全文获取类型
收费全文 | 2329篇 |
免费 | 33篇 |
国内免费 | 13篇 |
专业分类
化学 | 1410篇 |
晶体学 | 28篇 |
力学 | 83篇 |
数学 | 419篇 |
物理学 | 435篇 |
出版年
2020年 | 18篇 |
2019年 | 17篇 |
2018年 | 18篇 |
2017年 | 21篇 |
2016年 | 32篇 |
2015年 | 28篇 |
2014年 | 24篇 |
2013年 | 110篇 |
2012年 | 85篇 |
2011年 | 93篇 |
2010年 | 56篇 |
2009年 | 64篇 |
2008年 | 100篇 |
2007年 | 109篇 |
2006年 | 100篇 |
2005年 | 103篇 |
2004年 | 108篇 |
2003年 | 78篇 |
2002年 | 74篇 |
2001年 | 48篇 |
2000年 | 45篇 |
1999年 | 55篇 |
1998年 | 28篇 |
1997年 | 32篇 |
1996年 | 32篇 |
1995年 | 23篇 |
1994年 | 25篇 |
1993年 | 22篇 |
1992年 | 32篇 |
1991年 | 20篇 |
1990年 | 25篇 |
1989年 | 36篇 |
1988年 | 14篇 |
1987年 | 24篇 |
1986年 | 29篇 |
1985年 | 44篇 |
1984年 | 50篇 |
1983年 | 36篇 |
1982年 | 38篇 |
1981年 | 58篇 |
1980年 | 37篇 |
1979年 | 43篇 |
1978年 | 38篇 |
1977年 | 44篇 |
1976年 | 25篇 |
1975年 | 33篇 |
1974年 | 35篇 |
1973年 | 37篇 |
1972年 | 26篇 |
1970年 | 18篇 |
排序方式: 共有2375条查询结果,搜索用时 15 毫秒
141.
Howard Haubenstock Wei-Hong Yu George Odian 《Macromolecular rapid communications》1995,16(11):845-849
The anionic bulk polymerization of optically active (2R, 3S)-3,4-epoxy-1,2-O-isopropylidenebutane-1,2-diol ( 1 ) and its (2 S, 3 S) diastereomer 2 was studied. Molecular weights and optical activity measurements as well as carbon and proton NMR spectra are reported. The polymers show solvent dependent inversion of the sign of optical rotation. The NMR spectra are consistent with isotactic polymer chains. 相似文献
142.
143.
Waller MP Howard ST Platts JA Piltz RO Willock DJ Hibbs DE 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(29):7603-7614
The charge distribution of taurine (2-aminoethane-sulfonic acid) is revisited by using an orbital-based method that describes the density in a fixed molecular orbital basis with variable orbital occupation numbers. A new neutron data set is also employed to explore whether this improves the deconvolution of thermal motion and charge density. A range of molecular properties that are novel for experimentally determined charge densities are computed, including Weinhold population analysis, Mayer bond orders, and local kinetic energy densities, in addition to charge topological analysis and quantum theory of atoms-in-molecules (QTAIM) integrated properties. The ease with which a distributed multipole analysis can be performed on the fitted density matrix makes it straightforward to compute molecular moments, the lattice energy, and the electrostatic interaction energies of molecules removed from the crystal. Results are compared with high-level (QCISD) gas-phase calculations and band structure calculations employing density functional theory. Finally, the avenues available for extending the range of molecular properties that can be calculated from experimental charge densities still further using this approach are discussed. 相似文献
144.
Piyasena ME Real LJ Diamond RA Xu HH Gomez FA 《Analytical and bioanalytical chemistry》2008,392(5):877-886
Teicoplanin (teic) from Actinoplanes teichomyceticus is a glycopeptide antibiotic used to treat many Gram-positive bacterial infections. Glycopeptide antibiotics inhibit bacterial
growth by binding to carboxy-terminal d-Ala-d-Ala intermediates in the peptidoglycan of the cell wall of Gram-positive bacteria. In this paper we report the derivatization
of magnetic microspheres with teic (teic-microspheres). Fluorescence-based techniques have been developed to analyze the binding
properties of the microspheres to two d-Ala-d-Ala terminus peptides. The dissociation constant for the binding of carboxyfluorescein-labeled d-Ala-d-Ala-d-Ala to teic on microspheres was established via fluorimetry and flow cytometry and was determined to be 0.5 × 10−6 and 3.0 × 10−6 mol L−1, respectively. The feasibility of utilizing microparticles with fluorescence methods to detect low levels (the limit of bacterial
detection was determined to be 30 colon-forming units; cfu) of Gram-positive bacteria has been demonstrated. A simple microfluidic
experiment is reported to demonstrate the possibility of developing microsphere-based affinity assays to study peptide–antibiotic
interaction. 相似文献
145.
