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1.
2.
Molecular dynamics simulations of solid state recrystallization and grain growth in iron nanoparticles containing 1436 atoms were carried out. During the period of relaxation of supercooled liquid drops and during thermal annealing of the solids they froze to, changes in disorder were followed by monitoring changes in energy and the migration of grain boundaries. All 27 polycrystalline nanoparticles, which were generated with different grain boundaries, were observed to recystallize into single crystals during annealing. Larger grains consumed the smaller ones. In particular, two sets of solid particles, designated as A and B, each with two grains, were treated to generate 18 members of each set with different thermal histories. This provided small ensembles (of 18 members each) from which rates at which the larger grain engulfed the smaller one, could be determined. The rate was higher, the smaller the degree of misorientation between the grains, a result contrary to the general rule based on published experiments, but the reason was clear. Crystal A, which happened to have a somewhat lower angle of misorientation, also had a higher population of defects, as confirmed by its higher energy. Accordingly, its driving force to recrystallize was greater. Although the mechanism of recrystallization is commonly called nucleation, our results, which probe the system on an atomic scale, were not able to identify nuclei unequivocally. By contrast, our technique can and does reveal nuclei in the freezing of liquids and in transformations from one solid phase to another. An alternative rationale for a nucleation-like process in our results is proposed. 相似文献
3.
Dr. Shaoguang Zhang Dr. Peng Cui Tianchang Liu Qiuran Wang Thomas J. Longo Laura M. Thierer Dr. Brian C. Manor Dr. Michael R. Gau Dr. Patrick J. Carroll Prof. Dr. Georgia C. Papaefthymiou Prof. Dr. Neil C. Tomson 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(35):15327-15331
Despite their connection to ammonia synthesis, little is known about the ability of iron-bound, bridging nitrides to form N−H bonds. Herein we report a linear diiron bridging nitride complex supported by a redox-active macrocycle. The unique ability of the ligand scaffold to adapt to the geometric preference of the bridging species was found to facilitate the formation of N−H bonds via proton-coupled electron transfer to generate a μ-amide product. The structurally analogous μ-silyl- and μ-borylamide complexes were shown to form from the net insertion of the nitride into the E−H bonds (E=B, Si). Protonation of the parent bridging amide produced ammonia in high yield, and treatment of the nitride with PhSH was found to liberate NH3 in high yield through a reaction that engages the redox-activity of the ligand during PCET. 相似文献
4.
Dr. Damien Hudry Dr. Christos Apostolidis Dr. Olaf Walter Dr. Arne Janßen Dr. Dario Manara Dr. Jean‐Christophe Griveau Dr. Eric Colineau Dr. Tonya Vitova Tim Prüßmann Dr. Di Wang Dr. Christian Kübel Dr. Daniel Meyer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(33):10431-10438
Apart from its technological importance, plutonium (Pu) is also one of the most intriguing elements because of its non‐conventional physical properties and fascinating chemistry. Those fundamental aspects are particularly interesting when dealing with the challenging study of plutonium‐based nanomaterials. Here we show that ultra‐small (3.2±0.9 nm) and highly crystalline plutonium oxide (PuO2) nanocrystals (NCs) can be synthesized by the thermal decomposition of plutonyl nitrate ([PuO2(NO3)2] ? 3 H2O) in a highly coordinating organic medium. This is the first example reporting on the preparation of significant quantities (several tens of milligrams) of PuO2 NCs, in a controllable and reproducible manner. The structure and magnetic properties of PuO2 NCs have been characterized by a wide variety of techniques (powder X‐ray diffraction (PXRD), X‐ray absorption fine structure (XAFS), X‐ray absorption near edge structure (XANES), TEM, IR, Raman, UV/Vis spectroscopies, and superconducting quantum interference device (SQUID) magnetometry). The current PuO2 NCs constitute an innovative material for the study of challenging problems as diverse as the transport behavior of plutonium in the environment or size and shape effects on the physics of transuranium elements. 相似文献
5.
Birane Fall AbdelAziz Jalil Michael Gau Sumanth Chereddy Michael J. Zdilla Stephanie L. Wunder Parameswara Rao Chinnam 《Ionics》2018,24(2):343-349
A soft solid crystal composed of isoquinoline (IQ) and LiCl was prepared based on the concept of Pearson’s hard-soft acid-base (HSAB) theory. Single-crystal X-ray diffraction best described the isoquinoline3?(LiCl)2 as consisting of molecular Li4Cl4(isoquinoline)6 units, where the LiCl cluster is an array of edge-fused Li2Cl2 rhombs. Electrochemical impedance measurements on pressed pellets showed that conductivity occurs mainly through the bulk via a hopping mechanism, with a calculated activation energy of Ea = 67 kJ/mol. The high value of the activation energy was due to Li4Cl4 clusters that were well separated by intervening IQ ligands in the crystal structure, requiring large hops for ions to migrate through the lattice. 相似文献
6.
