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991.
Mössbauer spectra of KSnBr3·2H2O were very broad and could not fit Lorentz equation, suggesting unresolvable quadrupole doublets. Its quadrupole splitting was estimated to be about 0.25 mm/s from the separate experiments on frozen aqueous solutions of Sn(II)-Br? systems. Stability constants of bromostannate(II) complexes were determined at μ = 3.5 from the Δ-cL curve by the approximation method, which were in agreement with the literature values. 相似文献
992.
Skulan AJ Hanson MA Hsu HF Que L Solomon EI 《Journal of the American Chemical Society》2003,125(24):7344-7356
The spectroscopic properties and electronic structure of an Fe(2)(III,IV) bis-mu-oxo complex, [Fe(2)O(2)(5-Et(3)-TPA)(2)](ClO(4))(3) where 5-Et(3)-TPA = tris(5-ethyl-2-pyridylmethyl)amine, are explored to determine the molecular origins of the unique electronic and geometric features of the Fe(2)O(2) diamond core. Low-temperature magnetic circular dichroism (MCD) allows the two features in the broad absorption envelope (4000-30000 cm(-)(1)) to be resolved into 13 transitions. Their C/D ratios and transition polarizations from variable temperature-variable field MCD saturation behavior indicate that these divide into three types of electronic transitions; t(2) --> t(2) involving excitations between metal-based orbitals with pi Fe-O overlap (4000-10000 cm(-)(1)), t(2)/t(2) --> e involving excitations to metal-based orbitals with sigma Fe-O overlap (12500-17000 cm(-)(1)) and LMCT (17000-30000 cm(-)(1)) and allows transition assignments and calibration of density functional calculations. Resonance Raman profiles show the C(2)(h)() geometric distortion of the Fe(2)O(2) core results in different stretching force constants for adjacent Fe-O bonds (k(str)(Fe-O(long)) = 1.66 and k(str)(Fe-O(short)) = 2.72 mdyn/A) and a small ( approximately 20%) difference in bond strength between adjacent Fe-O bonds. The three singly occupied pi-metal-based orbitals form strong superexchange pathways which lead to the valence delocalization and the S = (3)/(2) ground state. These orbitals are key to the observed reactivity of this complex as they overlap with the substrate C-H bonding orbital in the best trajectory for hydrogen atom abstraction. The electronic structure implications of these results for the high-valent enzyme intermediates X and Q are discussed. 相似文献
993.
Boundary effects can have a profound influence on the electrophoretic behavior of a charged entity, in particular, when the entity is nonspherical and its surface conditions are dependent upon the nearby environment. In this study, the electrophoresis of a spheroid along the axis of an uncharged cylindrical pore is analyzed for the case where the electrical potential is low and the applied electric field is weak. We consider the case where the surface of a particle contains dissociable acidic and basic functional groups, which simulate biological colloids and entities covered by an artificial membrane. This leads to a mixed-type boundary value problem, which extends the conventional constant-surface-potential and constant-surface-charge-density models to a more general case. The effects of the particle aspect ratio, the relative magnitudes of particle and pore, the thickness of the double layer surrounding a particle, and the pH of the liquid phase on the electrophoretic mobility of a particle are investigated. Several interesting results are observed; for example, if the volume of a particle is fixed, its mobility may have a local maximum as the relative magnitudes of its two axes vary. 相似文献
994.
The efficient synthesis of 6H-benzo[c]chromen-6-one and dibenzo[c,h]chromen-6-one derivatives is described. Thus, treatment of arenediynes 1 and enediynes 5 with 5?mol % Ph3PAuCl and 10?mol % of AgSbF6 in refluxing toluene gave dibenzo[c,h]chromen-6-ones 4 and 6H-benzo[c]chromen-6-ones 6, in good yields, respectively. 相似文献
995.
