全文获取类型
收费全文 | 1212篇 |
免费 | 50篇 |
专业分类
电工技术 | 33篇 |
化学工业 | 196篇 |
金属工艺 | 17篇 |
机械仪表 | 28篇 |
建筑科学 | 30篇 |
矿业工程 | 5篇 |
能源动力 | 51篇 |
轻工业 | 149篇 |
水利工程 | 4篇 |
无线电 | 135篇 |
一般工业技术 | 170篇 |
冶金工业 | 265篇 |
原子能技术 | 13篇 |
自动化技术 | 166篇 |
出版年
2024年 | 2篇 |
2023年 | 8篇 |
2022年 | 14篇 |
2021年 | 20篇 |
2020年 | 18篇 |
2019年 | 25篇 |
2018年 | 30篇 |
2017年 | 39篇 |
2016年 | 21篇 |
2015年 | 20篇 |
2014年 | 30篇 |
2013年 | 65篇 |
2012年 | 45篇 |
2011年 | 34篇 |
2010年 | 44篇 |
2009年 | 53篇 |
2008年 | 48篇 |
2007年 | 46篇 |
2006年 | 46篇 |
2005年 | 36篇 |
2004年 | 36篇 |
2003年 | 31篇 |
2002年 | 33篇 |
2001年 | 35篇 |
2000年 | 25篇 |
1999年 | 36篇 |
1998年 | 91篇 |
1997年 | 68篇 |
1996年 | 49篇 |
1995年 | 28篇 |
1994年 | 33篇 |
1993年 | 20篇 |
1992年 | 17篇 |
1991年 | 18篇 |
1990年 | 17篇 |
1989年 | 13篇 |
1988年 | 11篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 6篇 |
1984年 | 2篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1977年 | 4篇 |
1976年 | 12篇 |
1975年 | 1篇 |
1973年 | 2篇 |
排序方式: 共有1262条查询结果,搜索用时 10 毫秒
111.
Fernandez J. Hidalgo S. Paredes J. Berta F. Rebollo J. Millan J. Serra-Mestres F. 《Electron Device Letters, IEEE》1989,10(5):212-215
An analytical ON-resistance expression for different designs of VDMOS (vertically diffused metal-oxide-semiconductor) devices which takes into consideration the two-dimensional (2-D) nature of the current flow is obtained. This expression differs from other models that overestimate this resistance for large cell spacings. This formulation is in close agreement with experimental points obtained from the interdigitated fabricated structures and with 2-D simulations. Moreover, the effect of a two-level oxide thickness on the ON resistance has been investigated for the interdigitated case 相似文献
112.
113.
Fernandez Martin Sonia del Rey Llorente Ignacio Fraile de Lerma Alberto 《Fire Technology》2021,57(3):1115-1134
Fire Technology - Tunnels are nowadays key elements in transport networks worldwide. To achieve a safe and efficient operation, a proper integration and design of Mechanical, Electrical and... 相似文献
114.
Daniela Russo Patrícia Valent?o Paula B. Andrade Eloy C. Fernandez Luigi Milella 《International journal of molecular sciences》2015,16(8):17696-17718
The present study aimed to investigate the phytochemical profile of leaf methanol extracts of fourteen Smallanthus sonchifolius (yacon) landraces and their antioxidant, anticholinesterase and antidiabetic activities that could lead to the finding of more effective agents for the treatment and management of Alzheimer’s disease and diabetes. For this purpose, antioxidant activity was assessed using different tests: ferric reducing ability power (FRAP), 2,2-diphenyl-1-picryl hydrazyl (DPPH), nitric oxide (˙NO) and superoxide (O2˙−) scavenging and lipid peroxidation inhibition assays. Anticholinesterase activity was investigated by quantifying the acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory activities, whereas antidiabetic activity was investigated by α-amylase and α-glucosidase inhibition tests. To understand the contribution of metabolites, phytochemical screening was also performed by high performance liquid chromatography-diode array detector (HPLC-DAD) system. Among all, methanol extract of PER09, PER04 and ECU44 landraces exhibited the highest relative antioxidant capacity index (RACI). ECU44 was found to be rich in 4,5-di-O-caffeoylquinic acid (CQA) and 3,5-di-O-CQA and displayed a good α-amylase and α-glucosidase inhibition, showing the lowest IC50 values. Flavonoids, instead, seem to be involved in the AChE and BChE inhibition. The results of this study revealed that the bioactive compound content differences could be determinant for the medicinal properties of this plant especially for antioxidant and antidiabetic activities. 相似文献
115.
