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121.
Gehan M. El-Subruiti Salah S. Massoud Aziza K. Chehata 《Transition Metal Chemistry》1996,21(5):437-441
Summary The trans-[Co(meen)2Cl2]Cl complex was prepared and characterized by elemental analysis, and u.v.-vis. and i.r. spectroscopies. The kinetics of the
primary aquation of trans-[Co(meen)2Cl2]+ in H2O and H2O-MeOH have been investigated over a wide range of solvent compositions and temperatures (45–60 °C). Plots of rate constants
(log k) versus the reciprocal of the dielectric constant of the medium (D
infs
sup−1
) and Grunwald-Winstein values of the solvent (Y) were non-linear. The variation of enthalpies (ΔH
*) and entropies (ΔS
*) of activation with solvent composition have been determined. Plots of ΔH
* or ΔS
*
versus the mole fraction of the solvent exhibit a maximum at x
2 ca. 0.1 and a minimum of x
2 ca. 0.3; a linear plot of ΔH
*
versus ΔS
* is obtained. Furthermore, the cycle relating the free energy of activation in H2O to that in H2O-MeOH shows that changes in the solvent structure in H2O-MeOH mixtures generally stabilize the five-coordinate cation in the transition state, more than the cation in the initial
state as the mole fraction of MeOH increases. The results are discussed and compared with other related systems. 相似文献
122.
The versatility of the carbonato complex [Co(trpn)CO3]ClO4·H2O as a good source for the preparation of a series of octahedral
cis-cobalt(III)-trpn complexes was demonstrated. The compound was used to synthesize complexes of the type [Co(trpn)XY]ClO4,
where XY= (NO2)2, (OCN)2, (SCN)2, (N3)2, (OH)2, (SCN)(NO2), C6H5O·PO3, p-NO2C6H4OPO3 and DPA. A second series of complexes
formulated as [Co(trpn)L](ClO4)2 were prepared where L=phCO2, p-NO2C6H4CO2, pic and amino acid anions of glycine, l-leucine,
and l-norvaline, as well as [Co(trpn)(dl-Hpha)](ClO4)3·4H2O (Hpha=phenylalanine). The isolated complexes were characterized
by elemental analyses, i.r. and u.v.–vis. spectra.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
123.
4-Hydroxypyridine-2,6-dicarboxylic acid (chelidamic acid, cdaH2) reacts with Mn(OAc)2 x 4H2O to form a 1D staircase structure with dimeric Mn(II) units connected by water clusters to form a 3D framework, {[Mn2(cda)2 x 4H2O] x 4H2O}n, 1, in aqueous pyridine at room temperature. The compound crystallizes in the triclinic space group P1 with a = 9.495(3), b =10.733(5), c = 11.065(4) A, alpha = 87.42(5), beta = 74.14(5), gamma = 80.07(2) degrees, U = 1068.5(9) A3, Z = 2, rho(calcd) = 1.915 g cm(-3), T = 100 K, mu = 1.28 mm(-1), R1 = 0.0453 (I > 2sigma(I)), wR2 = 0.1046, GOOF = 1.282. Upon removal of the water molecules by heating, the 3D structure breaks down. Thermogravimetric analysis, infrared, X-ray powder diffraction studies, and X-ray crystallography were performed to characterize this compound. Since the coordination polymer has diaqua-bridged Mn(II) centers, it was subjected to variable-temperature magnetic studies. 相似文献
124.
Salah Chafaa Jean Meullemeestre Marie-Jos Schwing Franois Vierling Volker Bhmer Walter Vogt 《Helvetica chimica acta》1993,76(4):1425-1434
UV/VIS Absorption spectra of nitrosubsituted (o-hydroxyphenyl)methylphosphonic acids (o-(phosphonomethyl)phenols) were measured as a function of pH at 25° in 0.1M NaClo4 solutions. Computational treatment of the whole set of optical density data between 200 and 500 nm resulted in the determination of the dissociation constants of these polyacids and also of the individual electronic spectra of all the species involved in the deprotonation sequence. The spectral behavior gives information on the structure of the anions formed and consequently the order of the subsequent deprotonation steps could be deduced. For the (2-hydroxy-3-nitro(or 5-nitro)phenyl)methylphosphonic acid and the 2-hydroxy-5-nitro-1,3-phenylenebis(methylphosphonic acid), the phenolic proton dissociates in the last step, while, in the case of (2-hydroxy-3,5-dinitrophenyl)methylphosphonic acid, the last dissociating proton comes from a P? OH group. An intermediate situation is found for (3-chloro-2-hydroxy-5-nitrophenyl)methylphosphonic acid. Generally, the deprotonation sequence is governed by intramolecular H-bonds involving the phenolic OH group. 相似文献
125.
