全文获取类型
收费全文 | 311627篇 |
免费 | 3812篇 |
国内免费 | 717篇 |
专业分类
电工技术 | 6205篇 |
综合类 | 561篇 |
化学工业 | 47177篇 |
金属工艺 | 10375篇 |
机械仪表 | 8866篇 |
建筑科学 | 7944篇 |
矿业工程 | 863篇 |
能源动力 | 8653篇 |
轻工业 | 31246篇 |
水利工程 | 2542篇 |
石油天然气 | 3687篇 |
武器工业 | 8篇 |
无线电 | 39867篇 |
一般工业技术 | 58729篇 |
冶金工业 | 56984篇 |
原子能技术 | 5493篇 |
自动化技术 | 26956篇 |
出版年
2021年 | 2360篇 |
2019年 | 2192篇 |
2018年 | 3660篇 |
2017年 | 3506篇 |
2016年 | 3597篇 |
2015年 | 2587篇 |
2014年 | 4488篇 |
2013年 | 14359篇 |
2012年 | 7444篇 |
2011年 | 10210篇 |
2010年 | 7968篇 |
2009年 | 9204篇 |
2008年 | 9678篇 |
2007年 | 9635篇 |
2006年 | 8561篇 |
2005年 | 7942篇 |
2004年 | 7795篇 |
2003年 | 7518篇 |
2002年 | 7359篇 |
2001年 | 7563篇 |
2000年 | 7240篇 |
1999年 | 7572篇 |
1998年 | 17775篇 |
1997年 | 12912篇 |
1996年 | 10141篇 |
1995年 | 7909篇 |
1994年 | 7228篇 |
1993年 | 6941篇 |
1992年 | 5302篇 |
1991年 | 5082篇 |
1990年 | 4946篇 |
1989年 | 4789篇 |
1988年 | 4686篇 |
1987年 | 3901篇 |
1986年 | 4018篇 |
1985年 | 4736篇 |
1984年 | 4281篇 |
1983年 | 4032篇 |
1982年 | 3614篇 |
1981年 | 3768篇 |
1980年 | 3466篇 |
1979年 | 3429篇 |
1978年 | 3239篇 |
1977年 | 3829篇 |
1976年 | 4866篇 |
1975年 | 2785篇 |
1974年 | 2665篇 |
1973年 | 2681篇 |
1972年 | 2221篇 |
1971年 | 1966篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Person identification using multiple cues 总被引:6,自引:0,他引:6
Brunelli R. Falavigna D. 《IEEE transactions on pattern analysis and machine intelligence》1995,17(10):955-966
This paper presents a person identification system based on acoustic and visual features. The system is organized as a set of non-homogeneous classifiers whose outputs are integrated after a normalization step. In particular, two classifiers based on acoustic features and three based on visual ones provide data for an integration module whose performance is evaluated. A novel technique for the integration of multiple classifiers at an hybrid rank/measurement level is introduced using HyperBF networks. Two different methods for the rejection of an unknown person are introduced. The performance of the integrated system is shown to be superior to that of the acoustic and visual subsystems. The resulting identification system can be used to log personal access and, with minor modifications, as an identity verification system 相似文献
993.
Occlusion of large atrial septal defects with a centering buttoned device: early clinical experience
EB Sideris M Leung JH Yoon CR Chen R Lochan AM Worms C Rey B Meier 《Canadian Metallurgical Quarterly》1996,131(2):356-359
A feasibility clinical study was conducted for the transcatheter occlusion of large ostium secundum atrial septal defects with the centering buttoned device. The centering buttoned device is a modification of the regular buttoned device in which a centering counter-occluder is sutured at the central 40% portion of the occluder. During centering it is stretched, forming a parachute-shaped structure and pulling the occluder over the center of the defect. During buttoning, the counter-occluder forms a double figure eight, opposing the right atrial side of the atrial septum. Occlusion was performed in 12 patients aged 6 to 56 years. All had been rejected for transcatheter occlusion by the regular buttoned device, because of either their defect size or the lack of adequate septal rim. The defect size varied between 23 and 31 mm, and the device size varied between 45 and 60 mm. Nine had immediate effective occlusions of their defects and three residual shunts. One patient with unbuttoning had hemolysis at 2 weeks and underwent surgery. Early results of the transcatheter occlusion of large atrial septal defects are promising, and larger clinical trials are justified. 相似文献
994.
