全文获取类型
收费全文 | 231篇 |
免费 | 2篇 |
国内免费 | 3篇 |
专业分类
化学 | 125篇 |
力学 | 10篇 |
数学 | 59篇 |
物理学 | 42篇 |
出版年
2014年 | 2篇 |
2013年 | 11篇 |
2012年 | 10篇 |
2011年 | 4篇 |
2010年 | 4篇 |
2009年 | 2篇 |
2008年 | 7篇 |
2007年 | 12篇 |
2006年 | 14篇 |
2005年 | 13篇 |
2004年 | 13篇 |
2003年 | 8篇 |
2002年 | 6篇 |
2001年 | 13篇 |
2000年 | 5篇 |
1999年 | 1篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1975年 | 4篇 |
1974年 | 8篇 |
1973年 | 6篇 |
1972年 | 2篇 |
1971年 | 6篇 |
1970年 | 3篇 |
1969年 | 2篇 |
1967年 | 1篇 |
1964年 | 2篇 |
1963年 | 1篇 |
1955年 | 1篇 |
1929年 | 2篇 |
1903年 | 1篇 |
排序方式: 共有236条查询结果,搜索用时 15 毫秒
101.
[reaction: see text] The first asymmetric aminohalogenation of functionalized alkenes has been established. The ionic liquid [bmim][BF4] was found to be the only effective media for success as normal organic solvents failed to give any product for this reaction. The reaction is also very convenient to perform by simply mixing the three reactants, cinnamates, N,N-dichloro-p-toluenesulfonamide, and catalyst, together with 4 A molecular sieves at room temperature in [bmim][BF4] in any convenient vial of appropriate size without special protection from inert gases. Good chemical yields (60-72%) and diastereoselectivities (up to 75% de) have been obtained with a good scope of substrates. The resulting individual diastereomers have been cleanly separated via column chromatography. The absolute stereochemistry of the reaction was unambiguously determined by X-ray structural analysis. 相似文献
102.
Debbie Cannon John N. Low Susan A. McWilliam Janet M. S. Skakle James L. Wardell Christopher Glidewell 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(5):600-603
Molecules of the title compound, C7H6N2O5S, are linked into sheets containing R22(10) and R66(42) rings by C—H?O hydrogen bonds [C?O 3.405 (3) and 3.511 (2) Å; C—H?O 159 and 169°], in which both acceptors are in the same nitro group. Comparisons are made with the hydrogen bonding in other nitrobenzenesulfenate esters. 相似文献
103.
Yanfei Yang Xiaodan Cao David W. Purkiss John F. Cannon Richard A. Bartsch 《Tetrahedron》2012,68(10):2233-2244
Di-ionizable calix[4]arene-1,3-crown-4 compounds locked in 1,3-alternate, cone, and partial-cone conformations are synthesized for evaluation in metal ion separations. The ionizable functions include carboxylic acid and N-(X)sulfonyl carboxamide groups in which the acidity is tuned by variation of the electron-withdrawing ability of X. Similar synthetic routes were employed for preparation of the cone and 1,3-alternate ligand series. A different preparative route utilizing protection and deprotection was required to obtain the partial-cone analogues. Ligand conformations were confirmed by their proton and/or carbon NMR spectra. X-ray diffraction verified an unusual 1,2-alternate conformation in the solid-state for one synthetic intermediate. Effects of ligand conformation and ionizable group variations on competitive solvent extractions of alkali and alkaline earth metal cations from aqueous solutions into chloroform were assessed. Single species solvent extractions of Hg2+ and Pb2+ were also performed. 相似文献
104.
Treatment of acylated adenosine N-oxides with carboxylic anhydrides and thiophenol resulted in pyrimidine ring opening followed by exocyclic ring closure. Ammonolysis gave 5-amino-4-(5-substituted-1,2,4-oxadiazol-3-yl)-1-(beta-d-ribofuranosyl)imidazole derivatives, whereas iodine in methanol selectively unmasked the 5-amino group. Related flexible nucleoside analogues can be prepared from adenine-type precursors. 相似文献
105.
L. Bianco R.D. Page I.G. Darby D.T. Joss J. Simpson J.S. Al-Khalili A.J. Cannon B. Cederwall S. Eeckhaudt S. Ertürk B. Gall M.B. Gómez Hornillos T. Grahn P.T. Greenlees B. Hadinia K. Heyde U. Jakobsson P.M. Jones R. Julin S. Juutinen S. Ketelhut M. Labiche M. Leino A.-P. Leppänen M. Nyman D. O'Donnell E.S. Paul M. Petri P. Peura A. Puurunen P. Rahkila P. Ruotsalainen M. Sandzelius P.J. Sapple J. Sarén C. Scholey N.A. Smirnova A.N. Steer P.D. Stevenson E.B. Suckling J. Thomson J. Uusitalo M. Venhart 《Physics letters. [Part B]》2010
106.
