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71.
A recently reported fiber-optic sensor based on a homogeneous fluorescence energy-transfer immunoassay operates in a continuous, reversible manner to quantify the anticonvulsant drug phenytoin (5,5-diphenylhydantoin). The chemical kinetics of the two simultaneous antibody-hapten (analyte) and antibody-hapten (labeled indicator) reactions in the sensor are now modeled mathematically. Simulation shows that the chemical response time is controlled by the dissociation rate constant and is independent of the association rate constant, and that an equalibrium chemical response can be achieved in minutes. The sensitivity and dynamic range of the analyte concentration which can be measured depends on the ratio of dissociation rate constants for the labeled and unlabeled hapten reactions, and on the total concentration of reactants in the sensor. The relative concentration ratios of antibody to labeled hapten has little impact on the sensitivity or dynamic range of the system, but can be optimized to provide the maximum amount of labeled hapten availble for instrumental measurement. 相似文献
72.
The kinetics and thermodynamics of atropisomerism within the protected kedarcidin chromophore aglycon 8, as well as a series of ansa-bridged synthetic intermediates leading to 8, were determined by 1H NMR spectroscopy. The data show that the ratio of atropisomeric forms of chloropyridine-bridged ansa intermediates is subject to wide variation with seemingly subtle structural variation. The vinyl bromide 4, for example, in the first X-ray structure determination of a kedarcidin ansa-bridged system, was found to exist as a single atropisomer in the solid state, but a nearly equal mixture (K = 0.70) of isomers in solution (t1/2 for isomer interconversion approximately 0.2 s at 20 degrees C). The aglycon 8, a 2.2:1 mixture of atropisomers, was found to undergo direct unimolecular biradical-forming cycloaromatization at ambient temperature in a mixture of 1,4-cyclohexadiene-benzene, without nucleophilic activation. The product 9 was formed as a single atropisomer (k = 2 x 10-4 s-1, t1/2 = 58 min, 81% yield), suggesting that the rate of atropisomerism within 8 is rapid with respect to cycloaromatization. The rate of cycloaromatization of 8 was found to be highly solvent-dependent, being more rapid in the presence of a good hydrogen-atom donor, consistent with the earlier model studies of Hirama et al. that showed that certain nine-membered cyclic (Z)-enediynes may equilibrate with their biradical cycloaromatization products. Incubation of 8 with beta-mercaptoethanol, under conditions mimicking experiments leading to DNA cleavage with kedarcidin, showed no evidence for nucleophilic activation. The product of direct cycloaromatization (9) was isolated instead. The evidence suggests that kedarcidin, like the enediyne agent C-1027, is capable of spontaneous thermal biradical formation without prior chemical activation. 相似文献
73.
An efficient strategy is described for the synthesis of enantiopure calystegine alkaloids. The key step employs a zinc-mediated fragmentation of benzyl-protected methyl 6-iodo-glycosides followed by in situ formation of the benzyl imine and Barbier-type allylation with zinc, magnesium, or indium metal. Stereochemistry in the pivotal allylation is controlled by the choice of the metal. The functionalized 1,8-nonadienes, thus formed, are converted into cycloheptenes by ring-closing olefin metathesis. Regioselective hydroboration and oxidation give the corresponding cycloheptanones, which are deprotected to afford the desired calystegines. Hereby, calystegine B(2), B(3), and B(4) are prepared from D-glucose, D-galactose, and D-mannose, respectively. This route constitutes the shortest synthesis of calystegine B(2) and gives rise to the first total syntheses of calystegine B(3) and B(4). 相似文献
74.
Anthony B. Cornwell Philip G. Harrison John A. Richards 《Journal of organometallic chemistry》1977,140(3):273-287
The reaction of organotin chlorides with the lithium salt of 7,7,8,8-tetracyanoquinodimethane (TCNQ) or hexaalkylditins with TCNQ yield stable organotin-substituted free radicals of the types R3SnTCNQ. (R = Me, n-Pr, n-Bu) and Me2Sn(TCNQ.)2. The reaction of hexaphenylditin with TCNQ yields a (σ → π) charge transfer complex of stoichiometry (Ph3SnSnPh3)·TCNQ, whilst [Me2SnCl(terpyridyl)+](TCNQ-·) was isolated from the reaction of [Me2SnCl(terpyridlyl)+][Me2SnCl3-] and LiTCNQ. The oxidation of hexaalkylditins by tetracyanoethylene (TCNE) yields stable free radicals of the type R3SnTCNE·, but treatment with 2,3,5,6-tetrachlorobenzoquinone yields either R3SnOC6Cl4O·-p (R = Me) or R3SnOC6Cl4OSnR3-p (R = n-Bu, Ph). Tin-119 Mössbauer spectroscopy shows that the derivatives R3SnTCNQ· and R3TCNE· have trigonally-bipyramidally coordinated tin with planar [SnC3] skeletons and bridging [TCNQ·] and [TCNE·] groups forming infinite one-dimensional chain structures. Me3SnOC6Cl4O·-p was inferred to possess a similar structure but with oxy bridges forming chains with a Sn---O---Sn---O backbone. Me2Sn(TCNQ·)2 has a structure intermediate between tetrahedral and octahedral with a non-linear MeSnMe unit and anisobidentate chelation by two TCNQ groups. The TCNQ derivatives were of two types: (i) “green” or “brown”, indicative of delocalisation of the Ione electron over the cyanoquinone ligand, and (ii) a “blue” form in which spin-pairing of the Ione electron between adjacent organic groups takes place. Me3SnTCNQ· may exist in both forms depending upon the mode of preparation. 相似文献
75.
