central conduction time. Needle electromyography demonstrated a chronic denervation pattern with large polyphasic motor units in several muscles of the upper limbs. Sensory symptoms were mild and limited to paresthesias in the fingertips. Sensory nerve conduction velocity and sensory nerve action potential amplitudes were normal in elbow-to-wrist and wrist-to-finger segments of the median and ulnar nerves, but there was a delayed cortical response and unrecognizable Erb's point and cervical responses in the somatosensory evoked potentials to median nerve electrical stimulation. Electrophysiologic examination was normal in most nerves of the lower limbs. These two patients, meeting clinical and electrophysiologic criteria of multifocal neuropathy with conduction block, demonstrate that sensory fibers may also be involved in this syndrome. 相似文献
1000.
G García-Bermúdez H Somacal MA Cardona A Filevich E Achterberg L Szybisz 《Canadian Metallurgical Quarterly》1995,51(3):1181-1191