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21.
A new anthraquinone glycoside, rubiayannone‐A ( 1 ), and a new coumarin, rubilatin‐A ( 2 ), together with twenty‐two known compounds were isolated and characterized from the roots of Rubia ustulata. A new anthraquinone, 2‐carbomethoxyanthraquinone ( 3 ), and rubiayannone‐A, 2‐formylanthraquinone were obtained from the roots of R. yunnanensis. The structures of those compounds were elucidated by spectroscopic methods. The antiplatelet aggregation activity of the isolated compounds 1, 4~6 were also discussed. 相似文献
22.
Herein, we demonstrate that silica films with perpendicular macroporous channels and accessible ordered mesopores can be conveniently prepared. The hierarchical macroporous–mesoporous silica films are synthesized by using zinc oxide nanorod array as macroporous template and CTAB surfactant as mesoporous template. In basic surfactant-containing solution, ordered mesoporous silica shells homogeneously grow on the zinc oxide nanorod array. The growth of the mesostructures do not require any chemical modification for the zinc oxide nanorod, which opens a new way for preparing hierarchical silica films with perpendicular mesochannels. The prepared hierarchical macroporous–mesoporous silica films possess a uniform thickness of 2 mm, large perpendicular macropores with a length of 1.8 mm and a width of 80 nm, and accessible ordered mesopores. Separation experiment demonstrates that this macroporous–mesoporous film can effectively separate biomolecules with different sizes. 相似文献
23.
Jing?Zhou Yuqi?Liu Liming?Tang Xinchen?Teng Ning?Tang Zhongxian?HuangEmail author 《中国科学B辑(英文版)》2003,46(1):64-74
Two mutants of the zinc finger protein, ZNF191 (243–368) I323W and R327W, are successfully obtained by site-directed mutagenesis.
The fluorescence spectrum is used to study the interaction between these two mutants and the oligonucleotides. The influence
of the mutation on the interaction has been studied using ethidium bromide (EB) as the fluorescence probe. The binding constants
of the I323W-DNA and R327W-DNA have been calculated and the possible binding models have been discussed. 相似文献
24.
Anand VG Venkatraman S Rath H Chandrashekar TK Teng W Ruhlandt-Senge K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(10):2282-2290
Modified octaphyrins with 34pi electrons have been synthesized and characterized following a simple synthetic methodology. An acid-catalyzed alpha,alpha coupling of tetrapyrranes containing furan, thiophene and selenophene rings resulted in the formation of the respective octaphyrins in relatively good yield. Solution studies by (1)H NMR and 2D NMR methods and single crystal Xray structural characterization reveal an almost flat structure with two heterocyclic rings inverted. Specifically, in 14 two selenophene rings (one on each biselenophene unit) are inverted while in 15 two furan rings (one on each bifuran unit) are inverted when the meso substituent are mesityl groups. On changing the mesityl substituent to m-xylyl group as in 19, the location of ring inversion shifts to pyrrole rings (one on each bipyrrole unit) indicating the dependence of structure on the meso substituents. UV/Vis studies, both in freebase and protonated forms reveal typical porphyrinic character and the aromatic nature of the octaphyrins. The Deltadelta values evaluated by (1)H NMR spectroscopy also support their aromatic nature. The protonated forms of octaphyrins bind TFA anion in a 1:2 ratio. The TFA anions are located one above and below the plane of the octaphyrin macrocycle and they are held by weak electrostatic NH-O interactions similar to that observed for protonated rubyrins. However, in the present case, there is an additional non-electrostatic CH-O interaction involving beta-CH of the inverted heterocyclic ring and the carbonyl oxygen of the TFA. Furthermore, inter molecular interactions between the Cbond;H of the meso-mesityl group and the fluorine of CF(3) group of bound TFA leads to the formation of one-dimensional supramolecular arrays with interplanar distance of 13 A between two octaphyrins. 相似文献
25.
采用ab initio RHF,MP2和B3LYP方法以及LanL2DZ和SDD基组计算了四面体锌族卤素阴离子化合物(MX42-,M=Zn(Ⅱ),Cd(Ⅱ),Hg(Ⅱ);X=F-,Cl-,Br-,I-)和钛族卤化物(MX4,M=Ti(Ⅳ),Zr(Ⅳ),Hf(Ⅳ);X=F-,Cl-,Br-,I-)的几何构型和振动频率。计算结果表明,LanL2DZ基组是合适的基组,能得到合理的电荷分布,几何参数以及振动频率。在锌族卤化物的计算中发现,角弯曲振动频率与实测值相当一致,键伸缩振动频率略为偏低,这主要是由于计算的键长略为偏长所致。MP2方法计算的振动频率更接近于实测值。在钛族卤化物的计算中,三种计算方法都相当地再现了实测值,而以B3LYP方法更为满意。 相似文献
26.
The variation of the translocation time with respect to the solvent quality was also studied. It showed that there is a transition, as the solvent quality improves from \poor to \good: when ABc, τ increases with increasing AB. When the chain length was changed, it was found that when the absorbed energy u0 was greater than uc, τ was proportional to N1:602; for u0相似文献
27.
