全文获取类型
收费全文 | 537篇 |
免费 | 35篇 |
国内免费 | 2篇 |
专业分类
化学 | 407篇 |
晶体学 | 1篇 |
力学 | 8篇 |
数学 | 29篇 |
物理学 | 129篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 21篇 |
2021年 | 33篇 |
2020年 | 25篇 |
2019年 | 25篇 |
2018年 | 33篇 |
2017年 | 12篇 |
2016年 | 28篇 |
2015年 | 17篇 |
2014年 | 25篇 |
2013年 | 22篇 |
2012年 | 33篇 |
2011年 | 35篇 |
2010年 | 37篇 |
2009年 | 17篇 |
2008年 | 43篇 |
2007年 | 32篇 |
2006年 | 36篇 |
2005年 | 26篇 |
2004年 | 16篇 |
2003年 | 13篇 |
2002年 | 13篇 |
2001年 | 2篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 7篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1991年 | 1篇 |
1988年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有574条查询结果,搜索用时 15 毫秒
21.
Prof. Marcus W. Drover Maeve C. Dufour Lindsay A. Lesperance-Nantau Rayni P. Noriega Dr. Kirill Levin Prof. Robert W. Schurko 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(49):11180-11186
Herein, we establish the preparation, characterization, and reactivity of a new diphosphine ligand, 1,2-bis(di(3-dicyclohexylboraneyl)propylphosphino)ethane (P2BCy4), a scaffold that contains four pendant boranes. An entryway into the coordination chemistry of P2BCy4 is established by using nickel, providing the octaboraneyl complex [Ni(P2BCy4)2]—this species contains a boron-rich secondary coordination sphere that reacts readily with Lewis bases. In the case of 4,4′-bipyridine, an air-sensitive coordination polymer is obtained. Characterization of this material by solid-state NMR and EPR spectroscopy reveals the presence of a charge-transfer polymer, which forms as a function of intramolecular Ni→4,4′-bpy electron transfer (ET), providing an array of oxidized nickel sites and reduced 4,4′-bpy radical anion sites. Notably, the related intermolecular reaction between the model fragments [Ni(dnppe)2] (dnppe=1,2-bis(di-n-propylphosphino)ethane) and a bis(boraneyl)-protected 4,4′-bpy, provides no ET. Overall, the P2BCy4 fragment provides a unique opportunity for Lewis base activation, in one case allowing for the facile construction of monomers for incorporation into redox-active macromolecules. 相似文献
22.
Kirill F. Sheberstov Eduard Sistaré Guardiola Damien Jeannerat 《Magnetic resonance in chemistry : MRC》2020,58(5):376-389
The fundamental concept of phase discussed in this tutorial aimed at providing students with an explanation of the delays and processing parameters they may find in nuclear magnetic resonance (NMR) pulse programs. We consider the phase of radio-frequency pulses, receiver, and magnetization and how all these parameters are related to phases and offsets of signals in spectra. The impact of the off-resonance effect on the phase of the magnetization is discussed before presenting an overview of how adjustment of the time reference of the free induction decay avoids first-order correction of the phase of spectra. The main objective of this tutorial is to show how the relative phase of a pulse and the receiver can be used to change the reference frequency along direct and indirect dimensions of NMR experiments. Unusual of phase incrementation with non-90° angles will be illustrated on one- and two-dimensional NMR spectra. 相似文献
23.
Kirill Kulish Cosimo Boldrini Dr. Marta Castiñeira Reis Dr. Juana M. Pérez Prof. Dr. Syuzanna R. Harutyunyan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(68):15843-15846
Two-step dearomative functionalization of naphthols promoted by Lewis acids and copper(I) catalysis was developed. Initially, Lewis acid complexation inverted the electronic properties of the ring and established an equilibrium with the dearomatized counterpart. Subsequent trapping of the dearomatized intermediate with organometallics as well as organophosphines was demonstrated and provided the corresponding dearomatized products. 相似文献
24.
Vereshchagin Anatoly N. Karpenko Kirill A. Elinson Michail N. Goloveshkin Alexander S. Ushakov Ivan E. Egorov Mikhail P. 《Research on Chemical Intermediates》2018,44(9):5623-5634
Research on Chemical Intermediates - A novel four-component stereoselective synthesis of polysubstituted piperidines is reported. The Knoevenagel–Michael–Mannich cascade of two... 相似文献
25.
