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991.
Boudreau J Courtemanche MA Fontaine FG 《Chemical communications (Cambridge, England)》2011,47(39):11131-11133
Species R(2)PCH(2)AlMe(2) (R = Me, Ph) are stable Lewis adducts but still react with CO(2) both in solution and in the solid state. The CO(2) adducts undergo a rearrangement unprecedented for ambiphilic molecules to form aluminium carboxylates. A new spirocyclic compound was also obtained by double Lewis pair activation of CO(2). 相似文献
992.
Several pure and Ag-doped gold surfaces were used as models of nanoporous gold catalysts where O(2) was suggested to be activated. Density functional theory (DFT) calculations show that residual Ag on Au is able to promote adsorption and to dissociate thermodynamically favorable O(2) with high rate constants. 相似文献
993.
Rodrigo E Morales S Duce S Ruano JL Cid MB 《Chemical communications (Cambridge, England)》2011,47(40):11267-11269
Heteroarylvinyl sulfone 1 has been successfully used as a new sulfonyl Michael acceptor in aminocatalytic reactions with branched aldehydes. Subsequent one-pot Julia-Kocienski olefination allows the challenging preparation of enantiomerically pure α-allylated aldehydes bearing C-α quaternary carbons. 相似文献
994.
Guidelli EJ Ramos AP Zaniquelli ME Baffa O 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2011,82(1):140-145
Colloidal silver nanoparticles were synthesized by an easy green method using thermal treatment of aqueous solutions of silver nitrate and natural rubber latex (NRL) extracted from Hevea brasiliensis. The UV–Vis spectra detected the characteristic surface plasmonic absorption band around 435 nm. Both NRL and AgNO3 contents in the reaction medium have influence in the Ag nanoparticles formation. Lower AgNO3 concentration led to decreased particle size. The silver nanoparticles presented diameters ranging from 2 nm to 100 nm and had spherical shape. The selected area electron diffraction (SAED) patterns indicated that the silver nanoparticles have face centered cubic (fcc) crystalline structure. FTIR spectra suggest that reduction of the silver ions are facilitated by their interaction with the amine groups from ammonia, which is used for conservation of the NRL, whereas the stability of the particles results from cis-isoprene binding onto the surface of nanoparticles. Therefore natural rubber latex extracted from H. brasiliensis can be employed in the preparation of stable aqueous dispersions of silver nanoparticles acting as a dispersing and/or capping agent. Moreover, this work provides a new method for the synthesis of silver nanoparticles that is simple, easy to perform, pollutant free and inexpensive. 相似文献
995.
Blanca Rojas de Gáscue José Luis Prin Gilma Hernández Enrique M. Vallés Arnaldo T. Lorenzo Alejandro J. Müller 《Journal of Thermal Analysis and Calorimetry》2011,103(2):669-678
The application of the Successive Self-nucleation and Annealing (SSA) thermal fractionation technique can yield detailed information
of the structural changes induced in linear polyethylene by irradiation. The production of tertiary carbons during the crosslinking
reactions can be equivalent to the structural heterogeneity present in branched polyethylenes since in both cases interruption
of the linear crystallizable sequences occurs, and these are structural differences that can be easily detected by thermal
fractionation. We demonstrate how correlations between melting point and short chain branching content employed for branched
polymers can be useful to characterize the distribution of chain heterogeneity produced by crosslinking. As the radiation
dose is increased and the crosslinking content also increases, the distribution of chain heterogeneity gets broader as detected
by SSA. When the results are coupled with morphological observations made by transmission electron microscopy, valuable information
on the morphological changes produced by crosslinking can also be ascertained, since the distribution of lamellar thicknesses
substantially broadens with crosslinking. Such a broad distribution can also be predicted from SSA by simple calculations
performed employing a modified version of the Gibbs–Thomson equation and is expected on the basis of random crosslinking reactions. 相似文献
996.
Machado AE Gomes WR Araújo DM Miglio HS Ueno LT De Paula R Cavaleiro JA Barbosa Neto NM 《Molecules (Basel, Switzerland)》2011,16(7):5807-5821
An imidazolium tetrasubstituted cationic porphyrin derivative (the free base and its Zn(II) complex) with five-membered heterocyclic groups in the meso-positions were synthesized using microwave irradiation, and the compounds obtained characterized by (1)H-NMR and mass spectrometry. We observed that under microwave irradiation the yield is similar to when the synthesis is performed under conventional heating, however, the time required to prepare the porphyrins decreases enormously. In order to investigate the electronic state of these compounds, we employed UV-Vis and fluorescence spectroscopy combined with quantum chemical calculations. The results reveal the presence, in both compounds, of a large number of electronic states involving the association between the Soret and a blue-shifted band. The Soret band in both compounds also shows a considerable solvent dependence. As for emission, these compounds present low quantum yield at room temperature and no solvent influence on the fluorescence spectra was observed. 相似文献
997.
