全文获取类型
收费全文 | 1051篇 |
免费 | 23篇 |
国内免费 | 9篇 |
专业分类
化学 | 667篇 |
晶体学 | 10篇 |
力学 | 17篇 |
数学 | 151篇 |
物理学 | 238篇 |
出版年
2020年 | 10篇 |
2019年 | 10篇 |
2018年 | 9篇 |
2017年 | 7篇 |
2016年 | 12篇 |
2015年 | 14篇 |
2014年 | 21篇 |
2013年 | 50篇 |
2012年 | 44篇 |
2011年 | 68篇 |
2010年 | 32篇 |
2009年 | 20篇 |
2008年 | 44篇 |
2007年 | 52篇 |
2006年 | 49篇 |
2005年 | 51篇 |
2004年 | 55篇 |
2003年 | 39篇 |
2002年 | 38篇 |
2001年 | 21篇 |
2000年 | 22篇 |
1999年 | 13篇 |
1998年 | 14篇 |
1997年 | 16篇 |
1996年 | 17篇 |
1994年 | 11篇 |
1993年 | 17篇 |
1992年 | 10篇 |
1991年 | 15篇 |
1990年 | 8篇 |
1989年 | 11篇 |
1988年 | 10篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 13篇 |
1984年 | 21篇 |
1983年 | 14篇 |
1982年 | 8篇 |
1981年 | 16篇 |
1980年 | 13篇 |
1979年 | 7篇 |
1978年 | 10篇 |
1977年 | 14篇 |
1976年 | 15篇 |
1975年 | 16篇 |
1974年 | 17篇 |
1973年 | 11篇 |
1972年 | 9篇 |
1971年 | 7篇 |
1970年 | 6篇 |
排序方式: 共有1083条查询结果,搜索用时 15 毫秒
1.
B. R. Harvey M. B. Lovett S. J. Boggis 《Journal of Radioanalytical and Nuclear Chemistry》1987,115(2):357-368
Selected experiences in the control of contamination and the threat it poses to the quality of analytical date are discussed in the context of the whole analytical process from collection of marine environmental samples, through handling and radiochemical separation, to the final interpretation of results. Examples include a demonstration of the contamination introduced during sediment core sectioning, contamination of sea water by a ship's pumping system, and the effect of filtration on the apparent partitioning of radionuclides between solid and liquid phases of sea water. 相似文献
2.
3.
4.
The purpose of the present study was to describe the effects ofacute laryngitis on some aerodynamic, acoustic, and perceptual measures. Eleven subjects with diagnosed acute laryngitis due to upper respiratory infection were recorded during a laryngitic episode and 1 week to 10 days after amelioration of the laryngitic condition. Fundamental frequency values, collapsed across the five vowels, were significantly reduced in the laryngitic compared with the normal speaking condition. The decrease in fundamental frequency associated with acute laryngitis suggests an increase in the mass of the vocal folds. In addition, aerodynamic values differed significantly for the laryngitic condition compared with the normal speaking condition, suggesting the presence of laryngeal hypofunction. Perceptual data indicated that speakers in the laryngitic condition were judged to have a hoarse voice when compared with the normal speaking condition. 相似文献
5.
Ben Craps Matthias R. Gaberdiel Jeffrey A. Harvey 《Communications in Mathematical Physics》2003,234(2):229-251
We study D-branes in the bosonic closed string theory whose automorphism group is the Bimonster group (the wreath product
of the Monster simple group with ℤ2). We give a complete classification of D-branes preserving the chiral subalgebra of Monster invariants and show that they
transform in a representation of the Bimonster. Our results apply more generally to self-dual conformal field theories which
admit the action of a compact Lie group on both the left- and right-moving sectors.
Received: 20 February 2002 / Accepted: 17 August 2002 Published online: 19 December 2002
Communicated by R.H. Dijkgraaf 相似文献
6.
Alex Harvey 《General Relativity and Gravitation》1990,22(12):1433-1445
The Kasner metric is one of the more widely studied metrics. Its usefulness for the construction of cosmological models and its utility for certain studies of elementary particles has made it particularly attractive for exploitation. Because of its simplicity it has been rediscovered many times and is itself very closely related to metrics given several years earlier by Weyl, Levi-Civita, and Wilson. The form in which Kasner presented it has been virtually forgotten in favor of the dynamic form of the synchronous Bianchi I metric. Kasner metrics may be either static or dynamic. To each static metric there is acognate dynamic metric andvice versa, and the two are related by a complex coordinate transformation. The characterization of a Kasner metric is by means of a set of parameters. It is possible for these to take on complex values with interesting consequences, In the discussion a curious error in the original paper is rectified and some new Kasner metrics are presented. The discussion throughout is confined to the vacuum metric. 相似文献
7.
