全文获取类型
收费全文 | 972篇 |
免费 | 25篇 |
国内免费 | 6篇 |
专业分类
化学 | 683篇 |
晶体学 | 8篇 |
力学 | 18篇 |
数学 | 156篇 |
物理学 | 138篇 |
出版年
2023年 | 6篇 |
2022年 | 18篇 |
2021年 | 19篇 |
2020年 | 17篇 |
2019年 | 11篇 |
2018年 | 12篇 |
2017年 | 13篇 |
2016年 | 25篇 |
2015年 | 24篇 |
2014年 | 29篇 |
2013年 | 69篇 |
2012年 | 67篇 |
2011年 | 73篇 |
2010年 | 48篇 |
2009年 | 35篇 |
2008年 | 75篇 |
2007年 | 76篇 |
2006年 | 62篇 |
2005年 | 50篇 |
2004年 | 30篇 |
2003年 | 36篇 |
2002年 | 36篇 |
2001年 | 13篇 |
2000年 | 24篇 |
1999年 | 9篇 |
1998年 | 11篇 |
1997年 | 12篇 |
1996年 | 6篇 |
1995年 | 9篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1991年 | 8篇 |
1990年 | 7篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1969年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有1003条查询结果,搜索用时 15 毫秒
991.
Jaime Vázquez Sylvain BernèsPankaj Sharma Javier PérezGuadalupe Hernández Alejandra TovarUlises Peña René Gutiérrez 《Polyhedron》2011,30(15):2514-2522
A set of new diastereopure unsymmetrical α-diimine ligands 2a-d derived from methylglyoxal and optically pure primary amines 1a-d afforded the new chiral Pd(II)-complexes (S,S)-3a, (S,S)-3b, (S,S)-3c, and (1S, 2S, 3S, 5R)-3d. All compounds have been characterized by IR, 1H, and 13C NMR spectroscopies along with MS-FAB+ spectrometry. The crystal and molecular structure for the complexes 3a, 3b and 3d have been fully confirmed by single-crystal X-ray studies. Likewise, complexes 3a-d have also been screened for their in vitro cytotoxicity against different classes of cancer: leukemia (K-562 CML), colon cancer (HCT-15), human breast adenocarcinoma (MCF-7), central nervous system (U-251 Glio) and prostate cancer (PC-3) cell lines. 相似文献
992.
Didier Astruc Cátia Ornelas Jaime Ruiz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(36):8936-8944
In this Concept article, we summarize and discuss recent reports on dendritic molecular electrochromic batteries. Giant dendrimers containing 3n+2 terminal tethers (n=generation number) and terminated by first‐raw late‐transition‐metal metallocenes, permethyl metallocenes and other sandwich complexes were shown to be redox robust. Indeed, they can be oxidized and reduced without decomposition and exist under two stable oxidation states (FeIII/II, CoIII/II). Thus, a pre‐determined number of electrons (up to 14 000) per dendrimer can be exchanged. Cyclic voltammetry showed a remarkable complete reversibility even up to 14 000 Fe and Co termini in metallodendrimers, indicating fast electron hoping among the redox sites and between dendrimers on a carbon surface covered by arylcarboxylate groups. The dendrimer sizes were measured by dynamic light scattering in solution and by AFM (subsequent to flattening in the condensed state also indicating that these metallodendrimers aggregate to form discrete nanoparticles of dendrimers, as atoms do). The metallodendrimer size varies considerably between the two redox forms due to tether extension of the cationic dendrimers upon oxidation, and a breathing mechanism was shown by atomic and electric force microscopy (AFM and EFM). When the redox potential is very negative, the reduced form is an electron‐reservoir system that can deliver a large number of electrons per dendrimer to various reducible substrates. These systems are thus potential dendritic molecular batteries with two different colors for the two redox forms (electrochromic behavior). 相似文献
993.