Chun‐Hsu Yen Yi‐Deng Lin Hsiang‐Wen Hsueh Yun‐Jen Shieh Pei‐Fang Wu Ting‐Shen Kuo Yi‐Chou Tsai 《中国化学会会志》2019,66(9):1048-1063
A new family of the quintuply bonded dichromium complexes [Cr2{μ‐κ2‐HC(N‐2,6‐R2C6H3)2}2(μ‐κ2‐HC[NAr]2)] (R = iPr, Ar = 4‐MeC6H4 ( 5 ), Ar = 3,5‐Me2C6H3 ( 6 ), and Ar = 2,6‐Me2C6H3 ( 7 ); R = Et, Ar = 4‐MeC6H4 ( 8 ), Ar = 3,5‐Me2C6H3 [ 9 ], and Ar = 2,6‐Et2C6H3 ( 10 )) with a heteroleptic lantern configuration was obtained upon the addition of one equivalent of amidinate to the quintuply bonded dichromium amidinates [Cr{μ‐κ2‐HC(N‐2,6‐R2C6H3)2}]2 (R = iPr, Et). Additionally, the same approach was applied to the preparation of the acetate derivative [Cr2{μ‐κ2‐HC(N‐2,6‐ iPr2C6H3)2}2(μ‐κ2‐CH3CO2)] ( 11 ), which represents the first example that the quintuply bonded dinuclear complex contains an oxygen‐containing ligand. Of particular interest is that the Cr‐Cr bond lengths in these new trigonal paddlewheel quintuple Cr‐Cr bond species are comparable with those in their precursor compounds. They show ultrashort Cr‐Cr bond lengths in a narrow range of 1.740–1.755 å on the basis of single‐crystal X‐ray crystallography. The small Mayer bond orders of the long Cr‐N bonds as well as divergent, C2v and D3h, structural conformations in 5 – 11 suggest that the metal–ligand interactions possess minor covalent character and the electrostatic interactions play a dominant role. As a result, these extremely short Cr‐Cr quintuple bonds are caused by the overlap between five pairs of d orbitals that do not involve much in metal–ligand bonding. Additionally, anionic lantern dichromium trisamidinates 5 – 10 can be chemically oxidized by one electron, supported by electrochemistry, and their ease to undergo oxidation is presumably associated with their neutral lantern dichromium trisamindinate products, whose structures inherently display a Jahn‐Teller distortion, exemplified by the structure of the homoleptic dichromium complex [Cr2{μ‐κ2‐HC(N‐2,6‐Et2C6H3)2}3] [ 12 ] determined by X‐ray crystallography. These results unambiguously support the Cr‐Cr quintuple bonding in these novel anionic lantern dichromium complexes. 相似文献
996.
Hsiang‐Chun Chang Jia‐Qi Li Ching‐Kai Lin Yu‐Jung Hsu Tsung‐Han Tu Yi‐Liang Hsieh Hsiu‐Hao Hsu Gene‐Hsiang Lee Yi‐Hung Liu Chi‐How Peng 《中国化学会会志》2019,66(9):1119-1133
Poly(di(pyridin‐2‐yl)methyl acrylate) (PDPyMA), which was obtained by the free radical polymerization of designed coordinative monomer of di(pyridin‐2‐yl)methyl acrylate, is able to coordinate with various metal ions to form heterogeneous catalysts for diverse catalytic reactions. The Pd and Cu complexes supported by PDPyMA were developed for the heterogeneous Suzuki‐Miyaura reaction and Friedel‐Crafts alkylation, respectively. The PDPyMA‐based catalysts showed no significant decline of reactivity after five times recycling. However, the hydrolysis of the PDPyMA backbone under alkaline conditions limited the catalytic efficiency of this heterogeneous catalyst so that the coordinative monomer was redesigned as 1,1‐di(pyridine‐2‐yl)‐2‐(4‐vinylphenyl)ethan‐1‐ol and then 2,2′‐(1‐methoxy‐2‐(4‐vinylphenyl)ethane‐1,1‐diyl)dipyridine (MVPhDPy). With copolymerization of N‐isopropyl acrylamide (NIPAM), the efficiency of polymer‐based heterogeneous catalysts could be further raised, demonstrated by the increased turn over number in the Suzuki‐Miyaura reaction, which approached 5,260 by using the catalyst formed from poly(MVPhDPy‐co‐NIPAM) and Pd(OAc)2. poly(MVPhDPy‐co‐NIPAM) copolymer, therefore, could be a versatile platform to support different metal ions for various heterogeneous catalytic reactions. 相似文献
997.