Evgen V. Govor Andrey B. Lysenko Alexander N. Chernega Judith A.K. Howard Andriy A. Mokhir Joachim Sieler Konstantin V. Domasevitch 《Polyhedron》2008
Reaction of copper(II) acetate, lanthanium(III) or gadolinium(III) nitrate (1/5 equiv.) with pyrazinohydroxamic acid (H2Pyzha) in DMF led to a series of new heterobimetallic 15-metallacrown-5 complexes. In a MeOH/H2O solution the complexes exist as molecular unassociated metallacrowns. In solid state their structures are more complicated as it has been confirmed by X-ray analysis: discrete molecular metallacrowns [Gd(NO3)2{Cu(pyzha)}5(DMF)4(NO3)] · 0.5C6H6 · H2O (1), [Gd(NO3)2{Cu(pyzha)}5(DMF)5](NO3) · 1.5DMF · 0.5H2O (2), [La(NO3)2{Cu(pyzha)}5(DMF)5]NO3 · 1.5DMF · 2C6H6 (3) are solvates, whereas compound [{La(NO3)2{Cu(pyzha)}5(DMF)5}2(μ2-NO3)](NO3) · 3DMF (4) is a dimer, where μ-bridged nitrate links two copper centres of the adjacent metallamacrocycles. Complex [Gd(NO3)2{Cu(pyzha)}5(DMF)2(H2O)(NO3)] · CH2Cl2 · DMF (5) self-associates into a polymer chain by means of one pyrazine moiety and the copper ring atom. Reaction of the molecular metallacrowns with excess of inorganic salts CdBr2 or Cu(OAc)2 proceeds as anion methathesis process affording heteroanionic metallacrowns: molecular [Gd(NO3)2{Cu(pyzha)}5(DMF)5] [Gd(NO3)2{Cu(pyzha)}5(DMF)4(H2O)][CdBr4] · 1.5DMF (6), and 3D hydrogen bonded polymer [La(μ2-OAc)(H2O)3{Cu(pyzha)}5 (H2O)4(NO3)](NO3) · 4H2O (7). 相似文献
146.
Elisabet Öberg Andreas Orthaber Marie-Pierre Santoni Fredrick Howard Sascha Ott 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-3):152-158
Abstract Attempts to utilize C-ethylenic phosphaalkenes in metathesis reactions are discussed. Unprecedented reactivity is observed where the vinylphosphaalkene undergoes the first step of the catalytic cycle and cross-metathesis with the phenylmethylene moiety of Grubbs 2nd generation catalyst. However, homo-metathesis reaction to form 1,6-diphosphahexa-1,3,5-triene is not observed, presumably due to steric constraints. 相似文献
147.
Stephen L. Howard Joyce E. Newberry Rosario C. Sausa Andrzej W. Miziolek 《Journal of the American Society for Mass Spectrometry》1993,4(2):152-158
A recently developed research apparatus for characterization of low-pressure premixed flames has been developed and was used to characterize the C2H4/N2O/Ar flame at 20 torr. This instrument incorporates several diagnostic techniques in one apparatus so that individual techniques can be quantitatively compared and the usable detection range (both in terms of resolution and species detection) expanded. Results discussed in this report include mass analysis by triple quadrupole mass spectrometer and temperature measurement by thermocouple. Concentration profiles in the one-dimensional flame include CO, N2, and C2H4, at nominal m/z 28 as well as CO2 and N2O at m/z 44. 相似文献
148.
Joan F. Boyar Howard J. Karloff 《Journal of Algorithms in Cognition, Informatics and Logic》1987,8(4)
We present NC algorithms for vertex and edge coloring planar graphs. The vertex coloring algorithm 5 colors any planar graph, and the edge coloring algorithm Δ edge colors planar graphs with Δ ≥ 23 (and Δ + 1 edge colors planar graphs with Δ < 23), where Δ is the maximum degree in the graph. 相似文献
149.
Richard Ian Cooper David John Watkin Howard D. Flack 《Acta Crystallographica. Section C, Structural Chemistry》2016,72(4):261-267
A study of post‐refinement absolute structure determination using previously published data was carried out using the CRYSTALS software package. We show that absolute structure determination may be carried out optimally using the analyses available in CRYSTALS, and that it is not necessary to have the separate procedures absolute structure determination and no interest in absolute structure as proposed by Flack [Chimia (2014), 68 , 26–30]. 相似文献
150.