全文获取类型
收费全文 | 826篇 |
免费 | 33篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 6篇 |
综合类 | 1篇 |
化学工业 | 272篇 |
金属工艺 | 2篇 |
机械仪表 | 5篇 |
建筑科学 | 39篇 |
矿业工程 | 2篇 |
能源动力 | 15篇 |
轻工业 | 65篇 |
水利工程 | 5篇 |
石油天然气 | 2篇 |
武器工业 | 8篇 |
无线电 | 170篇 |
一般工业技术 | 89篇 |
冶金工业 | 92篇 |
原子能技术 | 2篇 |
自动化技术 | 89篇 |
出版年
2023年 | 8篇 |
2022年 | 19篇 |
2021年 | 23篇 |
2020年 | 13篇 |
2019年 | 15篇 |
2018年 | 17篇 |
2017年 | 17篇 |
2016年 | 24篇 |
2015年 | 21篇 |
2014年 | 21篇 |
2013年 | 34篇 |
2012年 | 37篇 |
2011年 | 45篇 |
2010年 | 28篇 |
2009年 | 34篇 |
2008年 | 23篇 |
2007年 | 26篇 |
2006年 | 36篇 |
2005年 | 26篇 |
2004年 | 30篇 |
2003年 | 30篇 |
2002年 | 27篇 |
2001年 | 20篇 |
2000年 | 29篇 |
1999年 | 23篇 |
1998年 | 31篇 |
1997年 | 31篇 |
1996年 | 19篇 |
1995年 | 20篇 |
1994年 | 15篇 |
1993年 | 14篇 |
1992年 | 12篇 |
1991年 | 12篇 |
1990年 | 4篇 |
1989年 | 11篇 |
1988年 | 6篇 |
1987年 | 9篇 |
1986年 | 4篇 |
1985年 | 8篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1974年 | 2篇 |
1969年 | 3篇 |
1959年 | 1篇 |
排序方式: 共有864条查询结果,搜索用时 0 毫秒
61.
New sulfated zirconias covering a wide range of pore diameters from micropores to macropores have been prepared by a combined use of two different structure-directing templates. The catalytic performance of these sulfated zirconias for the n-butane isomerization could be improved significantly compared to a standard displaying a maximum rate of isomerization of 1490 μmol/g h at 423 K. The materials remained their high activity even at 348 K. Moreover, deactivated materials could be reactivated to the original activity in an air-flow at 673 K several times. The newly designed materials were fully characterized by XRD, XPS, TPD of ammonia, IR spectroscopy and N2 adsorption to describe the formation of active surface centres and their morphology. The formation of active pyrosulfates with sulfate bands above 1400 cm?1 was followed by DRIFTS. An increased ratio of Brønsted-to-Lewis centres could be detected which can be accounted for the unexpected high activity. 相似文献
62.
Marie Held Abraham P. Lee Clive Edwards Dan V. Nicolau 《Microelectronic Engineering》2010,87(5-8):786-789
Although filamentous fungi live in physically and chemically complex natural environments that require optimal survival strategies, both at colony and individual cell level, their growth dynamics are usually studied on homogenous media. This study proposes a new research methodology based on the purposeful design, fabrication and operation of microfluidics structures to examine the temporal and spatial responses of filamentous fungi. Two model fungal strains, the wild type of Neurospora crassa – a commonly used model organisms – and the ro-1 mutant strain of this species impaired in hyphal growth and morphology, have been chosen to demonstrate the potential of this new methodology. Time-lapse observations of both species show that filamentous fungi respond rapidly to the physically microstructured environment without any detectable temporal or spatial adjustment period. Despite their genetic differences, and consequently different growth behaviour, both strains present efficient space-search strategies enabling them to solve the microsized networks successfully and in similar periods, thus demonstrating that the space-searching algorithms are robust and mutation-independent. Additionally, the use of the proposed methodology could put in evidence new biological mechanisms responsible for the apical extension of filamentous fungi, beyond the classical theory based on the central role of Spitzenkörper. 相似文献
63.
64.
