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排序方式: 共有1711条查询结果,搜索用时 312 毫秒
931.
F. Bonfigli B. Jacquier F. Menchini R. M. Montereali P. Moretti E. Nichelatti 《辐射效应与固体损伤》2013,168(1-6):185-190
Highly stable F2 color centers are very efficiently produced in lithium fluoride (LiF) by electron beam irradiation at room temperature. We have fabricated optical microcavities in which the active medium is a low-energy electron beam irradiated LiF film, whose optical thickness is comparable with the peak wavelength (~668nm) of the F2 broad photoluminescence band. By selecting the proper electron beam energy, one can control the F2 color center depth distribution. This distribution influences the photoemission angular distribution of the microcavity, whose resonance properties are determined by the coupling of the depth profile of the defects with the pump electromagnetic field and microcavity modes. 相似文献
932.
E. Radzhabov 《辐射效应与固体损伤》2013,168(1-6):203-207
New emission bands were found in Ce3? doped SrF2 and BaF2 crystals under excitation into the charge transfer region. The bands at 4.85 eV in BaF2 and 4.35 eV SrF2 were found in all crystals with Ce-concentration from 0.001 to 1 mol.%, most prominent in 0.01% samples. Decay of luminescence was simple exponential in BaF2, decay time decreased from 1.3 ms at 65 K to 0.41 μs at 523 K. The decay curve in SrF2 shows t?0.3 dependence at room temperature. All experimental results were naturally explained by assumption that new emission belongs to radiative charge transfer recombination in Ce2?—Fio pairs with different distances between them. 相似文献
933.
New halophosphor K3Ca2(SO4)3F activated by Eu and Ce has been synthesized by a co-precipitation method and characterized according to its thermoluminescence. The formation of traps in rare earth doped K3Ca2(SO4)3F and the effects of γ-radiation dose on the glow curve are discussed. The glow curve of K3Ca2(SO4)3F:Ce shows a prominent single peak at 150°C, whereas K3Ca2(SO4)3F:Eu and K3Ca2(SO4)3F:Ce,Eu at 142°C and 192°C, respectively. A single glow peak indicates that there is only one set of trap being activated within the particular temperature range. The presented phosphors are also studied because of its fading, reusability and trapping parameters. There was just 2% fading during a period of 10 days, indicating no serious fading problem. Trapping parameters such as order of kinetics (b), activation energy (E) and frequency factor (S) were calculated by using Chen's half-width method. The observations presented in this paper are good for lamp phosphors as well as solid-state dosimeter. 相似文献
934.
Dendrite-shaped PbS has been successfully synthesized using hydrothermal method on a large scale. The formation of dendrite-shaped PbS was confirmed by scanning electron microscopy (SEM). A detailed study of variations in dielectric properties on frequency and temperature shows that composites of PVDF and dendrite-shaped PbS have significantly higher dielectric constant than PVDF/PbS nanoparticles (NP) nanocomposites due to low percolation threshold. 相似文献
935.
Within the scope of the present study, the three-dimensional (3D) samples from poly(vinylidene fluoride) plus lead zirconate titanate (PVDF+PZT) and silica+PZT powdered compositions were successfully prepared by the selective laser sintering (SLS) process. The optimal regimes for the layer-by-layer fabrication of 3D samples were determined both for wavelengths of 10.6 and 1.06 μm. The sample structure and element composition were characterized by the use of the scanning electronic microscope in combination with the energy dispersive X-ray spectrometry (EDX) analysis. It was shown that after the SLS process, the initial perovskite phase did not undergo any significant structural changes. The results of characterization tests testified to the decease of the sample density and opened porosity by the 2–5 times as compared to the solid PZT that seems to be useful for acoustic applications. A comparative estimate of the PVDF destruction process was fulfilled for the laser wavelength of 10.6 and 1.06 μm, by using infrared spectroscopy, photo calorimetrical and chromatography measurements, sol-gel and viscosity analysis. It was found that the structuring velocity had diametrically opposite behavior for these wavelengths: it grows with the laser power increase for λ = 10.6 μm and, vice versa, it falls for λ = 1.06 μm. 相似文献
936.
