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991.
熔锥型光纤耦合器宽带特性研究 总被引:7,自引:1,他引:6
报道了在常规熔锥型单模光纤定向耦合器工艺基础上,以氢氟酸腐蚀法,将两光纤耦合区直径腐蚀成适当比例,用水平直接熔融拉锥系统,将耦合区域拉制成非对称臂组合波导,从而获得了具有宽频带特性、且尺寸较小的单模光纤定向耦合器,实验结果说明:通过控制耦合区长度,可以使耦合器耦合功率在某个特定波长附近、预定小于100%分束比上具有相当平坦(宽带)特性;从而,通过控制组合波导的不同直径比,可望得到不同分束比宽带耦合 相似文献
992.
993.
合成了萘酞菁锌, 利用傅立叶红外光谱、元素分析和MALDI-TOF质谱等手段表征了分子结构; 循环伏安测试和吸收光谱确认了共轭体系的扩大使分子带隙下降. 根据材料加工性能的不同, 分别采用溶液法、层-层蒸镀(Layer-by-layer evaporation)法和单层分散旋涂法, 将给体分子萘酞菁锌与三种受体分子1-(3-甲氧基羧基)丙基-1-苯 基-[6,6]C61, C60和N,N’-二嘧啶基苝四羧基二酰亚胺进行了复合, 通过研究复合前后荧光变化, 确认了给体-受体两相界面处发生了由分子能级差引发的光致电荷转移, 为制备更宽光伏响应范围的太阳能电池器件提供了潜在的新途径. 相似文献
994.
The Seebeck coefficient enhancement due to an increase of density-of-states effective mass of electron has been found in n-type Bi1.9Lu0.1Te3. This enhancement is assumed to be related to forming the narrow and non-parabolic impurity (Lu) band with local maximum of electronic density of states lying near the Fermi level. Minimum in the specific electrical resistivity, ρ, originated from change of conductivity mechanism was observed at temperature Tm ≈ 11 K. Above Tm, the ρ change is due to decrease of electron mobility via acoustic phonon scattering. Below Tm, the variable-range hopping conductivity takes place. The electron hops between the localized states of the impurity energy band occur via tunneling process. Using the temperature and magnetic field dependences of ρ, the localization radius of electron was estimated as ≈6 nm. Two parts in the magnetic field dependence of the electrical resistivity were found at temperature of 2 K. At weak magnetic fields, the ρ change is in agreement with the variable-range hopping conductivity mechanism. At high magnetic fields, the positive and almost linear transverse and longitudinal magnetoresistances were observed at low temperatures. Both variable-range hopping conductivity and positive linear magnetoresistance are characteristics of disordered and inhomogeneous semiconductors. 相似文献
995.
996.
The effect on the hydrogen storage attributes of magnesium hydride (MgH2) of the substitution of Mg by varying fractions of Al and Si is investigated by an ab initio plane‐wave pseuodopotential method based on density functional theory. Three supercells, namely, 2×2×2, 3×1×1 and 5×1×1 are used for generating configurations with varying amounts (fractions x=0.0625, 0.1, and 0.167) of impurities. The analyses of band structure and density of states (DOS) show that, when a Mg atom is replaced by Al, the band gap vanishes as the extra electron occupies the conduction band minimum. In the case of Si‐substitution, additional states are generated within the band gap of pure MgH2—significantly reducing the gap in the process. The reduced band gaps cause the Mg? H bond to become more susceptible to dissociation. For all the fractions, the calculated reaction energies for the stepwise removal of H2 molecules from Al‐ and Si‐substituted MgH2 are much lower than for H2 removal from pure MgH2. The reduced stability is also reflected in the comparatively smaller heats of formation (ΔHf) of the substituted MgH2 systems. Si causes greater destabilization of MgH2 than Al for each x. For fractions x=0.167 of Al, x=0.1, 0.167 of Si (FCC) and x=0.0625, 0.1 of Si (diamond), ΔHf is much less than that of MgH2 substituted by a fraction x=0.2 of Ti (Y. Song, Z. X. Guo, R. Yang, Mat. Sc. & Eng. A 2004 , 365, 73). Hence, we suggest the use of Al or Si instead of Ti as an agent for decreasing the dehydrogenation reaction and energy, consequently, the dehydrogenation temperature of MgH2, thereby improving its potential as a hydrogen storage material. 相似文献
997.