Santiago Cabaleiro‐Martínez Jesús Castro Jaime Romero Jos A. García‐Vzquez Antonio Sousa 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(6):e249-e250
The title compound, [Co(H2O)6](CH3C6H4SO3)2, has a structure where the metal atom is surrounded by six molecules of water forming the cation and the anion is deprotonated 4‐toluenesulfonic acid. The Co atom is in a nearly regular octahedral coordination geometry, with Co—O distances between 2.0529 (14) and 2.0810 (16) Å, and angles ranging from 87.25 (9) to 92.75 (9)°. The supramolecular structure consists of parallel layers of cations and anions. The anions are arranged with their sulfonate groups directed towards the cation layer in an alternating fashion and form hydrogen bonds with the water molecules of the cation. 相似文献
994.
Augusto Rivera Mauricio Maldonado Jaime Ríos-Motta Miguel Angel Navarro Diego González-Salas 《Tetrahedron letters》2010,51(1):102-104
A one-pot good-yielding synthesis of 1-(alcoxymethyl)-1H-benzimidazoles and 1-((1H-benzimidazol-1-yl)methyl)-1H-benzotriazole from N1,N2-bis((1H-benzotriazol-1-yl)methyl)benzene-1,2-diamine (3) and alcohols is described. The synthesis of 3 from macrocyclic aminal 6H,13H-5:12,7:14-dimethanedibenzo-[d,i][1,3,6,8]tetraazecine (DMDBTA, 1) and benzotriazole is also described. Both these methods are simple, isolation of the products from the reaction mixtures is easy, and the yields are good. 相似文献
995.
In Situ and Theoretical Studies for the Dissociation of Water on an Active Ni/CeO2 Catalyst: Importance of Strong Metal–Support Interactions for the Cleavage of O–H Bonds 下载免费PDF全文
Dr. Javier Carrasco Dr. David López‐Durán Dr. Zongyuan Liu Dr. Tomáš Duchoň Dr. Jaime Evans Dr. Sanjaya D. Senanayake Dr. Ethan J. Crumlin Prof. Dr. Vladimir Matolín Dr. José A. Rodríguez Dr. M. Verónica Ganduglia‐Pirovano 《Angewandte Chemie (International ed. in English)》2015,54(13):3917-3921
Water dissociation is crucial in many catalytic reactions on oxide‐supported transition‐metal catalysts. Supported by experimental and density‐functional theory results, the effect of the support on O? H bond cleavage activity is elucidated for nickel/ceria systems. Ambient‐pressure O 1s photoemission spectra at low Ni loadings on CeO2(111) reveal a substantially larger amount of OH groups as compared to the bare support. Computed activation energy barriers for water dissociation show an enhanced reactivity of Ni adatoms on CeO2(111) compared with pyramidal Ni4 particles with one Ni atom not in contact with the support, and extended Ni(111) surfaces. At the origin of this support effect is the ability of ceria to stabilize oxidized Ni2+ species by accommodating electrons in localized f‐states. The fast dissociation of water on Ni/CeO2 has a dramatic effect on the activity and stability of this system as a catalyst for the water‐gas shift and ethanol steam reforming reactions. 相似文献
996.
Abdiel Del-Cid Pamela Ubilla María-Cristina Ravanal Exequiel Medina Inmaculada Vaca Gloria Levicán Jaime Eyzaguirre Renato Chávez 《Applied biochemistry and biotechnology》2014,172(1):524-532
Despite their potential biotechnological applications, cold-active xylanolytic enzymes have been poorly studied. In this work, 38 fungi isolated from marine sponges collected in King George Island, Antarctica, were screened as new sources of cold-active xylanases. All of them showed xylanase activity at 15 and 23 °C in semiquantitative plate assays. One of these isolates, Cladosporium sp., showed the highest activity and was characterized in detail. Cladosporium sp. showed higher xylanolytic activity when grown on beechwood or birchwood xylan and wheat bran, but wheat straw and oat bran were not so good inducers of this activity. The optimal pH for xylanase activity was 6.0, although pH stability was slightly wider (pH 5–7). On the other hand, Cladosporium sp. showed high xylanase activity at low temperatures and very low thermal stability. Interestingly, thermal stability was even lower after culture media were removed and replaced by buffer, suggesting that low molecular component(s) of the culture media could be important in the stabilization of cold-active xylanase activity. To the best of our knowledge, this study is the first report on extracellular xylanase production by fungi associated with Antarctic marine sponges. 相似文献
997.
