全文获取类型
收费全文 | 2489篇 |
免费 | 36篇 |
国内免费 | 6篇 |
专业分类
化学 | 1640篇 |
晶体学 | 7篇 |
力学 | 28篇 |
数学 | 506篇 |
物理学 | 350篇 |
出版年
2021年 | 15篇 |
2019年 | 17篇 |
2018年 | 19篇 |
2016年 | 36篇 |
2015年 | 34篇 |
2014年 | 36篇 |
2013年 | 65篇 |
2012年 | 65篇 |
2011年 | 85篇 |
2010年 | 52篇 |
2009年 | 49篇 |
2008年 | 68篇 |
2007年 | 73篇 |
2006年 | 68篇 |
2005年 | 54篇 |
2004年 | 70篇 |
2003年 | 33篇 |
2002年 | 46篇 |
2001年 | 49篇 |
2000年 | 33篇 |
1999年 | 25篇 |
1998年 | 26篇 |
1997年 | 31篇 |
1996年 | 44篇 |
1995年 | 39篇 |
1994年 | 41篇 |
1993年 | 32篇 |
1992年 | 32篇 |
1991年 | 28篇 |
1990年 | 37篇 |
1989年 | 29篇 |
1988年 | 28篇 |
1987年 | 34篇 |
1986年 | 18篇 |
1985年 | 54篇 |
1984年 | 44篇 |
1983年 | 42篇 |
1982年 | 20篇 |
1981年 | 45篇 |
1980年 | 40篇 |
1979年 | 28篇 |
1978年 | 39篇 |
1977年 | 38篇 |
1976年 | 26篇 |
1975年 | 33篇 |
1974年 | 33篇 |
1973年 | 23篇 |
1972年 | 18篇 |
1960年 | 19篇 |
1885年 | 15篇 |
排序方式: 共有2531条查询结果,搜索用时 15 毫秒
61.
Sren Arlt Vladana Petkovi Gerd Ludwig Thomas Eichhorn Heinrich Lang Tobias Rüffer Sanja Mijatovi Danijela Maksimovi-Ivani Goran N. Kaluerovi 《Molecules (Basel, Switzerland)》2021,26(7)
Neutral [Ru(η6-arene)Cl2{Ph2P(CH2)3SPh-κP}] (arene = benzene, indane, 1,2,3,4-tetrahydronaphthalene: 2a, 2c and 2d) and cationic [Ru(η6-arene)Cl(Ph2P(CH2)3SPh-κP,κS)]X complexes (arene = mesitylene, 1,4-dihydronaphthalene; X = Cl: 3b, 3e; arene = benzene, mesitylene, indane, 1,2,3,4-tetrahydronaphthalene, and 1,4-dihydronaphthalene; X = PF6: 4a–4e) complexes were prepared and characterized by elemental analysis, IR, 1H, 13C and 31P NMR spectroscopy and also by single-crystal X-ray diffraction analyses. The stability of the complexes has been investigated in DMSO. Complexes have been assessed for their cytotoxic activity against 518A2, 8505C, A253, MCF-7 and SW480 cell lines. Generally, complexes exhibited activity in the lower micromolar range; moreover, they are found to be more active than cisplatin. For the most active ruthenium(II) complex, 4b, bearing mesitylene as ligand, the mechanism of action against 8505C cisplatin resistant cell line was determined. Complex 4b induced apoptosis accompanied by caspase activation. 相似文献
62.
Dr. Julian Heinrich Dr. Karolina Bossak-Ahmad Mie Riisom Dr. Haleh H. Haeri Tasha R. Steel Vinja Hergl Alexander Langhans Corinna Schattschneider Jannis Barrera Dr. Stephen M. F. Jamieson Prof. Matthias Stein Prof. Dariush Hinderberger Prof. Christian G. Hartinger Prof. Wojciech Bal Prof. Nora Kulak 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(72):18093-18102
Redox-active Cu(II) complexes are able to form reactive oxygen species (ROS) in the presence of oxygen and reducing agents. Recently, Faller et al. reported that ROS generation by Cu(II) ATCUN complexes is not as high as assumed for decades. High complex stability results in silencing of the Cu(II)/Cu(I) redox cycle and therefore leads to low ROS generation. In this work, we demonstrate that an exchange of the α-amino acid Gly with the β-amino acid β-Ala at position 2 (Gly2→β-Ala2) of the ATCUN motif reinstates ROS production (•OH and H2O2). Potentiometry, cyclic voltammetry, EPR spectroscopy and DFT simulations were utilized to explain the increased ROS generation of these β-Ala2-containing ATCUN complexes. We also observed enhanced oxidative cleavage activity towards plasmid DNA for β-Ala2 compared to the Gly2 complexes. Modifications with positively charged Lys residues increased the DNA affinity through electrostatic interactions as determined by UV/VIS, fluorescence, and CD spectroscopy, and consequently led to a further increase in nuclease activity. A similar trend was observed regarding the cytotoxic activity of the complexes against several human cancer cell lines where β-Ala2 peptide complexes had lower IC50 values compared to Gly2. The higher cytotoxicity could be attributed to an increased cellular uptake as determined by ICP-MS measurements. 相似文献
63.
D. Thao Nguyen Matthias Freitag Christian Gutheil Dr. Kai Sotthewes Dr. Bonnie J. Tyler Dr. Marcus Böckmann Mowpriya Das Friederike Schlüter Prof. Dr. Nikos L. Doltsinis Prof. Dr. Heinrich F. Arlinghaus Prof. Dr. Bart Jan Ravoo Prof. Dr. Frank Glorius 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(32):13754-13759
64.
