全文获取类型
收费全文 | 925篇 |
免费 | 29篇 |
国内免费 | 8篇 |
专业分类
化学 | 636篇 |
晶体学 | 13篇 |
力学 | 7篇 |
数学 | 120篇 |
物理学 | 186篇 |
出版年
2023年 | 7篇 |
2022年 | 7篇 |
2021年 | 16篇 |
2020年 | 10篇 |
2019年 | 19篇 |
2018年 | 12篇 |
2017年 | 5篇 |
2016年 | 16篇 |
2015年 | 17篇 |
2014年 | 21篇 |
2013年 | 40篇 |
2012年 | 36篇 |
2011年 | 52篇 |
2010年 | 21篇 |
2009年 | 30篇 |
2008年 | 41篇 |
2007年 | 48篇 |
2006年 | 52篇 |
2005年 | 41篇 |
2004年 | 59篇 |
2003年 | 37篇 |
2002年 | 42篇 |
2001年 | 25篇 |
2000年 | 25篇 |
1999年 | 16篇 |
1998年 | 16篇 |
1997年 | 12篇 |
1996年 | 12篇 |
1995年 | 12篇 |
1994年 | 14篇 |
1993年 | 11篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1990年 | 18篇 |
1989年 | 8篇 |
1988年 | 9篇 |
1987年 | 8篇 |
1985年 | 11篇 |
1984年 | 14篇 |
1982年 | 7篇 |
1981年 | 12篇 |
1980年 | 8篇 |
1979年 | 9篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1975年 | 4篇 |
1973年 | 8篇 |
1968年 | 3篇 |
1966年 | 3篇 |
1935年 | 3篇 |
排序方式: 共有962条查询结果,搜索用时 15 毫秒
1.
Matt Visser Carlos Barceló Stefano Liberati 《General Relativity and Gravitation》2002,34(10):1719-1734
Condensed matter systems, such as acoustics in flowing fluids, light in moving dielectrics, or quasiparticles in a moving superfluid, can be used to mimic aspects of general relativity. More precisely these systems (and others) provide experimentally accessible models of curved-space quantum field theory. As such they mimic kinematic aspects of general relativity, though typically they do not mimic the dynamics. Although these analogue models are thereby limited in their ability to duplicate all the effects of Einstein gravity they nevertheless are extremely important—they provide black hole analogues (some of which have already been seen experimentally) and lead to tests of basic principles of curved-space quantum field theory. Currently these tests are still in the realm of gedanken-experiments, but there are plausible candidate models that should lead to laboratory experiments in the not too distant future. 相似文献
2.
3.
Bakul C. Dave Xiankui Hu Yogeeswari Devaraj Shirshak K. Dhali 《Journal of Sol-Gel Science and Technology》2004,32(1-3):143-147
There is a current need for alternative coatings that can provide corrosion resistance to metals or alloy surfaces due to the environmental hazards posed by conventional coatings. Herein, we report on novel organically-modified sol–gel coatings for the protection of metal and alloy surfaces. The basic concept of chemical conversion of metal surfaces is based on deposition of a hydrophobic, nonporous sol–gel barrier layer for surface protection and corrosion prevention. The properties of these organosilica coatings can be tuned by varying the composition of precursors. The evaluation of hydrophobicity, adhesive strength, and anticorrosion properties of organically-modified sol–gel derived coatings suggests their potential utility as technologically-compatible alternatives to conventional coatings. 相似文献
4.
Riaan Schmuhl Sankhanilay Roy Chowdhury Johan E. ten Elshof Albert van den Berg Dave H.A. Blank 《Journal of Sol-Gel Science and Technology》2004,31(1-3):249-252
Templated MCM-48 silica was prepared using CTAB as surfactant. The MCM-48 powders and thin films were characterized by different techniques. MCM-48 layers were deposited on macroporous α-alumina supports and silicon nitride microsieves. The water permeability of MCM-48 was compared with the permeability of conventional mesoporous γ-alumina membranes. The applicability of MCM-48 as ion-selective electric field-driven switchable interconnect for microfluidic devices was demonstrated. 相似文献
5.