John N. Low Paloma Arranz Justo Cobo M. Angeles Fontecha M. Luz Godino Rafael Lpez Debbie Cannon Antonio Quesada Christopher Glidewell 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(6):680-682
In the title compound, [Ca(C9H11N6O5)2(H2O)3], the Ca atom lies on a twofold rotation axis in C2/c and the three water molecules are all disordered, each over two sites having equal occupancy. The anion acts as a bridging ligand between pairs of Ca sites on the same twofold axis, thus forming a one‐dimensional coordination polymer, with the chains lying along the twofold axes. These chains are linked by multiple O—H?O and N—H?O hydrogen bonds into a single three‐dimensional framework. 相似文献
107.
108.
M.D. Wojcik M.C. Phillips B.D. Cannon M.S. Taubman 《Applied physics. B, Lasers and optics》2006,85(2-3):307-313
We demonstrate the performance of a novel infrared photoacoustic laser absorbance sensor for gas-phase species using an amplitude-modulated quantum cascade (QC) laser and a quartz tuning fork microphone. The photoacoustic signal was generated by focusing 5.3 mW of a Fabry–Pérot QC laser operating at 8.41 μm between the tines of a quartz tuning fork which served as a transducer for the transient acoustic pressure wave. The sensitivity of this sensor was calibrated using the infrared absorber Freon 134a by performing a simultaneous absorption measurement using a 31-cm absorption cell. The power and bandwidth normalized noise equivalent absorption sensitivity (NEAS) of this sensor was determined to be D=2.0×10-8 W cm-1/Hz1/2. A corresponding theoretical analysis of the instrument sensitivity is presented and is capable of quantitatively reproducing the experimental NEAS, indicating that the fundamental sensitivity of this technique is limited by the noise floor of the tuning fork itself. PACS 43.60.Vx; 43.58.Wc; 43.58.Hp; 84.40.Xb 相似文献
109.
Rednikov AY; Zhao Hong; Sadhal SS; Trinh EH 《The Quarterly Journal of Mechanics and Applied Mathematics》2006,59(3):377-397
The steady (acoustic) streaming associated with a sphericaldrop displaced from the velocity antinode of a standing waveis studied. The ratio of the particle size to the acoustic wavelengthis treated as small but non-zero, and the solution is developedin the form of a two-term expansion in terms of the correspondingsmallness parameter. The drop viscosity is assumed to be muchhigher than that of the surrounding fluid, which is the casefor a drop in a gas medium. There are essentially three distinctregions where the steady streaming flow is analysed: insidethe drop (internal circulation), in the Stokes shear-wave layerat the surface on the gas side, and the gas outside the Stokeslayer (the outer streaming region). Solutions for the internalcirculation and the outer streaming are obtained in the limitof small Reynolds number. Despite the gas-to-liquid viscosity ratio being small, the outerstreaming may be dramatically affected by the fact that thesphere is liquid as opposed to solid. The parameter that measuresthe effect of liquidity is essentially the viscosity ratio dividedby the relative (to the particle size) thickness of the Stokeslayer. The case of a solid sphere is recovered by letting thisparameter go to zero. 相似文献
110.
Mechanically Modulating the Photophysical Properties of Fluorescent Protein Biocomposites for Ratio‐ and Intensiometric Sensors
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Johnathan N. Brantley Constance B. Bailey Joe R. Cannon Katie A. Clark Prof. David A. Vanden Bout Prof. Jennifer S. Brodbelt Prof. Adrian T. Keatinge‐Clay Prof. Christopher W. Bielawski 《Angewandte Chemie (International ed. in English)》2014,53(20):5088-5092
Mechanically sensitive biocomposites comprised of fluorescent proteins report stress through distinct pathways. Whereas a composite containing an enhanced yellow fluorescent protein (eYFP) exhibited hypsochromic shifts in its fluorescence emission maxima following compression, a composite containing a modified green fluorescent protein (GFPuv) exhibited fluorescence quenching under the action of mechanical force. These ratio‐ and intensiometric sensors demonstrate that insights garnered from disparate fields (that is, polymer mechanochemistry and biophysics) can be harnessed to guide the rational design of new classes of biomechanophore‐containing materials. 相似文献