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941.
M. S. Bryant J. O. Lay M. P. Chiarelli 《Journal of the American Society for Mass Spectrometry》1992,3(4):360-371
An analytical strategy using fast atom bombardment (FAB) ionization and tandem mass spectrometry has been developed to determine the molecular weight and major fragment ions, and to provide limited structural characterization of low picomole levels of carcinogen-nucleoside adducts. This strategy consists of three main components: (1) the sensitivity for analysis by FAB combined with mass spectrometry is increased via chemical derivatization; (2) the nucleoside adducts are selectively detected by using constant neutral loss scans; and (3) structurally characteristic fragments are obtained by using daughter ion scans. Trimethylsilyl derivatized arylamine-nucleoside adducts have been detected at levels as low as a few picomoles by using this approach. After experimental determination of the mass of the BH 2 + fragment ion, daughter ion spectra have been used to probe the structure specificity associated with collision-activated decomposition of this fragment. With model C-8 substituted arylamine adducts [N-(deoxyguanosin-8-yl)-4-aminobiphenyl, N-(deoxyadenosin--yl)-4-aminobiphenyl, and N-(deoxyguanosin-8-yl)-2-aminofluorene], nucleoside-specific and carcinogen-specific fragmentation have been observed in daughter ion spectra. 相似文献
942.
O. V. Gusev M. A. Ievlev M. G. Peterleitner S. M. Peregudova L. I. Denisovich P. V. Petrovskii N. A. Ustynyuk 《Russian Chemical Bulletin》1996,45(7):1601-1607
A series of are necyc lope ntadienyl complexes,i. e., [Ru(5-c5R5)(6- are ne)]+ (1, R= H, arene = C6H6; 2, R = Me, arme = C6H6; 3, R = H, arctic = C6H3Me3; 4, R = Me, arene = C6H3Me3; 5, R = H, arene = C6Me6; 6, R = Me, arene = C6Me6) was studied by cyclic voltammetry. These compounds are capable of both oxidation and reduction. The reduction potential values depend on the number of methyl groups in the complex. Reduction of benzene complexes I and 2 by sodium amalgam in THF leads to the formation of decomplexation products, the addition of hydrogen to benzene, and dimerization of the benzene ligands. Both chemical and electrochemical reductions of mesitylene complexes3 and4 result in dimeric products [(5-C5R5)Ru(-5;5-Me3H3C6H3Me3)Ru(5-C5R5)] (14, R = H; 15, R = Me). The action of sodium amalgam on compound5 gives products of hydrogen addition to both hexamethylbenzene (17) and cyclopentadienyl (18) ligands along with the major product, the dimer [5-C5H5)Ru(-5; 5-Me6C6C6Me6)Ru(5-C5H5)] (16). In contrast to5, its permcthylated analog 6 is only capable of adding hydrogen to the hexamethylbenzene ligand.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1691–1697, July, 1996. 相似文献
943.
The amperometric detection of some organic sulphides in non-aqueous media using a horseradish peroxidase modified platinum electrode is reported. The performance of the electrode is based on the inhibitory effect of sulphides on the activity of peroxidase. The electrode responds rapidly to micromolar concentrations of the sulphides with linearities extending up to 0.4, 0.25 and 0.8 mmol/dm(3) for thiourea, ethylenethiourea, and mercaptoethanol, respectively. The current as peroxide concentration approaches infinity in the absence of any inhibitor (I(max)), and the apparent inhibition constant (K'(i)) for each inhibitor were evaluated. I(max)/K'(i), i.e. the percentage inhibition of sensor response per millimolar of each inhibitor, was calculated and used as a measure of the performance of the sensor in the determination of the organic sulphides. From these values the sensitivity trend of the biosensor for the organic sulphides is ethylenethiourea > thiourea > mercaptoethanol. The kinetic effects of other operational parameters such as mediator concentration, water content of the solvent and working potential were also evaluated to assess analytical performance. 相似文献
944.
We report three highly stereoselective pericyclic reactions occurring in cascade leading to the synthesis of Decalins skeletons possessing two contiguous quaternary centers. The tandem reaction is triggered by an oxy-Cope rearrangement to create in situ a 10-membered ring enol ether macrocyle 6, which immediately rearranges via a Claisen [3,3] shift to the corresponding E-cyclodec-6-en-1-one 7. The latter spontaneously cyclizes via a transannular ene reaction to produce Decalin 5. Analysis of the mechanism with respect to the origin of the high diastereoselectivity of the tandem oxy-Cope/Claisen/ene reaction is presented. 相似文献
945.
