全文获取类型
收费全文 | 279篇 |
免费 | 1篇 |
专业分类
化学 | 146篇 |
晶体学 | 2篇 |
力学 | 11篇 |
数学 | 38篇 |
物理学 | 83篇 |
出版年
2021年 | 2篇 |
2014年 | 4篇 |
2013年 | 7篇 |
2011年 | 12篇 |
2010年 | 5篇 |
2009年 | 9篇 |
2008年 | 11篇 |
2007年 | 5篇 |
2006年 | 7篇 |
2005年 | 8篇 |
2004年 | 9篇 |
2003年 | 11篇 |
2002年 | 6篇 |
2001年 | 7篇 |
2000年 | 15篇 |
1999年 | 7篇 |
1998年 | 5篇 |
1997年 | 2篇 |
1996年 | 9篇 |
1995年 | 15篇 |
1994年 | 3篇 |
1993年 | 11篇 |
1992年 | 5篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 2篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 6篇 |
1970年 | 4篇 |
1969年 | 2篇 |
1966年 | 2篇 |
1965年 | 1篇 |
1964年 | 1篇 |
1962年 | 1篇 |
1961年 | 1篇 |
1935年 | 2篇 |
1931年 | 1篇 |
排序方式: 共有280条查询结果,搜索用时 15 毫秒
71.
Reaction of 2,2′-bipyridine-6-carboxaldehyde with the appropriate aliphatic diamine in MeOH and subsequent reduction with NaBH4 gives the new, potentially hexadentate, ligands N,N′-bis(2,2′-bipyridin-6-ylmethyl)ethane-1,2-diamine (bmet), N,N′-bis(2,2′-bipyridin-6-ylmethyl)propane-1,3-diamine (bmpp) and N,N′-bis(2,2′-bipyridin-6-ylmethyl)hexane-1,6-diamine (bmhx). The syntheses and characterisation of these ligands are reported; the ligands are isolated as the hydrochloride salts, with purification effected by either recrystallisation or cation exchange chromatography. [Co(bmet)](ClO4)3 · H2O is obtained on reaction of bmet · 4.25HCl · 2.5H2O with Na3[Co(O2CO)3] · 3H2O, and X-ray structural analysis shows this to have a pair of very short Co–N bonds. The synthesis and characterisation of the first coordination complex containing 6-(aminomethyl)-2,2′-bipyridine (amb) is also described. 相似文献
72.
The compounds (π-C6H6)Ru(R)Cl(PPh3) (RCH3, C6H5), (π-C6H6)RuCl(π-C3H5) and [(π-C6H6)Ru(π-C5H5)]Cl are described. The 31P NMR spectra of a series of tertiary phosphine complexes of the π-benzeneruthenium system are also reported. 相似文献
73.
The concept of ionic character in and bond systems is considered in the light of recent definitions of orbital electronegativity [6, 14].
We wish to acknowledge financial support from the National Research Council of Canada. One of us (N.C.B.) thanks the council for the award of a studentship. 相似文献
Zusammenfassung Das Konzept des ionischen Charakters in und Bindungen wird im Lichte neuerer Definitionen von Orbitalelektronegativitäten diskutiert.
Résumé Le caractère ionique des liaisons et est discuté en tenant compte des définitions récentes de l'électronégativité des orbitales.
We wish to acknowledge financial support from the National Research Council of Canada. One of us (N.C.B.) thanks the council for the award of a studentship. 相似文献
74.
Ryan D Madder Chu-Young Kim Pooja P Chandra Jeffrey B Doyon Teaster A Baird Carol A Fierke David W Christianson Judith G Voet Ahamindra Jain 《The Journal of organic chemistry》2002,67(2):582-584
QSAR has been used to elucidate the origin of the hydrophobicity and binding affinity of a small library of fluoroaromatic inhibitors of F131V carbonic anhydrase II. Our analysis predicted the presence of a twisted amide conformation for several bound inhibitors, which we confirmed crystallographically. We also determined that the hydrophobicity of the inhibitors as a whole results from the fragment hydrophobicities of their fluorobenzyl rings, corrected for field effects and the presence of an intramolecular F.H contact in solution. The loss of this interaction on binding to the enzyme makes the affinity sensitive to the same terms, but with the opposite dependence on the F.H contact. In the case of the four inhibitors bound as twisted amides, this F.H contact must be retained to some extent in the bound state in order for their affinities to be consistent with our QSAR analysis of the entire set of 17 molecules. 相似文献
75.
