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651.
G. Szenes 《Radiation measurements》1995,25(1-4):39-42
A new thermal spike model is presented which predicts three regimes in the formation of latent tracks. At SeSet no track formation is expected. A logarithmic and a linear variation of the damage cross section versus Se is predicted for 2.7SetSeSet and SeSet, respectively. A simple expression is derived for the relation between Set and the thermal properties of the target. A comparison is made with experimental data on YIG and NiFe2O4 and a good agreement is found. 相似文献
652.
Marc M. Lamoureux C. L. Chakrabarti J. Craig Hutton Albert Kh. Gilmutdinov Yuri A. Zakharov D. Conrad Gr goire 《Spectrochimica Acta Part B: Atomic Spectroscopy》1995,50(14):1847-1867
The mechanism of aluminium spike formation and dissipation of aluminium atoms in electrothermal atomization absorption spectrometry has been investigated using two different approaches. The first approach employs a graphite electrothermal atomizer coupled to an inductively coupled plasma mass spectrometer (ICP-MS) in a configuration that allows simultaneous measurement of atomic, or molecular, absorption signals and mass spectrometric signals. Aluminium sub-oxide (AlO and Al2O) and CO(g) spikes in ICP-MS are correlated with the appearance of both Al atom spikes and Al-containing molecule spikes in absorption spectrometry. The aluminium carbide (AlC2) signal in ICP-MS is not coincident with the appearance of either Al atom spikes or Al-containing molecule spikes in absorption spectrometry. The second approach uses two different imaging systems, i.e. shadow spectral filming (SSF) and shadow spectral digital imaging (SSDI), to provide temporally and spatially resolved absorption profiles of Al atoms and Al-containing molecules during Al spike formation and dissipation. The transverse cross-sectional distribution of Al atoms and of Al-containing molecules in the graphite furnace are complementary to one another for both wall and platform atomization. The highest concentration of Al atoms is near the graphite surface, whereas the highest concentration of Al-containing molecular species is at the centre of the graphite tube. The Al-containing molecules observed in both wall and platform atomization consist of both gaseous Al-molecules and a non-uniformly distributed cloud of finely dispersed Al2O3(s,1) particles. A mechanism of formation that is consistent with the above experimental observations is presented. It is proposed that Al atom spikes are formed from gaseous Al2O precursors and that this reaction is triggered by the formation of a molten, condensed-phase Al4C3 melt. 相似文献
653.
654.
J. Bertran M. F. Ruiz-López D. Rinaldi J. L. Rivail 《Theoretical chemistry accounts》1992,84(3):181-194
Summary A Self-Consistent Reaction Field Model is used to study the effect of the molecular environment on the electronic distribution and on the equilibrium geometry of the water dimer in liquid water. Computations are performed at the 6-311G++(2d,2p) MP2 level. Comparison of the results for the monomer and the dimer, in a vacuum and in the liquid, is made in order to gain a deeper insight on the cooperative phenomenon. The discussion emphasizes the trends which should be considered for deriving more sophisticated water-water potentials. 相似文献
655.
Pandi PV Kole PL Rahul Mishra PK Shanmukha I Girish K Nagappa AN 《Colloids and surfaces. B, Biointerfaces》2004,35(3-4):243-248
The role of surface activity has been studied in the biological actions of ranitidine (RNT) and famotidine (FMT). The drugs have been shown to generate liquid membranes in series with a supporting membrane with the virtue of their amphiphilicity. Transport of histamine, acetylcholine, and ions (chloride, bicarbonate, potassium, sodium and calcium) have been studied in the presence of liquid membranes generated by surface-active RNT and FMT. The data on the modifications in the permeability of histamine, acetylcholine and ions indicate that the liquid membranes generated by RNT and FMT may play a significant role in their biological action.
The surface-active nature of the drugs has been discussed with relevance to their pharmacological effects. 相似文献
656.
