全文获取类型
收费全文 | 1239篇 |
免费 | 18篇 |
国内免费 | 3篇 |
专业分类
化学 | 642篇 |
晶体学 | 33篇 |
力学 | 30篇 |
数学 | 150篇 |
物理学 | 405篇 |
出版年
2021年 | 9篇 |
2020年 | 15篇 |
2019年 | 10篇 |
2018年 | 8篇 |
2017年 | 7篇 |
2016年 | 14篇 |
2015年 | 13篇 |
2014年 | 17篇 |
2013年 | 61篇 |
2012年 | 36篇 |
2011年 | 53篇 |
2010年 | 30篇 |
2009年 | 17篇 |
2008年 | 38篇 |
2007年 | 57篇 |
2006年 | 43篇 |
2005年 | 44篇 |
2004年 | 40篇 |
2003年 | 42篇 |
2002年 | 34篇 |
2001年 | 36篇 |
2000年 | 29篇 |
1999年 | 16篇 |
1998年 | 14篇 |
1997年 | 32篇 |
1996年 | 32篇 |
1995年 | 20篇 |
1994年 | 33篇 |
1993年 | 35篇 |
1992年 | 24篇 |
1991年 | 44篇 |
1990年 | 24篇 |
1989年 | 15篇 |
1988年 | 20篇 |
1987年 | 16篇 |
1986年 | 20篇 |
1985年 | 19篇 |
1984年 | 32篇 |
1983年 | 13篇 |
1982年 | 21篇 |
1981年 | 16篇 |
1980年 | 16篇 |
1979年 | 16篇 |
1978年 | 9篇 |
1977年 | 15篇 |
1976年 | 9篇 |
1975年 | 14篇 |
1974年 | 8篇 |
1973年 | 18篇 |
1972年 | 7篇 |
排序方式: 共有1260条查询结果,搜索用时 62 毫秒
61.
Falko Böttger‐Hiller Patrick Kempe Dr. Gerhard Cox Dr. Alexander Panchenko Dr. Nicole Janssen Dr. Albrecht Petzold Prof. Dr. Thomas Thurn‐Albrecht Lars Borchardt Dr. Marcus Rose Prof. Dr. Stefan Kaskel Colin Georgi Prof. Dr. Heinrich Lang Prof. Dr. Stefan Spange 《Angewandte Chemie (International ed. in English)》2013,52(23):6088-6091
62.
63.
Shelah considered a certain version of Strong Chang's Conjecture which we denote , and proved that it is equivalent to several statements, including the assertion that Namba forcing is semiproper. We introduce an apparently weaker version, denoted , and prove an analogous characterization of it. In particular, is equivalent to the assertion that the the Friedman‐Krueger poset is semiproper. This strengthens and sharpens results by Cox and sheds some light on problems posed by Usuba, Torres‐Perez and Wu. 相似文献
64.
In a recent survey Sutherland and Dewhurst itemized the extent to which various types of departments expected selected mathematical topics in the background of incoming undergraduates. Using the results of diagnostic tests it is possible to estimate the actual capability of students with given prior qualifications to provide a ‘probable preparedness’ in specific topics. This paper compares expectations with probable preparedness in a range of topics. It is found that while some departments have realistic expectations about the background of their incoming students, others seem over-optimistic about the mathematical knowledge of today's students. Sometimes, topics that the department actually requires must in fact be covered ab initio with the students that they recruit. 相似文献
65.
Kevin Becker Sebastian Pfütze Dr. Eric Kuhnert Prof. Dr. Russell J. Cox Prof. Dr. Marc Stadler Dr. Frank Surup 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(4):1438-1450
The diversity of azaphilones in stromatal extracts of the fungus Hypoxylon fragiforme was investigated and linked to their biosynthetic machineries by using bioinformatics. Nineteen azaphilone-type compounds were isolated and characterized by NMR spectroscopy and mass spectrometry, and their absolute stereoconfigurations were assigned by using Mosher ester analysis and electronic circular dichroism spectroscopy. Four unprecedented bis-azaphilones, named hybridorubrins A–D, were elucidated, in addition to new fragirubrins F and G and various known mitorubrin derivatives. Only the hybridorubrins, which are composed of mitorubrin and fragirubrin moieties, exhibited strong inhibition of Staphylococcus aureus biofilm formation. Analysis of the genome of H. fragiforme revealed the presence of two separate biosynthetic gene clusters (BGCs) hfaza1 and hfaza2 responsible for azaphilone formation. While the hfaza1 BGC likely encodes the assembly of the backbone and addition of fatty acid moieties to yield the (R)-configured series of fragirubrins, the hfaza2 BGC contains the necessary genes to synthesise the widely distributed (S)-mitorubrins. This study is the first example of two distant cross-acting fungal BGCs collaborating to produce two families of azaphilones and bis-azaphilones derived therefrom. 相似文献
66.
