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21.
Thale Z Johnson T Tenney K Wenzel PJ Lobkovsky E Clardy J Media J Pietraszkiewicz H Valeriote FA Crews P 《The Journal of organic chemistry》2002,67(26):9384-9391
A reinvestigation of sponge natural products from additional Indo-Pacific collections of Xestospongiacf. carbonaria and X. cf. exigua has provided further insights on the structures, biological activities, and biosynthetic origin of bisannulated acridines. These alkaloids include one known pyridoacridine, neoamphimedine (2), and three new analogues, 5-methoxyneoamphimedine (4), neoamphimedine Y (5), and neoamphimedine Z (6). A completely new acridine, alpkinidine (7), was also isolated. A disk diffusion soft agar assay, using a panel of five cancer cell lines (solid tumors and leukemias) and two normal cells, was used to evaluate the differential cytotoxicity (solid tumor selectivity) of the sponge semipure extracts and selected compounds including amphimedine (1), 2, 4, and 7. While all four compounds were solid tumor selective, 1 and 2 were the most potent and 4 was the most selective. The rationale used to characterize the new structures is outlined along with the related biosynthetic pathways envisioned to generate 2 and 7. 相似文献
22.
Bernskoetter WH Lobkovsky E Chirik PJ 《Journal of the American Chemical Society》2005,127(40):14051-14061
The rates of hydrogenation of the N2 ligand in the side-on bound dinitrogen compounds, [(eta(5)-C5Me4H)2Zr]2(mu2,eta(2),eta(2)-N2) and [(eta(5)-C5Me5)(eta(5)-C5H2-1,2-Me2-4-R)Zr]2(mu2,eta(2),eta(2)-N2) (R = Me, Ph), to afford the corresponding hydrido zirconocene diazenido complexes have been measured by electronic spectroscopy. Determination of the rate law for the hydrogenation of [(eta(5)-C5Me5)(eta(5)-C5H2-1,2,4-Me3)Zr]2(mu2,eta(2),eta(2)-N2) establishes an overall second-order reaction, first order with respect to each reagent. These data, in combination with a normal, primary kinetic isotope effect of 2.2(1) for H2 versus D2 addition, establish the first H2 addition as the rate-determining step in N2 hydrogenation. Kinetic isotope effects of similar direction and magnitude have also been measured for hydrogenation (deuteration) of the two other zirconocene dinitrogen complexes. Measuring the rate constants for the hydrogenation of [(eta(5)-C5Me5)(eta(5)-C5H2-1,2,4-Me3)Zr]2(mu2,eta(2),eta(2)-N2) over a 40 degrees C temperature range provided activation parameters of deltaH(double dagger) = 8.4(8) kcal/mol and deltaS(double dagger) = -33(4) eu. The entropy of activation is consistent with an ordered four-centered transition structure, where H2 undergoes formal 1,2-addition to a zirconium-nitrogen bond with considerable multiple bond character. Support for this hypothesis stems from the observation of N2 functionalization by C-H activation of a cyclopentadienyl methyl substituent in the mixed ring dinitrogen complexes, [(eta(5)-C5Me5)(eta(5)-C5H2-1,2-Me2-4-R)Zr]2(mu2,eta(2),eta(2)-N2) (R = Me, Ph), to afford cyclometalated zirconocene diazenido derivatives. 相似文献
23.
Wolfgang Oppolzer Roland Achini Emil Pfenninger Hans Peter Weber 《Helvetica chimica acta》1976,59(4):1186-1202
The N-allyl-N-cinnamyl amide 10 undergoes thermal cyclization to a 2:1-mixture of the trans- and cis-benz(f)isoindolines 11a and 12a . By comparison, the thermolysis of the corresponding bis-cinnamylamide 14 proceeds in a highly stereoselective manner to give the cis-fused[4+2]-adduct 16a . Similarly, the trans-fused stereoisomeric adducts 30a and 31a were obtained with high stereochemical control on heating the N-allyl-N-diphenylallyl amide 28 . The thermal transformations 4 → 5 + 6a and 17 → 18a + 20a show the competitive formation of [2+2]-adducts. An alternative approach to (substituted) benz[f]isoindolines 16 via the all-cis-isomer 24a has been developed. The described structures have been assigned on the basis of spectral evidence, chemical correlations and by X-ray-diffraction study of the isomer 16b . These results illustrate the utility of substituent interactions in order to direct intramolecular cyclo-additions at will towards either endo- or exo-products. 相似文献
24.
25.
Emil W. Kiss 《Algebra Universalis》1992,29(4):455-476
First a problem of Ralph McKenzie is answered by proving that in a finitely directly representable variety every directly indecomposable algebra must be finite. Then we show that there is no local proof of the fundamental theorem of Abelian algebras nor of H. P. Gumm's permutability results. This part may also be of interest for those investigating non-modular Abelian algebras. Finally we provide a Gumm-type characterization of the situation when twonot necessarily comparable congruences centralize each other. In doing this, we introduce a four variable version of the difference term in every modular variety. A two-terms condition is also investigated.Dedicated to the memory of András HuhnPresented by R. W. Quackenbush. 相似文献
26.
