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41.
Reduction of dislocation density and improvement of optical quality in ZnO layers by MgO-buffer annealing 总被引:1,自引:0,他引:1
Hiroki Goto Hisao Makino Agus Setiawan Takuma Suzuki Chihiro Harada Tsutomu Minegishi Meoung-Whan Cho Takafumi Yao 《Current Applied Physics》2004,4(6):637-639
Optical properties of ZnO thin films with/without MgO-buffer annealing were investigated by low and room temperature photoluminescence measurements. The ZnO films were grown on c-sapphire substrates by plasma-assisted molecular-beam epitaxy employing a thin MgO-buffer layer. Dislocation density of ZnO layer was reduced from 5.3 × 109 to 1.9 × 109 cm−2 by annealing MgO-buffer prior to the growth of ZnO. The intensity of free exciton emission from the sample with MgO-buffer annealing was almost twice of that from the sample without annealing, while the deep level emission from the sample with MgO-buffer annealing was about 1/3 of that without annealing. The MgO-buffer annealing improves optical quality of overgrown ZnO films. 相似文献
42.
J. Y. Lee J. H. Chang M. Yang H. S. Ahn S. N. Yi K. Goto K. Godo H. Makino M. W. Cho T. Yao J. S. Song 《Current Applied Physics》2004,4(6):611-614
Luminescence properties of CdTe/ZnSe fractional monolayer grown by atomic layer epitaxy have been investigated. To investigate the origin of the highly efficient luminescence, various optical spectroscopic methods such as, photoluminescence (PL), temporal/spatial resolved PL, temperature dependence PL, and excitation power dependence PL have been used. It is found that structural inhomogeneities affect dominant influence on the line width and line shape of luminescence. The luminescence intensity greatly enhanced by the localization of exciton at the disorder induced localized states. 相似文献
43.
The chemometric calibration performance was systematically investigated by two parameters (changing the chemical matrix as well as the signal-to-noise ratio) of the NIR (near-infrared) spectrum. Three different analytes (hexane, cyclohexane, toluene) were selected and heptane was used as a solvent. The degree of spectral difference significantly affected the calibration performance. The largest structural difference between the analyte and the solvent provided the best calibration result for a given signal-to-noise ratio. Additionally, the signal-to-noise ratio of the spectra also directly influenced the calibration performance. Overall, the spectral difference and signal-to-noise ratio were the major factors for governing the chemometric calibration performance, especially in the low-concentration range. 相似文献
44.
C. D. Schaper Y. M. Cho T. Kailath 《Applied Physics A: Materials Science & Processing》1992,54(4):317-326
A low-order model of rapid thermal processing (RTP) of semiconductor wafers is derived. The first-principles nonlinear model describes the static and dynamic thermal behavior of a wafer with approximate spatial temperature uniformity undergoing rapid heating and cooling in a multilamp RTP chamber. The model is verified experimentally for a range of operating temperatures from 400° C to 900° C and pressures of 1 Torr and 1 atmosphere in an inert N2 environment. Theoretical predictions suggest model validity over a still wider range of operating conditions. One advantage of the low-order model over previous high-order and statistical models is that the proposed model contains a small number of fundamental parameters and functions that, if necessary, are easily identifiable. Furthermore, because of reduced computational complexity, the low-order model can be used in real-time predictive applications including signal processing and process control design. In studying and verifying the model, the dynamic behavior of a semiconductor wafer undergoing rapid temperature changes is characterized. Close comparison between theory and experiment in terms of the wafer eigenvalue and dc gain is demonstrated; the strong nonlinear effects of temperature are shown. Convective heat transfer losses are also examined and are shown to increase with radial position on the wafer. 相似文献
45.
The possibility of Pt–Cr surface alloys formation on Pt(0 0 1) was investigated and their magnetism was calculated by the full-potential linearized augmented plane wave (FLAPW) method with eight different atomic configurations. The most stable structure was calculated to be the Pt-segregated L12 ferromagnetic surface alloy. A3B types (L12 or D022) were more stable compared to AB types (L10). It implies that the A3B type surface alloys may be formed when depositing a monolayer of Cr on Pt(0 0 1). It was found from the total energy calculations that there exists a strong tendency of the Pt segregation. The segregation further stabilizes the surface alloy significantly. The work function of the most stable surface alloy was calculated to be 6.02 eV and the magnetic moment of the surface Cr was much enhanced to 3.3 μB. It is a quite interesting finding that the coupling between Cr and Pt atoms on the surface plane is ferromagnetic in the Pt-segregated L12 ferromagnetic surface alloy, while the coupling is antiferromagnetic in the bulk. 相似文献
46.
47.
Yanlin Huang Kiwan Jang Wanxue Zhao Eunjin Cho Ho Sueb Lee Xigang Wang Dake Qin Ying Zhang Chanfang Jiang Hyo Jin Seo 《Journal of solid state chemistry》2007,180(12):3325-3332
Usually, Sm2+ ions could be reduced by heating the materials in reducing atmospheres. Exposure to ionizing radiations is also known to cause Sm3+→Sm2+ conversion. In this work, BaBPO5 doped with the samarium ion was prepared by high temperature solid-state reaction. Sm2+ ions were obtained by two different reduction methods, i.e., heating in H2 reduced atmosphere and X-ray irradiation. The measurements of X-ray diffraction (XRD), and scanning electron microscope (SEM) were investigated. It is found that the conversion of Sm3+→Sm2+ is very efficient in BaBPO5 hosts after X-ray irradiation. Sm2+ ions under these two reduction methods exhibit different characteristics that were studied by measurements of luminescence and decay. The results showed that the luminescence properties of Sm2+ ions in BaBPO5 were highly dependent on the sample preparation conditions. 相似文献
48.
Cyclic and acyclic β-bromovinyl aldehydes are cyclized with an array of arylhydrazines in toluene at 125 °C in the presence of a palladium catalyst and a phosphorus chelating ligand together with NaOtBu to give 1-aryl-1H-pyrazoles in moderate to good yields. 相似文献
49.
50.
J.-S. Kang G. Kim S.S. Lee S. Choi S. Cho S.W. Han H.J. Shin B.I. Min 《Journal of magnetism and magnetic materials》2006
The spatial concentration distribution and local electronic structure of ferromagnetic Ge1−xTx (T=Cr, Mn, Fe) DMS single crystals have been investigated by using scanning photoelectron microscopy (SPEM), X-ray absorption spectroscopy (XAS), and photoemission spectroscopy (PES). It is found that doped T ions in Ge1−xTx crystals are chemically phase-separated, suggesting that the observed ferromagnetism arises from the phase-separated T-rich phases in Ge1−xTx. 相似文献