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991.
Diffey B 《Photochemistry and photobiology》2008,84(2):371-375
Determining the variability of solar UV exposure of different members of a population by direct measurement demands high compliance over an extended period of time by a large number of people. An alternative approach is to model the variables that affect personal exposure and this is the basis of the method reported here, which uses a random sampling technique to explore variability of exposure at different times of the year by habitués. It is shown that there are large variations in daily personal erythemal exposure, more so for indoor workers living in northern Europe than those resident in Florida, which are due not only to seasonal changes in ambient, but just as importantly to seasonal variation in behavior. Not surprisingly, holiday and summer weekend exposure account for the largest daily UV doses. Northern Europeans who take their summer vacation in Florida can double their exposure during this period compared with holidaying at home and this illustrates just how important sun protection measures should be during recreational exposure in areas of high insolation if the annual UV burden is to be sensibly controlled. 相似文献
992.
993.
Kevin J. Coutinho Ron S. Dickson George A. Koutsantonis Brian W. Skelton Allan H. White Prof. Dr. 《无机化学与普通化学杂志》2008,634(4):669-674
Syntheses of the array of heterobimetallic complexes [(OC)3M(μ‐PPh2)2(μ‐O‐C(CHMe(CH2)2PPh2)RhL], M = Cr, Mo, W, L = tBuNC, are described, extending the previous study of the counterpart array for L = CO. A single crystal X‐ray structure determination is reported for the M = Mo adduct, enabling comparison with its previously reported L = CO counterpart, for which an improved redetermination is also reported. In the present complex the tBuNC ligand is found to be much more weakly bound (Rh‐C 2.026(5) Å) than the carbonyl group it displaces (Rh‐C 1.945(2) Å) with concomitant minor impact on the remainder of the rhodium ambience. 相似文献
994.
Zeta potential and electroosmotic mobility in microfluidic devices fabricated from hydrophobic polymers: 2. Slip and interfacial water structure 总被引:2,自引:0,他引:2
We discuss the structure of water at hydrophobic interfaces from the standpoint of its impact on electrokinetic phenomena in microfluidic devices fabricated from hydrophobic polymers such as Teflon or Zeonor. Water structuring at hydrophobic interfaces has been described as a source of interfacial charge (see Part 1, this issue), and dewetting phenomena, whether via depletion layers or nanobubbles, contribute to slip and enhanced apparent electrokinetic potentials. Issues concerning the impact of hydrodynamic slip and the role of diffuse interfacial structures are discussed. These issues are coupled with each other and with interfacial charge concerns, providing challenges for measurements of individual parameters. 相似文献
995.
Crow B Bishop M Kovalcik K Norton D George J Bralley JA 《Biomedical chromatography : BMC》2008,22(4):394-401
A rapid and high-throughput method for the determination of urinary levels of the oxidative stress biomarker, 8-hydroxy-2'-deoxyguanosine (8-OH-dG), has been developed and validated using liquid chromatography combined with electrospray ionization tandem mass spectrometry (LC-MS/MS). The assay features a cheap and readily available non-isotopic internal standard, a single-step filtration sample preparation, and a total analysis time of 6 min including column re-equilibration. The method was validated based on linearity, accuracy (100-106%), precision (CV < 7%), sample preparation stability (< or =5%, 72 h). Intra-laboratory patient ranges were established comparing children and adults (n = 345). 相似文献
996.
