全文获取类型
收费全文 | 380篇 |
免费 | 11篇 |
国内免费 | 3篇 |
专业分类
化学 | 287篇 |
晶体学 | 3篇 |
力学 | 1篇 |
数学 | 67篇 |
物理学 | 36篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2021年 | 3篇 |
2020年 | 4篇 |
2019年 | 5篇 |
2018年 | 3篇 |
2017年 | 9篇 |
2016年 | 6篇 |
2015年 | 3篇 |
2014年 | 8篇 |
2013年 | 15篇 |
2012年 | 29篇 |
2011年 | 19篇 |
2010年 | 12篇 |
2009年 | 13篇 |
2008年 | 18篇 |
2007年 | 26篇 |
2006年 | 19篇 |
2005年 | 29篇 |
2004年 | 28篇 |
2003年 | 13篇 |
2002年 | 15篇 |
2001年 | 3篇 |
2000年 | 4篇 |
1999年 | 3篇 |
1998年 | 8篇 |
1997年 | 4篇 |
1996年 | 10篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 1篇 |
1990年 | 10篇 |
1989年 | 13篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1971年 | 2篇 |
1907年 | 2篇 |
排序方式: 共有394条查询结果,搜索用时 31 毫秒
211.
Kido Soule MC Hore DK Jaramillo-Fellin DM Richmond GL 《The journal of physical chemistry. B》2006,110(33):16575-16583
Vibrational sum-frequency spectroscopy and surface tensiometry have been used to study the adsorption of m- and p-cyanophenol at the air-water interface. Spectra of the cyano (CN) group under different polarization schemes are utilized to determine its hydrogen bonding environment and orientation. For both isomers, it is found that the cyano group is hydrogen bonded at the interface but that the CN orientation is independent of surface density. The average CN tilt angle (theta(0)), however, is found to differ between the isomers, such that the CN group points down toward the aqueous phase for m-cyanophenol (theta(0) = 96-106 degrees ) but points up toward the vapor phase for the p-cyanophenol (theta(0) = 65-80 degrees ). In addition, this average tilt angle is distributed over a narrow range, sigma(0) < 10 degrees for the meta isomer and sigma(0) < 16 degrees for the para isomer. 相似文献
212.
Donna A. Chen Jay S. Ratliff Xiaofeng Hu Wesley O. Gordon Sanjaya D. Senanayake David R. Mullins 《Surface science》2010,604(5-6):574-587
The thermal decomposition of dimethyl methylphosphonate (DMMP) on crystalline ceria thin films grown on Ru(0 0 0 1) was studied by temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS) and infrared absorption reflection spectroscopy (IRAS). TPD experiments show that methanol and formaldehyde desorb as the two main products at 575 K, while water, formaldehyde and CO are produced above 800 K. IRAS studies demonstrate that DMMP adsorbs via the phosphoryl oxygen at 200 K, but the PO bond converts to a bridging OPO species at 300 K. DMMP decomposition initially occurs via POCH3 bond scission to form methyl methylphosphonate (MMP) and methyl phosphonate (MP) between 300 and 500 K; XPS and IRAS data are consistent with a methoxy intermediate on the surface at these temperatures. The more stable PCH3 bonds remain intact up to 700 K, and the only surface intermediate at higher temperatures is believed to be POx. Although the presence of POx decreases activity for DMMP decomposition, some activity on the ceria surface remains even after 7 cycles of adsorption and reaction. The ceria films become reduced by multiple DMMP adsorption-reaction cycles, with the Ce+4 content dropping to 30% after seven cycles. Investigations of DMMP reaction on reduced ceria surfaces show that CO and H2 are produced in addition to methanol and formaldehyde. Furthermore, DMMP decomposition activity on the reduced ceria films is almost completely inhibited after only 3 adsorption-reaction cycles. Similarities between DMMP and methanol chemistry on the ceria films suggest that methoxy is a key surface intermediate in both reactions. 相似文献
213.