The inexpensive natural phosphate, both alone and doped with potassium fluoride, is a new basic catalyst for the synthesis of α,β-unsaturated arylsulfones. Activation by water and benzyltriethylammonium chloride has also been investigated. When using an ammonium salt, natural phosphate doped with potassium fluoride is an excellent solid support for the synthesis of α,β-unsaturated arylsulfones, leading to excellent yields in a few minutes. 相似文献
126.
Mahamed G. H. Omran Salah al-Sharhan Ayed Salman Maurice Clerc 《Computational Optimization and Applications》2013,56(2):457-480
In this paper, we investigate the use of low-discrepancy sequences to generate an initial population for population-based optimization algorithms. Previous studies have found that low-discrepancy sequences generally improve the performance of a population-based optimization algorithm. However, these studies generally have some major drawbacks like using a small set of biased problems and ignoring the use of non-parametric statistical tests. To address these shortcomings, we have used 19 functions (5 of them quasi-real-world problems), two popular low-discrepancy sequences and two well-known population-based optimization methods. According to our results, there is no evidence that using low-discrepancy sequences improves the performance of population-based search methods. 相似文献
127.
128.
Feriel Necibi Saida Ben Salah Julien Roger Jean-Cyrille Hierso Taoufik Boubaker 《国际化学动力学杂志》2020,52(10):669-680
The kinetics of the reactions of 4-nitrobenzofurazane 1a , 4-nitrobenzothiadiazole 1b , and 4-nitrobenzoselenadiazole 1c with a series of 4-Y-substituted phenoxide anions 2a-e (Y = OMe, Me, H, Cl, and CN) in aqueous solution at 20°C were investigated photometrically. The derived second-order rate constants (k2) have been combined with the nucleophilicity parameters values of these series of anions 2a-e to determine the electrophilicity parameters E of electrophiles 1a-c according to the linear free-energy relationship (log k2)/s versus N. General reactivity of these electrophiles 1a-c is found to be fairly similar with E values ranging in −10.77 ± 0.61 < E < −7.53 ± 0.29. The comparison with structurally related neutral electron-deficient heteroaromatic and aromatic compounds revealed that 1a - c are more reactive than 1,3,5-trinitrobenzene, as benchmark aromatic electrophile used in nucleophilic addition or substitution processes. The rate constants for the reactions of 4-nitrobenzochalcogenadiazoles 1a-c with some other nucleophiles were measured and found to agree with those calculated from Mayr's equation. Finally, analysis of the rate data in terms of the Brønsted approach reveals that 1a-c exhibits especially low intrinsic reactivity in σ-adducts 3 forming reactions. 相似文献
129.
Huaji Liu Zhong Shen Salah‐Eddine Stiriba Yu Chen Wenqin Zhang Liuhe Wei 《Journal of polymer science. Part A, Polymer chemistry》2006,44(13):4165-4173
Novel multiarm star copolymers with poly(?‐caprolactone) (PCL) as the arms and hyperbranched polyethylenimine (HPEI) as the core have been successfully prepared by the tin(II) 2‐ethylhexanoate catalyzed ring‐opening polymerization of ?‐caprolactone (CL) with HPEI used directly as a macroinitiator. Not only primary but also secondary amine groups of HPEI participate in initiating the ring‐opening polymerization of CL with almost 100% initiation efficiency. The average degree of polymerization of the PCL arms can be controlled by the feed ratio of the monomers to the initiating sites. Because of the polarity difference of the PCL arms and HPEI core, the obtained multiarm star polymers display an inverted micellar structure with potential extraction and encapsulation of water‐soluble guests. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4165–4173, 2006 相似文献
130.
Periodica Mathematica Hungarica - The purpose of this paper is to give, through the second degree character, new characterizations of a part of the family of quasi-symmetric forms. In fact, thanks... 相似文献