全文获取类型
收费全文 | 69945篇 |
免费 | 6668篇 |
国内免费 | 4161篇 |
专业分类
电工技术 | 4887篇 |
技术理论 | 4篇 |
综合类 | 5671篇 |
化学工业 | 10338篇 |
金属工艺 | 4149篇 |
机械仪表 | 4326篇 |
建筑科学 | 4575篇 |
矿业工程 | 2073篇 |
能源动力 | 2139篇 |
轻工业 | 6203篇 |
水利工程 | 1703篇 |
石油天然气 | 1971篇 |
武器工业 | 577篇 |
无线电 | 9041篇 |
一般工业技术 | 8101篇 |
冶金工业 | 3850篇 |
原子能技术 | 1072篇 |
自动化技术 | 10094篇 |
出版年
2024年 | 291篇 |
2023年 | 1001篇 |
2022年 | 2108篇 |
2021年 | 2942篇 |
2020年 | 2199篇 |
2019年 | 1679篇 |
2018年 | 1887篇 |
2017年 | 2089篇 |
2016年 | 1812篇 |
2015年 | 2538篇 |
2014年 | 3292篇 |
2013年 | 4425篇 |
2012年 | 4876篇 |
2011年 | 5362篇 |
2010年 | 4755篇 |
2009年 | 4635篇 |
2008年 | 4747篇 |
2007年 | 4569篇 |
2006年 | 4084篇 |
2005年 | 3150篇 |
2004年 | 2541篇 |
2003年 | 2308篇 |
2002年 | 2573篇 |
2001年 | 2263篇 |
2000年 | 1491篇 |
1999年 | 929篇 |
1998年 | 1034篇 |
1997年 | 742篇 |
1996年 | 608篇 |
1995年 | 495篇 |
1994年 | 413篇 |
1993年 | 359篇 |
1992年 | 268篇 |
1991年 | 234篇 |
1990年 | 242篇 |
1989年 | 217篇 |
1988年 | 177篇 |
1987年 | 164篇 |
1986年 | 141篇 |
1985年 | 138篇 |
1984年 | 112篇 |
1983年 | 76篇 |
1982年 | 78篇 |
1981年 | 63篇 |
1980年 | 93篇 |
1979年 | 56篇 |
1978年 | 60篇 |
1977年 | 58篇 |
1976年 | 76篇 |
1975年 | 43篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
Nanocomposites based on poly(butylene terephthalate) (PBT) and an organoclay (Cloisite 30B) were prepared by melt blending using a twin‐screw extruder. Two kinds of PBTs, ie PBT‐A and PBT‐B, with different inherent viscosities (ηinh), were used for this study (ηinh of PBT‐A and PBT‐B were 0.74 and 1.48, respectively). Dispersion of the clay layers in the PBT nanocomposites was characterized by using X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Tensile and dynamic mechanical properties and non‐isothermal crystallization temperatures of the nanocomposites were also examined. Nanocomposites based on the higher‐viscosity PBT (PBT‐B) showed a higher degree of exfoliation of the clay and a higher reinforcing effect when compared to the composites based on the lower‐viscosity PBT (PBT‐A). The clay nanolayers dispersed in PBT matrices lead to increases in the non‐isothermal crystallization temperatures of the PBTs, with such increases being more significant for the PBT‐B nanocomposites than for the PBT‐A nanoocomposites. Copyright © 2004 Society of Chemical Industry 相似文献
112.
