全文获取类型
收费全文 | 5058篇 |
免费 | 121篇 |
国内免费 | 23篇 |
专业分类
电工技术 | 67篇 |
综合类 | 2篇 |
化学工业 | 654篇 |
金属工艺 | 104篇 |
机械仪表 | 80篇 |
建筑科学 | 44篇 |
矿业工程 | 4篇 |
能源动力 | 114篇 |
轻工业 | 147篇 |
水利工程 | 26篇 |
石油天然气 | 31篇 |
无线电 | 319篇 |
一般工业技术 | 670篇 |
冶金工业 | 2517篇 |
原子能技术 | 38篇 |
自动化技术 | 385篇 |
出版年
2023年 | 44篇 |
2022年 | 56篇 |
2021年 | 89篇 |
2020年 | 103篇 |
2019年 | 73篇 |
2018年 | 88篇 |
2017年 | 105篇 |
2016年 | 96篇 |
2015年 | 71篇 |
2014年 | 104篇 |
2013年 | 242篇 |
2012年 | 109篇 |
2011年 | 159篇 |
2010年 | 134篇 |
2009年 | 127篇 |
2008年 | 134篇 |
2007年 | 131篇 |
2006年 | 99篇 |
2005年 | 69篇 |
2004年 | 67篇 |
2003年 | 60篇 |
2002年 | 58篇 |
2001年 | 44篇 |
2000年 | 48篇 |
1999年 | 98篇 |
1998年 | 711篇 |
1997年 | 483篇 |
1996年 | 299篇 |
1995年 | 202篇 |
1994年 | 179篇 |
1993年 | 154篇 |
1992年 | 39篇 |
1991年 | 46篇 |
1990年 | 44篇 |
1989年 | 41篇 |
1988年 | 57篇 |
1987年 | 40篇 |
1986年 | 38篇 |
1985年 | 37篇 |
1984年 | 19篇 |
1983年 | 20篇 |
1982年 | 24篇 |
1981年 | 27篇 |
1980年 | 32篇 |
1979年 | 15篇 |
1978年 | 19篇 |
1977年 | 63篇 |
1976年 | 144篇 |
1975年 | 15篇 |
1971年 | 9篇 |
排序方式: 共有5202条查询结果,搜索用时 31 毫秒
991.
Deepak Kumar Nidhi Gupta Rina Ghosh Raghuvir H. Gaonkar Bikas C. Pal 《Journal of Functional Foods》2013,5(1):211-218
Carex baccans is used extensively as food additive for its medicinal and nutritional properties. Its extract demonstrated significant inhibition of α-glucosidase and α-amylase with IC50 43.32 ± 1.22 and 562.18 ± 5.98 μg/mL, respectively. A bio-assay guided approach was employed to identify the active constituent(s). Fractionation and purification of the extract led to the isolation of a potent inhibitor, (+)-α-viniferin, and of weak inhibitors smiglasides A and B. (+)-α-Viniferin was quantified in the extract and fractions using HPLC and the method was validated for linearity, limit of detection, limit of quantification, precision, and accuracy. The calibration curve showed good linearity (r2 > 0.999) in the range of 7.813–250 μg/mL. The identification of α-glucosidase and α-amylase inhibitory activity in C. baccans supports the possible use of the plant as functional food for the management of diabetes. The validated HPLC method for the study of plant extracts will be useful in future research. 相似文献
992.
Mitali Ghosal Prashan Kumar Chhetri Manas Kanti Ghosh 《International Journal of Food Properties》2013,16(7):1552-1564
Antioxidants are extremely important substances that possess the ability to protect the body from damage caused by free radical induced oxidative stress. Antioxidants are derived from dietary sources, such as fruits, vegetables, and beverages. In this study, the antioxidant activity of different maturity stages of two varieties of Cyphomandra betacea fruits of Darjeeling was evaluated in vitro. The radical scavenging properties on 2,2-diphenyl-1-picrylhydrazyl, superoxide anion, hydroxyl radical, lipid peroxidation, nitric oxide, and reducing power as well as the flavonoids, phenolics, lycopene, and total carotene contents of methanolic extracts of the fruits were determined. All fruit extracts, mainly the mature red fruit of purple-red variety exhibited strong scavenging activity towards all radicals tested due to the presence of relatively high total phenol, flavonoids, and lycopene as well as total carotene contents. The findings suggest that purple red variety of C. betacea fruit is endowed with antioxidant phytochemicals, which could provide protection against oxidative stress induced diseases. 相似文献
993.
In this research article, a new third-order voltage-mode active-C asymmetrical band pass filter is proposed. It uses three numbers of current-controlled current conveyors and three numbers of equal-valued capacitors. The topology has the following important features: uses only three active elements, uses three capacitors, uses all grounded capacitors and no resistor is suitable for integrated circuit design, there is no matching constraint, high input impedance, low output impedance, central frequency can easily be electronically controlled by bias current, and frequency response is asymmetrical in nature. The application of the proposed topology in the realisation of a voltage-mode sixth-order symmetrical band pass filter has been demonstrated. The workability of the proposed topology and sixth-order filter has been confirmed by simulation results using 0.35-µm Austria Micro Systems complementary metal oxide semiconductor technology. 相似文献
994.