Or Raifman Dr. Sofiya Kolusheva Dr. Said El Kazzouli Dr. Dina M. Sigano Dr. Noemi Kedei Dr. Nancy E. Lewin Ruben Lopez‐Nicolas Ana Ortiz‐Espin Juan C. Gomez‐Fernandez Dr. Peter M. Blumberg Dr. Victor E. Marquez Prof. Senena Corbalan‐Garcia Prof. Raz Jelinek 《Chembiochem : a European journal of chemical biology》2010,11(14):2003-2009
Synthetic diacylglycerol‐lactones (DAG‐lactones) are effective modulators of critical cellular signaling pathways, downstream of the lipophilic second messenger diacylglycerol, that activate a host of protein kinase C (PKC) isozymes and other nonkinase proteins that share similar C1 membrane‐targeting domains with PKC. A fundamental determinant of the biological activity of these amphiphilic molecules is the nature of their interactions with cellular membranes. This study examines the biological properties of charged DAG‐lactones exhibiting different alkyl groups attached to the heterocyclic nitrogen of an α‐pyridylalkylidene chain, and particularly the relationship between membrane interactions of the substituted DAG‐lactones and their respective biological activities. Our results suggest that bilayer interface localization of the N‐alkyl chain in the R2 position of the DAG‐lactones inhibits translocation of PKC isoenzymes onto the cellular membrane. However, the orientation of a branched alkyl chain at the bilayer surface facilitates PKC binding and translocation. This investigation emphasizes that bilayer localization of the aromatic side residues of positively charged DAG‐lactone derivatives play a central role in determining biological activity, and that this factor contributes to the diversity of biological actions of these synthetic biomimetic ligands. 相似文献
116.
Cekdar Vakifahmetoglu Paolo Colombo Alberto Pauletti Cristina Fernandez Martin Florence Babonneau 《International Journal of Applied Ceramic Technology》2010,7(4):528-535
SiOC glass monoliths possessing hierarchical porosity were produced by a one-pot processing method. Periodic mesoporous organosilica (PMO) particles were embedded into a foamed siloxane preceramic polymer. After pyrolysis at 1000°C in inert atmosphere, open celled, permeable SiOC ceramic monoliths with a high amount of pores, ranging in size from hundred of micrometers to a few nanometers, were obtained. The components possessed a specific surface area of 137 m2/g, indicating the retention of most of the mesopores after the pyrolytic conversion of the PMO precursor particles. These fillers converted to truncated rhombic dodecahedral SiOC mesoporous micron-sized grains, homogeneously distributed throughout the SiOC cellular matrix. The produced porous ceramics possessed compression strength of about 1.7 MPa, which is adequate for their use in several engineering applications. 相似文献
117.
