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991.
Laurence R. Doyle Ashley J. Wooles Stephen T. Liddle 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(20):6746-6749
Although reductive cleavage of dinitrogen (N2) to nitride (N3?) and hydrogenation with dihydrogen (H2) to yield ammonia (NH3) is accomplished in heterogeneous Haber–Bosch industrial processes on a vast scale, sequentially coupling these elementary reactions together with a single metal complex remains a major challenge for homogeneous molecular complexes. Herein, we report that the reaction of a chloro titanium triamidoamine complex with magnesium effects complete reductive cleavage of N2 to give a dinitride dititanium dimagnesium ditriamidoamine complex. Tandem H2 splitting by a phosphine–borane frustrated Lewis pair (FLP) shuttles H atoms to the N3?, evolving NH3. Isotope labelling experiments confirmed N2 and H2 fixation. Though not yet catalytic, these results give unprecedented insight into coupling N2 and H2 cleavage and N?H bond formation steps together, highlight the importance of heterobimetallic cooperativity in N2 activation, and establish FLPs in NH3 synthesis. 相似文献
992.
ABSTRACTThe addition of protein to fruit, as a protein-enriched food, can modify the nutritional intake of both components. To mimic the protein-polyphenol interaction, a model product composed of whey protein (WP) and epicatechin (epi) was evaluated with various compositions (0%–20% polyphenol/protein). The effect of high pressure (HP) processing as a preservation method was tested and compared with control samples. The formation of complexes was evaluated by nephelometry, and oxygen radical absorbance capacity (ORAC) measurement was used to examine the variation in antioxidant capacity. Interactions were observed at the proportion of epi/WP 1%–2% and 15%–20% mass ratio. A high increase in turbidity, due to WP denaturation, was observed after HP processing. ORAC assays show that the antioxidant capacity of the epicatechin solution was improved by 22% with WP addition at epi/WP 1%. Preservation by high pressure slightly reduced antioxidant capacity. 相似文献
993.
Laurence Brassart Kejie Zhao Zhigang Suo 《International Journal of Solids and Structures》2013,50(7-8):1120-1129
Of all materials, silicon has the highest capacity to store lithium, and is being developed as an electrode for lithium-ion batteries. Upon absorbing a large amount of lithium, the electrode swells greatly, with a volumetric change up to 300%. The swelling is inevitably constrained in practice, often leading to stress and fracture. Evidence has accumulated that the swelling-induced stress can be partially relieved by plastic flow, and that electrodes of small feature sizes can survive many cycles of lithiation and delithiation without fracture. Here we simulate a particle of an electrode subject to cyclic lithiation and delithiation. A recently developed theory of concurrent large swelling and finite-strain plasticity is used to co-evolve fields of stress, deformation, concentration of lithium, and chemical potential of lithium. We identify three types of behavior. When the yield strength is high and the charging rate is low, the entire particle deforms elastically in all cycles. When the yield strength is low and the charging rate is high, the particle (or part of it) undergoes cyclic plasticity. Under intermediate conditions, the particle exhibits the shakedown behavior: part of the particle flows plastically in a certain number of initial cycles, and then the entire particle remains elastic in subsequent cycles. We discuss the effect of the three types of behavior on the capacity and the electrochemical efficiency. 相似文献
994.
Juan Camilo Uribe Nicolas Jarrin Robert Prosser Dominique Laurence 《Flow, Turbulence and Combustion》2010,85(2):181-197
The flow around a trailing edge is computed with a new hybrid method designed to more clearly separate the effects of total
and sub-grid turbulent stress-modelling on the time-averaged and instantaneous velocity fields, and in turn, mean momentum
and kinetic energy balances. These two velocity fields independently define Reynolds averaged and sub-grid-scale viscosities,
and distinct stresses, at the same location. In particular, resolved eddies can emerge, or sweep in and out of the Reynolds
averaged near wall layer, without being dampened by higher levels of the viscosity in this RANS dominated layer. The two-field
hybrid model, first tested on channel flows, gives accurate predictions of mean velocities and stresses for different Reynolds
numbers and coarse meshes. For the trailing edge flow the results of the hybrid model are close to the reference fine LES
for mean velocity and turbulent content, whereas the DES-SST on the same coarse mesh gives too early separation. 相似文献
995.
A Zinc Phthalocyanine Based Periodic Mesoporous Organosilica Exhibiting Charge Transfer to Fullerenes 下载免费PDF全文
Dr. Florian Auras Dr. Yan Li Dr. Florian Löbermann Dr. Markus Döblinger Dr. Jörg Schuster Prof. Laurence M. Peter Prof. Dr. Dirk Trauner Prof. Dr. Thomas Bein 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(46):14971-14975
Periodic mesoporous organosilica (PMO) materials offer a strategy to position molecular semiconductors within a highly defined, porous network. We developed thin films of a new semiconducting zinc phthalocyanine‐bridged PMO exhibiting a face‐centered orthorhombic pore structure with an average pore diameter of 11 nm. The exceptional degree of order achieved with this PMO enabled us to create thin films consisting of a single porous domain throughout their entire thickness, thus providing maximal accessibility for subsequent incorporation of a complementary phase. The phthalocyanine building blocks inside the pore walls were found to be well‐aggregated, enabling electronic conductivity and extending the light‐harvesting capabilities to the near IR region. Ordered 3D heterojunctions capable of promoting photo‐induced charge transfer were constructed by impregnation of the PMO with a fullerene derivative. When integrated into a photovoltaic device, the infiltrated PMO is capable of producing a high open‐circuit voltage and a considerable photocurrent, which represents a significant step towards potential applications of PMOs in optoelectronics. 相似文献
996.
