全文获取类型
收费全文 | 59472篇 |
免费 | 7052篇 |
国内免费 | 4322篇 |
专业分类
电工技术 | 4418篇 |
技术理论 | 4篇 |
综合类 | 4958篇 |
化学工业 | 13060篇 |
金属工艺 | 6381篇 |
机械仪表 | 2188篇 |
建筑科学 | 4303篇 |
矿业工程 | 1093篇 |
能源动力 | 1864篇 |
轻工业 | 3223篇 |
水利工程 | 540篇 |
石油天然气 | 2097篇 |
武器工业 | 514篇 |
无线电 | 7148篇 |
一般工业技术 | 8469篇 |
冶金工业 | 5387篇 |
原子能技术 | 582篇 |
自动化技术 | 4617篇 |
出版年
2024年 | 301篇 |
2023年 | 1182篇 |
2022年 | 1812篇 |
2021年 | 2207篇 |
2020年 | 2336篇 |
2019年 | 2208篇 |
2018年 | 2012篇 |
2017年 | 2388篇 |
2016年 | 2376篇 |
2015年 | 2378篇 |
2014年 | 3198篇 |
2013年 | 3501篇 |
2012年 | 3856篇 |
2011年 | 4104篇 |
2010年 | 3025篇 |
2009年 | 3303篇 |
2008年 | 3086篇 |
2007年 | 3651篇 |
2006年 | 3370篇 |
2005年 | 2895篇 |
2004年 | 2407篇 |
2003年 | 2316篇 |
2002年 | 1988篇 |
2001年 | 1733篇 |
2000年 | 1425篇 |
1999年 | 1173篇 |
1998年 | 1006篇 |
1997年 | 894篇 |
1996年 | 705篇 |
1995年 | 633篇 |
1994年 | 567篇 |
1993年 | 396篇 |
1992年 | 383篇 |
1991年 | 294篇 |
1990年 | 282篇 |
1989年 | 248篇 |
1988年 | 124篇 |
1987年 | 91篇 |
1986年 | 90篇 |
1985年 | 59篇 |
1984年 | 73篇 |
1983年 | 38篇 |
1982年 | 50篇 |
1981年 | 46篇 |
1980年 | 52篇 |
1965年 | 31篇 |
1964年 | 49篇 |
1963年 | 39篇 |
1959年 | 32篇 |
1955年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
An Arctangent Unwrapping Technique of Photoelasticity Using Linearly Polarized Light at Three Wavelengths 总被引:2,自引:0,他引:2
Abstract: In the automatic measurements of the principal stress directions ψ and the total relative phase retardation ρ tol , ψ and ρ tol can be easily obtained by the phase unwrapping method using the arctangent function. However, only some published works exist on the measurements of ψ and ρ tol by photoelastic techniques using a linearly polarised incident light source. This paper presents the technique of applying an unwrapping by means of the arctangent function to photoelasticity. The technique overcomes the error associated with the quarter-wave plate by using an incident light of different wavelength and does not need an interpolation for the determination of ψ . The technique is validated by determining ψ and ρ tol for the well-known circular disk subjected to a diametral compressive load model. 相似文献
92.
Domjan Michael; Mahometa Michael J.; Mills Andrew D. 《Canadian Metallurgical Quarterly》2003,117(4):391
Two contrasting investigative techniques provided evidence consistent with the interpretation that female quail (Coturnix japonica) regulate male copulatory behavior by the duration of their immobility and through this behavioral mechanism they also control the rate of fertilization of their eggs. In Experiment 1, copulation tests with males and females from different genetic lines showed that the type of female that participated in a copulatory test significantly influenced the latency of the male's grab, mount, and cloacal contact responses and also determined the efficiency of the male's copulatory behavior. These measures of male performance were correlated with female immobility in Experiment 2, which used a more homogeneous population of quail. Furthermore, 2 of these measures (copulatory efficiency and the latency to make cloacal contact) were correlated with fertilization rate. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
93.
94.
A semi-Markov model is constructed that describes an arbitrarily structured multicomponent technological system and takes
into account its calendar maintenance. Using an aggregation algorithm, approximate values of stationary reliability characteristics
and an optimal term of maintenance work are determined for the system.
__________
Translated from Kibernetika i Sistemnyi Analiz, No. 2, pp. 69–86, March–April 2006. 相似文献
95.
