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941.
A Regio‐ and Diastereoselective Anodic Aryl–Aryl Coupling in the Biomimetic Total Synthesis of (−)‐Thebaine
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Alexander Lipp Dorota Ferenc Dr. Christoph Gütz Dr. Mario Geffe Nina Vierengel Dr. Dieter Schollmeyer Prof. Dr. Hans J. Schäfer Prof. Dr. Siegfried R. Waldvogel Prof. Dr. Till Opatz 《Angewandte Chemie (International ed. in English)》2018,57(34):11055-11059
The biosynthesis of thebaine is based on the regioselective, intramolecular, oxidative coupling of (R)‐reticuline. For decades, chemists have sought to mimic this coupling by using stoichiometric oxidants. However, all approaches to date have suffered from low yields or the formation of undesired regioisomers. Electrochemistry would represent a sustainable alternative in this respect but all attempts to accomplish an electrochemical synthesis of thebaine have failed so far. Herein, a regio‐ and diastereoselective anodic coupling of 3′,4′,5′‐trioxygenated laudanosine derivatives is presented, which finally enables electrochemical access to (?)‐thebaine. 相似文献
942.
It has been found that NaBH4 smoothly reduces the α-hydroxy-lactone moieties in ginkgolide and F-seco-ginkgolides to lactols. The reaction is rapid and stops at the lactol stage; the coordination of NaBH4 to the conformationally rigid cage structure is involved in both the initiation and termination stages. This facile reduction of ginkgolide lactones yields a variety of new ginkgolide lactols. 相似文献
943.
The CBS-QB3 method was used to calculate the gas-phase free energy difference between nine tetrazole derivatives and their anions, and the DPCM and CPCM continuum solvation methods were applied to calculate the free energy differences of solvation. The calculations were performed on both gas-phase and solvent-phase optimized structures. Absolute pKa calculations using the CPCM method and the gas-phase optimized structures yielded mean unsigned error of 0.4 pKa unit. The calculations were made with the routine settings implemented in Gaussian 98. The study is as accurate as the best reported so far for six carboxylic acids and phenols and, to our knowledge, the best reported for the acidities of heterocyclic compounds in solution. 相似文献
944.
Tanaka K Pescitelli G Di Bari L Xiao TL Nakanishi K Armstrong DW Berova N 《Organic & biomolecular chemistry》2004,2(1):48-58
Coumarins are associated with a variety of pharmacological activities which have led to the synthesis of numerous derivatives. However, no general method for determination of the absolute configuration of chiral coumarins is known. This has now been achieved for a series of dihydrofuroangelicins bearing a variety of C-8 substituted double bonds, synthesized in the racemic form and resolved through enantioselective chromatography. A combined chemical/chiroptical protocol has been developed in which the C[double bond, length as m-dash]C double bonds are replaced with a styrenoid chromophore through either (i) cross metathesis, (ii) Heck reaction, or (iii) a combined method of cross metathesis and Heck reaction with about 1 mg sample under mild conditions. The coupling between the styrenoid and coumarin chromophores gives rise to clear-cut exciton coupled CD curves, suitable for assignments of absolute configurations. The solution conformation of the styrenoid derivatives is determined by NMR and DFT molecular modeling; the electronic structure of the 7-hydroxy coumarin chromophore is also clarified by semi-empirical and TDDFT methods. The conformation thus derived, in conjunction with quantitative DeVoe's coupled-oscillator CD calculation, establishes the absolute configurations of the coumarins. The theoretical study described herein justifies the straightforward approach of the current chemical/exciton chirality protocol to this type of dihydrofuroangelicins. 相似文献
945.
We report on recent advances of our immunoassay for the hormone progesterone in cows milk. Detection is based on total internal reflectance fluorescence (TIRF), the binding-inhibition assay with an immobilized progesterone derivative, and a commercially available monoclonal antibody to progesterone as biological recognition element. The fully automated River Analyzer (RIANA) biosensor for unattended, cost-effective, and continuous monitoring of environmental pollution therefore was adapted for sensitive determination of progesterone in milk. First, the sensitivity and robustness of the existing progesterone assay for water analysis were improved, resulting in a detection limit (LOD) of only 0.2 pg mL–1 and a quantification limit (LOQ) of only 2.0 pg mL–1. These extraordinary results are the lowest detection and quantification limits for progesterone determination using biosensors yet reported in the literature. Second, the accurate indicator of ovulation was calibrated and detected in three different types of milk (UHT milk, fresh milk, and raw milk). For commercial milk and randomly procured raw milk nominal levels of progesterone are typically in the range 5–15 ng mL–1. Limits of detection (LOD) achieved for added progesterone (i.e. spiked samples) were between 45.5 and 56.1 pg mL–1 depending on milk type. Having in mind the 1:10 dilution factor, these results are still a success. For the first time a commercially available antibody was incorporated into an immunoassay for progesterone detection in bovine milk, giving a detection limit below 1 ng mL–1 for a fully automated biosensor. Thus the outstanding progress made with this biosensor in environmental monitoring and water analysis has now been successfully adapted to milk analysis for use in the field of reproduction management.Dedicated to the memory of Wilhelm Fresenius. 相似文献
946.
Nina Gommermann 《Tetrahedron》2005,61(48):11418-11426
A general preparation of functionalized primary chiral amines and amides from propargylamines has been developed. The chirality is established by an enantioselective three-component reaction of an aldehyde, a terminal alkyne and a secondary amine in the presence of copper(I) bromide/Quinap as the catalytic system leading to chiral propargylamines in high yields and enantioselectivities. Functionalization and reduction leads to various primary amines and amides. 相似文献
947.