The chemical composition of lipids from six human brains (60–73 years) is reported. The total lipids out of cortex, white matter, diencephalon and cerebellum, pons, and medulla oblongata have been isolated and the neutral lipids have been separated in cerebrosides, sphingomyelines, and lecithins. The highest amount of pure lipids is found in the white matter, the lowest in the cortex. The relation of neutral lipids to acid lipids as well as the amount of cholesterol are about equal for all regions. The white matter shows more cerebrosides and sphingomyelines than the cortex, the opposite being the case for lecithins. The differences are strongly significant. The fatty acids out of the different pure lipid fractions have been analysed as esters by gas chromatography. Stearic and lignoceric acid, and cerebronic and hydroxy nervonic acid respectively are main components of cerebrosides, with only little differences for the different brain regions. The fatty acids of sphingomyelines consist mainly of stearic and nervonic acid; in the white matter these two acids are present about in the same quantity, whereas stearic acid dominates in the cortex and the other sections. Lecithins contain above all palmitic and oleic acid. The amount of the latter in the white matter is higher than that of palmitic acid. 相似文献
76.
The total synthesis of tetrahydroisoquinoline alkaloids (+/-)-renieramycin G (4) and a lemonomycinone analogue (7) is described. A general strategy to synthesize both the mono- and bistetrahydroisoquinoline alkaloids from a common advanced intermediate, 17, is presented. 相似文献
77.
Relative intensities of the Stokes and anti-Stokes Raman lines associated with the I-I stretching mode of I2 and symmetric stretching mode of MnO?4 are presented. The data indicate that the maxima in the excitation profile of the anti-Stokes scattering are shifted from those of the Stokes scattering. The experimental Stokes/anti-Stokes intensity ratios agree with the theoretical values obtained with parameters from the electronic absorption spectra. 相似文献
78.
Haiwen Zhang David W. Norman Tracey M. Wentzell Alison M. Irving Janet P. Edwards Susan L. Wheaton Christopher M. Vogels Stephen A. Westcott Felix J. Baerlocher Andreas Decken 《Transition Metal Chemistry》2005,30(1):63-68
Reactions of salicylaldehydes with boronate ester derivatives of aniline have been examined. Addition of these Schiff base ligands to palladium acetate or Na2PdCl4 afforded novel boron-containing trans-bis(N-arylsalicylaldiminato) palladium complexes.Condensation of salicylaldehyde (2-HOC6H4C(O)H) with H2NC6H4Bpin (pin=1,2-O2C2Me4) afforded the boron-containing Schiff bases, 2-HOC6H4C(H)=NC6H4Bpin (1–3a). Similar reactivity with 2-hydroxy-5-nitrobenzaldehyde and 2-hydroxy-1-naphthaldehyde gave the corresponding Schiff bases (1-3b) and (1-3c), respectively. Reaction of Schiff bases (2) and (3) with palladium acetate or Na2PdCl4 afforded complexes of the type PdL2
(4,5), where L=deprotonated Schiff base. The molecular structure of the nitro-salicylaldehyde 4-Bpin palladium complex (5b) was characterized by an X-ray diffraction study. All new palladium compounds have been characterized fully and tested for their antifungal activity against Aspergillus niger and Aspergillus flavus. 相似文献
79.
An electrospray ionization (ESI) ambient pressure ion-mobility spectrometer (APIMS) interfaced to an orthogonal reflector time-of-flight mass spectrometer (TOFMS) was evaluated for the first time as a detector for the identification of phenylthiohydantoin (PTH)-derivatized amino acids, the final products in the Edman sequencing process of peptides and proteins. The drift and flight times of the twenty common PTH amino acids were characterized by a well-defined 2-D mobility/mass spectral pattern. The combination of mobility/mass modes of analysis gave rise to a unique trend-line formation for the series of PTH amino acids. In addition, each PTH amino acid had a unique reduced mobility constant K(o), thus enabling the differentiation of all the amino acid derivatives including the PTH-leucine and PTH-isoleucine isomers. More importantly it was shown that it was possible to resolve a complete reference mixture of PTH amino acids in a single experimental run in less than 1 min. Detection limits for the PTH amino acids were found to range from 1.04 to 3.52 ng; indicating that the limits of detection were less than 17.0 pmol for all of the PTH amino acids. 相似文献
80.
The coordination compound [Co(C10H7COO)2(H2O)3]2n
· 4nH2O was prepared by the reaction of 1-naphthoic acid and cobalt(II) acetate tetrahydrate in basic solution, and was fully characterized
by X-ray diffraction, element analysis, FTIR, TG-DTA and luminescent spectra. In the crystal the six-coordinated Co(II) centers
are linked into one-dimensional zigzag chains by water molecules, which are further assembled into a two-dimensional network through weak inter-chain C–H···π interactions.
The solid complex exhibits favorable fluorescent properties similar to those of free ligand at room temperature, which can
be assigned to the intraligand electronic transfer. 相似文献