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901.
Lishuang Fan Yu Zhang Zhikun Guo Bing Sun Da Tian Yujie Feng Naiqing Zhang Kening Sun 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(42):9314-9318
Flexible asymmetric supercapacitors are more appealing in flexible electronics because of high power density, wide cell voltage, and higher energy density than symmetric supercapacitors in aqueous electrolyte. In virtues of excellent conductivity, rich porous structure and interconnected honeycomb structure, three dimensional graphene aerogels show great potential as electrode in asymmetric supercapacitors. However, graphene aerogels are rarely used in flexible asymmetric supercapacitors because of easily re-stacking of graphene sheets, resulting in low electrochemical activity. Herein, flower-like hierarchical Mn3O4 and carbon nanohorns are incorporated into three dimensional graphene aerogels to restrain the stack of graphene sheets, and are applied as the positive and negative electrode for asymmetric supercapacitors devices, respectively. Besides, a strong chemical coupling between Mn3O4 and graphene via the C-O-Mn linkage is constructed and can provide a good electron-transport pathway during cycles. Consequently, the asymmetric supercapacitor device shows high rate cycle stability (87.8 % after 5000 cycles) and achieves a high energy density of 17.4 μWh cm−2 with power density of 14.1 mW cm−2 (156.7 mW cm−3) at 1.4 V. 相似文献
902.
Dr. Luca Fornasari Dr. Anna Olejniczak Dr. Federica Rossi Dr. Simone d'Agostino Prof. Michele R. Chierotti Prof. Roberto Gobetto Prof. Andrzej Katrusiak Prof. Dario Braga 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(22):5061-5069
The structures and solid-state dynamics of the supramolecular salts of the general formula [(12-crown-4)2 ⋅ DABCOH2](X)2 (where DABCO=1,4-diazabicyclo[2.2.2]octane, X=BF4, ClO4) have been investigated as a function of temperature (from 100 to 360 K) and pressure (up to 3.4 GPa), through the combination of variable-temperature and variable-pressure XRD techniques and variable-temperature solid-state NMR spectroscopy. The two salts are isomorphous and crystallize in the enantiomeric space groups P3221 and P3121. All building blocks composing the supramolecular complex display dynamic processes at ambient temperature and pressure. It has been demonstrated that the motion of the crown ethers is maintained on lowering the temperature (down to 100 K) or on increasing the pressure (up to 1.5 GPa) thanks to the correlation between neighboring molecules, which mesh and rotate in a concerted manner similar to spiral gears. Above 1.55 GPa, a collapse-type transition to a lower-symmetry ordered structure, not attainable at a temperature of 100 K, takes place, proving, thus, that the pressure acts as the means to couple and decouple the gears. The relationship between temperature and pressure effects on molecular motion in the solid state has also been discussed. 相似文献
903.
Poly (ether ether ketone) was irradiated with gamma rays or electron beam to investigate the radical process. The generated paramagnetic species were observed by electron spin resonance spectroscopy at ambient temperature and in liquid nitrogen. The effect of microwave power on saturation of the particular spectra and thermal annealing effects were determined. The following radicals were identified: radical anion, phenoxyl radical, and phenylperoxy radical. Despite the fact that the intermediates were formed as a result of backbone cleavage causing degradation, the macroscopic features were almost unaffected by irradiation up to dose of 1500 kGy. 相似文献
904.
905.
Marta Lenartowicz Andrzej Swinarew Grażyna Rymarz 《International Journal of Polymer Analysis and Characterization》2014,19(7):611-624
The article presents the impact of long-term (10 years of maintenance) use of polymer material, with the result of a gradual loss of primary physical and chemical properties and degradation. Under the influence of factors such as heat, water, sunlight, stress forces, sulfur oxides, nitrogen oxides, oxygen, metals, and microorganisms, polymers experience irreversible structural changes that cause a decrease in molecular weight or change in chemical composition. The problems mentioned in this article are known worldwide because of many possible applications for wide-area covers, roofing and others. 相似文献
906.
Norman S. Bhacca Frank R. Fronczek Andrzej Sygula 《Journal of chemical crystallography》1996,26(7):483-487
The crystal structure of an orthorhombic polymorph of the title compound, crystallized by sublimation, has been determined. Dehydroepiandrosterone, C19H28O2, space groupP212121 witha=6.6408(4)b=11.4423(11)c=22.085(2)Å,V=1678.2(4)Å3,Z=4. The structure was refined toR=0.051 for 2645 observed reflections. The conformation of the molecule is similar to that found in other polymorphs and solvates, with a chair A ring, an 8, 9 half-chair B ring, a chair C ring, and a 14 envelope D ring. Molecules are linked in chains by OH...O hydrogen bonds involving the carbonyl oxygen atom. The O...O distance is 2.855(3) Å, and the angle about H is 171(2)o. 相似文献
907.
