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161.
Summary The aquation ofcis-[(en)2Co(CO2H)2]+ tocis-[(en)2Co(OH2)(CO2H)]2+ is catalysed by Cu2+ and the rate equation, –d[complex]t/dt=(kCu[Cu2+]+kH [H+]) [complex)T is valid at [Cu2+]T=0.01–0.1, I=0.5 and [HClO4]=0.005 mol dm–3. The rate measurements are reported at 30, 35, 40 and 45°C and the rate and activation parameters for the Cu2+ and H+-catalysed paths are: kH(35°C)=(2.44±0.09)×10–2 dm3 mol–1 s–1, H=83±13 kJ mol–1, S=–8±42 JK–1 mol–1, k
Cu
(35°C)=(3.30±0.09)×10–3 dm3 mol–1 s–1, H=73.2±6.1 kJ mol–1, S=–55±20 JK–1 mol–1. The formate-bridged innersphere binuclear complex,cis-[(en)2Co{(O2CH)2Cu}]3+ may be involved as the catalytically active intermediate in the copper(II)-catalysed path, just as the corresponding H+-bridged species presumed to be present in the acidcatalysed path. 相似文献
162.
P. K. Mishra V. Chakra Vortty K. C. Dash N. R. Das S. N. Bhattacharyya 《Journal of Radioanalytical and Nuclear Chemistry》1992,162(2):289-298
Presence of thiocyanate ions results in appreciable extraction of Zr(IV) by Aliquat 336 from low aqueous HCl acidities, i.e., 0.1 to 4.5M. The variation of concentrations of HCl, thiocyanate and Aliquat 336 greatly influences the extent of extraction. Mixtures of Aliquat 336 and TOPO result in synergistic extraction of Zr and Hf from acidic thiocyanate media, the extracted species being the disolvate with TOPO. By controlled adjustment of HCl, SCN– and Aliquat 336 concentrations, separation of Zr, Nb and Hf is possible. A maximum separation factor (DNb/DZr) of 3675 has been achieved under certain conditions. 相似文献
163.
The interaction of (1,8)bis(2-hydroxybenzamido)3,6-diazaoctane (LH2) with iron(III) in acidic medium resulted in the formation of a mononuclear complex, Fe(LH3)4+ which further yielded, [Fe(LH2)]3+, [Fe(LH)]2+, and [FeL]+ due to protolytic equilibria. The formation of [Fe(LH3)]4+ was investigated under varying [H+]T (0.01–0.10 mol dm−3) and [Fe3+]T (1.00 × 10−3–1.70 × 10−2, [L]T = 1.0 × 10−4 mol dm−3) (I = 0.3 mol dm−3, 10% MeOH + H2O, 25.0 °C). The reaction was reversible and displayed monophasic kinetics; the dominant path involved Fe(OH)(OH2)
5
2+
and LH
4
2+
. The mechanism is essentially a dissociative interchange (I
d) and the dissociation of the aqua ligand from the encounter complex, [Fe(OH2)5OH2+, H4L2+] is rate limiting. The ligand binds iron(III) in a bidentate ([Fe(H3L)]4+), tetradentate ([Fe(H2L)]3+), pentadentate ([Fe(HL)]2+) and hexadentate fashion ([FeL]+) under varying pH conditions. Iron(III) promoted deprotonation of the amide and phenol moieties and chelation driven deprotonation
of the sec-NH
2
+
of the trien spacer unit are in tune with the above proposition. The mixed ligand complexes, [FeIII(LH)(X)] (X = N
3
−
, NCS−, ACO−) are also reversibly formed in solution thus indicating that there is a replaceable aqua ligand in the complex conforming
to its octahedral coordination, [Fe(LH)(OH2)]2+, the bound ligand is protonated at the sec-NH site. Despite the multidentate nature of the ligand the FeIII complexes are prone to reduction by sulfur(IV) and ascorbic acid. The redox reactions of different iron(III) species, FeIII(LHi) which involved ternary complex formation with the reductants have been investigated kinetically as a function of pH, [SIV]T and [ascorbic acid]T. The substantial pK perturbation of the bound ascorbate in [Fe(LH)(HAsc/Asc)]+/0 (ΔpK
{[Fe(LH)(HAsc)] − HAsc − } > 6) is considered to be compelling evidence for chelation of HAsc−/Asc2− leading to hepta coordination of iron(III) in the ascorbate complexes. A novel binuclear complex with composition, [FeIII
2C20N4H35O11 (NO3)] has been synthesized and characterized by i.r., u.v.–vis, e.s.r., e.s.i.-Mass, 57Fe Mossbauer spectroscopy and magnetic moment measurements. The complex was isolated as a mixture of two forms C
1 and C
2 with 75.3 and 24.7%, respectively as computed from Mossbauer data. The isomer shift (δ) (quadrupole splitting, ΔE
Q) are 0.32 mm s−1 (0.75 mm s−1) and 0.19 mm s−1 (0.68 mm s−1) for C
1 and C
2, respectively. The variable temperature magnetic moment measurements (10–300 K) of the sample showed that C
1 is an oxo dimer exhibiting antiferromagnetic interaction between the iron(III) atoms (S
1 = S
2 = 5/2, J = − 120 cm−1) while the dimer C
2 is a high spin species (S
1 = S
2 = 5/2) and exhibits normal paramagnetism obeying the Curie law. The cyclic voltametry response of the sample (DMF, [TEAP]
= 0.1 mol dm−3) displayed quasi-reversible responses at − 0.577 V and − 1.451 V (versus SCE). This is in tune with the fact that the C
2 species reverts rapidly in solution to the relatively more stable oxo-bridged dimer (C
1) which is reduced in two sequential steps: C1 + e− → [FeL]+ + FeII; [FeL]+ + e− → FeIIL, the high labilility of the FeII complex is attributed to the irreversibility. The X-band e.s.r. spectrum of the polycrystalline sample at room temperature
displayed a weak (unresolved) band at g = 4.2 and a strong band at g = 2.0 with hyperfine splitting due to the coordinated nitrogen (I = 1). At 77 K the band at g = 4.2 is intensified while that at g = 2 is broadened to the extent of near disappearance in agreement with the presence of the exchange coupled iron(III) centres.