A suite of 30 primarily estrogenic organic wastewater contaminants was measured in several influent/effluent wastewater samples from four municipal wastewater treatment plants and effluents from one bleached kraft pulp mill (BKME) using an ultra-trace analytical method based on gas chromatography-high resolution mass spectroscopy (GC-HRMS). In vitro recombinant yeast assay detection of the estrogenic equivalent (EEq) on whole and solid phase extracted (SPE) and fractionated wastewater was also performed. 19-norethindrone was the most frequently detected and abundant (26-224 ng/L) of all the synthetic estrogens/progesterones in the influent samples. 17alpha-ethinylestradiol was the more frequently detected synthetic estrogen/progesterone in the effluents occurring at or below 5 ng/L with some sporadic occurrences of up to 178 ng/L. The greatest levels of steroidal estrogens in municipal effluents were E1>E2>E3 which were all <20 ng/L. Nonylphenol and di(2-ethylhexyl) phthalate were found to be the highest non-steroidal synthetic compounds surveyed in both municipal influent and effluent samples, both occurring at 6-7 microg/L in municipal effluents. BKME contained relatively large amounts of the plant sterol stigmasterol (4 microg/L) but low amounts of fecal sterols, and steroidal estrogens (E2 only at 6 ng/L) when compared to the municipal effluents. In vitro EEq in the wastewater surveyed ranged from 9-106 ng E2/L and ranked from municipal influent>municipal effluent approximately BKME, with most of the estrogenicity fractionating in the 100% methanol SPE fraction followed by a secondary amount in the diethyl ether (for municipal) or methyl-tert butyl ether (for BKME) SPE fractions. Most correlations between chemical and in vitro estrogenic equivalency were weak (p>0.05 in most cases). Unexpected inverse correlations between in vitro estrogenic activity and concentrations of the estrogenic contaminant bisphenol A were found which likely contributed to the weakness of these correlations. A modified toxicity identification and evaluation procedure was continued with the SPE extracts from the more potent 100% methanol SPE fractions of municipal effluent. High performance liquid chromatography band elution retention times, based on in vitro estrogen detection, indicated that steroidal estrogens such as E2 were responsible for most of the estrogenicity of the samples. Subsequent collection and GC-MS analysis of active bands did not confirm the presence of steroidal estrogens, but expanded the possibility of phthalate esters (i.e. dibutyl phthalate) and natural sterols (i.e. beta-sitosterol) contributing to the overall estrogenic load. 相似文献
118.
Thayyath S. Anirudhan Noeline B. Fernandez Manohar D. Mullassery 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2012,87(5):714-722
BACKGROUND: Environmental pollution and its abatement have attracted much attention for some time. The problem of removing pollutants from water and wastewater has grown along with rapid industrialization. Formaldehyde polymerized banana stem (FPBS) having sulphonic acid groups was investigated as an adsorbent for cadmium(II) removal from aqueous solutions. RESULTS: The outstanding function of the adsorbent was demonstrated at pH 9.0. The adsorption efficiency of FPBS was compared with BS and results showed that FPBS was two times more effective than BS for cadmium(II) removal. Maximum recoveries of 97.3 and 90.3% for 10 and 25 mg L?1 initial concentrations were obtained at pH 9.0. Kinetic studies revealed that adsorption occurred in two stages: external mass transport in the first stage and intra‐particular diffusion in the second stage. Adsorption was found to be rapid and equilibrium was attained in 60 min. Among the various desorbing agents tested, 99.2% cadmium recovery was achieved with 0.1 mol L?1 HCl. CONCLUSIONS: The uptake efficiency of cadmium(II) by FPBS was determined. Repeated adsorption‐desorption study showed that FPBS can be used as an adsorbent for the removal and recovery of Cd(II) from aqueous solutions. Copyright © 2012 Society of Chemical Industry 相似文献
119.
Fernandez T. Garcia J.A. Tazon A. Mediavilla A. Pedro J.C. Garcia J.L. 《Electron Device Letters, IEEE》1999,20(11):557-559
In this work, a continuous nonlinear model for the Ids current source in recessed gate pseudomorphic HEMT heterostructures is proposed. A careful characterization of the DC, pulsed, and small-signal nonlinear distortion behaviour of this predominant nonlinearity has been employed in order to extract the model parameters. Being able to reproduce the current-voltage (I-V) behaviour as well as the higher order derivatives of the transconductance and output conductance, the equation is valid for an accurate control of the critical nonlinear distortion phenomena in HEMT applications. Comparisons between measured and simulated results prove its validity under both static and dynamic conditions for either large- or small-signal operation 相似文献
120.
Rodriguez-Garcia J.D. Guerra O. Roca E. Fernandez F.V. Rodriguez-Vazquez A. 《Electronics letters》1999,35(4):260-261
Circuit reduction is a fundamental first step in addressing the symbolic analysis of large analogue circuits. A new algorithm for simplification before generation is presented which is very efficient in terms of speed and the amount of circuit reduction, and solves the accuracy problems of previously reported approaches 相似文献