H. A. Cox 《International Journal of Mathematical Education in Science & Technology》2013,44(7):757-763
A study was conducted on high school students, comparing those with some music credits to those with none. No statistically significant difference was found in their mean math grade point averages (GPA) or their mean cumulative GPAs. Students were then separated into two groups based on the number of music credits. Students who had earned at least two music credits per grade level were placed into Group A. This category included ninth graders with two or more music credits, tenth graders with four or more music credits, eleventh graders with six or more music credits, and twelfth graders with eight or more music credits. The remaining students were placed into Group B. Group A students performed better than group B students. However, the differences were not statistically significant. Scatter plots indicated a slight upward trend in GPAs as the number of music credits increased. Lower GPAs were nonexistent as the music credits increased. 相似文献
67.
Amina Benylles Donald Cairns Philip J. Cox Graeme Kay 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(6):658-664
Reaction between cysteamine (systematic name: 2‐aminoethanethiol, C2H7NS) and L‐(+)‐tartaric acid [systematic name: (2R,3R)‐2,3‐dihydroxybutanedioic acid, C4H6O6] results in a mixture of cysteamine tartrate(1−) monohydrate, C2H8NS+·C4H5O6−·H2O, (I), and cystamine bis[tartrate(1−)] dihydrate, C4H14N2S22+·2C4H5O6−·2H2O, (III). Cystamine [systematic name: 2,2′‐dithiobis(ethylamine), C4H12N2S2], reacts with L‐(+)‐tartaric acid to produce a mixture of cystamine tartrate(2−), C4H14N2S22+·C4H4O62−, (II), and (III). In each crystal structure, the anions are linked by O—H...O hydrogen bonds that run parallel to the a axis. In addition, hydrogen bonding involving protonated amino groups in all three salts, and water molecules in (I) and (III), leads to extensive three‐dimensional hydrogen‐bonding networks. All three salts crystallize in the orthorhombic space group P212121. 相似文献
68.
Hakim Al Garalleh Ngamta Thamwattana Barry J. Cox James M. Hill 《Journal of mathematical chemistry》2013,51(8):2020-2032
Aquaporin is a family of small membrane-proteins that are capable of transporting nano-sized materials. In the present paper, we investigate the structure of these channels and provide information about the mechanism of individual molecules being encapsulated into aquaglyceroporin (GlpF) and aquaporin-1 (AQP1) channels by calculating the potential energy. In particular, we presents a mathematical model to determine the total potential energy for the interaction of the ammonia and nitric oxide molecules and different aquaporin channels which we assume to have a symmetrical cylindrical structure. We propose to describe these interactions in two steps. Firstly, we model the nitrogen atom as a discrete point and secondly, we model the three hydrogen atoms on the surface of a sphere of a certain radius. Then, we find the total potential energy by summing these interactions. Next, by considering the nitric oxide molecule as two discrete atoms uniformly distributed interacting with GlpF and AQP1 channels then gathering all pairs of interaction to determine the potential energy. Our results show that the ammonia and nitric oxide molecules can be encapsulated into both GlpF and AQP1 channels. 相似文献
69.
Principles for selecting potential infrared nematic liquid crystals are described. Optical and electro-optic properties of two cyanotolanes, 4-n-alkyl-4′-cyanotolanes and three commercial liquid-crystal mixtures were chosen for evaluation. Their applications for modulating infrared radiation are addressed. 相似文献
70.
We compare extensive experimental results for the
gravity-driven steady drainage of oil-in-water emulsions with two
theoretical predictions, both based on the assumption of Poiseuille flow.
The first is from standard foam drainage theory,
applicable at low aqueous volume fractions, for which a
correction is derived to account for the effects
of the confinement of the emulsion. The second arises
from considering the permeability of a model porous
medium consisting of solid sphere packings, applicable
at higher aqueous volume fractions. We find quantitative
agreement between experiment and the foam drainage theory at low
aqueous volume fractions. At higher aqueous volume
fractions, the reduced flow rate calculated from the
permeability theory approaches the master curve
of the experimental data. Our experimental data
demonstrates the analogy between the problem of electrical flow and liquid
flow through foams and emulsions. 相似文献