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71.
72.
Chao Wan Kun Huang Tiancheng Han Eunice S. P. Leong Weiqiang Ding Lei Zhang Tat‐Soon Yeo Xia Yu Jinghua Teng Dang Yuan Lei Stefan A. Maier Boris Luk'yanchuk Shuang Zhang Cheng‐Wei Qiu 《Laser \u0026amp; Photonics Reviews》2014,8(5):743-749
Supersized darkness in three dimensions surrounded by all light in free space is demonstrated theoretically and experimentally in the visible regime. The object staying in the darkness is similar to staying in an empty light capsule because light just bypasses it by resorting to destructive interference. A binary‐optical system is designed and fabricated based on achieving antiresolution (AR), by which electromagnetic energy flux avoids and bends smoothly around a nearly perfect darkness region. AR remains an unexplored topic hitherto, in contrast to the super‐resolution for realizing high spatial resolution. This novel scheme replies on smearing out the point spread function and thus poses less stringent limitations upon the object's size and position since the created dark (zero‐field) area reach 8 orders of magnitude larger than λ2 in cross‐sectional size. It functions very well with arbitrarily polarized beams in three dimensions, which is also frequency scalable in the whole electromagnetic spectrum. 相似文献
73.
74.
Manual shaking-enhanced, ultrasound-assisted emulsification microextraction (MS-USAEME) combined with ultraperformance liquid chromatography (UPLC) with UV detection has been developed for the determination of five endocrine-disrupting phenols (EDPs) in seawater samples and detergent samples: 4-tert-butylphenol (4-t-BP), 4-cumylphenol (4-CP), 4-tert-octylphenol (4-t-OP), 2,4-di-tert-butylphenol (2,4-di-t-BP) and 4-nonylphenol (4-NP). Optimum conditions were found to be: 25 μL 1-bromohexadecane as extraction solvent, 5 mL of aqueous sample and 1 g of NaCl to control the ionic strength; manual shaking for 10 s; ultrasonication for 1 min; centrifugation for 3 min at 5000 rpm (speed). For MS-USAEME, manual shaking for 10 s is essential for effective extraction when the ultrasonic extraction time is as brief as 1 min. The small volume of aqueous sample enhances the effect of manual shaking significantly. For seawater samples, the limit of detection (LOD) was 0.5-2.8 ng mL(-1), the limit of quantification (LOQ) was 1.8-9.3 ng mL(-1) with the relative standard deviation (RSD) in the range 4.2-10.3%. For detergent samples, the LOD was 0.4-2.4 ng mL(-1), LOQ was 1.6-8.2 ng mL(-1) and RSD 4.7-10.0%. The relative recovery was 96-109% for seawater samples and 81-106% for the detergent samples. 相似文献
75.
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77.
This paper describes five aspects of primary mathematics teacher education in Singapore: (a) the teaching profession in Singapore, (b) the structure of pre-service teacher education programs offered by the National Institute of Education, (c) self-reports of Singapore future primary mathematics teachers about the opportunities to learn mathematics-related contents offered by these programs, based on the Teacher Education and Development Study in Mathematics (TEDS-M) survey, (d) the performance of these future teachers in mathematics content knowledge and mathematics pedagogical content knowledge assessed by the TEDS-M study, and (e) the relationships of opportunities to learn with this performance. The paper concludes with some suggestions about how to improve the quality of initial teacher preparation in the areas of recruitment and training. 相似文献
78.
M. A. H. Mamun D. A. Johnson K. G. T. Hollands W. H. Leong 《Experiments in fluids》2008,44(4):647-659
The natural convective velocity field in an enclosed air-filled cubical cavity with two opposing isothermal faces and the
remaining four sides having a well-defined linear temperature rise from the cold to the hot face has been measured at different
physical orientations and Rayleigh (Ra) numbers. In particular, two components of the velocity at the mid-plane have been measured by using particle image velocimetry
(PIV) at Ra = 106 and 6 × 106 at each of two different physical orientations: heating-from-the-side (HFS), and heating-from-below (HFB). The 95% confidence
limit uncertainties in the measured velocity vectors are about 2% for laminar flow. The accuracy and integrity of the experiments
were validated by the comparison to some well-established CFD results at the HFS orientation at Ra = 106. It was concluded that the experimental method is sound and so findings at other orientations and at other values of Ra should have an accuracy consistent with the findings of the uncertainty analysis. Therefore, the other results can be confidently
used as benchmark data for testing CFD codes. The turbulence intensities at the mid-plane are also presented. 相似文献
79.
The capillary viscometer is used to measure the shear stress-shear rate relationship of a wide range of purely viscous fluids.
It is however not considered as an appropriate instrument for obtaining the yield stress and the post-yield behaviour of fluids
that have a yield stress. This is partly because conventional methods of processing the capillary viscometry data of purely
viscous fluids cannot be applied to similar data of fluids with yield stress. The unavoidable experimental noise in the capillary
data, particularly at low shear rates, also makes it difficult to obtain a reliable estimate of the yield stress from capillary
data. In this investigation the problem of converting the capillary viscometry data of yield stress fluids into a shear stress-shear
rate curve and a yield stress is formulated as a Volterra integral equation of the first kind. This is an ill-posed problem
i.e. noise in the data will be amplified by inappropriate methods of data processing. A method, based on Tikhonov regularisation
that takes into account the ill-posed nature of the problem, is then developed to solve this problem for fluids with yield
stress. The performance of this method is assessed by applying it to a set of “synthetic” capillary viscometry data with added
random noise and to a set of experimental data for a concentrated suspension of TiO2 taken from the literature. In both cases Tikhonov regularisation was able to extract the complete shear properties of these
fluids from capillary viscometry data alone.
Received: 22 November 1999/Accepted: 17 December 1999 相似文献
80.
T. Joseph Sahaya Anand Chua Kok Yau Yeow See Leong Lim Weng Keat Hng May Ting 《Current Applied Physics》2013,13(8):1674-1683
Effects of High Temperature Storage (HTS) and bonding toward microstructure change of intermetallic compound (IMC) at the wire bonding interface of 3 types of bond pad (Al, AlSiCu and NiPdAu) were presented in this paper. Optical and electron microscope analyses revealed that the IMC growth rate of samples under 175 and 200 °C HTS increased in the order of Al > AlSiCu > NiPdAu. Besides, higher HTS and bonding temperatures also promoted higher IMC thickness. The compositional study showed that higher HTS and bonding temperature developed rapid interdiffusion in bonding interface. In the mechanical ball shear test, a decrease of the shear force of Al and AlSiCu bond pads after 500 h HTS was believed due to poorly developed IMC at bonding interface. On the other hand, shear force degradation at 1000 h was due to excessive growth of IMC that in turn causes the formation of defects. For NiPdAu bond pad, increasing trend of shear force with HTS duration at 175 °C implied a good reliability of the Cu wire bonding. The rapid microscopic inspection on Cu wired Al bond pad under HTS 175 °C showed the IMC development from the periphery to the center of the ball bond. However, after 500 h voids started to develop until the crack was observed at 1000 h. 相似文献