全文获取类型
收费全文 | 487篇 |
免费 | 9篇 |
专业分类
化学 | 242篇 |
晶体学 | 3篇 |
力学 | 10篇 |
数学 | 62篇 |
物理学 | 179篇 |
出版年
2016年 | 5篇 |
2015年 | 8篇 |
2014年 | 6篇 |
2013年 | 20篇 |
2012年 | 18篇 |
2011年 | 15篇 |
2010年 | 9篇 |
2009年 | 10篇 |
2008年 | 25篇 |
2007年 | 22篇 |
2006年 | 20篇 |
2005年 | 16篇 |
2004年 | 20篇 |
2003年 | 8篇 |
2002年 | 16篇 |
2001年 | 5篇 |
2000年 | 14篇 |
1999年 | 10篇 |
1998年 | 7篇 |
1997年 | 8篇 |
1996年 | 14篇 |
1995年 | 5篇 |
1994年 | 8篇 |
1993年 | 6篇 |
1992年 | 13篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 12篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 8篇 |
1985年 | 12篇 |
1984年 | 6篇 |
1983年 | 9篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1978年 | 13篇 |
1976年 | 3篇 |
1975年 | 7篇 |
1974年 | 11篇 |
1973年 | 5篇 |
1972年 | 5篇 |
1970年 | 4篇 |
1969年 | 3篇 |
1968年 | 6篇 |
1967年 | 6篇 |
1966年 | 5篇 |
1965年 | 3篇 |
排序方式: 共有496条查询结果,搜索用时 46 毫秒
461.
462.
463.
Peter Bender 《International Journal of Mathematical Education in Science & Technology》2013,44(6):849-854
Within a mathemtaical theory, a structured set is called homogeneous,if its ‘parts’ cannot be distinguished from each other by statements of that theory. In Euclidean space geometry, among all convex surfaces and among all complete connected orientable 2‐manifolds with at least one regular point, there are only three types of homogeneous objects: the Euclidean plane, sphere and cylinder. 相似文献
464.
LL Handley R Azcón Ruiz Lozano JM CM Scrimgeour 《Rapid communications in mass spectrometry : RCM》1999,13(13):1320-1324
It has long been evident that plant (15)N chiefly reflects the processes which fractionate (15)N/(14)N rather than the (15)N of plant N source(s). It has emerged recently that one of the most important fractionating processes contributing to the whole plant (15)N is the presence/absence, type or species of mycorrhiza, especially when interacting with nutrient deficiency. Ecto- and ericoid mycorrhizas are frequently associated with (15)N-depleted foliar (15)N, commonly as low as -12 per thousand. As shown by the present study, plants having no mycorrhiza, or those infected with various species of arbuscular mycorrhiza (AM)-forming fungi, interact with varying concentrations of soil nitrogen [N] and moisture to enrich plant (15)N by as much as 3.5 per thousand. Hence the lack of a mycorrhiza, or variation in the species of AM-forming fungal associations, can account for about 25% of the usually reported variations of foliar (15)N found in field situations and do so by (15)N enrichment rather than depletion. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
465.
R. -D. Herzberg S. Moon S. Eeckhaudt P. T. Greenlees P. A. Butler T. Page A. V. Afanasjev N. Amzal J. E. Bastin F. Becker M. Bender B. Bruyneel J. F. C. Cocks I. G. Darby O. Dorvaux K. Eskola J. Gerl T. Grahn C. Gray-Jones N. J. Hammond K. Hauschild P. -H. Heenen K. Helariutta A. Herzberg F. Hessberger M. Houry A. Hürstel R. D. Humphreys G. D. Jones P. M. Jones R. Julin S. Juutinen H. Kankaanp?? H. Kettunen T. L. Khoo W. Korten P. Kuusiniemi Y. LeCoz M. Leino A. -P. Lepp?nen C. J. Lister R. Lucas M. Muikku P. Nieminen M. Nyman R. D. Page T. Page J. Pakarinen A. Pritchard P. Rahkila P. Reiter M. Sandzelius J. Saren Ch. Schlegel C. Scholey Ch. Theisen W. H. Trzaska J. Uusitalo A. Wiens H. J. Wollersheim 《The European Physical Journal A - Hadrons and Nuclei》2009,42(3):333-337
In-beam gamma-ray and conversion electron spectroscopic studies have been performed on the 253 No nucleus. A strongly coupled rotational band has been identified and the improved statistics allows an assignment of the band structure as built on the $\ensuremath 9/2^-[734]_{\nu}$ ground state. The results agree with previously known transition energies but disagree with the tentative structural assignments made in earlier work. 相似文献
466.
