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排序方式: 共有2814条查询结果,搜索用时 328 毫秒
951.
Janine Richter Saioa Elordui-Zapatarietxe Håkan Emteborg Ina Fettig Julie Cabillic Enrica Alasonati Fanny Gantois Claudia Swart Taner Gokcen Murat Tunc Burcu Binici Andres Rodriguez-Cea Tea Zuliani Adriana Gonzalez Gago Daniel Pröfrock Marjaana Nousiainen George Sawal Mirella Buzoianu Rosemarie Philipp 《Accreditation and quality assurance》2016,21(2):121-129
The European Water Framework Directive 2000/60/EC requires monitoring of organic priority pollutants in so-called whole water samples, i.e. in aqueous non-filtered samples that contain natural colloidal and suspended particulate matter. Colloids and suspended particles in the liquid phase constitute a challenge for sample homogeneity and stability. Within the joint research project ENV08 “Traceable measurements for monitoring critical pollutants under the European Water Framework Directive 2000/60/EC”, whole water test materials were developed by spiking defined amounts of aqueous slurries of ultra-finely milled contaminated soil or sediment and aqueous solutions of humic acid into a natural mineral water matrix. This paper presents the results of an European-wide interlaboratory comparison (ILC) using this type of test materials. Target analytes were tributyltin, polybrominated diphenyl ethers and polycyclic aromatic hydrocarbons in the ng/L concentration range. Results of the ILC indicate that the produced materials are sufficiently homogeneous and stable to serve as samples for, e.g. proficiency testing or method validation. To our knowledge, this is the first time that ready-to-use water materials with a defined amount of suspended particulate and colloidal matter have been applied as test samples in an interlaboratory exercise. These samples meet the requirements of the European Water Framework Directive. Previous proficiency testing schemes mainly employed filtered water samples fortified with a spike of the target analyte in a water-miscible organic solvent. 相似文献
952.
Benjamin Schwarz Dr. Johannes Forster McKenna K. Goetz Duygu Yücel Claudia Berger Prof. Dr. Timo Jacob Prof. Dr. Carsten Streb 《Angewandte Chemie (International ed. in English)》2016,55(21):6329-6333
Photosynthetic water oxidation in plants occurs at an inorganic calcium manganese oxo cluster, which is known as the oxygen evolving complex (OEC), in photosystem II. Herein, we report a synthetic OEC model based on a molecular manganese vanadium oxide cluster, [Mn4V4O17(OAc)3]3?. The compound is based on a [Mn4O4]6+ cubane core, which catalyzes the homogeneous, visible‐light‐driven oxidation of water to molecular oxygen and is stabilized by a tripodal [V4O13]6? polyoxovanadate and three acetate ligands. When combined with the photosensitizer [Ru(bpy)3]2+ and the oxidant persulfate, visible‐light‐driven water oxidation with turnover numbers of approximately 1150 and turnover frequencies of about 1.75 s?1 is observed. Electrochemical, mass‐spectrometric, and spectroscopic studies provide insight into the cluster stability and reactivity. This compound could serve as a model for the molecular structure and reactivity of the OEC and for heterogeneous metal oxide water‐oxidation catalysts. 相似文献
953.
Back Cover: Visible‐Light‐Driven Water Oxidation by a Molecular Manganese Vanadium Oxide Cluster (Angew. Chem. Int. Ed. 21/2016)
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954.
Dr. Samuel Dessources Dr. Claudia Morais Dr. Têko W. Napporn Prof. K. Boniface Kokoh 《Chemphyschem》2016,17(23):3964-3973
Hydrogen oxidation and evolution reactions (HOR and HER) are studied on PtxNi1?x/C materials synthesized by the bromide anion exchange method. Physicochemical characterization shows that this surfactant‐free method enables the preparation of well‐dispersed and effective catalysts for the processes involved in the anode of H2/O2 fuel cells (HOR) and the cathode of water electrolyzers (HER). The Pt‐based materials are modified with different Ni contents to decrease the amount of costly precious metal in the electrode materials. These modified Pt‐based materials are found to be electroactive for both reactions without additional overpotential. Kinetic parameters such as the Tafel slope, exchange (j0) and kinetic current densities, and the rate‐determining steps of the reaction mechanisms are determined for each Pt–Ni catalyst and compared to those obtained at the Pt/C surface in alkaline medium. The high j0 values that are obtained indicate a probable contribution of the surface structure of the catalysts due to their roughness and the presence of oxygenated Ni species even at low potentials. 相似文献
955.
Boot CM Amagata T Tenney K Compton JE Pietraszkiewicz H Valeriote FA Crews P 《Tetrahedron》2007,63(39):9903-9914
The structures and biological properties of peptides produced by two genera of marine-derived fungi, an atypical Acremonium sp., and a Metarrhizium sp., were explored. The Acremonium strain was isolated from a marine sponge and has previously been shown by our group to produce peptides from the efrapeptin and RHM families. The isolation and structural elucidation of the new linear pentadecapeptides efrapeptins Eα (1) and H (2) and N-methylated octapeptides RHM3 (3) and RHM4 (4) were carried out through a combination of 1D and 2D NMR techniques and tandem MS. Additional known efrapeptins E, F, and G and the known syctalidamides A and B were also isolated. The absolute configurations of 1-4 are proposed to be the same as the original compound families. The marine sponge-derived Metarrhizium sp. was shown to produce destruxin cyclic depsipeptides including A, B, B2, desmethyl B, E chlorohydrin, and E2 chlorohydrin. Efrapeptins Eα (1), F, and G each displayed IC50s of 1.3 nM against H125 cells, and destruxin E2 chlorohydrin displayed an IC50 of 160 nM against HCT-116 cells. An initial therapeutic assessment suggested a continuous (168 h) exposure of at least 2 ng/mL, or a daily (24 h) exposure of at least 300 ng/mL for H125 cells treated with efrapeptin G, and a continuous (168 h) exposure of at least 190 ng/mL for HCT-116 cells treated with destruxin E2 chlorohydrin, will cause 90% tumor cell death in vitro. 相似文献
956.
