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951.
Rejzek M Stockman RA van Maarseveen JH Hughes DL 《Chemical communications (Cambridge, England)》2005,(37):4661-4662
A tandem azide formation/intramolecular cycloaddition/triazoline fragmentation/Michael addition, which results in a non-symmetrical quinolizidine from an acyclic symmetrical precursor, is presented. 相似文献
952.
Addition of strained olefins, based on norbornene, norbornadiene,benzonorbornadiene or bicyclo [2.2.2] octene skeletons to π-allylic(hexafluoroacetylacetonato) palladium(II) complexes [(π-All)Pd(Hfacac)], gives “enyl” products derived from “insertion” of the olefin into the least substituted terminal allylicpalladium bond. The reaction involves an initial rapid and reversible formation of (gs-allyl)(π-olefin)Pd(Hfacac). The rate-determining step involves migration of a σ-allylic carbon atom from Pd to the coordinated olefin in a concerted cis—exo addition of PdC across the double bond. Remote electronegative substituents on the olefin do not affect the coordinative ability of the olefin towards Pd. They do however inhibit the migration of the σ-allylic ligand to the coordinated olefin. This observation is interpreted in terms of a small degree of polarization of the π-olefin—Pd bond in the transition state for the σ-allyl migration. 相似文献
953.
Summary The crystal and molecular structure oftrans-di(methylsulphito)bis(triphenylphosphine)platinum(II), Pt(SO3Me)2 (PPh3)2, derived from the reaction of Pt(PPh3)2 (O2) with SO2 in MeOH and in the presence of sodium tetraphenylborate(III), has been determined from diffractometer data. The complex crystallizes in the space group P ¯1- (Ci
1) with one molecule in a unit cell of dimensionsa = 9.744(2) Å,b = 10.062(3) Å,c = 11.153(2) Å; = 68.59(2)°, = 82.69(2)° and = 62.25(2)°. Leastsquares refinement has led to a value of the conventional R index (on F) of 0.031 for the 3308 reflections having F2>3(F0
2). The complex is a typical square-planar platinum(II) complex with the platinum atom lying on a crystallographically imposed centre of symmetry. The important structural parameters are Pt-P 2.369(1) Å, Pt-S 2.308(1) Å, and the oxygen atoms complete an approximate tetrahedron about the sulphur atoms with S-O 1.448(5) Å and S-O(Me) 1.620(5) Å. 相似文献
954.
Croce V Cosgrove T Dreiss CA Maitland G Hughes T 《Langmuir : the ACS journal of surfaces and colloids》2004,20(23):9978-9982
Small-angle neutron scattering studies were used to investigate the effect of adding an alcohol ethoxylate nonionic surfactant (d-C12E20) to aqueous solutions of a cationic surfactant, erucyl bis(hydroxyethyl) methylammonium chloride (EHAC), with and without salt (KCl). The systematic use of contrast-matching, by alternately highlighting or hiding one of the surfactants, confirms that mixed micelles are formed. In salt-free solutions, mixed spherical micelles are formed and a core-shell model combined with a Hayter-Penfold potential was used to describe the data. The core radius is dominated by the EHAC tails and the outer radius determined by the ethoxylate headgroups of the nonionic surfactant. Addition of KCl promotes micellar growth; however, results of varying the solvent contrast revealed that when the nonionic surfactant is incorporated into the wormlike structure micellar breaking is promoted. Thus, mixed wormlike micelles with shorter contour lengths compared to the pure EHAC worms are formed. 相似文献
955.
