全文获取类型
收费全文 | 736篇 |
免费 | 11篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 42篇 |
化学工业 | 121篇 |
金属工艺 | 11篇 |
机械仪表 | 17篇 |
建筑科学 | 11篇 |
能源动力 | 14篇 |
轻工业 | 46篇 |
水利工程 | 4篇 |
石油天然气 | 2篇 |
无线电 | 77篇 |
一般工业技术 | 125篇 |
冶金工业 | 197篇 |
原子能技术 | 14篇 |
自动化技术 | 68篇 |
出版年
2023年 | 6篇 |
2022年 | 10篇 |
2021年 | 21篇 |
2020年 | 4篇 |
2019年 | 11篇 |
2018年 | 6篇 |
2017年 | 4篇 |
2016年 | 14篇 |
2015年 | 7篇 |
2014年 | 14篇 |
2013年 | 21篇 |
2012年 | 18篇 |
2011年 | 22篇 |
2010年 | 24篇 |
2009年 | 32篇 |
2008年 | 24篇 |
2007年 | 16篇 |
2006年 | 25篇 |
2005年 | 21篇 |
2004年 | 14篇 |
2003年 | 18篇 |
2002年 | 19篇 |
2001年 | 21篇 |
2000年 | 24篇 |
1999年 | 23篇 |
1998年 | 76篇 |
1997年 | 44篇 |
1996年 | 34篇 |
1995年 | 21篇 |
1994年 | 27篇 |
1993年 | 16篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 10篇 |
1988年 | 9篇 |
1987年 | 5篇 |
1986年 | 8篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 10篇 |
1981年 | 3篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 7篇 |
1974年 | 3篇 |
1973年 | 3篇 |
排序方式: 共有749条查询结果,搜索用时 15 毫秒
81.
For a recently proposed perpendicular recording system, a composite anisotropy medium has been developed to improve the recording sensitivity of the perpendicular recording head. The medium is composed of a Fe-Ni soft magnetic film and a Co-Cr perpendicular anisotropy film, which are successively deposited on a base by an r. f. sputtering. By using the new double layer medium, an extremely high recording sensitivity could be obtained, compared with the single layer Co-Cr medium. The recording current needed to saturate the double layer film decreased to one-tenth of that for the single layer Co-Cr film. Although the Fe-Ni layer was soft magnetic material, neither deterioration of the frequency response nor peak shift was observed for the double layer film. The reproduction with a perpendicular head was also investigated, and a high output voltage and a high signal-to-noise ratio were obtained. 相似文献
82.
A high-sensitivity small-detectable-area Hi-Lo germanium avalanche photodiode (Ge APD) was developed for use in 1.55 ?m wavelength optical communication systems. This device has Hi-Lo (p+nn?) impurity profile. Its detectable area is 30 ?m in diameter for single-mode optical-fibre use. The minimum average received signal level obtained was ?40.5 dBm (at 450 Mbit/s, ? = 1.55 ?m, BER = 10?9, return-to-zero). This is 0.7 dB better than the value for the 80?m diameter similar structure Ge APD. 相似文献
83.
We report a natural experiment that took place in a cardiac intensive care unit (CICU). We had been alerted to the possibility that sunny rooms would be conducive to better outcomes by our findings in the psychiatric unit, and by reports that depressed cardiac patients did less well than those in normal mood. The 628 subjects were patients admitted directly to the CICU with a first attack of myocardial infarction (MI). Outcomes of those treated in sunny rooms and those treated in dull rooms were retrospectively compared for fatal outcomes and for length of stay in the CICU. Patients stayed a shorter time in the sunny rooms, but the significant difference was confined to women (2.3 days in sunny rooms, 3.3 days in dull rooms). Mortality in both sexes was consistently higher in dull rooms (39/335 dull, 21/293 sunny). We conclude that illumination may be relevant to outcome in MI, and that this natural experiment merits replication. 相似文献
84.
The maximum biting force in 82 male athletes and 12 male subjects without any particular athletic activity (nonathletes) were measured in order to evaluate the relationship between biting force and physical fitness in athletes. The results obtained were as follows. 1. The maximum biting force in athletes (50.8 +/- 17.4kg) were significantly (p < 0.01) higher than that in the nonathletes (28.1 +/- 9.1kg). The maximum biting forces in the men who belonged to the rugby or judo clubs were predominantly higher than in other subjects. 2. In men who masticated on the left side of the mouth, the habitual (i. e., left) biting force was significantly higher than the nonhabitual (i. e., right) biting force. In men who masticated on the right side of the mouth, the habitual (i. e., right) biting force was also higher than the nonhabitual (i. e., left) biting force, but was not significantly so. 3. There was a significant positive correlation between the biting force and grip strength and back strength in athletes. In athletes, there was a significant correlation between biting force and the numbers of chin-ups, the numbers for the side-step tests and the time for 50m running. 相似文献
85.