Dipl.-Ing. J. Blotevogel Leb.-Chem. A.-K. Reineke Prof. Dr. J. Hollender Dr. T. Held 《Grundwasser》2008,13(3):147-157
The German Federal Soil Protection and Contaminated Sites Ordinance (BBodSchV) requires the monitoring of NSO-heterocyclic hydrocarbons without specifying the extent of such analysis. An assessment procedure for the identification of NSO-heterocyclic priority substances was thus created within the “KORA” project (“Natural Attenuation: Retention and Degradation Processes Reducing Contaminations in Groundwater and Soil”) funded by the German Federal Ministry of Education and Research (BMBF). This assessment includes physicochemical properties, biodegradability, toxicity, and groundwater propagation of these substances at creosote-contaminated sites. In addition to unsubstituted compounds, the derived list of 20 priority NSO-heterocycles also contains substituted derivatives as well as relevant transformation products. 相似文献
65.
Loredana Elena Nita Aurica P Chiriac Sossio Cimmino Clara Silvestre Donatella Duraccio Cornelia Vasile 《Polymer International》2008,57(2):342-349
BACKGROUND: The possibility to use β‐cyclodextrin as biodegradable tensioactive and an electromagnetic field in order to improve the kinetic parameters of radical emulsion polymerization is of interest. Thus, the influence of different surfactants—sodium lauryl sulfate (SLS) and β‐cyclodextrin (CD)—on the pathway of emulsion polymerization of methyl methacrylate (MMA) and emulsion copolymerization of MMA with 2,3‐epoxypropyl methacrylate (GMA) performed with or without the presence of a continuous electromagnetic field (MF) was studied. RESULTS: The presence of the MF leads to a considerable increase of the conversion during the first part of the reaction if the classic surfactant (SLS) is used. The reactions performed without MF and with CD exhibit a decrease of the conversion and of the polymerization rate as compared with the variants using SLS. The swelling rate and the maximum degree of swelling vary with the surfactant nature and with the reaction conditions and MF presence. Data from thermogravimetry and differential scanning calorimetry evidence the dependences between the polymer characteristics and the preparation conditions. CONCLUSION: This research underlines the coupling possibilities of the influence of a MF—growth of the reaction rate and conversion explained through radical pairs mechanism—with a combination of the ‘cage’ effect and ‘conformational control’ afforded by CD. The presence of MF and CD during the syntheses leads to an increase of Tg and an increase of PMMA and P(MMA‐co‐GMA) thermal stability. Copyright © 2007 Society of Chemical Industry 相似文献
66.
Optimization Problems Related to Zigzag Pocket Machining 总被引:2,自引:0,他引:2
A fundamental problem of manufacturing is to produce mechanical parts from billets by clearing areas within specified boundaries
from the material. Based on a graph-theoretical formulation, the algorithmic handling of one particular machining problem—``zigzag
pocket machining'—is investigated. We present a linear-time algorithm that ensures that every region of the pocket is machined
exactly once, while attempting to minimize the number of tool retractions required. This problem is shown to be -hard for pockets with holes. Our algorithm is provably good in the sense that the machining path generated for a pocket
with h holes requires at most 5 . . . OPT + 6 . . . h retractions, where OPT is the (unknown) minimum number of retractions required by any algorithm. The algorithm has been implemented, and practical
tests for pockets without holes suggest that one can expect an approximation factor of about 1.5 for practical examples, rather
than the factor 5 as proved by our analysis.
Received July 3, 1997; revised September 7, 1997. 相似文献
67.
68.
69.
70.
Dobson M.C. Ulaby F.T. Brunfeldt D.R. Held D.N. 《Geoscience and Remote Sensing, IEEE Transactions on》1986,(4):453-461
Data takes on two ascending orbits of the Shuttle Imaging Radar-B (SIR-B) over an agricultural test site in west-central Illinois were used to establish end-to-end transfer functions for conversion of the digital numbers on the 8-bit image to values of the radar backscattering coefficient ?0 (m2/m2) in dB. The transfer function for each data take was defined by the SIR-B response to an array of six calibrated point targets of known radar cross section (transponders) and to a large number of area-extended targets also with known radar cross section as measured by externally calibrated, truck-mounted scatterometers. The radar cross section of each transponder at the SIR-B center frequency was measured on an antenna range as a function of the local angle of incidence. Two truck-mounted scatterometers observed 20-80 agricultural fields daily at 1.6 GHz with HH-polarization and at azimuth viewing angles and incidence angles equivalent to those of the SIR-B. The form of the transfer function is completely defined by the SIR-B receiver and the incoherent averaging procedure incorporated into production of the standard SIR-B image product. Assuming that the processing properly accounts for the antenna gain, all transfer function coefficients are known except for the thermal noise power and a system " constant" that has been shown to vary as a function of uncommanded changes in the effective SIR-B transmit power. 相似文献