P. I. H. Bastiaens S. G. Mayhew E. M. O'Naulláin A. van Hoek A. J. W. G. Visser 《Journal of fluorescence》1991,1(2):95-103
Both a mode-locked argon-ion laser and synchrotron radiation were used as excitation sources to obtain time-resolved polarized fluorescence of the two FAD cofactors in electron transferring flavoprotein fromMegasphaera elsdenii. Red-edge excited and blue-edge detected fluorescence anisotropy decay curves did not contain a fast relaxation process which was observed upon mainband excitation and detection. This relaxation was assigned to homo-energy transfer between the two FAD cofactors. Failure of energy transfer as observed with edge spectroscopy on this protein excludes restricted reorientational motion of the flavins as a possible mechanism of depolarization. From the global analysis of the fluorescence anisotropy decay surface obtained at multiple excitation and detection wavelengths, the distance between and the relative orientation of the flavins could be estimated. The methodology described has general applicability in other multichromophoric biopolymers and has the potential to acquire accurate geometrical parameters in these systems. 相似文献
6.
The intention of the research reported here was to seek explanations for low achievement in school mathematics, as conventionally assessed, that derive from broad understandings of mathematics as social. Such a broad social perspective can provide explanations for low achievement, which could lead to different understandings and hence to different teaching approaches. This study centered on 5- to 8-year-old children from a White working-class area in England. Data were collected during visits to the children in school, in their homes, and in the broader community over a 3-year period. Parents, teachers, and other professionals in the broad school context were interviewed, and data were also collected from school documents and policy statements. Interpretations of these data in terms of ways of understanding children's achievements in school mathematics are put forward. The potential effects of these factors on low schooled numeracy attainment are discussed, together with some possible strategic implications for practice and policy. 相似文献
7.
Dave J Adams Eric G Hope Peter J Pogorzelec 《Journal of organometallic chemistry》2004,689(8):1413-1417
The hydroformylation of long chain alkenes under fluorous biphase conditions and in neat perfluorocarbon solvents is reviewed. Special emphasis is placed upon the authors' evaluation of the steric and electronic influence of perfluoroalkylation on catalyst activity, regioselectivity and retention in the fluorocarbon phase. 相似文献
8.
Dave Auckly 《Proceedings of the American Mathematical Society》2005,133(3):885-889
Vidussi was the first to construct knotted Lagrangian tori in simply connected four-dimensional manifolds. Fintushel and Stern introduced a second way to detect such knotting. This note demonstrates that similar examples may be distinguished by the fundamental group of the exterior.
9.
Sankar Prasad Bhuniya Safikur Rahman Anshul J. Satyanand Mahendrasinh M. Gharia Ashok M. Dave 《Journal of polymer science. Part A, Polymer chemistry》2003,41(11):1650-1658
Maize starch was modified by allyl chloride adopting an interfacial reaction technique with cetyltrimethyl ammonium bromide as a phase‐transfer catalyst and pyridine as an acid acceptor. The degree of substitution was determined from an increasing carbon content of the modified starch. The percentage of carbon and hydrogen of the allyl‐modified starch was estimated by elemental analysis (C, H, and N), and the product characterization was done through 1H NMR and 13C NMR analyses. The allyl‐modified starch was then copolymerized with methacrylic acid and a combination of methacrylic acid and acrylamide at 50 and 70 °C with potassium persulfate as an initiator. The copolymer thus formed swelled in distilled water after neutralization with sodium carbonate. The percentage of absorption capacity of the hydrogels was determined with distilled water and 0.9% NaCl solution. The highest percentage of absorption, 6500%, was achieved for the developed hydrogel containing allyl starch and acrylic monomer in a 1.7:1 w/w ratio and acrylic monomer, namely, methacrylic acid and acrylamide in a 3.2:1 w/w ratio. The study on biodegradability of the developed hydrogel showed that the hydrogel is degradable in the presence of diastase (amylase). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1650–1658, 2003 相似文献
10.