全文获取类型
收费全文 | 196篇 |
免费 | 9篇 |
国内免费 | 1篇 |
专业分类
化学 | 156篇 |
晶体学 | 1篇 |
力学 | 4篇 |
数学 | 20篇 |
物理学 | 25篇 |
出版年
2023年 | 5篇 |
2022年 | 6篇 |
2021年 | 3篇 |
2020年 | 1篇 |
2019年 | 7篇 |
2018年 | 4篇 |
2017年 | 5篇 |
2016年 | 5篇 |
2015年 | 6篇 |
2014年 | 7篇 |
2013年 | 11篇 |
2012年 | 11篇 |
2011年 | 20篇 |
2010年 | 13篇 |
2009年 | 10篇 |
2008年 | 20篇 |
2007年 | 10篇 |
2006年 | 13篇 |
2005年 | 7篇 |
2004年 | 6篇 |
2003年 | 7篇 |
2002年 | 9篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1935年 | 1篇 |
排序方式: 共有206条查询结果,搜索用时 15 毫秒
21.
Aldrich CC Venkatraman L Sherman DH Fecik RA 《Journal of the American Chemical Society》2005,127(25):8910-8911
The polyketide synthase-derived pikromycin thioesterase (Pik TE) is unique in its ability to catalyze the cyclization of 12- and 14-membered macrolactones. In this investigation, the total synthesis of the natural hexaketide chain elongation intermediate as its N-acetyl cysteamine (NAC) thioester has been achieved, and its reaction with Pik TE demonstrated the ability of Pik TE to catalyze its macrolactonization to the natural product 10-deoxymethynolide. A steady-state kinetic analysis of the hexaketide chain intermediate with Pik TE was done. A preliminary substrate specificity study with unnatural hexaketide analogues was accomplished, demonstrating the importance of total synthesis in obtaining access to advanced polyketide intermediates. The results show the sensitivity of Pik TE to minor substrate modifications, and illustrate the potential use of thioesterases as versatile macrolactonization catalysts. 相似文献
22.
Courtney?L.?Sherman Jennifer?S.?BrodbeltEmail author Alan?P.?Marchand Bhaskar?Poola 《Journal of the American Society for Mass Spectrometry》2005,16(7):1162-1171
The self-assembly of ligand-metal-ligand sandwich complexes involving a novel quinoxaline-containing crown ether, 1, was studied by electrospray ionization mass spectrometry (ESI-MS). Donor-acceptor π-stacking interactions between the electron-poor
quinoxaline group of 1 and electron-rich benzene groups from benzo- or dibenzo-18-crown-6 were found to significantly enhance the formation of mixed-ligand
sandwich complexes with a free energy gain of up to 17 kJ/mol relative to sandwich formation involving macrocycles without
such aromatic functionalities. The relative intensities of the sandwich complexes were greatest with the alkali metals Na+, K+, and Rb+ as well as with the ammonium ion in equimolar concentrations with the macrocycles. The preferential formation of the mixed-ligand
sandwich complexes demonstrated that donor-acceptor π-stacking interactions contribute to the assembly of molecular structures
and can be monitored by ESI-MS. 相似文献
23.
Felim A Toussaint A Phillips CR Leca D Vagstad A Fensterbank L Lacôte E Malacria M 《Organic letters》2006,8(2):337-339
[reaction: see text] One-pot hypervalent iodine-mediated oxidations of arylsulfinamides to arylsulfonimidates is reported. Contrary to the case of alkylsulfinamides, use of iodosobenzene was not satisfactory. The reaction worked best with diacetoxyiodosobenzene (DIB) and a mild base (MgO). The influence of substituents on the iodine(III) reagent arene has been examined. 相似文献
24.
Leitch AA McKenzie CE Oakley RT Reed RW Richardson JF Sawyer LD 《Chemical communications (Cambridge, England)》2006,(10):1088-1090
The N-ethyl pyrazine-bridged bis-1,2,3-dithiazolyl radical (R(1) = Et) associates at room temperature as a C-C bonded sigma-dimer which, on heating, converts to a laterally S-S sigma-bonded structure. 相似文献
25.
Courtney C. Roberts Nicole M. Camasso Eric G. Bowes Melanie S. Sanford 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(27):9202-9206
Described is a systematic comparison of factors impacting the relative rates and selectivities of C(sp3)?C and C(sp3)?O bond‐forming reactions at high‐valent Ni as a function of oxidation state. Two Ni complexes are compared: a cationic octahedral NiIV complex ligated by tris(pyrazolyl)borate and a cationic octahedral NiIII complex ligated by tris(pyrazolyl)methane. Key features of reactivity/selectivity are revealed: 1) C(sp3)?C(sp2) bond‐forming reductive elimination occurs from both centers, but the NiIII complex reacts up to 300‐fold faster than the NiIV, depending on the reaction conditions. The relative reactivity is proposed to derive from ligand dissociation kinetics, which vary as a function of oxidation state and the presence/absence of visible light. 2) Upon the addition of acetate (AcO?), the NiIV complex exclusively undergoes C(sp3)?OAc bond formation, while the NiIII analogue forms the C(sp3)?C(sp2) coupled product selectively. This difference is rationalized based on the electrophilicity of the respective M?C(sp3) bonds, and thus their relative reactivity towards outer‐sphere SN2‐type bond‐forming reactions. 相似文献
26.