Eosin Y as a Direct Hydrogen‐Atom Transfer Photocatalyst for the Functionalization of C−H Bonds 下载免费PDF全文
Xuan‐Zi Fan Dr. Jia‐Wei Rong Hao‐Lin Wu Quan Zhou Dr. Hong‐Ping Deng Jin Da Tan Cheng‐Wen Xue Dr. Li‐Zhu Wu Dr. Hai‐Rong Tao Dr. Jie Wu 《Angewandte Chemie (International ed. in English)》2018,57(28):8514-8518
Eosin Y, a well‐known economical alternative to metal catalysts in visible‐light‐driven single‐electron transfer‐based organic transformations, can behave as an effective direct hydrogen‐atom transfer catalyst for C?H activation. Using the alkylation of C?H bonds with electron‐deficient alkenes as a model study revealed an extremely broad substrate scope, enabling easy access to a variety of important synthons. This eosin Y‐based photocatalytic hydrogen‐atom transfer strategy is promising for diverse functionalization of a wide range of native C?H bonds in a green and sustainable manner. 相似文献
908.
Reversible SC‐SC Transformation involving [4+4] Cycloaddition of Anthracene: A Single‐Ion to Single‐Molecule Magnet and Yellow‐Green to Blue‐White Emission 下载免费PDF全文
Xin‐Da Huang Yan Xu Kun Fan Prof. Dr. Song‐Song Bao Prof. Dr. Mohamedally Kurmoo Prof. Dr. Li‐Min Zheng 《Angewandte Chemie (International ed. in English)》2018,57(28):8577-8581
In search of magneto‐optic materials, the mononuclear compounds LnIII(depma)(NO3)3(hmpa)2 (Ln=Dy, Gd) were synthesized. The anthracene moieties undergo [4+4] dimerization when irradiated at 365 nm without loss of crystallinity. The Dy compound switches from a single‐ion to a single‐molecule magnet with doubling of the spin reversal barrier energy and from yellow‐green to blue‐white emission. The dimerization is reversed by heating at 100 °C or partially on light irradiating at 254 nm. The results suggest that lanthanide phosphonates with anthracene are promising smart materials displaying synergistic magneto‐optic property. 相似文献
909.
In this work, a new polymer resin with a functional groups capable of holding trace metals has been synthesized. The structure of polymer resin has been examined by BET-N2 method analyzer, IR spectrometer, scanning electron microscope (SEM) and elemental microanalyser. The synthesized polymer resin was used for the simultaneous separation and preconcentration of the trace metals from various tea and herbal plants samples. After extraction process, flame atomic absorption spectrometry (FAAS) was used to determine the trace metals. The analytical parameters and solid phase extraction (SPE) performance such as pH, sample volume, flow rates of sample, flow rates of eluent, concentration, volume and type of eluent and effect of interference ions, were investigated. The limits of detection (DL) of the SPE procedure for trace metals, were calculated to be (3s) in the range of 0.9?4.0 μg L?1 (n = 21) and the factors of preconcentration (PF) were obtained at 200 for Cd, Co, Cu, Fe, Ni and Zn, and at 50 for Cr, Mn and Pb ions and the relative standard deviation (RSD) at ≤ 2% (n = 11). 相似文献
910.
Andrzej Wolan Justyna A. Kowalska-Six Holisoa Rajerison Michèle Césario Marie Cordier Yvan Six 《Tetrahedron》2018,74(38):5248-5257
Two types of bicyclic N-cyclopropyl glycine ester derivatives have been prepared and put under scrutiny as possible precursors of azomethine ylides. The results demonstrate that they can indeed participate in 1,3-dipolar cycloaddition reactions with dipolarophiles, as illustrated in the cases of phenyl vinyl sulfone, N-phenylmaleimide, diethyl fumarate and diethyl maleate. The relative configurations of the major diastereoisomers produced are consistent with the predicted generation of azomethine ylide species, reacting in concerted cycloaddition processes. This unprecedented way of generating such 1,3-dipoles provides access to functionalised pyrrolizidine and pyrrolidine derivatives, that would be difficult to make directly by more classic methods. It was also found that using phenyl vinyl sulfone or N-phenylmaleimide as the dipolarophile reactant, a domino nucleophilic conjugate addition/1,3-dipolar cycloaddition process may operate competitively. 相似文献