全文获取类型
收费全文 | 5056篇 |
免费 | 70篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 54篇 |
综合类 | 3篇 |
化学工业 | 494篇 |
金属工艺 | 41篇 |
机械仪表 | 62篇 |
建筑科学 | 102篇 |
矿业工程 | 2篇 |
能源动力 | 48篇 |
轻工业 | 316篇 |
水利工程 | 19篇 |
石油天然气 | 14篇 |
无线电 | 409篇 |
一般工业技术 | 570篇 |
冶金工业 | 2725篇 |
原子能技术 | 20篇 |
自动化技术 | 250篇 |
出版年
2021年 | 35篇 |
2020年 | 14篇 |
2019年 | 25篇 |
2018年 | 32篇 |
2017年 | 36篇 |
2016年 | 29篇 |
2015年 | 31篇 |
2014年 | 42篇 |
2013年 | 147篇 |
2012年 | 76篇 |
2011年 | 115篇 |
2010年 | 80篇 |
2009年 | 77篇 |
2008年 | 89篇 |
2007年 | 99篇 |
2006年 | 98篇 |
2005年 | 89篇 |
2004年 | 84篇 |
2003年 | 89篇 |
2002年 | 83篇 |
2001年 | 77篇 |
2000年 | 88篇 |
1999年 | 118篇 |
1998年 | 846篇 |
1997年 | 495篇 |
1996年 | 315篇 |
1995年 | 215篇 |
1994年 | 171篇 |
1993年 | 202篇 |
1992年 | 57篇 |
1991年 | 68篇 |
1990年 | 75篇 |
1989年 | 91篇 |
1988年 | 89篇 |
1987年 | 69篇 |
1986年 | 63篇 |
1985年 | 63篇 |
1984年 | 29篇 |
1983年 | 39篇 |
1982年 | 42篇 |
1981年 | 46篇 |
1980年 | 45篇 |
1979年 | 30篇 |
1978年 | 30篇 |
1977年 | 82篇 |
1976年 | 137篇 |
1975年 | 26篇 |
1974年 | 20篇 |
1973年 | 18篇 |
1972年 | 18篇 |
排序方式: 共有5129条查询结果,搜索用时 31 毫秒
1.
2.
3.
Crosstalk between microstrip transmission lines 总被引:1,自引:0,他引:1
Hill D.A. Cavcey K.H. Johnk R.T. 《Electromagnetic Compatibility, IEEE Transactions on》1994,36(4):314-321
Methods for prediction of crosstalk between microstrip transmission lines are reviewed and simplified for the weak-coupling case. Classical coupled transmission line theory is used for uniform lines, and potential and induced EMF methods are used for crosstalk between nonuniform lines. It is shown that the potential method is equivalent to classical coupled transmission line theory for the case of uniform lines. An experiment was performed for uniform coupled microstrip lines for frequencies from 50 MHz to 5 GHz, and good agreement between theory and measurement was obtained for both near- and far-end crosstalk 相似文献
4.
Lead content of rice collected from various areas in the world 总被引:1,自引:0,他引:1
ZW Zhang CS Moon T Watanabe S Shimbo M Ikeda 《Canadian Metallurgical Quarterly》1996,191(1-2):169-175
Rice samples consumed by local populations were collected between 1990 and 1995 in 17 areas in the world, mostly from Asia (10 areas), but also from 7 areas outside of Asia. In total, 1528 samples were obtained (about one half from Japan) and were analyzed for lead (Pb) by electrothermal atomic absorption spectrometry. When the Pb contents in rice samples were classified into 10 areas in Asia, the highest and the lowest geometric means (GMs) were for Indonesia (38 ng/g) and Australia (2 ng/g), respectively. Among 7 regions outside Asia, the GM was highest for Spain (58 ng/g) and the lowest for the USA. (3 ng/g). Moreover, inter-regional differences were significant, when more than 100 samples from one area were divided into 3-9 regions and GMs for regions were compared. There was a marked difference in Pb contents in rice by areas and regions in the world. Nevertheless, comparison by area of the present results with those reported in literature show that there has been no substantial reduction in Pb in rice in the past decade either in Japan or elsewhere in the world. 相似文献
5.
D Galasko T Saitoh Y Xia LJ Thal R Katzman LR Hill L Hansen 《Canadian Metallurgical Quarterly》1994,44(10):1950-1951
We determined apolipoprotein E (ApoE) genotypes in 122 autopsied demented patients. The frequency of the ApoE epsilon 4 allele was 39.6% in Alzheimer's disease (AD), 29.0% in the Lewy body variant of AD (LBV), and 6.25% in diffuse Lewy body disease. For AD and LBV patients, the epsilon 4 frequency was significantly higher than that reported in nondemented controls (10 to 15%). Therefore, LBV and AD share ApoE epsilon 4 as a genetic risk factor, providing further evidence that these conditions overlap. 相似文献
6.
7.
8.
A device that harnesses the mechanical energy of skeletal muscle contracting in a linear configuration has been implanted in goats. This energy convertor transforms muscle work to hydraulic energy that could drive a variety of cardiac assist devices. The device is mounted with a rib clamp and plate affixed to the sternum by cortical bone screws. A transcutaneous hydraulic line carries a silicon based working fluid to an external system that controls the muscle load. In 60 to 70 kg goats, the latissimus dorsi insertion was reattached to the energy convertor. A Telectronics myostimulator with intramuscular electrodes stimulated the latissimus dorsi. In acute implants, hydraulic pressures in excess of 150 psi were obtained. Chronic implantation of the device allowed system evaluation in the conscious unanesthetized animal. Two weeks after implant, hydraulic pressures in excess of 200 psi were obtained and energy transferred to the external loading system exceeded 1 J per contraction. Six weeks after implant, the device continued to cycle freely. These initial results are very promising and suggest an implantable energy convertor is feasible. Development of an energy convertor is an important step toward tether-free skeletal muscle powered cardiac assist devices. 相似文献
9.
Pre-transplant nephrectomy was done in a 25-year-old man for calculous pyelonephritis using a retroperitoneal laparoscopic approach with a newly devised ligature applicator-dissector- kidney retractor. 相似文献
10.
E Bazopoulou-Kyrkanidou P Neou CS Bartsocas S Kyrkanides I Fanourakis 《Canadian Metallurgical Quarterly》1995,6(3):227-232
PURPOSE: To select ideal radiologic projections for mapping and ablation of tachycardias of right ventricular outflow tract (RVOT). METHODS: Ten hearts from human corpses were studied utilizing radiopaque material to identify the pulmonary valve and three distinct sites on this valve: septal anterior (A), septal posterior (P) and free-wall (L). Next, the hearts were filmed in the frontal plane and in oblique projections with 15 degrees increments to the right and to the left. The projections in which the sites were lateralized on the valve, eased radiologic interpretation and were considered ideal for mapping and ablation. Depending on the proximity of the sites to the lateral extremes of the pulmonary valve, the projections were considered ideal ( ), intermediary (++) and inadequate (+). RESULTS: Projections [table: see text] CONCLUSION: The A site of RVOT was best indicated in the 60 and 45 degrees left anterior oblique projections; the 0 degree postero anterior projection was best for mapping the P site; the L region was best explored in the 60 degrees right anterior oblique projection. 相似文献