Thorium(IV) alkyl and aryl complexes of the type (C(5)Me(5))(2)ThR(2)(R = CH(2)Ph, Ph) have been found to mediate the facile ring-opening and dearomatization of the pyridine ring of pyridine N-oxide under ambient conditions to afford the first thorium eta(2)-(O,N)-oximate complexes. 相似文献
998.
Dr. Alexis Tigreros Dr. Sandra-L. Aranzazu María-C. Ríos Prof. Jaime Portilla 《European journal of organic chemistry》2023,26(15):e202300089
A novel family of pyrazolo[1,5-a]pyrimidine-dioxaborinine (PP-DB) hybrid dyes was synthesized by the direct construction of the dioxaborinine (DB) fragment on the pyrazolo[1,5-a]pyrimidine (PP) ring, which implies the formation of four new bonds in a one-pot manner. The dyes’ optical properties were investigated and compared with the starting pyrazolo[1,5-a]pyrimidines; a study evidencing large fluorescence quantum yields in products (φf up to 69 %) due to an intramolecular charge transfer (ICT) process from the PP core to a ring of DB (PP→DB) that is absent in precursors (φf=0.03–0.30). Time-dependent density functional theory (TD-DFT) calculations confirmed the fluorescence process involved in the novel dyes, where their ICT limits the non-radiative process due to the restricted rotation in the D−A system. The present work provides insight into how phenyl and DB ring incorporation impact the optical properties of this new group of hybrids dyes based on PP-DB. 相似文献
999.
Ignacio Benito-Gómez Prof. Luis Méndez Dr. Jaime Suárez Prof. Jimena D. Gorfinkiel Dr. Ismanuel Rabadán 《Chemphyschem》2023,24(19):e202300305
We have investigated the dissociation of a resonant state that can be formed in low energy electron scattering from H2O+. We have chosen the second triplet resonance above the state of H2O+ whose autoionization mainly produces H2O+ ( ). We have considered both dissociation of the resonant state itself, dissociative recombination (DR), or the dissociation of the H2O+ cation after autodetachment, dissociative excitation (DE). The time-evolution of a wave packet on the potential energy surfaces of the resonance and cationic states shows, for the initial conditions studied, that the probability for DR is about 38 % while the probability for DE is negligible. 相似文献
1000.
Kevin M. Holder Benjamin R. Spears Molly E. Huff Morgan A. Priolo Eva Harth Jaime C. Grunlan 《Macromolecular rapid communications》2014,35(10):960-964
Super gas barrier nanocoatings are recently demonstrated by combining polyelectrolytes and clay nanoplatelets with layer‐by‐layer deposition. These nanobrick wall thin films match or exceed the gas barrier of SiOx and metallized films, but they are relatively stiff and lose barrier with significant stretching (≥10% strain). In an effort to impart stretchability, hydrogen‐bonding polyglycidol (PGD) layers are added to an electrostatically bonded thin film assembly of polyethylenimine (PEI) and montmorillonite (MMT) clay. The oxygen transmission rate of a 125‐nm thick PEI‐MMT film increases more than 40x after being stretched 10%, while PGD‐PEI‐MMT trilayers of the same thickness maintain its gas barrier. This stretchable trilayer system has an OTR three times lower than the PEI‐MMT bilayer system after stretching. This report marks the first stretchable high gas barrier thin film, which is potentially useful for applications that require pressurized elastomers.