全文获取类型
收费全文 | 47739篇 |
免费 | 5797篇 |
国内免费 | 4269篇 |
专业分类
电工技术 | 3428篇 |
技术理论 | 2篇 |
综合类 | 7643篇 |
化学工业 | 2464篇 |
金属工艺 | 2340篇 |
机械仪表 | 3700篇 |
建筑科学 | 3598篇 |
矿业工程 | 1022篇 |
能源动力 | 972篇 |
轻工业 | 2671篇 |
水利工程 | 1230篇 |
石油天然气 | 1058篇 |
武器工业 | 612篇 |
无线电 | 5664篇 |
一般工业技术 | 5534篇 |
冶金工业 | 1494篇 |
原子能技术 | 574篇 |
自动化技术 | 13799篇 |
出版年
2024年 | 85篇 |
2023年 | 635篇 |
2022年 | 983篇 |
2021年 | 1242篇 |
2020年 | 1334篇 |
2019年 | 1228篇 |
2018年 | 1238篇 |
2017年 | 1466篇 |
2016年 | 1599篇 |
2015年 | 1672篇 |
2014年 | 2538篇 |
2013年 | 2903篇 |
2012年 | 3301篇 |
2011年 | 3603篇 |
2010年 | 2873篇 |
2009年 | 3077篇 |
2008年 | 3130篇 |
2007年 | 3709篇 |
2006年 | 3247篇 |
2005年 | 2882篇 |
2004年 | 2445篇 |
2003年 | 2035篇 |
2002年 | 1716篇 |
2001年 | 1434篇 |
2000年 | 1242篇 |
1999年 | 1045篇 |
1998年 | 825篇 |
1997年 | 726篇 |
1996年 | 652篇 |
1995年 | 584篇 |
1994年 | 490篇 |
1993年 | 357篇 |
1992年 | 312篇 |
1991年 | 250篇 |
1990年 | 232篇 |
1989年 | 211篇 |
1988年 | 133篇 |
1987年 | 76篇 |
1986年 | 38篇 |
1985年 | 46篇 |
1984年 | 37篇 |
1983年 | 42篇 |
1982年 | 31篇 |
1981年 | 17篇 |
1980年 | 21篇 |
1979年 | 12篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1964年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
苯并噁嗪树脂作为一类新型的热固性树脂,具有分子设计性强、阻燃性能和耐腐蚀性能优异、固化时不需要强酸、无小分子放出等优点,在航空、建筑、电子等领域获得了广泛应用。本文主要介绍了苯并噁嗪单体的合成方法(溶剂法、无溶剂法和悬浮法)、降低苯并噁嗪开环聚合温度的方法(合成具有特殊基团的苯并噁嗪单体、添加催化剂)及苯并噁嗪树脂在形状记忆聚合物中的应用(与其他聚合物混合,纯苯并噁嗪化学改性),对苯并噁嗪形状记忆聚合物目前存在的问题进行了概述并对苯并噁嗪形状记忆聚合物的发展前景做出了展望。 相似文献
52.
Gina Cavaliere Giovanna Trinchese Nadia Musco Federico Infascelli Chiara De Filippo Vincenzo Mastellone Valeria Maria Morittu Pietro Lombardi Raffaella Tudisco Micaela Grossi Vincenzo Monda Monica I. Cutrignelli Antonietta Messina Serena Calabrò Heleena B. Moni Luigi Stradella Giovanni Messina Marcellino Monda Maria Pina Mollica 《Journal of dairy science》2018,101(3):1843-1851
Excessive energy intake may evoke complex biochemical processes characterized by inflammation, oxidative stress, and impairment of mitochondrial function that represent the main factors underlying noncommunicable diseases. Because cow milk is widely used for human nutrition and in food industry processing, the nutritional quality of milk is of special interest with respect to human health. In our study, we analyzed milk produced by dairy cows fed a diet characterized by a high forage:concentrate ratio (high forage milk, HFM). In view of the low n-6:n-3 ratio and high content of conjugated linoleic acid of HFM, we studied the effects of this milk on lipid metabolism, inflammation, mitochondrial function, and oxidative stress in a rat model. To this end, we supplemented for 4 wk the diet of male Wistar rats with HFM and with an isocaloric amount (82 kJ, 22 mL/d) of milk obtained from cows fed a diet with low forage:concentrate ratio, and analyzed the metabolic parameters of the animals. Our results indicate that HFM may positively affect lipid metabolism, leptin:adiponectin ratio, inflammation, mitochondrial function, and oxidative stress, providing the first evidence of the beneficial effects of HFM on rat metabolism. 相似文献
53.
