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101.
Laurens Kooijman Dr. Matthias Schuster Christian Baumann Simon Jurt Dr. Frank Löhr Dr. Boris Fürtig Prof. Dr. Peter Güntert Prof. Dr. Oliver Zerbe 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(47):21151-21158
To achieve efficient proton pumping in the light-driven proton pump bacteriorhodopsin (bR), the protein must be tightly coupled to the retinal to rapidly convert retinal isomerization into protein structural rearrangements. Methyl group dynamics of bR embedded in lipid nanodiscs were determined in the dark-adapted state, and were found to be mostly well ordered at the cytosolic side. Methyl groups in the M145A mutant of bR, which displays only 10 % residual proton pumping activity, are less well ordered, suggesting a link between side-chain dynamics on the cytosolic side of the bR cavity and proton pumping activity. In addition, slow conformational exchange, attributed to low frequency motions of aromatic rings, was indirectly observed for residues on the extracellular side of the bR cavity. This may be related to reorganization of the water network. These observations provide a detailed picture of previously undescribed equilibrium dynamics on different time scales for ground-state bR. 相似文献
102.
Forrest Nichols Dr. Jia En Lu Rene Mercado Ryan Dudschus Prof. Frank Bridges Prof. Shaowei Chen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(18):4136-4142
Electrochemical hydrogen generation is a rising prospect for future renewable energy storage and conversion. Platinum remains a leading choice of catalyst, but because of its high cost and low natural abundance, it is critical to optimize its use. In the present study, platinum oxide nanoparticles of approximately 2 nm in diameter are deposited on carbon nitride (C3N4) nanosheets by thermal refluxing of C3N4 and PtCl2 or PtCl4 in water. These nanoparticles exhibit apparent electrocatalytic activity toward the hydrogen evolution reaction (HER) in acid. Interestingly, the HER activity increases with increasing Pt4+ concentration in the nanoparticles, and the optimized catalyst even outperforms commercial Pt/C, exhibiting an overpotential of only −7.7 mV to reach the current density of 10 mA cm−2 and a Tafel slope of −26.3 mV dec−1. The results from this study suggest that the future design of platinum oxide catalysts should strive to maximize the Pt4+ sites and minimize the formation of the less active Pt2+ species. 相似文献
103.
Michał Dąbrowski Dr. Przemysław Wyrębek Dr. Damian Trzybiński Prof. Krzysztof Woźniak Prof. Karol Grela 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(17):3782-3794
Robust, selective, and stable in the presence of ethylene, ruthenium olefin metathesis pre-catalyst, {[3-benzyl-1-(10-phenyl-9-phenanthryl)]-2-imidazolidinylidene}dichloro(o-isopropoxyphenylmethylene)ruthenium(II), Ru-3 , bearing an unsymetrical N-heterocyclic carbene (uNHC) ligand, has been synthesized. The initiation rate of Ru-3 was examined by ring-closing metathesis and cross-metathesis reactions with a broad spectrum of olefins, showing an unprecendented selectivity. It was also tested in industrially relevant ethenolysis reactions of olefinic substrates from renewable feedstock with very good yields and selectivities. 相似文献
104.
Xin-Yi Du Prof. Dr. Quan-Song Li 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(56):12891-12897
N,C-chelate organoboron compounds are widely employed as photoresponsive and optoelectronic materials due to their efficient photochromic reactivity. It was found in experiments that two diphenyl-substituted organoboron compounds, namely B(ppy)Ph2 (ppy=2-phenylpyridyl) and B(iba)Ph2 (iba=N-isopropylbenzylideneamine), show distinct photochemical reactivity. B(ppy)Ph2 is inert on irradiation, whereas B(iba)Ph2 undergoes photoinduced transformations, yielding BN-cyclohepta-1,3,5-triene via a borirane intermediate. In this work, the complete active space self-consistent field and its second-order perturbation (CASPT2//CASSCF) methods were used to investigate the photoinduced reaction mechanisms of B(ppy)Ph2 and B(iba)Ph2. The calculations showed that the two compounds isomerize to borirane in the same way by passing a transition state in the S1 state and a conical intersection between the S1 and S0 states. The energy barriers in the S1 state of 0.54 and 0.26 eV for B(ppy)Ph2 and B(iba)Ph2, respectively, were explained by analyzing the charge distributions of minima in S0 and S1 states. The results provide helpful insights into the excited-state dynamics of organoboron compounds, which could assist in rational design of boron-based photoresponsive materials. 相似文献
105.
We report extensive computational studies of some novel intermolecular systems and their properties. Recombination of alkali-halide counterions separated by a noncovalently trapped hydrocarbon molecule is prevented by significant potential energy barriers, resulting in unusual metastable insertion complexes. These systems are extremely polar, while the inserted molecule is strongly counter-polarized, leading to significant cooperative nonadditivity effects. The compression and electric field produced by the counterions favours isomerization of the trapped molecule via a significant reduction of the barriers to bond rearrangement, in a field-induced mechanochemical process. The predicted IR intensity spectra clearly reflect (1) formation of the insertion complex, rather than simple attachment of alkali halide, and (2) isomerization of the trapped molecule, thus allowing experimental access to these events. 相似文献
106.