Ronaldo S. Nunes Gilbert Bannach José M. Luiz Flávio J. Caires Claudio T. Carvalho Massao Ionashiro 《Journal of Thermal Analysis and Calorimetry》2011,106(2):525-529
Solid-state compounds of general formula Ln2L3·nH2O, where L represents 1,4-bis(3-carboxy-3-oxo-prop-1-enyl)benzene and Ln = La, Ce, Pr, Nd, Sm, were synthesized. Complexometric
titrations with EDTA, thermogravimetry (TG), differential thermal analysis (DTA), differential scanning calorimetry (DSC),
X-ray powder diffractometry, elemental analysis and infrared spectroscopy have been employed to characterize and to study
the thermal behavior of these compounds in dynamic air atmosphere. The results led to information about the composition, dehydration,
crystallinity, and thermal decomposition of the synthesized compounds. 相似文献
998.
Luiz K. C. de Souza Juliana J. R. Pardauil José R. Zamian Geraldo N. da Rocha Filho Carlos E. F. da Costa 《Journal of Thermal Analysis and Calorimetry》2011,106(2):355-361
Al-modified MCM-41, La-modified MCM-41, and Ce-modified MCM-41 mesoporous materials were prepared with different molar ratios
(Si/M = 10; 25; 50; 100 and 200) at room temperature. The materials were characterized using XRD, BET–BJH, and TG–DTA. The
XRD showed four peaks, due to the ordered hexagonal array of parallel silica tubes, which could be indexed as (100), (110),
(200), and (210), assuming a hexagonal unit cell. The surface area decreased as the concentration of the metal incorporated
in the material increased. The thermal stability of the materials was around 650 °C. The CeO2 phase made the mass transfer process more difficult, hindering Hofmann degradation and favoring oxidation. 相似文献
999.
Taís Vanessa Gabbay Alves Eraldo José Madureira Tavares Fauze Ahmad Aouada Charles Alberto Brito Negrão Marcos Enê Chaves Oliveira Anivaldo Pereira Duarte Júnior Carlos Emmerson Ferreira da Costa José Otávio Carréra Silva Júnior Roseane Maria Ribeiro Costa 《Journal of Thermal Analysis and Calorimetry》2011,106(3):717-724
This paper reports the thermal characterization of polyacrylamide-co-methylcellulose hydrogels and the constituent monomers (acrylamide and methylcellulose). Polymeric materials can be used
to produce hydrogels, which can be natural, synthetic, or a mixture. The hydrogels described here were obtained by free radical
polymerization, in the presence of N,N′-methylene-bis-acrylamide as a cross-linker agent. Four acrylamide concentrations were used for the synthesis of hydrogels:
3.6, 7.2, 14.7, and 21.7% (w/v). The materials so obtained were analyzed by TG, DTG, DSC, and FT-IR. The TG curves of acrylamide
and methylcellulose showed three mass loss events. In DSC curves, the acrylamide exhibited one melting peak at 84.5 °C, and
methylcellulose indicated one exothermic event. Nevertheless, acrylamide was considered more stable than methylcellulose.
The TG curves of the hydrogels exhibited three mass loss events, and on the DSC curves, three endothermic events were observed.
It was verified that the different acrylamide proportions influenced the thermic behavior of hydrogels, and that the authors
considered the 7.2% hydrogel a promising drug carrier system. The absorption bands were well defined, confirming the presence
of the functional groups in the samples. 相似文献
1000.
Hugo R. Fernandes Dilshat U. Tulyaganov Ashutosh Goel José M. F. Ferreira 《Journal of Thermal Analysis and Calorimetry》2011,103(3):827-834
This article aims to shed some light on the structure and thermo-physical properties of lithium disilicate glasses in the
system Li2O–SiO2–Al2O3–K2O. A glass with nominal composition 23Li2O–77SiO2 (mol%) (labelled as L23S77) and glasses containing Al2O3 and K2O with SiO2/Li2O molar ratios (3.13–4.88) were produced by conventional melt-quenching technique in bulk and frit forms. The glass-ceramics
(GCs) were obtained from nucleation and crystallisation of monolithic bulk glasses as well as via sintering and crystallisation
of glass powder compacts. The structure of glasses as investigated by magic angle spinning-nuclear magnetic resonance (MAS-NMR)
depict the role of Al2O3 as glass network former with four-fold coordination, i.e., Al(IV) species while silicon exists predominantly as a mixture
of Q
3
and Q
4
(Si) structural units. The qualitative as well as quantitative crystalline phase evolution in glasses was followed by differential
thermal analysis (DTA), X-ray diffraction (XRD) adjoined with Rietveld-reference intensity ratio (R.I.R.) method, Fourier
transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The possible correlation amongst structural
features of glasses, phase composition and thermo-physical properties of GCs has been discussed. 相似文献