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801.
Barma DK Kundu A Zhang H Mioskowski C Falck JR 《Journal of the American Chemical Society》2003,125(11):3218-3219
(Z)-alpha-Fluoro-, (Z)-alpha-chloro-, and (Z)-alpha-bromoacrylates were obtained with unprecedented yield and stereocontrol (>99%) via addition of the corresponding commercial trihaloacetates to aldehydes at room temperature using stoichiometric Cr(II) salts or catalytic Cr(II) with a regeneration system. The intermediate 2,2-dihalo-3-hydroxy adducts could be isolated in good yields under conditions of limited reagent at 0 degrees C. 相似文献
802.
Transfer free energies of some ions from water to dimethylsulfoxide-water and urea-water mixtures 总被引:1,自引:0,他引:1
The standard free energies of transfer (G
t
o
) of some electrolytes from water to aqueous mixtures of dimethylsulfoxide (DMSO) and of urea have been split into the contribution from individual ions by use of the reference electrolyte Ph
4
AsBPh
4
(RE), where Ph=phenyl. For each of the solvents, G
t
o
(Ph
4
AsBPh
4
) was determined from the solubility products of the salts KBPh
4
, Ph
4
AsPi, and KPi, where Pi=picrate ion. The observed G
t
o
(i) values for the individual ions are strikingly different from the corresponding values obtained by the simultaneous extrapolation (SE) procedure reported earlier. 相似文献
803.
Patra A Batra S Joshi BS Roy R Kundu B Bhaduri AP 《The Journal of organic chemistry》2002,67(16):5783-5788
The Baylis-Hillman (BH) reaction of substituted 5-isoxazolecarboxaldehydes with cyclohexenone in the presence of TiCl(4) invariably lead to the formation of hemiacetals beside the BH adducts. A similar reaction in the presence of DABCO, DBU, or 3-HQN yielded minor quantities of phenols in addition to the usual BH adducts. Similar to 5-isoxazolecarboxaldehydes, the TiCl(4)-mediated BH reaction of cyclohexenone with various benzaldehydes also furnishes hemiacetals in considerable yields. The reaction mechanism involving the formation of alpha-chloromethyl enone as an intermediate has been proposed. The synthesis of hemiacetals 5 and 14 from compound 4 in the presence of cyclohexenone and cyclopentenone, respectively, under acidic conditions indicates that enolization and aromatization of the cyclohexene ring are the key steps in the reaction mechanism. 相似文献
804.
A Langmuir monolayer of stearic acid on pure water and in the presence of certain divalent metal ions such as Cd and Pb at pH approximately 6.5 of the subphase water collapses at constant area, while for other divalent ions such as Mg, Co, Zn, and Mn at the same subphase pH the monolayer collapses nearly at constant pressure. Films of stearic acid with Cd, Pb, Mn, and Co in the subphase (at pH approximately 6.5) have been transferred onto hydrophilic Si(001) using a horizontal deposition technique, just after and long after collapse. Electron density profiles obtained from X-ray reflectivity analysis show that a three-molecular-layer structure starts to form just after constant area collapse, where in the lowest molecular layer, in contact with the substrate, molecules are in asymmetric configuration, i.e., both hydrocarbon tails are on the same side of the metal-bearing headgroup that touches the substrate, while the molecules above the first layer are in symmetric conformation of the tails with respect to the headgroups. Further along collapse, when the surface pressure starts to rise again with a decrease in area, more layers with molecules in the symmetric configuration are added, but the coverage is poor. On the other hand, only bimolecular layers form after constant pressure collapse, with the lower and upper layers having molecules in asymmetric and symmetric configurations, respectively, and the upper molecular layer density increases with compression of the monolayer after collapse. A "Ries mechanism" for constant area collapse and a "folding and sliding mechanism" for constant pressure collapse have been proposed. 相似文献
805.
Phatik Chandra Kundu 《Fresenius' Journal of Analytical Chemistry》1963,196(4):246-248
Summary Calcium and magnesium were estimated separately and in a mixture with EDTA (Titriplex III) using aluminon as metal indicator. Methylene blue is used for screening the yellow colour at the end point. The estimation should be carried out in theph range 8.5–9.9. Ammonia-ammonium chloride buffer was required for the estimation. Total hardness for a number of water samples was also determined.
Zusammenfassung Calcium und Magnesium werden allein oder in Mischung (als Summe) mit Hilfe von ÄDTA-Lösung titriert, wobei Aluminon zusammen mit Methylenblau als Indicator dient. Die Bestimmung soll imph-Bereich 8,5–9,9 (NH4OH-NH4Cl-Puffer) durchgeführt werden. Sie eignet sich auch zur Gesamthärte-Bestimmung in Wasserproben.相似文献
806.
