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991.
Evgeny V. Buravlev Irina Yu. Chukicheva Mikhail F. Borisenkov Aleksandr V. Kutchin 《合成通讯》2013,43(24):3670-3676
The work is devoted to a convenient procedure of the synthesis of 2,2′- and 4,4′-methylenebisphenols with alkyl substituents in heterogeneous catalysis. This compounds were obtained with yields up to 87% by reflux of 2,4- or 2,6-dialkylphenols with HCHO in n-octane in the presence of KSF clay. We found that the antioxidant activity on DPPH test for two novel methylenebisphenols having isobornyl fragments was comparable with control drugs. 相似文献
992.
Evgeny V. Tretyakov Svyatoslav E. TolstikovGalina V. Romanenko Artem S. BogomyakovDmitry V. Stass Marsil K. KadirovKirill V. Holin Oleg G. SinyashinVictor I. Ovcharenko 《Polyhedron》2011,30(18):3232-3237
An approach to the synthesis of nitronyl nitroxide 2,2′-(buta-1,3-diyne-1,4-diyl)bis(4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole 3-oxide 1-oxyl) (4) was developed. Compound 4 is the first diradical with nitronyl nitroxide groups directly linked through a diacetylene fragment. In solid phase the diradicals are arranged in stacks with parallel CC fragments, with the distances between the terminal carbon atoms of the neighboring diacetylene groups (T and d) being 6.170 and 4.466 Å, respectively, and the angle between the translation vector and the median line passing through the CCCC fragment of 45.9°. The values of T and d are outside the range of structural criteria allowing a topochemical reaction. Thus UV irradiation does not initiate solid phase polymerization of 4. After exposure at 373 K for 1 h the crystals of 4 turn dark-brown, become X-ray amorphous and lose the majority of their paramagnetic centers without significantly changing their mass. Upon further heating up to 400-420 K the product explodes, releasing about 360 kJ/mol of heat. A diluted solution of 4 in 1,4-dioxane produces an EPR spectrum typical of a strong exchange (a multiplet of nine broadened lines with A4N = 0.35 mT), indicating the efficiency of the CCCC fragment as an exchange channel. The character of the experimental μeff(T) dependence for 4 indicates a strong intramolecular antiferromagnetic-type exchange interaction (J/kB ∼ −104 K) and the dominating weak intermolecular ferromagnetic exchange. 相似文献
993.
Stavitski E Pidko EA Couck S Remy T Hensen EJ Weckhuysen BM Denayer J Gascon J Kapteijn F 《Langmuir : the ACS journal of surfaces and colloids》2011,27(7):3970-3976
Some Metal Organic Frameworks (MOFs) show excellent performance in extracting carbon dioxide from different gas mixtures. The origin of their enhanced separation ability is not clear yet. Herein, we present a combined experimental and theoretical study of the amino-functionalized MIL-53(Al) to elucidate the mechanism behind its unusual high efficiency in CO(2) capture. Spectroscopic and DFT studies point out only an indirect role of amine moieties. In contrast to other amino-functionalized CO(2) sorbents, no chemical bond between CO(2) and the NH(2) groups of the structure is formed. We demonstrate that the functionalization modulates the "breathing" behavior of the material, that is, the flexibility of the framework and its capacity to alter the structure upon the introduction of specific adsorbates. The absence of strong chemical interactions with CO(2) is of high importance for the overall performance of the adsorbent, since full regeneration can be achieved within minutes under very mild conditions, demonstrating the high potential of this type of adsorbents for PSA like systems. 相似文献
994.
Vedernikov AI Ushakov EN Efremova AA Kuz'mina LG Moiseeva AA Lobova NA Churakov AV Strelenko YA Alfimov MV Howard JA Gromov SP 《The Journal of organic chemistry》2011,76(16):6768-6779
4,4'-Bipyridine and 2,7-diazapyrene derivatives (A) having two ammonioalkyl N-substituents were synthesized. The complex formation of these compounds with bis(18-crown-6)stilbene (D) was studied by spectrophotometry, cyclic voltammetry, (1)H NMR spectroscopy, and X-ray diffraction analysis. In MeCN, π-donor D and π-acceptors A form supramolecular 1:1 (D·A) and 2:1 (D·A·D) charge-transfer complexes. The D·A complexes have a pseudocyclic structure as a result of ditopic binding of the ammonium groups to the crown-ether fragments. The better the geometric matching between the components, the higher the stability of the D·A complexes (log K up to 9.39). A key driving force of the D·A·D complex formation is the excessive steric strain in the precursor D·A complexes. The pseudocyclic D·A complexes involving the ammoniopropyl derivative of 4,4'-bipyridine were obtained as single crystals. Crystallization of the related ammonioethyl derivative was accompanied by transition of the D·A complexes to a structure of the (D·A)(m) coordination polymer type. 相似文献
995.
Hg(AuF6)2 crystallizes at 200 K in the orthorhombic space group Pbcn (No. 60) with a = 917.67(7) pm, b = 971.59(8) pm, c = 962.04(8) pm, and Z = 4. Mercury atoms are coordinated by eight fluorine atoms with six short and two long Hg-F contacts. HgF8 polyhedra share their four vertices and two edges with six AuF6 units forming a tridimensional framework.The results of X-ray diffraction analysis on single crystals of AgFAuF6 are in agreement with previously known powder X-ray diffraction data (Casteel et al, J. Solid State Chem. 96 (1992) 84-96). AgFAuF6 crystallizes orthorhombic in the space group Pnma (No. 62), a = 717.06(7) pm, b = 761.67(7) pm, c = 1013.61(10) pm at 200 K, Z = 4. 相似文献
996.
