全文获取类型
收费全文 | 747篇 |
免费 | 17篇 |
国内免费 | 26篇 |
专业分类
化学 | 442篇 |
晶体学 | 20篇 |
力学 | 22篇 |
综合类 | 1篇 |
数学 | 60篇 |
物理学 | 245篇 |
出版年
2023年 | 5篇 |
2022年 | 23篇 |
2021年 | 11篇 |
2020年 | 12篇 |
2019年 | 7篇 |
2018年 | 4篇 |
2017年 | 7篇 |
2016年 | 14篇 |
2015年 | 9篇 |
2014年 | 33篇 |
2013年 | 28篇 |
2012年 | 44篇 |
2011年 | 62篇 |
2010年 | 38篇 |
2009年 | 28篇 |
2008年 | 37篇 |
2007年 | 31篇 |
2006年 | 29篇 |
2005年 | 30篇 |
2004年 | 24篇 |
2003年 | 15篇 |
2002年 | 16篇 |
2001年 | 12篇 |
2000年 | 12篇 |
1999年 | 7篇 |
1998年 | 7篇 |
1997年 | 6篇 |
1996年 | 12篇 |
1995年 | 11篇 |
1994年 | 15篇 |
1993年 | 19篇 |
1992年 | 24篇 |
1991年 | 14篇 |
1990年 | 13篇 |
1989年 | 15篇 |
1988年 | 8篇 |
1987年 | 10篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 3篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1976年 | 9篇 |
1975年 | 7篇 |
1974年 | 4篇 |
1937年 | 4篇 |
排序方式: 共有790条查询结果,搜索用时 69 毫秒
61.
Ji‐Zheng Sun Kao‐Shan Chen Hai‐Li Liu Rob vanSoest Yue‐Wei Guo 《Helvetica chimica acta》2010,93(3):517-521
Two new uncommon epoxy‐substituted nitrogenous bisabolene‐type sesquiterpenes, 3‐formamido‐7,8‐epoxy‐α‐bisabolane ( 4 ), 3‐isocyano‐7,8‐epoxy‐α‐bisabolane ( 5 ), together with three known related sesquiterpenes, 1 – 3 , were isolated from the Hainan sponge Axinyssa sp. Their structures were determined on the basis of extensive spectroscopic analyses and by comparison of their NMR data with those of structurally related compounds. 相似文献
62.
We have investigated rarely observed 77Se J-couplings (spin-spin couplings) in the mixed-metal face-capped octahedral clusters [Re5OsSe8(CN)6]3- and [Re4Os2Se8(CN)6]2- at natural abundance. To the best of our knowledge, these are the first observations of Se-Se spin-spin interactions between mu3-Se sites, important for stereochemical assignments in hexarhenium analogues, Chevrel phase materials, and similar cluster materials. NMR techniques such as COSY, INADEQUATE, and 2D J-resolved spectroscopy have been used in conjunction to study these interactions. The two isomers (cis and trans) of [Re4Os2Se8(CN)6]2- were distinguishable, and selective isotopic labeling of [Re5OsSe8(CN)6]3- with 13CN ligands enabled resonances to be assigned by observing the 2J (Se-M-C) couplings. For [Re5OsSe8(CN)6]3-, two different 2J (Se-M-Se) couplings were measurable on a single cluster, and these are related to one another through spin-spin interactions across a face diagonal or along an edge of the cube of inner selenium ligands. A rigorous analysis based on combinatorial math has been invoked to assign the couplings on the basis of the probability of multiple-spin interactions. The face diagonal association is found to result in a J-coupling interaction larger in magnitude than that from coupling along an edge of the cube-information critical for making stereochemical assignments of selenium sites. 相似文献
63.
Li T Hassanali AA Kao YT Zhong D Singer SJ 《Journal of the American Chemical Society》2007,129(11):3376-3382
We report experimental and theoretical studies on water and protein dynamics following photoexcitation of apomyoglobin. Using site-directed mutation and with femtosecond resolution, we experimentally observed relaxation dynamics with a biphasic distribution of time scales, 5 and 87 ps, around the site Trp7. Theoretical studies using both linear response and direct nonequilibrium molecular dynamics (MD) calculations reproduced the biphasic behavior. Further constrained MD simulations with either frozen protein or frozen water revealed the molecular mechanism of slow hydration processes and elucidated the role of protein fluctuations. Observation of slow water dynamics in MD simulations requires protein flexibility, regardless of whether the slow Stokes shift component results from the water or protein contribution. The initial dynamics in a few picoseconds represents fast local motions such as reorientations and translations of hydrating water molecules, followed by slow relaxation involving strongly coupled water-protein motions. We observed a transition from one isomeric protein configuration to another after 10 ns during our 30 ns ground-state simulation. For one isomer, the surface hydration energy dominates the slow component of the total relaxation energy. For the other isomer, the slow component is dominated by protein interactions with the chromophore. In both cases, coupled water-protein motion is shown to be necessary for observation of the slow dynamics. Such biologically important water-protein motions occur on tens of picoseconds. One significant discrepancy exists between theory and experiment, the large inertial relaxation predicted by simulations but clearly absent in experiment. Further improvements required in the theoretical model are discussed. 相似文献
64.