An efficient, high yielding one-pot synthesis of 4-substituted cyclopropyl phenyl methanones bound to RAM and WANG resins has been developed. The resin bound cyclopropyl phenyl methanone served as a combinatorial scaffold for the generation of structurally diverse alicyclic compounds. 相似文献
807.
Atom-efficient cross-coupling reactions of triarylbismuths with acyl chlorides under Pd(0) catalysis
The atom-efficient cross-coupling reaction of triarylbismuths with a variety of aliphatic, aromatic, and hetero-aromatic acyl chlorides was demonstrated to afford high yields of cross-coupled ketones under palladium catalysis. The corresponding cross-coupling reaction with diacid chlorides also furnished bis-coupled ketones in good yields. 相似文献
808.
Roy Ramkrishna Das Debasis Banerjee Manas Sinha Chittaranjan Mahapatra Ambikesh 《Transition Metal Chemistry》2001,26(1-2):205-211
The reactions of benzimidazole (Bimz) with dichloro{2-(arylazo)pyridine}palladium(II), [Pd(aap)Cl2
(3), aap = RC6H4N= N-2-C5H4N; R = H(a), o-Me(b), m-Me(c), p-Me(d), p-Cl(e)] and dichloro{2-(arylazo)pyrimidine}palladium(II), [Pd(aapm)Cl2
(4), aapm = RC6H4N=N-2-C6H3N2; R = H(a), o-Me(b), m-Me(c), p-Me(d), p-Cl(e)] were followed separately. The kinetics were examined under pseudo-first order conditions with reference to Bimz in MeCN at 385 and 390 nm, respectively and at 298 K using a u.v.–vis. spectrophotometer. The product was isolated and characterised as trans-Pd(Bimz)2Cl2. The reaction between Pd(aap)Cl2 and Bimz follows the rate law, rate = K[Bimz]2[Pd(aap)Cl2], a single step process, whereas biphasic behaviour is observed for the reaction between Pd(aapm)Cl2 and Bimz; each step is first order with respect to the concentration of complex and to Bimz. The rate data support a nucleophilic association path and the rate decreases upon addition of Cl–(LiCl). The aryl ring substituent of the arylazoheterocycle influences the substitution rate as follows: k(e) > k(a) > k(d) > k(c) > k(b). The k-values are linearly correlated with Hammett constants with usual deviations for the m-Me and o-Me substituents because of their steric crowding. The rate follows the order: k(aap) > k(aapm). This is unusual with reference to the -acidity order of the heterocycles, pyridine < pyrimidine, as the increased -acidity will enhance the nucleophilic association. The charge density calculation by MNDO method shows that in the pyrimidine ring of arylazopyrimidine, the peripheral m-N(uncoordinated) carries a high negative charge which may retard the nucleophilic association rate. This effect is absent in the pyridine ring of arylazopyridine and may be the reason for the faster single step nucleophilic substitution in Pd(aap)Cl2. 相似文献
809.
The deprotonation constants of adenine (ADE) [K1 and K2], adenosine (ADO) [K1 and K2], 5-adenosine monophosphate (5-AMP) [K1, K2 and K3] and adenosine triphosphate (ATP) [K3 and K4] have been obtained for aqueous soutions from emf measurements on cells such as Pt, H2 (g, 1 atm)/HA(m1), NaA(m2), KI(m3)/AgI-Ag (where HA is the corresponding acid of ADE, ADO, 5-AMP and ATP) at different temperatures. The pK values were fitted by the temperature equation: pK=AT1+B+CT by the least squares method and the related thermodynamic quantities viz. G
o
, TS
o
and H
o
were calculated from the coefficients A, B and C. 相似文献
810.
Standard free energies of transfer (G
t
o
) of alkali metal chlorides MCl (M=Li, Na, K, Rb, Cs) and of potassium bromide and iodide from ethylene glycol to its isodielectric mixtures containing 20, 40, and 60 wt. % acetonitrile have been determined from emf measurements at 25°C. The standard potentials of the M/M+, the Ag–AgBr, and the Ag–AgI electrodes have been calculated using auxiliary emf measurements. All electrolytes were found to be increasingly destabilized in mixed solvents of increasing acetonitrile content; the relative order of cation destabilization is Li+>Na+>K+>Rb+>Cs+ and that of anion destabilization is Cl–>Br–>I–, both following (a) the order of increasing softness of ions and increasing interaction with the soft base, acetonitrile,and (b) the order of decreasing hydrogen-bonding propensity of ions and decreasing interactions with the hard base, ethylene glycol. 相似文献