全文获取类型
收费全文 | 431篇 |
免费 | 29篇 |
专业分类
化学 | 306篇 |
晶体学 | 2篇 |
力学 | 11篇 |
数学 | 54篇 |
物理学 | 87篇 |
出版年
2023年 | 10篇 |
2022年 | 10篇 |
2021年 | 14篇 |
2020年 | 18篇 |
2019年 | 12篇 |
2018年 | 5篇 |
2017年 | 8篇 |
2016年 | 24篇 |
2015年 | 21篇 |
2014年 | 28篇 |
2013年 | 30篇 |
2012年 | 29篇 |
2011年 | 38篇 |
2010年 | 22篇 |
2009年 | 20篇 |
2008年 | 26篇 |
2007年 | 19篇 |
2006年 | 16篇 |
2005年 | 16篇 |
2004年 | 18篇 |
2003年 | 12篇 |
2002年 | 9篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1997年 | 5篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 8篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 6篇 |
1990年 | 2篇 |
1988年 | 1篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1979年 | 2篇 |
1909年 | 1篇 |
排序方式: 共有460条查询结果,搜索用时 15 毫秒
451.
Electrophiles such as Me(+), Ag(+), or protons react with the five-coordinate Ir(III) complex [IrClH(biPSi)] (biPSi = κ-P,P,Si-Si(Me){(CH(2))(3)PPh(2)}(2)) by abstracting its chloride ligand. The resulting species can be stabilized by a variety of L ligands to give the cationic complexes [IrH(biPSi)L(2)](+). The derivative [IrH(biPSi)(NCMe)(2)](+) has been subjected to a kinetic study regarding the facile dissociations of its acetonitrile ligands. The presence of water changes the course of the reaction producing dihydride complexes that contain the silanol ligand κ-O,P,P-HOSi(Me){(CH(2))(3)PPh(2)}(2) (biPSiOH). The water activation product [IrH(2)(biPSiOH)(NCMe)](CF(3)SO(3)) undergoes insertion reactions with ethylene and phenylacetylene. The use of hydrolyzable fluorinated counterions such as PF(6)(-) or BF(4)(-) further modifies the reaction by provoking the incorporation of fluoride at the silicon atom of the former biPSi ligand. The dihydride resulting after such a process, [IrH(2)(biPSiF)(NCMe)(2)]BF(4) (biPSiF = κ-P(2)-FSi(Me){(CH(2))(3)PPh(2)}(2)), displays a trans-chelating diphosphine ligand. When dehydrogenating the Ir center, spontaneously or using ethylene as hydrogen acceptor, the diphosphine backbone undergoes a Si-C bond cleavage leading to a new Ir(III) species with κ-P,Si and κ-C,P chelate ligands. 相似文献
452.
Gitto R De Luca L Ferro S Agnello S Russo E De Sarro G Chimirri A 《Chemical & pharmaceutical bulletin》2010,58(12):1602-1605
We have previously disclosed that some 6,7-dimethoxyisoquinoline derivatives are able to produce anticonvulsant effects in different animal models of epilepsy. Following these studies this paper describes the synthesis of a small series of new 1-aryl-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolines strictly related to previously reported analogues. This novel series of isoquinolines was designed on the basis of well defined structure-active relationship (SAR) information already acquired for this class of anticonvulsant agents. The pharmacological effects of the new synthesized compounds were evaluated against audiogenic seizures in Dilute Brown non-Agouti (DBA/2) mice. The preliminary pharmacological screening led to the identification of a new active molecule the 2-acetyl-1-(4'-methylphenyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline (6d) that displayed significant anticonvulsant activity. Computational studies helped to rationalize these obtained pharmacological results. 相似文献
453.
