全文获取类型
收费全文 | 1443篇 |
免费 | 28篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 70篇 |
综合类 | 3篇 |
化学工业 | 385篇 |
金属工艺 | 29篇 |
机械仪表 | 31篇 |
建筑科学 | 17篇 |
矿业工程 | 1篇 |
能源动力 | 49篇 |
轻工业 | 155篇 |
水利工程 | 4篇 |
石油天然气 | 2篇 |
无线电 | 108篇 |
一般工业技术 | 221篇 |
冶金工业 | 257篇 |
原子能技术 | 43篇 |
自动化技术 | 100篇 |
出版年
2023年 | 12篇 |
2022年 | 23篇 |
2021年 | 19篇 |
2020年 | 11篇 |
2019年 | 23篇 |
2018年 | 27篇 |
2017年 | 17篇 |
2016年 | 25篇 |
2015年 | 20篇 |
2014年 | 34篇 |
2013年 | 91篇 |
2012年 | 51篇 |
2011年 | 49篇 |
2010年 | 45篇 |
2009年 | 47篇 |
2008年 | 59篇 |
2007年 | 56篇 |
2006年 | 46篇 |
2005年 | 64篇 |
2004年 | 34篇 |
2003年 | 33篇 |
2002年 | 32篇 |
2001年 | 27篇 |
2000年 | 27篇 |
1999年 | 36篇 |
1998年 | 111篇 |
1997年 | 66篇 |
1996年 | 59篇 |
1995年 | 34篇 |
1994年 | 24篇 |
1993年 | 24篇 |
1992年 | 20篇 |
1991年 | 14篇 |
1990年 | 13篇 |
1989年 | 12篇 |
1988年 | 13篇 |
1987年 | 12篇 |
1986年 | 11篇 |
1985年 | 10篇 |
1984年 | 22篇 |
1983年 | 17篇 |
1982年 | 12篇 |
1981年 | 8篇 |
1980年 | 16篇 |
1979年 | 3篇 |
1978年 | 17篇 |
1977年 | 12篇 |
1976年 | 16篇 |
1973年 | 9篇 |
1971年 | 3篇 |
排序方式: 共有1475条查询结果,搜索用时 0 毫秒
991.
A medium-band speech coder is proposed that uses a weighted vector quantization scheme in the transformed domain. The linear prediction residue is transformed and vector-quantized. In order to control the quantization errors in the transformed domain, adaptively weighted matching is used instead of conventional adaptive bit allocation. Therefore, the residual signal can be reconstructed by the decoder, even if the spectral envelope parameters are destroyed due to transmission errors. This coder is also capable of maintaining higher SNR (signal-to-noise ratio) performance than time-domain vector quantization coders for a wide range of computation complexities and bit rates. Coded speech is natural and unaffected by background noise. The mean opinion score for this coder at 7.2 kb/s is comparable to that of 5.5-bit log PCM coded speech sampled at 6.4 kHz 相似文献
992.
Transmission power cables are heated by conductor current. The morphology of the XLPE insulation may be changed by thermal aging. Disk-shaped insulating materials with semiconductive electrodes were used to understand this thermal effect against the dielectric breakdown strengths. The disk specimens were aged at 80 and 100°C before the breakdown strength measurements. These results showed that the dielectric breakdown strengths were improved with aging time. Analytical investigation of the insulating materials indicated that there were morphological changes such as increases of the lamella thickness and the spherulite diameter and decrease of the averaged lamella angle through heating. Cable specimens aged thermally with the same condition as the risk specimens also were observed with similar morphological changes in the insulation. Therefore it is concluded that the promotion of the crystallization by thermal aging is effective in improving the breakdown strength of the XLPE insulation unless it causes extreme deterioration. 相似文献
993.
994.
Unselected 580 male and 779 female junior and senior high school students were subjected to the tilting test and informations on 11 autonomic dysregulation symptoms and complaints were taken by interviews. Results of the analyses of the data are summarized as follows: 1) Number of symptoms and complaints possessed by each individual distributes continuously but nonrandomly among testees; that is, individuals having no symptom and those having 5 or more symptoms are significantly more numerous than those expected from random distribution, indicating accumulation of the symptoms into some individuals. 2) Some specific symptoms tend to coincide with each other. 3) Principal component analyses disclosed that the first principal component can explain only 16-20% of the observed variation in the presence or absence of symptoms and complaints, suggesting that numerous factors are responsible for the occurrence of the symptoms. 4) Measurements of the blood pressures and the pulse rate, and their responses to the postural change show continuous, normal distributions, and significantly correlate to each other. 5) The responses to the tilting test are increased with the increase of number of symptoms and complaints possessed by the testees. 相似文献
995.
