全文获取类型
收费全文 | 24896篇 |
免费 | 1965篇 |
国内免费 | 1057篇 |
专业分类
电工技术 | 1287篇 |
技术理论 | 3篇 |
综合类 | 1463篇 |
化学工业 | 4384篇 |
金属工艺 | 1368篇 |
机械仪表 | 1571篇 |
建筑科学 | 1755篇 |
矿业工程 | 937篇 |
能源动力 | 796篇 |
轻工业 | 1735篇 |
水利工程 | 468篇 |
石油天然气 | 1486篇 |
武器工业 | 158篇 |
无线电 | 2693篇 |
一般工业技术 | 3211篇 |
冶金工业 | 1528篇 |
原子能技术 | 235篇 |
自动化技术 | 2840篇 |
出版年
2024年 | 108篇 |
2023年 | 451篇 |
2022年 | 696篇 |
2021年 | 1025篇 |
2020年 | 762篇 |
2019年 | 682篇 |
2018年 | 800篇 |
2017年 | 853篇 |
2016年 | 783篇 |
2015年 | 950篇 |
2014年 | 1217篇 |
2013年 | 1528篇 |
2012年 | 1552篇 |
2011年 | 1642篇 |
2010年 | 1469篇 |
2009年 | 1347篇 |
2008年 | 1361篇 |
2007年 | 1260篇 |
2006年 | 1235篇 |
2005年 | 1085篇 |
2004年 | 767篇 |
2003年 | 703篇 |
2002年 | 720篇 |
2001年 | 606篇 |
2000年 | 552篇 |
1999年 | 615篇 |
1998年 | 547篇 |
1997年 | 444篇 |
1996年 | 400篇 |
1995年 | 340篇 |
1994年 | 327篇 |
1993年 | 232篇 |
1992年 | 181篇 |
1991年 | 135篇 |
1990年 | 79篇 |
1989年 | 73篇 |
1988年 | 86篇 |
1987年 | 57篇 |
1986年 | 40篇 |
1985年 | 31篇 |
1984年 | 18篇 |
1983年 | 13篇 |
1982年 | 17篇 |
1981年 | 14篇 |
1980年 | 9篇 |
1979年 | 15篇 |
1977年 | 13篇 |
1976年 | 17篇 |
1975年 | 6篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 13 毫秒
991.
pH-Sensitive Micelles Based on Double-Hydrophilic Poly(methylacrylic acid)-Poly(ethylene glycol)-Poly(methylacrylic acid) Triblock Copolymer 总被引:1,自引:0,他引:1
Youhua Tao Ren Liu Xiaoya Liu Mingqing Chen Cheng Yang Zhongbin Ni 《Nanoscale research letters》2009,4(4):341-343
pH-sensitive micelles with hydrophilic core and hydrophilic corona were fabricated by self-assembling of triblock copolymer
of poly(methylacrylic acid)-poly(ethylene glycol)-poly(methylacrylic acid) at lower solution pH. Transmission electron microscopy
and laser light scattering studies showed micelles were in nano-scale with narrow size distribution. Solution pH value and
the micelles concentration strongly influenced the hydrodynamic radius of the spherical micelles (48–310 nm). A possible mechanism
for the formation of micelles was proposed. The obtained polymeric micelle should be useful for biomedical materials such
as carrier of hydrophilic drug. 相似文献
992.
Song Li Gaowu W. Qin T Wenli Pei Yuping Ren Yudong Zhang Claude Esling Liang Zuo 《Journal of the American Ceramic Society》2009,92(3):631-635
Three simple capping molecules (urea, 3-aminopropanol, and polyethylene glycol) with different functional groups (−NH2 for urea, −NH2 and −OH for 3-aminopropanol, and −O− for polyethylene glycol) have been designed to prepare magnetite (Fe3 O4 ) particles with various shapes. The crystal structure, morphologies, and magnetic properties of the products have been characterized by X-ray diffraction, electron microscopy, and vibrating sample magnetometer. The results indicate that the capping functional groups play a major role in determining the size, shape, and thus magnetic properties of the magnetite nanocrystals. The morphology evolution of the magnetite under the hydrothermal condition is discussed in detail, particularly for the interaction between the various capping groups and surface structure and chemistry of the nanocrystals. 相似文献
993.
