全文获取类型
收费全文 | 4394篇 |
免费 | 58篇 |
国内免费 | 10篇 |
专业分类
化学 | 3113篇 |
晶体学 | 20篇 |
力学 | 68篇 |
数学 | 934篇 |
物理学 | 327篇 |
出版年
2019年 | 34篇 |
2016年 | 71篇 |
2015年 | 51篇 |
2014年 | 34篇 |
2013年 | 113篇 |
2012年 | 89篇 |
2011年 | 140篇 |
2010年 | 102篇 |
2009年 | 114篇 |
2008年 | 140篇 |
2007年 | 139篇 |
2006年 | 146篇 |
2005年 | 130篇 |
2004年 | 104篇 |
2003年 | 101篇 |
2002年 | 103篇 |
2001年 | 54篇 |
2000年 | 72篇 |
1999年 | 61篇 |
1998年 | 59篇 |
1997年 | 56篇 |
1996年 | 71篇 |
1995年 | 79篇 |
1994年 | 59篇 |
1993年 | 68篇 |
1992年 | 96篇 |
1991年 | 95篇 |
1990年 | 77篇 |
1989年 | 71篇 |
1988年 | 60篇 |
1987年 | 65篇 |
1986年 | 68篇 |
1985年 | 84篇 |
1984年 | 90篇 |
1983年 | 84篇 |
1982年 | 81篇 |
1981年 | 107篇 |
1980年 | 61篇 |
1979年 | 80篇 |
1978年 | 74篇 |
1977年 | 92篇 |
1976年 | 66篇 |
1975年 | 79篇 |
1974年 | 85篇 |
1973年 | 64篇 |
1972年 | 55篇 |
1971年 | 48篇 |
1970年 | 37篇 |
1967年 | 31篇 |
1962年 | 29篇 |
排序方式: 共有4462条查询结果,搜索用时 15 毫秒
131.
132.
Helmut Kauffmann 《Colloid and polymer science》1940,93(1):86-103
Ohne Zusammenfassung 相似文献
133.
Helmut Unkelbach 《Mathematische Zeitschrift》1940,46(1):329-336
Ohne ZusammenfassungHerrn Oskar Perron zum 60. Geburtstag am 7. Mai 1940 gewidmet. 相似文献
134.
Helmut Wallner 《Zeitschrift für Physik A Hadrons and Nuclei》1939,114(5-6):368-378
135.
136.
Juan Alfonso Redondo Enrique Martínez‐Campos Laetitia Plet Mnica Prez‐Perrino Rodrigo Navarro Guillermo Corrales Abhay Pandit Helmut Reinecke Alberto Gallardo Jos Luis Lpez‐Lacomba Alfonso Fernndez‐Mayoralas Carlos Elvira 《Macromolecular rapid communications》2016,37(7):575-583
The incorporation of cyclodextrins (CDs) to nonviral cationic polymer vectors is very attractive due to recent studies that report a clear improvement of their cytocompatibility and transfection efficiency. However, a systematic study on the influence of the CD derivatization is still lacking. In this work, the relevance of β‐CD permethylation has been addressed by preparing and evaluating two series of copolymers of the cationic N‐ethyl pyrrolidine methacrylamide (EPA) and styrenic units bearing pendant hydroxylated and permethylated β‐CDs (HCDSt and MeCDSt, respectively). For both cell lines, CDs permethylation shows a strong influence on plasmid DNA complexation, “in vitro” cytocompatibility and transfection efficiency of the resulting copolymers over two murine cell lines. While the incorporation of the hydroxylated CD moiety increased the cytotoxicity of the copolymers in comparison with their homopolycationic counterpart, the permethylated copolymers have shown full cytocompatibility as well as superior transfection efficiency than the controls. This behavior has been related to the different chemical nature of both units and tentatively to a different distribution of units along the polymeric chains. Cellular internalization analysis with fluorescent copolymers supports this behavior.
137.
Dr. Christina Enengl Dr. Sandra Enengl Sandra Pluczyk Dr. Marek Havlicek Prof. Mieczyslaw Lapkowski Dr. Helmut Neugebauer Prof. Eitan Ehrenfreund 《Chemphyschem》2016,17(23):3836-3844
In this work, we focus on the formation of different kinds of charge carriers such as polarons and bipolarons upon p‐type doping (oxidation) of the organic semiconductor poly(3‐ hexylthiophene‐2,5‐diyl) (P3HT). We elucidate the cyclic voltammogram during oxidation of this polymer and present spectroscopic changes upon doping in the UV/Vis/near‐IR range as well as in the mid‐IR range. In the low‐oxidation regime, two absorption bands related to sub‐gap transitions appear, one in the UV/Vis range and another one in the mid‐IR range. The UV/Vis absorption gradually decreases upon further doping while the mid‐IR absorption shifts to lower energy. Additionally, electron paramagnetic resonance (EPR) measurements are performed, showing an increase of the EPR signal up to a certain doping level, which significantly decreases upon further doping. Furthermore, the absorption spectra in the UV/Vis range are analyzed in relation to the morphology (crystalline vs. amorphous) by using theoretical models. Finally, the calculated charge carriers from cyclic voltammogram are linked together with optical transitions as well as with the EPR signals upon p‐type doping. We stress that our results indicate the formation of polarons at low doping levels and the existence of bipolarons at high doping levels. The presented spectroscopic data are an experimental evidence of the formation of bipolarons in P3HT. 相似文献
138.
Dr. Shaodong Zhou Dr. Jilai Li Dr. Maria Schlangen Prof. Dr. Helmut Schwarz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(9):3073-3076
Carbon‐atom extrusion from the ipso‐position of a halobenzene ring (C6H5X; X=F, Cl, Br, I) and its coupling with a methylene ligand to produce acetylene is not confined to [LaCH2]+; also, the third‐row transition‐metal complexes [MCH2]+, M=Hf, Ta, W, Re, and Os, bring about this unusual transformation. However, substrates with substituents X=CN, NO2, OCH3, and CF3 are either not reactive at all or give rise to different products when reacted with [LaCH2]+. In the thermal gas‐phase processes of atomic Ln+ with C7H7Cl substrates, only those lanthanides with a promotion energy small enough to attain a 4fn5d16s1 configuration are reactive and form both [LnCl]+ and [LnC5H5Cl]+. Branching ratios and the reaction efficiencies of the various processes seem to correlate with molecular properties, like the bond‐dissociation energies of the C?X or M+?X bonds or the promotion energies of lanthanides. 相似文献
139.
Dr. Shaodong Zhou Dr. Jilai Li Dr. Maria Schlangen Prof. Dr. Helmut Schwarz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(21):7225-7228
High‐level electronic structure calculations, in combination with Fourier transform ion cyclotron resonance (FT‐ICR) mass spectrometric studies, permit the mechanism by which closed‐shell, “naked” [TaO2]+ brings about C?H bond activation of methane to be revealed. These studies also help to understand why the lighter congeners of [MO2]+ (M=V, Nb) are unreactive under ambient conditions. 相似文献
140.