全文获取类型
收费全文 | 667篇 |
免费 | 27篇 |
国内免费 | 2篇 |
专业分类
化学 | 436篇 |
晶体学 | 3篇 |
力学 | 29篇 |
数学 | 68篇 |
物理学 | 160篇 |
出版年
2022年 | 6篇 |
2021年 | 15篇 |
2020年 | 9篇 |
2019年 | 8篇 |
2018年 | 6篇 |
2017年 | 5篇 |
2016年 | 19篇 |
2015年 | 17篇 |
2014年 | 20篇 |
2013年 | 39篇 |
2012年 | 53篇 |
2011年 | 59篇 |
2010年 | 25篇 |
2009年 | 22篇 |
2008年 | 37篇 |
2007年 | 42篇 |
2006年 | 34篇 |
2005年 | 40篇 |
2004年 | 21篇 |
2003年 | 21篇 |
2002年 | 22篇 |
2001年 | 6篇 |
2000年 | 15篇 |
1999年 | 6篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 8篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1992年 | 9篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 9篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1978年 | 10篇 |
1977年 | 2篇 |
1976年 | 9篇 |
1975年 | 8篇 |
1974年 | 5篇 |
1973年 | 6篇 |
1972年 | 7篇 |
1926年 | 2篇 |
排序方式: 共有696条查询结果,搜索用时 15 毫秒
161.
Champagne B Botek E Nakano M Nitta T Yamaguchi K 《The Journal of chemical physics》2005,122(11):114315
The basis set and electron correlation effects on the static polarizability (alpha) and second hyperpolarizability (gamma) are investigated ab initio for two model open-shell pi-conjugated systems, the C(5)H(7) radical and the C(6)H(8) radical cation in their doublet state. Basis set investigations evidence that the linear and nonlinear responses of the radical cation necessitate the use of a less extended basis set than its neutral analog. Indeed, double-zeta-type basis sets supplemented by a set of d polarization functions but no diffuse functions already provide accurate (hyper)polarizabilities for C(6)H(8) whereas diffuse functions are compulsory for C(5)H(7), in particular, p diffuse functions. In addition to the 6-31G(*)+pd basis set, basis sets resulting from removing not necessary diffuse functions from the augmented correlation consistent polarized valence double zeta basis set have been shown to provide (hyper)polarizability values of similar quality as more extended basis sets such as augmented correlation consistent polarized valence triple zeta and doubly augmented correlation consistent polarized valence double zeta. Using the selected atomic basis sets, the (hyper)polarizabilities of these two model compounds are calculated at different levels of approximation in order to assess the impact of including electron correlation. As a function of the method of calculation antiparallel and parallel variations have been demonstrated for alpha and gamma of the two model compounds, respectively. For the polarizability, the unrestricted Hartree-Fock and unrestricted second-order M?ller-Plesset methods bracket the reference value obtained at the unrestricted coupled cluster singles and doubles with a perturbative inclusion of the triples level whereas the projected unrestricted second-order M?ller-Plesset results are in much closer agreement with the unrestricted coupled cluster singles and doubles with a perturbative inclusion of the triples values than the projected unrestricted Hartree-Fock results. Moreover, the differences between the restricted open-shell Hartree-Fock and restricted open-shell second-order M?ller-Plesset methods are small. In what concerns the second hyperpolarizability, the unrestricted Hartree-Fock and unrestricted second-order M?ller-Plesset values remain of similar quality while using spin-projected schemes fails for the charged system but performs nicely for the neutral one. The restricted open-shell schemes, and especially the restricted open-shell second-order M?ller-Plesset method, provide for both compounds gamma values close to the results obtained at the unrestricted coupled cluster level including singles and doubles with a perturbative inclusion of the triples. Thus, to obtain well-converged alpha and gamma values at low-order electron correlation levels, the removal of spin contamination is a necessary but not a sufficient condition. Density-functional theory calculations of alpha and gamma have also been carried out using several exchange-correlation functionals. Those employing hybrid exchange-correlation functionals have been shown to reproduce fairly well the reference coupled cluster polarizability and second hyperpolarizability values. In addition, inclusion of Hartree-Fock exchange is of major importance for determining accurate polarizability whereas for the second hyperpolarizability the gradient corrections are large. 相似文献
162.
S. M. Johnson J. A. C. Bland P. J. Brown A. Benoit H. Capellmann J. Flouquet H. Spille F. Steglich K. R. A. Ziebeck 《Zeitschrift für Physik B Condensed Matter》1985,59(4):401-406
Magnetic fluctuations in CeCu2Si2 were directly observed, both above the superconducting transition temperatureT
C as well as below. Spatial correlations of the magnetisation density belowT
C are weak, resulting in an essentially wavevector independent magnetic response. The intensity observed within an energy window of ±5 THz centred on =0 THz corresponds to 1µ
per Ce atom. Higher energy excitations peaking between 7–10 THz were observed and are probably due to higher crystal field levels. 相似文献
163.