GCM analysis of the collective properties of lead isotopes with exact projection on particle numbers
P.-H. Heenen A. Valor M. Bender P. Bonche H. Flocard 《The European Physical Journal A - Hadrons and Nuclei》2001,11(4):393-402
We present a microscopic analysis of the collective behaviour of the lead isotopes in the vicinity of 208Pb. In this study, we rely on a coherent approach based on the Generator Coordinate Method (GCM) including exact projection
on N and Z numbers within a collective space generated by means of the constrained Hartree-Fock BCS method. With the same Hamiltonian
used in HF + BCS calculations, we have performed a comprehensive study including monopole, quadrupole and octupole excitations
as well as pairing vibrations. We find that, for the considered nuclei, the collective modes which modify the most the conclusions
drawn from the mean-field theory are the octupole and pairing vibrations.
Received: 31 May 2001 / Accepted: 23 August 2001 相似文献
467.
eref Demirayak Zafer ahin Merve Erta Emre Fatih Bülbül Ceysu Bender Sevde Nur Biltekin Barkin Berk Begüm Nurpelin Salk Serkan Levent Leyla Yurtta 《Journal of heterocyclic chemistry》2019,56(12):3370-3386
Dementia is a cognitive disorder mostly associated with Alzheimer's disease (AD) in addition to being seen in many other diseases of the central nervous system (CNS). The limited number of drugs is not sufficient to provide adequate improvement to increase the quality of life of patients suffering from this symptom; therefore, all treatment options should be evaluated in detail. In this study, new molecules, [2‐(4‐(2/3/4‐substituted phenyl)piperazin‐1‐yl)‐4‐phenylthiazol‐5‐yl][3/4‐substituted phenyl]methanone derivatives ( 1‐44 ), were obtained and analyzed in terms of their anticholinesterase activities. Kinetic mode and molecular interactions were also evaluated. An enzyme inhibition study was undertaken on acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) using the Ellman method. Maestro program was used in molecular modeling studies. Forty‐four compounds were evaluated on AChE and BChE enzymes at 10?3 and 10?4 concentrations. The inhibition concentrations were calculated as 0.268μM to 2.104μM for six compounds ( 4 , 5 , 16 , 27 , 37 , and 38 ) on AChE. Compound 5 including the 4‐methoxy substituent (IC50: 0.268μM) and compound 38 containing the 4‐methoxy and 3‐methyl substituents (IC50: 0.286μM) showed the highest AChE inhibitory activity. They were further examined in terms of hydrogen bonding with Arg296 and Ar‐Ar interaction with Trp286. The activity of compound 5 was also assessed in mixed‐type kinetic mode. 相似文献
468.
Requiring that a Hamiltonian be Hermitian is overly restrictive. A consistent physical theory of quantum mechanics can be built on a complex Hamiltonian that is not Hermitian but satisfies the less restrictive and more physical condition of space-time reflection symmetry (PT symmetry). One might expect a non-Hermitian Hamiltonian to lead to a violation of unitarity. However, if PT symmetry is not spontaneously broken, it is possible to construct a previously unnoticed symmetry C of the Hamiltonian. Using C, an inner product whose associated norm is positive definite can be constructed. The procedure is general and works for any PT-symmetric Hamiltonian. Observables exhibit CPT symmetry, and the dynamics is governed by unitary time evolution. This work is not in conflict with conventional quantum mechanics but is rather a complex generalization of it. 相似文献
469.
We report on the use of X-ray photoelectron spectroscopy and scanning electron microscopy equipped with energy dispersive spectroscopy to investigate the metallic content of wear debris from prosthetic knees. Synovial fluid aspirated from patients with prosthetic knees was centrifuged, rinsed and dried, resulting in small deposits of wear debris. We identify the presence and composition of metal wear debris from the femoral, tibial, and in some cases the patellar prosthetic components. We also demonstrate the inhomogeneous size, shape, and distribution of the wear particles, and both lateral and vertical elemental inhomogeneity. This points to the necessity of using a combination of techniques for studying such wear debris. The ability to detect the presence of certain metals within the synovial fluid of patients, even when surgical inspection did not identify wear of specific components, may have far reaching implications in the biomedical and prosthetics communities. 相似文献
470.
1,3-Ditellurole was synthesized and shown to oxidize to the 1,3-ditellurolylium ion, which rearranges to a 1,2-ditellurolylium ion. 相似文献