全文获取类型
收费全文 | 703篇 |
免费 | 19篇 |
国内免费 | 3篇 |
专业分类
化学 | 424篇 |
晶体学 | 4篇 |
力学 | 22篇 |
数学 | 79篇 |
物理学 | 196篇 |
出版年
2023年 | 5篇 |
2022年 | 6篇 |
2021年 | 8篇 |
2020年 | 14篇 |
2019年 | 11篇 |
2018年 | 9篇 |
2017年 | 8篇 |
2016年 | 11篇 |
2015年 | 11篇 |
2014年 | 14篇 |
2013年 | 41篇 |
2012年 | 38篇 |
2011年 | 42篇 |
2010年 | 17篇 |
2009年 | 17篇 |
2008年 | 22篇 |
2007年 | 34篇 |
2006年 | 39篇 |
2005年 | 33篇 |
2004年 | 28篇 |
2003年 | 19篇 |
2002年 | 22篇 |
2001年 | 12篇 |
2000年 | 15篇 |
1999年 | 13篇 |
1998年 | 7篇 |
1997年 | 13篇 |
1996年 | 19篇 |
1995年 | 9篇 |
1994年 | 11篇 |
1993年 | 10篇 |
1992年 | 8篇 |
1991年 | 9篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1985年 | 10篇 |
1984年 | 14篇 |
1983年 | 9篇 |
1982年 | 5篇 |
1981年 | 13篇 |
1980年 | 5篇 |
1979年 | 10篇 |
1978年 | 7篇 |
1977年 | 11篇 |
1976年 | 4篇 |
1974年 | 9篇 |
1973年 | 5篇 |
1969年 | 3篇 |
1966年 | 3篇 |
排序方式: 共有725条查询结果,搜索用时 15 毫秒
31.
The use of a supported phosphorus pentoxide reagent in the synthesis of selected nitriles is discussed. 相似文献
32.
Ketones and aldehydes are conveniently and rapidly reduced to the corresponding alcohols in good yields using sodium borohydride under sealed-tube microwave conditions in either 95% ethanol or water. In purely aqueous systems, highly aliphatic substrates are sluggish, but this can be overcome by introducing sodium dodecyl sulfate (SDS) at the critical micelle concentration. With a 2:1 substrate/borohydride ratio and a reaction temperature of 100 °C, reduction is typically complete within 1 min in 95% ethanol and 5 min in water/SDS. The methodology is well suited for parallel and combinatorial synthetic approaches. 相似文献
33.
Treatment of carboxylic acids with a “supported” phosphorus pentoxide reagent provides a convenient route to the corresponding anhydrides. 相似文献
34.
Honglin Li Fengyu Liu Yi Xiao Perry J. Pellechia Mark D. Smith Xuhong Qian Guiren Wang Qian Wang 《Tetrahedron》2014
We have revisited the synthesis of a series of ICT fluorophores, which were reported to have a core structure of 8-oxo-8H-acenaphtho[1,2-b]pyrrol-9-carbonitrile. However, based on the 2D NMR and X-ray diffraction analysis, their core structure was corrected as 1-oxo-1H-phenalene-2,3-dicarbonitrile (1). Compound 1 shows a highly electron-deficient nature and can easily undergo oxidative SNArH reaction on the naphthyl ring to produce a series of novel ICT fluorophores. The regioselectivity of this substitution reaction was studied by introduction of representative nucleophiles. Moreover, due to the strong rigidity and efficient ICT nature, the obtained fluorescent dyes display very good spectroscopic properties even in an aqueous environment. 相似文献
35.
