全文获取类型
收费全文 | 72428篇 |
免费 | 5531篇 |
国内免费 | 2720篇 |
专业分类
电工技术 | 3846篇 |
技术理论 | 6篇 |
综合类 | 4408篇 |
化学工业 | 12393篇 |
金属工艺 | 3922篇 |
机械仪表 | 4799篇 |
建筑科学 | 5152篇 |
矿业工程 | 2376篇 |
能源动力 | 2227篇 |
轻工业 | 4760篇 |
水利工程 | 984篇 |
石油天然气 | 5231篇 |
武器工业 | 460篇 |
无线电 | 7568篇 |
一般工业技术 | 9318篇 |
冶金工业 | 3786篇 |
原子能技术 | 746篇 |
自动化技术 | 8697篇 |
出版年
2024年 | 206篇 |
2023年 | 1199篇 |
2022年 | 1802篇 |
2021年 | 2809篇 |
2020年 | 2142篇 |
2019年 | 1904篇 |
2018年 | 2247篇 |
2017年 | 2471篇 |
2016年 | 2051篇 |
2015年 | 2684篇 |
2014年 | 3423篇 |
2013年 | 4194篇 |
2012年 | 4346篇 |
2011年 | 4856篇 |
2010年 | 4175篇 |
2009年 | 3952篇 |
2008年 | 3849篇 |
2007年 | 3712篇 |
2006年 | 3794篇 |
2005年 | 3434篇 |
2004年 | 2284篇 |
2003年 | 2083篇 |
2002年 | 1870篇 |
2001年 | 1637篇 |
2000年 | 1800篇 |
1999年 | 2036篇 |
1998年 | 1757篇 |
1997年 | 1406篇 |
1996年 | 1397篇 |
1995年 | 1178篇 |
1994年 | 938篇 |
1993年 | 709篇 |
1992年 | 539篇 |
1991年 | 421篇 |
1990年 | 323篇 |
1989年 | 249篇 |
1988年 | 220篇 |
1987年 | 138篇 |
1986年 | 101篇 |
1985年 | 89篇 |
1984年 | 59篇 |
1983年 | 35篇 |
1982年 | 42篇 |
1981年 | 28篇 |
1980年 | 22篇 |
1979年 | 13篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1975年 | 5篇 |
1945年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Ammonium-based ionic liquid monomers and their corresponding polymers [poly(ionic liquid)s] are synthesized and characterized for CO2 sorption. The polymers have much higher CO2 sorption capacities than the room-temperature ionic liquids and imidazolium-based poly(ionic liquid)s. For example, P[VBTMA][PF6] with polystyrene backbone has a CO2 sorption capacity of 10.67 mol%. The CO2 sorption is selective over N2 and O2. The effects of cation, backbone, substituent, anion and crosslinking on CO2 sorption are discussed. The sorption mechanism study indicates that CO2 sorption by the poly(ionic liquid)s is a bulk and surface phenomenon. 相似文献
992.
Hee-Kyun Shin Hyunho Shin Seo-Yong Cho Kug Sun Hong 《Journal of the American Ceramic Society》2005,88(9):2461-2465
Effects on phase evolution caused by the addition of a new sintering agent, lithium borosilicate, Li2 O·B2 O3 ·SiO2 (LBS) glass to 0.9MgTiO3 –0.1CaTiO3 ceramic and resultant dielectric properties were investigated. The added LBS glass, a liquid phase sintering agent, significantly lowered the densification temperature from 1300° to about 950°C, while yielding decomposition of MgTiO3 into MgTi2 O5 and Mg2 TiO4 . At the same time, the by-products of the decomposition reaction, MgO and TiO2 , were dissolved into the glass network. Such phase evolution partly compensated the influence of deleterious glass addition so that the specimen demonstrated fairly good apparent dielectric properties. 相似文献
993.
994.
A novel method of grafting ring-opening polymerization of l-lactide (LLA) onto the surface of hydroxyapatite nano-particles (n-HAP) was developed. PLLA was directly connected onto the HAP surface through a chemical linkage. The PLLA-g-HAP particles could be stably dispersed in organic solvent such as chloroform for several weeks. The n-HAP particles still retained the original dimension and shape after the grafting of PLLA. Compared with the 31P MAS-NMR spectrum of pure HAP powders, there appeared a downfield displacement of 1.2 ppm in the spectrum of PLLA-g-HAP. Fourier transformation infrared (FT-IR) spectra further confirmed the existence of PLLA on the surface of PLLA-g-HAP. The amount of grafted polymer determined by thermal gravimetric analysis (TGA) was about 6% in weight. The tensile strength and elongation at break of the PLLA/PLLA-g-HAP composite containing 8 wt% of PLLA-g-HAP were 55 MPa and about 10-13%, respectively, while those of the PLLA/n-HAP composites were 40 MPa and 3-5%, respectively. 相似文献
995.
