首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1161篇
  免费   49篇
  国内免费   12篇
电工技术   11篇
综合类   2篇
化学工业   322篇
金属工艺   21篇
机械仪表   25篇
建筑科学   17篇
能源动力   54篇
轻工业   108篇
水利工程   3篇
石油天然气   12篇
无线电   133篇
一般工业技术   275篇
冶金工业   59篇
原子能技术   3篇
自动化技术   177篇
  2024年   5篇
  2023年   25篇
  2022年   52篇
  2021年   73篇
  2020年   66篇
  2019年   50篇
  2018年   64篇
  2017年   47篇
  2016年   44篇
  2015年   29篇
  2014年   70篇
  2013年   100篇
  2012年   49篇
  2011年   85篇
  2010年   56篇
  2009年   37篇
  2008年   44篇
  2007年   37篇
  2006年   33篇
  2005年   20篇
  2004年   30篇
  2003年   32篇
  2002年   23篇
  2001年   13篇
  2000年   15篇
  1999年   15篇
  1998年   14篇
  1997年   9篇
  1996年   6篇
  1995年   7篇
  1994年   10篇
  1993年   9篇
  1992年   10篇
  1991年   3篇
  1990年   5篇
  1989年   4篇
  1988年   4篇
  1987年   6篇
  1985年   4篇
  1984年   2篇
  1983年   2篇
  1982年   3篇
  1981年   2篇
  1979年   2篇
  1978年   2篇
  1977年   1篇
  1976年   2篇
  1974年   1篇
排序方式: 共有1222条查询结果,搜索用时 15 毫秒
971.
Lipoxygenase from soybean was encapsulated and the effect of different carrier materials (whey protein, gum arabic, whey protein along with sodium alginate and maltodextrin) on enzyme stability during spray drying was studied and compared with freeze drying. The addition of polyethylene glycol (PEG-4000) during spray drying evidently enhanced enzyme stability. Total activity of lipoxygenase after spray drying was 1.14 × 104(whey protein isolate), 1.2 × 104(gum arabic), 1.09 × 104 (whey protein isolate + sodium alginate), 1.44 × 104(maltodextrin), and 1.55 × 104(PEG + maltodextrin). Highest enzyme activity recovery of 72.02% was achieved with the combined addition of maltodextrin and PEG-4000. Moisture, scanning electron microscopy analysis, and storage studies were carried out for spray- and freeze-dried enzyme.  相似文献   
972.
Heterogeneous Mn(III) chiral salen complexes are prepared through covalent attachment of salen ligand on silica gel via chloropropyl spacer and subsequent complexation with manganese. The complexes are well characterized by IR, UV/VIS, TGA and elemental analysis. Epoxidation of unfunctionalised prochiral olefins by Mn(III) chiral salen complexes using iodosobenzene and m-CPBA as the terminal oxidants and NMO as a co-oxidant was achieved with good yields albeit low enantiomeric excess.  相似文献   
973.
Removal of water from the crude petroleum during its extraction and refining process is one of the major problems faced by petroleum industries, so in this study a superabsorbent has been synthesized from Psyllium and acrylic acid based polymers under the influence of gamma radiations using hexamine as a crosslinker. After optimizing various reaction parameters, the optimized superabsorbent has been tested for its selective water absorption capacity from different oil–water emulsions as a function of time, temperature, pH, and NaCl concentration. The synthesized superabsorbent has been found to be highly selective toward water absorption with maximum percent swelling of 8560% in petrol–water emulsion. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011  相似文献   
974.
The performance of new composite metal foams (CMFs) under bending was evaluated with simultaneous acoustic emission (AE) monitoring on samples processed by cast and powder metallurgy (PM) techniques. The results showed high maximum strength in all samples up to 86 MPa with more ductile failure in PM samples. Acoustic emission behavior confirmed that the dominating failure mechanism of cast CMF is the brittle fracture of intermetallic phases that mostly exist at the interface of the steel spheres with the aluminum matrix, whereas in PM samples (100 pct steel), the failure is governed by the propagation of preexisting microporosities in the matrix resulting in a complete ductile failure. SEM imaging of the fracture surfaces supported these findings.  相似文献   
975.
ABSTRACT

Image super-resolution (SR) techniques aim to estimate high-resolution (HR) image from low-resolution (LR) image. Existing SR method has slow convergence and recovery of high-frequency details are inaccurate. To overcome these issues, two algorithms have been proposed for image SR based on non-local means improved iterative back projection (NLM-IIBP), deep convolutional neural network improved iterative back projection (DCNN-IIBP) to produce high-resolution images with low noise, minimal blur by restoring high-frequency details. In NLM-IIBP denoised images have been interpolated using cubic B-spline interpolation and processed using IIBP based on guided bilateral method. NLM preserves the edges effectively, but does not consider high dimensional information and over smoothing during noise minimization. To further improve the resolution, NLM is replaced by DCNN. DCNN denoising method suppresses different noises at different noise levels. The proposed algorithms have been analysed and compared with existing approaches using various parameters to prove the effectiveness.  相似文献   
976.
