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191.
The electrode behavior and microstructure of freshly prepared (La0.8Sr0.2)0.9MnO3 (LSM) electrodes were investigated under various polarization conditions. The original, large agglomerates in freshly prepared LSM electrodes were broken down into sphere-shaped grains when exposed to cathodic or anodic current passage of 200 mA cm–2 at 800 °C in air for 3 h. Microstructural changes under cathodic polarization could be related to the pronounced diffusion and migration of oxygen vacancies and Mn ions on the LSM surface and lattice expansion, while lattice shrinkage under oxidation conditions most likely contributes to the structural changes under anodic polarization. Such morphological changes were irreversible and were found to be beneficial to the performance of freshly prepared LSM electrodes. Freshly prepared LSM electrodes behaved very differently with respect to the cathodic and anodic current passage treatment. 相似文献
192.
CuO超细粉体的形貌与红外特性研究 总被引:16,自引:0,他引:16
CuO作为一种多功能精细无机材料,在印染、陶瓷、玻璃及医药等领域的应用已有数十年的历史,作为催化剂的主要活性成分,近年来在氧化、加氢、C1化学合成、NOx还原、CO及碳氢化合物燃烧、精细化工等多种催化反应中也得到了广泛的应用。可以推测,当CuO材料的粒度达到纳米级时,将使它的功能更加独特,应用更为广泛。因此CuO纳米材料的制备方法、聚集状态、与其他组分或载体的作用状况及催化活性等成为当前功能材料发展的研究热点之一犤1~8犦。我们在前文中报道了直接热解Cu2(OH)2CO3所得CuO粒径小、分布均匀、比表面积大,… 相似文献
193.
Dynamic surface elasticity of polymer solutions 总被引:1,自引:0,他引:1
B. A. Noskov 《Colloid and polymer science》1995,273(3):263-270
The surfaces of surfactant solutions exhibit viscoelastic dilational behavior which may be investigated by modern optical and mechanical methods. The present study focuses on the dynamic dilational properties of the polymer solution — gas interface. Linear flexible polymer chains at the surface are considered as consisting of trains, lying on the surface, and loops and tails that protrude into the liquid. The Rouse model is used to describe the inner dynamics of the trains, whereas their motion relative to their neighbors on the surface can be described with the help of the reptation conception. An expression for the complex dynamic dilational surface elasticity has been derived. Although, in general, the relaxation of the surface tension is characterized by an infinite series of relaxation times, it is shown that for many systems the dynamics of the surface layer can be described approximately by only two main relaxation times. The dispersion equation, which was obtained earlier for solutions of conventional surfactants, is shown to be fulfilled for polymer solutions also. 相似文献
194.
表面电沉积Ni—La2O3复合镀层的Fe26Cr1Mo不锈钢的氧化行为研究 总被引:3,自引:0,他引:3
Fe26Cr1Mo不锈钢在900℃氧化时,生成的氧化层在冷却过程中大量剥落,经表面共电沉积NiLa2O3复合镀层后,抗热循环能力明显提高。 相似文献
195.
Growing environmental concerns and the need for alternatives for oil
and natural gas resulted in intensive researches on ultra clean coal (UCC).
Therefore, the researches related to practice and application of various methods
to produce UCC become more important. Thermal characterization of chemically
demineralized coals by thermogravimetric analysis method is presented in this
study. The aim of the study is to provide thermal data for HF–HNO3
leaching system used for the production of UCC. Coal samples were first physically
enriched by density separation. Then the enriched portion was chemically demineralized
by using HF and HNO3, respectively. Ash content of coal samples were reduced
to a range of 0.12–0.41% by chemical demineralization process. The petrographic,
ultimate and proximate analyses were carried out to determine main features
of samples. Physically and chemically enriched coal samples were then analyzed
in a TG by two different techniques separately. The first technique covered
thermal characterization of samples under non-isothermal conditions. Characteristic
temperatures for each sample were obtained from the TG and DTG data. The second
technique involved the determination of reactivity of in situ produced chars
of each sample. 相似文献
196.
This work focuses on problems regarding empirical retention modelling and optimization of separation in ion chromatography. Influences of eluent flow rate and concentration of eluent competing ion (OH–) on separation of seven inorganic anions (fluoride, chloride, nitrite, sulphate, bromide, nitrate, and phosphate) were investigated. Artificial neural networks and multiple linear regression retention models in combination with several criteria functions were used and compared in global optimization process. It can be seen that general recommendations for optimization of separation in ion chromatography is application of chromatography exponential function criterion in combination with artificial neural networks retention model. 相似文献
197.
