全文获取类型
收费全文 | 1154篇 |
免费 | 50篇 |
国内免费 | 6篇 |
专业分类
化学 | 968篇 |
晶体学 | 9篇 |
力学 | 12篇 |
数学 | 116篇 |
物理学 | 105篇 |
出版年
2023年 | 14篇 |
2022年 | 49篇 |
2021年 | 43篇 |
2020年 | 21篇 |
2019年 | 24篇 |
2018年 | 25篇 |
2017年 | 8篇 |
2016年 | 41篇 |
2015年 | 49篇 |
2014年 | 43篇 |
2013年 | 75篇 |
2012年 | 86篇 |
2011年 | 113篇 |
2010年 | 47篇 |
2009年 | 57篇 |
2008年 | 98篇 |
2007年 | 69篇 |
2006年 | 48篇 |
2005年 | 76篇 |
2004年 | 55篇 |
2003年 | 30篇 |
2002年 | 35篇 |
2001年 | 12篇 |
2000年 | 6篇 |
1999年 | 9篇 |
1998年 | 8篇 |
1997年 | 6篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有1210条查询结果,搜索用时 15 毫秒
81.
Martina Mazzoni Lorenzo Franco Alberta Ferrarini Carlo Corvaja Giovanni Zordan Gianfranco Scorrano 《Liquid crystals》2013,40(2):203-208
A nitroxide [60]fullerene adduct containing a pyrrolidine-1-oxyl group has been synthesized. Its orientational order in the nematic phase of the liquid crystal solvent 4,4′-azoxyanisole (PAA) has been measured from the variation of the EPR spectral parameters on passing from the isotropic to the nematic phase. Highly resolved EPR lines allow for precise evaluation of the shifts of the g, a N and a H values. Since the g and the hyperfine tensors are known, the order matrix could be obtained. This is compared with the one calculated with a theoretical model based on short range solute-solvent interactions, which predicts a considerable degree of orientation of the molecular axes, despite the almost spherical shape of the molecule. The agreement with experimental findings is quite good and it is further improved if a bent structure of the pyrrolidine ring is taken into account. 相似文献
82.
Vermeulen W Filliers W García C Manzanaro S Montalvo D Polanco C Spillemaeckers F Van Hoof B Winderickx G Somers I Rodriguez-Campos I 《Magnetic resonance in chemistry : MRC》2008,46(12):1198-1202
This article presents the structure elucidation of four new compounds, formed during the hemisynthetic preparation of trabectedin, an anti-tumor natural product from Ecteinascidia turbinata. We report herein on the use of UV, MS and NMR spectroscopic data along with (1)H and (13)C spectral assignments obtained by means of 1D and 2D homo- and heteronuclear NMR techniques. 相似文献
83.
An efficient protocol for the synthesis of new functionalized indenes 3 was successfully realized. Thus the coupling reaction of allyl acetate 2 with Grignard reagents in the presence of a catalytic amount of LiCuBr2 at low temperature afforded pure ethyl 1-alkyl-1H-indenes-2-carboxylate 3 in good yields. 相似文献
84.
A Bis‐Sulfonyl O,C,O Aryl Pincer Ligand and its Tin(II) Complex: Synthesis,Structural Studies,and DFT Calculations 下载免费PDF全文
Mohammad El Ezzi Romaric Lenk Dr. David Madec Dr. Jean‐Marc Sotiropoulos Sonia Mallet‐Ladeira Dr. Annie Castel 《Angewandte Chemie (International ed. in English)》2015,54(3):805-808
The efficiency of the deprotonated aryl bis‐sulfone [2,6‐{(p‐tolyl)SO2}2C6H3]? as an O,C,O‐coordinating pincer‐type ligand was described. The bis‐sulfone precursor was synthesized using a straightforward palladium‐catalyzed cross‐coupling reaction. As a result of directed ortho metalation (DoM) through sulfonyl groups, a selective lithiation of the aryl group was achieved and the corresponding carbanion was isolated and its structure determined by single‐crystal X‐ray diffraction analysis. A heteroleptic tin(II) complex has been prepared by a nucleophilic substitution reaction. Crystallographic analysis and DFT calculations indicate that the bis‐sulfonyl moiety acts as a new O,C,O‐coordinating pincer‐type ligand with intramolecular S?O coordination to a tin(II) center. The cis form with the two nonbonded oxygen atoms of the sulfonyl groups on the same side is preferentially obtained. 相似文献
85.
