全文获取类型
收费全文 | 5502篇 |
免费 | 174篇 |
国内免费 | 12篇 |
专业分类
电工技术 | 259篇 |
综合类 | 10篇 |
化学工业 | 1356篇 |
金属工艺 | 119篇 |
机械仪表 | 125篇 |
建筑科学 | 129篇 |
矿业工程 | 2篇 |
能源动力 | 201篇 |
轻工业 | 531篇 |
水利工程 | 17篇 |
石油天然气 | 3篇 |
无线电 | 496篇 |
一般工业技术 | 859篇 |
冶金工业 | 937篇 |
原子能技术 | 150篇 |
自动化技术 | 494篇 |
出版年
2023年 | 38篇 |
2022年 | 73篇 |
2021年 | 133篇 |
2020年 | 46篇 |
2019年 | 58篇 |
2018年 | 112篇 |
2017年 | 85篇 |
2016年 | 138篇 |
2015年 | 85篇 |
2014年 | 161篇 |
2013年 | 282篇 |
2012年 | 248篇 |
2011年 | 291篇 |
2010年 | 214篇 |
2009年 | 248篇 |
2008年 | 271篇 |
2007年 | 216篇 |
2006年 | 182篇 |
2005年 | 197篇 |
2004年 | 155篇 |
2003年 | 165篇 |
2002年 | 147篇 |
2001年 | 122篇 |
2000年 | 97篇 |
1999年 | 118篇 |
1998年 | 404篇 |
1997年 | 235篇 |
1996年 | 152篇 |
1995年 | 111篇 |
1994年 | 114篇 |
1993年 | 103篇 |
1992年 | 46篇 |
1991年 | 49篇 |
1990年 | 36篇 |
1989年 | 61篇 |
1988年 | 34篇 |
1987年 | 34篇 |
1986年 | 42篇 |
1985年 | 39篇 |
1984年 | 36篇 |
1983年 | 37篇 |
1982年 | 22篇 |
1981年 | 27篇 |
1980年 | 23篇 |
1979年 | 26篇 |
1978年 | 28篇 |
1977年 | 38篇 |
1976年 | 49篇 |
1975年 | 12篇 |
1974年 | 16篇 |
排序方式: 共有5688条查询结果,搜索用时 15 毫秒
991.
In order to prepare phosphoric acid resins (RGPs) with large cation exchange capacities, effects of porosity and cross-linking of the precursory poly(glycidyl methacrylate-co-divinylbenzene) beads on their functionalization with phosphoric acid were studied. Two series of precursory copolymers were prepared: one was prepared by changing the amount of divinylbenzene (1–25 mol %) but by fixing that of isobutyl acetate (porogen) at 140 vol % per monomer mixture; the other by changing the amount of the porogen (40–160 vol %) but by fixing that of the cross-linker at 10 mol %. It was clarified that porosity of the precursors plays an important role in the functionalization. Highly porous precursors were functionalized with high efficiency; for example, even the precursors containing 10 mol % of divinylbenzene resulted in RGPs having cation exchange capacities as large as 6–7 meq/g, so long as BET specific surface areas of the precursors were greater than ca. 30 m2/g. The selectivity study has revealed that RGP exhibits the characteristic metal ion selectivity. Lithium ion was adsorbed in preference to sodium and potassium ions; and so-called hard Lewis acid cations, such as uranyl, ferric, and aluminum ions, are adsorbed even from strongly acidic media (1 < pH < 2). Among common divalent metal ions, in addition, the resin exhibits the highest selectivity toward lead ion. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1327–1334, 1997 相似文献
992.
This work aims to develop a reliable method to predict mechanical properties of friction-stir-welded 6 xxx-series alloys with experimentally measured welding heat input. A calorimetrical method was utilized to experimentally measure the welding heat input in the friction stir welded of aluminum alloy 6063-T5. Good correlations between the input variables, i.e., welding parameters and physical properties of the materials, and the welding heat inputs obtained with experimental measurements were discovered. The welding heat input can be predicted using the empirical equation derived based on these correlations. Moreover, the results suggested that the thermal conductivities of the welded alloys affected the welding heat input significantly. Mechanical properties, including hardness and tensile properties, of friction-stir-welded aluminum alloy 6063 were in good correlation to the heat input obtained with experimental measurement. These correlations were explained by the evolution of the strengthening precipitates during welding. This work proposed a reliable new route to predict these mechanical responses through the estimation of heat input. 相似文献
993.
