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951.
Patrícia R. Pinto Luis C. Mendes Marcos L. Dias C. Azuma 《Colloid and polymer science》2006,284(5):529-535
Silica was obtained by sol–gel process through hydrolysis and condensation of tetraethyl orthosilicate (TEOS) using molar
fraction of H2O/TEOS=9 under alkaline catalysis, at different reaction times (5 min to 24 h). At the end of each time, the reaction medium
appeared as a suspended microparticle system. After solvent evaporation, the yield was calculated to be around 100% and practically
independent of the time of reaction. The silica had its surface modified through the condensation reaction with acryloyl chloride
forming organically modified silica. The unmodified and modified silica were characterized by thermogravimetry and derivative
thermogravimetry (TG/DTG), infrared spectrometry (FT-IR), size particle and optical microscopy (OM). The acrylic content was
independent of the reaction time. The methodology represents an alternative route to obtain silica with an unsaturated organic
group, able to polymerize and stabilize up to 300–400°C. The modified material has a potential application as compatibilizing
filler in dental composite. 相似文献
952.
A method is described for the separation of quaternary alkylbenzylammonium compounds as well as alkyl pyridinium salts by
capillary electrophoresis using direct UV detection. The influence of the organic buffer modifier on the electrophoretic behaviour
of the analytes is discussed. In addition to fused silica capillaries, also C8, C18 and neutral surface coatings are used.
Separation is also performed in completely non-aqueous media. The results of method development are applied to the determination
of cationic surfactants in cosmetics and pharmaceuticals. A comparison with HPLC with respect to efficiency, reproducibility
and detection limits is presented.
Received: 1 July 1996 / Revised: 6 November 1996 / Accepted: 10 November 1996 相似文献
953.
The acidity constants of guanylyl(3'-->5')guanosine (GpG(-)) and 2'-deoxyguanylyl(3'-->5')-2'-deoxyguanosine [d(GpG)(-)] for the deprotonation of their (N1)H sites were measured by potentiometric pH titrations in aqueous solution (25 degrees C; I = 0.1 M, NaNO(3)). The same method was used for the determination of the stability constants of the 1:1 complexes formed between Mg(2+), Ni(2+), or Cd(2+) (= M(2+)) and (GG-H)(2-), and in the case of Mg(2+) also of (GG-2H)(3-), where GG(-) = GpG(-) or d(GpG)(-). The stability constants of the M(GG)(+) complexes were estimated. The acidity constants of the H(dGuo)(+) and dGuo species (dGuo = 2'-deoxyguanosine) and the stability constants of the corresponding M(dGuo)(2+) and M(dGuo-H)(+) complexes were also measured. Comparison of these and related data allows the conclusion that N7 of the 5'G unit in GG(-) is somewhat more basic than the one in the 3'G moiety; the same holds for the (N1)(-) sites. On the basis of comparisons with the stability constants measured for the dGuo complexes, it is concluded that M(2+) binding of the GG dinucleoside monophosphates occurs predominantly in a mono-site fashion, meaning that macrochelate formation is not very pronounced. Indeed, it was a surprise to find that the stabilities of the complexes of dGuo or (dGuo-H)(-) and the corresponding ones derived from GG(-) are so similar. Consequently, it is suggested that in the M(GG)(+) and M(GG-H) complexes the metal ion is mainly located at N7 of the 5'G unit since this is the more basic site allowing also an outer-sphere interaction with the C6 carbonyl oxygen and because this coordination mode is also favorable for an electrostatic interaction with the negatively charged phosphodiester bridge. It is further suggested that Mg(2+) binding (which is rather weak compared to that of Ni(2+) and Cd(2+)) occurs mainly in an outer-sphere mode, and on the basis of the so-called Stability Ruler it is concluded that the binding properties of Zn(2+) to the GG species are similar to those of Ni(2+) and Cd(2+). 相似文献
954.
Renato Capasso Antonio Evidente Carla Visca Liloana Gianfreda Michele Maremonti Guido Greco 《Applied biochemistry and biotechnology》1997,61(3):365-377
Pure-grade oleuropein, a bitter, hypotensive, phenolic glucoside, was obtained from organic extracts of olive plant leaves
by two Chromatographic steps. The purified compound was characterized by spectroscopic NMR and FAB-MS methods. The glucoside
underwent chemical and enzymatic hydrolysis. Aglycone was characterized by spectroscopic methods (1H-NMR and FAB-MS). Glucose was measured by enzymatic methods. The enzymatic hydrolysis of oleuropein was carried out by a
soluble β-glucosidase. The reaction was characterized in terms of kinetic parameters, optimal pH value, activation energy,
inhibition constant by glucose, and thermal stability. Preliminary experiments were also performed in a continuousflow ultrafiltration
membrane reactor. The cut-off of the membrane was lower than the molecular-weight of the enzyme, thus determining β-glucosidase
confinement within the reactor. Under these conditions, β-glucosidase had a good long-term stability. This is an encouraging
result in view of possible industrial applications. 相似文献
955.
Reactions of some [M(η5-C5H5)2L2]n+ complexes (M Mo, W; L = ligand; n = 0, 1, 2) with NaBH4 and LiAlH4 are reported. New neutral and cationic hydride derivatives of the type [M(η5-C5H5)2HL]m+ (m = 0, 1) are described, in particular the six halohydride complexes [M(η5-C5H5)2HX]. The deuteration studies were carried out, but the results do not lead to definite conclusions about the mechanism. 相似文献
956.
