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81.
Systematic studies were performed on SnCl2-mediated carbonyl allylation reaction between aldehydes and allyl halides in fully aqueous media. Totally three valuable reaction systems were discovered, which were SnCl2/CuCl2, SnCl2/TiCl3, and SnCl2/PdCl2. They all provided good to excellent yields in the allylation of aliphatic and aromatic aldehydes under very mild and convenient conditions. SnCl2, by itself, was also found to be effective for the allylation reaction when allyl bromide was employed. However, the SnCl2-only reaction could only tolerate very small amount of water as the solvent. The SnCl2/CuCl2, SnCl2/TiCl3, and SnCl2/PdCl2-mediated reactions exhibited good regioselectivity favoring the γ-adduct when cinnamyl halides were employed as the allylation reagent. The same reactions with cinnamyl halides also showed good diastereoselectivity favoring the anti-product. Mechanistic studies using proton NMR techniques suggested that the additive (i.e., CuCl2, TiCl3, PdCl2) could accelerate the formation of allyltin intermediate, but this step was shown not to be the most important for the allylation. Thus we proposed that the Lewis acid catalysis effect exerted by the additive was the main reason for the observed reactivity enhancement. 相似文献
82.
B. Schoofs T. Mouganie B. A. Glowacki V. Cloet S. Hoste I. Van Driessche 《Journal of Sol-Gel Science and Technology》2007,41(2):113-122
Today, the deposition of coated conductors on a variety of substrates is often performed using a vacuum or low pressure technique.
However, obtaining uninterrupted deposition at high speed, increasing flexibility in composition and attaining independence
of geometric constraints of the substrates are areas in which vacuum techniques will need sustained development in order to
answer industrial demands. The development of the next generation of deposition methods, based on deposition under atmospheric
environment and from aqueous precursor solutions is a real challenge. This work describes the deposition of thin NdBa2Cu3O7-y layers on SrTiO3 single crystals based on a new sol-gel dip coating process using aqueous precursor solutions. Two inorganic aqueous sol-gel
routes were investigated, a metal nitrate–citric acid based and a metal acetate–triethanol amine based solution. Using detailed
thermal analysis, it is shown that adjusting the different parameters during thermal treatment can be used to control the
morphology of the films. Also special attention is given to the microstructure of the thin film because of its relevance to
the superconducting transport properties of the coated conductor system. 相似文献
83.
Alexander Apelblat Emanuel Manzurola Zoya Orekhova 《Journal of solution chemistry》2007,36(8):1023-1035
Conductivity measurements of glutaric acid and disodium glutarate in dilute aqueous solutions were performed in the 288.15
to 323.15 K temperature range. The limiting equivalent conductances of glutarate anions, λ
o(HGlut−,T) and λ
o(1/2Glut2−,T), and the dissociation constants of glutaric acid, K
1(T) and K
2(T), were derived by the use of the Onsager and the Quint and Viallard conductivity equations. The applied molecular model was
successfully confirmed by analyzing the conductivities of sodium hydrogen glutarate at 298.15 K. 相似文献
84.
Summary The partial resolution of some drug enantiomers by counter-current extraction in an aqueous two-phase system using bovine serum albumin (BSA) or ovomucoid (OVM) as chiral discriminator is described. The phase system was prepared with dextran 40, polyethylene glycol and a protein. Ofloxacin (OFLX) enantiomer was well recognized by the BSA system, whereas the enantiomers of carvedilol (-blocker) and DG-5128 (a new oral hypoglycaemic drug) were hardly recognized by the OVM system. The distribution coefficients of (S)-, (R)- and rac-OFLX varied with pH. Good enantioselectivity for OFLX was obtained at relatively high pH ( pH 9). The crude optically enriched OFLX enantiomers were extracted from the aqueous fractions and finally purified by thin-layer chromatography. 相似文献
85.