994.
Abe Yasunori Semboshi Satoshi Masahashi Naoya Lim Sung Hwan Choi Eun-Ae Han Seung Zeon 《Metallurgical and Materials Transactions A》2023,54(3):928-938
Metallurgical and Materials Transactions A - Conductive spring wires for application in electrical components require high strength, high electrical conductivity, and convenient manufacturability.... 相似文献
995.
Keiko Azuma Katsunari Ippoushi Hidekazu Ito Hisao Higashio Junji Terao 《Journal of the science of food and agriculture》1999,79(14):2010-2016
The antioxidative effects of vegetable extracts were evaluated using linoleic acid emulsion and liposomal phospholipid suspension systems. First, the antioxidative activities of water, ethanol and 2% metaphosphoric acid extracts of the vegetables were investigated by measuring the rate of oxygen consumption in the peroxidation of linoleic acid initiated by a radical generator, 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH), with a Clark electrode in the absence of metal chelators. Ethanol extracts of moroheiya and perilla exhibited the highest antioxidative activities. Without metal chelators, 12 ethanol extracts and one water extract acted as prooxidants, and this phenomenon could be attributed to the prooxidant action of ascorbic acid in the presence of free transition metal ions. Next, peroxyl radical-scavenging activities of vegetable extracts were examined by adding a metal chelator, diethylenetriaminepentaacetic acid (DTPA), to the linoleic acid emulsion system. The results were compared with their antioxidative activities in phospholipid bilayers by measuring the inhibition of lipid peroxidation in large unilamellar vesicles composed of egg yolk phosphatidylcholine (PC). A good correlation was observed between the antioxidative activities obtained from these two systems. The antioxidative activities in the liposomal phospholipid suspension system correlated with total contents of ascorbic acid and polyphenols in vegetable extracts. © 1999 Society of Chemical Industry 相似文献
996.
Styrene‐divinylbenzene or glycidylmethacrylate‐divinyl‐benzene were copolymerized in powdery polypropylene suspended in water and the resultant polymer composites were blended with a definite amount of polypropylene. The products consisted of polypropylene and the fine particles of the copolymer, which were uniformly dispersed in polypropylene phase. These products were melt‐spun to prepare polypropylene fibers containing the fine particles and then the fibers were stretched to make the fibers microporous. Some properties were estimated: porosity, 1.6–19.7%; average pore size, 0.004–0.009 µm; and specific surface, 9–137 m2/g. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 722–727, 1999 相似文献
997.
Hisayasu Mitsui Ryoji Kumazawa Rie Aizawa Tatsuki Okamoto Tetsuo Ito Masaki Kanegami 《Electrical Engineering in Japan》1999,129(4):24-31
Experiments and investigations were carried out on the voltage life of a bar-coil model with a nickel-plated copper conductor covered with mica-alumina composite insulation at a temperature range of 550–850 °C. Diffusion of copper into the insulation layer was observed on the specimens aged for a long period. Insulation with mica paper gave faster diffusion speed and shorter voltage life than insulation with mica flake. The diffusion speed became higher with an increase in temperature. The ac current gradually increased with aging time and increased rapidly just before breakdown. There was the relationship I = aEn (a, n: constants) between ac current I and applied stress E, and n was approximately equal to 1 in the region where thermal unbalance did not occur. Arrhenius's law held in the relationship between ac current and aging time. Therefore, the breakdown mechanism might be that the effective insulation thickness decreased due to copper diffusion into the insulation layer and the ac current increased gradually until thermal breakdown in the last stage. If copper diffuses into the insulation layer, even with no voltage application, the aging time required to decrease the breakdown voltage to a certain level (the voltage life) obeys Arrhenius's law. If the voltage life is dominated by diffusion into the insulation layer, the activation energy for voltage life in the aging test becomes twice that for diffusion, both with and without voltage application. © 1999 Scripta Technica, Electr Eng Jpn, 129(4): 24–31, 1999 相似文献
998.