INFLUENCE OF SAMPLE THICKNESS ON ISOTHERMAL CRYSTALLIZATION KINETICS OF POLYMERS IN A CONFINED VOLUME 总被引:2,自引:0,他引:2
Hui Sun Zhi-ying Zhang Shi-zhen Wu Bin Yu Chang-fa Xiao 《高分子科学》2005,(6):657-663
Isothermal crystallization process of polymers in a confined volume was simulated in the case of instantaneous nucleation by use of the Monte Carlo method. The influence of sample thickness on some kinetic parameters of crystallization was quantitatively evaluated. It was found that there was a critical thickness value. Influence of thickness on the crystallization behavior was only found for samples of thickness near and less than the critical value. For thick samples the Avrami plot showed straight lines with a turning point at the late stage of crystallization due to the secondary crystallization. When the thickness was near or less than the critical value a primary turning point appeared in the Avrami plot at the very beginning of the crystallization process. A model was proposed to explain the mechanism of this phenomenon. According to this model the critical thickness value is related to the nucleation density or the average distance between adjacent nuclei, and the primary turning point is an indication of a transformation of crystal growth geometry from a three-dimensional mode to a two-dimensional one. Analysis of experimental results of PEO isothermally crystallized at 53.5℃ was consistent with the proposed model. 相似文献
657.
以丙烯酸(AA)和甲基丙烯酸二乙氨基乙酯(DEAM)形成的离子复合物和丙烯酰胺(AAm)为单体,采用自由基聚合制备了一系列新型的离子键交联聚两性电解质凝胶(PADA凝胶).非接触直流电场的实验表明,该离子键交联的PADA凝胶在电场下发生溶蚀现象,该现象鲜见文献报道.PADA凝胶的溶蚀速率与电场强度、溶液浓度、pH值、酸碱基团摩尔比、溶液离子价态等诸多因素有关,如溶蚀随电压的升高而增大,随盐溶液浓度的加大而增大.其溶蚀动力学研究表明PADA凝胶的溶蚀度随时间线性的增加,即溶蚀速率在整个实验时间内基本保持恒定. 相似文献
658.
659.
Dynamic friction, sliding friction, and the stick-slip phenomenon have been studied on compacted polymer powders during high-velocity compaction. It is particularly important from a practical point of view to distinguish the stick-slip mechanism and the sliding mechanism which occur concurrently. A practical experimental system has been successfully developed to study the dry frictional force and to measure the sliding coefficient between the polymer powder particles and the die wall during high-velocity compaction. Two new components have been introduced as relaxation assists to improve the compaction process by reducing the frictional forces. It was found that the relaxation assist device leads to an improvement in the polymer powder compaction process by giving a more homogeneous opposite velocity and a better locking of the powder bed in the compacted form with less change in dimensions. The subsequent movement of the particles can be reduced and the powder bed attains a higher density with a minimum total elastic spring-back. The relative time of the stick-slip phenomenon during the compacting stage is also reduced so that the time needed to transfer from an intermittent stick-slip state to a smooth sliding state is reduced and the powder bed slides smoothly. It was found that the dynamic, dry frictional force is intermittent (stick-slip mechanism) at low compaction rates but that at high compaction rates is becomes more smooth (sliding mechanism). Both mechanisms depend on the nature of the powder and on the compaction conditions. At the beginning of the compaction stage, the sliding coefficient decreases due to an increase in the radial to axial stress ratio until the maximum pressure has been reached. During the reorganization stage, more time is needed for large particles to move, rotate and slide due to their relatively large diameter and mass. As a result, the reorganization stage is extended and the stick-slip phenomenon is observed more with increasing particle size. Much better transfer of the pressure throughout the powder bed and less loss of pressure lead to a higher sliding coefficient due to the overall friction during the compaction process. It was found that the sliding coefficient is proportional to the density.
A more homogeneous density distribution in the compacted powder and a smaller pressure loss during compaction has a major influence on the sliding coefficient and on the quality of the compacted material. 相似文献
660.
Jianyong Ma Shijie Liu Yunxia Jin Cheng Xu Jianda Shao Zhengxiu Fan 《Optics Communications》2008,281(12):3295-3300
We demonstrate that the surface relief guided-mode resonant gratings with specified central wavelength and FWHM in the visible wavelength range can be designed by analyzing the complex poles of Reflectance and transmission coefficient matrix algorithm (RTCM), a variant of S-matrix propagation algorithm proposed for calculation of multilayer gratings. In addition, FWHM is computed with couple-mode (CM) theory of resonant gratings which is firstly extended by Norton et al. in calculation of waveguide grating. Furthermore, the side band reflections of the filter can be reduced to less than 5% in the visible wavelength with the antireflection (AR) design technique widely used in the thin-film field. 相似文献