全文获取类型
收费全文 | 355篇 |
免费 | 5篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 4篇 |
化学工业 | 52篇 |
金属工艺 | 2篇 |
机械仪表 | 32篇 |
建筑科学 | 13篇 |
矿业工程 | 2篇 |
能源动力 | 15篇 |
轻工业 | 23篇 |
水利工程 | 1篇 |
无线电 | 49篇 |
一般工业技术 | 65篇 |
冶金工业 | 49篇 |
原子能技术 | 11篇 |
自动化技术 | 44篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 2篇 |
2019年 | 4篇 |
2018年 | 8篇 |
2017年 | 10篇 |
2016年 | 7篇 |
2015年 | 5篇 |
2014年 | 15篇 |
2013年 | 24篇 |
2012年 | 7篇 |
2011年 | 14篇 |
2010年 | 12篇 |
2009年 | 18篇 |
2008年 | 11篇 |
2007年 | 16篇 |
2006年 | 10篇 |
2005年 | 6篇 |
2004年 | 8篇 |
2003年 | 7篇 |
2002年 | 7篇 |
2001年 | 5篇 |
2000年 | 8篇 |
1999年 | 3篇 |
1998年 | 21篇 |
1997年 | 23篇 |
1996年 | 8篇 |
1995年 | 9篇 |
1994年 | 7篇 |
1993年 | 9篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1966年 | 1篇 |
1964年 | 1篇 |
排序方式: 共有362条查询结果,搜索用时 0 毫秒
71.
Nidhi Taneja Gaurav Bhatnagar Balasubramanian Raman Indra Gupta 《Multimedia Tools and Applications》2013,67(3):593-606
Joint watermarking and encryption is an upcoming security solution that combines leading but complementary techniques to achieve an enhanced security level. Real time applications using joint watermarking and encryption framework has three requirements: data to be efficiently compressed, watermarking technique to sustain compression, and encryption technique to be developed in a way so as not to disturb the compression efficiency. Finding an optimal solution that combines the three techniques while fulfilling these requirements is a challenging problem. This paper thus, proposes a wavelet domain based joint watermarking and encryption framework that employs singular value decomposition based watermark embedding and sign bit encryption prior to compression. The varying significance of different subbands has been considered to encrypt the data without adversely effecting the compression ratio. Experimental analysis using various evaluation parameters and attack scenarios has revealed the ability of the proposed framework to prove content-ownership, even from the encrypted data. Comparative analysis with the existing techniques reflect its ability to provide better security with less computational resources. This makes it a preferable solution for data security at all stages of data archival, transmission or distribution. 相似文献
72.
Preeti Verma Poornendu Chaturvedi J. S. B. S. Rawat Manohar Kumar Surendra Pal Mahesh Bal D. S. Rawal Harsh Hanuman Prasad Vyas Partha Ghosal P. K. Bhatnagar 《Journal of Materials Science: Materials in Electronics》2007,18(6):677-680
Activation of abnormal emitting sites in Carbon Nano Tube (CNT) field emitters and their elimination is reported. CVD grown,
patterned CNT was used as cathode for field emission studies. We encountered the problem of current non-uniformity in CNT
cathode. This non-uniformity was attributed to abnormally active emitting sites during voltage ramp-up. The sudden increase
in current resulted in region of positive slope in F–N curve, which can’t be explained by conventional F–N theory. Also the
grown CNTs can be a mixture of metallic and semi conducting nature, which may cause deviation from the conventional F–N theory.
We could eliminate abnormally active sites by electric field treatment, thereby increasing current uniformity and stability.
The work is underway to understand the deviation in FN curve at high fields. 相似文献
73.
Biomass has been recognized as a major world renewable energy source to supplement declining fossil fuel sources of energy. Biomass derived transportation fuels have not only the potential to replace conventional fuels but can also be utilized as blending components for improving the quality of these fuels. The biocrude obtained from Euphorbia antisyphilitica, identified as the most potential petrocrop was investigated as a potential source for liquid fuels. The feed was studied for yield conversion data under different catalyst to feed ratio at various temperatures. Maximum middle distillates selectivity was observed at catalyst/oil ratio 4 and 6 and reaction temperature 500 °C. The main constituents of the gaseous products are C3, C4 and C5. The liquid fuels are highly aromatic with low olefinic content. 相似文献
74.