Brewer CA Brizuela F Wachulak P Martz DH Chao W Anderson EH Attwood DT Vinogradov AV Artyukov IA Ponomareko AG Kondratenko VV Marconi MC Rocca JJ Menoni CS 《Optics letters》2008,33(5):518-520
We have demonstrated near-wavelength resolution microscopy in the extreme ultraviolet. Images of 50 nm diameter nanotubes were obtained with a single ~1 ns duration pulse from a desktop-size 46.9 nm laser. We measured the modulation transfer function of the microscope for three different numerical aperture zone plate objectives, demonstrating that 54 nm half-period structures can be resolved. The combination of near-wavelength spatial resolution and high temporal resolution opens myriad opportunities in imaging, such as the ability to directly investigate dynamics of nanoscale structures. 相似文献
27.
Michael Courtney 《Applied Acoustics》2008,69(10):925-928
This article describes two acoustic methods to measure bullet velocity with an accuracy of 1% or better. In one method, a microphone is placed within 0.1 m of the gun muzzle and a bullet is fired at a steel target 45 m away. The bullet’s flight time is the recorded time between the muzzle blast and sound of hitting the target minus the time for the sound to return from the target to the microphone. In the other method, the microphone is placed equidistant from both the gun muzzle and the steel target 91 m away. The time of flight is the recorded time between the muzzle blast and the sound of the bullet hitting the target. In both cases, the average bullet velocity is simply the flight distance divided by the flight time. 相似文献
28.
Courtney Ngai Colomba M. Sanchez-Marsetti Prof. Dr. W. Hill Harman Prof. Richard J. Hooley 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(52):23711-23715
An endohedrally functionalized self-assembled Fe4L6 cage complex can catalyze oxa-Pictet—Spengler cyclizations of tryptophols and various aldehyde derivatives, showing strong rate accelerations and size-selectivity. Selective molecular recognition of substrates controls the reactivity, and the cage is capable of binding and activating multiple different species along the multistep reaction pathway. The combination of a functionalized active site, size-selective reactivity, and multistep activation, all from a single host molecule, illustrates the biomimetic nature of the catalysis. 相似文献
29.
Dr. Michela Parafioriti Dr. Minghong Ni Maurice Petitou Dr. Courtney J. Mycroft-West Dr. Timothy R. Rudd Dr. Neha S. Gandhi Prof. Vito Ferro Prof. Jeremy E. Turnbull Dr. Marcelo A. Lima Dr. Mark A. Skidmore Prof. David G. Fernig Dr. Edwin A. Yates Dr. Antonella Bisio Dr. Marco Guerrini Dr. Stefano Elli 《Chemistry (Weinheim an der Bergstrasse, Germany)》2023,29(1):e202202599
Infection of host cells by SARS-CoV-2 begins with recognition by the virus S (spike) protein of cell surface heparan sulfate (HS), tethering the virus to the extracellular matrix environment, and causing the subunit S1-RBD to undergo a conformational change into the ‘open’ conformation. These two events promote the binding of S1-RBD to the angiotensin converting enzyme 2 (ACE2) receptor, a preliminary step toward viral-cell membrane fusion. Combining ligand-based NMR spectroscopy with molecular dynamics, oligosaccharide analogues were used to explore the interactions between S1-RBD of SARS CoV-2 and HS, revealing several low-specificity binding modes and previously unidentified potential sites for the binding of extended HS polysaccharide chains. The evidence for multiple binding modes also suggest that highly specific inhibitors will not be optimal against protein S but, rather, diverse HS-based structures, characterized by high affinity and including multi-valent compounds, may be required. 相似文献
30.
Dr. Lauren K. Macreadie Karam B. Idrees Courtney S. Smoljan Prof. Omar K. Farha 《Angewandte Chemie (International ed. in English)》2023,62(28):e202304094
Metal-organic frameworks (MOFs) are a class of porous materials with high surface areas, which are acquiring rapid attention on an exponential basis. A significant characteristic of MOFs is their ability to act as adsorbents to selectively separate component mixtures of similar size, thereby addressing the technological need for an alternative approach to conventional distillation methods. Recently, MOFs comprising a 3-Dimensional (3D) linker have shown outstanding capabilities for difficult separations compared to the parent 2-Dimensional (2D) analogue. 3D-linkers with a polycyclic core are underrepresented in the MOF database due to the widespread preferred use of 2D-linkers and the misconceived high-cost of 3D linkers. We summarize the recent research of 3D-linker MOFs and highlight their beneficial employment for selective gas and hydrocarbon adsorption and separation. Furthermore, we outline forecasts in this area to create a platform for widespread adoption of 3D-linkers in MOF synthesis. 相似文献