日用陶瓷在日常生活中的应用就是为了使人们的生活方便,同时还起着美化生活的作用。为了使日用瓷更适合人们的审美要求,在装饰上需要不断地进行探索。点、线、面作为装饰中最基本的元素,它们的有机结合充分表达了设计师的情感,而且陶瓷装饰的艺术性、思想性,都可以通过点、线、面的有机结合来体现。现在的日用陶瓷装饰设计越来越趋向于简洁化,从目前国内乃至国际市场来看,简约设计已成为一种时尚、一种趋势、一种不变的经典主题。 相似文献
994.
Copper(I) chloride catalysts with a loading of 20 wt%, supported on silica–titania mixed oxides with Si/Ti ratios of 1, 5, 10 and 50 were prepared by conventional and microwave heating methods and tested in the oxidative carbonylation of methanol to dimethyl carbonate (DMC). X-ray diffraction (XRD), nitrogen adsorption, X-ray photoelectron spectroscopy (XPS) and thermal gravimetric analysis (TGA) were used to examine the bulk and surface properties of the CuCl/SiO2–TiO2 catalysts. Quantum-chemical calculations were performed to explore the interaction of CuCl with the silica–titania support. Microwave heating showed some significant advantages over the conventional heating method, with markedly reduced preparation temperature and time, and provided improved catalytic activity in the oxidative carbonylation of methanol. The catalytic behavior of CuCl/SiO2–TiO2 in the test reaction studied was strongly dependent on the support composition. Incorporation of tetrahedral Ti(IV) species into the silica matrix could enhance the interaction of copper species with the oxide support. The improved catalytic performance of CuCl/SiO2–TiO2 in the DMC synthesis can be understood by the existence of the strong coordination interactions between the Cu+ centers of CuCl and the bridging oxygen atoms at the Si–O–Ti bonds in the silica–titania support. 相似文献
995.
Global phase behavior of imidazolium ionic liquids and compressed 1,1,1,2‐tetrafluoroethane (R‐134a)
Novel processes involving ionic liquids with refrigerant gases have recently been developed. Here, the complete global phase behavior has been measured for the refrigerant gas, 1,1,1,2‐tetrafluoroethane (R‐134a) and 1‐n‐alkyl‐3‐methyl‐imidazolium ionic liquids with the anions hexafluorophosphate [PF6], tetrafluoroborate [BF4] and bis(trifluoromethylsulfonyl)imide [Tf2N] from ~0°C to 105°C and to 33 MPa. All of the systems studied were Type V from the classification scheme of Scott‐van Konynenburg with regions of vapor‐liquid equilibrium, miscible/critical regions, vapor‐liquid‐liquid equilibrium, and upper and lower critical endpoints (UCEP and LCEP). The effect of the alkyl chain length has been investigated, for ethyl‐([EMIm]), n‐butyl‐([BMIm]), and n‐hexyl‐([HMIm]). With increasing chain length, the temperature of the lower critical end points increases and pressure at the mixture critical points decrease. With a common cation, the temperature of the LCEP increased and the mixture critical point pressures decreased in the order of [BF4], [PF6], and [Tf2N]. © 2008 American Institute of Chemical Engineers AIChE J, 2009 相似文献
996.