164.
Cristina Canal Sandrine Villeger Benoit Rouffet Pilar Erra 《Applied Surface Science》2008,254(18):5959-5966
The efficiency of surface treatments by plasma and post-discharge plasma processes is greatly dependent on the density of active species, such as neutral atoms in post-discharges. Therefore, many diagnostics exist to detect the presence and measure the concentrations of these species, but they often require expensive instrumentation and highly qualified personnel. These conditions are not often met when the process is industrially used and it becomes important to imagine simple indicators allowing to validate that the correct operating conditions are reached. In the present paper, we present the first results on the investigation of an inexpensive and easy to use visual indicator able to quantify the atomic species density in nitrogen post-discharge plasma processes. It is based on the differential recombination coefficients of N-atoms on metallic/textile fibres which are intrinsically bonded together in a fabric matrix which serves as support for a thermochromic ink. The specific heating of the metallic fibres by N-atom recombination heats the whole of the fabric, leading to a visible colour change of the thermochromic ink, and therefore, of the indicator. Through modelling, it was possible to estimate that the inclusion of copper fibres to a pure cotton matrix leads to a 60% increase of the global N-atom recombination coefficient of the fabric, sufficient enough to provide a clearly visible colour change. 相似文献
165.
Murugesan Velayutham Martin Poncelet Timothy D. Eubank Benoit Driesschaert Valery V. Khramtsov 《Molecules (Basel, Switzerland)》2021,26(9)
Alterations in viscosity of biological fluids and tissues play an important role in health and diseases. It has been demonstrated that the electron paramagnetic resonance (EPR) spectrum of a 13C-labeled trityl spin probe (13C-dFT) is highly sensitive to the local viscosity of its microenvironment. In the present study, we demonstrate that X-band (9.5 GHz) EPR viscometry using 13C-dFT provides a simple tool to accurately measure the microviscosity of human blood in microliter volumes obtained from healthy volunteers. An application of low-field L-band (1.2 GHz) EPR with a penetration depth of 1–2 cm allowed for microviscosity measurements using 13C-dFT in the living tissues from isolated organs and in vivo in anesthetized mice. In summary, this study demonstrates that EPR viscometry using a 13C-dFT probe can be used to noninvasively and rapidly measure the microviscosity of blood and interstitial fluids in living tissues and potentially to evaluate this biophysical marker of microenvironment under various physiological and pathological conditions in preclinical and clinical settings. 相似文献
166.
Dnyaneshwar V. Palaskar Aurélie Boyer Eric Cloutet Jean‐François Le Meins Benoit Gadenne Carine Alfos Céline Farcet Henri Cramail 《Journal of polymer science. Part A, Polymer chemistry》2012,50(9):1766-1782
A series of novel fatty acid‐based diols were designed and synthesized from sunflower and ricin oils using optimized chemical reactions and purifications. These diols were categorized in two different types: (i) fatty acid‐based monoester containing diols (FAmE‐1 to FAmE‐6) and (ii) fatty acid‐based diester containing diols (FAdE‐1 to FAdE‐8). Their synthesis involved a series of reactions such as transesterification, epoxidation, ring opening of epoxide, and thiol‐ene additions. Analyses of these new fatty acid‐based diols were performed by HPLC/GC and NMR spectroscopy. The latter were then demonstrated as polyurethane (PU) precursors in the bulk polymerization with isophorone diisocyanate in the presence of dibutyl tin dilaurate as a catalyst. The effects of the diol nature and purity on the PU synthesis and properties were investigated. The structural characterization of the different PUs was carried out by means of FTIR, 1H NMR, and 1H DOSY NMR spectroscopy. The thermomechanical and rheological properties of these new PUs were found dependent on the chemical structure and purity of the diol building block. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
167.
168.
The most important rheological and mathematical features of the pom–pom model are presently used to compare and improve other
constitutive models such as the Giesekus and Phan-Thien–Tanner models. A pragmatic methodology is selected that allows derivation
of simple constitutive equations, which are suited to possible software implementation. Alterations to the double convected
pom–pom, Phan-Thien–Tanner and Giesekus models are proposed and assessed in rheometric flows by comparing model predictions
to experimental data.
相似文献
Benoit Debbaut (Corresponding author)Email: |
169.
170.
Benoit Louis Dr. M. Maciel Pereira Prof. Fabiana M. Santos Pierre M. Esteves Prof. Jean Sommer Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(2):573-576
The heterogeneous acid‐catalyzed activation step of alkanes leading to the reaction intermediates (carbocationic or alkoxy species) was up to now the matter of a longstanding controversy. Gas chromatography and online mass spectroscopy measurements show that H2 and methane are formed over H‐zeolites, whereas HD and CH3D are formed over D‐zeolites as the primary products in the reaction with isobutane. These results indicate that σ‐bond protolysis by strong acid sites is the first step for hydrocarbon activation on these catalysts at mild temperatures (473 K), in analogy to the activation path occurring in liquid superacid media. 相似文献