Judd-Ofelt parameters obtained from the absorption spectra of Eu3+ ions doped in PbO-PbF2 glasses are intermediate between the values for fluoride and phosphate glass matrices. Eu3+ ions are coordinated to both oxide and fluoride ions. The calculated transition probabilities (As-1) for the laser transition5Do→7F2 are 171 and 170 for 30PbO-70PbF2 and 70PbO-30PbF2 glasses respectively and are significantly lower compared to phosphate glasses. The calculated (βR cal) and experimental (βRexpt) branching ratios for this transition show good agreement. The emission spectra display high energy transitions in the
440–570 nm region, a characteristic of parent matrices with low energy phonons such as the tellurite, germanate and fluoride
glasses. The electron-phonon coupling strengths deduced from the excitation spectra of Eu3+ are 10.2 x 10−3 and 9.5 x l0−3 for 30PbO-70PbF2 and 70PbO-30PbF2 glasses respectively. The relative emission intensities of the low energy transitions to high energy transitions and the
ratios of the most intense transitions5D0→7F2/5D0→7F7 significantly vary for the two glasses providing evidence for clustering of Eu3+ ions with increase in its concentration and increasing PbO content. 相似文献
998.
L. S. Cavalcante J. C. Sczancoski F. S. De Vicente M. T. Frabbro M. Siu Li J. A. Varela E. Longo 《Journal of Sol-Gel Science and Technology》2009,49(1):35-46
Ba[Zr0.25Ti0.75]O3 (BZT) thin films were synthesized by the complex polymerization method and heat treated at 400 °C for different times and
at 700 °C for 2 h. These thin films were analyzed by X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy,
field emission gun-scanning electron microscopy (FEG-SEM) and atomic force microscopy (AFM), Ultraviolet–visible (UV–vis)
absorption spectroscopy, electrical and photoluminescence (PL) measurements. FEG-SEM and AFM micrographs showed that the microstructure
and thickness of BZT thin films can be influenced by the processing times. Dielectric constant and dielectric loss of BZT
thin films heat treated at 700 °C were approximately 148 and 0.08 at 1 MHz, respectively. UV–vis absorption spectra suggested
the presence of intermediary energy levels (shallow and deep holes) within the band gap of BZT thin films. PL behavior was
explained through the optical band gap values associated to the visible light emission components. 相似文献
999.
Markus Lau Stefan Lbus Ralf Courths Samed Halilov Herbert Gollisch Roland Feder 《Annalen der Physik》1993,505(5):450-464
High-resolution normal photoemission (ARPE) spectra have been recorded for Cu3Au(111) with the use of polarized synchrotron and rare-gas resonance radiation in the photon energy range from 9 to 27 eV. It is for the first time that dispersions of the gold-like bands have been found experimentally. Using a fully relativistic layer-KKR photoemission formalism, occupied and unoccupied bands as well as one-step-model photoemission spectra have been calculated. The comparison of calculated spectra with experimental ones and the observation of direct-transition resonances upon photon energy near the Brillouin zone-center reveal a shift of the unoccupied ground-state bands by about +2.5 eV (self-energy shift). The direct-transition structures in the experimental spectra have been exploited to determine the dispersions of the occupied bands along the [111] direction (A line in k space). In order to determine the wave vector of the experimental direct transitions we used as final state that calculated unoccupied band along [111], which also exists in pure copper and gold up to about 20 eV above the Fermi energy (“unfolded” band structure), shifted by + 2.5 eV. The experimental occupied bands with Cu character are in very good agreement with theory after shifting the latter by about 0.3 eV to lower energy, whereas somewhat bigger discrepancies exist for the gold-like bands. 相似文献
1000.
In this paper we report the experimental Compton profile of polycrystalline molybdenum. The measurements have been made by
scattering 59.54 keVγ-rays and are compared with the recent band structure calculation of Janiet al. [4]. These results have also been compared with our calculation based on the renormalized-free-atom model for different 4d-5s configurations. It is found that the present experimental data are relatively in good agreement with the band structure calculation. 相似文献