O Hirashima H Ogawa S Oshima T Sakamoto Y Honda S Sakata T Masuda Y Miyao H Yasue 《Canadian Metallurgical Quarterly》1995,130(5):933-939
The fibrinolytic system is impaired in patients with acute myocardial infarction (AMI). The primary regulatory element of fibrinolytic activity is plasminogen activator inhibitor (PAI). There are no reports, however, on the serial changes of PAI activity after thrombolysis or coronary angioplasty in patients with AMI undergoing emergency coronary angiography. This study was designed to examine the difference in the change of fibrinolytic activity between patients with AMI who underwent thrombolytic therapy with recombinant tissue-plasminogen activator (rTPA) and those who underwent direct percutaneous coronary angioplasty (PTCA). We measured the serial changes of PAI activity and tissue plasminogen activator (TPA) antigen after rTPA therapy or direct PTCA. Twenty-two patients received emergency coronary angiography and were treated with rTPA intravenously. Twenty patients underwent direct PTCA. Plasma PAI activity levels were increased on admission and further increased within 24 hours in patients treated with rTPA and in those treated with direct PTCA. In the thrombolysis group, there were two peaks in plasma PAI activity levels (IU/ml) at 4 hours (27.0 +/- 2.9) and at 16 hours (25.6 +/- 2.5) after the initiation of rTPA infusion. However, in the direct PTCA group, there was one peak of PAI activity (IU/ml) at 16 hours (23.9 +/- 2.7) after the initiation of direct PTCA. In conclusion, the PAI activity has two peaks in the thrombolysis group and one peak in the direct PTCA group. 相似文献
996.
997.
The influence of organic sulfur compounds and metals on the texture of the mesophase formed in pitch during the carbonization process was investigated by the addition of organic sulfur compounds and organometallic compounds to the cracked oil obtained from Khafji asphalt and polyvinyl chloride (PVC) pitch. These pitches, containing sulfur and metals, have been examined by polarised light microscopy, and quinoline insolubles (QI), sulfur and metal contents were determined. The existence of either organic sulfur compounds or organometallic compounds in the pitch has no effect on mesophase texture. However, the coexistence of sulfur and metals (such as vanadium or nickel) has a great effect on mesophase texture. From these results, sulfur and metals coexisting in the pitch have a catalytic effect which activates the thermal decomposition and the thermal polymerization reactions of the pitch. Furthermore, the precursors of mesophase (β resin) are formed abundantly in the pitch by these reactions. These precursors promote the nucleation of mesophase spherules, and a large number of mesophase spherules are formed in the pitch at the same time. Therefore, these spherules coalesce with each other before growing to large spheres and lead to a fine mosaic texture. 相似文献
998.
Chikahisa Honda Katsunori Muraoka Tadasu Takuma Masanori Akazaki Fumihiro Kinoshita Osamu Katahira 《Electrical Engineering in Japan》1994,114(7):32-43
The possibility of laser-induced lightning has been investigated for the future application in the protection of electric power systems from lightning strokes. This technique induces lightning strokes artificially along a laser-produced breakdown plasma channel and conducts them to a harmless place on the ground. To clarify the plasma formation mechanism and the discharge (sparkover) induction process, sparkover induction experiments are performed for two types of long-gap electrode configurations, plate-to-rod and plate-to-plate, with a 50-J TEA CO2 laser. In the present paper, the sparkover voltage characteristics and interferometric measurement on laser-produced plasma mainly are described, together with sparkover induction for a series of metal beads arranged equidistantly which simulate a plasma channel. 相似文献
999.
The antiviral activity of ribavirin was studied in hamsters infected with subacute sclerosing panencephalitis (SSPE) virus. Ribavirn did not improve the survival of infected hamsters when administered intraperitoneally at the maximal nonlethal dose of 50 mg/kg/day for 10 days. However, when administered intracranially, ribavirin improved the survival of infected hamsters in a dose-dependent manner. The 50% effective dose was calculated to be 1.4 mg/kg/day, and the selectivity index, based on the ratio of the 50% lethally toxic dose (31 mg/kg/day) to the 50% effective dose, was 22. When begun 12 h, but not 36 h, postinfection, ribavirin at a dose of 10 mg/kg/day completely prevented mortality and inhibited the replication of SSPE virus in brains of infected hamsters. Intrathecal or intraventricular administration of ribavirin should be explored for potential use in the treatment of patients with SSPE. 相似文献
1000.