S. Sawamura M. Tsuchiya T. Ishigami Y. Taniguchi K. Suzuki 《Journal of solution chemistry》1993,22(8):727-732
Solubility of naphthalene in water was measured at 25°C and pressures up to 200 MPa. The solubility decreased with increasing pressure. From the pressure coefficient of the solubility, the volume change V accompanying the dissolution was estimated as 13.8±0.4 cm
3
-mol
–1
. Further we estimated the volume change V
CH
accompanying hydrophobic hydration as –0.1±0.6 cm
3
-mol
–1
using the V value, the molar volume of crystalline naphthalene, and the partial molar volume of naphthalene in n-heptane. This V
CH
is much larger (i.e., less negative) than that for hydrophobic hydration of alkyl-chain compounds and suggests that the hydration structure of naphthalene differs from that of alkyl-chain compounds. 相似文献
86.
The interaction of uni-univalent salt with cationic liposomes in aqueous suspension has been investigated by means of dynamic light scattering measurements and the hydrodynamic radius of the resulting aggregates has been evaluated for different ionic strengths. We observe the simultaneous presence of two different steady-state structures, in the 100–500 nm and 5 μm range, respectively, whose relative concentrations depend on the salt content. This behavior differs from that observed in usual charge stabilized colloidal suspensions and that giving rise to lipoplex formation in presence of polynucleotides. This peculiar behavior is briefly discussed in the light of Derjaguin–Landau–Verwey–Overbeek (DLVO) colloidal stability theory. 相似文献
87.
The equilibrium constants and molar absorptivities for the fast formation of a 1:3 complex between cadmium(II) (Cd(II)) and dithizonate anion, in the presence of cationic and non-ionic surfactants, allowed a simple and fast spectrophotometric determination of total cadmium. Indeed, the molar absorptivities of the Cd(II)-dithizone (Dz) complex formed in the presence of the neutral Triton X-100 and cationic cetyltrimethylammonium bromide (CTAB) surfactants are almost twice the value observed in the standard method and the maxima of absorption are shifted by about 40 nm when compared with the standard method. Clearly, the use of neutral and cationic surfactants promotes a higher value of the molar absorptivities of the complex, resulting in an increase in the sensitivity of the method. Application of the method to the desorption of Cd(II) ions from clays is illustrated. 相似文献
88.
Jef Peeters Peter Neeskens Marcus Eli Brewster 《Journal of inclusion phenomena and macrocyclic chemistry》2007,57(1-4):137-139
Pirodavir, 4-[2-[1-(6-Methyl-3-pyridazinyl)-4-piperidinyl]ethoxy]benzoic acid ethyl ester, is an antiviral compound which
has low aqueous solubility (<0.01 mg/ml). The compound is a weak base (pKa 5.8) with high lipophicity (logP 4.44). Ionization
of the compound increases the solubility in acidic medium to 2.3 mg/ml at pH 2.4. However, a low pH is not acceptable for
nasal application as this would induce irritation.
Extensive solubility studies were performed using different types of substituted cyclodextrins in order to select an appropriate
derivate capable of increasing solubility to an acceptable level for formulations for nasal application. Aqueous solubility
of pirodavir increased in a linear fashion with increasing concentration of most of the substituted cyclodextrins. However,
using 2-hydropropyl-β-cyclodextrin (HPBCD) the solubility increased in a non-linear fashion. Based on these studies HPBCD
was selected as the most appropriate excipient.
To support a clinical study on the treatment of rhinovirus cold by intranasal Pirodavir formulations were developed containing
up to 5 mg/ml of pirodavir and up to 10% of HPBCD. Stability of the formulations was studied and found to be acceptable. 相似文献
89.
Solubility of lanthanum oxide was measured by thermal analysis. The solubility in alkali cryolites is rather high, because of chemical reactions between lanthanum oxide and cryolites. In Li3AlF6-La2O3, alumina precipitates, in the other systems the mixed oxide LaAlO3 is formed. In La2O3-Li3AlF6 the eutectic point is at 9.5 mol% La2O3 and 755 °C. The eutectic points in La2O3-Na3AlF6 and La2O3-K3AlF6 are at 11.5 mol% La2O3, and at 937 and 934 °C, respectively. 相似文献
90.
The ostwald absorption coefficient of argon was measured in aqueous solutions of two surfactants; sodium n-octanoate and in sodium dodecylsulfate, at several concentrations and at a few temperatures between 10–25°C. The free energies, entropies and enthalpies of solution were computed. A tentative interpretation of the results is given, based on a competition between the solubilization and the salting-out effects of the surfactants. 相似文献