Donna R. Sterling Juanita Jo Matkins Wendy M. Frazier Mollianne G. Logerwell 《School science and mathematics》2007,107(4):134-147
This paper reports on creative partnerships to create learning communities to benefit students, parents, and teachers in the urban setting. Science Camp is a university day camp offering problem‐based science exploration for urban middle school students and an introduction to college life. For parents it is an opportunity to learn about college opportunities for their children and to gather information about funding sources. For middle school science teachers and preservice teachers it is a learning laboratory for conducting problem‐based learning in the urban setting. The findings describe the effects of the learning communities on the transformation of students, parents, preservice teachers, and in‐service teachers. 相似文献
214.
215.
Rationalization of an Unusual Solvent‐Induced Inversion of Enantiomeric Excess in Organocatalytic Selenylation of Aldehydes
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. Jordi Burés Dr. Paul Dingwall Prof. Dr. Alan Armstrong Prof. Dr. Donna G. Blackmond 《Angewandte Chemie (International ed. in English)》2014,53(33):8700-8704
An unusual solvent‐induced inversion of the sense of enantioselectivity observed in the α‐selenylation of aldehydes catalyzed by a diphenylprolinol silyl ether catalyst is correlated to the presence of intermediates formed subsequent to the highly selective C? Se bond‐forming step in the catalytic cycle. This work provides support for a mechanistic concept for enamine catalysis and includes a general role for “downstream intermediates” in selectivity outcomes in organocatalysis. 相似文献
216.
Gabrielle A. Leith Allison M. Rice Brandon J. Yarbrough Anna A. Berseneva Richard T. Ly Charles N. Buck Denis Chusov Amy J. Brandt Donna A. Chen Benjamin W. Lamm Morgan Stefik Kenneth S. Stephenson Mark D. Smith Aaron K. Vannucci Perry J. Pellechia Sophya Garashchuk Natalia B. Shustova 《Angewandte Chemie (International ed. in English)》2020,59(15):6000-6006
The effect of donor (D)–acceptor (A) alignment on the materials electronic structure was probed for the first time using novel purely organic porous crystalline materials with covalently bound two‐ and three‐dimensional acceptors. The first studies towards estimation of charge transfer rates as a function of acceptor stacking are in line with the experimentally observed drastic, eight‐fold conductivity enhancement. The first evaluation of redox behavior of buckyball‐ or tetracyanoquinodimethane‐integrated crystalline was conducted. In parallel with tailoring the D‐A alignment responsible for “static” changes in materials properties, an external stimulus was applied for “dynamic” control of the electronic profiles. Overall, the presented D–A strategic design, with stimuli‐controlled electronic behavior, redox activity, and modularity could be used as a blueprint for the development of electroactive and conductive multidimensional and multifunctional crystalline porous materials. 相似文献
217.
Donna J. Cedio-Fengya 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2007,105(4):357-379
In this paper we investigate the electrostatic problem of determining conductivity profiles from the knowledge of boundary
currents and voltages. We obtain an improved estimate for the voltage potential of a two-dimensional conductor having finitely
many circular inclusions and piecewise constant conductivity profile. We derive an asymptotic expansion for the voltage potential
in terms of the reference voltage potential and the location, size, and conductivity of the inhomogeneities. This representation
is used to formulate the nonlinear least squares problem for estimating the location and size of the inhomogeneities. Required
boundary data for the voltage potential are generated numerically by solving a system of integral equations. Computational
experiments are presented to demonstrate the effectiveness of our identification procedure. 相似文献
218.
Fabio Mazzotti Leonardo Di Donna Barbara Macchione Loredana Maiuolo Enzo Perri Giovanni Sindona 《Rapid communications in mass spectrometry : RCM》2009,23(10):1515-1518
Crop control is an important issue in both developed and developing countries. An environmentally friendly approach is represented by the so‐called Integrated Pest Management (IPM), whereby synthetic pesticides are only applied as a last resort, under the strict control of suitable experts. European and US regulatory authorities, such as the US EPA, are constantly assessing the risks of exposure to the organophosphate (OP) class of pesticides and, among these, specifically dimethoate. The use of dimethoate is still allowed in many crops, including olives, which once was based in the Mediterranean area but now is expanding rapidly throughout the world. An important aspect of IPM protocols is represented by the availability of reliable and sensitive methods to detect pesticides residues. This paper describes an isotope dilution dimethoate assay based on the application of electrospray ionization tandem mass spectrometry (ESI‐MS/MS) by means of a deuterium‐labeled internal standard. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
219.
220.