Sebastian Scharf Eduard Kovalski Tobias Rüffer Alexander Hildebrandt Heinrich Lang 《无机化学与普通化学杂志》2020,646(22):1820-1833
The synthesis of [Ti6O4(OiPr)8(O2CPh)8] ( 3 ) and [RuCl(N≡CR)5][RuCl4(N≡CR)2] ( 4a , R = Me; 4b , R = Ph), [Ru(N≡CPh)6][RuCl4(N≡CPh)2] ( 5 ) and [H3O][RuCl4(N≡CMe)2] ( 7a ) is discussed. Crystallization of 5 from CH2Cl2 gave trans-[RuCl2(N≡CPh)4] ( 6 ). The solid-state structures of 3 , 4a , b , 5 , 6 and 7a are reported. Complex 4b forms a 3D network, while 6 displays a 2D structure, due to π-interactions between the benzonitrile ligands. The (spectro)electrochemical behavior of 4a , b and 6 was studied at 25 and –72 °C and the results thereof are compared with [NEt4][RuCl4(N≡CMe)2] ( 7b ) and [RuCl(N≡CPh)5][PF6] ( 8 ). The electrochemical response of the cation and the anion in 4a , b are independent from each other. [RuCl(N≡CR)5]+ possesses one reversible RuII/RuIII process. However, [RuCl4(N≡CMe)2]– was shown to be prone to ligand exchange and disproportionation upon formation of either a RuIV and RuII species at 25 °C, while at –72 °C the rapid conversion of the electrochemically formed species is hindered. In situ IR and UV/Vis/NIR studies confirmed the respective disproportionation reaction products of the aforementioned oxidation and reduction, respectively. 相似文献
65.
D. Thao Nguyen Matthias Freitag Christian Gutheil Kai Sotthewes Bonnie J. Tyler Marcus Bckmann Mowpriya Das Friederike Schlüter Nikos L. Doltsinis Heinrich F. Arlinghaus Bart Jan Ravoo Frank Glorius 《Angewandte Chemie (International ed. in English)》2020,59(32):13651-13656
A novel photoresponsive and fully conjugated N‐heterocyclic carbene (NHC) has been synthesized that combines the excellent photophysical properties of arylazopyrazoles (AAPs) with an NHC that acts as a robust surface anchor (AAP‐BIMe). The formation of self‐assembled monolayers (SAMs) on gold was proven by ToF‐SIMS and XPS, and the organic film displayed a very high stability at elevated temperatures. This stability was also reflected in a high desorption energy, which was determined by temperature‐programmed SIMS measurements. E‐/Z‐AAP‐BIMe@Au photoisomerization resulted in reversible alterations of the surface energy (i.e. wettability), the surface potential (i.e. work function), and the conductance (i.e. resistance). The effects could be explained by the difference in the dipole moment of the isomers. Furthermore, sequential application of a dummy ligand by microcontact printing and subsequent backfilling with AAP‐BIMe allowed its patterning on gold. To the best of our knowledge, this is the first example of a photoswitchable NHC on a gold surface. These properties of AAP‐BIMe@Au illustrate its suitability as a molecular switch for electronic devices. 相似文献
66.
It is shown that for any 4-regular graph G there is a collection F of paths of length 4 such that each edge of G belongs to exactly two of the paths and each vertex of G occurs exactly twice as an endvertex of a path of F. This proves a special case of a conjecture of Bondy. © 1996 John Wiley & Sons, Inc. 相似文献
67.
68.
Hans-Joachim Nees Uwe Bergstrßer Heinrich Heydt Manfred Regitz 《Heteroatom Chemistry》1993,4(5):525-530
The (diazoalkyl)phosphanes 4a–e undergo [4 + 1]-cycloaddition reactions with the tetrahalo-orthobenzoquinones 5a,b to furnish the previously unknown (diazoalkyl)phosphoranes 6a–h . The structure of product 6h has been investigated by X-ray crystallography. 相似文献
69.
In this paper we revisit old swelling data on polymer networks that have not been interpreted theoretically on a closed molecular basis. If the osmotic pressure of the swollen network is compared to the osmotic pressure of the corresponding uncrosslinked solution unsolved problems appear, when the relative osmotic pressure is plotted against the degree of swelling, i.e. the deformation due to swelling. A significant maximum appears which cannot be explained by any of the recently derived elastic models, such as junction constraint or other entanglement models. It is suggested in this paper that the maximum is a consequence of structural heterogeneities of fractal nature. If such fractal heterogeneities are assumed a strong maximum in the relative osmotic pressure can be reproduced. The physical reason is the different thermodynamic behavior of uncrosslinked linear chains and crosslinked self-similar (non-linear) polymers. The conclusion is supported by numerical (Monte Carlo) simulations. 相似文献
70.
The strain amplitude dependence of the viscoelastic properties of eight different carbon blacks dispersed in two different rubbery networks is investigated and evaluated within the Cole-Cole approach for the complex elastic modulus at fixed temperature and frequency. This approach is based on the Kraus model of strain-dependent filler agglomeration-deagglomeration rates. We find a non-integer universal shape exponent of the Cole-Cole process that obviously depends only on the surrounding polymer matrix but is independent of the filler grade. The exponent can be related to the fractal dimension of the carbon black surface. 相似文献