全文获取类型
收费全文 | 422篇 |
免费 | 25篇 |
国内免费 | 5篇 |
专业分类
化学 | 253篇 |
晶体学 | 6篇 |
力学 | 34篇 |
数学 | 30篇 |
物理学 | 80篇 |
无线电 | 49篇 |
出版年
2024年 | 2篇 |
2023年 | 1篇 |
2022年 | 7篇 |
2021年 | 14篇 |
2020年 | 22篇 |
2019年 | 13篇 |
2018年 | 15篇 |
2017年 | 13篇 |
2016年 | 20篇 |
2015年 | 13篇 |
2014年 | 23篇 |
2013年 | 48篇 |
2012年 | 42篇 |
2011年 | 49篇 |
2010年 | 26篇 |
2009年 | 14篇 |
2008年 | 17篇 |
2007年 | 16篇 |
2006年 | 8篇 |
2005年 | 7篇 |
2004年 | 5篇 |
2003年 | 12篇 |
2002年 | 12篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 1篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有452条查询结果,搜索用时 35 毫秒
71.
72.
Mehran Aliahmad C. André T. Salama 《Analog Integrated Circuits and Signal Processing》1998,17(3):261-274
This paper presents a 30 V line driver for short loop subscriber line interface circuit applications. The high voltage line drivers was implemented in a low-voltage 0.8 m BiCMOS process using 30 V extended-drain MOS transistors, fully compatible with the low voltage technology. Using a Quasi-Current Mirror architecture for the output stage, the line driver is capable of delivering more than 30 mA current into the lines with an idle current as low as 1 mA, satisfying the short loop requirements. With less than 0.24 mm2 area, the circuit can be easily integrated with low-voltage circuitry on a single chip. 相似文献
73.
74.
Let A be a Banach algebra which does not contain any nonzero idempotent element, let γ > 0, and let
. We show that if
then
. We also show, assuming a suitable spectral condition on x, that if
, then
Received: 12 July 2006 Revised: 31 January 2007 相似文献
75.
Afsaneh Mehran 《manuscripta mathematica》2007,123(2):205-235
Besides its construction as a quotient of an abelian surface, a Kummer surface can be obtained as the quotient of a K3 surface
by a -action. In this paper, we classify all such K3 surfaces. Our classification is expressed in terms of period lattices and
extends Morrison’s criterion of K3 surfaces with a Shioda–Inose structure. Moreover, we list all the K3 surfaces associated
to a general Kummer surface and provide very geometrical examples of this phenomenon. 相似文献
76.
Javanbakht M Badiei A Ganjali MR Norouzi P Hasheminasab A Abdouss M 《Analytica chimica acta》2007,601(2):172-182
A new functionalized nanoporous silica gel with dipyridyl group (DPNSG) was synthesized. Then, the potentiometric response of the copper(II) ion was investigated at a carbon paste electrode chemically modified with this newly designed functionalized nanoporous silica gel. The electrodes with DPNSG proportions of 15.0% (w/w) demonstrated very stable potentials. Calibration plots with Nernstian slopes for Cu2+ were observed, 28.4 (±1.0) mV decade−1, over a wide linear concentration range (1.0 × 10−7 to 1.0 × 10−2 M). The electrode exhibited a detection limit of 8.0 × 10−8 M. Moreover, the selectivity coefficients measured by the match potential method in acetate buffer, pH 5.5, were investigated. The electrode presented a response time of ∼50 s, high performance, high sensitivity in a wide range of cation activities and good long-term stability (more than 9 months). The method was satisfactory and was used to determine the copper ion concentration in waste waters, contaminated by this metal. 相似文献
77.
A new diffusion-based solid-phase microextraction (SPME) time-weighted average (TWA) field water sampling device was developed and investigated by field trial. The sampler is constructed with copper tube and caps and a commercial SPME fiber assembly. The device possesses all advantages of SPME; it is solvent-free, reusable, combines sampling, isolation and enrichment into one step, and the fiber can be directly injected into a gas chromatograph for analysis with a commercial SPME fiber holder, without further treatment. Field trials in Laurel Creek (Waterloo, Ont., Canada) and Hamilton Harbour (Hamilton, Ont., Canada) illustrated that the device is durable, easy to deploy, and the mass uptake of the device is independent of the face velocity. The device provides good precision [relative standard deviations (RSDs) are less than 20%] and the data obtained with this device are quite comparable to those obtained with the spot sampling method, which demonstrates that the newly developed SPME water sampling device is suitable for long-term monitoring of organic pollutants in water. 相似文献
78.
Charged spin-3/2 fields are coupled to an extended gauge model without the total suppression of the vector degrees of freedom which usually takes place as a consequence of simultaneously imposing the Maxwell and Rarita-Schwinger U(1) symmetries. 相似文献
79.
Mehran Javanbakht Hamid Khoshsafar Mohammad Reza Ganjali Parviz Norouzi Mehdi Adib 《Electroanalysis》2009,21(14):1605-1610
The aim of this work was to obtain an adsorptive stripping voltammetric method for the Ce(III) determination at a carbon paste electrode, chemically modified with N'‐[(2‐hydroxyphenyl)methylidene]‐2‐furohydrazide (NHMF). The electroanalytical procedure comprised two steps: the Ce(III) chemical accumulation at ?200 mV followed by the electrochemical detection of the Ce(III)/NHMF complex, using anodic stripping voltammetry. The factors, influencing the adsorptive stripping performance, were optimized including the modifier quantity in the paste, the electrolyte concentrations, the solution pH and the accumulation potential or time. The resulting electrode demonstrated a linear response over a wide range of Ce(III) concentration (5.0–90 nmol dm?3). The detection limit was found to be 0.8 nmol dm?3 on the basis of a signal to noise ratio of 3. The precision for six determinations of 10 and 55 nmol dm?3 Ce(III) was 5.6% and 2.1% (relative standard deviation), respectively. Application of the procedure to the determination of cerium in phosphate rock and wastewater samples gave good results. 相似文献
80.
Acoustic analysis of the vocal tract during vowel production by finite-difference time-domain method
Takemoto H Mokhtari P Kitamura T 《The Journal of the Acoustical Society of America》2010,128(6):3724-3738
The vocal tract shape is three-dimensionally complex. For accurate acoustic analysis, a finite-difference time-domain method was introduced in the present study. By this method, transfer functions of the vocal tract for the five Japanese vowels were calculated from three-dimensionally reconstructed magnetic resonance imaging (MRI) data. The calculated transfer functions were compared with those obtained from acoustic measurements of vocal tract physical models precisely constructed from the same MRI data. Calculated transfer functions agreed well with measured ones up to 10 kHz. Acoustic effects of the piriform fossae, epiglottic valleculae, and inter-dental spaces were also examined. They caused spectral changes by generating dips. The amount of change was significant for the piriform fossae, while it was almost negligible for the other two. The piriform fossae and valleculae generated spectral dips for all the vowels. The dip frequencies of the piriform fossae were almost stable, while those of the valleculae varied among vowels. The inter-dental spaces generated very small spectral dips below 2.5 kHz for the high and middle vowels. In addition, transverse resonances within the oral cavity generated small spectral dips above 4 kHz for the low vowels. 相似文献