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991.
Quinazoline Carboxylic Acids. An Easy Route to (4-Oxo-3,4-dihydroquinazolin-3-yl)-alkanoic Acids, (4-Oxo-3,4-dihydro-1,2,3-benzotriazin-3-yl)-alkanoic Acids and their Esters A new route was found for the synthesis of (4-Oxo-3,4-dihydroquinazolin-3-yl)-alkanoic acids ( 8 ) and (4-Oxo-3,4-dihydro-1,2,3-benzotriazin-3-yl)-alkanoic acids ( 6 ) by cyclization of the N-(2-aminobenzoyl)amino acids 5 with HCOOH or HNO2. 2H-3,1-Benzoxazine-2,4(1H)-diones ( 1 ) reacted with glycine esters to 2 , which were cyclized by HNO2 to the esters 4 . Ester 4 was hydrolyzed to 6 (X = CH2). Diones 1 reacted with the most common amino acids (as the ammonium salt of tertiary amine) to amino-alkanoic acids 5 , which were cyclized with orthoformate to 7 or 8 depending on the reaction conditions. 相似文献
992.
Intermittency effects in high Reynolds number turbulence (Re103–106) are calculated from the Navier-Stokes equation in Fourier-Weierstrass approximation. First, the probability density functions (PDF) of scale resolved turbulent signals is found to be Gaussian for large scales, whereas for smaller scales the PDF changes (in agreement with experiment) to a more and more stretched exponential type. This is due to intermittent small scale fluctuations which are caused by the competition between turbulent energy transfer downscale and viscous energy loss. Second, we calculate the moments of ther-averaged energy dissipation rate
r
(x) and theirr-scaling exponents (m/3). Our results well agree with experiment and numerical simulations of the full Navier-Stokes equations ((2)=0.29±0.02). We analytically show that the common identification between the (m/3) and the corrections (m) to classical scaling of the velocity structure functions (Kolmogorov's refined similarity hypothesis) is doubtful, because even Gaussian 1
u
1-PDFs (characterizing non intermittent flow) lead to (m/3)0. 相似文献
993.
Siegfried Vieth Egon Gründemann Klaus Jähnisch Gabriele Winter Günter Reck 《Monatshefte für Chemie / Chemical Monthly》1991,122(12):1035-1045
Summary Reactions of -chloro--cyano--(5-nitrofur-2-yl)-acrylic acid derivatives with malonic acid derivatives in the presence of collidine yield the allyl anions3a–d. The pyridines4, 8 or9 are formed by cyclization of3 under acidic conditions. The 2-chloropyridine4a reacts with nucleophiles under substitution. The treatment of ethyl dichloropropionate1b with C-H-acidic compounds provided the cyclopropanes11 or12, the configurations of which were determined by13C-NMR spectroscopy. The results of the X-ray structure analysis of8c are discussed.
Furylvinylhalogenide, 12. Mitt.: Reaktionen von -Chlor--(5-nitrofur-2-yl)--cyanacrylsäurederivaten mit Malonsäurederivaten
Zusammenfassung Die Umsetzung von -Chlor--cyan--(5-nitrofur-2-yl)-acrylsäurederivaten mit Malonsäurederivaten in Gegenwart von Collidin führt zu Allylanionen3a–d. Unter sauren Bedingungen cyclisiert3 zu den Pyridinen4, 8 oder9. Das 2-Chlorpyridin4a reagiert mit Nukleophilen unter Substitution. Setzt man den Dichlorpropionsäureester1b mit C-H-aciden Verbindungen in Gegenwart von Collidin um, so werden die Cyclopropane11 bzw.12 gebildet, deren Konfigurationen mit Hilfe der13C-NMR-Spektroskopie bestimmt wurden. Die Ergebnisse der Röntgenkristallstrukturanalyse von8c werden diskutiert.相似文献
994.
Siegfried Nobel 《Journal of Theoretical Probability》1991,4(2):261-284
LetX
1,X
2,... be i.i.d. random variables with values in a simply connected nilpotent Lie groupG. Assume the laws of
to be weakly convergent to a probability measure onG,
n
Aut(G), and (k
n)n strictly increasing in. In this paper we want to characterize the possible limit laws. We obtain that every limit law is continuously embeddable and we prove a kind of functional limit theorem. Further, we study the connections between two different concepts of stability (resp. semistability) and limit laws. Finally, we describe the various domains of attraction of measures (resp. of convolution semigroups). 相似文献
995.
Back Cover: A Regio‐ and Diastereoselective Anodic Aryl–Aryl Coupling in the Biomimetic Total Synthesis of (−)‐Thebaine (Angew. Chem. Int. Ed. 34/2018)
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996.
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
997.
Regioselective Metal‐ and Reagent‐Free Arylation of Benzothiophenes by Dehydrogenative Electrosynthesis
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Sebastian Lips Dr. Dieter Schollmeyer Prof. Dr. Robert Franke Prof. Dr. Siegfried R. Waldvogel 《Angewandte Chemie (International ed. in English)》2018,57(40):13325-13329
A novel strategy for the synthesis of biaryls consisting of a benzothiophene and a phenol moiety is reported. These heterobiaryls are of utmost interest for pharmaceutical, biological, and high‐performance optoelectronic applications. The metal‐ and reagent‐free, electrosynthetic, and highly efficient method enables the generation of 2‐ and 3‐(hydroxyphenyl)benzo[b]thiophenes in a regioselective fashion. The described one‐step synthesis is easy to conduct, scalable, and inherently safe. The products are afforded in high yields of up to 88 % and with exquisite selectivity. The reaction also features a broad scope and tolerates a large variety of functional groups. 相似文献
998.
999.
Reactions of Tetrakis[bis(trimethylsilyl)methyl]dialane(4) with Methylisothiocyanate and Phenylisocyanate – Insertion into the Al? Al Bond and Fragmentation Tetrakis[bis(trimethylsilyl)methyl]dialane(4) 1 reacts with methyl isothiocyanate under cleavage of the C?S double bond and insertion of the remaining isonitrile fragment into the Al? Al bond. As shown by crystal structure determination a three-membered AlCN heterocycle ( 4 ) is formed by the interaction of the nitrogen lone pair with one unsaturated Al atom leading to an acute angle at the aluminium center N? Al? C of 36.6°. In contrast the reaction with the hard base phenyl isocyanate yields a mixture of many unknown compounds, from which only one ( 5 ) could be isolated in a very poor yield. The crystal structure of 5 reveals only one dialkyl aluminium fragment and a chelating ligand formed by the trimerization of the isocyanate under loss of one CO group and addition of a hydrogen atom. 5 was also synthesized by the specific reaction of the chloro dialkyl aluminium compound (R = CH(SiMe3)2) with Li[H5C6? N?C(O)? N(C6H5)? C(O)? N(H)? C6H5]. 相似文献
1000.
Mirko ZajaStephen J Connon Aideen M DunneMichael Rivard Nicole BuschmannJan Jiricek Siegfried Blechert 《Tetrahedron》2003,59(34):6545-6558
A series of olefin metathesis catalysts with modified isopropoxybenzylidene ligands were synthesised, and the effects of ligands on the rate of metathesis investigated. Increased steric hinderance ortho to the isopropoxy group enhanced reaction rates. In the case of N-heterocyclic carbene complexes, decreasing electron density at both the chelating oxygen atom and the RuC bond accelerated reaction rates appreciably. Catalysts containing a tricyclohexylphosphane ligand, followed the same trend with regard to benzylidene electrophilicity, while higher electron density at oxygen enhanced reaction rates. 相似文献