Yung-Sen Lin Ping-Ju Sung Tzung-Han Tsai Ming-Ho Hsieh Hsiang Chen Chia-Feng Lin Chyuan Hauer Kao 《Journal of Solid State Electrochemistry》2016,20(3):743-757
An investigation is conducted on enhancing lithium-ion intercalation and conduction performance of transparent organo tantalum oxide (TaO y C z ) films, by addition of lithium via a fast co-synthesis onto 40 Ω/□ flexible polyethylene terephthalate/indium tin oxide substrates at the short exposed durations of 33–34 s, using an atmospheric pressure plasma jet (APPJ) at various mixed concentrations of tantalum ethoxide [Ta(OC2H5)5] and lithium tert-butoxide [(CH3)3COLi] precursors. Transparent organo-lithiated tantalum oxide (Li x TaO y C z ) films expose noteworthy Li+ ion intercalation and conduction performance for 200 cycles of reversible Li+ ion intercalation and deintercalation in a 1 M LiClO4-propylene carbonate electrolyte, by switching measurements with a potential sweep from ?1.25 to 1.25 V at a scan rate of 50 mV/s and a potential step at ?1.25 and 1.25 V, even after being bent 360° around a 2.5-cm diameter rod for 1000 cycles. The Li+ ionic diffusion coefficient and conductivity of 6.2?×?10?10 cm2/s and 6.0?×?10?11 S/cm for TaO y C z films are greatly progressed of up to 9.6?×?10?10 cm2/s and 7.8?×?10?9 S/cm for Li x TaO y C z films by co-synthesis with an APPJ. 相似文献
65.
A salt-inclusion stannosilicate, [Na3F][SnSi3O9], has been synthesized using a flux-growth method and characterized by single-crystal X-ray diffraction. The structure consists of six-membered silicate rings linked via corner sharing by SnIVO6 octahedra to form a 3-D framework that delimits two types of channels. The F atoms and Na atoms are located in the structural channels and form a dimer with the anti-Al2Cl6(g) structure. This stannosilicate adopts a new structure and is the first metal silicate that contains both Na+ and F- ions in the channels. The 19F and 29Si MAS NMR and 23Na MQMAS NMR spectra are consistent with the crystallographic results. 相似文献
66.
Yang T. L. Kao C. L. Kuo C. E. Yeh H. C. Li W. J. Li H. T. Chen C. Y. 《Chemistry of Natural Compounds》2022,58(5):825-827
Chemistry of Natural Compounds - A novel bibenzyl derivative, hydrangchinenin (1), was isolated from the stems of Hydrangea chinensis Maxim. (Hydrangeaceae). Its structure was determined on the... 相似文献
67.
68.
Chen C. Y. Kao C. L. Yeh H. C. Li H. T. Wu M. D. Cheng M. J. Li W. J. 《Chemistry of Natural Compounds》2022,58(3):385-386
Chemistry of Natural Compounds - A new ketone, vicamazone (4-(2-butoxyethoxy)-4-methylpentan-2-one) (1), was isolated from the leaves of Victoria amazonica (Nymphaeaceae). The structure of the new... 相似文献
69.
70.
Shyh-Dar Lee Ging-Ho Hsiue Chen-Yu Kao 《Journal of polymer science. Part A, Polymer chemistry》1996,34(1):141-148
Polyacrylic acid (PAA) was grafted onto the surface of silicone rubber membrane (SR) by plasma-induced graft copolymerization (PIP). Ar-plasma was used to activate the surface of SR. Also, a determination was made of the influences of plasma treatment power, pressure, time, grafted copolymerization reaction time, and monomer concentration on polymerization yield. The surface properties of SR were measured by ATR-FTIR, ESCA, and SIMS. In those analyses, the elemental composition and different carbon bindings on the surface of SR were examined by ESCA with the amount of O1s/C1s being approximately 0.7 at 60 s by Ar-plasma treatment (60 W, 200 mtorr). The peroxide group introduced on SR was measured via 1,1-diphenyl-2-picryhydrazyl (DPPH). The optimum amount of peroxide groups was 6.85 × 10−8 mol/cm2 at 60 s of Ar-plasma treatment. The peroxide group (33D peak) was introduced onto the surface of SR by negative spectra of SIMS analysis after SR treatment by Ar-plasma. An increase was obtained in grafted polymerization yield with a region of 5 to 50% (v/v) of acrylic acid aqueous solution. Both sites of polyacrylic acid were detected after staining by toluidine blue O. That is, a homobifunctional membrane was developed via this surface modification method. © 1996 John Wiley & Sons, Inc. 相似文献