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51.
《Analytical letters》2012,45(2):337-346
ABSTRACT Pongamol and karanjin, naturally present in karanja (Pongamia glabra) oil possess potential UV A and UV B sunscreen activities, respectively. A reverse phase high performance liquid chromatography (RP-HPLC) method has been developed for direct estimation of these constituents of karanja oil. This method of analysis requires no sample preparation of active ingredients. The analysis uses methanol, water and acetic acid in the ratio of 85: 13.5: 1.5 as mobile phase at a flow rate of 0.5 ml/ min on a Kromasil 100 C18 column, ex Tracer (250mm X46mm, particle size 5 microns) and dual wavelength detection at 350 and 300 nm. 2-ethylhexyl-p-methoxy cinnamate (Parsol MCX) was used as the internal standard. The identical UV spectrum of the chromatographic region (upslope, apex and downslope) confirmed that the analysis was free from substrate interference. The detection limits for pongamol and karanjin were found to be 0.1 μg/ml. 相似文献
52.
Xuefei Guo Timothy Meyung Yeoheung Yun Vesselin N. Shanov H. Brian Halsall William R. Heineman 《Electroanalysis》2012,24(11):2045-2048
Solid contact (SC) ion‐selective electrodes (ISEs) have been recognized as the next generation of ISEs. In this work, the electrical conductivity and mechanical strength of a carbon nanotube (CNT) tower enable it to play the dual roles of transducer and substrate for micro SC‐ISEs. The electrode had a close to Nernstian slope of 35 mV/decade aCa2+, a linear range of four orders of magnitude of calcium ion activity (10?5.6 to 10?1.8 M), and a detection limit of 1.6×10?6 M. The simplified fabrication by a one‐step drop casting makes miniaturizing SC‐ISEs and fabricating sensor arrays easier to achieve. 相似文献
53.
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55.
Walter Stcklein 《Chemie in Unserer Zeit》2006,40(1):32-40
Biosensors are analytical devices incorporating biological material (receptor) intimately associated with or integrated within a physicochemical transducer. Advantages are the high selectivity for analyte detection. Examples given comprise the very successful commercial blood glucose biosensors made for the self‐control by the diabetic patients. Other biosensors are part of an analytic system, including the sensor chips of surface plasmon resonance or interferometry based devices, piezoelectric or reflectometric sensors capable of direct measurement of mass changes, and thermometric and other reagentless sensors. The development of nanotubes‐based devices allows for significant enhancment of the signal‐tonoise ratio of the biosensors. A milestone on the way towards miniaturization and parallelization of biosensors is the recently developed and prize‐winning electronic DNA chip. 相似文献
56.
采用移位算子方法把时域有限差分法推广应用于二维磁各向异性色散介质—磁化铁氧体中.证明了电磁波横向入射二维轴向磁化铁氧体目标情形下,电磁波可按目标的轴向分解为横电波(TE波)和横磁波(TM波),且TE波的散射特性与铁氧体介质无关,而TM波的散射特性与介质电磁参量密切相关,同时对其物理原因进行了分析.通过采用移位算子方法处理磁化铁氧体频域本构关系,得到该情形下目标电磁散射的移位算子时域有限差的迭代计算公式,同时解决了电磁波在各向异性和频率色散介质中传播的问题.计算了轴向磁化铁氧体涂敷VonKarman型导体柱的TM波双站雷达散射截面,分析了铁氧体参量对目标双站雷达散射截面的影响.结果表明:恰当地选择铁氧体参量能有效地减少目标的雷达散射截面,本文时谐因子取exp〔jωt〕. 相似文献
57.
Xianming Sun Haihua Wang Yiping Han Xiaowei Shi 《International Journal of Infrared and Millimeter Waves》2007,28(11):993-1001
A melting layer of precipitation is composed of melting snow particles, and we modeled them by three-layered spherical particles,
in which the innermost layer is air, the middle ice and the outermost water. Based on this model, the radar reflectivity,
together with the specific phase shift and the specific attenuation of a melting layer of precipitation, were computed at
1–100 GHZ by using the Mie theory. The radar bright band is explained by this model. We compared our numerical results with
that in the literature Zhang (IEEE Transactions on Antennas and Propagation 42(3):347–356, 1994), Zhang (IEEE Transactions
on Antennas and Propagation 42(3):492–500, 1994). It demonstrates that the three-layered snow sphere model is appropriate
and practicable, so the computed results are more accurate. This study can be used in radar remote sensing and satellite-earth
communications. 相似文献
58.
Wenqin Wang 《International Journal of Infrared and Millimeter Waves》2006,27(11):1433-1444
In remote sensing applications, there is a special interest in the lightweight, cost effective, and high resolution imaging
sensors. The combination of linearly frequency modulated continuous wave (LFMCW) technology and synthetic aperture radar (SAR)
technique can lead to such a sensor. This paper concentrates on the analysis of waveform errors in millimeter-wave (MMW) LFMCW
SAR. The generating scheme of millimeter-wave LFMCW waveforms with phase locked loop (PLL) and direct digital synthesizer
(DDS) combined frequency synthesizer is investigated. The impacts of quantization errors, spurs, and frequency nonlinearities
are analyzed. Simulation results show that the quality of LFMCW waveforms has a direct influence on the SAR images. Hence
a scheme of frequency synthesizer to achieve high performance MMW LFMCW waveform is proposed. This synthesizer driven by a
DDS array can adaptive suppress the spurious level without degradation of excellent frequency linearity and fast switching
speed. 相似文献
59.
Phase quantization of diffractive elements usually requires uniformly distributed phase levels in the domain [0,2 π]. In this paper we discuss two alternate quantization schemes. In the first one the phases are uniformly distributed in a domain [0,φ0], with φ0 < 2π. The second scheme employs non-equidistant levels in the phase domain [0,2 π]. Both schemes are useful to reduce quantization errors in diffractive elements, without increasing fabrication complexity. 相似文献
60.
Pavel Anzenbacher Jr. Ryuhei Nishiyabu Manuel A. Palacios 《Coordination chemistry reviews》2006,250(23-24):2929
This is a first review devoted to N-confused calix[4]pyrroles (NCCPs). NCCPs are a relatively recent arrival to the family of the pyrrole-based anion binding macrocycles, being for the first time identified in 1999. Yet, in a relatively short time these calix[4]pyrrole (CP) isomers attracted attention of the community of research groups interested in anion binding and sensing. This is because they are relatively easy to synthesize, but mainly because they posses anion-binding properties that are different from that of regular calix[4]pyrroles. The difference in anion-binding properties stems from a different binding mode between the NCCP and anion. While the regular CPs adopt in the complex an ideal cone-like conformation where all four pyrroles-NHs engage in hydrogen bonding to the anion, the inverted pyrroles do not allow forming the cone. NCCPs bind anions via a confused cone (CC), by three NH hydrogen bonds with an anion and a CH–anion contact. This different binding mode results also in different anion-binding affinity and selectivity compared to regular CPs. Also, the inverted pyrroles offer a unique possibility for selective chemical modification of the receptor. The corresponding colorimetric sensors were tested for anion binding applications. The results of colorimetric assays for anions are presented and potential applications discussed. 相似文献