全文获取类型
收费全文 | 6594篇 |
免费 | 743篇 |
国内免费 | 1967篇 |
专业分类
化学 | 4641篇 |
晶体学 | 243篇 |
力学 | 2044篇 |
综合类 | 52篇 |
数学 | 329篇 |
物理学 | 1995篇 |
出版年
2024年 | 29篇 |
2023年 | 114篇 |
2022年 | 287篇 |
2021年 | 318篇 |
2020年 | 280篇 |
2019年 | 211篇 |
2018年 | 156篇 |
2017年 | 297篇 |
2016年 | 343篇 |
2015年 | 294篇 |
2014年 | 375篇 |
2013年 | 484篇 |
2012年 | 437篇 |
2011年 | 466篇 |
2010年 | 436篇 |
2009年 | 492篇 |
2008年 | 478篇 |
2007年 | 544篇 |
2006年 | 424篇 |
2005年 | 402篇 |
2004年 | 402篇 |
2003年 | 361篇 |
2002年 | 274篇 |
2001年 | 206篇 |
2000年 | 199篇 |
1999年 | 149篇 |
1998年 | 140篇 |
1997年 | 123篇 |
1996年 | 110篇 |
1995年 | 77篇 |
1994年 | 76篇 |
1993年 | 44篇 |
1992年 | 63篇 |
1991年 | 41篇 |
1990年 | 32篇 |
1989年 | 21篇 |
1988年 | 28篇 |
1987年 | 21篇 |
1986年 | 23篇 |
1985年 | 9篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1979年 | 8篇 |
1978年 | 2篇 |
1974年 | 1篇 |
1971年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有9304条查询结果,搜索用时 31 毫秒
121.
122.
研究了4个偶氮染料在酸性介质中的电还原性质。偶氮基在酸性介质中的还原均为不可逆四电子一步全还原。邻、对位上有吸电子基(如—CO_2Bu-n)的偶氮基较间位有吸电子基时更易被还原。分子中同时含有偶氮基和硝基时,偶氮基先被还原。 相似文献
123.
1 INTRODUCTION Coordination chemistry has been playing an important role in nonlinear optical (NLO) materi- als [1~3] in recent years. It has been found that tetrahedral or square pyramidal molecular configurations are useful for designing transparent second-harmonic generation (SHG) materials from coordination compounds[4]. It has also been reported that the pyridyl-based metal complexes can exhibit SHG effects[5]. Recently, we have successfully synthesized a new coordination compoun… 相似文献
124.
This paper reported the research results concerning the surface characterization ofpolystyrene-graft-w-stearyl poly(ethylene oxide) (PS-g-SPEO) by means of XPS,contactangle measurement and TEM, and its in vitro blood compatibility assessment by measuringthe plasma recalcification time (RT) and partial thromboplastin time (PTT). The XPSresults demonstrated that the surface and bulk composition of the PS-g-SPEO graftcopolymers differ remarkably from each other,and that SPEO component was constantlyenriched at the copolymer/air interface. Contact angle studies indicated that the surfacewater wettability can be adjusted effectively by changing the composition of the copolymer.PS-g-SPEO graft copolymers can undergo microphase separation as clearly illustrated byTEM photographs. The relationship between the surface properties of PS-g-SPEO graftcopolymer and its blood compatibility was also discussed. 相似文献
125.
126.
127.
128.
The novel fluorinated distyrylarylene, 4,4'-bis(2,2-di(4-fluorophenyl)vinyl)biphenyl (DFPVBi), was synthesized and fully characterized. The structure was confirmed with IR, 1↑H NMR, 13↑C NMR, 19↑F NMR and MS analyses. Its electronic and photoluminescence properties were investigated by UV-Vis absorption, cyclic voltammetry and fluorescence spectroscopy. The energy levels of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are --5.77 and --2.75 eV, respectively. The electroluminescence proper- ties of the organic light-emitting diode fabricated by DFPVBi were also studied. The device exhibits a pure blue emission peaked at 454 nm, which indicates a maximum luminance of 5872 cd/m
^2 at 14.2 V and a maximum current efficiency of 2.82 cd/A at 10V, respectively. 相似文献
129.
Runru Liu Dapeng Xu Shuang Li Zhe Lü Yanfeng Xue Deyong Wang Wenhui Su 《Frontiers of Chemistry in China》2006,1(4):398-401
In this paper, perovskite oxide SmCoO3 was prepared by the solid-state reaction method using Co2O3 and Sm2O3 as raw materials. The structure and properties of the samples were investigated by XRD, Raman spectral techniques, and DC
measurements and so on. The results of XRD and Raman spectra showed that the mixtures of Co2O3 and Sm2O3 can react to produce a single phase perovskite oxide SmCoO3 around 1353 K. The single-phase SmCoO3 changes from an insulator to a semi-conductor and transition occurs around 470 K. The thermal expansion coefficient (2.17
× 10−5 K−1) of the single-phase SmCoO3 is approximately equal to that of doped LaGaO3, but much bigger than that of SDC(Ce0.85Sm0.15O2) above 873 K. 相似文献
130.
Atsushi Itagaki Kazuki Nakanishi Kazuyuki Hirao 《Journal of Sol-Gel Science and Technology》2003,26(1-3):153-156
The phase separation behavior of gelling systems containing the mixture of 3-functional and 4-functional alkoxysilanes has been investigated. The relation between the starting composition and resultant macroporous morphology was examined using tetramethoxysilane (TMOS) and vinyltrimethoxysilane (VTMS) as starting alkoxysilanes, formamide (FA) as an additive, under an acidic condition. Up to TMOS:VTMS molar ratio of 0.5:0.5, the phase relation remained almost unchanged from that of pure TMOS system which exhibits morphology with well-defined co-continuous macropores in a very limited concentration region. On the VTMS-rich side typically TMOS:VTMS = 0.2:0.8, however, the co-continuous macroporous morphology was obtained in a broader composition range than those of either pure TMOS or VTMS system. A dome-like pseudo binary region was obtained with the two-phase region extending toward FA-rich direction. The domain size and pore volume of the gels with macroporous morphology could be controlled by alkoxide:water ratio and total solvent fraction, respectively. 相似文献