全文获取类型
收费全文 | 15562篇 |
免费 | 2634篇 |
国内免费 | 2973篇 |
专业分类
化学 | 15439篇 |
晶体学 | 103篇 |
力学 | 258篇 |
综合类 | 106篇 |
数学 | 72篇 |
物理学 | 5191篇 |
出版年
2024年 | 45篇 |
2023年 | 228篇 |
2022年 | 461篇 |
2021年 | 640篇 |
2020年 | 766篇 |
2019年 | 593篇 |
2018年 | 546篇 |
2017年 | 612篇 |
2016年 | 673篇 |
2015年 | 688篇 |
2014年 | 860篇 |
2013年 | 1393篇 |
2012年 | 1099篇 |
2011年 | 1052篇 |
2010年 | 816篇 |
2009年 | 935篇 |
2008年 | 955篇 |
2007年 | 1131篇 |
2006年 | 943篇 |
2005年 | 827篇 |
2004年 | 766篇 |
2003年 | 809篇 |
2002年 | 654篇 |
2001年 | 499篇 |
2000年 | 438篇 |
1999年 | 346篇 |
1998年 | 307篇 |
1997年 | 284篇 |
1996年 | 293篇 |
1995年 | 236篇 |
1994年 | 201篇 |
1993年 | 172篇 |
1992年 | 193篇 |
1991年 | 119篇 |
1990年 | 110篇 |
1989年 | 92篇 |
1988年 | 63篇 |
1987年 | 59篇 |
1986年 | 44篇 |
1985年 | 41篇 |
1984年 | 35篇 |
1983年 | 13篇 |
1982年 | 17篇 |
1981年 | 23篇 |
1980年 | 27篇 |
1979年 | 17篇 |
1978年 | 9篇 |
1977年 | 9篇 |
1976年 | 7篇 |
1973年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
21.
Shufeng Zuo 《Applied Surface Science》2006,253(5):2508-2514
Al-pillared clays supported rare earths (RE/Al-PILC) are prepared and used as supports of palladium catalysts for deep oxidation of low concentrations of benzene (130-160 ppm). The supports and catalysts are characterized by X-ray powder diffraction (XRD), FT-IR, BET, transmission electron microscopy (TEM) and temperature-programmed reduction (H2-TPR). The results show that Al-pillaring results in a strong increase in the basal spacing (d0 0 1) from about 1.2 to 1.8 nm, and an increase in the BET surface area from 63.6 (±3.2) to 238.8 (±11.9) m2/g. Activity tests of deep oxidation of low concentration benzene show catalysts supported on Al-PILC and RE/Al-PILC are obviously more active than that on raw clay. Pd/6% Ce/Al-PILC, in particular, can catalyze the complete oxidation of low concentration benzene at a temperature as low as about 290 °C. 相似文献
22.
23.
The excitation of eigen surface waves by tubular electron beams in cylindrical discharge devices is studied. The influence of the wave‐field azimuthal structure on the excitation efficiency and nonlinear stage of the plasmabeam instability is investigated both numerically and analytically. Analytical expressions for the saturation amplitude and excitation efficiency of the wave under study are derived. They are found to agree well with results obtained by numerical modelling of the plasma‐beam interaction presented in this paper. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
24.
Debendra K. Mohapatra Dhananjoy Mondal Mukund S. Chorghade Mukund K. Gurjar 《Tetrahedron letters》2006,47(52):9215-9219
The non-proteinogenic amino acid 3-hydroxy-4-methylproline (HMP) is an active constituent of some potent antimicrobials including echinocandins, nostopeptins, pneumocandins, sporiofungin and mulundocandins. A synthesis has been achieved in 10 steps with 29% overall yield; the Evans’ aldol reaction using Crimmins’ modified method was pivotal to the success of the strategy. 相似文献
25.
空心阴极灯激发的微波等离子体炬原子/离子荧光光谱研究--钙的原子/离子荧光光谱 总被引:2,自引:0,他引:2
用强短脉冲供电技术的空心阴极灯作激发源、微波等离子体炬作原子/离子化器,建立了原子/离子荧光光谱实验装置。详细研究了微波等离子体功率、观察高度、空心阴极灯电流等因素对原子/离子荧光信号强度的影响,测量了系统对Ca的原子/离子荧光光谱的检出限。 相似文献
26.
27.
Homo-apioneplanocin A was efficiently synthesized via stereoselective hydroxymethylation, regio- and chemoselective hydroboration, and chemoselective oxidation as key steps from d-ribose. 相似文献
28.
High temperature oxidation of metals leads to residual stresses both in the metal and in the growing oxide. In this work, the evolution of this residual stresses is theoretically predicted in the growing oxide layers. The origin of these stresses is based on a microstructural model. Using experimental results providing from the oxidation kinetics, and an analysis proposed to describe the growth strain occurring in the thin layers, a set of equations is established allowing determining the stresses evolution with oxidation time. Then, the model is compared with experimental results obtained on both α-Fe and phosphated α-Fe, oxidised at different temperatures. Numerical data are extracted from experiments either with an asymptotic formulation or with an inverse method. These two methods give good agreement with experiments and allow extracting the model parameters. 相似文献
29.
30.
HUA Jianjun LIU Yanhong & ZHANG Zhihe . Institute of Physics Chinese Academy of Sciences Beijing China . College of Biomedical Engineering Capital University of Medical Sciences Beijing China Correspondence should be addressed to Hua Jianjun 《中国科学G辑(英文版)》2004,(1)
Adustyplasmacanbedefinedasacomplicatedplasmacontainingsmallsolidmattercalleddustgrainsordustparticles,whichareusuallychargednegatively,duetoelectronshighermobilitythanion,bycollectingelectronsandionsfromthebackgroundplasma.Theuniverseisfilledwithdustyplasmassuchasplanetaryrings,comettails,andnebulae.Also,inindustrialplasmaprocessing,particulatessuspendedinplasmaarethemajorcontaminationinsemiconductormanufacture.Studiesondustyplasmahavebeenextendedtofar-flungtopicssuchaswaves,instabilities,stro… 相似文献