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131.
A synthesis of α1-(Cbz-aminoalkyl)-α2-(hydroxyalkyl)phosphinic esters was achieved by the 1,2-addition of the appropriate aldehyde to Cbz-protected phosphinic analogues of amino acid esters in the presence of at least three equivalents of trimethylsilyl chloride and NEt3. The complete deprotection of the product esters could be achieved in one step using 35% HBr in acetic acid. 相似文献
132.
Gawroński J Grycz P Kwit M Rychlewska U 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(18):4210-4215
The absolute configuration and the conformation of 9,10-trans-disubstituted 9,10-dihydrophenanthrenes, known chiral metabolites of phenanthrene-9,10-oxide, have been determined by circular dichroism. The absolute configuration assignment is based on the sign of the long-wavelength Cotton effect (A-band), which is conformation invariant and originates from benzylic chirality. This provides a new interpretation of the Mislow biphenyl-helicity rule for the case of the 9,10-dihydrophenanthrene chromophore. The sign of the B-band Cotton effect reflects the conformation of the biphenyl chromophore in 9,10-dihydrophenanthrenes. It is shown that the origin of chiroptical properties of 9,10-dihydrophenanthrenes is closely related to those of 5,6-trans-disubstituted 1,3-cyclohexadienes. 相似文献
133.
Marcin Marczak Lidia Wolska Wojciech Chrzanowski Jacek Namieśnik 《Mikrochimica acta》2006,155(3-4):331-348
Volatile organic compounds (VOCs), due to their toxicity and persistence in the environment, are particularly important pollutants.
Some of these compounds are mutagens, teratogens or carcinogens, while others are responsible for the degradation of organoleptic
parameters such as taste and odour of water. This review focuses on a number of key procedural steps in the analysis of volatile
organic compounds (VOCs) in water samples. A wide spectrum of techniques for the isolation and preconcentration of the aforementioned
pollutants for trace organic analysis by gas chromatography are presented and discussed. The advantages and disadvantages
of these techniques are discussed and novel developments are also taken into consideration. 相似文献
134.
The structure of 1-hydroxy-1,2,3-benzotriazolium diphenyl phosphate (HOBt/DPP) has been investigated by X-ray analysis. The compound crystallizes in the monoclinic space group P21/n with Z = 4 and the following lattice parameters: a = 11.711(2), b = 12.727(2) and c = 12.794(3) Å, β = 105.12(2)°, V = 1840.9(6) Å3. The structure was solved by direct methods and refined on F2 to R values of wR2 = 0.084 and R1 = 0.034 for 1985 observed reflections. HOBt/DPP has an ionic structure with very short OHO and NHO hydrogen bonds linking the different ions. Owing to these hydrogen bonds, infinite screw-shaped chains which are twisted parallel to the y-axis are formed. 相似文献
135.
136.
Görgen JJ Comfort JR Tinsley JR Averett T DeKorse J Franklin B Ritchie BG Kyle G Klein A Berman B Burleson G Cranston K Faucett JA Jarmer JJ Knudson JN Penttilä S Tanaka N Brinkmöller B Dehnhard D Yen YF Hoibråten S Breuer H Flanders BS Khandaker MA Naples DL Zhang D Barlett ML Hoffmann GW Purcell M 《Physical review letters》1991,66(17):2193-2196
137.
G. T. Jones R. W. L. Jones B. W. Kennedy D. R. O. Morrison M. M. Mobayyen S. Wainstein M. Aderholz D. Hantke E. Hoffmann U. F. Katz J. Kern N. Schmitz W. Wittek H. P. Borner G. Myatt D. Radojicic S. Burke 《Zeitschrift fur Physik C Particles and Fields》1991,51(2):205-208
Using data obtained with the bubble chamber BEBC at CERN, the inclusivef 2 (1270) meson production invp and \(\bar vp\) charged current reactions is studied. It is found thatf 2 production occurs mainly in events with a hadronic invariant massW?7 GeV. In these events, the averagef 2 multiplicity is about half the average ρO multiplicity, and thex F andp T 2 distributions of thef 2 agree in shape with those of the ρO. The predictions of a semi-empirical model (Wells model) are in accord with the measured multiplicities atW>7 GeV, whereas at lowerW the model predicts too largef 2 multiplicities. 相似文献
138.
