全文获取类型
收费全文 | 222篇 |
免费 | 11篇 |
国内免费 | 4篇 |
专业分类
化学 | 152篇 |
力学 | 10篇 |
数学 | 22篇 |
物理学 | 53篇 |
出版年
2024年 | 2篇 |
2023年 | 5篇 |
2022年 | 10篇 |
2021年 | 13篇 |
2020年 | 9篇 |
2019年 | 10篇 |
2018年 | 10篇 |
2017年 | 5篇 |
2016年 | 9篇 |
2015年 | 7篇 |
2014年 | 16篇 |
2013年 | 15篇 |
2012年 | 13篇 |
2011年 | 11篇 |
2010年 | 12篇 |
2009年 | 9篇 |
2008年 | 11篇 |
2007年 | 8篇 |
2006年 | 5篇 |
2005年 | 6篇 |
2004年 | 3篇 |
2003年 | 5篇 |
2002年 | 7篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1996年 | 1篇 |
1995年 | 4篇 |
1993年 | 1篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1980年 | 2篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有237条查询结果,搜索用时 171 毫秒
151.
Aliakbar Ahmadi Mohammad Zaman Kassaee Alireza Fattahi 《Journal of Physical Organic Chemistry》2018,31(3)
Anticancer character of gold cluster has been indicated through its free radical scavenging properties. This is in contrast to its free radical promoting ability suggested by other workers. Here, we address this controversy by probing the stabilizing effects of Au3 cluster on RO? vs its impacts on RO–H bond dissociation enthalpy, at B3LYP/ LACVP+* level (R═H, methyl, ethyl, n‐propyl, i‐propyl, n‐butyl, t‐butyl, and phenyl). In the presence of Au3 cluster, bond dissociation enthalpy of O–H bond and the spin density at the RO? oxygen are reduced dramatically. These are clear evidences for both the Au3 facilitation of the RO–H bond breakage and its scavenging of RO? radical. Since O–Au anchoring bond is responsible for the interaction of Au3 cluster and ROH (or RO?), its nature was interpreted by means of the quantum theory of atoms in molecules and the natural bond orbital. The results indicate that O–Au bond is stronger and has more covalent character in RO?–Au3 than in ROH–Au3. The interaction of Au3 cluster with RO? is 1.5 to 3 times more than that with ROH. As a result, gold cluster scavenging property appears more prominent than its free radical initiation activity. 相似文献
152.
153.
154.
Bibi Narjes Haerizade Mohammad Zaman Kassaee Hassan Zandi Maryam Koohi Ali A. Ahmadi 《Journal of Physical Organic Chemistry》2014,27(11):902-908
High‐level Density Functional Theory calculations, coupled with appropriate isodesmic reaction, are employed to investigate the effects of α‐carbon, ammonium, phosphorus, and sulfur ylides, cyclization, and unsaturation on the stability, multiplicity, and reactivity of novel singlet (S) and triplet (T) carbenes. Among them the highly π‐donating α‐ammonium ylide is found to exert the highest stabilizing effect on the carbenic center. α‐Ammonium ylides resist dimerization and hydrogenation. They show wider singlet–triplet energy gap (ΔΕS–T), broader band gap (ΔΕHOMO–LUMO), and higher nucleophilicity compared to the reported stable N‐heterocyclic carbenes. Aromatic cyclic unsaturated ammonium, phosphorus, and sulfur ylide carbenes appear more stable than their saturated cyclic analogs which are in turn more viable than their acyclic counterparts. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
155.
Nisar Ali ;Baoliang Zhang ;Hepeng Zhang ;Wajed Zaman ;Wei Li ;Qiuyu Zhang 《Particuology》2014,(6):59-65
Inorganic/organic poly(methylmethacrylate-acrylic acid-divinylbenzene) iron oxide Janus magnetic nanoparticles(P(MMA-AA-DVB)/Fe3O4) with strong magnetic domains and unique surface functionalities were prepared using a solvothermal process.The P(MMA-AA-DVB) nanoparticles were prepared via soapfree emulsion polymerization and used as a precursor for preparing Janus nanoparticles.The morphology and magnetic properties of the magnetic Janus nanoparticles formed were characterized using a laser particle size analyzer,transmission electron microscopy,Fourier transform infrared spectroscopy,vibrating sample magnetometry,and thermogravimetric analysis.The synthesized P(MMA-AA-DVB)/Fe3O4 magnetic Janus nanoparticles were characterized by a Janus structure and possessed a stable asymmetric morphology after being dually functionalized.The particle size,magnetic content,and magnetic domain of the P(MMA-AA-DVB)/Fe3O4 magnetic Janus nanoparticles were 200 nm,40%,and 25 emu/g,respectively.The formation mechanism of the Janus nanoparticles was also investigated,and the results revealed that the reduction of Fe3+ ions and growth of Fe3O4 took place on the surface of the P(MMA-AA-DVB) polymeric precursor particles.The size of the Janus particles could be controlled by narrowing the size distribution of the P(MMA-AA-DVB) precursor nanoparticles. 相似文献
156.