Transient spectroscopic characterization of the ring‐opening reaction of tetrahydrochromeno[2,3‐dimethyl]indole
下载免费PDF全文
![点击此处可从《Journal of Physical Organic Chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Ariel S. Marshall Robert A. Rogers Joseph W. Perry W. J. Brittain 《Journal of Physical Organic Chemistry》2016,29(5):221-226
Tetrahydrochromeno is a structural variant of spiropyran that undergoes a reversible ring‐opening to generate a colored nitrophenolate intermediate. Earlier work confirmed this intermediate through trimethylsilyl cyanide trapping under continuous irradiation. We have performed transient absorption spectroscopy to further characterize the mechanism of the ring‐opening reaction. Excitation at 355 nm produced a transient species with an absorption maximum at 445 nm, which we assign to the nitrophenolate unit of the ring‐opened product. The transient absorption decays after ~970 ns with small optical density changes corresponding to a 0.15 quantum yield. Exposure to oxygen did not exhibit a significant deleterious effect on the photoisomerization of the chromeno dye. Time‐dependent density functional theory corroborated spectroscopic assignments of the starting chromeno and the putative ring‐opened intermediate. The excited state behavior of this system parallels the structurally similar oxazine system reported by Raymo and coworkers. The one significant difference is the longer lifetime of the photochemically generated intermediate from chromeno. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
36.
Azobenzene‐Functionalized Metal–Organic Polyhedra for the Optically Responsive Capture and Release of Guest Molecules
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Jinhee Park Dr. Lin‐Bing Sun Ying‐Pin Chen Zachary Perry Prof. Dr. Hong‐Cai Zhou 《Angewandte Chemie (International ed. in English)》2014,53(23):5842-5846
Stimuli‐responsive metal–organic polyhedra (srMOPs) functionalized with azobenzene showed UV‐irradiation‐induced isomerization from the insoluble trans‐srMOP to the soluble cis‐srMOP, whereas irradiation with blue light reversed this process. Guest molecules were trapped and released upon cis‐to‐trans and trans‐to‐cis isomerization of the srMOPs, respectively. This study provides a new direction in the ever‐diversifying field of MOPs, while laying the groundwork for a new class of optically responsive materials. 相似文献
37.
(+/-)-4,12-Dihydroxy[2.2]paracyclophane [(+/-)-PHANOL] is readily prepared from [2.2]paracyclophane by an improved synthetic protocol. Enzymatic kinetic resolution of its bis-acetate proceeds with good enantioselection. Separation, hydrolysis, and recrystallization provides both enantiomers of PHANOL in high enantiopurity. 相似文献
38.
Perry N Binder PM 《Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics》1999,60(1):459-463
We propose a measure of complexity for symbolic sequences, which is based on conditional probabilities, and captures computational aspects of complexity without the explicit construction of minimal deterministic finite automata (DFA). Moreover, if the sequence is obtained from a dynamical system through a suitable encoding and its equations of motion are known, we show how to estimate the regions of phase space that correspond to computational states with statistically equivalent futures (causal states). 相似文献
39.
Charge transport in poly(methylphenylsilane): The case for superimposed disorder and polaron effects
H. Bssler P. M. Borsenberger R. J. Perry 《Journal of Polymer Science.Polymer Physics》1994,32(9):1677-1685
Careful analysis of the temperature dependence of the hole mobility in poly (methylphenylsilane) indicates that the functional dependence is between an Arrhenius law and a ln μ ∝ T?2 law as predicted by a model of disorder-controlled hopping. This is attributed to the superposition of disorder and polaron effects. A method is presented for separating the two contributions. The evolution of time-of-flight photocurrent transients with decreasing temperature is consistent with the disorder parameter derived from the temperature dependence of the mobility. © 1994 John Wiley & Sons, Inc. 相似文献
40.
The polymer-bound quinone2 has been prepared and used in column form with organic solvents for the convenient preparation of other quinones. In contrast to the solution reaction hydrocyanation of this quinone by the Thiele-Meisenheimer reaction did not yield a useful proportion of polymer-bound dicyanohydroquinone but instead gave a mixture of products including much monocyanohydroquinone. Helferich and Bodenbender's 2,3-dicyanocyclohexan-1, 4-dione is in fact wholly the di-enol and is a likely intermediate in the hydrocyanation of benzoquinone, being oxidised by the latter to 2,3-dicyanocyclohex-2-ene-1, 4-dione which tautomerises to the observed product, 2,3-dicyanohydroquinone. A lower accessibility to polymer-bound reactants as compared with those in solution is implied by these results. 相似文献