Oleg?G.?Salnikov Danila?A.?Barskiy Dudari?B.?Burueva Yulia?K.?Gulyaeva Bair?S.?Balzhinimaev Kirill?V.?Kovtunov Igor?V.?KoptyugEmail author 《Applied magnetic resonance》2014,45(10):1051-1061
Hydrogenation of propyne to propene over Pd/aluminosilicate fiberglass catalyst in the temperature range 175–350 °C was investigated with the use of parahydrogen-induced polarization (PHIP) technique. Activation energies for both pairwise and non-pairwise H2 addition routes were estimated. It was found that at 175–275 °C the activation energies for hydrogen addition to the triple bond of propyne have similar values (about 60–70 kJ/mol) for both routes of hydrogen addition. At higher temperatures (275–350 °C), the rate constant for pairwise hydrogen addition reaches a maximum value while the rate constant for non-pairwise hydrogen addition continues to increase with increasing temperature. 相似文献
26.
Kirill A. Kopotun 《Journal of Approximation Theory》1998,94(3):481-493
It is shown that an algebraic polynomial of degree k−1 which interpolates ak-monotone functionfatkpoints, sufficiently approximates it, even if the points of interpolation are close to each other. It is well known that this result is not true in general for non-k-monotone functions. As an application, we prove a (positive) result on simultaneous approximation of ak-monotone function and its derivatives inLp, 0<p<1, metric, and also show that the rate of the best algebraic approximation ofk-monotone functions (with bounded (k−2)nd derivatives inLp, 1<p<∞, iso(n−k/p). 相似文献
27.
Koptyug IV Kovtunov KV Burt SR Anwar MS Hilty C Han SI Pines A Sagdeev RZ 《Journal of the American Chemical Society》2007,129(17):5580-5586
We demonstrate the creation and observation of para-hydrogen-induced polarization in heterogeneous hydrogenation reactions. Wilkinson's catalyst, RhCl(PPh3)3, supported on either modified silica gel or a polymer, is shown to hydrogenate styrene into ethylbenzene and to produce enhanced spin polarizations, observed through NMR, when the reaction was performed with H2 gas enriched in the para spin isomer. Furthermore, gaseous phase para-hydrogenation of propylene to propane with two catalysts, the Wilkinson's catalyst supported on modified silica gel and Rh(cod)(sulfos) (cod = cycloocta-1,5-diene; sulfos = -O3S(C6H4)CH2C(CH2PPh2)3) supported on silica gel, demonstrates heterogeneous catalytic conversion resulting in large spin polarizations. These experiments serve as a direct verification of the mechanism of heterogeneous hydrogenation reactions involving immobilized metal complexes and can be potentially developed into a practical tool for producing catalyst-free fluids with highly polarized nuclear spins for a broad range of hyperpolarized NMR and MRI applications. 相似文献
28.
Deraeve C Guo Z Bon RS Blankenfeldt W DiLucrezia R Wolf A Menninger S Stigter EA Wetzel S Choidas A Alexandrov K Waldmann H Goody RS Wu YW 《Journal of the American Chemical Society》2012,134(17):7384-7391
Post-translational attachment of geranylgeranyl isoprenoids to Rab GTPases, the key organizers of intracellular vesicular transport, is essential for their function. Rab geranylgeranyl transferase (RabGGTase) is responsible for prenylation of Rab proteins. Recently, RabGGTase inhibitors have been proposed to be potential therapeutics for treatment of cancer and osteoporosis. However, the development of RabGGTase selective inhibitors is complicated by its structural and functional similarity to other protein prenyltransferases. Herein we report identification of the natural product psoromic acid (PA) that potently and selectively inhibits RabGGTase with an IC(50) of 1.3 μM. Structure-activity relationship analysis suggested a minimal structure involving the depsidone core with a 3-hydroxyl and 4-aldehyde motif for binding to RabGGTase. Analysis of the crystal structure of the RabGGTase:PA complex revealed that PA forms largely hydrophobic interactions with the isoprenoid binding site of RabGGTase and that it attaches covalently to the N-terminus of the α subunit. We found that in contrast to other protein prenyltransferases, RabGGTase is autoinhibited through N-terminal (α)His2 coordination with the catalytic zinc ion. Mutation of (α)His dramatically enhances the reaction rate, indicating that the activity of RabGGTase is likely regulated in vivo. The covalent binding of PA to the N-terminus of the RabGGTase α subunit seems to potentiate its interaction with the active site and explains the selectivity of PA for RabGGTase. Therefore, psoromic acid provides a new starting point for the development of selective RabGGTase inhibitors. 相似文献
29.