Oxidative chemical polymerization of aniline was carried out using peroxydisulphate and peroxomonosulphate as a lone initiator in an aqueous acidic medium in the presence of Rayon fiber. The Rayon fiber was tested for the chemical grafting of polyaniline onto it. The content of polyaniline (wt %) in the backbone was found to vary while varying the [M], [I], and (amount of Rayon fiber) during the polymerization of aniline. Various graft parameters like rate of grafting, % grafting, and % efficiency were calculated. Rate of homopolymerization was also followed for both cases. The chemical grafting was confirmed using FTIR spectroscopy, cyclic voltammetry, weight loss study, and conductivity measurements. Probable mechanism has been proposed to explain the experimental results obtained. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 468–478, 2001  相似文献   
977.
The implementation of three parallel sorting algorithms, namely binary sort, odd-even transposition sort and bitonic sort, on a network of transputers is analysed in the paper. The variation in the performance of these algorithms as the number of processors and sort size are changed is investigated. Experimental results show that when up to eight transputers are used, connected as a linear pipeline configuration, all three algorithms can achieve reasonable speedup ratios. The bitonic sort, binary sort odd-even transposition sort achieve speedup ratios of 5, 4.4 and 4, respectively, when eight processors are used to sort 100,000 integers. Analytical models are derived which can be used to predict the performance of the three algorithms when a linear pipeline configuration is used. The predicted performance of the algorithms is compared with the experimental performance in order to validate the model. When the models are used to predict the performance using 16 transputers, it is found that the speedup does not significantly improve compared to the performance achieved with eight transputers. This shows that interprocessor communication has a significant effect on the algorithmic performance when a larger number of processors are used. The conclusions reinforce the fact that the binary and bitonic sorting algorithms are not well-suited to a linear pipeline configuration and that they may perform better if a different topology were used, for example a mesh or a cube connection scheme. Further, the analytical technique used for performance modelling as elaborated in the paper can be employed profitably for other multiprocessor systems as well.  相似文献   
978.
Transition-metal selenides are considered as one of the promising anode materials for potassium ion batteries (PIBs) due to their high theoretical capacities. However, addressing the issue of irreversibility caused by the large volume changes during potassiation/depotassiation, especially at high rates, remains a major challenge. This challenge is tackled by constructing nickel-iron selenide (NFS) with a unique hierarchically porous donut-like morphology using a simple template-free solvothermal strategy. With the bimetallic strategy and well-designed architecture, the donut-like NFS displays outstanding potassium storage performance, exhibiting a high reversible capacity (458 mAh g−1 even after 100 cycles at a slow rate of 0.1 A g−1), an impressive rate capability up to 10 A g−1 (≈10 mA cm−2), and an excellent capacity retention over 1000 cycles at 2 A g−1. By combining theoretical and experimental techniques, a two-stage intercalation-conversion reaction mechanism is put forward. This work provides an effective approach to develop bimetallic selenides electrode materials for applications in PIBs and potentially for other energy storage devices.  相似文献   
979.
The polycrystalline samples of Ba5BiTi3Nb7O30 (hereafter BBTN) belonging to ferroelectric oxide family of tungsten bronze structure were prepared by high temperature solid-state reaction method. Preliminary X-ray analysis of the samples provided the lattice parametersa=11·9331 Å,b=14·9684 Å, andc=7·0193 Å, and also formation of a single-phase orthorhombic structure at room temperature (303 K). Detailed studies of dielectric constant (ε) and loss (tanδ) as a function of frequency (500 Hz to 10 KHz) at room temperature and also as a function of temperature (liquid nitrogen to 160°C) show the dielectric anomaly and structural phase transition at 16·8°C.  相似文献   
980.
The bisphthalonitrile (PN) thermosets series (poly(Baph), poly(Bafph), and poly(Bzph)) were prepared and subjected to 100 and 500 kGy γ-ray irradiation dose from cobalt-60 (60Co) as a source. The main objective of this present study was to investigate the effects of gamma irradiation on the chemical structure, thermomechanical, mechanical, and thermal stabilities, which were studied by using a Fourier transform infrared (FTIR), dynamic mechanical analysis, bending test, and thermogravimetric analysis, respectively. The PN resins characteristics bands, namely, nitrile, triazine ring, and phthalocyanine, were not affected on γ-ray irradiation. However, remarkable changes were observed in the chemical structures of benzene, alkyl and  CF3, which indeed slightly declined the thermal stabilities, thermomechanical and flexural properties. The decrease in properties could be ascribed to the scission of molecular chains and rupture of chemical bonds of PN resin as confirmed by the FTIR. The poly(Bafph) showed a maximum decline in the thermal stabilities and mechanical properties due to the existence of  CF3 in the polymer skeleton, which could not be crosslinked again once scission occurs under radiation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48313.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号