Catalytic Promiscuity of Transaminases: Preparation of Enantioenriched β‐Fluoroamines by Formal Tandem Hydrodefluorination/Deamination 下载免费PDF全文
Dr. Aníbal Cuetos Marina García‐Ramos Eva‐Maria Fischereder Dr. Alba Díaz‐Rodríguez Prof. Gideon Grogan Prof. Vicente Gotor Prof. Wolfgang Kroutil Dr. Iván Lavandera 《Angewandte Chemie (International ed. in English)》2016,55(9):3144-3147
Transaminases are valuable enzymes for industrial biocatalysis and enable the preparation of optically pure amines. For these transformations they require either an amine donor (amination of ketones) or an amine acceptor (deamination of racemic amines). Herein transaminases are shown to react with aromatic β‐fluoroamines, thus leading to simultaneous enantioselective dehalogenation and deamination to form the corresponding acetophenone derivatives in the absence of an amine acceptor. A series of racemic β‐fluoroamines was resolved in a kinetic resolution by tandem hydrodefluorination/deamination, thus giving the corresponding amines with up to greater than 99 % ee. This protocol is the first example of exploiting the catalytic promiscuity of transaminases as a tool for novel transformations. 相似文献
454.
Hugo Fanlo‐Virgós Dr. Andrea‐Nekane R. Alba Saleh Hamieh Mathieu Colomb‐Delsuc Prof. Dr. Sijbren Otto 《Angewandte Chemie (International ed. in English)》2014,53(42):11346-11350
In biology enzyme concentrations are continuously regulated, yet for synthetic catalytic systems such regulatory mechanisms are underdeveloped. We now report how a substrate of a chemical reaction induces the formation of its own catalyst from a dynamic molecular network. After complete conversion of the substrate, the network disassembles the catalyst. These results open up new opportunities for controlling catalysis in synthetic chemical systems. 相似文献
455.
A Trifluorinated Thiazoline Scaffold Leading to Pro‐apoptotic Agents Targeting Prohibitins 下载免费PDF全文
Dr. Alba Pérez‐Perarnau Dr. Sara Preciado Dr. Claudia Mariela Palmeri Cristina Moncunill‐Massaguer Dr. Daniel Iglesias‐Serret Dr. Diana M. González‐Gironès Dr. Miriam Miguel Dr. Satoki Karasawa Dr. Satoshi Sakamoto Dr. Ana M. Cosialls Dr. Camila Rubio‐Patiño José Saura‐Esteller Dr. Rosario Ramón Dr. Laia Caja Dr. Isabel Fabregat Dr. Gabriel Pons Prof. Hiroshi Handa Prof. Fernando Albericio Prof. Joan Gil Prof. Rodolfo Lavilla 《Angewandte Chemie (International ed. in English)》2014,53(38):10150-10154
A new class of small molecules, with an unprecedented trifluorothiazoline scaffold, were synthesized and their pro‐apoptotic activity was evaluated. With an EC50 in the low micromolar range, these compounds proved to be potent inducers of apoptosis in a broad spectrum of tumor cell lines, regardless of the functional status of p53. Fast structure–activity relationship studies allowed the preparation of the strongest apoptosis‐inducing candidate. Using a high performance affinity purification approach, we identified prohibitins 1 and 2, key proteins involved in the maintenance of cell viability, as the targets for these compounds. 相似文献
456.
NMR Fingerprints of the Drug‐like Natural‐Product Space Identify Iotrochotazine A: A Chemical Probe to Study Parkinson’s Disease 下载免费PDF全文
Dr. Tanja Grkovic Dr. Rebecca H. Pouwer Marie‐Laure Vial Luca Gambini Alba Noël Dr. John N. A. Hooper Dr. Stephen A. Wood Dr. George D. Mellick Prof. Dr. Ronald J. Quinn 《Angewandte Chemie (International ed. in English)》2014,53(24):6070-6074
The NMR spectrum of a mixture of small molecules is a fingerprint of all of its components. Herein, we present an NMR fingerprint method that takes advantage of the fact that fractions contain simplified NMR profiles, with minimal signal overlap, to allow the identification of unique spectral patterns. The approach is exemplified in the identification of a novel natural product, iotrochotazine A ( 1 ), sourced from an Australian marine sponge Iotrochota sp. Compound 1 was used as a chemical probe in a phenotypic assay panel based on human olfactory neurosphere‐derived cells (hONS) from idiopathic Parkinson’s disease patients. Compound 1 at 1 μM was not cytotoxic but specifically affected the morphology and cellular distribution of lysosomes and early endosomes. 相似文献
457.