Co1 - xNix (x = 0, 0.2 and 0.3) thin films of thickness about 1500 Å were electron-beam evaporated onto silicon and polymide substrates at various oblique angles . In-plane coercivities and squareness ratios both along and transverse to the incidence plane were examined. Also, the angular variations of coercivity of films prepared at = 0 ° to 85 ° were investigated. The magnetic anisotropy changes from an in-plane anisotropy with the easy axis perpendicular to the incidence plane to an out-of-plane anisotropy parallel to the incidence plane, the transition occuring at about 60 °. Also discussed is the effect of the substrate temperature on the magnetic properties and columnar microstructure of the oblique-evaporated films. At room temperature, there is a small drop in coercivity at = 60 ° before a sharp rise in coercivities to 1400 Oe as the oblique angle increases. 相似文献
7.
Erin Turner Amy Roth McDuffie Amanda Sugimoto Julia Aguirre Tonya Gau Bartell Corey Drake 《Mathematical Thinking and Learning》2019,21(1):1-27
The role of language in mathematics teaching and learning is increasingly highlighted by standards and reform movements in the US. However, little is known about teachers’, and especially early career teachers’ (ECTs) practices and understandings related to language in mathematics instruction. This multiple case study explored the language-related understandings and practices of six ECTs in diverse elementary classrooms. Using iterative cycles of analysis, we found that all ECTs regularly attended to students’ mathematical vocabulary use and development. Yet, there was variability in ECTs’ focus on how to teach mathematical vocabulary, expectations for students’ precise use of mathematical terminology, and the use of multiple languages during instruction. These findings indicate that ECTs need more targeted support during teacher preparation and early career teaching in order to better support all students’ language development in the mathematics classroom. 相似文献
8.
Pavel V. Bondarenko Tonya P. Second Vlad Zabrouskov Alexander A. Makarov Zhongqi Zhang 《Journal of the American Society for Mass Spectrometry》2009,20(8):1415-1424
Mass and top-down analyses of 150-kDa monoclonal immunoglobulin gamma (IgG) antibodies were performed on an Orbitrap analyzer.
Three different sample delivery methods were tested including (1) infusion of an off-line desalted IgG sample using nano-electrospray;
(2) on-line desalting followed by a step elution with a high percentage of organic solvent; and (3) reversed-phase HPLC separation
and on-line mass and top-down analyses of disulfide isoforms of an IgG2 antibody. The accuracy of mass measurements of intact
antibody was within ±2 Da (15 ppm). The glycoforms of intact IgG antibodies separated by 162 Da were baseline resolved. In-source
fragmentation of the intact antibodies produced mainly 115 residue fragments including N-terminal variable domains of heavy
and light chains. The sequence coverage (the number of cleavages) was greatly increased after reduction of disulfide bonds
and HPLC/MS/MS analysis of light and heavy chains using collision-induced dissociation in the ion trap of the LTQ-Orbitrap.
This is an attractive alternative to peptide mapping for characterization and monitoring of post-translational modifications
attributed to minimal sample preparation, high speed of the mass/top-down analysis, and relatively minor method-induced sample
modifications. 相似文献
9.
Daniel F. Kienle João V. de Souza Erik B. Watkins Tonya L. Kuhl 《Analytical and bioanalytical chemistry》2014,406(19):4725-4733
The thickness and refractive index of 1,2-dipalmitoyl-sn-glycero-3-phosphatidyl choline (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE) monolayers Langmuir--Blodgett (LB) deposited on mica were measured in dry air and bulk water using multiple-beam interferometry (MBI). Measurements of thickness using atomic force microscopy (AFM) of identical monolayers, and X-ray reflectivity (XRR) of the monolayers on quartz were taken for comparison. The measurement of the properties of solid-supported monolayers in dry air allows lipid optical properties to be determined free from solvent effects. The thickness and refractive index measured by MBI were 25.5?±?0.6 Å and 1.485?±?0.007 for DPPE monolayers, and 23.9?±?0.5 Å and 1.478?±?0.006 for DPPC monolayers in dry air. These thicknesses are consistent with the other techniques used in this work as well as other measurements in the literature. The refractive indices of solid-supported lipid monolayers have not been previously measured. The values are higher than previous measurements on black lipid films done by reflectometry, which is attributed to increased lipid packing density and the absence of hydrocarbon solvents. Applying water to the monolayers had no measurable effect on their properties, indicating that any change in hydration was below detection. Figure
? 相似文献
10.
Y. Chushak L.S. Bartell 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):43-46
A set of molten gold clusters, each with 1157 gold atoms, was studied by molecular dynamics simulations as the clusters underwent
freezing at three different temperatures. Most of the clusters attained an icosahedral structure upon freezing, a structure
found to be stable to mild annealing. Other structures observed were imperfect truncated decahedral, truncated octahedral
and hexagonal close packed structures. The role of kinetics in the process of cluster solidification is discussed.
Received 6 November 2000 相似文献