Tetravalent metal phosphates (M=Zr, Ti, and Sn) were prepared and characterized by XRD, surface properties, and TG-DTA. The cation exchange and sorption behavior of these metal phosphates toward transition metal ions such as Cu(2+), Co(2+), and Ni(2+) have been studied comparatively as a function of temperature and concentration. The adsorption process was found to increases with increase in temperature and concentration. The selectivity order for alpha-titanium and alpha-tin phosphates is Cu(2+)>Co(2+)>Ni(2+), whereas for alpha-zirconium phosphate it is Cu(2+)>Ni(2+)>Co(2+). The ion exchange capacity of alpha-titanium phosphate is greater than those of other phosphates, which is explained on the basis of the surface behavior, disorderness of the system, degree of hydrolysis of incoming guest adsorbate metal ions, and structural steric hindrance of the exchangers during adsorption and sorption. The distribution coefficient, Gibbs free energy, enthalpy, and entropy values indicate that the ion-exchange processes are spontaneous. 相似文献
198.
J. S. Guo E. D. Sudol J. W. Vanderhoff M. S. El-Aasser 《Journal of polymer science. Part A, Polymer chemistry》1992,30(5):691-702
Particle nucleation in the polymerization of styrene microemulsions was found to take place throughout the polymerization as indicated by measurements of the particle number as a function of conversion. A mechanism based on the nucleation in the microemulsion droplets was proposed to explain the experimental findings although homogeneous nucleation and coagulation during polymerization were not completely ruled out. A thermodynamic model was developed to simulate the partitioning of monomer in the different phases during polymerization. The model predicts that the oil cores of the microemulsion droplets were depleted early in the polymerization (4% conversion). Due to the high monomer/polymer swelling ratio of the polymer particles, most of the monomer resides in the polymer particles during polymerization. The termination of chain growth inside the polymer particles was attributed to the chain transfer reaction to monomer. The low n? (less than 0.5) of the microemulsion system was attributed to the fast exit of monomeric radicals. 相似文献
199.
With the combination of the the stoichiometric displacement model for retention (SDM-R) in reversed phase liquid chromatography (RPLC) and the stoichiometric displacement model for adsorption (SDM-A) in physical chemistry,the total number of moles of the re-solvated methanol of stationary phase side.nr,and that of solute side in the mobile phase,q,corresponding the one mole of the desorbing solute,were separately determined and referred as the characterization parameters of the contributions of the adsorption mechanism and partition mechanism to the solute retention,respectively.A chromatographic system of insulin,using mobile phase consisting of the pseudo-homologue of alcohols(methanol,ethanol and 2-propanol)-water and trifluoroacetic acid was employed.The maximum number of the methanol layers on the stationary phase surface was found to be 10.6,only 3 of which being valid in usual RPLC,traditionally referred as a volume process in partition mechanism.However,it still follows the SDM-R.Both of q and nr of insulin were found not to be zero,indicating that the retention mechanism of insulin is a mixed mode of partition mechanism and adsorption mechanism.When methanol is used as the organic modifier,the ratio of q/nr was 1.13,indicating the contribution to insulin retention due to partition mechanism being a bit greater than that due to adsorption mechanism.A linear relationship between q,or nr and the carbon number of the pseudo-homologue in the mobile phase was also found.As a methodology for investigating the retention mechanism retention and behavior of biopolymers.a homologue of organic solvents as the organic modifier in mobile phase has also been explored. 相似文献
200.
介电弹性体在电场作用下将产生形变,为获得高的变形能,需对介电弹性体施以较强的电场,而强电场的施加可能诱发力电耦合失稳导致失效。针对光热敏感介电凝胶力电耦合变形行为,基于热力学和连续介质力学理论建立力电耦合变形模型,分析了光强、温度以及预拉伸对光热敏感介电凝胶力电耦合变形行为的影响,结果表明:无预拉伸时,随着电场强度的增大,光热敏感介电凝胶最终发生力电失稳,光强越小、温度越低发生力电失稳时的临界电压越高;预拉伸可显著改善力电稳定性,施加等双轴预拉伸后,凝胶厚度方向的伸长率显著变小,电场强度随电位移增大而线性增大,未出现力电失稳现象。 相似文献