Gulías M Collado A Trillo B López F Oñate E Esteruelas MA Mascareñas JL 《Journal of the American Chemical Society》2011,133(20):7660-7663
We report a ruthenium-catalyzed (2 + 2) intramolecular cycloaddition of allenes and alkenes. We have found that the use of the ruthenium complex RuH(2)Cl(2)(P(i)Pr(3))(2), which has previously gone unnoticed in catalytic applications, is crucial for the observed reactivity. The reaction proceeds under mild conditions and is fully diastereoselective, providing a practical entry to a variety of bicyclo[3.2.0]heptane skeletons featuring cyclobutane rings. 相似文献
458.
Oxazolones or azlactones are among the most‐common starting materials for the synthesis of quaternary amino acids. Since the seminal works of Steglich and co‐workers until the recent examples from Ooi and co‐workers, azlactones have been the focus of intense research. Oxazolones are also widely used in organometallic chemistry; however, with the “renaissance” of organocatalysis, this reagent has emerged as an important starting material for a broad range of new organocatalytic asymmetric methodologies. In this Focus Review, we aim to cover all of these new organocatalytic methodologies. We begin by discussing the dynamic kinetic resolution reactions developed with azlactones. Then, we disclose the organocatalytic rearrangements. Finally, we focus on the use of oxazolones as nucleophiles in organocatalytic processes. 相似文献
459.
In this work the deformation and fracture behavior of PP/EVOH blends compatibilized with ionomer Na+ at room and low temperature was studied. Uniaxial tensile tests on dumb-bell samples and fracture tests on single-edge notched bending (SENB) specimens were performed for 10 wt.% and 20 wt.% EVOH blends with different ionomer content at 23 °C and −20 °C. The incorporation of EVOH to PP led to less ductile materials in tension as judged by the lower values of the ultimate tensile strain displayed by all PP/EVOH blends in comparison to neat PP. In contrast, the ionomer Na+ addition partially counteracted this effect. The compatibilizing effect of ionomer Na+ was also evident in fracture results since higher values of the fracture parameter were obtained for the ternary blends. SEM observations also confirmed this effect. On the other hand, PP/EVOH blends exhibited different fracture behavior with test temperature. All blends showed “pseudo stable” behavior at room temperature characterized by apparently stable crack growth that could not be externally controlled. On the contrary, blends behaved as semi-brittle at −20 °C with some amount of stable crack growth preceding unstable brittle fracture. Finally, irrespectively of the temperature or the ionomer content all PP/EVOH blends exhibited more ductile fracture behavior with a higher tendency to stable crack propagation than neat polypropylene. 相似文献
460.
Dr. Ana B. Caballero Laia Terol‐Ordaz Dr. Alba Espargaró Guillem Vázquez Dr. Ernesto Nicolás Dr. Raimon Sabaté Prof. Patrick Gamez 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(21):7268-7280
Brain copper imbalance plays an important role in amyloid‐β aggregation, tau hyperphosphorylation, and neurotoxicity observed in Alzheimer's disease (AD). Therefore, the administration of biocompatible metal‐binding agents may offer a potential therapeutic solution to target mislocalized copper ions and restore metallostasis. Histidine‐containing peptides and proteins are excellent metal binders and are found in many natural systems. The design of short peptides showing optimal binding properties represents a promising approach to capture and redistribute mislocalized metal ions, mainly due to their biocompatibility, ease of synthesis, and the possibility of fine‐tuning their metal‐binding affinities in order to suppress unwanted competitive binding with copper‐containing proteins. In the present study, three peptides, namely HWH , HKCH , and HAH , have been designed with the objective of reducing copper toxicity in AD. These tripeptides form highly stable albumin‐like complexes, showing higher affinity for CuII than that of Aβ(1‐40). Furthermore, HWH , HKCH , and HAH act as very efficient inhibitors of copper‐mediated reactive oxygen species (ROS) generation and prevent the copper‐induced overproduction of toxic oligomers in the initial steps of amyloid aggregation in the presence of CuII ions. These tripeptides, and more generally small peptides including the sequence His‐Xaa‐His at the N‐terminus, may therefore be considered as promising motifs for the future development of new and efficient anti‐Alzheimer drugs. 相似文献