全文获取类型
收费全文 | 2336篇 |
免费 | 31篇 |
国内免费 | 14篇 |
专业分类
化学 | 1411篇 |
晶体学 | 28篇 |
力学 | 83篇 |
数学 | 419篇 |
物理学 | 440篇 |
出版年
2020年 | 18篇 |
2019年 | 17篇 |
2018年 | 19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 | 59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2381条查询结果,搜索用时 10 毫秒
91.
92.
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
93.
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
94.
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
95.
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
96.
We study the electrically driven spreading of dielectric liquid films in wedge-shaped gaps across which a potential difference is applied. Our experiments are in a little-studied regime where, throughout the dynamics, the electrical relaxation time is long compared to the time for charge to be convected by the fluid motion. We observe that at a critical normal electric field the hump-shaped leading edge undergoes an instability in the form of a single Taylor cone and periodic jetting ensues, after which traveling waves occur along the trailing thin film. We propose a convection-dominated mechanism for charge transport to describe the observed dynamics and rationalize the viscosity dependence of the self-excited dynamics. 相似文献
97.
98.
A. R. W. McKellar James B. Burkholder John J. Orlando Carleton J. Howard 《Journal of Molecular Spectroscopy》1988,130(2)
The ν3 fundamental band of the formyl radical, HCO, in the 5.3-μm region has been observed at high resolution (0.0025 cm−1, unapodized) using a Fourier transform spectrometer. The HCO radicals were formed by the reaction of F atoms with H2CO in a fast-flow multiple-traversal absorption cell. A total of 298 lines were measured with an accuracy of about 0.0004 cm−1 and assigned to transitions with values of the rotational quantum numbers N and Ka up to 20 and 5, respectively. These data greatly improve the knowledge of the HCO ν3 line positions and (v1v2v3) = (001) vibrational state molecular parameters as compared to earlier laser magnetic resonance studies of this band, especially for higher values of N. The ν1 fundamental band of HCO was also observed and an analysis of these data agrees well with the recent study of Dane et al. [J. Chem. Phys. 88, 2121–2128 (1988)]. 相似文献
99.
A 0–1probability space is a probability space (, 2,P), where the sample space -{0, 1}
n
for somen. A probability space isk-wise independent if, whenY
i
is defined to be theith coordinate or the randomn-vector, then any subset ofk of theY
i
's is (mutually) independent, and it is said to be a probability spacefor p
1,p
2, ...,p
n
ifP[Y
i
=1]=p
i
.We study constructions ofk-wise independent 0–1 probability spaces in which thep
i
's are arbitrary. It was known that for anyp
1,p
2, ...,p
n
, ak-wise independent probability space of size
always exists. We prove that for somep
1,p
2, ...,p
n
[0,1],m(n,k) is a lower bound on the size of anyk-wise independent 0–1 probability space. For each fixedk, we prove that everyk-wise independent 0–1 probability space when eachp
i
=k/n has size (n
k
). For a very large degree of independence —k=[n], for >1/2- and allp
i
=1/2, we prove a lower bound on the size of
. We also give explicit constructions ofk-wise independent 0–1 probability spaces.This author was supported in part by NSF grant CCR 9107349.This research was supported in part by the Israel Science Foundation administered by the lsrael Academy of Science and Humanities and by a grant of the Israeli Ministry of Science and Technology. 相似文献
100.