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991.
Sharon Gustard Jalal Fadili Emma J. Williams Laurance D. Hall T. Adrian Carpenter Matthew Brett Edward T. Bullmore 《Magnetic resonance imaging》2001,19(10):389-1331
The effect of slice orientation on reproducibility and sensitivity of 3T fMRI activation using a motor task has been investigated in six normal volunteers. Four slice orientations were used; axial, oblique axial, coronal and sagittal. We applied analysis of variance (ANOVA) to suprathreshold voxel statistics to quantify variability in activation between orientations and between subjects. We also assessed signal detection accuracy in voxels across the whole brain by using a finite mixture model to fit receiver operating characteristic (ROC) curves to the data. Preliminary findings suggest that suprathreshold cluster characteristics demonstrate high motor reproducibility across subjects and orientations, although a significant difference between slice orientations in number of activated voxels was demonstrated in left motor cortex but not cerebellum. Subtle inter-orientation differences are highlighted in the ROC analyses, which are not obvious by ANOVA; the oblique axial slice orientation offers the highest signal detection accuracy, whereas coronal slices give the lowest. 相似文献
992.
The π0 spectrum in the KL0 → 3π decay was measured using a wire chambers magnetic spectrometer. In the usual approximation, the matrix element can be expressed as: M2 ≈ 1 + 2a0(MK/Mπ2)(2Tπ0−Tπ0max) + a1(MK2/Mπ4)(2Tπ0−Tπ0max)2. We obtained a0 = −0.282 ± 0.011 and a1 consistent with zero. 相似文献
993.
Ciminiello P Dell'Aversano C Dello Iacovo E Fattorusso E Forino M Tartaglione L Rossi R Soprano V Capozzo D Serpe L 《Analytical and bioanalytical chemistry》2011,401(3):1043-1050
Blooms of Ostreopsis spp. have been recently reported along the Mediterranean coasts of Spain, France, Italy, and Greece posing serious risks
to human health. Occurrence of Ostreopsis spp. may result in palytoxin contamination of seafood and, in order to prevent sanitary risks, the need exists to develop
efficient extraction procedures to be coupled to rapid and sensitive monitoring methods of palytoxin-like compounds in seafood.
In the present study, the best conditions for both extraction of palytoxin from seafood and palytoxin quantification by using
liquid chromatography tandem mass spectrometry (LC-MS/MS) were investigated. Three seafood matrices (mussels, sea-urchins,
and anchovies) were selected and five different extraction systems were tested, namely: the official protocol for extraction
of lipophilic toxins and various aqueous methanol or acetonitrile solutions (MeOH/H2O 1:1, MeOH/H2O 8:2, MeCN/H2O 8:2 and MeOH 100%). Extraction with MeOH/H2O 8:2 provided the best results in terms of accuracy and matrix interference on LC-MS/MS detection of palytoxin. Accuracy
and intra-day reproducibility (n = 3) were evaluated for all the selected matrices but only for mussels at three spiking concentration levels, including the
provisional limit proposed by the Community Reference Laboratory for marine biotoxins (250 μg kg−1). Limits of quantitation of palytoxin in mussels, sea-urchins and anchovies tissues were calculated using matrix-matched
standards; taking into account extraction efficiency of MeOH/H2O 8:2, they resulted to be 228, 343, and 500 μg kg−1, respectively. 相似文献
994.
Powell NA Ciske FL Clay EC Cody WL Downing DM Blazecka PG Holsworth DD Edmunds JJ 《Organic letters》2004,6(22):4069-4072
[reaction: see text] Chiral 1-aryl-6-(hydroxymethyl)-2-ketopiperazines can be prepared via an operationally simple, 6-exo epoxide ring-opening cyclization to form the ketopiperazine C6-N1 bond in high yields and with excellent enantiomeric purity. 相似文献
995.
Marianne Blazso Emma Jakab Tamas Szekely Bernd Plage Hans-rolf Schulten 《Journal of polymer science. Part A, Polymer chemistry》1989,27(3):1027-1043
Low- and high-molecular mass thermal decomposition products of five polyquinones with different linking aromatic structures have been analyzed by pyrolysis–gas chromatography and by direct (in-source) pyrolysis–field ionization mass spectrometry. The quantity of carboxyl groups present in the polymer is obtained by the amounts of carbon dioxide found by pyrolysis–gas chromatography. Assuming a radical thermal decomposition mechanism the distribution of ketoacidic and quinonoid segments along the macromolecular ladder could be estimated from the high-molecular mass products measured by pyrolysis–field ionization mass spectrometry. A random distribution of the two different segments was found for polyquinones with biphenylene and dibenzofuran subunits, while a structure built up of blocks of two or more identical segments was obtained for polyquinones with dibenzothiophene and diphenylmethane subunits. At the same time the anomalous structural moieties in the polyquinone ladders are also clarified with the help of the identification of the unexpected pyroysis products. Oxidated and bis-dibenzothiophene and bis-diphenylmethane subunits were found. The observed temperature dependence for the appearances of the thermal degradation products indicates that condensation and elimination reactions are taking place under the described pyrolysis conditions. Condensation in the ketoacidic segments forming new quinonoid segments proved to be important in the polymer which was a 100% poly(ketoacid), but negligible in the polyquinones containing ketoacidic segments up to 60%. 相似文献
996.