Tetyana Levchenko Yuri Plyuto Nina Kovtyukhova 《Journal of Sol-Gel Science and Technology》2007,43(3):269-274
Possibility of the post-synthesis functionalisation of the template-free and template-structured silica films of ca. 200 nm
thickness on glass slides was evaluated. The films were prepared by dip-coating from TEOS sol–gel precursor in the absence
or presence of CTAB template. It has been found out that the template-structured silica films can be functionalised with Ag
nanoparticles via [Ag(NH3)2]NO3 ion-exchange or with adsorbed Methylene Blue (MB) cationic dye due to the presence of the well-organised mesopores after
template removal. In contrast, only the external geometric surface of the template-free silica films appeared to be accessible
for modifier molecules. Possibility of functionalisation of the multi-layered template-structured silica film depends on the
sequence of dip-coating and calcination steps upon their preparation. When preparation includes reiteration of dip-coating
and calcination steps, only the latest top silica film appears to be accessible to modifier molecules. When preparation includes
successive dip-coating cycles accomplished by calcination of the final multi-layered film, all pores appear to be accessible
since their formation occurs via simultaneous removal of the template molecules over the whole thickness of the multi-layered
template-structured silica film. 相似文献
948.
The crystal structures of two monomeric copper(II) carboxylates with 2-aminopyridine have been determined by X-ray diffraction. The hexanoate complex crystallizes as its acetonitrile solvate [Cu(C6H11O2)2(C5H6N2)2 · CH3CN] in the triclinic space group P-1 with a = 8.1020(6), b = 13.7106(9), c = 13.7673(9) Å, = 113.79(1), = 103.86(1), and = 94.38(4). The heptanoate compound shows an unsolvated structure [Cu(C7H13O2)2(C5H6N2)2] and also crystallizes in the triclinic space group P-1 with the following cell parameters: a = 8.4487(9), b = 12.238(1), c = 13.504(2) Å, = 87.034(9), = 77.489(9), and = 71.41(1)°. Both compounds contain the CuO4N2 chromophore, with ligands arranged around the copper center in a cis mode. 2-Aminopyridine is coordinated through the endocyclic nitrogen atom. The ortho position of the amino group, with respect to the pyridine nitrogen atom, allows the formation of both, intra-and intermolecular hydrogen bonds. 相似文献
949.
Nina G. Furmanova Natalya I. Sorokina Valery I. Andrianov Ursula Bologa Alexandru T. Balaban 《Structural chemistry》1991,2(7):651-654
The structure of 1-(3,5-dimethyl-2-furyl)-3-(p-tolyl)-prop-2-en-1-one, C16H16O2 is determined by single-crystal x-ray diffractometry. Crystals are triclinic,
, a=7.381(7), b=8.871(5), c=10.745(13) Å, =93.53(7), =102.25(8),=95.43(7)°, V=682(1) Å3, Z=2, dcalc=1.170 g cm–3, (Cu K)=1.54178 Å,=5.697 cm–1, M=270.30, F(000)=256, R=0.077 for 1601 unique observed reflections. The trans-geometry of the C=C double bond, thes-cis-geometry of the C=C-C=O moiety, and thes-trans arrangement of the carbonyl and furane oxygen atoms are proved. 相似文献
950.
Fujimoto Y Fishkin N Pescitelli G Decatur J Berova N Nakanishi K 《Journal of the American Chemical Society》2002,124(25):7294-7302
To gain information on the conformation of the 11-cis-retinylidene chromophore bound to bovine opsin, the enantiomeric pair (2a and 2b) of 11-cis-locked bicyclo[5.1.0]octyl retinal (retCPr) 2 was prepared and its conformation was investigated by NMR, geometry optimization, and CD calculations. This compound is also of interest since it contains a unique moiety in which a chiral cyclopropyl group is flanked by triene and enal chromophores, and hence would clarify the little-known chiroptical contribution of a cyclopropyl ring linked to polyene systems. NMR revealed that the seven-membered ring of retCPr adopts a twist chair conformation. The NMR-derived structure constraints were then used for optimizing the geometry of 2 with molecular mechanics and ab initio methods. This revealed that enantiomer 2a with a 11 beta,12 beta-cyclopropyl group exists as two populations of diastereomers depending on the twist around the 6-s bond; however, the sense of twist around the 12-s is positive in both rotamers. The theoretical Boltzmann-weighted CD obtained with the pi-SCF-CI-DV MO method and experimental spectra were consistent, thus suggesting that the conjugative effect of the cyclopropyl moiety is minimal. It was found that only the beta-cyclopropyl enantiomer 2a, but not the alpha-enantiomer 2b, binds to opsin. This observation, together with earlier retinal analogues incorporation results, led to the conclusion that the chromophore sinks into the N-terminal of the opsin receptor from the side of the 4-methylene and 15-aldehyde, and that the binding cleft accommodates 11-cis-retinal with a slightly positive twist around C12/C13. A reinterpretation of the previously published negative CD couplet of 11,12-dihydrorhodopsin also leads to a chromophoric C12/C13 twist conformation with the 13-Me in front as in 1b. Such a conformation for the chromophore accounts for both the observed biostereoselectivity of retCPr 2a and the observed negative couplet of 11,12-dihydro-Rh7. 相似文献