全文获取类型
收费全文 | 225486篇 |
免费 | 2221篇 |
国内免费 | 708篇 |
专业分类
化学 | 107714篇 |
晶体学 | 3292篇 |
力学 | 7819篇 |
综合类 | 4篇 |
数学 | 18355篇 |
物理学 | 60173篇 |
无线电 | 31058篇 |
出版年
2016年 | 2502篇 |
2015年 | 1797篇 |
2014年 | 2633篇 |
2013年 | 8309篇 |
2012年 | 5569篇 |
2011年 | 6962篇 |
2010年 | 4932篇 |
2009年 | 5167篇 |
2008年 | 7034篇 |
2007年 | 7531篇 |
2006年 | 7312篇 |
2005年 | 6731篇 |
2004年 | 6172篇 |
2003年 | 5578篇 |
2002年 | 5492篇 |
2001年 | 7027篇 |
2000年 | 5576篇 |
1999年 | 4575篇 |
1998年 | 3797篇 |
1997年 | 3827篇 |
1996年 | 3727篇 |
1995年 | 3455篇 |
1994年 | 3329篇 |
1993年 | 3216篇 |
1992年 | 3716篇 |
1991年 | 3605篇 |
1990年 | 3416篇 |
1989年 | 3441篇 |
1988年 | 3294篇 |
1987年 | 2933篇 |
1986年 | 2759篇 |
1985年 | 3635篇 |
1984年 | 3654篇 |
1983年 | 3073篇 |
1982年 | 3212篇 |
1981年 | 3153篇 |
1980年 | 3010篇 |
1979年 | 3116篇 |
1978年 | 3355篇 |
1977年 | 3143篇 |
1976年 | 3110篇 |
1975年 | 2928篇 |
1974年 | 2870篇 |
1973年 | 2897篇 |
1972年 | 1896篇 |
1971年 | 1606篇 |
1968年 | 2038篇 |
1967年 | 2209篇 |
1966年 | 2017篇 |
1965年 | 1580篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Xin Sun Qiang Lu Moroz V. Takeuchi H. Gebara G. Wetzel J. Shuji Ikeda Changhwan Shin Tsu-Jae King Liu 《Electron Device Letters, IEEE》2008,29(5):491-493
A tri-gate bulk MOSFET design utilizing a low-aspect-ratio channel is proposed to provide an evolutionary pathway for CMOS scaling to the end of the roadmap. 3-D device simulations indicate that this design offers the advantages of a multi-gate FET (reduced variability in performance and improved scalability) together with the advantages of a conventional planar MOSFET (low substrate cost and capability for dynamic threshold-voltage control). 相似文献
102.
A parallel method for time discretization of parabolic equations based on Laplace transformation and quadrature 总被引:5,自引:0,他引:5
We consider the discretization in time of an inhomogeneous parabolicequation in a Banach space setting, using a representation ofthe solution as an integral along a smooth curve in the complexleft half-plane which, after transformation to a finite interval,is then evaluated to high accuracy by a quadrature rule. Thisreduces the problem to a finite set of elliptic equations withcomplex coefficients, which may be solved in parallel. The paperis a further development of earlier work by the authors, wherewe treated the homogeneous equation in a Hilbert space framework.Special attention is given here to the treatment of the forcingterm. The method is combined with finite-element discretizationin spatial variables. 相似文献
103.
Rajoo R. Lim S.S. Wong E.H. Hnin W.Y. Seah S.K.W. Tay A.A.O. Iyer M. Tummala R.R. 《Advanced Packaging, IEEE Transactions on》2008,31(2):377-385
A wafer level packaging technique has been developed with an inherent advantage of good solder joint co-planarity suitable for wafer level testing. A suitable weak metallization scheme has also been established for the detachment process. During the fabrication process, the compliancy of the solder joint is enhanced through stretching to achieve a small shape factor. Thermal cycling reliability of these hourglass-shaped, stretch solder interconnections has been found to be considerably better than that of the conventional spherical-shaped solder bumps. 相似文献
104.
K. Morigaki K. Takeda H. Hikita C. Ogihara P. Roca i Cabarrocas 《Journal of Non》2008,354(19-25):2131-2134
Our model for light-induced defect creation in hydrogenated amorphous silicon is applied to its kinetics, i.e., the growing curve of light-induced dangling bond density as a function of illumination time, which is fitted to a stretched exponential function. Two parameters β and τ involved in the function are estimated as functions of saturated dangling bond density in terms of our model. These are compared with two experimental results, i.e., our results obtained from ESR measurements and Shimakawa et al.’s results obtained from photoconductivity measurements. The saturated dangling bond density is also measured as a function of the generation rate of free carriers. The experimental results are compared with calculated results and discussed. 相似文献
105.