S Srivastava SJ Watowich JM Petrash SK Srivastava A Bhatnagar 《Canadian Metallurgical Quarterly》1999,38(1):42-54
Aldose reductase (AR) is a member of the aldo-keto reductase superfamily. Due to its ability to catalyze the formation of sorbitol from glucose during hyperglycemic and hypertonic stress, the aldose-reducing property of AR has been accepted as its main physiological and pathological function. Nonetheless, AR is a poor catalyst for glucose reduction and displays active-site properties unexpected of a carbohydrate-binding protein. We, therefore, examined the catalytic properties of AR with a series of naturally occurring aldehydes, compatible in their hydrophobicity to the large apolar active site of the enzyme. Our results show that recombinant human AR is an efficient catalyst for the reduction of medium- to long-chain unbranched saturated and unsaturated aldehydes. The enzyme displayed selective preference for saturated aldehydes, such as hexanal, and unsaturated aldehydes, such as trans-2-octenal and nonenal as well as their 4-hydroxy derivatives. Short-chain aldehydes such as propanal and acrolein were reduced less efficiently. Branched derivatives of acrolein or its glutathione conjugate (GS-propanal) were, however, reduced with high efficiency. In the absence of NADPH, the alpha, beta unsaturated aldehydes caused covalent modification of the enzyme. On the basis of electrospray mass spectrometric analysis of the wild-type and site-directed mutants of AR (in which the solvent exposed cysteines were individually replaced with serine), the site of modification was identified to be the active-site residue, Cys 298. The unsaturated aldehydes, however, did not modify the enzyme bound to NADPH and did not inactivate the enzyme during catalysis. Modeling studies indicate that the large hydrophobic active site of AR can accommodate a large number of aldehydes without changes in the structure of the binding site or movement of side chains. High hydrophobicity due to long alkyl chains or apolar substituents appears to stabilize the interaction of the aldehyde substrates with the enzyme. Apparently, such hydrophobic interactions provide substrate selectivity and catalytic efficiency of the order achievable by hydrogen bonding. Since several of the aldehydes reduced by AR are either environmental and pharmacological pollutants or products of lipid peroxidation, the present studies provide the basis of future investigations on the role of AR in regulating aldehyde metabolism particularly under pathological states associated with oxidative stress and/or aldehyde toxicity. 相似文献
75.
In this paper, we propose two differential relaying strategies; Active User Strategy (AUS) and Passive Users Relaying Strategy
(PURS), which could be used by the base-station to transmit data of two users over downlink channels in a two-user cooperative communication network. Differential schemes are used so the users do not require the knowledge of channel gains for decoding of their data. The
performance of both schemes is evaluated for the decode-and-forward, selection relaying, and incremental relaying protocols.
For the decode-and-forward protocol, the performance heavily depends upon the signal-to-noise ratio (SNR) of the link between
source and relay. We propose a conditional probability of error based approach, which can be used to regulate the erroneous
relaying of data. Both AUS and PURS are able to achieve performance gains as compared to the direct transmission differential
scheme in the case of selection relaying and incremental relaying protocols at high SNRs. The proposed schemes perform better
than their counterpart of the amplify-and-forward differential relaying proposed previously. 相似文献
76.
Multiple urethral calculi are rarely found in children. We report herein two unusual cases of children found to have multiple urethral calculi. In one, the calculi formed proximal to a stricture and in the other they formed within a diverticulum. Both patients required urethrotomy for removal of the calculi. A unique cause of urethral stricture is also described in case 1. 相似文献
77.
A critical assessment of the merits of core-spinning by means of comparisons of the strength and extension of core-spun yarns with all-staple-fibre yarns forms the basis of this paper. Core-spinning was done by introducing the filament under tension into the drafted strand as the latter entered the front rollers of the ring-frame. A 20-den (2.2-tex) nylon monofilament was used as core, and three types of staple-fibre covering were investigated. The effects of twist, pre-tension, and feeding arrangements on the geometrical disposition and tensile properties of the yarns were examined. Improvements in strength are, in general, realized at low twists by the incorporation of the filament and by further constraining it to occupy the core. The contribution of the components to the yarn strength and the process of breaking were also subjected to a detailed study. The studies reported provide an interesting insight into the extent of cohesion developed between the fibres during the straining of the yarn and its influence on the process of breaking and ultimately on yarn extension. 相似文献
78.
