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441.
Dizinc Lactide Polymerization Catalysts: Hyperactivity by Control of Ligand Conformation and Metallic Cooperativity 下载免费PDF全文
Arnaud Thevenon Dr. Charles Romain Michael S. Bennington Dr. Andrew J. P. White Hannah J. Davidson Prof. Sally Brooker Prof. Charlotte K. Williams 《Angewandte Chemie (International ed. in English)》2016,55(30):8680-8685
Understanding how to moderate and improve catalytic activity is critical to improving degradable polymer production. Here, di‐ and monozinc catalysts, coordinated by bis(imino)diphenylamido ligands, show remarkable activities and allow determination of the factors controlling performance. In most cases, the dizinc catalysts significantly out‐perform the monozinc analogs. Further, for the best dizinc catalyst, the ligand conformation controls activity: the catalyst with “folded” ligand conformation shows turnover frequency (TOF) values up to 60 000 h?1 (0.1 mol % loading, 298 K, [LA]=1 m ), whilst that with a “planar” conformation is much slower, under similar conditions (TOF=30 h?1). Dizinc catalysts also perform very well under immortal conditions, showing improved control, and are able to tolerate loadings as low as 0.002 mol % whilst conserving high activity (TOF=12 500 h?1). 相似文献
442.
Daniela Torres-Díaz Dr. Romain Basalgète Assoc. Prof. Mathieu Bertin Prof. Jean-Hugues Fillion Prof. Xavier Michaut Assoc. Prof. Lionel Amiaud Prof. Anne Lafosse 《Chemphyschem》2023,24(9):e202200912
X-Ray irradiation of interstellar ice analogues has recently been proven to induce desorption of molecules, thus being a potential source for the still-unexplained presence of gaseous organics in the coldest regions of the interstellar medium, especially in protoplanetary disks. The proposed desorption mechanism involves the Auger decay of excited molecules following soft X-ray absorption, known as X-ray induced electron-stimulated desorption (XESD). Aiming to quantify electron induced desorption in XESD, we irradiated pure methanol (CH3OH) ices at 23 K with 505 eV electrons, to simulate the Auger electrons originating from the O 1s core absorption. Desorption yields of neutral fragments and the effective methanol depletion cross-section were quantitatively determined by mass spectrometry. We derived desorption yields in molecules per incident electron for CO, CO2, CH3OH, CH4/O, H2O, H2CO, C2H6 and other less abundant but more complex organic products. We obtained desorption yields remarkably similar to XESD values. 相似文献
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445.
Hervé Dekkiche Antoine Buisson Adam Langlois Paul‐Ludovic Karsenti Prof. Laurent Ruhlmann Dr. Romain Ruppert Prof. Pierre Harvey 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(30):10484-10493
We report the preparation of several new porphyrin homodimers bridged by a platinum(II) ion in which very intense electronic communication through the coordination link occurs. Moreover, the synthesis of a new porphyrin dyad and its photophysical properties are reported. This dyad exhibits the fastest singlet energy transfer ever reported for synthetic systems between a zinc(II) porphyrin and a porphyrin free base. This extremely fast transfer (~100 femtoseconds) is in the same range as the fastest one measured in natural systems. This feature is due to the platinum(II) linker, which allows for strong MO couplings between the two porphyrin units as experimentally supported by electrochemistry and corroborated by DFT computations. 相似文献
446.
Romain Linard Nerea Zaldua Thomas Josse Julien De Winter Manuela Zubitur Agurtzane Mugica Amaia Iturrospe Arantxa Arbe Olivier Coulembier Alejandro J. Müller 《Macromolecular rapid communications》2016,37(20):1676-1681
The synthesis of symmetric cyclo poly(ε‐caprolactone)–block–poly(l (d )‐lactide) (c(PCL–b–PL(D)LA)) by combining ring‐opening polymerization of ε‐caprolactone and lactides and subsequent click chemistry reaction of the linear precursors containing antagonist functionalities is presented. The two blocks can sequentially crystallize and self‐assemble into double crystalline spherulitic superstructures. The cyclic chain topology significantly affects both the nucleation and the crystallization of each constituent, as gathered from a comparison of the behavior of linear precursors and cyclic block copolymers. The stereochemistry of the PLA block does not have a significant effect on the nonisothermal crystallization of both linear and cyclo PCL‐b‐PDLA and PCL‐b‐PLLA copolymers.
447.
Guillaume Lafitte Veronique Parnet Romain Pierre Catherine Raffin Rodolphe Vatinel Branislav Musicki Loic Tomas Claire Bouix-Peter Gilles Ouvry Sebastien Daver Jean-Marie Arlabosse Jean-Guy Boiteau Thibaud Gerfaud Craig S. Harris 《Tetrahedron》2018,74(40):5974-5986
During our research looking for novel inverse agonists of RORγt, we identified a potent sulfoximine-based modulator as one of our pre-clinical candidates for the topical treatment for psoriasis. Herein, we describe the various routes we evaluated during the lead generation and optimization phases and the final route chosen for scale-up to deliver the first 100?g of API. 相似文献
448.
