全文获取类型
收费全文 | 353篇 |
免费 | 8篇 |
专业分类
电工技术 | 6篇 |
化学工业 | 48篇 |
金属工艺 | 3篇 |
机械仪表 | 6篇 |
建筑科学 | 9篇 |
能源动力 | 6篇 |
轻工业 | 21篇 |
水利工程 | 6篇 |
无线电 | 71篇 |
一般工业技术 | 33篇 |
冶金工业 | 129篇 |
自动化技术 | 23篇 |
出版年
2021年 | 3篇 |
2019年 | 2篇 |
2018年 | 6篇 |
2017年 | 5篇 |
2016年 | 7篇 |
2015年 | 6篇 |
2014年 | 3篇 |
2013年 | 15篇 |
2012年 | 15篇 |
2011年 | 16篇 |
2010年 | 7篇 |
2009年 | 6篇 |
2008年 | 13篇 |
2007年 | 11篇 |
2006年 | 16篇 |
2005年 | 4篇 |
2004年 | 4篇 |
2003年 | 4篇 |
2002年 | 4篇 |
2001年 | 7篇 |
2000年 | 9篇 |
1999年 | 7篇 |
1998年 | 48篇 |
1997年 | 16篇 |
1996年 | 19篇 |
1995年 | 12篇 |
1994年 | 16篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 5篇 |
1977年 | 7篇 |
1976年 | 10篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1972年 | 4篇 |
1971年 | 2篇 |
1970年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有361条查询结果,搜索用时 15 毫秒
81.
Pumps or fans often exist in multiples or configurations that are interdependent within a process Without applying a drive to each unit, it, is still possible to achieve the benefits of drive control by taking advantage of synchronization and using one drive to control several pumps within a process. Several benefits may be realized while keeping capital outlays reasonable. Possible applications must be identified and evaluated separately to ensure economic payback and benefits. The method and configuration chosen will impact the evaluation. A synchronous transfer system of pump control for series or parallel arrangements of pumps can be very beneficial from process or economic standpoints. Along with reduced initial capital outlay and installation costs, savings can also be realized in operating costs since the process is now continuously variable and does not require throttling. The AFD will provide improved process control as well as the benefit of soft starts and reduced voltage drops. A closed transition is preferred for synchronizing and desynchronizing to provide accurate phase alignment at the moment of connection to the second source. Minimizing the voltage phase difference will reduce current and torque transients important to providing a long motor life. 相似文献
82.
Traditional lab automation systems are highly centralized: dispatch and coordination of activities are mediated by a system controller, usually via a single, monolithic control procedure. This approach, while conceptually simple, makes changes to the system difficult; adding or removing instruments and functionality can be a daunting task. In addition, most automated systems are tied to particular development languages and protocols, making operation in heterogeneous environments (i.e., the real world) problematic, since instrument software comes in many different implementations.We present a peer-to-peer architecture for lab automation, using an XML-based communication protocol. The architecture consists of peer instrument servers, an XML communication layer, and an open control center. Each instrument peer can control, be controlled by, and communicate information to other instrument peers to fulfill the automation task. Our protocol is based on XML-RPC, a lightweight communication standard built atop HTTP.This provides an open and flexible means of peer-to-peer interfacing. The control center serves as a convenient, Web-based interface to manage the instruments. The automated procedure can be distributed across all available instrument peers (each instrument assigned a set of responsibilities); the controller implements a limited set of high-level instructions. The software components included in our prototype system are implemented in various programming languages, including Java, C/C++, Visual Basic, and LabVIEW. Our approach facilitates rapid development of laboratory automation systems. 相似文献
83.
The total N content of kidney beans (Phaseolus vulgaris) was found to increase on germination. The overall amino acid composition however changed very little. Rats fed on a diet containing raw beans lost more weight than the protein-free controls (negative n.p.u. value). Germination was found to bring about a gradual improvement in nutritive value probably through the elimination of some of the toxic constituents of the seed. The near doubling of the amount of trypsin inhibitors by the 8th day of germination taken together with the substantial improvement in the nutritive value of the bean appeared to rule out trypsin inhibitors as the main toxic components of raw beans. 相似文献
84.
AJ Johnstone JC Lohlun JD Miller CA McIntosh A Gregori R Brown PA Jones SI Anderson JL Tocher 《Canadian Metallurgical Quarterly》1993,7(6):501-506
Soft drug analogs of methscopolamine (4 a-c) were tested for mydriatic activity in rabbits' eyes. After unilateral administration of equieffective doses, the AUC24hrs and the mydriatic recovery times were found to be significantly lower with the soft drugs compared to methscopolamine. At equieffective doses, the AUC24hrs for soft drugs ranged from 22.4% to 60% of that of methscopolamine. Significant dilation of the untreated eye was observed with methscopolamine but not with the soft drugs after unilateral administration. Soft drug 4a exhibited only 10.4% of the AUC6hrs (untreated eye) of that of methscopolamine. Shorter durations of mydriatic action combined with potentially reduced systemic side effects make these compounds candidates for further study. In vitro rabbit transcorneal penetration of soft analog 4a was found to be significantly higher than methscopolamine. 相似文献
85.
Chang P.S. Mead J.B. Knapp E.J. Sadowy G.A. Davis R.E. McIntosh R.E. 《Antennas and Propagation, IEEE Transactions on》1996,44(1):58-73
This paper presents 35, 95, and 225 GHz polarimetric radar backscatter data from snowcover. It compares measured backscatter data with detailed in situ measurements of the snowcover including microstructural anisotropies within the snowpack. Observations of backscatter mere made during melt-freeze cycles, and measurable differences in the normalized radar cross section between older metamorphic snow and fresh low-density snow were observed. In addition, these data show that the average phase difference between the copolarized terms of the scattering matrix, Svvand Shh , is nonzero for certain snow types. This phase difference was found to be related to snowpack features including anisotropy, wetness, density, and particle size. A simple backscatter model based on measured particle size and anisotropy is found to predict the Mueller matrix for dry snowcover with reasonable accuracy 相似文献
86.
