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881.
Differential scanning calorimetry (DSC) has been applied to characterize the glass transition behavior of the blends formed by bisphenol-A polycarbonate (PC) with a tetrafunctional epoxy (tetraglycidyl-4,4′-diaminodiphenyl methane, TGDDM) cured with 4,4′-diaminodiphenylsulphone (DDS). A rare miscibility in the complete composition range has been demonstrated in these blends. Additionally, the blend morphology was examined using scanning electron microscopy (SEM) and a homogeneous single-phase PC/epoxy network has been observed in the blends of all compositions. Moreover, polycarbonate incorporation has been found to exert a distinct effect on the cure behavior of the epoxy blends. The cure reaction rates for the epoxy-PC blends were significantly higher due to the presence of PC. In addition, the cure mechanism of the epoxy blends was no longer autocatalytic. An n-th order reaction mechanism with n = 1.2 to 1.5 has been observed for the blends of DDS-cured epoxy with PC of various compositions studied using DSC. The proposed n-th order kinetic model has been found to describe well the cure behavior of the epoxy/PC blends up to the vitrification point. © 1995 John Wiley & Sons, Inc. 相似文献
882.
Transient behaviors of interacting electrical double layers 总被引:1,自引:0,他引:1
The unsteady-state potential and space charge distributions between two identical, planar parallel charged surfaces immersed
in an a:b electrolyte solution are examined theoretically. The effects of the ratio of the diffusivities of counterions and coions,
D
con/D
co, the mean diffusivity (D
con
D
co)1/2, and the separation distance between two surfaces, H, on the transient distributions of electrical potential and space charges are investigated. The result of numerical simulation
reveals that the extent of a system to reach its new equilibrium state depends largely on the magni-tude of a scaled time
ν(=Dtκ2). For a fixed H, the greater the value of ν, the closer a system to its new equilibrium state. For constant H and ν, the smaller the ratio (D
con/D
co), the greater the deviation of a system from its new equilibrium state. In addition, the effect of D
con on this deviation is greater than that of D
co.
Received: 3 September 1997 Accepted: 16 October 1997 相似文献
883.
The diffusion of azo-dye (DR-1) in a planar liquid crystals host (5CB) at various temperatures has been investigated by laser-induced
holographic grating relaxation technique. The decay of the diffraction intensity provides information about the diffusion
of photoexcited azo-dye molecules. The relaxation time constants can be derived from the time dependence of the diffraction
intensity fitted by a single exponential function. Thus, the diffusion coefficients parallel and perpendicular to the director
of liquid crystals at various temperatures can be obtained from the plots of the reciprocal of the relaxation time versus
the square of the grating vector. From the analysis of the holographic grating relaxation, the diffusion is faster along the
molecular director than for the perpendicular case, and the diffusion increases with rising temperature either parallel or
perpendicular to the nematic director of liquid crystals.
PACS 42.40.Eq; 42.40.Lx 相似文献
884.
The electromigration (EM) that occurs in a Cu/Sn-9Zn/Cu lamella was investigated for hillock formation at room temperature
with a current density of 103 A/cm2 for up to 230 h. Hillocks and cavities grew in the middle of the bulk solder and at the cathode, respectively. The formation
of hillocks was ascribed to a compressive stress resulting from the diffusion of Sn atoms driven by electromigration and Cu-Zn
compound formation. 相似文献
885.
A sensitive HPLC-electrochemical detection method was developed for the analysis of gliclazide (GL) in human plasma. After deproteination of 100 microL of plasma by acetonitrile, evaporation, and reconstitution, GL was separated on a C18 column (150 mm x 4.6 mm) by the mobile phase (70 mM disodium tetraborate, pH 7.5, containing 26.5% of acetonitrile). The regression equations were linear (r> 0.9990) over the range of 50 nM to 4.00 microM. The precision and accuracy of intra- and inter-day analysis were less than 5.3 and 0.93% for relative standard deviation and relative error, respectively. The limit of detection for plasma was 10 nM for GL (S/N = 3, 10 microL injection). This newly developed method was applied for monitoring blood levels with one healthy volunteer dosing with a GL tablet. 相似文献
886.