Moinard-Chécot D Chevalier Y Briançon S Beney L Fessi H 《Journal of colloid and interface science》2008,317(2):458-468
A detailed investigation into the mechanisms of nanocapsule formation by means of the two stages "emulsion-diffusion" process is reported. Such widely used process is still poorly understood. An emulsion of oil, polymer and ethyl acetate is fabricated as a first step; dilution with pure water allows ethyl acetate to diffuse out from the droplets, leaving a suspension of nanocapsules at the end. It has been shown that the size of nanocapsules was related to the chemical composition of the organic phase and the size of primary emulsion through a simple geometrical relationship. As a consequence, most of the properties of the nanocapsules were decided at the emulsification step. The influence of several formulation and processing parameters of the primary emulsion was studied accordingly. The thin polymer membrane of nanocapsules was observed by means of cryo-fracture electron microscopy. Finally two experiments were designed for a mechanistic investigation of the diffusion step. A step-by-step diffusion of the organic solvent takes place by successive partition equilibria of ethyl acetate between the droplets and aqueous phase. A time-resolved experiment shows the fast diffusion (less than 20 ms) related to the small droplet size of the emulsion. 相似文献
997.
Observed pseudo-first-order rate constants (k(obs)) of the hydride-transfer reactions from isopropyl alcohol (i-PrOH) to two NAD(+) analogues, 9-phenylxanthylium ion (PhXn(+)) and 10-methylacridinium ion (MA(+)), were determined at temperatures ranging from 49 to 82 degrees C in i-PrOH containing various amounts of AN or water. Formations of the alcohol-cation ether adducts (ROPr-i) were observed as side equilibria. The equilibrium constants for the conversion of PhXn(+) to PhXnOPr-i in i-PrOH/AN (v/v = 1) were determined, and the equilibrium isotope effect (EIE = K(i-PrOH)/K(i-PrOD)) at 62 degrees C was calculated to be 2.67. The k(H) of the hydride-transfer step for both reactions were calculated on the basis of the k(obs) and K. The corresponding deuterium kinetic isotope effects (e.g., KIE(OD)(H) = k(H)(i-PrOH)/k(H)(i-PrOD) and KIE(beta-D6)(H) = k(obs)(i-PrOH)/k(obs)((CD3)2CHOH)), as well as the activation parameters, were derived. For the reaction of PhXn(+) (62 degrees C) and MA(+) (67 degrees C), primary KIE(alpha-D)(H) (4.4 and 2.1, respectively) as well as secondary KIE(OD)(H) (1.07 and 1.18) and KIE(beta-D6)(H) (1.1 and 1.5) were observed. The observed EIE and KIE(OD)(H) were explained in terms of the fractionation factors for deuterium between OH and OH(+)(OH(delta+)) sites. The observed inverse kinetic solvent isotope effect for the reaction of PhXn(+) (k(obs)(i-PrOH)/k(obs)(i-PrOD) = 0.39) is consistent with the intermolecular hydride-transfer mechanism. The dramatic reduction of the reaction rate for MA(+), when the water or i-PrOH cosolvent was replaced by AN, suggests that the hydride-transfer T.S. is stabilized by H-bonding between O of the solvent OH and the substrate alcohol OH(delta+). This result suggests an H-bonding stabilization effect on the T.S. of the alcohol dehydrogenase reactions. 相似文献
998.
Baker MV Brown DH Heath CH Skelton BW White AH Williams CC 《The Journal of organic chemistry》2008,73(23):9340-9352
This paper describes the synthesis, structural characterization, and solution behavior of some xylyl-linked imidazolium and benzimidazolium cyclophanes decorated with alkyl or alkoxy groups. The addition of alkyl/alkoxy chains to the cyclophanes allows for studies in chlorinated solvents, whereas previous solution studies of azolium cyclophanes have generally required highly polar solvents. The azolium cyclophanes may exist in a syn/syn conformation (azolium rings mutually syn, arene rings mutually syn) or a syn/anti conformation (azolium rings mutually syn, arene rings mutually anti). The preferred conformation is significantly affected by (i) binding of bromide (ion pairing) to the protons on the imidazolium or benzimidazolium rings, which occurs in solutions of bromide salts of the cyclophanes in chlorinated solvents, and (ii) the addition of alkoxy groups to the benzimidazolium cyclophanes. These structural modifications have also led to cyclophanes that adopt conformations not previously identified for similar azolium cyclophane analogues. Detailed (1)H NMR studies for one cyclophane identified binding of bromide at two independent sites within the cyclophane. 相似文献
999.
