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991.
Although known since the 1950s, free-radical carbonylation has not received much attention until only recently. In the last few years the application of modern free-radical techniques has revealed the high synthetic potential of this reaction as a tool for introducing CO into organic molecules. Clearly now is the time for a renaissance of this chemistry. Under standard conditions (tributyltin hydride/CO) primary, secondary, as well as tertiary alkyl bromides and iodides can be efficiently converted into the corresponding aldehydes. Aromatic and α,β-unsaturated aldehydes can also be prepared from the parent aromatic and vinylic iodides. If the reaction is carried out in the presence of alkenes containing an electron-withdrawing substituent, the initially formed acyl radical subsequently adds to the alkene, leading to a general method for the synthesis of unsymmetrical ketones. This three-component coupling reaction can be extended successfully to allyltin-mediated reactions. Thus, β,γ-enones can be prepared from organic halides, CO, and allyltributylstannanes. In a remarkable one-pot procedure alkyl halides can be treated with a mixture of alkene, allyltributylstannane, and carbon monoxide in a four-component coupling reaction that provides β-functionalized δ,?-unsaturated ketones by the formation of three new C? C bonds. The reaction of 4-pentenyl radicals with CO leads to acyl radical cyclization, which provides a useful method for the synthesis of cyclopentanones. Certain useful one-electron oxidations can be combined efficiently with free-radical carbonylations. These findings and others discussed in this article clearly demonstrate that free-radical carbonylation can now be considered a practical alternative to transition metal mediated carbonylation. 相似文献
992.
The orientation and relaxation behavior of compatible blends of poly(methyl methacrylate) (PMMA) and poly(vinyl chloride) (PVC) was investigated. The deformation was performed at 9 K above the glass transition temperature. Based on birefringence and IR-dichroic measurements, it was found that the orientation of PMMA is strongly increased in the blends as compared to pure PMMA at identical draw ratios.The orientation of PVC, on the other hand, is not changed by blending. The results are discussed in terms of friction coefficients and their enhancement by molecular interactions.Dedicated to Prof. E. W. Fischer on the occasion of his 665th birthday 相似文献
993.
Gregor Trimmel Rita Badheka Florence Babonneau Jerome Latournerie Phillip Dempsey Djamila Bahloul-Houlier Julien Parmentier Gian Domenico Soraru 《Journal of Sol-Gel Science and Technology》2003,26(1-3):279-283
The sol-gel method was used to prepare two different starting gels containing SiCH3-groups for the preparation of SiOC ceramics. To understand the role of Si—H bonds in the incorporation of carbon into the SiOC network, gels prepared from a 1:2 mixture of triethoxysilane and methyldiethoxysilane (THDH2) and solely methyltriethoxysilane (TMe) were investigated. Thermogravimetric analysis coupled with mass spectroscopy (TG-MS) in inert atmosphere was performed to attain an insight into the decomposition reactions involved during gel-glass transformation. Samples calcined at different temperatures up to 1000°C were characterized by 29Si and 13C magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy. The presence of SiH groups in the starting gel allows an efficient conversion of Si—CH3 groups into CSi4 sites at lower temperatures. As a result, despite a much lower amount of carbon in the starting THDH2 gel (C/Si = 0.33) compared to the TMe gel (C/Si = 1), the amount of carbon inserted into the SiOC network of both glasses is equivalent, but the TMe sample contains the 10 fold amount of free carbon. 相似文献
994.
《Electroanalysis》2003,15(4):287-293
Homooxacalix[3]arene derivatives are effective ionophores for constructing serotonin‐selective membrane electrodes. An electrode based on one of the derivatives, tris(methoxyphenylpropyloxy)hexahomooxacalix[3]arene‐triethyl ether, with potassium tetrakis(p‐chlorophenyl)borate (20 mol% relative to the ionophore) as an ionic additive and bis(2‐ethylhexyl) sebacate as a solvent mediator in a poly(vinyl chloride) membrane matrix, displayed much better selectivity for serotonin than for various organic ammonium ions and inorganic cations. The electrode exhibited a near‐Nernstian response to serotonin in the concentration range of 2×10?4 to 1×10?2 M with a slope of 56.4 mV per concentration decade in physiological saline containing 150 mM NaCl and 10 mM Na2HPO4/NaH2PO4 (pH 7.4). The limit of the detection was 8×10?5 M. The selectivity pattern of this electrode was quite different from that of an electrode using calix[6]arene‐hexaacetic acid hexaethyl ester, a well‐known ionophore for primary organic ammonium ions, which did not induce an enhanced response to serotonin. The developed electrode was used for the active loading of serotonin in liposomes induced by transmembrane pH gradients. 相似文献
995.
Mitsuru Ueda Takayoshi Yokoo Takeo Nakamura 《Journal of polymer science. Part A, Polymer chemistry》1994,32(15):2989-2995
A general method for the preparation of aromatic poly (ether-sulfone-amide)s has been developed. Polymerization is based on the palladium-catalyzed polycondensation of aromatic dibromides containing ether sulfone structural units, aromatic diamines, and carbon monoxide. Reactions were carried out in N, N-dimethylacetamide (DMAc) in the presence of palladium catalyst, triphenylphosphine, and 1,8-diazabicyclo [5,4,0]–7–undecene (DBU), and gave a series of poly (ether-sulfone-amide)s with inherent viscosities up to 0.86 dL/g under mild conditions. The polymers were quite soluble in strong acids, dipolar aprotic solvents, and pyridine. Thermogravimetry of the polymers showed excellent thermal stability, indicating that 10% weight losses of the polymers were observed in the range above 470°C in air. The glass transition temperatures of the polymers were around 230°C, which are higher than those of poly (ether-sulfone) analogues. These polymers also showed the good tensile strengths and tensile modulus. © 1994 John Wiley & Sons, Inc. 相似文献
996.