A new method for cellulose membrane fabrication and the determination of its characteristics 总被引:5,自引:0,他引:5
A novel method to fabricate semipermeable cellulose membranes based on cellulose regeneration of a dry membrane cast by the neutralization reaction is presented in this paper. In this method, an environmentally acceptable cellulose dissolution procedure is employed to prepare the membrane casting solution comprised of microcrystalline cellulose dissolved in aqueous NaOH. Moreover, a new cast drying/cellulose regeneration technique is proposed and successfully applied to prepare membranes after the exploitation of the conventional immersion precipitation method, which results in the formation of granular cellulose particles rather than membranes due to the low cellulose concentration (<5 wt%) in the cast. In the present technique, the cellulose concentration in the membrane cast is dramatically increased through water evaporation, and glycerin is utilized in the cellulose regeneration process to achieve a gentle neutralization reaction. As a result, defect-free membranes with a uniform structure are developed. A detailed investigation is also presented concerning the effects of membrane forming parameters, i.e., the concentrations of cellulose, solvent, and acid, and the membrane thickness, on membrane properties. In addition, by coordinating the molecular separation experiments via the ultrafiltration process against a number of macromolecules with various molecular weights, the fabricated membranes are demonstrated to be capable of sieving molecules with a MW above 50,000. 相似文献
887.
Li HB Li J Wong HT Chang CY Chen CP Fang JM Hu CH Kuo WS Lai WP Lee FS Lee SC Lin ST Luo CS Liu Y Qiu JF Sheng HY Singh V Su RF Teng PK Tong WS Wang SC Xin B Yeh TR Yue Q Zhou ZY Zhuang BA 《Physical review letters》2003,90(13):131802
A search of neutrino magnetic moment was carried out at the Kuo-Sheng Nuclear Power Station at a distance of 28 m from the 2.9 GW reactor core. With a high purity germanium detector of mass 1.06 kg surrounded by scintillating NaI(Tl) and CsI(Tl) crystals as anti-Compton detectors, a detection threshold of 5 keV and a background level of 1 kg(-1) keV(-1) day(-1) at 12-60 keV were achieved. Based on 4712 and 1250 h of reactor ON and OFF data, respectively, the limit on the neutrino magnetic moment of mu(nu;(e))<1.3x10(-10)mu(B) at 90% confidence level was derived. An indirect bound of the nu;(e) radiative lifetime of m(3)(nu)tau(nu)>2.8x10(18) eV(3) s can be inferred. 相似文献
888.
A novel optical heterodyne surface-plasmon resonance (SPR) biosensor with a Zeeman laser is proposed. Two surface plasma waves are excited by two correlated p-polarized waves in a SPR device of the Kretschmann configuration. Two reflected p waves are optically heterodyned such that the magnitude of the heterodyned signal is proportional to the multiplication of two attenuated reflected p waves. Then the detection sensitivity and the dynamic range based on this amplitude-sensitive method are enhanced. In the experiment, the kinetics between mouse immunoglobulin G (IgG) and rabbit antimouse IgG is obtained from sensograms of various concentrations of antimouse IgG. A detection sensitivity of 0.2 nM was achieved. In addition, a concentration of 5 ng/ml of protein G interacting with mouse IgG was measured successfully. 相似文献
889.
Sheng-Jyh Wang Lun-Chia Kuo Hsin-Haw Jong Zong-Han Wu 《IEEE transactions on image processing》2005,14(8):1043-1056
This paper presents a new approach to represent an image by "verge points," which are defined as high-curvature points on the image surface. This representation offers a compact and reversible way to preserve the essence of the original image. Various applications, such as compression, edge detection, image enhancement, and image editing, can be achieved based on this representation. In this paper, the whole procedure for verge point representation is presented. Based on these verge points, image reconstruction can be easily achieved via iterative linear interpolation. These extracted verge points with compatible properties are further linked into verge curves to offer more compact representation. Progressive representation is also developed based on a multiscale extraction scheme. Some potential applications are then presented to demonstrate the versatility of this representation. 相似文献
890.
High frequency ultrasonic imaging (e.g. >30 MHz) from blood is difficult due to its tenuous backscattered pressure and the interference from adjacent tissues as well. To increase the sensitivity focused transducer has to be used, thus raising the complexity of interpreting the received signals. A numerical simulation of the ultrasonic scattering property from erythrocyte and rouleaux based on boundary element method was performed with experimental results based on a modified substitution method. The results (proportional relationship between backscattered pressure and frequency and the frequency limit for Rayleigh scattering) closely coincide with experimental data for erythrocyte. Rouleaux model results also show the dependence of degree of red cell aggregation on backscattering properties. The boundary element method serves as a good means to calculate the acoustic scattering from blood cells under arbitrary incident waves. 相似文献