J. Lowe S.H. Chew J.M. Nelson C.E. Waltham G.J. Pyle G.T.A. Squier S. Baird C.J. Batty P. Sharman P. Bird A.S. Clough K.R. Parker 《Nuclear Physics B》1982,209(1):16-28
The reaction K?p → Λγ, produced by K? stopping in a liquid hydrogen target, has been studied using a NaI(Tl) gamma-ray spectrometer. The branching ratio is based on 1355 events assigned to this branch. This is in conflict with a previous experiment, but agrees with one of the two published calculations, when recent values for the coupling constants and scattering amplitudes are used. 相似文献
76.
The compound [HNMe2Ph][NpB(C6F5)3](Np =(CH3)3CCH2) reacts with dimethylzirconocenes to give active propylene polymerization catalysts which are significantly more active and give higher molecular weight polypropylene than do the catalysts obtained using B(C6F5)3; the [NpB(C6F5)3]- anion is for steric reasons more weakly coordinating than is [MeB(C6F5)3]-. 相似文献
77.
R. Kloch P. E. G. Baird M. G. Boshier M. J. Macpherson C. W. P. Palmer D. N. Stacey V. Stacey 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1987,6(4):315-317
We have measured isotope shifts in λ326.1 nm of CdI using a pressure-scanned interferometer. The results are, in GHz: 116–106, ?2.222 (30); 113–108, ?1.052(10); 111–110, ?0.049 (12); 111–106, ?1.048 (10). Results for stable isotopes in λ326.1 nm are needed in the interpretation of existing measurements on radioactive cadmium isotopes. The new data are more precise than early atomic beam measurements but are reasonably consistent with them. 相似文献
78.
Aaron P.R. Eberle Gregorio M. Vélez-García Donald G. Baird Peter Wapperom 《ournal of non Newtonian Fluid Mechanics》2010,165(3-4):110-119
The common approach for simulating the evolution of fiber orientation during flow in concentrated suspensions is to use an empirically modified form of Jeffery's equation referred to as the Folgar–Tucker (F-T) model. Direct measurements of fiber orientation were performed in the startup of shear flow for a 30 wt% short glass fiber-filled polybutylene terephthalate (PBT-30); a matrix that behaves similar to a Newtonian fluid. Comparison between predictions based on the F-T model and the experimental fiber orientation show that the model over predicts the rate of fiber reorientation. Rheological measurements of the stress growth functions show that the stress overshoot phenomenon approaches a steady state at a similar strain as the fiber microstructure, at roughly 50 units. However, fiber orientation measurements suggest that a steady state is not reached as the fiber orientation continues to slowly evolve, even up to 200 strain units. The addition of a “slip” parameter to the F-T model improved the model predictions of the fiber orientation and rheological stress growth functions. 相似文献
79.
Francoise Sauriol Dr. Elizabeth Wong Angela M. H. Leung Irja Elliott Donaghue Michael C. Baird Prof. Tebikie Wondimagegn Dr. Tom Ziegler Prof. 《Angewandte Chemie (International ed. in English)》2009,48(18):3342-3345
Caught in the act : An alkyl alkene ZrIV complex (see picture; Cp=C5H5) has been synthesized and characterized for the first time. The alkene bonding mode is highly asymmetric, and C2 is quite carbocationic. There is also evidence for rotation about the C1? C2 bond. This extremely unusual complex provides an exemplar of previously unknown intermediates in Ziegler–Natta and carbocationic polymerization reactions of alkenes.
80.
This paper chronicles the conceptual development, proof of principle experiments, and recent advances in the palladium-catalyzed cross-coupling reactions of the conjugate bases of organosilanols. The discovery that led to the design and refinement of this process represents a classical illustration of how mechanistic studies can provide a fertile ground for the invention of new reactions. On the basis of a working hypothesis (which ultimately proved to be incorrect) and the desire to effect silicon-based cross-coupling without the agency of fluoride activation, a mild and practical palladium-catalyzed cross-coupling of alkenyl-, aryl-, and heteroaryl silanolates has been developed. The mechanistic underpinnings, methodological extensions, and the successful applications of this technology to the synthesis of complex molecules are described. 相似文献