Michael I. Bruce Natasha N. Zaitseva Brian W. Skelton 《Journal of organometallic chemistry》2008,693(17):2887-2897
Several complexes containing Co3 carbonyl clusters end-capping carbon chains of various lengths are described. Pd(0)/Cu(I)-catalysed reactions between {Co3{μ3-C(CC)2Au(PPh3)}(μ-dppm)(CO)7 and I(CC)2SiMe3 or FcCCI gave {Co3{μ3-C(CC)xR}(μ-dppm)(CO)7 [x = 4, R = SiMe33; x = 3, R = Fc 8]; treatment of 3 with NaOMe and AuCl(PPh3) gave 4 [x = 4, R = Au(PPh3)]. Related preparations of Co3{μ3-C(CC)2[Ru(PP)Cp′]}(μ-dppm)n(CO)9−2n [PP = (PPh3)2, Cp’ = Cp, n = 1, 5; PP = dppe, Cp′ = Cp∗, n = 1, 6; 0, 7] are also described. Syntheses of bis-cluster complexes {Co3(μ-dppm)(CO)7}2(μ-Cx) (x = 14, 12; 16, 9; 18, 11; 26, 10) - the latter being the longest cluster-capped Cx chains so far described - and the mercury-bridged compounds Hg{(CC)xC[Co3(μ-dppm)(CO)7]}2 (x = 1, 13; 2, 14) are reported. The molecular structures of 7, 12, 13 and 14, as well as of Co3(μ3-CCCSiMe3)(μ-dppm)(CO)6(PPh3) (15) and Co3{μ3-CC(O)OEt}(μ-dppm)(CO)7 (16), are reported. 相似文献
1000.
Lindsay T. Byrne George A. Koutsantonis Brian W. Skelton Allan H. White 《Journal of organometallic chemistry》2008,693(10):1738-1750
The trimetallic clusters [Ru3(CO)10(dppm)], [Ru3(CO)12] and [RuCo2(CO)11] react with a number of multifunctional secondary phosphine and tertiary arsine ligands to give products consequent on carbonyl substitution and, in the case of the secondary phosphines, PH activation. The reaction with the unresolved mixed P/S donor, 1-phenylphosphino-2-thio(ethane), HSCH2CH2PHPh ( LH2), gave two products under various conditions which have been characterised by spectroscopic and crystallographic means. These two complexes [Ru3(μ-dppm)(H)(CO)7(LH)] and [Ru3(μ-dppm)(H)(CO)8(LH)Ru3(μ-dppm)(CO)9], show the versatility of the ligand, with it chelating in the former and bridging two Ru3 units in the latter. The stereogenic centres in the molecules gave rise to complicated spectroscopic data which are consistent with the presence of diastereoisomers. In the case of [Ru3(CO)12] the reaction with LH2 gave a poor yield of a tetranuclear butterfly cluster, [Ru4(CO)10(L)2], in which two of the ligands bridge opposite hinge wingtip bonds of the cluster. A related ligand, HSCH2CH2AsMe(C6H4CH2OMe), reacted with [RuCo2(CO)11] to give a low yield of the heterobimetallic Ru-Co adduct, [RuCo(CO)6(SCH2CH2AsMe(C6H4CH2OMe))], which appears to be the only one of its type so far structurally characterised.The secondary phosphine, HPMe(C6H4(CH2OMe)) and its oxide HP(O)Me(C6H4(CH2OMe)) also react with the cluster [Ru3(CO)10(dppm)] to give carbonyl substitution products, [Ru3(CO)5(dppm)(μ2-PMe(C6H4CH2OMe))4], and [Ru3H(CO)7(dppm)(μ2,η1-P(O)Me(C6H4CH2OMe))]. The former consists of an open Ru3 triangle with four phosphide ligands bridging the metal-metal bonds; the latter has the O atom symmetrically bridging one Ru-Ru bond, the P atom being attached to a non-bridged Ru atom. 相似文献