A striking characteristic of human memory is that pictures are remembered better than words. We examined the neural correlates of memory for pictures and words in the context of episodic memory encoding to determine material-specific differences in brain activity patterns. To do this, we used positron emission tomography to map the brain regions active during encoding of words and pictures of objects. Encoding was carried out by using three different strategies to explore possible interactions between material specificity and types of processing. Encoding of pictures resulted in greater activity of bilateral visual and medial temporal cortices, compared with encoding words, whereas encoding of words was associated with increased activity in prefrontal and temporoparietal regions related to language function. Each encoding strategy was characterized by a distinctive activity pattern, but these patterns were largely the same for pictures and words. Thus, superior overall memory for pictures may be mediated by more effective and automatic engagement of areas important for visual memory, including medial temporal cortex, whereas the mechanisms underlying specific encoding strategies appear to operate similarly on pictures and words. 相似文献
87.
Alongitudinal study was conducted in four indicator villages of PHC Shankargarh, District Allahabad, U.P. from July 1991 to June 1992 to have information on seasonality of indoor resting anopheline species in silica sand/hard stone quarry area. Fourteen anopheline species namely, An. aconitus (0.35%), An. annularis (17.03%), An. barbirostris (0.09%), An. culicifacies (36.74%), An. fluviatilis (0.13%), An. nigerrimus (0.01%), An. pallidus (4.40%), An. splendidus (0.02%), An. stephensi (0.01%), An. subpictus (40.84%), An. tessellatus (0.15%), An. turkhudi (0.004%), An. vagus (0.20%) and An. varuna (0.02%) were collected. An. culicifacies, An. subpictus and An. annularis were found throughout the year. An. fluviatilis, An. pallidus, An. vagus and An. aconitus were also observed in all the seasons except extreme summer. However, An. barbirostris and An. splendidus were collected only in monsoon/post-monsoon and winter seasons. An. tessellatus and An. stephensi were recorded in winter and spring seasons. An. nigerrimus and An. varuna were recorded in winter, while An. turkhudi in spring. Prolonged high vector density may be attributed to the extended malaria transmission in this area. 相似文献
88.
MC White JP Tulsky P Reilly HW McIntosh TM Hoynes J Goldenson 《Canadian Metallurgical Quarterly》1998,2(6):506-512
PURPOSE: To assess the effect of insurance status on the probability of admission and subsequent health status of patients presenting to emergency departments. SUBJECTS AND METHODS: We performed a prospective cohort study of patients with common medical problems at five urban, academic hospital emergency departments in Boston and Cambridge, Massachusetts. The outcome measure for the study was admission to the hospital from the emergency department and functional health status at baseline and follow-up. RESULTS: During a 1-month period, 2,562 patients younger than 65 years of age presented with either abdominal pain (52%), chest pain (19%) or shortness of breath (29%). Of the 1,368 patients eligible for questionnaire, 1,162 (85%) completed baseline questionnaires, and of these, 964 (83%) completed telephone follow-up interviews 10 days later. Fifteen percent of patients were uninsured and 34% were admitted to the hospital from the emergency department. Uninsured patients were significantly less likely than insured patients to be admitted, both when adjusting for urgency, chief complaint, age, gender and hospital (odds ratio = 0.5, 95% confidence interval 0.3 to 0.7), and when additionally adjusting for comorbid conditions, lack of a regular physician, income, employment status, education and race (odds ratio = 0.4, 95% confidence interval 0.2 to 0.8). However, there were no differences in adjusted functional health status between admitted and nonadmitted patients by insurance status, either at baseline or at 10-day follow-up. CONCLUSIONS: Uninsured patients with one of three common chief complaints appear to be less frequently admitted to the hospital than are insured patients, although health status does not appear to be affected. Whether these results reflect underutilization among uninsured patients or overutilization among insured patients remains to be determined. 相似文献
89.
Liu H.C. Jenkins G.E. Brown E.R. McIntosh K.A. Nichols K.B. Manfra M.J. 《Electron Device Letters, IEEE》1995,16(6):253-255
We have demonstrated heterodyne detection up to an intermediate frequency of 26.5 GHz using quantum well infrared photodetectors. A CO 2 laser and a lead-salt tunable diode laser were used as the infrared sources. Heterodyne detection experiments measure the high frequency behavior of photoexcited electrons and their transport properties. We have also carried out microwave rectification experiments which measure the high frequency behavior associated with the dark-current electron-transport processes 相似文献
90.
The optimum transient radiation from an arbitrary antenna 总被引:2,自引:0,他引:2
Pozar D. Schaubert D. McIntosh R. 《Antennas and Propagation, IEEE Transactions on》1984,32(6):633-640
Bounds on the optimum transient radiation from an arbitrary antenna enclosed by a spherical surface of specified size are presented. The optimization criterion is either maximization of the radiated electric field amplitude at a specified time and far-zone position, or maximization of the radiated energy density in a specified time interval for a particular far-zone position. The latter optimization results in the prolate spheroidal wave functions. In both cases, the total energy radiated by the antenna is constrained to be 1 J, and the antenna excitation is assumed to be bandlimited. The performance of the optimum arbitrary antenna is compared to that of optimized practical antennas, such as dipoles and arrays of dipoles. The effect of a sidelobe constraint is also studied. 相似文献