全文获取类型
收费全文 | 74536篇 |
免费 | 5945篇 |
国内免费 | 2857篇 |
专业分类
电工技术 | 4025篇 |
技术理论 | 6篇 |
综合类 | 4503篇 |
化学工业 | 12916篇 |
金属工艺 | 4055篇 |
机械仪表 | 4893篇 |
建筑科学 | 5300篇 |
矿业工程 | 2455篇 |
能源动力 | 2278篇 |
轻工业 | 4873篇 |
水利工程 | 1042篇 |
石油天然气 | 5342篇 |
武器工业 | 469篇 |
无线电 | 7851篇 |
一般工业技术 | 9628篇 |
冶金工业 | 3974篇 |
原子能技术 | 764篇 |
自动化技术 | 8964篇 |
出版年
2024年 | 325篇 |
2023年 | 1338篇 |
2022年 | 2219篇 |
2021年 | 3056篇 |
2020年 | 2292篇 |
2019年 | 2035篇 |
2018年 | 2364篇 |
2017年 | 2569篇 |
2016年 | 2153篇 |
2015年 | 2786篇 |
2014年 | 3509篇 |
2013年 | 4313篇 |
2012年 | 4425篇 |
2011年 | 4936篇 |
2010年 | 4236篇 |
2009年 | 4019篇 |
2008年 | 3913篇 |
2007年 | 3755篇 |
2006年 | 3841篇 |
2005年 | 3472篇 |
2004年 | 2304篇 |
2003年 | 2101篇 |
2002年 | 1882篇 |
2001年 | 1653篇 |
2000年 | 1808篇 |
1999年 | 2061篇 |
1998年 | 1786篇 |
1997年 | 1439篇 |
1996年 | 1417篇 |
1995年 | 1195篇 |
1994年 | 964篇 |
1993年 | 730篇 |
1992年 | 559篇 |
1991年 | 433篇 |
1990年 | 328篇 |
1989年 | 260篇 |
1988年 | 226篇 |
1987年 | 143篇 |
1986年 | 121篇 |
1985年 | 96篇 |
1984年 | 66篇 |
1983年 | 43篇 |
1982年 | 42篇 |
1981年 | 31篇 |
1980年 | 25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 13 毫秒
991.
992.
Uniform polystyrene (PSt) particles with the size of 1.9 μm were first prepared via dispersion polymerization, and then used as the seeds in a second‐stage dispersion copolymerization of styrene (St) and methacrylic acid (MAA) to produce carboxyl‐carrying microspheres. The PSt seed particles were swollen by monomer mixture of St and MAA, including an oil‐soluble initiator 2,2′‐azobisiso‐butyronitrile (AIBN), before polymerization. Finally, uniform PS/P(St/MAA) (polydispersity index, PDI = 1.02) microspheres with the size of 2.2 μm were obtained. The average particle size and size distribution of the final microspheres were investigated. MAA contents between 54 and 97 mg/g were detected from the PS/P(St/MAA) particles produced under different conditions. Dispersion medium has great influence on the kinetics of polymerization, due to its effect on the partitioning of monomers, solvents, and initiator in the particle phase, probably as well as on the conformation of the dispersion agent on the surface of the particles. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3586–3591, 2006 相似文献
993.
994.
995.
The nanocomposites of polyamide1010 (PA1010) filled with carbon nanotubes (CNTs) were prepared by melt mixing techniques. The isothermal melt‐crystallization kinetics and nonisothermal crystallization behavior of CNTs/PA1010 nanocomposites were investigated by differential scanning calorimetry. The peak temperature, melting point, half‐time of crystallization, enthalpy of crystallization, etc. were measured. Two stages of crystallization are observed, including primary crystallization and secondary crystallization. The isothermal crystallization was also described according to Avrami's approach. It has been shown that the addition of CNTs causes a remarkable increase in the overall crystallization rate of PA1010 and affects the mechanism of nucleation and growth of PA1010 crystals. The analysis of kinetic data according to nucleation theories shows that the increment in crystallization rate of CNTs/PA1010 composites results from the decrease in lateral surface free energy. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3794–3800, 2006 相似文献
996.
997.
998.
999.
Ya-Ping Sun Robert D. Miller R. Sooriyakumaran Josef Michl 《Journal of Inorganic and Organometallic Polymers》1991,1(1):3-35
A comprehensive study of the electronic absorption and emission spectra and the fluorescence quantum yield and lifetime of seven poly(di-n-alkylsilane)s and of three isotopically labelled poly(di-n-hexylsilane)s in hydrocarbon solution at room temperature is reported. Also reported are fluorescence polarization and carbon tetrachloride quenching of fluorescence of poly(di-n-hexylsilane). The observed fluorescence spectra, quantum yield, and polarization depend on the selected excitation energy in a very characteristic fashion, whereas the fluorescence lifetime does not; however, it depends on the selected emission energy. These characteristic dependencies are qualitatively accounted for by the previously proposed segment distribution model if one assumes that the photophysical behavior at higher excitation energies is strongly affected by the presence of a low-lying weakly allowed state in short-segment chromophores and the behavior at lower excitation energies is dictated by the selective excitation of emitting long-segment chromophores. 相似文献
1000.
可编程脉冲吞除频率合成器是应用微程序控制技术和脉冲吞除技术构成的一种新颖的数字式频率合成器,它的电路结构简单,可以在不改变输入基准频率和电路结构的前提下,通过“编程”来改变输出频率。所产生的输出频率准确稳定,且能灵活改变。文章阐述了这种新型频率合成器设计的数学依据,并以SN368遥测地震仪控制系统主时钟电路为实例,对其电路结构和工作原理进行了深入剖析。图3表2参4 相似文献