Joel L. Lebowitz Harvey A. Rose Eugene R. Speer 《Journal of statistical physics》1988,50(3-4):657-687
We investigate the statistical mechanics of a complex fieldø whose dynamics is governed by the nonlinear Schrödinger equation. Such fields describe, in suitable idealizations, Langmuir waves in a plasma, a propagating laser field in a nonlinear medium, and other phenomena. Their Hamiltonian $$H(\phi ) = \int_\Omega {[\frac{1}{2}|\nabla \phi |^2 - (1/p) |\phi |^p ] dx}$$ is unbounded below and the system will, under certain conditions, develop (self-focusing) singularities in a finite time. We show that, whenΩ is the circle and theL 2 norm of the field (which is conserved by the dynamics) is bounded byN, the Gibbs measureυ obtained is absolutely continuous with respect to Wiener measure and normalizable if and only ifp andN are such that classical solutions exist for all time—no collapse of the solitons. This measure is essentially the same as that of a one-dimensional version of the more realisitc Zakharov model of coupled Langmuir and ion acoustic waves in a plasma. We also obtain some properties of the Gibbs state, by both analytic and numerical methods, asN and the temperature are varied. 相似文献
8.
Density functional theory calculations are reported concerning the dissociative mechanism for alkene metathesis by ruthenium dichloride catalysts, including both bisphosphine and diaminocarbene/phosphine complexes. The calculations use a hierarchy of models, ranging from [(L)(PH(3))Ru(Cl)(2)(CH(2))](L=PH(3) or diaminocarbene) through the larger [(L)(PMe(3))Ru(Cl)(2)(CHPh)] to the "real"[(L)(PCy(3))Ru(Cl)(2)(CHPh)]. Calculations show that the rate-limiting step for metathesis is either ring closing from an alkene complex to form a ruthena-cyclobutane, or ring-opening of the latter intermediate to form an isomeric alkene complex. The higher efficiency of the diaminocarbene based catalysts is due to the stabilization of the formal +iv oxidation state of the ruthenium centre in the metallacycle. This effect is partly masked in the smaller model systems due to a previously unnoticed stereoelectronic effect. The calculations do not reproduce the experimental observation whereby the initiation step, phosphine dissociation, is more energetically demanding and hence slower for the diaminocarbene-containing catalyst system than for the bisphosphine. Further calculations on the corresponding bond energies using a variety of DFT and hybrid DFT/molecular mechanics methods all find instead a larger phosphine dissociation energy for the bisphosphine catalyst. This reversed order of binding energies would in fact be the one expected based on the stronger trans influence of the diaminocarbene ligand. The discrepancy with experiment is small and could have a number of causes which are discussed here. 相似文献
9.
In current clinical practice, photodynamic therapy (PDT) is carried out with prescribed drug doses and light doses as well as fixed drug-light intervals and illumination fluence rates. This approach can result in undesirable treatment outcomes of either overtreatment or undertreatment because of biological variations between different lesions and patients. In this study, we explore the possibility of improving PDT dosimetry by monitoring drug photobleaching and photoproduct formation. The study involved 60 mice receiving the same drug dose of a novel verteporfin-like photosensitizer, QLT0074, at 0.3 mg/kg body weight, followed by different light doses of 5, 10, 20, 30, 40 or 50 J/cm2 at 686 nm and a fluence rate of 70 mW/cm2. Photobleaching and photoproduct formation were measured simultaneously, using fluorescence spectroscopy. A ratio technique for data processing was introduced to reliably detect the photoproduct formed by PDT on mouse skin in vivo. The study showed that the QLT0074 photoproduct is stable and can be reliably quantified. Three new parameters, photoproduct score (PPS), photobleaching score (PBS) and percentage photobleaching score (PBS%), were introduced and tested together with the conventional dosimetry parameter, light dose, for performance on predicting PDT-induced outcome, skin necrosis. The statistical analysis of experimental results was performed with an ordinal logistic regression model. We demonstrated that both PPS and PBS improved the prediction of skin necrosis dramatically compared to light dose. PPS was identified as the best single parameter for predicting the PDT outcome. 相似文献
10.
Inelastic electron tunneling spectroscopy (IETS) is a relatively new form of vibrational spectroscopy which is able to address problems previously unsolved by either IR or Raman. It is particularly useful for surface analysis. 相似文献