Gamut mapping is a color transformation technique to solve a problem caused by mismatch of gamuts among imaging devices. One plausible goal of gamut mapping is to find a reproduction that is perceptually closest to the corresponding original image when an exact color matching is not possible. Several measures to quantify the perceptual difference between images have been proposed and applied to the gamut mapping problem. However most of the measures, such as average color difference, are applied on a pixel‐wise basis and show poor correlation with human visual perception. This article describes a model of the perceptual image difference for a given pair of images, which takes the human's contrast sensitivity into account and applies the model to a gamut mapping for generating a reproduction with minimum perceptual image difference. The model has a multispatial‐frequency channel structure with tunable peak gains for each channel, which are determined by psychophysical experiments, so that the model output fits the observer's sensitivity to the image difference. A gamut‐mapped image with minimum perceptual image difference is obtained by an iterative minimization process. To evaluate the proposed method, subjective evaluation experiments are performed to construct ratio scales that measure perceptual image difference of gamut‐mapped reproductions generated by the proposed and pixel‐wise methods. Results show that the reproductions by the proposed method are perceived as perceptually closest to the original, and the model's estimate of perceptual difference correlates better with the experimentally measured perceived image difference than other pixel‐wise measures. © 1999 John Wiley & Sons, Inc. Col Res Appl, 24, 280–291, 1999 相似文献
999.
Yukie Tanaka Kyaw Thu Aung Mitsuaki Ono Akihiro Mikai Anh Tuan Dang Emilio Satoshi Hara Ikue Tosa Kei Ishibashi Aya Ono-Kimura Kumiko Nawachi Takuo Kuboki Toshitaka Oohashi 《International journal of molecular sciences》2021,22(23)
Medication-related osteonecrosis of the jaw (MRONJ) is related to impaired bone healing conditions in the maxillomandibular bone region as a complication of bisphosphonate intake. Although there are several hypotheses for the onset of MRONJ symptoms, one of the possible causes is the inhibition of bone turnover and blood supply leading to bone necrosis. The optimal treatment strategy for MRONJ has not been established either. BMP-2, a member of the TGF-β superfamily, is well known for regulating bone remodeling and homeostasis prenatally and postnatally. Therefore, the objectives of this study were to evaluate whether cyclophosphamide/zoledronate (CY/ZA) induces necrosis of the bone surrounding the tooth extraction socket, and to examine the therapeutic potential of BMP-2 in combination with the hard osteoinductive biomaterial, β-tricalcium phosphate (β-TCP), in the prevention and treatment of alveolar bone loss around the tooth extraction socket in MRONJ-like mice models. First, CY/ZA was intraperitoneally administered for three weeks, and alveolar bone necrosis was evaluated before and after tooth extraction. Next, the effect of BMP-2/β-TCP was investigated in both MRONJ-like prevention and treatment models. In the prevention model, CY/ZA was continuously administered for four weeks after BMP-2/β-TCP transplantation. In the treatment model, CY/ZA administration was suspended after transplantation of BMP-2/β-TCP. The results showed that CY/ZA induced a significant decrease in the number of empty lacunae, a sign of bone necrosis, in the alveolar bone around the tooth extraction socket after tooth extraction. Histological analysis showed a significant decrease in the necrotic alveolar bone around tooth extraction sockets in the BMP-2/β-TCP transplantation group compared to the non-transplanted control group in both MRONJ-like prevention and treatment models. However, bone mineral density, determined by micro-CT analysis, was significantly higher in the BMP-2/β-TCP transplanted group than in the control group in the prevention model only. These results clarified that alveolar bone necrosis around tooth extraction sockets can be induced after surgical intervention under CY/ZA administration. In addition, transplantation of BMP-2/β-TCP reduced the necrotic alveolar bone around the tooth extraction socket. Therefore, a combination of BMP-2/β-TCP could be an alternative approach for both prevention and treatment of MRONJ-like symptoms. 相似文献
1000.
The mechanism of enhanced PVC impact strength of poly(vinyl chloride) modified by an acrylic graft copolymer was studied by the three-point bending test on a U-notched bar. In the mechanism, the void formation from the modifier released the constrained strain. The release suppresses the stress below the fibril strength in the material; consequently, stable deformation can develop over a large area and, thus, the impact strength of PVC modified by the acrylic graft copolymer is improved. © 1996 John Wiley & Sons, Inc. 相似文献