Kirill Nikitin Helge Müller-Bunz Gérard Jaouen Michael J. McGlinchey 《Journal of organometallic chemistry》2010,695(4):595-608
The McMurry coupling of (tetraphenylcyclobutadiene)cobalt(cyclopentadienyl) ketones, (C4Ph4)Co[C5H4C(O)R], where R = Me, 3a, or Et, 3b, with a range of substituted benzophenones furnished a series of cobaltifens, organometallic analogues of tamoxifen whereby a phenyl ring has been replaced by an organo-cobalt sandwich moiety. These systems of the general formula (η4-C4Ph4)Co[η5-C5H4C(R)C(Ar)Ar′], where R = Me or Et, and Ar = Ar′ = p-C6H4X where X is OH, 2a and 2b, OMe, 2c and 2d, OBn, 2e and 2f, or O(CH2)2NMe2, 12a and 12b, and where Ar = C6H4OH and Ar′ = C6H4O(CH2)2NMe2, 2g and 2h, have been characterised by NMR spectroscopy and/or X-ray crystallography. The effect of 2a and 2b, 2g and 2h, and 12a and 12b on the growth of MCF-7 (hormone-dependent) and MDA-MB-231 (hormone-independent breast cancer cells) was studied. The dihydroxycobaltifens 2a and 2b exhibit a strong estrogenic effect on MCF-7 cells while the aminoalkyl-hydroxycobaltifens, 2g and 2h, were found to be only slightly cytotoxic on MDA-MB-231 cells (IC50 = 27.5 and 17 μM); surprisingly, however, the bis-(dimethylaminoethoxy)cobaltifens, 12a and 12b were shown to be highly cytotoxic towards both cell lines (IC50 = 3.8 and 2.5 μM). 相似文献
30.
Polar Red‐Emitting Rhodamine Dyes with Reactive Groups: Synthesis,Photophysical Properties,and Two‐Color STED Nanoscopy Applications 下载免费PDF全文
Dr. Kirill Kolmakov Dr. Christian A. Wurm M. Sc. Dirk N. H. Meineke Dipl.‐Biol. Fabian Göttfert Prof. Vadim P. Boyarskiy Dr. Vladimir N. Belov Prof. Stefan W. Hell 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(1):146-157
The synthesis, reactivity, and photophysical properties of new rhodamines with intense red fluorescence, two polar residues (hydroxyls, primary phosphates, or sulfonic acid groups), and improved hydrolytic stability of the amino‐reactive sites (NHS esters or mixed N‐succinimidyl carbonates) are reported. All fluorophores contain an N‐alkyl‐1,2‐dihydro‐2,2,4‐trimethylquinoline fragment, and most of them bear a fully substituted tetrafluoro phenyl ring with a secondary carboxamide group. The absorption and emission maxima in water are in the range of 635–639 and 655–659 nm, respectively. A vastly simplified approach to red‐emitting rhodamines with two phosphate groups that are compatible with diverse functional linkers was developed. As an example, a phosphorylated dye with an azide residue was prepared and was used in a click reaction with a strained alkyne bearing an N‐hydroxysuccinimid (NHS) ester group. This method bypasses the undesired activation of phosphate groups, and gives an amphiphilic amino‐reactive dye, the solubility and distribution of which between aqueous and organic phases can be controlled by varying the pH. The presence of two hydroxyl groups and a phenyl ring with two carboxyl residues in the dyes with another substitution pattern is sufficient for providing the hydrophilic properties. Selective formation of a mono‐N‐hydroxysuccinimidyl ester from 5‐carboxy isomer of this rhodamine is reported. The fluorescence quantum yields varied from 58 to 92 % for free fluorophores, and amounted to 18–64 % for antibody conjugates in aqueous buffers. The brightness and photostability of these fluorophores facilitated two‐color stimulated emission depletion (STED) fluorescence nanoscopy of biological samples with high contrast and minimal background. Selecting a pair of fluorophores with absorption/emission bands at 579/609 and 635/655 nm enabled two‐color channels with low cross‐talk and negligible background at approximately 40 nm resolution. 相似文献