本文提出平行催化体系的对位叠式循环方波伏安法,并对共作了系统的研究,推导了这一方法的催化电流理论方程,并用验验证这理论的正确性,得到其各脉冲电流皆为同方向,对位叠式循环催化电流相当于将电流叠加4次,而波形不受方波幅度大小的影响,因而灵敏度和分辨率有较大提高,优于其它方波伏安法。 相似文献
997.
The title compound (1) was prepared by the reaction of 3,5-bis(CF3)C6H3P(i-C3H7)2 (L1) and Co2(CO)8. Its solubility in supercritical carbon dioxide was measured at varying temperatures and pressures using a modified analytical extraction device. Solubility data were determined in the temperature and pressure ranges between 40 and 70 °C and between 100 and 300 bar, respectively. The solubility of 1 is lower compared to (p-CF3C6H4)3P, but much higher than for transition metal complexes bearing phosphines without fluorinated substituents. 相似文献
998.
合成甲醇的催化剂Rh-ZnO/MWNTs的研究 总被引:2,自引:0,他引:2
研究新型的由多壁碳纳米管(MWNTs)负载的, ZnO助催的铑基甲醇合成催化剂. 当铑含量达到4%(w)时,催化剂具有较高的比表面积(99.6 m2•g-1), 催化剂的反应活化能为68.8 kJ•mol-1.在563 K, 1 MPa下,催化剂的最高催化活性和甲醇选择性分别为411.4 mg/gcat.•h和96.7%. TEM、TPR和TPD等表征结果显示,碳纳米管能增加Rh在催化剂表面的分散度,提高催化剂的还原温度并能增加氢物种的吸附量,这些结果将有助于更好地了解催化剂中各组分间的协同作用和催化活性中心本质. 相似文献
999.
Abdollah Salimi Abdollah Noorbakhsh Hussein Mamkhezri Raoof Ghavami 《Electroanalysis》2007,19(10):1100-1108
A new H2O2 enzymeless sensor has been fabricated by incorporation of thionin onto multiwall carbon nanotubes (MWCNTs) modified glassy carbon electrode. First 50 μL of acetone solution containing dispersed MWCNTs was pipetted onto the surface of GC electrode, then, after solvent evaporations, the MWCNTs modified GC electrode was immersed into an aqueous solution of thionin (electroless deposition) for a short period of time <5–50 s. The adsorbed thin film of thionin was found to facilitate the reduction of hydrogen peroxide in the absence of peroxidase enzyme. Also the modified electrode shows excellent catalytic activity for oxygen reduction at reduced overpotential. The rotating modified electrode shows excellent analytical performance for amperometric determination of hydrogen peroxide, at reduced overpotentials. Typical calibration at ?0.3 V vs. reference electrode, Ag/AgCl/3 M KCl, shows a detection limit of 0.38 μM, a sensitivity of 11.5 nA/μM and a liner range from 20 μM to 3.0 mM of hydrogen peroxide. The glucose biosensor was fabricated by covering a thin film of sol–gel composite containing glucose oxides on the surface of thionin/MWCNTs modified GC electrode. The biosensor can be used successfully for selective detection of glucose based on the decreasing of cathodic peak current of oxygen. The detection limit, sensitivity and liner calibration rang were 1 μM, 18.3 μA/mM and 10 μM–6.0 mM, respectively. In addition biosensor can reach 90% of steady currents in about 3.0 s and interference effect of the electroactive existing species (ascorbic acid–uric acid and acetaminophen) is eliminated. The usefulness of biosensor for direct glucose quantification in human blood serum matrix is also discussed. This sensor can be used as an amperometric detector for monitoring oxidase based biosensors. 相似文献
1000.
A novel flow-injection amperometric method was proposed for the sensitive and enzymeless determination of hydrogen peroxide based on its electrocatalytic reduction at a palladium nanoparticle-modified pretreated pencil graphite electrode in a laboratory-constructed electrochemical flow cell. Cyclic voltammograms of the unmodified and modified electrodes were recorded in pH 7.0 phosphate buffer containing 0.10 M KCl at a scan rate of 50?mV s?1 for the investigation of electrocatalytic reduction of hydrogen peroxide at the palladium nanoparticle-modified pretreated pencil graphite electrode. Cyclic voltammograms of the pretreated pencil graphite electrode revealed an irreversible oxidation peak and a weak reduction peak of hydrogen peroxide at +1100?mV and –450?mV vs. an Ag/AgCl/KCl saturated reference electrode. However, the reduction of hydrogen peroxide was observed at –100?mV with an increase in current in the cyclic voltammograms of the palladium nanoparticle-modified pretreated pencil graphite electrode compared to the unmodified electrode. These results indicate that the palladium nanoparticle-modified pretreated pencil graphite electrode exhibits efficient electrocatalytic activity for the reduction of hydrogen peroxide. A linear concentration range was obtained between .01 and 10.0?mM hydrogen peroxide with a detection limit of 3.0 µM from flow injection amperometric current–time curves recorded in pH 7.0 phosphate buffer at –100?mV and a 2.0?mL min?1 flow rate. The novelty of this work relies on its use of a laboratory-constructed flow cell constructed for the pencil graphite electrode using these inexpensive, disposable, and electrochemically reactive modified electrodes for the amperometric determination of hydrogen peroxide in a flow injection analysis system. 相似文献