Quentin?LouveauxEmail author Laurence?A.?Wolsey 《4OR: A Quarterly Journal of Operations Research》2003,1(3):173-207
In this survey we attempt to give a unified presentation of a variety of results on the lifting of valid inequalities, as well as a standard procedure combining mixed integer rounding with lifting for the development of strong valid inequalities for knapsack and single node flow sets. Our hope is that the latter can be used in practice to generate cutting planes for mixed integer programs. The survey contains essentially two parts. In the first we present lifting in a very general way, emphasizing superadditive lifting which allows one to lift simultaneously different sets of variables. In the second, our procedure for generating strong valid inequalities consists of reduction to a knapsack set with a single continuous variable, construction of a mixed integer rounding inequality, and superadditive lifting. It is applied to several generalizations of the 0-1 single node flow set.Received: December 2002, Revised: April 2003, AMS classification:
90C11, 90C27Laurence A. Wolsey: Corresponding author: CORE, Voie du Roman Pays 34, 1348 Louvain-la-Neuve, Belgium. The first author is supported by the FNRS as a research fellow. This paper presents research results of the Belgian Program on Interuniversity Poles of Attraction initiated by the Belgian State, Prime Ministers Office, Science Policy Programming. The scientific responsibility is assumed by the authors.Laurence A. Wolsey: This research was also supported by the European Commission GROWTH Programme, Research Project LISCOS, Large Scale Integrated Supply Chain Optimization Software Based on Branch-and-Cut and Constraint Programming Methods, Contract No. GRDI-1999-10056, and the project TMR-DONET nr. ERB FMRX-CT98-0202. 相似文献
997.
Synthetically generated metallopeptides have the potential to serve a variety of roles in biotechnology applications, but the use of such systems is often hampered by the inability to control secondary reactions. We have previously reported that the Ni(II) complex of the tripeptide lll-asparagine-cysteine-cysteine, lll-Ni(II)-NCC, undergoes metal-facilitated chiral inversion to dld-Ni(II)-NCC, which increases the observed superoxide scavenging activity. However, the mechanism for this process remained unexplored. Electronic absorption and circular dichroism studies of the chiral inversion reaction of Ni(II)-NCC reveal a unique dependence on dioxygen. Specifically, in the absence of dioxygen, the chiral inversion is not observed, even at elevated pH, whereas the addition of O(2) initiates this reactivity and concomitantly generates superoxide. Scavenging experiments using acetaldehyde are indicative of the formation of carbanion intermediates, demonstrating that inversion takes place by deprotonation of the alpha carbons of Asn1 and Cys3. Together, these data are consistent with the chiral inversion being dependent on the formation of a Ni(III)-NCC intermediate from Ni(II)-NCC and O(2). The data further suggest that the anionic thiolate and amide ligands in Ni(II)-NCC inhibit Cα-H deprotonation for the Ni(II) oxidation state, leading to a stable complex in the absence of O(2). Together, these results offer insights into the factors controlling reactivity in synthetic metallopeptides. 相似文献
998.
Rania Aro Amandine Nachtergael Claudio Palmieri Laurence Ris Pierre Duez 《Molecules (Basel, Switzerland)》2022,27(21)
Tetrahydroisoquinoline (THIQ) alkaloids and their derivatives have a structural similarity to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a well-known neurotoxin. THIQs seem to present a broad range of actions in the brain, critically dependent on their catechol moieties and metabolism. These properties make it reasonable to assume that an acute or chronic exposure to some THIQs might lead to neurodegenerative diseases including essential tremor (ET). We developed a method to search for precursor carbonyl compounds produced during the Maillard reaction in overcooked meats to study their reactivity with endogenous amines and identify the reaction products. Then, we predicted in silico their pharmacokinetic and toxicological properties toward the central nervous system. Finally, their possible neurological effects on a novel in vitro 3D neurosphere model were assessed. The obtained data indicate that meat is an alkaloid precursor, and we identified the alkaloid 1-benzyl-1,2,3,4-tetrahydroisoquinoline-6,7-diol (1-benz-6,7-diol THIQ) as the condensation product of phenylacetaldehyde with dopamine; in silico study of 1-benz-6,7-diol-THIQ reveals modulation of dopamine receptor D1 and D2; and in vitro study of 1-benz-6,7-diol-THIQ for cytotoxicity and oxidative stress induction does not show any difference after 24 h contact for all tested concentrations. To conclude, our in vitro data do not support an eventual neurotoxic effect for 1-benz-6,7-diol-THIQ. 相似文献
999.
Prof. Laurence D. Barron Prof. Pedro Cintas 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(4):1476-1477
A recent mathematical analysis by Michel Petijean aimed at solving the Barron/Mislow controversy concerning the chirality or otherwise of a non-translating spinning cone concluded that both are right: the controversy is a matter of an arbitrary choice of a conversion factor. This reassessment highlights the different physicochemical properties of a stationary spinning cone and a chiral molecule and concludes that Petitjean's analysis is misleading. 相似文献
1000.