全文获取类型
收费全文 | 2835篇 |
免费 | 134篇 |
国内免费 | 20篇 |
专业分类
电工技术 | 63篇 |
综合类 | 8篇 |
化学工业 | 632篇 |
金属工艺 | 61篇 |
机械仪表 | 82篇 |
建筑科学 | 92篇 |
矿业工程 | 6篇 |
能源动力 | 186篇 |
轻工业 | 230篇 |
水利工程 | 18篇 |
石油天然气 | 40篇 |
无线电 | 325篇 |
一般工业技术 | 585篇 |
冶金工业 | 220篇 |
原子能技术 | 21篇 |
自动化技术 | 420篇 |
出版年
2024年 | 12篇 |
2023年 | 64篇 |
2022年 | 100篇 |
2021年 | 146篇 |
2020年 | 129篇 |
2019年 | 124篇 |
2018年 | 146篇 |
2017年 | 149篇 |
2016年 | 152篇 |
2015年 | 79篇 |
2014年 | 145篇 |
2013年 | 253篇 |
2012年 | 182篇 |
2011年 | 190篇 |
2010年 | 136篇 |
2009年 | 142篇 |
2008年 | 109篇 |
2007年 | 89篇 |
2006年 | 51篇 |
2005年 | 46篇 |
2004年 | 35篇 |
2003年 | 40篇 |
2002年 | 42篇 |
2001年 | 33篇 |
2000年 | 24篇 |
1999年 | 32篇 |
1998年 | 46篇 |
1997年 | 32篇 |
1996年 | 42篇 |
1995年 | 33篇 |
1994年 | 30篇 |
1993年 | 15篇 |
1992年 | 15篇 |
1991年 | 9篇 |
1990年 | 14篇 |
1989年 | 4篇 |
1988年 | 13篇 |
1987年 | 11篇 |
1986年 | 10篇 |
1985年 | 13篇 |
1984年 | 8篇 |
1983年 | 10篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1976年 | 8篇 |
1973年 | 2篇 |
1964年 | 1篇 |
排序方式: 共有2989条查询结果,搜索用时 15 毫秒
71.
Berk Ozsayin Emre Yilmaz Medine Ispir Hasan Ozkaynak Ercan Yuksel Alper Ilki 《Construction and Building Materials》2011,25(10):4017-4024
The mechanical characteristics of infill walls retrofitted with carbon fiber reinforced polymer (CFRP) sheets are really important for the realistic prediction of seismic performance of the vulnerable reinforced concrete (RC) frames retrofitted through CFRP strengthened infill walls. In this study, 36 hollow brick wall specimens were tested either under uniaxial compression or diagonal tension before and after retrofitting externally with CFRP sheets. The test parameters are the dimensions of the walls, the orientation of holes of bricks, the type of mortar, the amount of CFRP sheets and the details of strengthening application. At the end of the tests, a significant contribution of CFRP sheets on the mechanical characteristics of hollow brick walls was observed in terms of several important structural design parameters such as Young and shears moduli, axial and shears strengths as well as the deformation capacity. Finally, the strength and deformability characteristics of the walls and frames retrofitted with CFRP sheets were predicted analytically. The predictions were in good agreement with the experimental data. 相似文献
72.
Modulus of elasticity is an important parameter used for the structural assessment and retrofitting of concrete structures. In this study, an experimental investigation on the modulus of elasticity of concrete was carried out, the results of which is presented. 60 mixtures were prepared, in which the effects of water/cement ratio, maximum size of the aggregate, aggregate type, and fly ash content were investigated. In order to obtain very low quality concrete, the water/cement ratios were increased to as high as 2.2. Modulus of elasticity of the concretes was obtained according to ASTM C469. Compressive strength and ultrasound pulse velocities of the concretes were also recorded. The experimentally obtained modulus of elasticity values were compared with those calculated by using prediction models given in a selection of codes of practice. Dynamic moduli of elasticity of the concretes were also obtained. 相似文献
73.