Nonlinear Dynamics - In this paper, we introduce a SEIATR compartmental model to analyze and predict the COVID-19 outbreak in the Top 5 affected countries in the world, namely the USA, India,... 相似文献
157.
Naik H. Kim G. N. Kim K. Zaman M. Sahid M. Yang S. -C. Lee M. W. Kang Y. R. Shin S. G. Cho M. -H. Goswami A. Song T. Y. 《The European Physical Journal A - Hadrons and Nuclei》2014,50(7):1-13
We investigate the parity-violating nucleon-nucleon potential as obtained in chiral effective field theory. By using resonance saturation we compare the chiral potential to the more traditional one-meson-exchange potential. In particular, we show how parameters appearing in the different approaches can be compared with each other and demonstrate that analyses of parity violation in proton-proton scattering within the different approaches are in good agreement. In the second part of this work, we extend the parity-violating potential to next-to-next-to-leading order. We show that generally it includes both one-pion- and two-pion-exchange corrections, but the former play no significant role. The two-pion-exchange corrections depend on five new low-energy constants which only become important if the leading-order weak pion-nucleon constant h π turns out to be very small. 相似文献
158.
Luther W. White
Musharraf Zaman
《Applied mathematics and computation》1998,90(2-3):181-203A porous media model is derived describing the accumulation and flow of fluid within a domain. The model consists of a differential expression determining the saturated fluid subdomain and a relation describing the pressure distribution within that domain. The wellposedness and numerical solution of a simplified problem is presented and a validation using field rainfall outflow data collected from a highway roadbed is discussed. 相似文献
159.
M. Saeed Arayne Najma Sultana M. Kamran Zaman 《Accreditation and quality assurance》2008,13(8):431-432
The concept of good manufacturing practice (GMP) is not new; its roots are very old. The incidents that gave birth to the
concept of GMP are summarized in this article. The journey from the FDA toward GMP is highlighted in chronological order.
These regulations are mandatory for pharmaceutical industries in order to manufacture quality products. 相似文献
160.
Substituent effects on cyclonona‐3,5,7‐trienylidenes: a quest for stable carbenes at density functional theory level
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)
Maryam Koohi Mohammad Zaman Kassaee Bibi Narjes Haerizade Monireh Ghavami Samaneh Ashenagar 《Journal of Physical Organic Chemistry》2015,28(8):514-526
Nine boat‐shaped cyclonona‐3,5,7‐trienylidenes are compared and contrasted with respect to their multiplicity, nucleophilicity, electrophilicity, band gap (ΔEHOMO ? LUMO), Natural bond orbital (NBO) atomic charge, force constant, as well as the aptitude for dimerization, and rearrangement through proper isodesmic reactions at B3LYP/AUG‐cc‐pVTZ and B3LYP/6‐311++G**//B3LYP/6‐31+G* levels of theory. The nine cyclic carbenes include unsubstituted (1CH2) plus eight α‐cyclopropylcyclonona‐3,5,7‐trienylidenes, which are substituted with ?‐SiMe2, ?‐NMe, ?‐PMe, ?‐O, ?‐S, ?‐CH2, ?‐cyclopropyl, and ?‐CMe2 (2SiMe2, 2NMe, 2PMe, 2O, 2S, 2CH2, 2cyclopropyl, and 2CMe2, respectively). The latter eight species enjoy the stabilizing interaction of the occupied Walsh orbital of cyclopropyl with the vacant pπ orbital of the carbene center (Walshcyclopropyl → pπ carbene). Among them, the singlet closed shell 2NMe appears the most promising for exhibiting the highest relative singlet–triplet energy gap (ΔEs ? t = 27.1 kcal mol?1). In contrast, the least stable derivative is triplet 2SiMe2, which exhibits the lowest relative ΔEs ? t of ?5.5 kcal mol?1. The overall trend of ΔEs‐t is 2NMe > 2PMe > 2S > 2O > 2cyclopropyl > 2CMe2 > 2CH2 > 1CH2 > 2SiMe2. With one negative force constant, the unsubstituted 1CH2 turns out to be a transition state, whereas the rest emerge as minima. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献