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881.
Gamal R. Saad Nagwa H.S. Ahmed Abdelgawad A. Fahmi Mohamed M. Kaddah 《Liquid crystals》2013,40(8):1285-1297
ABSTRACTThe effect of introducing a lateral methyl substitution into the previously investigated laterally neat four-ring analogues, 4-substituted phenylazo phenyl 4?-(4?-alkoxyphenylazo) benzoates (Ina–e), on their mesophase behaviour was investigated for the newly prepared five homologous series of 4-substituted phenylazo phenyl 4?-(3?-methyl-4?-alkoxyphenylazo) benzoates (IIna–e). Within each homologous series, the alkoxy group varies between 6, 8, 10, 12, 14, and 16 carbons, while the substituent, X, is a polar group that alternatively changes between the electron-donating (CH3O and CH3) groups, and the electron-withdrawing (Br and NO2) groups, including the unsubstituted homologues (IInc). Their mesophase stabilities were determined by DSC and phases identified by PLM. The results showed that independent of the alkoxy-chain length or the polarity of the substituent X, the nematic phase is predominant with relatively high stability and wide temperature ranges. All compounds show a good thermal stability in the mesophases domain, except the nitro and Br substituted derivatives bearing short alkoxy chain length. Comparison of the mesophase behaviour was also made between the present series and corresponding three-ring laterally CH3-substituted azo/ester analogues. UV-vis absorption spectra revealed that derivatives with electron donating or an electron withdrawing groups exhibited redshifts of the π→π* transition compared with unsubstituded derivative. 相似文献
882.
Piotr Haj?asz 《Mathematische Annalen》2009,343(4):801-823
We prove that Lipschitz mappings are dense in the Newtonian–Sobolev classes N
1,p
(X, Y) of mappings from spaces X supporting p-Poincaré inequalities into a finite Lipschitz polyhedron Y if and only if Y is [p]-connected, π
1(Y) = π
2(Y) = · · · = π
[p](Y) = 0, where [p] is the largest integer less than or equal to p.
This work was supported by the NSF grant DMS-0500966. 相似文献
883.
884.
In a previous work, we studied the retention behavior of monovalent and divalent carboxylic acids on a highly cross-linked polystryene-divinylbenzene anion-exchange column (IonPac AS4A-SC) using a carbonate-based buffer, and a retention model was applied to the chromatographic data obtained. In this work we characterized the retention of carboxylates (formic, acetic, propionic, lactic, pyruvic, oxalic, malonic, succinic, fumaric, maleic, tartaric, glutaric, adipic, malic, mucic, trans-beta-hydromuconic, trans,trans-muconic acids) on a column with higher hydrophilicity (IonPac AS11) according to analyte and stationary phase properties, using previously investigated eluent compositions and comparing the retention data obtained. Moreover, the effect of organic modifiers (CH3OH and CH3CN) in the eluent on the retention factors was also evaluated. The chromatographic data obtained on the IonPac AS11 column were fitted by the retention model and allowed one to obtain and to compare ion-specific selectivity constants (parameters of the model) with the ones obtained with the previous column. 相似文献
885.
Magdi M. Naoum Abdelgawad A. Fahmi Gamal R. Saad Mohamed H. Ali 《Liquid crystals》2017,44(11):1664-1677
Eight homologous series of 2-(or 3-)substituted phenyl 4?-(4″-alkoxy (2?-, or 3″-substituted phenylazo) benzoates (InXY) were prepared in which the suffix ‘X’ refers to the lateral substituent X attached to the terminal benzene ring that carries the alkoxy group, and the suffix ‘Y’ refers to the substituent attached to the other terminal phenyl group. Within each homologous series, the length of the terminal alkoxy group varies from 8 to 16 carbons, while the lateral polar substituents, X and Y, alternatively varies between CH3 and F. The mesophase behaviour was investigated by differential scanning calorimetry and identified by polarised optical microscopy. The results were discussed in terms of the polarity and steric effects of the two lateral substituents. Comparative correlations were made to investigate the effect of the second lateral substituent on the mesophase behaviour of the previously investigated mono-laterally substituted analogues. UV–vis spectroscopic study revealed that the compounds I8XY exhibited two absorption bands: low intense bands at 254–263 and a broad band at 364–376 nm. These bands are attributed to the π–π? transition of the phenyl rings and the whole mesogenic portion. 相似文献
886.
A. F. Saad C. T. Zhang R. Collatz P. Kleinheinz R. Menegazzo R. Broda K. H. Maier H. Grawe M. Schramm R. Schubart M. Lach J. Heese J. Eberth W. Krolas S. Hofmann H. Folger J. Blomqvist 《Zeitschrift für Physik A Hadrons and Nuclei》1995,351(3):247-248
In-beam- andn-measurements have for the first time identified excited states in the
72
157
Hf85 nucleus and have established its yrast levels up to 6.5 MeV and I=(51/2). The results of parameter-free 11-particle recoupling calculations in the framework of the shell model for the configurationsh
11
2/8
f
7
2/3
andh
11
2/8
f
7
2/2
h9/2 are in excellent agreement with the observed levels up to 39/2 at 4.758 MeV. A weakly populated 52 ns 29/2+ yrast isomer at 2.876 MeV is assigned as the three-neutron configurationf7/2h9/2i13/2. 相似文献
887.
