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991.
992.
本文用变分法求出了非线性轴向不均匀自聚焦光纤轴对称场的解析解。对于线性情形,变分解与其他文献的结果相同。 相似文献
993.
A segment-based speech recognition scheme is proposed. The basic idea is to model explicitly the correlation among successive frames of speech signals by using features representing contours of spectral parameters. The speech signal of an utterance is regarded as a template formed by directly concatenating a sequence of acoustic segments. Each constituent acoustic segment is of variable length in nature and represented by a fixed dimensional feature vector formed by coefficients of discrete orthonormal polynomial expansions for approximating its spectral parameter contours. In the training, an automatic algorithm is proposed to generate several segment-based reference templates for each syllable class. In the testing, a frame-based dynamic programming procedure is employed to calculate the matching score of comparing the test utterance with each reference template. Performance of the proposed scheme was examined by simulations on multi-speaker speech recognition for 408 highly confusing isolated Mandarin base-syllables. A recognition rate of 81.1% was achieved for the case using 5-segment, 8-reference template models with cepstral and delta-cepstral coefficients as the recognition features. It is 4.5% higher than that of a well-modelled 12-state, 5-mixture CHMM method using cepstral, delta cepstral, and delta-delta cepstral coefficients 相似文献
994.
The objective of the study is to examine the ease of applicability of three scattering models. This is done by considering the time taken to numerically evaluate these models and comparing their predictions as a function of surface roughness, frequency, incident angle and polarization with the moment method solution in two dimensions. In addition, the complexity of the analytic models in three dimensions and their analytic reduction to high and low frequency regions are also compared. The selected models are an integral equation model (IEM), a full wave model (FWM), and the phase perturbation model (PPM). It is noted that in three dimensions, the full-wave model requires an evaluation of a 10-fold integral, the phase perturbation model requires a 4- and 2-fold integral while the integral equation model is an algebraic equation in like polarization under single scattering conditions. In examining frequency dependence of IEM and PPM in two dimensions numerically, the same model expression is used for all frequency calculations, it is found that both the IEM and PPM agree with the moment method solution from low to high frequencies numerically 相似文献
995.
Tzuen-Hsi Huang Ming-Jer Chen 《Electron Devices, IEEE Transactions on》1995,42(2):321-327
Base current reversal phenomenon is newly observed in a CMOS compatible high gain n-p-n gated lateral bipolar transistor. We attribute this phenomenon to avalanche generation as verified experimentally and by two-dimensional device simulation. Detailed investigation reveals that: (i) the multiplication ratio increases exponentially with the collector voltage or equivalently the peak field at the surface collector corner; and (ii) the multiplication ratio is independent of not only the low level base-emitter forward biases applied but also the base width of the transistors fabricated by the same process. Design guideline for suppression of the base current reversal has been established such as to fully realize the potential of the gated lateral bipolar transistors, i.e., a very high current gain of 11,600 can be maintained as long as the power supply voltage is less than the critical value of 1.78 V. On the other hand, new application directly employing this phenomenon has been suggested. Comparisons between the base current reversal phenomenon in the gated lateral bipolar transistor and that in the vertical bipolar transistor have also been performed and significant differences between the two have been drawn and have been adequately explained 相似文献
996.
As the passivation layer on the top of undoped offset region for offset-gate structured poly-Si TFTs is exposed to hydrogen plasma, a lightly-doped-like drain region could be equivalently self-induced. The hydrogenated polycrystalline silicon thin-film transistor of this structure, named self-induced lightly-doped-drain (SI-LDD) poly-Si TFTs, was first developed with liquid-phase deposition oxide as both the gate insulator and the passivation layer. This paper describes the optimum hydrogenation condition, and the electrical characteristics for the novel SI-LDD poly-Si TFTs. The effects of DC electrical stress on SI-LDD poly-Si TFTs are also described. Finally a model is proposed to explain the degradation phenomena observed in our SI-LDD devices 相似文献
997.
An improved slot etch technique based on an Si planar doped layer has been applied to gate recessing in the fabrication of AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistors (HEMTs). The devices exhibited comparable gm with much better breakdown and leakage behaviour than conventional pseudomorphic HEMT devices 相似文献
998.
The electromagnetic scattering from an anisotropic cylinder is analysed using the FD-MEI method. Some numerical results, which are in good agreement with the exact solutions when available, are given 相似文献
999.
40-GHz polymer electrooptic phase modulators 总被引:1,自引:0,他引:1
Wenshen Wang Datong Chen Fetterman H.R. Yongqiang Shi Steier W.H. Dalton L.R. 《Photonics Technology Letters, IEEE》1995,7(6):638-640
A broad-band high-frequency traveling wave electrooptic phase modulator made from stable nonlinear optical polymers has been tested. Using a 1.319-μm light source, single-mode operation was achieved with high-input optical power, resulting in improved modulation depths and signal-to-noise ratios. The high-frequency optical modulation was observed up to 40 GHz using external microwave mixers. Direct optical-heterodyne detection of electrooptic phase modulation has also been demonstrated with high sensitivity at 40 GHz. The devices were tested with 105 W/cm2 power density for 21 hours, and have showed no observable decay in nonlinearity 相似文献
1000.