Hughes RP Ward AJ Golen JA Incarvito CD Rheingold AL Zakharov LN 《Dalton transactions (Cambridge, England : 2003)》2004,(17):2720-2727
A series of palladium(II) and platinum(II) complexes possessing pentafluorophenyl ligands of the general formula [M(L-L)(C6F5)Cl][space](M = Pd 3; L-L=tmeda (N,N,N',N',-tetramethylethylenediamine) a; 1,2-bis(2,6-dimethylphenylimino)ethane) b; dmpe (1,2-bis(dimethylphosphino)ethane) c; dcpe (1,2-bis(dicyclohexylphosphino)ethane) d; Pt ; L-L=tmeda a; 1,2-bis[3,5-bis(trifluoromethyl)phenylimino]-1,2-dimethylethane b; dmpe c; dcpe d) were readily synthesized from the dimer [M(C6F5)(tht)(mu-Cl)2] (M=Pd 1b, Pt 2b; tht=tetrahydrothiophene) and the corresponding bidentate ligand. In the case of palladium, the corresponding iodo analogues (6a-c) were readily synthesized in a one-pot reaction from [Pd2(dba)3], iodopentafluorobenzene, and the appropriate ligand. The platinum complexes 4c-d were then converted to the water complexes [Pt(L-L)(C6F5)(OH2)]OTf (L-L =dmpe 7a; dcpe 7b)via reaction with AgOTf in the presence of water. Attempts to convert the palladium complexes 3c-d to the corresponding water complexes resulted in the disproportionation of the intermediate water complex to form [Pd(L-L)(C6F5)2] (L-L=dmpe 8) or [Pd(L-L)2][OTf]2(L-L=dcpe 9). Upon standing in solution for prolonged periods, complex 7a undergoes an identical disproportionation reaction to the Pd analogues to form [Pt(L-L)(C6F5)2] (L-L=dmpe 10). Complexes 4c and 4d were converted to the corresponding hydrides (11b-c, respectively) using two different hydride sources: 11a was formed by the reaction of with NaBH4 in refluxing THF, while 11b was synthesized in near quantitative yield using [Cp2ZrH2] in refluxing THF. Attempts to synthesize eta2-tetrafluorobenzyne complexes [Pt(L-L)(C6F4)] (L-L=dmpe, dcpe) from reaction of 11a-b with butyllithium were unsuccessful. The molecular structures of 3a,4a, 4c, 4d, 6b, 7a, 8, 11b and have been determined by X-ray crystallographic studies, and are discussed. 相似文献
956.
Sineshchekov V Koppel L Hughes J Lamparter T Zeidler M 《Journal of photochemistry and photobiology. B, Biology》2000,56(2-3):145-153
The recombinant phytochrome of the moss Ceratodon purpureus (CP2) expressed in Saccharomyces cerevisiae and reconstituted with phycocyanobilin (PCB) was investigated using fluorescence spectroscopy. The pigment had an emission maximum at 670 nm at low temperature (85 K) and at 667 nm at room temperature (RT) and an excitation maximum at 650-652 nm at 85 K (excitation spectra could not be measured at RT). Both spectra had a half-band width of approx. 30-35 nm at 85 K. The fluorescence intensity revealed a steep temperature dependence with an activation energy of fluorescence decay (Ea) of 5.9-6.4 and 12.6-14.7 kJ mol(-1) in the interval from 85 to 210 K and from 210 to 275 K, respectively. The photochemical properties of CP2/PCB were characterised by the extent of the red-induced (lambda(a) = 639 nm) Pr conversion into the first photoproduct lumi-R at 85 K (gamma1) of approximately 0.07 and into Pfr at RT (gamma2) of approximately 0.7. From these characteristics, CP2/PCB can be attributed to the Pr" photochemical type with gamma1 < or = 0.05, which comprises the minor phyA fraction (phyA"), phyB, Adiantum phy1 and Synechocystis Cph1 in contrast to the major phyA' fraction (Pr' type with gamma1 = 0.5). Within the Pr" type, it is closer to phyA" than to phyB and Cph1. 相似文献
957.