In this paper, the design geometry of Ferroelectric Dopant Segregated Schottky Barrier Tunnel Field Effect Transistor (Fe DS-SBTFET) has been proposed. Various electrical properties such as ION/IOFF ratio and subthreshold swing (SS) of the proposed design have been premeditated and compared with different asymmetric structures. The impact of various types and thickness of buffer on the ferroelectric properties have been analysed. The device has been optimised for various doping concentrations and lengths of the dopant segregated layer (DSL). The digital applications of the proposed device in terms of complementary TFET digital inverter circuit have been studied. The transient characteristics and the delay parameters by considering various ferroelectric thicknesses have been analysed. Moreover, the transfer characteristics and electric field have been explored in the presence and absence of ferroelectric layer to obtain a better insight into the ferroelectric properties of the proposed structure. The electric field at the tunnelling junction is enhanced by the presence of ferroelectric layer which improves the ON current. The structure with ferroelectric thickness of 6 nm provides the best ION/IOFF ratio of 1.2 × 109 and SS of 14 mV/dec. 相似文献
995.
Polymeric nanocomposites (PNCs) have drawn a special attention of researchers from all over the world. But microfiber-reinforced composites still remain the workhorse for the structural applications. The amalgamation of PNCs with microfiber-reinforced composites will open new vistas in advanced composites. This concept of continuous fiber reinforced nano-reinforced-matrix composites (CRNCs) will revolutionize the advanced composite technologies. The nanoscopic dimensions and extreme aspect ratios inherited by nanoreinforcements cause unique characteristics such as extensive interfacial area, large number density, and so on. CRNCs would offer unprecedented combination of properties to make them suitable for most of the load-bearing structural applications. 相似文献
996.
Shiv Sankar Bhattacharya Alka Mishra Dilipkumar Pal Ashoke Kumar Ghosh Amitava Ghosh Subham Banerjee 《Polymer-Plastics Technology and Engineering》2013,52(9):878-884
Initially interpenetrating network (IPN) hydrogel was prepared by dispersing xanthan gum (XG) into poly(vinyl alcohol) (PVA) backbone in an aqueous medium. Polyacrylic acid (PAA)/Poly (vinyl alcohol)-Xanthan gum IPN superabsorbent composite were fabricated well by dispersing the prepared IPN hydrogel in acrylic acid and polymerized in a complete aqueous environment through chemical cross-linking method. These superabsorbent polymeric composites were analytically evaluated by scanning electron microscopy (SEM), Fourier Transform Infrared Spectra (FTIR), Thermal analysis (DSC) and X-ray diffraction (XRD) analysis. Simultaneously water absorbency, swelling kinetics and water retention abilities of this prepared superabsorbent polymeric composites were also investigated systematically. 相似文献
997.
M. Hauser M. Wendler S. Ghosh Chowdhury A. Weiß J. Mola 《Materials Science & Technology》2015,31(12):1473-1478
An in situ magnetic device was employed to quantify the deformation induced martensite in a Fe–19Cr–3Mn–4Ni–0.15C–0.15N (wt-%) steel during tensile testing in the temperature range of ?40 to 22°C. The new device consists of an electromagnetic field which serves to magnetise the martensite phase as it forms during tensile loading and a second coil to detect the effective electrical potential difference induced by the magnetisation of tensile specimens. To implement the in situ measurement system, a correlation was necessary between the induced electrical potential difference and the deformation induced martensite fractions during uniaxial static tensile tests. The correlation procedure was found to require only the quantification of deformation induced martensite content in a tensile specimen strained until fracture using an ex situ magnetic saturation unit. 相似文献
998.
The operation of HVDC converters is discrete in nature. It is, therefore, proper to take into account the discrete behavior of converter operation while developing the system model for small signal stability analysis. This paper presents the development of such a system model, which also explicitly includes the effect of phase angle of respective AC bus voltages. A modular approach has been adopted for the formulation of complete state space system model. Utilizing the system model, the stability is examined in the controller parameter plane using eigenvalue analysis. The stability domains thus obtained are validated through detailed dynamic digital simulation. 相似文献
999.
M. Ghosh Chaudhuri J. Basu G. C. Das S. Mukherjee M. K. Mitra 《Journal of the American Ceramic Society》2013,96(2):385-390
Nanostructured Aluminum Nitride (AlN) has been prepared by carbothermal reduction followed by nitridation (CTRN) of alumina gel over a temperature range 1200°C–1350°C and time period of 30 min to 3 h. Before heat treatment the gel is repeatedly evacuated and purged with ammonia. The nanopores of the gel are filled with ammonia which acts as a source of in situ nitrogen at heat‐treatment temperature. Dextrose also decomposes at the reduction temperature and generates ultrafine carbon. The stability diagram of the carbon saturated Al–N–O system is constructed and it shows that extremely low partial pressure of oxygen is required for the stability of AlN. The ultrafine carbon as well as hydrogen from the cracking of ammonia is not sufficient to create the extremely low partial pressure of oxygen required for the stabilization of AlN. So the sample is heat treated in charcoal boat in nitrogen atmosphere to achieve an extremely low partial pressure of oxygen required for the formation of AlN. The material has been characterized through XRD, FESEM, and HRTEM analyses. The spherical particle size of AlN is obtained ~21 nm. 相似文献
1000.
Mesoporous γ‐Al2O3 powders with nanofiber and nanorod‐like structures were synthesized using boehmite sols in the presence of triblock copolymer, P123 in ethanol by solvothermal process at different temparatures (100°C–165°C) followed by calcination at 400°C–1000°C. The powders were characterized by low‐ and wide‐angle X‐ray diffraction (XRD), N2 adsorption–desorption, and transmission electron microscopy (TEM). The adsorption efficiency of the powders with Congo red (CR) was studied by UV–vis spectroscopy. The γ‐Al2O3 phase became stable up to 1000°C. The nanorods obtained at 165°C had narrower pore size distribution (PSD) than nanofibers synthesized at 100°C, the former showed higher CR adsorption efficiency. The stepwise growth mechanism of nanofibers to nanorods conversion with increase in solvothermal temperatures was illustrated. 相似文献