Wen‐Bin Liau Yu‐Ting Sun Ling‐Yueh Yang Lee‐Yih Wang Wen‐Yen Chiu Kuo‐Huang Hsieh Sheng‐Mao Tseng 《应用聚合物科学杂志》2006,102(6):5406-5413
The polyaniline (PANI)‐coated polystyrene (PS) latexes were synthesized, and the electrically conductive films were prepared thereafter. The weight ratio of PANI was 5%. Thermal analysis of the latices was performed using DSC and TGA. In this study, the electrically conductive films were prepared above the PS glass transition temperature (Tg). During the film formation, the effects of the annealing temperature and atmosphere (air or N2) on the film resistance were investigated. In addition, the film morphology was observed utilizing scanning electron microscopy. The film resistance decreased in the initial heating stage due to the increasing temperature and the compaction of film. Then the film resistance increased with further annealing due to the aging of PANI. Typically, the film resistance was about 6000 Ω/sq, and the conductivity was 0.3 S/cm. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5406–5413, 2006 相似文献
996.
997.
Poly(lactic acid) (PLA) and wheat starch are biodegradable polymers derived from renewable sources. A previous study showed that thermally blending starch and PLA in the presence of methylenediphenyl diisocyanate (MDI) enhanced the mechanical properties of the blends. In this work, blends of PLA with various levels of wheat starch and MDI were hot mixed at 180°C then hot‐pressure molded at 175°C to form test specimens. The blends were characterized for mechanical properties, fracture microstructure, and water absorption. Pure PLA had a tensile strength of 62.7 MPa and elongation of 6.5%. The blend with 45% wheat starch and 0.5 wt % MDI gave the highest tensile strength of about 68 MPa with about 5.1% elongation. The blend with 20% starch and 0.5 wt % MDI had the lowest tensile strength of about 58 MPa with about 5.6% elongation. Dynamic mechanical analysis showed that storage modulus increased and tan δ decreased as starch level increased, but almost leveled off when starch level reached 45% or higher. Water absorption of the blends increased significantly with starch content. Yet the blend, if water proofed on its surface, has potential for short‐term disposable applications. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1257–1262, 2002; DOI 10.1002/app.10457 相似文献
998.
本文叙述了以区域法计算辐射传热的数学模型。在区域法中,系统被分为表面区和气体区,区域数取决于所要求的结果精度和计算时间。炉子的温度分布可通过解每区的能量平衡而得。作为Hottel和Cohen的原始开发,直接交换面积限于立方体和正方形;本文给出了在方箱炉、圆筒炉中任何两区之间直接交换面积方程式的推导。这些方程式可适用于任何大小的矩形、共轴圆筒壁、炉底环形区和其他形状。 本文提供了一个关于烃类一段蒸汽转化炉和圆筒炉的设计方法。计及反应动力学、对流传热、管内压降,采用区域法计算这些炉子的温度分布,从而预言工艺气、烟气、管表面和耐火墙表面的温度分布。计算结果与工厂实测数据相吻合。 相似文献
999.
孙华 《单片机与嵌入式系统应用》2014,(7):72-75
本文设计一种基于NXP公司的LPC812微控制器和SLRC610射频芯片的RFID模块方法。该模块采用内置天线,预留串口与外部通信。该模块性能优良、易于集成到RFID系统中,使用户更专注于系统功能方面的设计。 相似文献
1000.
嵌入式系统的运行需要可靠性和实时性的保证,因此良好的可靠性和实时性是嵌入式系统软件设计的重要标准。同时为了使软件系统的鲁棒性更强,嵌入式系统的设计需要一个非常好的软件架构。这里介绍了一种基于MCU平台的嵌入式系统软件架构方法。在这个方法中,事件驱动机制的引入满足了对软件架构的要求,主程序中不仅采用了优先调度机制,同时也加入了软件抗干扰措施,这些都使系统的实时性和可靠性得到了明显的提高。设计实验比较由该方法得到的软件架构与原始软件架构的实时性,得出由该方法优化后的软件架构确实具有更好的性能。 相似文献