Sonia Jam Masume Ghalbi Ahangary Ahmad Tavasoli Kambiz Sadaghiani Ali Nakhaei Pour 《Reaction Kinetics and Catalysis Letters》2006,89(1):71-79
Summary An integrated process for producing liquid fuels from synthesis gas via a two-stage Fischer-Tropsch (FT) reaction is disclosed. An iron catalyst was used in the first bed of a fixed-bed reactor
followed by a ruthenium promoted cobalt catalyst in the second bed. The activity and selectivity of the dual-bed system were
assessed and compared with those using catalysts in a single bed system, separately. The methane selectivity in the dual-bed
reactor was about 11% less compared to that of the single-bed system. The C5+ selectivity for the dual-bed reactor was 19.7% higher than that of the single-bed system. 相似文献
86.
Dr. Sunyoung Lee Dr. Sonia Diab Pierre Queval Dr. Muriel Sebban Dr. Isabelle Chataigner Prof. Serge R. Piettre 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(22):7181-7192
Non‐stabilized azomethine ylide 4 a reacts smoothly at room temperature with a variety of uncomplexed aromatic heterocycles and carbocycles on the condition that the ring contains at least one or two electron‐withdrawing substituents, respectively. Aromatic substrates, including pyridine and benzene derivatives, participate as 2 π components in [3+2] cycloaddition reactions and interact with one, two, or three equivalent(s) of the ylide, depending on their structure and substitution pattern. Thus, this process affords highly functionalized polycyclic structures that contain between one and three pyrrolidinyl ring(s) in useful yields. These results indicate that the site selectivity of the cycloaddition reactions strongly depends on both the nature and the positions of the substituents. In most cases, the second 1,3‐dipolar reaction occurs on the opposite face to the one that contains the first pyrrolidinyl ring. DFT calculations on model compounds indicate that a concerted mechanism features a low activation barrier. 相似文献
87.
Dr. Jorge Carballido‐Landeira Sonia Goy‐López Prof. Dr. Alberto P. Muñuzuri Prof. Dr. Pablo Taboada Prof. Dr. Víctor Mosquera 《Chemphyschem》2012,13(5):1347-1353
The spontaneous in situ formation of one‐dimensional (1D) assemblies of gold nanoparticles (NP) in oleylamine/bis(2‐ethylhexyl) sulfosuccinate sodium salt/water/octane (OAm/AOT/w/o) microemulsions by exploiting both the aurophilic bonding between OAm and gold salt, and the interactions between OAm and AOT surfactant is presented. Control on the structure of the resulting assemblies is achieved by changing in the solvent quality, the [Au]/[AOT] molar ratio and the presence of different cosolutes. A possible mechanism of the formation of the 1D parallel Au NP arrays is proposed. 相似文献
88.
Luca Sancineto Carmine Ostacolo David Ortega-Alarcon Ana Jimenez-Alesanco Laura Ceballos-Laita Sonia Vega Olga Abian Adrian Velazquez-Campoy Silvia Moretti Agnieszka Dabrowska Pawel Botwina Aleksandra Synowiec Anna Kula-Pacurar Krzysztof Pyrc Nunzio Iraci Claudio Santi 《Molecules (Basel, Switzerland)》2021,26(19)
The COVID-19 pandemic outbreak prompts an urgent need for efficient therapeutics, and repurposing of known drugs has been extensively used in an attempt to get to anti-SARS-CoV-2 agents in the shortest possible time. The glycoside rutin shows manifold pharmacological activities and, despite its use being limited by its poor solubility in water, it is the active principle of many pharmaceutical preparations. We herein report our in silico and experimental investigations of rutin as a SARS-CoV-2 Mpro inhibitor and of its water solubility improvement obtained by mixing it with l-arginine. Tests of the rutin/l-arginine mixture in a cellular model of SARS-CoV-2 infection highlighted that the mixture still suffers from unfavorable pharmacokinetic properties, but nonetheless, the results of this study suggest that rutin might be a good starting point for hit optimization. 相似文献
89.
Favero LB Giuliano BM Melandri S Maris A Ottaviani P Velino B Caminati W 《The journal of physical chemistry. A》2005,109(33):7402-7404
The molecular beam Fourier transform microwave spectrum of 1,4-dioxane-trifluoromethane has been assigned and measured. The two subunits form a cage stabilized by one C-H...O and two C-H...F weak hydrogen bonds. The C-H...O link involves the axial lone pair of one of the two equivalent ring oxygens, while the two C-H...F bridges connect trifluoromethane to the two axial hydrogens in positions 3 and 5. The dissociation energy has been estimated from the D(J) centrifugal distortion parameter to be approximately 6.8 kJ/mol. 相似文献
90.