Pattern recognition and data mining software based on artificial neural networks applied to proton transfer in aqueous environments 下载免费PDF全文
In computational physics proton transfer phenomena could be viewed as pattern classification problems based on a set of input features allowing classification of the proton motion into two categories: transfer 'occurred' and transfer 'not occurred'. The goal of this paper is to evaluate the use of artificial neural networks in the classification of proton transfer events, based on the feed-forward back propagation neural network, used as a classifier to distinguish between the two transfer cases. In this paper, we use a new developed data mining and pattern recognition tool for automating, controlling, and drawing charts of the output data of an Empirical Valence Bond existing code. The study analyzes the need for pattern recognition in aqueous proton transfer processes and how the learning approach in error back propagation (multilayer perceptron algorithms) could be satisfactorily employed in the present case. We present a tool for pattern recognition and validate the code including a real physical case study. The results of applying the artificial neural networks methodology to crowd patterns based upon selected physical properties (e.g., temperature, density) show the abilities of the network to learn proton transfer patterns corresponding to properties of the aqueous environments, which is in turn proved to be fully compatible with previous proton transfer studies. 相似文献
107.
Effects of chemical substitution in CeRu2Si2, a well-studied heavy fermion system and YbPd2Si2 have been investigated through magnetic susceptibility and x-ray diffraction in the systems CeRu
x
Si2, CeRu2−x
Os
x
Si2, CeRu2Si2−x
Ge
x
and YbPd2Si2−x
Ge
x
. Replacing silicon by germanium generates normal chemical pressure effect, namely, Ce and Yb atoms in CeRu2Si2 and YbPd2Si2 became more and less magnetic respectively. With increasing Ge concentration, CeRu2Si2−x
Ge
x
exhibits larger susceptibility at low temperature, goes to an antiferromagnetic state and finally becomes ferromagnetic.
In YbPd2Si2−x
Ge
x
, increasing Ge concentration drives Yb atoms to more divalent state. Electronic effects are more pronounced in CeRu2−x
Os
x
Si2 though CeRu2Si2 and CeOs2Si2 have very nearly the same lattice parameters. It is conjectured that CeRu2Si2−x
Ge
x
may be the first Ce-based heavy fermion having a magnetic ground state.
The authors felicitate Prof. D S Kothari on his eightieth birthday and dedicate this paper to him on this occasion. 相似文献
108.
Wen Deng Xiaping Zhong Yuyang Huang Liangyue Xiong Shuhe Wang Jianting Guo Qiwei Long 《中国科学A辑(英文版)》1999,42(1):87-92
Positron lifetime measurements have been performed in binary Fe3Al and Fe3Al doping with Nb or Si alloys. The densities of valence electrons of the bulk and microdefects in all tested samples have
been calculated by using the positron lifetime parameters. Density of valence electron is low in the bulk of Fe3Al alloy. It indicates that, the 3d electrons in a Fe atom have strong-localized properties and tend to form covalent bonds
with Al atoms, and the bonding nature in Fe3Al is a mixture of metallic and covalent bonds. The density of valence electron is very low in the defects of Fe3Al grain boundary, which makes the bonding cohesion in grain boundary quite weak. The addition of Si to Fe3Al gives rise to the decrease of the densities of valence electrons in the bulk and the grain boundary thus the metallic bonding
cohesion. This makes the alloy more brittle. The addition of Nb to Fe3Al results in the decrease of the ordering energy of the alloy and increases the density of valence electron and the bonding
cohesion of the grain boundary. However, since the radius of Nb atom is larger than that of Fe atom, when Nb atoms substitute
for Fe atoms, they will distort the lattice and enlarge the volume of the lattice, which decreases the density of valence
electron and the cohesion of metallic bond in the bulk of the alloy.
Project supported by the National Natural Science Foundation of China (Grant No. 59561001) and the Foundation of Guangxi Education
Committee. 相似文献
109.
B. Buliński K. Malinowski A. Michalik P. Niżegorodcew 《Isotopes in environmental and health studies》2013,49(7):261-265
The present paper makes an attempt of the interpretation of the tracer measurements by means of transfer function. Obtained data of residence time of catalyst in xylene isomerization column inserted in previous paper [1] were used to the identification of dynamic properties of individual sections of the column. 相似文献
110.
采用紫外光电子能谱,研究了新型有机发光材料八芳基环辛四烯(OPCOT)在金属Ru(0001)表面上的电子结构,以及它们之间的相互作用.位于费米能级以下43,69,93和114eV处的4个谱峰分别来自于OPCOT材料中苯环的πCC,σCC,σCH和σHH轨道,位于30eV处的谱峰反映了8个苯环聚合后具有π轨道特性的C—C键.OPCOT材料的价带顶位于费米能级以下25eV处,OPCOT材料在Ru(0001)表面上的功函数为395eV.150℃以下,OPCOT材料可以在Ru(0001)表面稳定存在.随温度的升高,OPCOT材料主要以脱附的形式减少
关键词:
八芳基环辛四烯
光电子能谱
价电子结构
脱附 相似文献