Guilherme S. Pandolfi Felipe G. Pinheiro Rodrigues Paulo J. Modenesi 《Welding International》2018,32(3):188-199
This paper evaluates indications of arc constriction by the thermal and electrical insulation caused by oxides of a single component in A-TIG welding of austenitic stainless steels. Changes in arc dimensions, in its electric voltage and in weld bead morphology caused by three oxide fluxes (SiO2, Cr2O3 e Al2O3) applied with two surface densities (30 e 60 g/m2), and with and without a flux-free central strip (of 1, 2 and 4 mm) were studied. Results showed no significant change in the width of the electric arc for the experimental conditions used, therefore not supporting a possible mechanical constriction in the electric arc by oxide electrical and thermal insulation. Lateral filming indicated that the arc is delayed by the fluxes with silica causing the strongest effect. The presence of a clean central strip in the flux layer decreased weld penetration and weld bead cross section, besides the reduction of the width of the bead. Therefore, the results of the present work seem to support Marangoni convection as the main mechanism responsible for increasing penetration in A-TIG welding of stainless austenitic steels. 相似文献
54.
A new type of stretchable poly(caprolactone)/graphene oxide (PCL/GO) aerogel with fast chemo‐responsive shape memory effect is fabricated by one‐step method of a sol‐gel procedure. The PCL/GO aerogels show uniformly circular and interconnected pores formed by twisted PCL nanolayers. GO platelets improve the crystallinity of PCL and increase the fracture stress and strain by 150% and 300% respectively, although the GO loading is only 0.5%. The dramatic increment of break strain is attributed to the uniform and circular pores that can afford large deformation and the interaction of GO and PCL. The aerogels can be programmed by external stress at ambient temperature without heating and recover upon ethyl acetate (EA) in 1 s. The fast chemo‐responsive shape recovery is ascribed to the fast wrinkle of the PCL nanolayers that decrease the diffusion time greatly and the interconnected micrometer pores that are in favor of penetrating for EA molecules. 相似文献
55.
破产理论是保险数学中的重要问题,它可以为保险公司决策者提供一个非常有用的早期风险预警手段.本文研究了一个带潜在延迟索赔和随机保费收入的复合二项风险模型.利用矩母函数的技巧,得到了 Gerber-Shiu 期望折罚函数的递推公式.特别地,还得到了贴现因子为 1 的特殊情形下的 Gerber-Shiu 期望折罚函数的解析表达式.最后还得到了实际应用中的一些重要的破产特征量,包括破产概率,破产时赤字的密度函数,破产前盈余与破产时赤字的联合密度函数,以及导致破产的索赔密度函数等. 相似文献
56.
57.
针对反射面成型的复杂影响因素,提出平面桁架构建的定日镜面形支撑结构优化技术路线. 利用模拟仿真、数值计算和优化算法等方法,解析20 m2定日镜面形定义技术路线的4个组成环节:面形规格及宽高比、上弦杆的截面矩、平面桁架组间距的最优值、机加工中工艺控制要点的量化. 试制小型定日镜进行实验,分析光斑形状和能流密度分布特性,并与理想球面形光斑比较,两者的拟合优度大于0.98. 实验结果表明,当反射镜宽高比取1.2,上弦杆截面矩取40 000 mm4,桁架组间距取950 mm,上弦杆和斜杆的开孔公差小于0.9 mm时,反射面形的质量提升. 研究从原理和实践上证明了该优化技术路线的可行性. 相似文献
58.
59.
《Ceramics International》2020,46(13):20751-20768
“Weibull statistics” for strength distribution analysis refers to either the ordinary Weibull distribution function or the Weibull statistical fracture theory. The ordinary Weibull distribution function is an empirical distribution function on an equal footing with other type of classical empirical distributions such as normal and log-normal distributions for fitting the statistical data of various random variables nonexclusive to materials strength. It has no explicit physical meaning and cannot be used for size scaling and prediction of strength. The Weibull statistical fracture theory is a weakest-link statistical fracture model for a solid with the strength distribution of an elemental volume being described by the ordinary Weibull distribution function. It has the capability of size scaling and prediction of strength for specimens with different geometries and different loading modes. The three-parameter Weibull statistical fracture theory in uniaxial flexure of prismatic beams is reformulated and validated by both numerical and real strength experiments of different ceramics. 相似文献
60.
Because of the introduction of new processing parameters in water-assisted injection molding (WAIM), processes control has become more difficult. First, design of experiment (DOE) was carried out by using optimized Latin hypercubes (Opt LHS). On the basis of this, computational fluid dynamics (CFD) method was used to simulate and calculate hollowed core ratios and wall thickness differences of cooling water pipe at different positions. Then inverse radial basis function (RBF) neural network model reflecting the fitting relationship between processing parameters and molding quality was established, and accuracy of the model was detected by cross validation. Finally, expected molding quality was applied to predict processing parameters, and the obtained molding quality under the predicted processing parameters was verified by computer aided engineering (CAE) simulation and experimental methods. The results showed that mean relative precisions of processing parameters such as melt temperature, delay time, short shot size, water pressure, and mold temperature for inverse RBF model were 98.6%, 93.6%, 98.5%, 93.9%, and 97.9%, respectively, which met the accuracy requirements. Furthermore, compared with expected values of hollowed core ratios and wall thickness differences, the average errors of CAE and experiment were 2.3% and 4.9%, respectively. 相似文献