B. A. Rudenko N. P. Shoromov M. A. Kumakhov O. O. Naida 《Journal of Analytical Chemistry》2005,60(10):956-960
The possibilities for multicapillary tubes with channels 3–10 μm in diameter and a total number of channels of about 2 × 105−106 to be used as chromatographic columns are studied. It is shown that substances with a sufficiently high boiling point can
be separated at temperatures of 20–30°C in 2–3 min with an efficiency of about 1500 theoretical plates per meter (300 theoretical
plates for a 20-cm column).
__________
Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 10, 2005, pp. 1075–1079.
Original Russian Text Copyright ? 2005 by Rudenko, Shoromov, Kumakhov, Naida. 相似文献
946.
[reaction: see text] A new Prins-type cyclization between homopropargylic alcohol and aldehydes in the presence of FeX(3) to obtain 2-alkyl-4-halo-5,6-dihydro-2H-pyrans in good yield is described. Osmium-catalyzed cis dihydroxylation provided direct access to trans-2-alkyl-3-hydroxy-tetrahydro-pyran-4-ones. Anhydrous ferric halides are also shown to be excellent catalysts for the standard Prins cyclization using homoallylic alcohol. Isolation of an intermediate acetal provides substantiation of a proposed mechanism. 相似文献
947.
O. V. Sizova V. I. Baranovskii N. V. Ivanova A. I. Panin 《Journal of Structural Chemistry》1996,37(4):525-536
The electronic spectra of the [Ru(NH3)5pz]2+, [Ru(NH3)5pz]3+, and [Ru(CN)5pz]3− complexes are calculated by the CI INDO method. The effect of solvation on the spectra is considered in a point charge approximation
and in terms of the parametric model of a charged sphere enveloping the metal fragment. Interrelation of these approaches
is discussed. Data on the molecular electrostatic potentials created by the complexes are presented to substantiate the models.
St. Petersburg State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 4, pp. 603–618, July–August, 1996.
Translated by I. Izvekova 相似文献
948.
A rapid, sensitive, precise and accurate high-performance liquid chromatographic assay with fluorescence detection was developed for the determination of buprenorphine in human, rabbit, pig and dog plasma. It is comprised of only a one-step extraction procedure with hexane-isoamyl alcohol at pH 9.25 and reversed-phase chromatography on a muPorasil column. The recoveries of buprenorphine and nalbuphine (internal standard) were greater than 90%. Calibration graphs were linear over the concentration range 3-300 ng/ml with a coefficient of variation, both within-day and between-day, of less than 9% at any level. The limit of detection was 1.0 ng/ml of plasma based on a signal-to-noise ratio of 3. Eight other clinically used narcotics were investigated to check for potential interferences and their analytical conditions. The possible decomposed compounds of buprenorphine were also checked for the specificity of this assay. The method has been successfully applied to the stability and pharmacokinetic studies of buprenorphine. Buprenorphine in plasma did not decompose significantly at -20 degrees C for four weeks. Pharmacokinetic application in six rabbits and a surgical patient revealed that buprenorphine followed a linear three-compartment model with two distribution phases. The two distribution and elimination half-lives and the clearance of buprenorphine were 1.32, 24.8 and 230 min and 224 ml/min in human plasma, and 0.94, 12.5 and 232 min and 30 ml/min in rabbit plasma. 相似文献
949.
Vladimir O. Gelmboldt Eduard V. Ganin Konstantin V. Domasevitch 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(9):o530-o534
In bis(2‐carboxypyridinium) hexafluorosilicate, 2C6H6NO2+·SiF62−, (I), and bis(2‐carboxyquinolinium) hexafluorosilicate dihydrate, 2C10H8NO2+·SiF62−·2H2O, (II), the Si atoms of the anions reside on crystallographic centres of inversion. Primary inter‐ion interactions in (I) occur via strong N—H...F and O—H...F hydrogen bonds, generating corrugated layers incorporating [SiF6]2− anions as four‐connected net nodes and organic cations as simple links in between. In (II), a set of strong N—H...F, O—H...O and O—H...F hydrogen bonds, involving water molecules, gives a three‐dimensional heterocoordinated rutile‐like framework that integrates [SiF6]2− anions as six‐connected and water molecules as three‐connected nodes. The carboxyl groups of the cation are hydrogen bonded to the water molecule [O...O = 2.5533 (13) Å], while the N—H group supports direct bonding to the anion [N...F = 2.7061 (12) Å]. 相似文献
950.
The syntheses of three newly designed bryostatin analogues are reported. These simplified analogues, which lack the A-ring present in the natural product but possess differing groups at C9, were obtained using a divergent approach from a common intermediate. All three analogues exhibit potent, single-digit nanomolar affinity to protein kinase C. 相似文献