全文获取类型
收费全文 | 16436篇 |
免费 | 108篇 |
国内免费 | 519篇 |
专业分类
电工技术 | 241篇 |
综合类 | 79篇 |
化学工业 | 1744篇 |
金属工艺 | 594篇 |
机械仪表 | 899篇 |
建筑科学 | 968篇 |
矿业工程 | 320篇 |
能源动力 | 100篇 |
轻工业 | 3295篇 |
水利工程 | 319篇 |
石油天然气 | 301篇 |
武器工业 | 69篇 |
无线电 | 846篇 |
一般工业技术 | 5890篇 |
冶金工业 | 324篇 |
原子能技术 | 165篇 |
自动化技术 | 909篇 |
出版年
2022年 | 28篇 |
2021年 | 42篇 |
2018年 | 19篇 |
2016年 | 28篇 |
2015年 | 44篇 |
2014年 | 55篇 |
2013年 | 76篇 |
2012年 | 1754篇 |
2011年 | 2294篇 |
2010年 | 481篇 |
2009年 | 235篇 |
2008年 | 1464篇 |
2007年 | 1389篇 |
2006年 | 1136篇 |
2005年 | 1015篇 |
2004年 | 876篇 |
2003年 | 699篇 |
2002年 | 675篇 |
2001年 | 532篇 |
2000年 | 560篇 |
1999年 | 375篇 |
1998年 | 213篇 |
1997年 | 185篇 |
1996年 | 166篇 |
1995年 | 145篇 |
1994年 | 166篇 |
1993年 | 128篇 |
1992年 | 125篇 |
1991年 | 158篇 |
1990年 | 156篇 |
1989年 | 158篇 |
1988年 | 126篇 |
1987年 | 144篇 |
1986年 | 115篇 |
1985年 | 153篇 |
1984年 | 149篇 |
1983年 | 154篇 |
1982年 | 137篇 |
1981年 | 105篇 |
1980年 | 98篇 |
1979年 | 98篇 |
1978年 | 52篇 |
1977年 | 24篇 |
1976年 | 33篇 |
1975年 | 33篇 |
1974年 | 25篇 |
1973年 | 18篇 |
1965年 | 25篇 |
1964年 | 25篇 |
1958年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Manes G Tortoli P Andreuccetti F Avitabile G Atzeni C 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1988,35(1):14-21
An approach to dynamic focusing of ultrasound linear array scanners is presented, leading to the unique capability of implementing a focus that continuously tracks the return signal along the penetration depth. An electronically variable lens is obtained by a heterodyning process, in which the phases of echo signals at the array elements are equalized by mixing with suitable reference oscillations. These are generated by control of a single voltage-controlled oscillator, whose frequency is properly varied in synchronism with the delay of signal from different depths. The technique has been experimentally demonstrated by modifying the focusing processor of a conventional echographic linear scanner. Superior performances have been obtained with respect to fixed-focus operation mode. The image quality results are comparable with those of multizone-focus operation mode, in which the focus is varied over more transmit/receive cycles at the expense of lower frame rate. 相似文献
52.
Mechanically deboned chicken meat (MDCM) was washed with water, 0·5% NaCl or 0·5% NaHCO(3) solutions. Approximately 75·5% of the total hemoprotein pigments were removed by washing of MDCM with a sodium bicarbonate solution which resulted in the best colour improvements in the samples. Approximately 18·7% of total lipids were removed as a result of aqueous washing. The yield of proteins ranged from 56·5% after one washing with water to 43·4% after washing with water and then with a sodium bicarbonate solution. The Hunter L and a colour parameters of the samples correlated well with the total hemoproteins (correlation coefficients -0·984 and +0·947, respectively); corresponding correlation coefficient with the Hunter b value was only +0·693. 相似文献
53.
54.
55.
56.
57.
Wright RC Riederer SJ Lee JN Farzaneh F De Castro JB 《IEEE transactions on medical imaging》1987,6(2):165-168
This work presents methods for estimating relaxation times T1 and T2 and proton density using a real time digital video processor. This device performs each mathematical step of the fitting algorithms in one video frame interval (1/30 s). Two-point fits of T1 and T2 may be generated in approximately 15 video frame intervals or about 0.5 s; generation of a T2 image from four acquired images requires about 30 video frame intervals or about 1 s. The hardware is common to many commercial MR scanners and requires no array processor. Such high-speed techniques can expedite the clinical use of computed images and facilitate the implementation of image synthesis. 相似文献
58.
Modified quadratic discriminant functions and the application to chinese character recognition 总被引:8,自引:0,他引:8
Kimura F Takashina K Tsuruoka S Miyake Y 《IEEE transactions on pattern analysis and machine intelligence》1987,(1):149-153
Issues in the quadratic discriminant functions (QDF) are discussed and two types of modified quadratic disriminant functions (MQDF1, MQDF2) which are less sensitive to the estimation error of the covariance matrices are proposed. The MQDF1 is a function which employs a kind of a (pseudo) Bayesian estimate of the covariance matrix instead of the maximum likelihood estimate ordinarily used in the QDF. The MQDF2 is a variation of the MQDF1 to save the required computation time and storage. Two discriminant functions were applied to Chinese character recognition to evaluate their effectiveness, and remarkable improvement was observed in their performance. 相似文献
59.
This paper studied the changing principles of carbon content in direct reduction iron (DRI) and liquid iron in the COREX melting gasifier. Under the normal working conditions of experimental equipment, liquid nitrogen was poured into the melting gasifier from its tuyere to cool down quickly. And then seven cross sections were made to study the carburization reaction and its characteristics of the solid iron and the liquid iron, and also the reaction of carbon between the slag and the metal. According to the results, the influences of the thickness of the semi-coke layer and the temperature on the carbon content of liquid iron in the COREX melting gasifier were confirmed. 相似文献
60.
G.Y. Sha F.C. Jiang D. Wang D.K. Liu and R.T.Department of Mechanical Engineering Harbin Engineering University Harbin ChinaShenyang National Laboratory for Materials Science Institute of Metal Research The Chinese Academy of Sciences Shenyang China 《金属学报(英文版)》2002,15(6):556-560
An experimental-numerical method for measuring dynamic crack propagating velocities under stress wave loading is established in this paper. The experiments of the three-point bend specimen are done on the improved Hopkinson bar. Deflection of loading point, dynamic load and instantaneous crack length are measured, then crack propagating velocities are calculated. Experiments on 40Cr steel show that the results given by this method have a good agreement with that obtained by the resistance fracture gage method. Therefore this method is feasible for measuring crack propagating velocities under high loading rate and will have wide application. 相似文献