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31.
The isotropic ESR spectra of a number of phosphonyl radicals (X2O), the dimethylphosphinyl radical, and the phosphoranyl radical (MeO)3OBu-t, are described, and accurate values of the phosphorus hyperfine splittings and g-factors are reported. For X2O, the value of a(P) increases and the g-factor decreases as the electronegativity of X increases. There is a linear relationship between a(P) for X2O and 1J(PH) for X2P(O)H, but the same relationship does not hold for Me2P- and Me2PH. The spectrum of the di-n-hexylphosphonyl radical shows coupling to two pairs of α-methylene protons, and this non-equivalence is attributed to the pyramidal structure of the phosphonyl radical. 相似文献
32.
Workman JA Garrido NP Sançon J Roberts E Wessel HP Sweeney JB 《Journal of the American Chemical Society》2005,127(4):1066-1067
The first examples of highly enantioselective [2,3]-sigmatropic rearrangements of acyclic allylic ammonium ylids are reported. Thus, a range of N-{2'-[(N'-allyl-N',N'-dialkyl)ammonium]}acetyl camphor sultams undergo rearrangement at 0 degrees C in DME solution with high diastereofacial control (up to 99:1 dr) to give allylglycines in generally high yield. The power of the method has been demonstrated in a rapid and efficient synthesis of (R)-allyl glycine. 相似文献
33.
John A. Montgomery James R. Piper Robert D. Elliott Eugene C. Roberts Carroll Temple Y. Fulmer Shealy 《Journal of heterocyclic chemistry》1979,16(3):537-539
Eighteen derivatives of 2,4-diamino-6-methylpteridine related to methotrexate and aminopterin have been prepared from 6-(bromomethyl)-2,4-pteridinediamine by nucleophilic displacement reactions. None of these compounds showed any antileukemic acitivity. 相似文献
34.
S. V. Nochur G. R. Jacobson M. F. Roberts A. L. Demain 《Applied biochemistry and biotechnology》1992,37(1):33-41
Fungi were screened for important industrial enzymes produced from industrial chips and sawdust of laurel (Louro inamui, Ocotea cymbarum) and cedar (Cedro, Cedrella odorata). Seven hyphomycetes and one zygomycete were isolated and characterized. Two different media for testing the enzymatic activities
were used. In general, in potato dextrose (1%) medium (M-3) a preponderancy of ligninolytic over cellulolytic enzymes was
observed. In potato infusion-sawdust wood (1%) medium (M-4) the cellulolytic, xylanolytic, and lipolytic enzymes were efficiently
induced. Significant modulation of enzyme production by the carbon source was found in the extracted fungi from self-heated
industrial chips piles of cedar and laurel trees at the Amazonian region. 相似文献
35.
Alexander Chernega Dirk. L. Elend Christian A.P. Smethurst Paul M. Roberts Andrew D. Smith G. Darren Smyth 《Tetrahedron》2007,63(30):7036-7046
A three-step protocol for the asymmetric synthesis of a range of β-substituted Baylis-Hillman products has been developed. This procedure involves the diastereoselective conjugate addition of lithium (R)-N-methyl-N-(α-methylbenzyl)amide to an α,β-unsaturated ester to generate an N-protected β-amino ester in high de. Subsequent asymmetric aldol reaction via deprotonation with LDA, transmetallation with B(OMe)3 and addition of an aldehyde gives a range of syn-aldol products in moderate to high de. Purification of the syn-aldol products to homogeneity followed by tandem N-oxidation and Cope elimination gives the desired β-substituted Baylis-Hillman products in good yield and high de and ee. 相似文献
36.
