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931.
In this paper we present photoionization cross sections of the Cu and Al dimers and tetramers. The local spin density method is applied to calculate the electronic structure and the ground state potential. The cross sections are calculated using the continuum multiple scattering method, and a basic analysis of the photoionization process is given within the independent particle picture. 相似文献
932.
The optical emission characteristics of biaxially compressed InAs
x
P1−
x
/InP strained single quantum well (QW) structures, with nominal compositionx=0.67, have been investigated using photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies. The highly
strained QWs exhibit intense and narrow PL in the 0.9–1.5 μm wavelength range, similar to the lattice-matched InGaAs(P)/InP
system. The 20 K PLE spectra exhibit well-resolved features attributed ton=1 heavy hole (E1H1) and light hole (E1L1) transitions in the 1.0–1.5 μm wavelength range. In addition, features attributed
to transitions betweenn=2 electrons and heavy holes (E2H2), and betweenn=1 electrons and unconfined holes (E1Hf), were observed. The energy splitting between the heavy-hole and light-hole bands
was found to be a sensitive measure of the band offsets in the system. The best prediction of this splitting was obtained
for a valence band offset of δE
V
∼0.25δE
G
. This value of band offset was in agreement with the energy position of the E1Hf transition. The observed transition energies
were also compared with the results of a finite square well model, taking into account the effects of strain, and the results
offer further support for the band offset assignment. This study indicates that the InAsP system may be advantageous for application
in strained-layer optoelectronic devices operating in the 1.3–1.6 μm wavelength range. 相似文献
933.
Extensive numerical experiments on the scattering from a thin perfectly conducting square plate have been carried out to assess the performance of the exact analytical expressions for the electromagnetic field of a rectangular patch with uniform and linear distributions of current, in connection with the method of moments. Two solution schemes, employing pulses and roof-top functions for approximating the surface current on the plate, have been used. Convergence rates and results for the two solution schemes are compared with each other, as well as with an efficient solution by A.W. Glisson and D.R. Wilton (1980). The overall performance indicated by the numerical experiments suggests that it would be useful to use the exact numerical expressions in the solution of problems where accurate computation of the field radiated by such current sources is required 相似文献
934.
beta-Glucosidase and beta-glucuronidase of human and rat fecal bacteria were induced by cultivation in alkaline media although their growths were not affected. When a bacterium isolated from human feces producing each enzyme was cultured in a medium at pH 5 for 12-15 h and then adjusted to pH 8, beta-glucosidase and beta-glucuronidase were induced 9.2-fold and 11.5-fold, respectively. 相似文献
935.
Park Y.K. Granlund S.W. Cline T.W. Tzeng L.D. French J.S. Delavaux J.-M.P. Tench R.E. Korotky S.K. Veselka J.J. DiGiovanni D.J. 《Photonics Technology Letters, IEEE》1992,4(2):179-182
The authors have achieved a 2.488 Gb/s, 318 km repeaterless transmission without any fiber dispersion penalty through a nondispersion-shifted fiber in a direct detection system. The system was loss limited with a T-R power budget of 57 dB. Three key components enabled the authors to achieve this result: (1) a Ti:LiNbO3 external amplitude modulator enabling a dispersion-free transmission, (2) erbium-doped fiber amplifiers increasing the transmitting power to +16 dBm, and (3) an erbium-doped fiber preamplifier enabling a high-receiver sensitivity of -4.1 dBm for 10-9 BER. To the author's knowledge, this result is the longest repeaterless transmission span length ever reported for direct detection at this bit rate. From the experimental results and a theoretical model, the authors identified the sources of the receiver sensitivity degradation from the quantum limit (-48.6 dBm) and estimated the practically achievable receiver sensitivity of ~-44 dBm (~-124 photons/bit) for 2.5 Gb/s optical preamplifier detection 相似文献
936.
An all-fibre interferometer which allows the measurement of the movement (speed and distance) of a vibrating body is presented. An electronic signal processing scheme is used and this is contrasted with the measurement of velocity through an optical processing technique, which is however, more complex and expensive to implement. The overall simplicity of the electronic technique, the low cost of components and the use of an all-fibre arrangement make this an attractive system to implement where the more limited information available is sufficient for monitoring purposes. 相似文献
937.
Thomas J. Cloonan Gaylord W. Richards Anthony L. Lentine Frederick B. McCormick John R. Erickson 《Optical and Quantum Electronics》1992,24(4):S415-S442
Free-space optical implementations of switching networks have been proposed to circumvent many of the system-level problems that may be encountered in systems that require many high-density, high-bandwidth connections. The details of a new class of switching network (the EGS network), that is well-suited to free-space implementations, is described. The common control injection problem that plagues most free-space photonic networks, i.e. how can control information from an electronic source be injected into the network for applications that require relatively high network reconfiguration rates, is examined. A new technique for control injection, called embedded control, which permits network operation even with relatively high network reconfiguration rates is also proposed. 相似文献
938.
An interpolation theorem is determined for the case when there are a finite number of arbitrarily placed sampling instants and the interpolation function is the output of a known filter. They are also the interpolation functions with the specified properties that have minimum energy. The theorem is used to determine the input to a communications channel given a finite number of samples of its output. This provides a generalization of matched filters and a perspective on the benefits of fractionally spaced equalization. The theorem is also used to construct masks of a family of pulses that are specified by the range of pulse voltages at a finite number of sampling instants. The theory determines how the pulse masks thus constructed is transformed when the pulse family is transmitted through a filter such as a length of transmission line 相似文献
939.
Rein H.-M. Schmidt L. Worner K. Pieper W. 《Solid-State Circuits, IEEE Journal of》1991,26(12):1840-1846
A versatile analog four-quadrant multiplier IC with large bandwidth (DC to 6 GHz and 10 Gb/s) and large dynamic range is presented. It was mainly developed for differential-phase-shift-keying (DPSK) phase demodulator and polarization diversity receivers in coherent optical-fiber transmission systems. The circuit consumes 450 mW and only needs a single power supply of -5 V. The circuit principle used allows exact symmetry with respect to both linear inputs, which reduced multiplication errors. In the intended application, especially, the time jitter and the offset voltage of the output pulse patterns are reduced to negligible values. The IC was realized in a 1.25-μm double-polysilicon bipolar technology 相似文献
940.
The moment-method technique utilizing entire domain basis functions is applied to the analysis of large, axially symmetric reflector antennas. The electric surface current is modeled as a finite series of sinusoids whose domain consists of the entire generating curve. This expansion results in a matrix size of less than 5% of that produced with subdomain basis functions. Only a slight increase in the CPU requirements occurs from this analysis. The results from this technique show good agreement when compared to both physical optics and a subdomain-based moment-method formulation on small, axially fed paraboloidal and hyperboloidal reflector antennas. Extension to a large 100-λ paraboloidal reflector with f/D=0.4 produces results comparable to that obtained using physical optics. Convergence is obtained with as few as two expansion terms per wavelength. Discretization of the generating curve with four points per wavelength leads to results which agree within 0.5 dB over data from a more densely defined curve 相似文献