Electronic supplementary material Electronic supplementary material is available for this article at
and accessible for authorised users.
An erratum to this article is available at . 相似文献
164.
165.
S.P. Dash D. Goll H.D. Carstanjen 《Applied Physics A: Materials Science & Processing》2008,91(3):379-383
Highly resolved Co depth profiles have been obtained during the initial stages of Co growth on Si(100) at low temperature
(-60 °C) by in situ high-resolution Rutherford backscattering spectrometry. We found extensive Co in-diffusion in the submonolayer
growth regime even at this low temperature, besides Co on top of the Si surface. The amount of diffused-in Co is larger than
the amount of Co at the Si surface. Every second Si layer is depleted of Co, starting at the Si surface, thus giving rise
to compositional oscillations of Co in the Si(100) lattice. At this low temperature the growth of metallic Co on the Si surface
is observed at 0.1 ML of deposited Co, which continues for higher coverages. At much higher coverage (5.93 ML of Co) almost
exclusively low Co content silicides are formed at the Co/Si interface. The data presented here are compared with previous
room temperature deposition data and are different in several aspects.
PACS 68.35.-p; 68.55.ag; 75.47.-m; 82.80.Yc 相似文献
166.
Abe K Adachi I Aihara H Asano Y Aulchenko V Aushev T Bakich AM Balagura V Banerjee S Barberio E Barbero M Bay A Bedny I Bitenc U Bizjak I Blyth S Bondar A Bozek A Bracko M Brodzicka J Browder TE Chang P Chao Y Chen A Chen KF Chen WT Cheon BG Chistov R Choi SK Choi Y Chuvikov A Cole S Dalseno J Danilov M Dash M Dong LY Dragic J Drutskoy A Eidelman S Enari Y Fratina S Gabyshev N Gershon T Go A Gokhroo G Golob B Gorisek A Haba J Hara T Hastings NC Hayasaka K Hayashii H Hazumi M Hinz L Hokuue T 《Physical review letters》2005,95(23):231802
We report measurements of B meson decays to two kaons using 253 fb(-1) of data collected with the Belle detector at the KEKB energy-asymmetric e+ e- collider. We find evidence for signals in B+ --> K0 K+ and B0 --> K0 K0 with significances of 3.0sigma and 3.5sigma, respectively. (Charge-conjugate modes are included.) The corresponding branching fractions are measured to be [symbol: see text](B+ --> K0 K+) = (1.0 +/- 0.4 +/- 0.1) x 10(-6) and [symbol: see text](B0 --> K0 K0) = (0.8 +/- 0.3 +/- 0.1) x 10(-6). These decay modes are examples of hadronic bd transitions. No signal is observed in the decay B0 --> K+ K-, and we set an upper limit of 3.7 x 10(-7) at 90% confidence level. 相似文献
167.
Methylalumoxane (MAO) was found to be an active catalytic precursor for the chemo- and regioselective dimerization of a wide range of aryl- and alkyl-substituted terminal alkynes yielding the corresponding geminal dimers A. For an olefin-functionalized terminal alkyne (RC&tbd1;CH, R = MeC=CH(2)), the geminal dimer undergoes an intermolecular [4 + 2] cycloaddition forming compound B. 相似文献
168.
Colloid and Polymer Science - The kinetics of aqueous polymerization of acrylamide and methacrylamide initiated by potassium peroxydiphosphate has been investigated. The kinetic orders with respect... 相似文献
169.
Summary The kinetics of iodination of malonate and pyruvate in the title complexes are reported at 35.0 °C and I=0.3 M. The reaction is first order in substrate and zeroth order in [I2]. This result is commensurate with rate determining enolisation of the active methylene and methyl groups of the malonate and pyruvate respectively. The reaction is catalysed by H2O, OH– and by the buffer anions used. The rate data suggest that the malonate methylene group in the [Co(en)2-O2CCH2CO2]2+ chelate is considerably more active towards electrophilic substitution than is the case in [Co(NH3)5O2CCH2CO2]2+. 相似文献
170.