Hughes RP Laritchev RB Zakharov LN Rheingold AL 《Journal of the American Chemical Society》2005,127(17):6325-6334
The iridium(perfluoropropyl)(vinyl) complex CpIr(PMe(3))(n-C(3)F(7))(CH=CH(2)) (5) has been prepared. It has been characterized by X-ray crystallography, and its ground state conformation in solution has been determined by (19)F{(1)H} HOESY NMR studies. It reacts with the weak acid lutidinium iodide to afford the eta(1)-allylic complex CpIr(PMe(3))((Z)-CH(2)CH=CFC(2)F(5))I (6), which has also been characterized crystallographically. The mechanism of C-F bond activation and C-C bond formation leading to 6 has been elucidated in detail by studying the reaction of 5 with lutidinium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate [LutH(+)B(ArF)(4)(-)], containing a weakly coordinating counteranion. The main kinetic product of this reaction, determined by (19)F{(1)H} HOESY studies at -50 degrees C, is the endo-CpIr(PMe(3))(anti-eta(3)-CH(2)CHCFCF(2)CF(3))[B(ArF)(4)] diastereomer 9, along with a small amount of the exo-syn-isomer 8. Isomer 9 rearranges at -20 degrees C to its exo-anti isomer 7, and subsequently to the thermodynamically favored exo-syn-isomer 8, which has been isolated and crystallographically characterized. Complex 8 reacts with iodide to afford complex6. On the basis of the unambiguously defined kinetically controlled stereochemistry of 9 and 8, a detailed mechanism for the C-F activation/C-C coupling reaction is proposed, the principal conclusion of which is that C-F activation is completely diastereoselective. 相似文献
958.
The TECRA Salmonella Visual Immunoassay (VIA) using Rappaport-Vassiliadis RV[R10] as a single selective enrichment broth has Final Action approval (AOAC Method 998.09). TECRA has recently developed a protocol (TECRA ULTIMA), which involves the addition of a new additive to a 1 mL aliquot of the RV[R10] broth, prior to the heat-killing step, thereby allowing the RV[R10] broth to be tested directly in the kit and thus eliminating the need for the 2 h post-enrichment in M broth. An in-house validation study was conducted to compare the modified AOAC Method 998.09 to the reference culture method. Three foods were used in the study: Naturally contaminated raw ground poultry at high (10-50 cells/25 g), and low (1-5 cells/25 g) levels; and milk powder and peanut butter, artificially inoculated at low and high levels with Salmonella bovismorbificans and S. enterica Mbandaka, respectively. Twenty test portions were analyzed for each level with 10 uninoculated control samples per food. Overall, no significant differences (p <0.05) were observed when the proportion of positive test portions for the modified VIA were compared with that for the reference method. This minor modification, which employs the additive (provided in the TECRA ULTIMA SALMONELLA Test Kit) to permit the direct analysis of RV[R10] broth has demonstrated the utility of the TECRA ULTIMA SALMONELLA protocol. It is recommended that the minor modification to Method 998.09 be approved First Action as an additional option within the method. 相似文献
959.
In this study, the choice of electrolyte systems for the separation and detection of a range of chlorophenoxyacetic acids and chlorophenols by means of capillary zone electrophoresis (CZE) is discussed. A series of acetate buffers over the buffering capacity pH range 4.03-5.5 were initially chosen for the separation. It was found that chlorophenoxyacetic acids could be separated at pH 4.03 and 4.5 but the most satisfactory separation of chlorophenols was obtained at pH 5.5. The factors affecting separation selectivity, including the addition of organic modifiers, was also studied. The use of 25% 2-butanol, 5% ethylene glycol and 10% acetonitrile as organic solvents resulted in the total separation of both classes of these compounds but poor peak shape of chlorophenols resulted and a number of chlorophenoxyacetic acids were not well separated. A borate-phosphate buffer gave improved peak shape of chlorophenols. Further improved separation of the components of the mixture was obtained by the addition of 2 mM fully methylated-beta-cyclodextrin to the 35 mM borate- 60 mM phosphate buffer at pH 6.5, maintaining good peak shape. In this case, separation of the two compound classes, chlorophenoxyacetic acids and chlorophenols, is achieved, with complete resolution of individual compounds in less than 5 min with high efficiency (of the order of 150,000 plates for the ca. 40 cm column). The method is applied to a commercial 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide mixture. 相似文献
960.
The modes of bonding in several norbornenyl complexes of palladinm(II) and platinum(II) has been investigated by both 1H and 13C NMR spectroscopy. Analysis of internal 1H1H, 13C1H, and 195Pt13C coupling constants indicate considerable distortion of the norbornenyl ligand in these complexes relative to organic norbornenes. The nature of this distortion is compatible with a π-homoallylic bonding scheme. 相似文献