Shivani Dhall Manasvi Kumar Mehar Bhatnagar B.R. Mehta 《International Journal of Hydrogen Energy》2018,43(37):17921-17927
In the present work, role of palladium (Pd) and tin oxide (SnO2) nanoparticles (NPs) deposited on graphene has been investigated in terms of dual gas sensing characteristics of ethanol and H2 between two temperatures. The incorporation of nanoparticles into graphene has been observed which results a large change in the sensing response towards these gases. It is investigated that, incorporation of isolated Pd NPs on the graphene facilitates the room temperature sensing of H2 gas with fast response and recovery time whereas, isolated SnO2 NPs on graphene enables the detection of ethanol at 200 °C. However, combination of isolated Pd and SnO2 NPs on graphene shows improved sensitivity and good selectivity towards H2 and ethanol, usually not observed in chemiresistive gas sensors. Catalytic PdH interaction and corresponding change in work function of nanoparticles on hydrogenation resulting in modifications in electronic exchange between Pd, SnO2 and graphene are responsible for the observed behavior. These results are important for developing a new class of chemiresistive type gas sensor based on change in the electronic properties of the graphene and NPs interfaces. 相似文献
79.
Rohit R. Shahi Ashish Bhatnagar Sunita K. Pandey Viney Dixit O.N. Srivastava 《International Journal of Hydrogen Energy》2014
The present investigations are focused on the effect of different Ti-based catalysts (Ti, TiO2, TiCl3 and TiF3) on de/re-hydrogenation characteristics of nanocrystalline MgH2. Desorption temperature of milled MgH2 lowers from 380 to 350, 340, 310 and 260 °C with the addition of Ti, TiO2, TiCl3 and TiF3 respectively. The rehydrogenation characteristics are also improved through the deployment of Ti-based catalysts. Among all Ti based additives, TiF3 is found to be the most effective catalyst for hydrogen sorption from nano MgH2. The better catalytic effect of TiF3 over other Ti-based catalyst can be explained on the basis of temperature programmed reduction (TPR) studies. TPR experiments performed for different Ti additives, reveals that there is no oxidation/reduction reaction below 400 °C except for TiF3. The TPR profile of TiF3 shows some oxidation/reduction reaction exhibits at 200 °C. In order to further improve the sorption characteristics and cyclability of TiF3 catalyzed nano MgH2, we have investigated the effect of SWCNTs in MgH2+TiF3 sample. De/rehydrogenation characteristics reveal the synergistic effect of SWCNTs and TiF3 in MgH2+TiF3 sample. The details of the improvement in sorption behavior of MgH2–TiF3 in presence of SWCNTs are described and discussed. 相似文献
80.
Amit Kumar Dixit Deepti Bhatnagar Vineet Kumar D. Chawla K. Fakhruddin Deepak Bhatnagar 《Journal of Functional Foods》2012,4(1):197-206
The in vitro antioxidant potential and in vivo radioprotective ability of soy isoflavones was studied. Male Wistar rats were orally administered with soybean isoflavones (60 mg/kg) for 21 days followed by gamma irradiation exposure. Survival studies in rats exposed at 10 Gy and endogenous spleen colony forming unit assay (CFU) at 6.0 Gy were performed in order to find radioprotective and immunomodulatory nature of the compound. The rat liver post mitochondrial supernatant and erythrocytes were used to measure lipid peroxidation (LPO) and glutathione (GSH) content along with various antioxidant enzymes like superoxide dismutase (SOD), catalase (CAT) and glutathione-S-transferase (GST) after gamma irradiation exposure at 2.0 Gy. Pretreatment with soy isoflavone, prior to gamma irradiation resulted in the increased survival rate of the animals as compared to irradiated group. CFU counts in the isoflavone treated group followed by gamma irradiation at 6 Gy were significantly high as compared to control and the irradiated group, showing immunomodulatory nature of the isoflavones. Pretreatment with isoflavones also significantly reduced the LPO, enhanced the activity of antioxidant enzymes and improved haematological and histological parameters. The present study suggests that supplementation with isoflavone has potent antioxidant activity and act as probable radioprotector against gamma radiation induced oxidative damage. 相似文献