The synthesis of 2′,6′-diazafolic acid was accomplished by the condensation of 2-acetylamino-4(3H)pteridinone-6-earboxaldehyde (XIV) with diethyl N-[(5-amino-2-pyrimidinyl)carbonyl]-L-glutamate (XIII) followed by reduction of the anil double bond and alkaline hydrolylic cleavage of the N2-acetyl and ethyl ester protecting groups. Intermediate XIII was prepared by starling with 5-nitro-2-styrylpyrimidine (VI) and proceeding via 5-arnino-2-styrylpyrimidine (IX). The henzyloxycarbonyl derivative of IX was prepared and oxidized to the corresponding 5-benzyloxycarbonylaminopyrimidine-2-carboxylic acid (XI). The coupling of XI with diethyl L-glutamate followed by hydrogenolysis of the henzyloxycarbonyl function afforded the desired intermediate XIII. 2′,6′-Diazafolic acid was a potent inhibitor of Streptococcus faecium and displayed marginal activity against leukemia 1,1210 in mice. 相似文献
37.
[reaction: see text]. Polyethylene glycol (PEG)-bound poly-L-leucine acts as a THF-soluble catalyst for the Juliá-Colonna asymmetric epoxidation of enones. Excellent enantioselectivities may be obtained even with short chain length polyleucine. FT-IR investigations have determined that the catalytically active polyleucine components of these copolymers have an alpha-helical structure. 相似文献
38.
R.M.G. Roberts 《Tetrahedron》1980,36(22):3281-3287
The rates of reaction of Tl (III) tris(trifluoroacetate) with benzene toluene and t-butylbenzene in solvent trifluoroacetic acid have been measured by an NMR method. The reaction products have been unambiguously determined from the thallium-hydrogen coupling constants. In the case of toluene, p-tolylthallium bis(trifluoroacetate) crystallised from reaction mixtures.Thalliation was shown to be reversible and to be between one and two orders of magnitude slower than mercuriation. The inductive order of the reactivity (tBu > Me ? H) was found in contrast to the hyperconjugative order for mercuriation. Hammett plots using σ+ values yielded a ? value of ?7.4 but the limited data correlated better with σ values (? = ?12.8). A primary isotope effect of 5.0 was found for toluene indicating rate-determining proton transfer. The mechanism is discussed in the light of these and other findings. In addition the rates of interconversion of the products of mercuriation of toluene are reported from NMR data. 相似文献
39.
P. John Roberts 《Theoretical chemistry accounts》1969,14(3):184-191
In the limiting case of the free-electron theory where the electron motion is constricted to one dimension, the one-dimensional Coulomb potential gives rise to divergent interaction integrals. It is shown that a proposal by Olszewski to remove the divergenses by first evaluating the integrals in the three-dimensional case and then passing to the limit of one dimension only is incorrect, and that convergent integrals may only be obtained by suitably modifying the original one-dimensional Coulomb potential between particles.
Zusammenfassung In dem Grenzfall des Modells der Freien Elektronen, in dem die Elektronenbewegung auf eine Dimension eingeschrÄnkt ist, ergibt das eindimensionale Coulombpotential divergente Wechselwirkungsintegrale. Es wird gezeigt, da\ ein Vorschlag von Olszewski zur Aufhebung der Divergenz durch übergang von dreidimensionalen zum eindimensionalen Integral falsch ist. Konvergente Integrale können nur durch geeignete VerÄnderung des ursprünglichen eindimensionalen Coulombpotentials erhalten werden.
Résumé Dans le cas limite de la théorie de l'électron libre à une dimension, le potentiel coulombien donne lieu à des intégrales d'interaction divergentes. On montre que la proposition d'Oszewski pour éliminer les divergences, en évaluant d'abord les intégrales tridimensionnelles et en passant à la limite à une dimension, est incorrecte et que des intégrales convergentes ne peuvent Être obtenues qu'en modifiant le potentiel coulombien unidimensionnel entre particules.相似文献
40.
Treatment of dimethyl ketene with ethoxyacetylene 1a, 1-ethoxyoct-1-yne 1b, and 1-ethoxytetrade-1-yne 1c afforded the 3-ethoxycyclobutenones 2a–c. Hydrolysis of 2a–c with dilute hydrochloric acid gave the cyclobutane-1,3-diones 3a–c. The 1H NMR spectra of these compounds indicate that in CDCl3 solution 2,2-dimethylcyclobutane-1,3-dione 3a exists as the diketone, whereas the 2,2,4-trialkylcyclobutane-1,3-diones 3b and 3c exist as the monoenols. 相似文献