Oleg E. Korneychik Artem M. Abakumov Marina G. Rozova Konstantin V. Pokholok Evgeny V. Antipov 《Journal of solid state chemistry》2011,184(12):3150-3157
Pb2.85Ba2.15Fe4SnO13, a new n=5 member of the anion-deficient perovskite based AnBnO3n−2 (A=Pb, Ba, B=Fe, Sn) homologous series, was synthesized by the solid state method. The crystal structure of Pb2.85Ba2.15Fe4SnO13 was investigated using a combination of neutron powder diffraction, electron diffraction, high angle annular dark field scanning transmission electron microscopy and Mössbauer spectroscopy. It crystallizes in the Ammm space group with unit cell parameters a=5.7990(1) Å, b=4.04293(7) Å and c=26.9561(5) Å. The Pb2.85Ba2.15Fe4SnO13 structure consists of quasi two-dimensional perovskite blocks separated by 1/2[110](1?01)p crystallographic shear (CS) planes. The corner-sharing FeO6 octahedra at the CS planes are transformed into edge-sharing FeO5 distorted tetragonal pyramids. The octahedral positions in the perovskite blocks between the CS planes are jointly taken up by Fe and Sn, with a preference of Sn towards the position at the center of the perovskite block. The chains of FeO5 pyramids and (Fe,Sn)O6 octahedra of the perovskite blocks delimit six-sided tunnels at the CS planes occupied by double chains of Pb atoms. The compound is antiferromagnetically ordered below TN=368±15 K. 相似文献
997.
A combined experimental and computational study of the ionic‐liquid‐mediated dehydration of glucose and fructose by CrII and CrIII chlorides has been performed. The ability of chromium to selectively dehydrate glucose to 5‐hydroxymethylfurfural (HMF) in the ionic liquid 1‐ethyl‐3‐methyl imidazolium chloride does not depend on the oxidation state of chromium. Nevertheless, CrIII exhibits higher activity and selectivity to HMF than CrII. Anhydrous CrCl2 and CrCl3?6 H2O readily catalyze glucose dehydration with HMF yields of 60 and 72 %, respectively, after 3 h. Anhydrous CrCl3 has a lower activity, because it only slowly dissolves in the reaction mixture. The transformation of glucose to HMF involves the formation of fructose as an intermediate. The exceptional catalytic performance of the chromium catalysts is explained by their unique ability to catalyze glucose to fructose isomerization and fructose to HMF dehydration with high selectivity. Side reactions leading to humins by means of condensation reactions take predominantly place during fructose dehydration. The higher HMF selectivity for CrIII is tentatively explained by the higher activity in fructose dehydration compared to CrII. This limits the concentration of intermediates that are involved in bimolecular condensation reactions. Model DFT calculations indicate a substantially lower activation barrier for glucose isomerization by CrIII compared to CrII. Qualitatively, glucose isomerization follows a similar mechanism for CrII and CrIII. The mechanism involves ring opening of D ‐glucopyranose coordinated to a single Cr ion, followed by a transient self‐organization of catalytic chromium complexes that promotes the rate‐determining hydrogen‐shift step. 相似文献
998.
Galina L. Levit Dmitry A. GruzdevVictor P. Krasnov Evgeny N. ChulakovLiliya Sh. Sadretdinova Marina A. EzhikovaMikhail I. Kodess Valery N. Charushin 《Tetrahedron: Asymmetry》2011,22(2):185-189
The acylative kinetic resolution of racemic 2-methyl-1,2,3,4-tetrahydroquinoline and 2,3-dihydro-3-methyl-4H-1,4-benzoxazine using acyl chlorides of N-phthaloyl-(S)-phenylalanine, N-phthaloyl-3-(4-nitrophenyl)-(S)-alanine and N-phthaloyl-O-methyl-(S)-tyrosine as chiral resolving agents has been carried out. It is shown that the effectiveness of an acylative kinetic resolution depends on the electronic effects of substituents in the phenyl fragment of the acylating agent and increases as the electron-donating properties of the para-substituent (OMe > H > NO2) in phenyl fragment of N-phthaloyl-3-aryl-(S)-alanyl chlorides increase; conducting the process at a reduced temperature also contributes to an enhancement of the kinetic resolution. 相似文献
999.
Acoustic measurements using synchrotron radiation have been performed on glassy GeSe2 up to pressures of 9.6 GPa. A minimum observed in the shear-wave velocity, associated anomalous behavior in Poisson's ratio, and discontinuities in elastic moduli at 4 GPa are indicative of a gradual structural transition in the glass. This is attributed to a network rigidity minimum originating from a competition between two densification mechanisms. At pressures up to 3 GPa, a conversion from edge- to corner-sharing tetrahedra results in a more flexible network. This is contrasted by a gradual increase in coordination number with pressure, which leads to an overall stiffening of the glass. 相似文献
1000.
We propose a class of schemes for robust population transfer between quantum states that utilize trains of coherent pulses, thus forming a generalized adiabatic passage via a wave packet. We study piecewise stimulated Raman adiabatic passage with pulse-to-pulse amplitude variation, and piecewise chirped Raman passage with pulse-to-pulse phase variation, implemented with an optical frequency comb. In the context of production of ultracold ground-state molecules, we show that with almost no knowledge of the excited potential, robust high-efficiency transfer is possible. 相似文献