降凝剂对高蜡稠油的改性效果及机理研究 总被引:5,自引:0,他引:5
实验研究了工业品原油降凝剂WHP改善含蜡56.9%、其中96.6%为正构烷烃的胜利郑王庄稠油流动性的效果。WHP含乙烯/醋酸乙烯/乙烯醇嵌段聚醚三元共聚物30%-35%。在60℃将WHP加入稠油中,测定其凝点和32℃、0-42.6 s^-1范围5个剪切速率下的黏度,均随WHP加量的增加(50-300 mg/L)而降低,200 mg/L为最佳加量,在该加量下0.32 s^-1黏度由34.16 Pa·s降至79.2 mPa·s,凝点(℃)、屈服值(Pa)、稠度系数(Pa·s^n)分别由49.0、32.42、31.57降至39.5、0.1297、0.02142,流型指数由0.1176升至0.9790。由黏温曲线求出,加入200mg/L WHP使该稠油析蜡点由65℃降至58℃,反常点由70℃降至50℃。根据空白和加剂原油扫描电镜照片显示的蜡晶形态,利用共晶机理分析讨论了WHP这种高分子表面活性剂的降凝、降黏、改善流动性的作用。图3表3参5。 相似文献
96.
Polyurethanes were prepared from pure 4,4′-diphenylmethane diisocyanate (MDI), 1,4-butane diol (BDO) or 1,2-ethane diol (EDO) and α,ω-hydroxyl poly(propylene oxide) (PPO) by reaction injection moulding (RIM). Hard segment (MDI + BDO or EDO) level was 45–50 wt%. The PPO had about 20% ethylene oxide copolymerized in at the chain ends to provide 80% primary OH end groups. Mn was varied from 2000 to 4000. Dibutyl tin dilaurate catalyst and mould temperature were varied. Dynamic mechanical, wide-angle X-ray, differential scanning calorimeter, molecular weight and tensile elongation measurements were made on the RIM polyurethanes. At low reaction rates (low catalyst or temperature) highly crystalline, well phase separated but low molecular weight polymers were produced. At high catalyst or temperature levels more poorly phase separated but high molecular weight, tough polymers resulted. Higher Mn PPO gave better phase separation and EDO gave higher melting temperatures. Preventing hard segment crystallinity by substituting asymmetric MDI or glycols resulted in phase compatibility. 相似文献
97.
98.
Nuclear magnetic resonance (n.m.r.) studies of 19F nuclei in a random copolymer of vinylidene fluoride and trifluoroethylene were performed at 9.14 MHz and 20.0 MHz. The free induction decays (FIDs) were analysed in terms of two T2 components attributed to the amorphous and crystalline portions of the polymer. The changes in crystallinity as well as the effects of the ferroelectric transition were observed during cycles of heating and cooling between 20°C and 140°C. The crystalline component of the FID lengthens by a factor of 2 at 100°C on heating and decreases by this factor at 60°C on cooling, thus exhibiting the thermal hysteresis of this ferroelectric transition. The spin-lattice relaxation was also investigated. From measurements at 9.14 MHz the observed longitudinal relaxation time T1 appears to be dominated by the dynamics of the amorphous phase and exhibits no anomaly through the phase transition. However, from measurements at 20 MHz, well defined minima of T1 were observed, which are associated with the ferroelectric transition (especially after repeated annealing of the samples). Results are discussed in terms of the crystalline phase structure, which appears dynamically disordered above the ferroelectric phase transition. An analogy is considered with the plastic phase transitions encountered in molecular crystals. 相似文献
99.
Kazutaka Chibana Chaedong Kang Masashi Okada Koji Matsumoto Tetsuo Kawagoe 《International Journal of Refrigeration》2002,25(2):83
Water-silicone oil emulsion with an additive, (C2H5O)3SiC3H6NH2, was examined as a heat storage material. A spiral tube used as a heat exchanger was immersed in a low temperature bath and the emulsion was circulated in the tube to make ice continuously. Ice was separated from the ice–liquid suspension in an outlet tank. The amount of formed ice, the temperatures of the inlet and the outlet of the heat exchanger, and the temperatures in the tube wall were measured and the overall heat transfer coefficient and the heat flux through the tube were calculated. Experiments were carried out, varying the flow rate, the temperature of cooling brine, and the thickness of tube wall. The condition under which slurry ice was formed continuously without adhesion of ice to the cooling wall was clarified. Though decrease in the thermal resistance of the tube increased the rate of ice formation or raised the brine temperature, it narrowed the range of the flow rate and of the brine temperature in which slurry ice was formed continuously. 相似文献
100.
引入自然对流换热系数 ,将固液蓄能数学模型简化为仅用能量方程加以描述。并通过实验测得相变过程的实际温度场 ,证明了自然对流固液相变换热的影响不可忽略 ,验证了固液相变界面移动速率随自然对流换热系数的增大而增大的定性关系 相似文献