139.
Upon reacting P(4)S(3) with AgAl(hfip)(4) and AgAl(pftb)(4) [hfip = OC(H)(CF(3))(2); pftb = OC(CF(3))(3)], the compounds Ag(P(4)S(3))Al(hfip)(4) 1 and Ag(P(4)S(3))(2)(+)[Al(pftb)(4)](-) 2 formed in CS(2) (1) or CS(2)/CH(2)Cl(2) (2) solution. Compounds 1 and 2 were characterized by single-crystal X-ray structure determinations, Raman and solution NMR spectroscopy, and elemental analyses. One-dimensional chains of [Ag(P(4)S(3))(x)](infinity) (x = 1, 1; x = 2, 2) formed in the solid state with P(4)S(3) ligands that bridge through a 1,3-P,S, a 2,4-P,S, or a 3,4-P,P eta(1) coordination to the silver ions. Compound 2 with the least basic anion contains the first homoleptic metal(P(4)S(3)) complex. Compounds 1 and 2 also include the long sought sulfur coordination of P(4)S(3). Raman spectra of 1 and 2 were assigned on the basis of DFT calculations of related species. The influence of the silver coordination on the geometry of the P(4)S(3) cage is discussed, additionally aided by DFT calculations. Consequences for the frequently observed degradation of the cage are suggested. An experimental silver ion affinity scale based on the solid-state structures of several weak Lewis acid base adducts of type (L)AgAl(hfip)(4) is given. The affinity of the ligand L to the silver ion increases according to P(4) < CH(2)Cl(2) < P(4)S(3) < S(8) < 1,2-C(2)H(4)Cl(2) < toluene. 相似文献
140.
Bihlmeier A Gonsior M Raabe I Trapp N Krossing I 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(20):5041-5051
The unexpected but facile preparation of the silver salt of the least coordinating [(RO)3Al‐F‐Al(OR)3]? anion (R=C(CF3)3) by reaction of Ag[Al(OR)4] with one equivalent of PCl3 is described. The mechanism of the formation of Ag[(RO)3Al‐F‐Al(OR)3] is explained based on the available experimental data as well as on quantum chemical calculations with the inclusion of entropy and COSMO solvation enthalpies. The crystal structures of (RO)3Al←OC4H8, Cs+[(RO)2(Me)Al‐F‐Al(Me)(OR)2]?, Ag(CH2Cl2)3+[(RO)3Al‐F‐Al(OR)3]? and Ag(η2‐P4)2+[(RO)3Al‐F‐Al(OR)3]? are described. From the collected data it will be shown that the [(RO)3Al‐F‐Al(OR)3]? anion is the least coordinating anion currently known. With respect to the fluoride ion affinity of two parent Lewis acids Al(OR)3 of 685 kJ mol?1, the ligand affinity (441 kJ mol?1), the proton and copper decomposition reactions (?983 and ?297 kJ mol?1) as well as HOMO level and HOMO–LUMO gap and in comparison with [Sb4F21]?, [Sb(OTeF5)6]?, [Al(OR)4]? as well as [B(RF)4]? (RF=CF3 or C6F5) the [(RO)3Al‐F‐Al(OR)3]? anion is among the best weakly coordinating anions (WCAs) according to each value. In contrast to most of the other cited anions, the [(RO)3Al‐F‐Al(OR)3] anion is available by a simple preparation in conventional inorganic laboratories. The least coordinating character of this anion was employed to clarify the question of the ground state geometry of the Ag(η2‐P4)2+ cation (D2h, D2 or D2d?). In agreement with computational data and NMR spectra it could be shown that the rotation along the Ag‐(P‐P‐centroid) vector has no barrier and that the structure adopted in the solid state depends on packing effects which lead to an almost D2h symmetric Ag(η2‐P4)2+ cation (0 to 10.6° torsion) for the more symmetrical [Al(OR)4]? anion, but to a D2 symmetric Ag(η2‐P4)2+ cation with a 44° twist angle of the two AgP2 planes for the less symmetrical [(RO)3Al‐F‐Al(OR)3]? anion. This implies that silver back bonding, suggested by quantum chemical population analyses to be of importance, is only weak. 相似文献