This paper concerns the asymptotic behavior of solutions and their gradients to linear and nonlinear elliptic equations with singular coefficients of fuchsian type. 相似文献
997.
998.
Dr. Monika Krupová Patrycja Leszczenko Ewa Sierka Sára Emma Hamplová Dr. Radek Pelc Dr. Valery Andrushchenko 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(63):e202201922
Vibrational circular dichroism (VCD) spectroscopy has been widely used to study (bio)molecules in solution. However, its solid-state applications have been restricted due to experimental limitations and artifacts. Having overcome some of them, the first VCD study of nucleoside crystals is now presented. A two-orders-of-magnitude enhancement of VCD signal was observed due to high molecular order in the crystals and resulting supramolecular chirality. This allowed to obtain high-quality VCD spectra within minutes using minute amounts of samples. The VCD technique is extremely sensitive in detecting changes in a crystal order and is able to distinguish different hydration states of crystals. This elevates it to a new level, as a fast and efficient tool to study chiral crystalline samples. This study demonstrates that VCD is capable of near-instantaneous detection of hydration polymorphs and crystal degradation, which is of substantial interest in pharmaceutical industry (quality and stability control). 相似文献
999.
Mark Pampuch Emma J.L. Walker Bogumil J. Karas 《Current Opinion in Green and Sustainable Chemistry》2022
Synthetic genomics is an emerging field where large-scale DNA engineering is used to study and produce organisms of interest. Here we propose the marine diatom, Phaeodactylum tricornutum, as a candidate for a synthetic genome project and describe some of the strategies to bring this design, termed Pt-syn1.0, to life. This project is fueled by the emergence of a completed genome assembly, powerful methods for manipulating large-scale DNA, and effective DNA delivery methods. We propose that a recombination-deficient strain be created as a prerequisite to downstream genome manipulation to preserve any genetic modifications. In addition, the synthetic genome will be split between 50 chromosomes of approximately 500 kbp each to allow for easy construction and delivery. The establishment of a Pt-syn1.0 strain will lay the foundation for a streamlined engineering platform for P. tricornutum, alleviating many of the current constraints, and would drive diatom research and biotechnology into the next era. 相似文献
1000.
Emily A. Boyd Julie A. Hopkins Leseberg Emma L. Cosner Davide Lionetti Wade C. Henke Victor W. Day Prof. James D. Blakemore 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(13):e202104389
Half-sandwich rhodium monohydrides are often proposed as intermediates in catalysis, but little is known regarding the redox-induced reactivity accessible to these species. Herein, the bis(diphenylphosphino)ferrocene (dppf) ligand has been used to explore the reactivity that can be induced when a [Cp*Rh] monohydride undergoes remote (dppf-centered) oxidation by 1e−. Chemical and electrochemical studies show that one-electron redox chemistry is accessible to Cp*Rh(dppf), including a unique quasi-reversible RhII/I process at −0.96 V vs. ferrocenium/ferrocene (Fc+/0). This redox manifold was confirmed by isolation of an uncommon RhII species, [Cp*Rh(dppf)]+, that was characterized by electron paramagnetic resonance (EPR) spectroscopy. Protonation of Cp*Rh(dppf) with anilinium triflate yielded an isolable and inert monohydride, [Cp*Rh(dppf)H]+, and this species was found to undergo a quasireversible electrochemical oxidation at +0.41 V vs. Fc+/0 that corresponds to iron-centered oxidation in the dppf backbone. Thermochemical analysis predicts that this dppf-centered oxidation drives a dramatic increase in acidity of the Rh−H moiety by 23 pKa units, a reactivity pattern confirmed by in situ 1H NMR studies. Taken together, these results show that remote oxidation can effectively induce M−H activation and suggest that ligand-centered redox activity could be an attractive feature for the design of new systems relying on hydride intermediates. 相似文献