Copéret C Chabanas M Petroff Saint-Arroman R Basset JM 《Angewandte Chemie (International ed. in English)》2003,42(2):156-181
Surface organometallic chemistry is an area of heterogeneous catalysis which has recently emerged as a result of a comparative analysis of homogeneous and heterogeneous catalysis. The chemical industry has often favored heterogeneous catalysis, but the development of better catalysts has been hindered by the presence of numerous kinds of active sites and also by the low concentration of active sites. These factors have precluded a rational improvement of these systems, hence the empirical nature of heterogeneous catalysis. Catalysis is primarily a molecular phenomenon, and it must involve well-defined surface organometallic intermediates and/or transition states. Thus, one must be able to construct a well-defined active site, test its catalytic performance, and assess a structure-activity relationship, which will be used, in turn-as in homogeneous catalysis-to design better catalysts.By the transfer of the concepts and tools of molecular organometallic chemistry to surfaces, surface organometallic chemistry can generate well-defined surface species by understanding the reaction of organometallic complexes with the support, which can be considered as a rigid ligand. This new approach to heterogeneous catalysis can bring molecular insight to the design of new catalysts and even allow the discovery of new reactions (Ziegler-Natta depolymerization and alkane metathesis). After more than a century of existence, heterogeneous catalysis can still be improved and will play a crucial role in solving current problems. It offers an answer to economical and environmental problems faced by industry in the production of molecules (agrochemicals, petrochemicals, pharmaceuticals, polymers, basic chemicals). 相似文献
449.
Sophie Romain Dr. Carole Duboc Dr. Frank Neese Prof. Eric Rivière Dr. Lyall R. Hanton Dr. Allan G. Blackman Dr. Christian Philouze Dr. Jean‐Claude Leprêtre Prof. Alain Deronzier Dr. Marie‐Noëlle Collomb Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(4):980-988
The mononuclear manganese bis‐terpyridine complex [Mn(tolyl‐terpy)2](X)3 ( 1 (X)3; X=BF4, ClO4, PF6; tolyl‐terpy=4′‐(4‐methylphenyl)‐2,2′:6′,2“‐terpyridine), containing Mn in the unusual +III oxidation state, has been isolated and characterised. The 1 3+ ion is a rare example of a mononuclear MnIII complex stabilised solely by neutral N ligands. Complex 1 3+ is obtained by electrochemical oxidation of the corresponding MnII compound 1 2+ in anhydrous acetonitrile. Under these conditions the cyclic voltammogram of 1 2+ exhibits not only the well‐known MnII/MnIII oxidation at E1/2=+0.91 V versus Ag/Ag+ (+1.21 V vs. SCE) but also a second metal‐based oxidation process corresponding to MnIII/MnIV at E1/2=+1.63 V (+1.93 V vs. SCE). Single crystals of 1 (PF6)3?2 CH3CN were obtained by an electrocrystallisation procedure. X‐ray analysis unambiguously revealed its tetragonally compressed octahedral geometry and high‐spin character. The electronic properties of 1 3+ were investigated in detail by magnetic measurements and theoretical calculations, from which a D value of +4.82 cm?1 was precisely determined. Density functional and complete active space self consistent field ab initio calculations both correctly predict a positive sign of D, in agreement with the compressed tetragonal distortion observed in the X‐ray structure of 1 (PF6)3?2 CH3CN. The different contributions to D were calculated, and the results show that 1) the spin–orbit coupling part (+2.593 cm?1) is predominant compared to the spin–spin interaction (+1.075 cm?1) and 2) the excited triplet states make the dominant contribution to the total D value. 相似文献
450.
The PC-SAFT equation of state is a very popular and promising model for fluids that employs a complicated pressure-explicit mathematical function (and can therefore not be solved analytically at a specified pressure and temperature, contrary to classical cubic equations). In this work, we demonstrate that in case of pure fluids, the PC-SAFT equation may exhibit up to five different volume roots whereas cubic equations give at the most three volume roots (and yet, only one or two volume roots have real significance). The consequence of this strongly atypical behaviour is the existence of two different fluid–fluid coexistence lines (the vapour-pressure curve and an additional liquid–liquid equilibrium curve) and two critical points for a same pure component, which is obviously physically inconsistent. In addition to n-alkanes, nearly 60 very common pure components (branched alkanes, cycloalkanes, aromatics, esters, gases, and so on) were tested out and without any exception, we can claim that all of them exhibit this undesired behaviour. In addition, such similar phenomena (i.e. existence of more than three volume roots) may also arise with mixtures. From a computational point of view, most of the algorithms used for solving equations of state only search for three roots at the most and are thus likely to be inefficient when an equation of state gives more than three volume roots. To overcome this limitation, a simple procedure allowing to identify all the possible volume roots of an equation of state is proposed. 相似文献