全文获取类型
收费全文 | 2936篇 |
免费 | 69篇 |
国内免费 | 10篇 |
专业分类
化学 | 2078篇 |
晶体学 | 41篇 |
力学 | 61篇 |
数学 | 384篇 |
物理学 | 451篇 |
出版年
2022年 | 28篇 |
2021年 | 29篇 |
2020年 | 43篇 |
2019年 | 37篇 |
2018年 | 24篇 |
2017年 | 28篇 |
2016年 | 46篇 |
2015年 | 48篇 |
2014年 | 70篇 |
2013年 | 151篇 |
2012年 | 139篇 |
2011年 | 177篇 |
2010年 | 98篇 |
2009年 | 77篇 |
2008年 | 157篇 |
2007年 | 176篇 |
2006年 | 152篇 |
2005年 | 177篇 |
2004年 | 165篇 |
2003年 | 122篇 |
2002年 | 135篇 |
2001年 | 48篇 |
2000年 | 37篇 |
1999年 | 29篇 |
1998年 | 32篇 |
1997年 | 33篇 |
1996年 | 43篇 |
1995年 | 31篇 |
1994年 | 42篇 |
1993年 | 35篇 |
1992年 | 30篇 |
1991年 | 41篇 |
1990年 | 25篇 |
1989年 | 19篇 |
1988年 | 23篇 |
1987年 | 17篇 |
1986年 | 23篇 |
1985年 | 29篇 |
1984年 | 29篇 |
1983年 | 23篇 |
1982年 | 35篇 |
1981年 | 31篇 |
1980年 | 23篇 |
1979年 | 30篇 |
1978年 | 29篇 |
1977年 | 19篇 |
1976年 | 20篇 |
1975年 | 16篇 |
1974年 | 19篇 |
1973年 | 15篇 |
排序方式: 共有3015条查询结果,搜索用时 15 毫秒
131.
132.
133.
Bert C. Lynn Mara Tsesarskaja Otto F. Schall Jeanette C. Hernandez Shigeru Watanabe Toshio Takahashi 《Supramolecular chemistry》2013,25(3-4):253-260
Abstract The interactions of macrocyclic polyethers with alkali and alkaline earth cations have been well studied and much about their chemistry is now well understood. Less well examined or comprehended are hydrogen bond interactions. A combination of ion selective electrode binding constant determination techniques and fast atom bombardment mass spectrometry are brought to bear on this problem. It is found that all-oxygen crown ethers and their derivatives exhibit quite different complexation behaviour with ammonium salts than do their various azacrown counterparts. 相似文献
134.
Ram Raghava Robert M. Caddell Lynn Buege Anthony G. Atkins 《Journal of Macromolecular Science: Physics》2013,52(4):655-665
The through thickness total strains of hydrostatically bulged domes of materials are usually determined indirectly. The in-plane circumferential strains are readily measured, and then constancy of volume is invoked to determine the “missing” or unknown strain. Some of our recent work with polymers has shown that volume constancy in large-scale deformation does not hold so that the usual computations of stress and strain during bulging of sheet may be in error. We describe an electrical device that reduces such errors by directly measuring the through thickness (and, thus, the thickness “strain”) for nonmetallic materials. 相似文献
135.
136.
Stacey M. Frumm Zi Peng Fan Kenneth N. Ross Jeremy R. Duvall Supriya Gupta Lynn VerPlank Byung-Chul Suh Edward Holson Florence F. Wagner William B. Smith Ronald M. Paranal Christopher F. Bassil Jun Qi Giovanni Roti Andrew L. Kung James E. Bradner Nicola Tolliday Kimberly Stegmaier 《Chemistry & biology》2013,20(5):713-725
137.
Dr. Carmine D'Agostino Dr. Tatyana Kotionova Dr. Jonathan Mitchell Dr. Peter J. Miedziak Prof. David W. Knight Dr. Stuart H. Taylor Prof. Graham J. Hutchings Prof. Lynn F. Gladden Dr. Mick D. Mantle 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(35):11725-11732
In recent work, it was reported that changes in solvent composition, precisely the addition of water, significantly inhibits the catalytic activity of Au/TiO2 catalyst in the aerobic oxidation of 1,4‐butanediol in methanol due to changes in diffusion and adsorption properties of the reactant. In order to understand whether the inhibition mechanism of water on diol oxidation in methanol is generally valid, the solvent effect on the aerobic catalytic oxidation of 1,3‐propanediol and its two methyl‐substituted homologues, 2‐methyl‐1,3‐propanediol and 2,2‐dimethyl‐1,3‐propanediol, over a Au/TiO2 catalyst has been studied here using conventional catalytic reaction monitoring in combination with pulsed‐field gradient nuclear magnetic resonance (PFG‐NMR) diffusion and NMR relaxation time measurements. Diol conversion is significantly lower when water is present in the initial diol/methanol mixture. A reactivity trend within the group of diols was also observed. Combined NMR diffusion and relaxation time measurements suggest that molecular diffusion and, in particular, the relative strength of diol adsorption, are important factors in determining the conversion. These results highlight NMR diffusion and relaxation techniques as novel, non‐invasive characterisation tools for catalytic materials, which complement conventional reaction data. 相似文献
138.
Mary Margaret CapraroAuthor Vitae Song A. AnAuthor VitaeTingting MaAuthor Vitae A. Fabiola Rangel-ChavezAuthor VitaeAdam HarbaughAuthor Vitae 《The Journal of Mathematical Behavior》2012,31(1):105-116
Open-ended problems have been regarded as powerful tools for teaching mathematics. This study examined the problem solving of eight mathematics/science middle-school teachers. A semi-structured interview was conducted with (PTs) after completing an open-ended triangle task with four unique solutions. Of particular emphasis was how the PTs used a specific heuristic strategy. The results showed that the primary strategy PTs employed in attempting to solve the triangle problem task was guess and check; however, from the PTs’ reflections, we found there existed misapplications of guess and check as a systematic problem-solving strategy. In order to prepare prospective teachers to effectively teach, teacher educators should pay more attention to the mathematical proficiency of PTs, particularly their abilities to systematically and efficiently use guess and check while solving problems and explain their solutions and reasoning to middle-school students. 相似文献
139.
Bert C. Lynn Jesus V. Mallén Servando Muñoz Minsook Kim George W. Gokel 《Supramolecular chemistry》2013,25(3-4):195-197
Abstract Bola-amphiphiles having two aza-18-crown-6 ether rings attached by a covalent spacer (O—O) and an analogous tris (macrocycle) (O—O—O) have been prepared and their cation complexation behavior has been assessed by fast atom bombardment and collisionally activated dissociation tandem mass spectrometry; the key finding is that two cations may simultaneously be complexed by a two- or three-crown system and that this complexation may also involve an anion. 相似文献
140.