Hasan Yalcin Ismet ?zt��rk Eray Tuluk?u Osman Sa?dic 《Journal für Verbraucherschutz und Lebensmittelsicherheit》2011,6(2):197-202
Sar? 85 (Linum usitatissimum L.) linseed variety was used in this study. Linseed was cultivated at 2008 (LS-08) and 2009 (LS-09) without fertilizer. In addition, at 2009 diammonium phosphate [(NH4)2HPO4] and ammonium nitrate (NH4NO3) were applied (LSF-09). The linseeds were analyzed for protein, ash and oil contents and fatty acid compositions. There were differences among harvesting years for oil, protein and ash contents of the seeds. The greater oil and protein contents were obtained during LS-08 compared with LS-09. There were no significant difference in protein and ash content between LS-09 and LSF-09 while a significant difference was observed in oil content. Seed protein, oil and ash contents were significantly affected by the harvesting year, but only oil content was affected by the fertilizer treatment. There are significant differences in palmitic, stearic, oleic, ??-linolenic and arachidic acid between LS-08 and LS-09. While palmitic, stearic, oleic acid decreased, ??-linolenic and arachidic acid increased during 2009 harvesting year. LSF-09 has the highest amount of ??-linolenic acid. The fertilizing treatment seems to have an increasing effect on the amount of ??-linolenic acid, while it has a decreasing effect on the oleic acid content. 相似文献
74.
Alok Kumar Rai N. K. Singh Sang-Kwon Lee K. D. Mandal D. Kumar Om Parkash 《Journal of Materials Science: Materials in Electronics》2011,22(9):1286-1289
Dielectric properties of iron doped CaCu3Ti4O12 (CCTO), viz. CaCu3Ti3.9Fe0.1O12 (CCTFO) prepared by a novel semi-wet route have been investigated. X-ray diffraction of powder sintered at 900 °C show formation of single phase solid solution. Energy dispersive X-ray spectroscopy (EDX) confirmed the presence of CuO rich phase at grain boundaries of CCTFO. Nature of dielectric relaxation observed above room temperature is studied using complex plane impedance analysis and modulus spectroscopy. It has been found that out of the two relaxations reported earlier above room temperature, one occurring at lower temperature is due to grainboundaries interfacial polarization. 相似文献
75.
Sumantra Mandal A. K. Bhaduri V. Subramanya Sarma 《Metallurgical and Materials Transactions A》2011,42(4):1062-1072
Dynamic recrystallization (DRX) behavior in hot deformed (by uniaxial compression in a thermomechanical simulator in the temperatures range 1173 K to 1373 K [900 °C to 1100 °C]) Ti-modified austenitic stainless steel was studied using electron back scatter diffraction. Grain orientation spread with a “cut off” of 1 deg was a suitable criterion to partition dynamically recrystallized grains from the deformed matrix. The extent of DRX increased with strain and temperature, and a completely DRX microstructure with a fine grain size ~4 μm (considering twins as grain boundaries) was obtained in the sample deformed to a strain of 0.8 at 1373 K (1100 °C). The nucleation of new DRX grains occurred by the bulging of the parent grain boundary. The DRX grains were twinned, and a linear relationship was observed between the area fraction of DRX grains and the number fraction of Σ3 boundaries. The deviation from the ideal misorientation of Σ3 boundaries decreased with an increase in the fraction of Σ3 boundaries (as well as the area fraction of DRX) signifying that most Σ3 boundaries are newly nucleated during DRX. The generation of these Σ3 boundaries could account for the formation of annealing twins during DRX. The role of Σ3 twin boundaries on DRX is discussed. 相似文献
76.
Mahdi N. Mahyari Hasan Karimi Hasan Naseh Mehran Mirshams 《Journal of Mechanical Science and Technology》2010,24(10):1997-2006
The focus of the present study is to investigate the effectiveness of installing vortex breakers at the outlet of launch vehicle tanks on postponing vortex formation and decreasing the critical height of propellants while discharging. Analytical results in the absence of a vortex breaker show that the effects of the Weber and Reynolds numbers in the flow field can be ignored for values greater than 720 and 1.1 × 105, respectively; and critical height can be considered as a function of Froude number under aforementioned conditions. The analytical criteria are verified by two-dimensional, axis symmetrical, transient and two-phase numerical model. Eventually, some experiments are conducted to examine the effectiveness of the applied vortex breakers in reduction of the critical height of propellant. Experimental results show that a 30% decrease can be achieved in critical height by using a particular type of vortex breaker. Additionally, the carried out simulations for an existing two-stage launch vehicle indicate a 13% increase in orbital altitude, which in turn proves the considerable improvement in launch vehicle mass/energetic capabilities. 相似文献
77.