The ethylenediamine trmsition metal complexes1-9 of the type M(en)2X2 (M = Co, Ni, Cu, Pd, Pt and × = I, Br, C1, NO3, C104) have infrared spectra of complicated nature which have been used for the study of conformation of the chelate ring. In dihydrldobis ZnC14 ethylenediamlne transition metal complexes, the hydrogen bonding and the presence of ZnCl4 further complicates the vibrational spectra. With a view to study this, the present study of dihydridobis (ethylenedianlne) osnlum tetrachloro zincate was carried out. 相似文献
937.
The ferroelectric-to-paraelectric phase transition in poly(vinylidene fluoride-trifluoroethylene) copolymers has been investigated by differential scanning calorimetry and dielectric techniques. The transition appears to be very dependent on the crystallization kinetics and thermal history. The anomalies accompanying the transition show that the structural transformations are complex. In particular, the 30 mol % TrFE sample presents the most remarkable effects. The results are discussed in terms of the existence of a possible intermediate crystalline phase. The role of defects and of the anchored amorphous phase have also been considered. 相似文献
938.
基于平面声源的三层有源隔声结构系统易于实现且具有良好的低频隔声性能,实现该系统需解决的关键问题是误差信号的检测.本文将压电传感薄膜聚偏氟乙烯(polyvinylidene fluoride, PVDF)阵列检测简支梁辐射模态的理论拓展到二维结构, 并应用到三层隔声结构实现误差传感的优化设计.根据三层结构中特殊的能量传输规律, 对误差传感方案中目标函数的选取、PVDF数目确定以及传感系统优化等问题进行深入分析.研究表明, 由于辐射板能量主要集中在有限个振动模态上, 只需将少数经固定系数加权的PVDF薄膜输出电流求和即可获得前三阶辐射模态幅值.辐射模态幅值的检测值与理论值符合良好, 保证传感精度的同时有效简化了系统.
关键词:
三层有源隔声结构
误差传感策略
压电传感薄膜阵列
辐射模态 相似文献
939.
Microporous poly(vinylidene fluoride) (PVDF) membranes were prepared by thermally induced phase separation (TIPS) at different quenching temperatures with benzophenone as the diluent. The crystallization behavior and crystal structure of PVDF in PVDF/benzophenone systems were investigated by differential scanning calorimetry (DSC) and wide angle X‐ray diffraction (WAXD). The different PVDF concentrations had a remarkable effect on PVDF crystallization behavior and resulted in different membrane structures. Spherulitic structures were vague when the PVDF/benzophenone solution was quenched to ?8°C; however, discernable spherulitic structures were obtained when quenched to 34 and 49°C. Additionally, two phase separation mechanisms (solid–solid (S–S) and solid–liquid (S–L) phase separation) were observed during membrane preparation. It was revealed by scanning electron microscopy (SEM) that microporous membranes had more discernable spherulitic structures formed by S–L phase separation than by S–S phase separation, which induced macrovoids and irregular pores on the fracture surfaces of membranes. 相似文献
940.
Xuyun Wang Xuehai Yue Xin Wang Qingjie Guo 《Journal of Macromolecular Science: Physics》2013,52(5):880-889
Poly(vinylidene fluoride) (PVDF) membranes were prepared by the immersion precipitation method. Effects of the maturation time of dopes on the morphology and crystallization of the prepared membranes were investigated. The analysis showed that the maturation time played an important role in determining the morphology of the prepared membranes. For the dope prepared in the initial day, liquid–liquid demixing preceded solid–liquid demixing in the process of the membrane formation. The morphology of the cross section of the prepared membrane (M1) was finger-like structures with a sponge substrate beneath the porous skin. During the maturation, the dopes underwent a microscopic phase separation and the PVDF crystallized, which resulted in the existence of micro-liquid phases and micro-solid phase crystalline areas in the dopes. In the process of the membrane formation, liquid–liquid demixing took place by nucleation and growth of droplets of the polymer rich phase in the micro-liquid phase. The micro-solid phase crystallites were connected together by the polymer chains, and formed a three-dimensional network gelation morphology. The crystal structure of M1 was mainly β crystals. With increasing maturation time of the dopes, the proportion of β decreased crystals, but that of α crystals increased for the prepared membranes. 相似文献