Theoretical Studies on Electronic Structures and Spectroscopy of Fluorescent Arylamino Fumaronitrile
A new series of fluorescent arylamino fumarinitrile derivatives was designed and optimized using density function theory at the B3LYP/6-31G* level. Based on the optimized geometries, the electronic, fluorescent and 13C NMR spectra are calculated with INDO/CIS, CIS-ZINDO TD, and B3LYP/6-31G* methods, respectively. Starting with the first of the series, the LUMO-HOMO energy gaps of the derivatives become wider and the fluorescent wavelengths and the main peaks in the electronic spectra are blue-shifted owing to the large steric effect of naphthyl rings. On the contrary, the energy gaps of the derivatives turn narrow, and the fluorescent wavelengths and the main peaks in the electronic spectra are red-shifted since hydroxyl groups improve the symmetry and extend the conjugation system. The chemical shifts of sp2-C on the phenyl rings are moved upfield, while chemical shifts of carbon atoms on the cyano groups and those connected with the cyano groups are changed downfield in the presence of hydroxyl groups. 相似文献
28.
Sahar Erfanian Yewang Zhou Amar Razzaq Azhar Abbas Asif Ali Safeer Teng Li 《Entropy (Basel, Switzerland)》2022,24(10)
Bitcoin (BTC)—the first cryptocurrency—is a decentralized network used to make private, anonymous, peer-to-peer transactions worldwide, yet there are numerous issues in its pricing due to its arbitrary nature, thus limiting its use due to skepticism among businesses and households. However, there is a vast scope of machine learning approaches to predict future prices precisely. One of the major problems with previous research on BTC price predictions is that they are primarily empirical research lacking sufficient analytical support to back up the claims. Therefore, this study aims to solve the BTC price prediction problem in the context of both macroeconomic and microeconomic theories by applying new machine learning methods. Previous work, however, shows mixed evidence of the superiority of machine learning over statistical analysis and vice versa, so more research is needed. This paper applies comparative approaches, including ordinary least squares (OLS), Ensemble learning, support vector regression (SVR), and multilayer perceptron (MLP), to investigate whether the macroeconomic, microeconomic, technical, and blockchain indicators based on economic theories predict the BTC price or not. The findings point out that some technical indicators are significant short-run BTC price predictors, thus confirming the validity of technical analysis. Moreover, macroeconomic and blockchain indicators are found to be significant long-term predictors, implying that supply, demand, and cost-based pricing theories are the underlying theories of BTC price prediction. Likewise, SVR is found to be superior to other machine learning and traditional models. This research’s innovation is looking at BTC price prediction through theoretical aspects. The overall findings show that SVR is superior to other machine learning models and traditional models. This paper has several contributions. It can contribute to international finance to be used as a reference for setting asset pricing and improved investment decision-making. It also contributes to the economics of BTC price prediction by introducing its theoretical background. Moreover, as the authors still doubt whether machine learning can beat the traditional methods in BTC price prediction, this research contributes to machine learning configuration and helping developers use it as a benchmark. 相似文献
29.
Xiaoyu Chen Zhijie Teng Yingqi Liu Jun Lu Lianfa Bai Jing Han 《Entropy (Basel, Switzerland)》2022,24(10)
Infrared-visible fusion has great potential in night-vision enhancement for intelligent vehicles. The fusion performance depends on fusion rules that balance target saliency and visual perception. However, most existing methods do not have explicit and effective rules, which leads to the poor contrast and saliency of the target. In this paper, we propose the SGVPGAN, an adversarial framework for high-quality infrared-visible image fusion, which consists of an infrared-visible image fusion network based on Adversarial Semantic Guidance (ASG) and Adversarial Visual Perception (AVP) modules. Specifically, the ASG module transfers the semantics of the target and background to the fusion process for target highlighting. The AVP module analyzes the visual features from the global structure and local details of the visible and fusion images and then guides the fusion network to adaptively generate a weight map of signal completion so that the resulting fusion images possess a natural and visible appearance. We construct a joint distribution function between the fusion images and the corresponding semantics and use the discriminator to improve the fusion performance in terms of natural appearance and target saliency. Experimental results demonstrate that our proposed ASG and AVP modules can effectively guide the image-fusion process by selectively preserving the details in visible images and the salient information of targets in infrared images. The SGVPGAN exhibits significant improvements over other fusion methods. 相似文献
30.
We report the first amine nucleophilic approach for the modular construction of enantioenriched protected α-quaternary amino acids. The key to success is the use of an alcohol solvent, which makes a rationally designed COOMe-bonded Cu-allenylidene electrophilic intermediate stable enough to couple with amine nucleophiles before its decomposition. The reaction features wide functional group tolerance with high enantioselectivity, typically >90% ee, and is amenable to the modification of commercially available bioactive molecules. The resultant protected α-amino acids could be readily converted into a number of precious enantioenriched amines featuring α-hindered tertiary carbon centers, which are otherwise synthetically quite challenging, including those of α-amino aldehyde, peptides or α-vinyl amino ester with >92% ee in excellent yields. This protocol could be utilized for the synthesis of the protected bioactive α-ethylnorvaline in 3 steps, a significant advancement in comparison to an 11-step sequence reported previously.We report the first amine nucleophilic approach for the modular construction of enantioenriched protected α-quaternary amino acids. 相似文献