J. Song H. Jiang Z.J. Liu D.Y. Khang Y. Huang J.A. Rogers C. Lu C.G. Koh 《International Journal of Solids and Structures》2008,45(10):3107-3121
A finite-deformation theory is developed to study the mechanics of thin buckled films on compliant substrates. Perturbation analysis is performed for this highly nonlinear system to obtain the analytical solution. The results agree well with experiments and finite element analysis in wavelength and amplitude. In particular, it is found that the wavelength depends on the strain. Based on the accurate wavelength and amplitude, the membrane and peak strains in thin films, and stretchability and compressibility of the system are also obtained analytically. 相似文献
106.
We show that determining the minimum number of resolve filters that need to be added to a set of two-dimensional (2-D) prefix filters so that the filter set can implement a given policy using the first-matching-rule-in-table tie breaker is NP-hard. Additionally, we develop a fast O(nlogn+s) time, where n is the number of filters and s is the number of conflicts, plane-sweep algorithm to detect and report all pairs of conflicting 2-D prefix filters. The space complexity of our algorithm is O(n). On our test set of 15 2-D filter sets, our algorithm runs between 4 and 17 times as fast as the 2-D trie algorithm of A. Hari et al. (2000) and uses between 1/4th and 1/8th the memory used by the algorithm of Hari et al. On the same test set, our algorithm is between 4 and 27 times as fast as the bit-vector algorithm of Baboescu and Varghese (2002) and uses between 1/205 and 1/6 as much memory. We introduce the notion of an essential resolve filter and develop an efficient algorithm to determine the essential resolve filters of a prefix filter set. 相似文献
107.
The synthesis and characterization of a new homologous series of compounds, the 2-cyano-1,3-phenylene bis[4-(4-n-alkoxyphenyliminomethyl)benzoates] derived from 2-cyanoresorcinol is reported. All the compounds are enantiotropic mesogens and exhibit the fascinating B7 mesophase. The characterization of the mesophase was performed using polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction and electro-optical studies. 相似文献
108.
A four-way monolithic GaAs travelling-wave power divider/combiner has been designed, fabricated and evaluated. With a design centre frequency of 20 GHz, a bandwidth of from 10 GHz to 30 GHz has been measured. The insertion loss per dividing or combining action is less than 0.5 dB, with isolation between ports no worse than 20 dB. The input/output VSWRs are better than 2:1 across the same band. This divider/combiner can readily be used with monolithic GaAs power FET amplifiers to produce a several-fold increase in output powers over the 10 to 30 GHz frequency range. 相似文献
109.
In this paper, we examine methods of characterizing somatosensory evoked potentials (SEP's) in both the time and frequency domains. We have found that the truncated impulse response (TIR) method produced an accurate time domain model of the SEP signals at model orders greatly reduced from the original state space matrix. The TIR method was valuable for smoothing signals that were slightly corrupted by noise. In this case, the simulated data sequence was close to the original data sequence in the mean squared error sense. For signals that were greatly corrupted by noise, the TIR method was not able to perform as well. Therefore, the TIR method was not a feature extraction method but was valuable for data simulation. In the frequency domain, we have used the autoregressive moving average model (ARMA) to parameterize the SEP signal. An overdetermined set of Yule-Walker equations was created to determine the autoregressive (AR) parameters of the original data with the model order established by the singular value decomposition. From these AR parameters, a residual time series was generated which was used to find the moving average parameters. The resulting ARMA model was used to produce a simulated data sequence. The frequency domain characteristics of the simulated sequence and the corresponding power spectral density of the ARMA filter were very close to the periodogram of the original data sequence. Accurate parameterization was achieved for the SEP waveforms at low filter lengths. 相似文献
110.
J. Berkemeier T. Dirksmeyer G. Klempt H. G. Purwins 《Zeitschrift für Physik B Condensed Matter》1986,65(2):255-258
It is observed experimentally that a periodic array of resistively coupled LC-oscillators with ans-shaped nonlinearity exhibits stable non-uniform voltage and current distributions. The dependence of the resulting structure on the coupling resistance and the boundary conditions is investigated. The structure is rather insensitive to variations of the boundary values. The experiments are well described by a two-variable reaction-diffusion equation. 相似文献