全文获取类型
收费全文 | 974篇 |
免费 | 20篇 |
国内免费 | 8篇 |
专业分类
化学 | 660篇 |
晶体学 | 14篇 |
力学 | 34篇 |
数学 | 157篇 |
物理学 | 137篇 |
出版年
2023年 | 6篇 |
2020年 | 11篇 |
2019年 | 7篇 |
2018年 | 12篇 |
2016年 | 15篇 |
2015年 | 10篇 |
2014年 | 13篇 |
2013年 | 54篇 |
2012年 | 45篇 |
2011年 | 38篇 |
2010年 | 32篇 |
2009年 | 23篇 |
2008年 | 52篇 |
2007年 | 48篇 |
2006年 | 61篇 |
2005年 | 42篇 |
2004年 | 46篇 |
2003年 | 35篇 |
2002年 | 42篇 |
2001年 | 18篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1998年 | 7篇 |
1997年 | 12篇 |
1996年 | 10篇 |
1995年 | 13篇 |
1994年 | 8篇 |
1993年 | 19篇 |
1992年 | 14篇 |
1991年 | 10篇 |
1990年 | 13篇 |
1989年 | 8篇 |
1988年 | 12篇 |
1987年 | 11篇 |
1986年 | 10篇 |
1985年 | 24篇 |
1984年 | 21篇 |
1983年 | 8篇 |
1982年 | 25篇 |
1981年 | 14篇 |
1980年 | 17篇 |
1979年 | 16篇 |
1978年 | 9篇 |
1977年 | 5篇 |
1976年 | 12篇 |
1974年 | 8篇 |
1973年 | 14篇 |
1972年 | 10篇 |
1971年 | 6篇 |
1968年 | 5篇 |
排序方式: 共有1002条查询结果,搜索用时 15 毫秒
1.
Emily K. Corlett Helen Blade Leslie P. Hughes Philip J. Sidebottom David Walker Richard I. Walton Steven P. Brown 《Magnetic resonance in chemistry : MRC》2020,58(11):1026-1035
Single-crystal X-ray diffraction structures of the 5-amino-2-methylpyridinium hydrogen fumarate salt have been solved at 150 and 300 K (CCDC 1952142 and 1952143). A base–acid–base–acid ring is formed through pyridinium-carboxylate and amine-carboxylate hydrogen bonds that hold together chains formed from hydrogen-bonded hydrogen fumarate ions. 1H and 13C chemical shifts as well as 14N shifts that additionally depend on the quadrupolar interaction are determined by experimental magic angle spinning (MAS) solid-state nuclear magnetic resonance (NMR) and gauge-including projector-augmented wave (GIPAW) calculation. Two-dimensional homonuclear 1H-1H double-quantum (DQ) MAS and heteronuclear 1H-13C and 14N-1H spectra are presented. Only small differences of up to 0.1 and 0.6 ppm for 1H and 13C are observed between GIPAW calculations starting with the two structures solved at 150 and 300 K (after geometry optimisation of atomic positions, but not unit cell parameters). A comparison of GIPAW-calculated 1H chemical shifts for isolated molecules and the full crystal structures is indicative of hydrogen bonding strength. 相似文献
2.
Here we describe the story behind the link between molecular chirality and macroscopic phenomena, the latter being a probe for the direct assignment of absolute configuration of chiral molecules. First, a brief tour of the history of molecular stereochemistry, starting with the classic experiment reported by Pasteur in 1848 on the separation of enantiomorphous crystals of a salt of tartaric acid, and his conclusion that the molecules of life are chiral of single-handedness. With time, this study raised, inter alia, two fundamental questions: the absolute configuration of chiral molecules and how a molecule of given configuration shapes the enantiomorphous morphology of its crystal. As for the first question, following the beginning of crystal structure determination by X-ray diffraction in 1912, it took almost 40 years before Bijvoet assigned molecular chirality through the esoteric method involving anomalous X-ray scattering. We have been able to address and link both questions through ‘everyday concepts of left and right’ (in the words of Jack Dunitz) by the use of ‘tailor-made’ auxiliaries. By such means, it proved possible to reveal, through morphology, etch patterns, epitaxy and symmetry reduction of both chiral and, paradoxically, centrosymmetric crystals, the basic chiral symmetry of the molecules of life, the α-amino acids and sugars. 相似文献
3.
Thomas E. Murphy Stuart Pilorz Leslie Prufert‐Bebout Brad Bebout 《Photochemistry and photobiology》2015,91(4):862-868
This article presents the design, construction and characterization of a novel type of light probe for measuring the angular radiance distribution of light fields. The differential acceptance angle (DAA) probe can resolve the directionality of a light field in environments with steep light gradients, such as microbial mats, without the need to remove, reorient, and reinsert the probe, a clear advantage over prior techniques. The probe consists of an inner irradiance sensor inside a concentric, moveable light‐absorbing sheath. The radiative intensity in a specific zenith direction can be calculated by comparing the irradiance onto the sensor at different acceptance angles. We used this probe to measure the angular radiance distribution of two sample light fields, and observed good agreement with a conventional radiance probe. The DAA probe will aid researchers in understanding light transfer physics in dense microbial communities and expedite validation of numerical radiative transfer models for these environments. 相似文献
4.
Yuval Freed Leslie Banks-Sills 《Journal of the mechanics and physics of solids》2007,55(10):2157-2180
Crack growth resistance of shape memory alloys (SMAs) is dominated by the transformation zone in the vicinity of the crack tip. In this study, the transformation toughening behavior of a slowly propagating crack in an SMA under plane strain conditions and mode I deformation is numerically investigated. A small-scale transformation zone is assumed. A cohesive zone model is implemented to simulate crack growth within a finite element scheme. Resistance curves are obtained for a range of parameters that specify the cohesive traction-separation constitutive law. It is found that the choice of the cohesive strength t0 has a great influence on the toughening behavior of the material. Moreover, the reversibility of the transformation can significantly reduce the toughening of the alloy. The shape of the initial transformation zone, as well as that of a growing crack is determined. The effect of the Young's moduli ratio of the martensite and austenite phases is examined. 相似文献
5.
6.
AbstractInteractions of glucopyranose, fructopyranose and sucrose with a proteinaceous receptor model have been examined to validate the stereomolecular mechanisms of sweet taste proposed for sugars. The methylene groups at C-6 of glucose, at C-1 and C-6 of fructose and at C-6, C-1' and C-6' of sucrose appear to play an important role as dispersive interaction centres with the receptor. 相似文献
7.
8.
Leslie W. Deady Andrew B. Hughes Indumathy B. Mahadevan Nurul H. Quazi Leann M. Tilley 《合成通讯》2013,43(5):803-820
The synthesis of fluorescent 2,10-derivatives of the title chromophore are described. The substituents contain amino-reactive N-hydroxysuccinimde ester and thiol-reactive iodoacetamide groups for attachment to biomolecules. A phosphate derivative was also prepared as an enzyme substrate. 相似文献
9.
10.