Weiskopf D Schmitt EK Klühr MH Dertinger SK Steinem C 《Langmuir : the ACS journal of surfaces and colloids》2007,23(18):9134-9139
In a recent paper, we hypothesized that the continuous increase in membrane conductance observed for nano-BLMs is the result of an independent rupturing of single membranes or membrane patches covering the pores of the porous material. To prove this hypothesis, we prepared micro-BLMs on porous silicon substrates with a pore size of 7 mum. The upper surface of the silicon substrate was coated with a gold layer, followed by the chemisorption of 1,2-dipalmitoyl-sn-glycero-3-phosphothioethanol (DPPTE) and subsequent addition of a droplet of 1,2-diphytanoyl-sn-glycero-3-phosphocholine (DPhPC) dissolved in n-decane. The lipid membranes were fluorescently labeled and investigated by means of fluorescence microscopy and impedance spectroscopy. Impedance spectroscopy revealed the formation of pore-suspending bilayers with high membrane resistance. Increases in membrane capacitance and membrane conductance were observed. This increase in membrane conductance could be unambiguously related to the individual rupturing of membranes suspending the pores of the porous material as visualized by means of fluorescence microscopy. Moreover, by fluorescence recovery after photobleaching experiments, we investigated the lateral mobility of the lipids within the micro-BLMs leading to a mean effective diffusion coefficient of Deff = (14 +/- 1) microm2/s. 相似文献
957.
Effect of surface parameters on the performance of IgG-arrayed hydrogel chips: a comprehensive study
Derwinska K Gheber LA Sauer U Schorn L Preininger C 《Langmuir : the ACS journal of surfaces and colloids》2007,23(21):10551-10558
In this article, the assay performance of 3D polyurethane (PU) hydrogel surfaces, used either plain or modified with cross linkers and additives in a direct immunoassay for IgG, is correlated with chip surface parameters such as water content and expansion, mechanical stability, hydrophilicity, thickness, and surface topography. Commercial chip surfaces ARChip Epoxy, Nexterion slide H and HydroGel are used as references. A strong correlation between assay sensitivity and physical surface parameters was found only for various hydrogels of the same chemical composition, in which cases assay sensitivity increases with decreasing hydrogel concentration as well as decreasing roughness, water content, and expansion. However, as is the case with all hydrogels tested, more hydrophobic layers with low water content are more highly reproducible from one measurement to another. 相似文献
958.
Mechanism of inhibition of human secretory phospholipase A2 by flavonoids: rationale for lead design 总被引:1,自引:0,他引:1
Lättig J Böhl M Fischer P Tischer S Tietböhl C Menschikowski M Gutzeit HO Metz P Pisabarro MT 《Journal of computer-aided molecular design》2007,21(8):473-483
The human secretory phospholipase A2 group IIA (PLA2-IIA) is a lipolytic enzyme. Its inhibition leads to a decrease in eicosanoids
levels and, thereby, to reduced inflammation. Therefore, PLA2-IIA is of high pharmacological interest in treatment of chronic
diseases such as asthma and rheumatoid arthritis. Quercetin and naringenin, amongst other flavonoids, are known for their
anti-inflammatory activity by modulation of enzymes of the arachidonic acid cascade. However, the mechanism by which flavonoids
inhibit Phospholipase A2 (PLA2) remained unclear so far. Flavonoids are widely produced in plant tissues and, thereby, suitable
targets for pharmaceutical extractions and chemical syntheses. Our work focuses on understanding the binding modes of flavonoids
to PLA2, their inhibition mechanism and the rationale to modify them to obtain potent and specific inhibitors. Our computational
and experimental studies focused on a set of 24 compounds including natural flavonoids and naringenin-based derivatives. Experimental
results on PLA2-inhibition showed good inhibitory activity for quercetin, kaempferol, and galangin, but relatively poor for
naringenin. Several naringenin derivatives were synthesized and tested for affinity and inhibitory activity improvement. 6-(1,1-dimethylallyl)naringenin
revealed comparable PLA2 inhibition to quercetin-like compounds. We characterized the binding mode of these compounds and
the determinants for their affinity, selectivity, and inhibitory potency. Based on our results, we suggest C(6) as the most
promising position of the flavonoid scaffold to introduce chemical modifications to improve affinity, selectivity, and inhibition
of PLA2-IIA by flavonoids. 相似文献
959.
Jia C Liu SX Tanner C Leiggener C Neels A Sanguinet L Levillain E Leutwyler S Hauser A Decurtins S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(13):3804-3812
To study the electronic interactions in donor-acceptor (D-A) ensembles, D and A fragments are coupled in a single molecule. Specifically, a tetrathiafulvalene (TTF)-fused dipyrido[3,2-a:2',3'-c]phenazine (dppz) compound having inherent redox centers has been synthesized and structurally characterized. Its electronic absorption, fluorescence emission, photoinduced intramolecular charge transfer, and electrochemical behavior have been investigated. The observed electronic properties are explained on the basis of density functional theory. 相似文献
960.