M Schietroma A Risetti F Carlei MV Santirocco F Muzi G Maggi C De Santis CL Recchia D Iannucci R Rampa M Simi 《Canadian Metallurgical Quarterly》1996,48(4):43-46
Adhesions have been suggested as a possible cause of chronic abdominal pain, but the reports of their etiological role conflict. Lysis of adhesions has been proposed as the therapeutic modality of choice, although the reports of success are controversial. The aim our prospective study was to determine whether laparoscopic adhesiolysis ameliorates chronic abdominal pain in patients with abdominal adhesions. Forty-one patients with chronic abdominal pain lasting for more than 6 months, but with no abnormal findings other than adhesions found at laparoscopy, underwent laparoscopic adhesiolysis. 37 patients (90.2%) were available for follow-up after a median time interval of 18 months (range: 12-41 months). Twenty-two patients (59.4%) were free from abdominal pain and 9 (24.3%) patients reported significant amelioration of their pain. Six (16.2%) patients had no amelioration. In conclusion the laparoscopy is an effective tool for the evaluation of patients with chronic abdominal pain, and laparoscopic adhesiolysis cures of ameliorates chronic abdominal pain in more than 80% of patients. 相似文献
995.
N Ivanovska S Philipov R Istatkova P Georgieva 《Canadian Metallurgical Quarterly》1996,54(2-3):143-151
The antimicrobial and immunological properties of ethanol extracts, non-alkaloid, tertiary alkaloid and quaternary alkaloid fractions, obtained from roots and aerial parts of Isopyrum thalictroides were examined. The non-alkaloid fraction from aerial parts inhibited the growth of seven test microorganisms and was the most effective suppressor of classical pathway (CP) complement activity in normal human serum (NHS) and guinea pig serum (GPS). The alkaloid fractions, containing quaternary alkaloids expressed suppressive effect on mitogen-induced splenocyte proliferation. The in vitro antibody response against sheep red blood cells (anti-SRBC) was inhibited by ethanol extracts and quaternary alkaloid fraction. The intraperitoneal (i.p.) application of ethanol extract and tertiary alkaloid fraction from aerial parts showed that they possess in vivo effect on alternative pathway (AP) complement activity, anti-SRBC response and delayed type hypersensitivity (DTH). 相似文献
996.
Richards-Kortum R. Mahadevan-Jansen A. Ramanujam N. 《Circuits and Devices Magazine, IEEE》1996,12(4):34-40
A novel non-invasive technique for detecting cancer and precancer offers a viable adjunct to biopsies. Here, we summarize the principles of optical spectroscopy and present some of the highlights obtained with the successful application of fluorescence and Raman spectroscopy for cancer and precancer detection 相似文献
997.
The device degradation under ac and dc stress have been discussed and a relationship between the two has been established,. We have shown that the commonly used lifetime criteria of 10% linear current degradation for 10 years for a transistor under dc stress is overly conservative for representing the circuit operating lifetime. Using experimental and simulated data for inverter chains, we proposed that a meaningful equivalent lifetime based on 10% Idl degradation under dc stress is 1 year lifetime (for a 10 year circuit lifetime based on 54b degradation in ring oscillator frequency). We also compared this criteria to actual circuit degradation for microprocessors and a DRAM. For DSP microprocessors with 0.8 μm LDD transistors, the projected lifetime was more than 200 years at 5.5 V, with a corresponding 10% I dr lifetime of 20 years. For 1 Mb DRAMs with 1 pm LDD transistors, the 5% speed degradation lifetime at 5.5 V was more than 100 years, whereas the individual transistors had 10% Idl lifetime of 4 years. These circuit results support the 10% Idl transistor lifetime. We believe these criterion should be very safe and reasonable for digital IC chips currently in the field, as well as those in future design and development 相似文献
998.
Sabate J.A. Jovanovic M.M. Lee F.C. Gean R.T. 《Industrial Electronics, IEEE Transactions on》1995,42(1):63-71
The analysis and design of an LCC resonant inverter for a 20 kHz AC distributed power system are presented. Several resonant converter topologies are assessed to determine their suitability for high efficiency power conversion, under resistive and reactive loads. Two LCC-resonant inverter designs were implemented. One with all switches operating with zero voltage switching (ZVS), and another with two switches operating with ZVS and two switches with zero current switching (ZCS). The experimental results are presented along with a performance comparison of the two versions 相似文献
999.
1000.