Prata CA Zhao Y Barthelemy P Li Y Luo D McIntosh TJ Lee SJ Grinstaff MW 《Journal of the American Chemical Society》2004,126(39):12196-12197
Delivering a missing gene or a functional substitute of a defective gene has the potential to revolutionize current medical care. Of the two gene delivery approaches, viral and synthetic vectors, synthetic cationic vectors possess several practical advantages but suffer from poor transfection efficiency. A new approach to gene delivery using charge-reversal amphiphiles is described. This synthetic vector transforms from a cationic to an anionic amphiphile intracellularly. This amphiphile performs two roles: first, it binds and then releases DNA, and second, as an anionic multicharged amphiphile, it destabilizes lipid bilayers. A charge-reversal amphiphile was synthesized and fully characterized, including the supramolecular complex it forms with DNA. Enhanced gene transfection was observed using these vectors compared to current cationic amphiphiles. 相似文献
957.
Ângela F. S. S. Mendonça Florbela A. Dias Isabel M. S. Lampreia 《Journal of solution chemistry》2007,36(1):13-26
Ultrasound speeds in aqueous binary mixtures of diethylamine (DEA) were measured across the entire composition range at five
temperatures between 278.15 and 308.15 K. Isentropic compressibilities, κ
S
, were calculated from the ultrasound speed and density data. The excess molar isentropic compressions, K
S,m
E, were estimated and their variation with the mole fraction of the amine were fitted by the Redlich–Kister equation. Excess
partial molar isentropic compressions, K
S,i
E, were then obtained, allowing separation of the role of each component in the mixing process. Interesting insights are gained
from the analysis of the temperature and composition dependence of K
S,i
E, principally in the water-rich region. A comparison of the limiting values of this property with those of the limiting excess
partial molar isobaric expansion, E
P,i
E,∞, previously published, clearly shows the different sensitivity of these two differential thermodynamic properties to the
mixing process. The different behavior of the temperature dependence of K
S,i
E,∞ in the systems, water + DEA, and water + 2-diethylaminoethanol (DEEA), are also analyzed and interpreted in terms of changes
in the solute configuration, the degree of hydrolysis and solute-solvent interactions. 相似文献
958.
The reaction of sulfenamide 3 with (TMS)3SiH initiated by the decomposition of AIBN at 76 °C has been studied in some detail. The reaction is a rare example of a radical chain-branching process. The two main products are dialkylamine 4 and the thiosilane 5. It is also established that 2-mercaptobenzothiazole (2) is formed in a substantial yield as one of the by-products. The mechanism of this chain autocatalytic reaction is complex due to a mix of different radical chain reactions and some discussion is provided. The amine obtained in a quantitative yield can arise from two independent routes of attack of (TMS)3Si radical on sulfenamide 3. The minor route affords thiol 2 that can act as a catalyst for the major route during the reaction course and then gives a salt with secondary amine, which precipitates upon cooling. The origin of autocatalysis is discussed in some detail. 相似文献
959.
Two of the most suitable analytical techniques used in the field of cultural heritage are NIR (near-infrared) and Raman spectroscopy. FT-Raman spectroscopy coupled to multivariate control charts is applied here for the development of a new method for monitoring the conservation state of pigmented and wooden surfaces. These materials were exposed to different accelerated ageing processes in order to evaluate the effect of the applied treatments on the goods surfaces. In this work, a new approach based on the principles of statistical process control (SPC) to the monitoring of cultural heritage, has been developed: the conservation state of samples simulating works-of-art has been treated like an industrial process, monitored with multivariate control charts, owing to the complexity of the spectroscopic data collected.The Raman spectra were analysed by principal component analysis (PCA) and the relevant principal components (PCs) were used for constructing multivariate Shewhart and cumulative sum (CUSUM) control charts. These tools were successfully applied for the identification of the presence of relevant modifications occurring on the surfaces. CUSUM charts however proved to be more effective in the identification of the exact beginning of the applied treatment. In the case of wooden boards, where a sufficient number of PCs were available, simultaneous scores monitoring and residuals tracking (SMART) charts were also investigated. The exposure to a basic attack and to high temperatures produced deep changes on the wooden samples, clearly identified by the multivariate Shewhart, CUSUM and SMART charts. A change on the pigment surface was detected after exposure to an acidic solution and to the UV light, while no effect was identified on the painted surface after the exposure to natural atmospheric events. 相似文献
960.
A mixture of [HB(3,5-(CF3)2Pz)3]Ag(eta 2-toluene) and [(Me)2ATI]GeCl in CH2Cl2, rather than undergoing metathesis, formed a 1:1 adduct [HB(3,5-(CF3)2Pz)3]Ag<--GeCl[(Me)2ATI] (1, where [HB(3,5-(CF3)2Pz)3] = hydrotris(3,5-bis(trifluoromethyl)pyrazolyl)borate and [(Me)2ATI] = N-methyl-2-(methylamino)troponiminate) featuring a silver-germanium bond. Solutions of 1 (in CH2Cl2 or toluene) did not precipitate AgCl even after several days. However, it easily underwent metathesis with CF3SO3Ag, leading to the chloride-free product [HB(3,5-(CF3)2Pz)3]Ag<--Ge(OSO2CF3)[(Me)2ATI] (2). Compounds 1 and 2 were characterized by X-ray crystallography. The Ag-Ge bond distances of 1 and 2 are 2.4215(9) and 2.4116(10) A, respectively. 相似文献