Hussein K. Amusa Dr. Sagir Adamu Dr. Abeer S. Arjah Dr. Saad A. Al-Bogami Dr. Sameer Al-Ghamdi Prof. Shaikh A. Razzak Prof. Mohammad M. Hossain 《化学:亚洲杂志》2021,16(13):1792-1806
The kinetics of oxidative cracking of n-hexane to light olefins using the lattice oxygen of VOx/SrO-γAl2O3 catalysts has been investigated. Kinetic experiments were conducted in a CREC Riser Simulator (CERC: Chemical Reactor Engineering Center), which mimics fluidized bed reactors. The catalyst's performance is partly attributed to the moderate interaction between active VOx species and the SrO-γAl2O3 support. This moderate interaction serves to control the release of lattice oxygen to curtail deep oxidation. The incorporation of basic SrO component in the support also helped to moderate the catalyst's acidity to checkmate excessive cracking. Langmuir-Hinshelwood model was applied to formulate the rate equations. The intrinsic kinetic parameters were obtained by fitting the experimental data to the kinetic model using a nonlinear regression algorithm at a 95% confidence interval, implemented in MATLAB. n-Hexane transforms to olefins at a specific reaction rate of 1.33 mol/gcat.s and activation energy of 119.2 kJ/mol. These values when compared with other duplets (i. e., ki° and EA) for paraffins to olefins, show that indeed olefins are stable products of the oxidative conversion of n-hexane over VOx/SrO-γAl2O3 under a fluidized bed condition. Values of activation energy for all COx formation routes indicate that intermediate paraffins are likely to be cracked to form CH4 than to be converted directly to COx. On the other hand, olefins may transform partly, and directly to COx (E9=9.65 kJ/mol) than to form CH4 (E8=89.1 kJ/mol) in the presence of excess lattice oxygen. Overall, olefins appear to be stable to deep oxidation due to the role of SrO in controlling the amount of lattice oxygen of the catalyst at the reaction temperature. 相似文献
888.
Saad Alghamdi Shaheed Ur Rehman Nashwa Talaat Shesha Hani Faidah Muhammad Khurram Sabi Ur Rehman 《Molecules (Basel, Switzerland)》2020,25(23)
According to WHO report, globally about 10 million active tuberculosis cases, resulting in about 1.6 million deaths, further aggravated by drug-resistant tuberculosis and/or comorbidities with HIV and diabetes are present. Incomplete therapeutic regimen, meager dosing, and the capability of the latent and/or active state tubercular bacilli to abide and do survive against contemporary first-line and second line antitubercular drugs escalate the prevalence of drug-resistant tuberculosis. As a better understanding of tuberculosis, microanatomy has discovered an extended range of new promising antitubercular targets and diagnostic biomarkers. However, there are still no new approved antitubercular drugs of routine therapy for several decades, except for bedaquiline, delamanid, and pretomanid approved tentatively. Despite this, innovative methods are also urgently needed to find potential new antitubercular drug candidates, which potentially decimate both latent state and active state mycobacterium tuberculosis. To explore and identify the most potential antitubercular drug candidate among various reported compounds, we focused to highlight the promising lead derivatives of isoniazid, coumarin, griselimycin, and the antimicrobial peptides. The aim of the present review is to fascinate significant lead compounds in the development of potential clinical drug candidates that might be more precise and effective against drug-resistant tuberculosis, the world research looking for a long time. 相似文献
889.
Saad M. Alshehri Jahangeer Ahmed Tansir Ahamad Norah Alhokbany Prabhakarn Arunachalam Abdullah M. Al-Mayouf Tokeer Ahmad 《Journal of Sol-Gel Science and Technology》2018,87(1):137-146
Brick-shaped zinc tungstate nanoparticles have been synthesized by ecofriendly solvent-free process using molten salts. Zinc tungstate nanobricks (ZnWO4 Nbs) were characterized by powder x-ray diffraction (PXRD), FTIR, Raman, energy dispersive and electron microscopic studies. ZnWO4 Nbs are used as the multifunctional electrode materials to oxygen generation reactions (OGR), oxygen reduction reactions (ORR) and supercapacitors (SCs) as well as photo-catalysts in the waste-water treatment by the degradation of organic dyes. Low overpotential (?10?=?0.475?V), low tafel slope (140?mV/dec), high current density (~70?mA/cm2) and good stability of the electrodes are the key results of the present studies for water electrolysis (OGR/ORR). ZnWO4 Nbs have also shown great interest in supercapacitors with efficient charge–discharge activities in 1?M KOH. The specific capacitance and energy density of ZnWO4 Nbs were found to be 250?F/g and 80?Wh/kg, respectively, at 5?mV/s, these values are relatively higher than that of previously reported specific capacitance and energy density value of metal tungstate nanoparticles. ZnWO4 Nbs as the photo-catalysts work very significantly for photocatalytic degradation of aqueous MB dye solution (~85 % in 3?h) in neutral medium. 相似文献
890.
Wireless sensor networks as the key infrastructure of the new networking paradigm are vulnerable against different kinds of attacks. Therefore, ensuring a secure communication between the sensor nodes is important. One of the most critical issues in this regard is the key distribution mechanism. Due to the random deployment of the sensors in the target area, key pre-distribution is a promising approach, in which a list of keys, so-called key-ring, is pre-distributed to each sensor node before deployment. To establish a secure communication, two nodes must share a common key from their key-rings. In this paper, we consider a hybrid key pre-distribution approach based on the symmetric design. We propose a new scheme, which is a modification of the hybrid symmetric design in order to improve the connectivity and resilience. Considering the trade-off between resilience and connectivity, we introduce a new parameter based on the application requirement. The experimental results and analytical analysis approve the efficiency of our proposed approach and introduced parameter. 相似文献