Poly[2‐methoxy‐5‐(2′‐ethyl‐hexyloxy)‐para‐phenylene vinylene] (MEH‐PPV)/silica nanoparticle hybrid films were prepared and characterised. Three kinds of materials were compared: parent MEH‐PPV, MEH‐PPV/silica (hybrid A films), and MEH‐PPV/coupling agent MSMA/silica (hybrid B films), in which MSMA is 3‐(trimethoxysilyl) propyl methacrylate. It was found that the hybrid B films could significantly prevent macrophase separation, as evidenced by scanning electron and fluorescence microscopy. Furthermore, the thermal characteristics of the hybrid films were largely improved in comparison with the parent MEH‐PPV. The UV‐visible absorption spectra suggested that the incorporation of MSMA‐modified silica into MEH‐PPV could confine the polymer chain between nanoparticles and thus increase the conjugation length. The photoluminescence (PL) studies also indicated enhancement of the PL intensity and quantum efficiency by incorporating just 2 wt% of MSMA‐modified silica into MEH‐PPV. However, hybrid A films did not show such enhancement of optoelectronic properties as the hybrid B films. The present study suggests the importance of the interface between the luminescent organic polymers and the inorganic silica on morphology and optoelectronic properties. Copyright © 2004 Society of Chemical Industry 相似文献
113.
石油工程项目管理机制 总被引:7,自引:3,他引:4
为了妥善处理石油工程项目中的委托-代理关系,研究了委托-代理模型和石油工程项目管理中的激励约束机制,分析了激励机制、监督机制和选择机制在石油工程项目运行管理中的重要性.只有用有效的契约去激励技术服务公司,才能使服务公司在追求自身效益最大化的同时也为实现石油公司的最大效益而尽最大努力;只有对技术服务公司的作业实施监督,才能形成对技术服务公司的有效约束;采用激励性承包方式、实施综合性评标和组建工程项目动态联盟能够防止逆向选择.分析表明,在最优激励安排下,激励强度与项目面临的不确定性、承包商的边际成本及其风险规避系数负相关,与承包商的边际生产率正相关,还与其他可观测变量相关.在最优监督水平下,作业公司的边际生产率越高,边际成本越低,越容易监督,监督带来的边际收益越高.对于那些监督比较困难的项目,可以通过加强惩罚力度的方式弥补难以有效监督的不足.激励性承包方式可以减小逆向选择造成的危害,组建动态联盟可以进一步加强激励作用,降低道德风险,解决逆向选择问题.参8 相似文献
114.
Trieu-Kien Truong Yaotsu Chang Yan-Haw Chen Lee C.D. 《Communications, IEEE Transactions on》2005,53(5):749-754
In this paper, two algebraic decoders for the (103, 52, 19) and (113, 57, 15) quadratic residue codes, which have lengths greater than 100, are presented. The results have been verified by software simulation that programs in C++ language have been executed to check possible error patterns of both quadratic residue codes. 相似文献
115.
116.
117.
Jen-Chwen Lin T. Leo Ngai Y. Austin Chang 《Metallurgical and Materials Transactions A》1986,17(7):1241-1245
Defect equilibria for binary semiconducting compound phases which exhibit ionized native donor and acceptor defects were considered,
and equations describing the pressure-temperature-composition relationships for these compound phases were derived. These
equations were used to analyze experimental data from the literature for tin telluride. Excellent agreement was obtained between
calculated thermodynamic and phase boundary values and experimental data. The approach presented is readily extended to obtain
equations for the thermodynamic properties of ternary and higher order semiconducting compound phases. 相似文献
118.
几项涂层性能测试方法简介 总被引:1,自引:1,他引:0
介绍了涂层盐雾试验、耐候性能试验、雾影、附着力等性能测试的方法和设备,探讨了其性能检测技术中的影响因素。 相似文献
119.
通过梳理管理学界对战略联盟的定义,发现价值链的鸸释同样适用于大学问的战略联盟。通过对已有的大学战略联盟的分析,提出了名校联盟与非名校联盟间的若干差异,最后提出了我国大学联盟战略的若干建议。 相似文献
120.
This study used different metals to modify Rh/Al2O3 catalysts for NO reduction in a simulated waste incineration flue gas containing 6% O2. The characteristics of the modified catalysts were analyzed using BET, TEM and XRD. The results of the experiment reveal that Na addition can significantly affect the properties of Rh/Al2O3 catalysts on the BET surface area and Rh metal dispersion. Furthermore, Na addition was found to significantly enhance the NO conversion of Rh/Al2O3 at 250–350 °C. On the contrary, Cu, Ni, and Co addition was found to have slight suppression effects. 相似文献