WT Hsieh CJ Hsu BR Capraro T Wu CM Chen S Yang T Baumgart 《Langmuir : the ACS journal of surfaces and colloids》2012,28(35):12838-12843
Cellular membrane deformation and the associated redistribution of membrane-bound proteins are important aspects of membrane function. Current model membrane approaches for studying curvature sensing are limited to positive curvatures and often require complex and delicate experimental setups. To overcome these challenges, we fabricated a wavy substrate by imposing a range of curvatures onto an adhering lipid bilayer membrane. We examined the curvature sorting of several peripheral proteins binding to the wavy membrane and observed them to partition into distinct regions of curvature. Furthermore, single-molecule imaging experiments suggested that the curvature sensing of proteins on low-curvature substrates requires cooperative interactions. 相似文献
998.
As shown in the literature, gold nanoparticles (NPs) were popularly used in the fields of catalyst and surface-enhanced Raman scattering (SERS). In this work, size-controllable Au NPs coated on TiO(2) are synthesized by adjusting the pH of solutions based on sonoelectrochemical methods. The size-controlled Au NPs on TiO(2), ranging from 2 to 80 nm in diameter, can be obtained by varying the pH of solutions from 3 to 7 and placing the sample for 3 h before sonoelectrochemical reductions. The optimal particle sizes of Au NPs on TiO(2) to obtain the strongest SERS effects under an irradiation of 785 nm for probe molecules of adsorbed Rhodamine 6G (R6G) and deposited polypyrrole (PPy) are all ca. 60 nm. 相似文献
999.
The dynamics of S(3P2,1,0; 1D2; 1S0) production from the 193 nm photodissociation of CH3SH has been examined by 2+1 resonance-enhanced-multiphoton-ionization (REMPI) techniques. Using the rate equation scheme, we have rationalized the intensities of S(3P2,1,0; 1D2; 1S0) observed according to the sequential two-photon dissociative pathways, (A): CH3SH + hv (193 nm) → CH3S + hv (193 nm) → S and (B): CH3SH + hv (193 nm) → HS + hv (193 nm) → S, as the major mechanisms for S production. We have satisfactorily fitted the photodissociation laser power dependencies for S(3P) and S(1D) produced from CH3SH by invoking photodissociation cross sections and branching ratios S(3P)/S(1D) for CH3S and HS similar to those determined previously in the 193 nm photodissociation of CH3SCH3 and H2S. This observation supports that the 193 nm photodissociation of CH3S and HS prepared from CH3SH yield predominantly S(lD) and S(3P), similar to the cases for CH3S prepared from CH3SCH3 and for HS prepared from H2S, respectively. A small amount of S(1S0) observed from the 193 nm photodissociation of CH3SH is attributed to pathway (B). 相似文献
1000.
In this study, antipathogenic activities of the twig essential oil and its constituents from Chamaecyparis formosensis Matsum were evaluated in vitro against six plant pathogenic fungi. The essential oil from the fresh twigs was isolated using hydrodistillation in a Clevenger-type apparatus, and characterized by GC-FID and GC-MS. Twenty-five compounds were identified, representing 98.9% of the oil. The main components were beta-eudesmol (25.1%), tau-muurolol (21.6%), elemol (15.0%), totarol (14.9%), and alpha-cadinol (12.4%). The twig oil (500 mcirog/mL) showed growth inhibitory activity against the phytopathogenic fungi, Fusarium oxysporum, Pestalotiopsis funereal, and Ganoderma austral, with antifungal indices of 92.7%, 71.1%, and 87.7%, respectively. In addition, the oil suppressed totally the growth of Rhizoctonia solani, Colletotrichum gloeosporioides, and Fusarium solani. In order to ascertain the source compounds of these antipathogenic activities, the main components were individually evaluated. Tau-Muurolol and alpha-cadinol exhibited excellent activity against F. oxysporum, R. solani, C. gloeosporioides, and F. solani, with IC50 < 50 microg/mL. These compounds also efficiently inhibited the mycelial growths of P. funereal and G. austral. Thus, alpha-cadinol and tau-muurolol could be considered as potential natural fungicides for controlling fungal pathogens and worth. 相似文献