Changlin Li Yanqin Wang Bianfang Shi Jiawen Ren Xiaohui Liu Yangang Wang Yun Guo Yanglong Guo Guanzhong Lu 《Microporous and mesoporous materials》2009,117(1-2):104-110
MFI nanozeolite microspheres with intercrystal mesopores were synthesized by a steam-assisted crystallization–aggregation method, starting with close packed amorphous SiO2 or Al-containing SiO2 colloidal nanoparticles. The obtained samples with different Si/Al ratios were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy (SEM)/ transmission electron microscopy (TEM) observations, nitrogen adsorption analyses and 27Al magic angle spinning nuclear magnetic resonance (NMR). The SEM images clearly showed that the mean size of nanozeolite microspheres was ca. 0.5–3 μm, agglomerated from zeolite nanocrystals and varied with different Si/Al ratios. N2 sorption analyses as well as TEM micrographs indicated the dual-porosity of samples, one is from intracrystal micropores, and the other is from intercrystal mesopores. 27Al MAS-NMR suggested nearly all of the Al atoms were located at tetrahedral-coordinated sites in the framework. Furthermore, nanozeolite microspheres with various Si/Al ratios, even Si/Al equal to five, could be prepared by this facile route and less structure-directing agent was needed compared to conventional approach. This simple method could be easily extended to prepare other hierarchically structured zeolites. 相似文献
997.
Zheng-Fang Tian Hai-Bao Duan Hong Zhou Xiao-Ming Ren Hui Zhang Qing-Jin Meng 《Inorganic chemistry communications》2009,12(2):148-150
A charge-transfer compound, [NO2BzPz][Ni(mnt)2] (NO2BzPz+ = 1-(4′-nitrobenzyl)pyrazinium and mnt2? = maleonitriledithiolate), has been structurally characterized, which shows rare noncovalently intermolecular interactions between lone-pair electron and electron-deficient pyrazine rings (NO2?π and CN?π), theoretical analysis reveals that such intermolecular interactions can be attributed to Coulomb interaction. The paramagnetic [Ni(mnt)2]? anions in [NO2BzPz][Ni(mnt)2] form a dimerized stack and strong antiferromagnetic coupling interaction is observed in such a spin dimer which lead to weak paramagnetic feature in this compound. 相似文献
998.
Polylactide (PLA) and calcium carbonate (CaCO3) were melt blended using a twin‐screw extruder. The morphology of PLA/CaCO3 composites was observed by scanning electronic microscopy. The linear and nonlinear shear rheological behaviors of PLA/CaCO3 melts were investigated by an advanced rheology expended system. The results show that the CaCO3 particles are evenly dispersed in the PLA matrix. The incorporation of low CaCO3 content (<20%) causes the reduction of the storage moduli, loss moduli, and dynamic viscosities whereas high CaCO3 content (>30%) leads to the increase of the storage moduli, loss moduli, and dynamic viscosities. The composites with high CaCO3 content show pseudo‐solid‐like behaviors at low frequency. High CaCO3 content also results in a significant increase of flow activation energy and a dramatic decrease of flow index n, which is in consistent with the more serious shear‐thinning tendency of high‐filled PLA composites melts. The particular rheological responses might be attributed to the formation and destruction of the percolating network. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 相似文献
999.
Bingli Pan Junfang Ren Qunfeng Yue Bin Liu Junyan Zhang Shengrong Yang 《Polymer Composites》2009,30(2):147-153
Attapulgite (AT) clay was firstly treated with sodium polyacrylate (PAS), then polyamide 6 (PA6)/AT nanocomposites were prepared by simple melt compounding. Transmission electron microscope (TEM) and Fourier transform infrared spectrometry (FT‐IR) of treated AT confirm the success of purifying and surface modification of the original AT by PAS. X‐ray diffraction spectra for the nanocomposites show that the microstructure of AT in PA6 matrix is almost unchanged. It indicates that a strong interfacial adhesion exists between AT and PA6 matrix through analyzing fracture surfaces of the nanocomposites, the variation of glass transition temperature (Tg) obtained by dynamic mechanical analysis, and interfacial interaction factors; field emission scanning electron microscopy on the fracture surfaces of the nanocomposites shows that a uniform dispersion of AT is obtained. The above two aspects conform to the improvement of mechanical and thermal properties of the nanocomposites. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers 相似文献
1000.