Peter E. D. Love Purnendu Mandal Jim Smith Heng Li 《Construction Management & Economics》2013,31(5):567-574
Rework that is experienced in construction projects is often caused by errors made during the design process. Factors that contribute to design errors are identified and used to design and develop a systems dynamics model, which is used to simulate a number of practical scenarios that can be used to reduce design errors and rework. The model presented in this paper can enable design and project managers to understand better the process of design documentation and how design errors occur in construction projects. 相似文献
78.
In this study, L-cystein modified bentonite-cellulose (cellu/cys-bent) nanocomposite was synthesized and characterized by XRD, FTIR, SEM with EDS, TGA, and TEM techniques. In order to optimize the process the effect of various operational parameters such as pH, adsorbent dosage, contact time, and temperature were also investigated. The adsorption experiments were carried out in initial concentrations range of 20-100 mg L?1and the adsorbent affinity for metal ions was found to be in order of Cu2+ > Pb2+ > Cd2+. The optimum pH for adsorption of Cu2+ and Cd2+ was observed at 5 while for Pb2+ it was pH 6. Based on the Langmuir model, the maximum adsorption capacity of Cu2+, Pb2+, and Cd2+ at 50?C was found to be 32.36, 18.52, and 16.12 mg g?1, respectively. The Langmuir isotherm and pseudo-second order model were found to be better fitted than the other isotherms and kinetic models. The results of thermodynamic parameters confirmed the process to be endothermic and spontaneous in nature. 相似文献
79.
Mohammad Tajul Islam Shahadat Hossain Khan Md Mahadi Hasan 《Coloration Technology》2016,132(3):255-264
An attempt was made to print cotton fabric with pigments using a new thickening agent based on Aloe vera gel in combination with sodium alginate. The results were compared with the standard conventional printing recipe containing synthetic thickener, and a favourable effect of Aloe vera introduction was achieved. The results show that the properties of the printed fabric (sharpness, colour yield, overall fastness properties, softness, and water vapour transmission) are dependent on the percentage of Aloe vera gel in the thickener combination, the concentration of printing auxiliaries, and the curing conditions. Optimal printing properties were achieved by using a printing paste containing 80% Aloe vera/20% sodium alginate (700 g kg?1), pigment (50 g kg?1), binder (145 g kg?1), fixer (10 g kg?1), and ammonium sulfate (5 g kg?1), followed by drying at 85 °C for 5 min and curing at 150 °C for 3 min. The sample printed with the new recipe showed superior rubbing fastness and handle properties, with a slightly lower colour yield, when compared with the sample printed with synthetic thickener. Finally, economic issues arising from synthetic thickener substitution are highlighted. 相似文献
80.
Shaikh A. Ali Shamsuddeen A. Haladu Mohammad A. J. Mazumder Hasan A. Al-Muallem 《Iranian Polymer Journal》2016,25(9):747-756
An aqueous solution of diallylammonium salts (CH2 = CHCH2)2NH+(CH2)3A? having A? as: CO2 ? (I), PO3H2 Cl? (II) and SO3 ? (III) in 1:1:1 mol ratio underwent ammonium persulfate-initiated ter cyclopolymerization to yield pH-responsive zwitterionic polymer IV with random placements of the monomers in the same ratio. During dialysis, PO3H2Cl? of the incorporated monomer units of II upon depletion of HCl became PO3H?. Likewise, azobisisobutyronitrile-initiated cyclopolymerization of I, II, III, and SO2 in a mole ratio of 1:1:1:3 provided pH-responsive tetrapolymer V in over 90 % yield with random and alternative placements of I–III and SO2 units, respectively, in the same ratio as the feed. Polyzwitterions (PZs) IV and V were insoluble in salt-free water but soluble in the presence of salts. The critical salt concentrations required to promote water solubility of PZ IV were determined to be 0.356 M NaCl, 0.237 M NaBr and 0.128 M NaI, whereas for PZ V the corresponding values were found to be 2.25, 1.26 and 0.862 M, respectively. PZs IV and V were converted into anionic polyelectrolytes VI and VII upon basification with NaOH. The viscosity and antiscalant behaviors of VI and VII were examined. The polymers demonstrated remarkable scale inhibition efficacies; at a dose of 10 ppm, both IV (+NaOH) and V (+NaOH) delayed the precipitation of CaSO4 from its supersaturated solution up to 920 and over 4000 min, respectively. For a small concentration of 5 ppm of polymer V, a scale inhibition of 100 % over 100 min verified it to be a potential effective antiscalant additive in reverse osmosis plants. 相似文献