Emil Wolff 《Fresenius' Journal of Analytical Chemistry》1864,3(1):85-115
Ohne ZusammenfassungBegutachtet von den Commissionsmitgliedern: Dr. Bretschneider, Dr. Grouven, Professor Dr. Knop, Dr. Peters, Dr. Stohmann und Dr. Zöller.Bei der ersten Wanderversammlung deutscher Agriculturchemiker, welche im Mai 1863 zu Leipzig gehalten wurde, sind zum Behufe der Ausarbeitung gemeinsam zu befolgender Methoden und Untersuchungssysteme Commissionen ernannt worden. Als erste Frucht von deren Arbeiten ist in den Landw. Versuchs-Stationen, dem Organ für wissenschaftliche Forschungen auf dem Gebiete der Landwirthschaft, herausgegeben von Dr. Fr. Nobbe, Band VI, der Entwurf zurBodenanalyse von Dr. Emil Wolff, begutachtet von den andern Commissionsmitgliedern, veröffentlicht worden. Ich theile denselben im Einverständniss mit dem Herrn Verfasser auch an dieser Stelle mit, einerseits um den löblichen Zweck, welchen die Wanderversammlung der deutschen Agriculturchemiker im Auge hat, nach Kräften zu fördern, andererseits die mancherlei neuen Methoden, welche bei agriculturchemischen Untersuchungen in Gebrauch gekommen sind, auch in den Kreisen zu verbreiten, welchen die speciell agriculturchemischen Schriften nicht zu Gesicht kommen. Ich füge hinzu, dass die kleine Modification auf S. 94, sowie die Anmerkungen ebendaselbst in Folge brieflicher Mittheilung des Herrn Prof. Wolff aufgenommen worden sind. Dem Wunsche desselben, dass ich meinerseits Bemerkungen zufügen möchte, werde ich gerne entsprechen, so bald ich Zeit finde, betreffende Experimentaluntersuchungen vorzunehmen. R. F. 相似文献
27.
[reaction: see text] Additions of lithium acetylides and n-BuLi to N-alkyl ketimines mediated by BF(3)-Et(2)O in THF afford hindered tert-alkylamines in moderate to good yields. Stereochemical results and crystal structures of three BF(3)-imine complexes suggest that allylic strain strongly influences conformation and may be an important determinant of reactivity and selectivity. 相似文献
28.
It is shown that, contrary to common belief, monochromatic light beams are, in general, not spatially completely coherent, i.e., they will, in general, not produce fringes of unit visibility in a Young's double pinhole interference experiment. We cite experiments with laser modes which confirm this result. 相似文献
29.
Abstract The synthesis and characterization of new vinyl chloride-p-acryloyloxyazobenzene copolymers are reported. Kinetics of photoinduced trans-cis and thermal cis-trans isomerization of azo pendant groups in copolymer have also been investigated, and the kinetic parameters were evaluated. An azo acrylate model compound was used for comparison. 相似文献
30.
Emil Tashev Tania Tosheva Stoycho Shenkov Anne-Sophie Chauvin Victoria Lachkova Rosica Petrova 《Supramolecular chemistry》2013,25(7):447-457
The synthesis and characterization of several new phosphorus-containing partially lower rim substituted derivatives of 5,11,17,23-tetra(t-butyl) calix(4)arene (I) and 5,11,17,23-tetra(t-octyl)calix(4)arene (II), namely 5,11,17,23-tetra(t-butyl)-25,27-dihydroxy-26,28-bis(diphenylphosphinoyl-oxy) calix(4)arene (IV); 5,11,17,23-tetra(t-butyl)-25-hydroxy-26,27,28-tris(tetramethyldiamido-phosphinoyl-oxy) calix(4)arene (Vb); 5,11,17,23-tetra(t-butyl)-25,27-dihydroxy-26,28-bis(dimethyl-phosphinoyl-methoxy) calix(4)arene (VI); 5,11,17,23-tetra (t-octyl)-25,27-dihydroxy-26,28-bis(dimethyl-phosphinoyl-methoxy) calix(4)arene (VII) are reported. The structure of the synthesized calix(4)arene derivatives are identified and confirmed by elemental analysis, IR, 1H, 13C, 31P{1H} NMR spectroscopy and mass spectrometry as and X-ray crystallographic analysis of 5,11,17,23-tetra(t-butyl)-25,27-dihydroxy-26,28-bis(dimethyl-phosphinoyl-methoxy) calix(4)arene VI. According to the NMR spectra, all calix(4)arenes are in cone conformation. 相似文献