86.
T Kouyama M Yamamoto N Kamiya H Iwasaki T Ueki I Sakurai 《Canadian Metallurgical Quarterly》1994,236(4):990-994
A novel ordered assemblage of bacteriorhodopsin, a transmembrane protein functioning as a light-driven proton pump, is found in its three-dimensional crystal. Atomic force microscope images of the crystal surface reveal that spherical protein clusters with a diameter of approximately 50 nm are hexagonally close-packed. Electron micrographs of mechanically disintegrated crystals show that the inside of the protein cluster is filled with the mother liquor. The crystal is made up of hollow protein clusters. When disintegrated crystals are illuminated in the presence of a lipophilic anion, a significant alkalization of the external medium occurs. This result indicates that the protein cluster contains native lipids and that the cytoplasmic side of the protein faces the external medium. X-ray diffraction patterns and the observed diameter of the spherical shell suggest that approximately 200 bacteriorhodopsin trimers are aligned on a polyhedral surface lattice. Another remarkable feature of the spherical assemblies of bacteriorhodopsin is that they fuse with each other at low ionic strength and occasionally form a tubular or doughnut-like structure. The concept of membrane protein polymorphism is introduced on the basis of these observations, and it is used to describe the dynamic structure of some other biological membranes. 相似文献
87.
Application-specific integrated circuit (ASIC) ML4425 is often used for sensorless control of permanent-magnet (PM) brushless direct current (BLDC) motor drives. It integrates the terminal voltage of the unenergized winding that contains the back electromotive force (EMF) information and uses a phase-locked loop (PLL) to determine the proper commutation sequence for the BLDC motor. However, even without pulsewidth modulation, the terminal voltage is distorted by voltage pulses due to the freewheel diode conduction. The pulses, which appear very wide in an ultrahigh-speed (120 kr/min) drive, are also integrated by the ASIC. Consequently, the motor commutation is significantly retarded, and the drive performance is deteriorated. In this paper, it is proposed that the ASIC should integrate the third harmonic back EMF instead of the terminal voltage, such that the commutation retarding is largely reduced and the motor performance is improved. Basic principle and implementation of the new ASIC-based sensorless controller will be presented, and experimental results will be given to verify the control strategy. On the other hand, phase delay in the motor currents arises due to the influence of winding inductance, reducing the drive performance. Therefore, a novel circuit with discrete components is proposed. It also uses the integration of third harmonic back EMF and the PLL technique and provides controllable advanced commutation to the BLDC motor. 相似文献
88.
A new method for automated planning, refinement of skeletal plans, has been developed for the problem of experiment design in the domain of molecular biology. The method resulted from a study of the problem-solving behavior of scientists which showed that design usually consisted of look-up of abstracted plans followed by hierarchical plan-step refinement. The skeletal plan method has been implemented through two generations of problem-solving systems, the second generation involving a synthesis with the metaplanning approach of Stefik. 相似文献
89.
90.
Translocation of peptidyl-tRNA from the ribosomal A- to the P-site in the eukaryotic system was extensively investigated using a model system, in which translocation of Phe-tRNA from the A- to the P-site was examined by using the puromycin reaction, and the following results were obtained. 1) The puromycin reaction but not the translocation reaction proceeded at 0 degrees C. Since the latter could be demonstrated at 30 degrees C, it was possible to analyze translocation per se separately from the puromycin reaction. 2) Translocation was completely dependent on the elongation factor-2 (EF-2) and required the presence of GTP, which could be replaced by GMP-P(NH)P provided that the stoichiometric amount of EF-2 with respect to the amount or ribosomes was present. It was further demonstrated that translocation observed in the presence of GTP was catalytic, while that in the presence of GMP-P(NH)P was stoichiometric, indicating that hydrolysis of GTP was required for the catalytic reutilization of EF-2. 3) Translocation promoted by EF-2 in the presence of GMP-P(NH)P could be reversed, which suggests that hydrolysis of GTP is indispensable of the translocation reaction to proceed catalytically and unidirectionally forward. 相似文献