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41.
42.
Carra C Iordanova N Hammes-Schiffer S 《Journal of the American Chemical Society》2003,125(34):10429-10436
Theoretical calculations of a model for tyrosine oxidation in photosystem II are presented. In this model system, an electron is transferred to ruthenium from tyrosine, which is concurrently deprotonated. This investigation is motivated by experimental measurements of the dependence of the rates on pH and temperature (Sj?din et al. J. Am. Chem. Soc. 2000, 122, 3932). The mechanism is proton-coupled electron transfer (PCET) at pH < 10 when the tyrosine is initially protonated and is single electron transfer (ET) for pH > 10 when the tyrosine is initially deprotonated. The PCET rate increases monotonically with pH, whereas the single ET rate is independent of pH and is 2 orders of magnitude faster than the PCET rate. The calculations reproduce these experimentally observed trends. The pH dependence for the PCET reaction arises from the decrease in the reaction free energies with pH. The calculations indicate that the larger rate for single ET arises from a combination of factors, including the smaller solvent reorganization energy for ET and the averaging of the coupling for PCET over the reactant and product hydrogen vibrational wave functions (i.e., a vibrational overlap factor in the PCET rate expression). The temperature dependence of the rates, the solvent reorganization energies, and the deuterium kinetic isotope effects determined from the calculations are also consistent with the experimental results. 相似文献
43.
Treatment of [Ti(O-i-Pr)(2)Cl(2)] with NaL(OEt) (L(OEt)(-) = [CpCo[P(O)(OEt)(2)](3)](-), Cp = eta(5)-C(5)H(5)) afforded [L(OEt)Ti(O-i-Pr)(2)Cl] that reacted with HCl in ether to give [L(OEt)TiCl(3)] (1). The average Ti-O and Ti-Cl distances in 1 are 1.975 and 2.293 A, respectively. Reaction of titanyl sulfate with NaL(OEt) in water followed by addition of HBF(4) afforded [L(OEt)TiF(3)] (2), the Ti-O and Ti-F distances of which are 2.020(2) and 1.792(2) A, respectively. The Zr(IV) analogue [L(OEt)ZrF(3)] (3) was prepared similarly from zirconyl nitrate, NaL(Oet), and HBF(4) in water. The Zr-O and average Zr-F distances in 3 are 2.139(2) and 1.938(2) A, respectively. Treatment of 1 with tetrachlorocatechol (H(2)Cl(4)cat) afforded [L(OEt)Ti(Cl(4)cat)Cl] (4). The average Ti-O(P), Ti-O(C), and Ti-Cl distances in 4 are 1.972, 1.926, and 2.334 A, respectively. Hydrolysis of 4 in the presence of Et(3)N yielded the mu-oxo dimer [(L(OEt))(2)Ti(2)(Cl(4)cat)(2)(mu-O)] (5). The average Ti-O(P), Ti-O(C), and Ti-O(Ti) distances in 5 are 2.027, 1.926, and 1.7977(9) A. Treatment of 1 with 1,1'-binaphthol (BINOLH(2)) in the presence of Et(3)N afforded [(L(OEt))(2)Ti(2)(mu-O)(2)(mu-BINOL)] x 2BINOLH(2) (6.2BINOLH(2)). Complex 1 is capable of catalyzing ring opening of epoxides with Me(3)SiN(3) under solvent-free conditions presumably via a Ti-azide intermediate. 相似文献
44.
Sharon E. Davis A. Cameron Church Rebecca C. Tummons Charles F. Beam 《Journal of heterocyclic chemistry》1997,34(4):1159-1162
C(α)-Carboxylic acid esters were treated with excess lithium diisopropylamide, condensed with methyl salicylates or methyl thiosalicylate, followed by acid cyclization to either 4-hydroxy-3-substituted, 2H-1-benzopyran-2-ones (coumarins), or 2H-1-benzothiopyran-2-ones (thiocoumarins). 相似文献
45.
Lu XX Tang HS Ko CC Wong JK Zhu N Yam VW 《Chemical communications (Cambridge, England)》2005,(12):1572-1574
The anion-assisted shift of trans-cis isomerization equilibrium of a palladium(II) complex containing acetanilide functionalities brought about by allosteric hydrogen bonding interactions has been established by UV/Vis, 1H NMR, 31P NMR and ESI-MS studies. 相似文献
46.
Shahriare Ghammamy Monir Rahnama Baghy Wong Wing-Tak Kheiroallah Mehrani Saied Maleki 《Transition Metal Chemistry》2007,32(2):257-261
The complex of propyltriphenylphosphonium bromochromate(VI), PrPh3P[CrO3Br] is easily synthesized in nearly quantitative yield using a direct reaction of chromium(VI) oxide and propyltriphenylphosphonium
bromide. This compound is a versatile reagent for the efficient and selective oxidation of organic substrates, in particular
for alcohols to their corresponding aldehydes or ketones, under mild conditions. This compound was characterized by IR, UV/Visible,
13C-n.m.r. and 1H-n.m.r. techniques. It crystallized in the monoclinic form and its crystal and molecular structure have been determined by
X-ray crystallography. 相似文献
47.
Zorbas V Kanungo M Bains SA Mao Y Hemraj-Benny T Misewich JA Wong SS 《Chemical communications (Cambridge, England)》2005,(36):4598-4600
A spatially confined photocatalytic oxidation of a thin film of synthetic textile azo dye (Procion Red MX-5B) using TiO2-functionalized AFM probes is described. 相似文献
48.
Howard C. Clark Anil B. Goel Chun S. Wong 《Journal of organometallic chemistry》1980,190(4):C101-C104
Simple synthetic routes to the mixed ligand complexes PtLL'X2 and PtLL'XY (L' = PEt3; L = phosphine, arsine, etc.; X = Cl and Y = Cl, H or Me) are described; unexpectedly, these display an extensive chemistry without disproportionation, although in some cases ligand scrambling does occur. 相似文献
49.
Thermal decomposition of bis(hexamethylbenzene)iron(0) in the presence of carbon monoxide yields a novel carbonyl iron complex, [C6(CH3)6]Fe(CO)2. The cyclohexadiene complex [C6(CH3)6]Fe(C6H8) is obtained from reaction of bis(hexamethylbenzene)iron(0) with either 1,3-cyclohexadiene or benzene, and the yield is much greater in the presence of hydrogen gas. Interaction of bis-(hexamethylbenzene)iron(0) with 2-butyne induces a catalytic cyclotrimerization to give more hexamethylbenzene. Kinetic and isotope distribution studies indicate that the primary step in these reactions is not a direct loss of one ring ligand, but rather an insertion of the iron center into one of the ligand methyl CH bonds, leading to a benzyl hydride complex species. Mechanisms for the subsequent reactions of this iron hydride species are proposed. 相似文献
50.
Wong KT Fang FC Cheng YM Chou PT Lee GH Wang Y 《The Journal of organic chemistry》2004,69(23):8038-8044
A new series of aza-substituted analogues 3-5 based on the 1,4-bis(phenylethynyl)benzene moiety have been synthesized by the selective Pd-catalyzed Sonogashira coupling reaction from 5-bromo-2-iodopyrimidine (1). In these linear molecules, the dipolar pyrimidine moiety is introduced as a probe to investigate factors that control the intermolecular interactions over the crystal engineering. The results reveal that the manner of packing changes both dipolar interactions between linear pyrimidine-containing molecules and transition moments simultaneously, resulting in remarkably different photophysical properties. Due to their versatile dipole-dipole and face-to-face pi-piinteractions in a crystal motif, further applications on the design of ordered crystalline materials for the field effect transistors are promising. 相似文献