全文获取类型
收费全文 | 5949篇 |
免费 | 260篇 |
国内免费 | 34篇 |
专业分类
化学 | 2763篇 |
晶体学 | 53篇 |
力学 | 193篇 |
数学 | 1213篇 |
物理学 | 973篇 |
无线电 | 1048篇 |
出版年
2023年 | 70篇 |
2022年 | 121篇 |
2021年 | 182篇 |
2020年 | 177篇 |
2019年 | 197篇 |
2018年 | 199篇 |
2017年 | 182篇 |
2016年 | 291篇 |
2015年 | 176篇 |
2014年 | 255篇 |
2013年 | 401篇 |
2012年 | 375篇 |
2011年 | 373篇 |
2010年 | 215篇 |
2009年 | 246篇 |
2008年 | 293篇 |
2007年 | 267篇 |
2006年 | 210篇 |
2005年 | 184篇 |
2004年 | 165篇 |
2003年 | 134篇 |
2002年 | 125篇 |
2001年 | 114篇 |
2000年 | 85篇 |
1999年 | 62篇 |
1998年 | 51篇 |
1997年 | 55篇 |
1996年 | 72篇 |
1995年 | 69篇 |
1994年 | 59篇 |
1993年 | 70篇 |
1992年 | 55篇 |
1991年 | 58篇 |
1990年 | 41篇 |
1989年 | 44篇 |
1988年 | 39篇 |
1987年 | 47篇 |
1986年 | 48篇 |
1985年 | 43篇 |
1984年 | 33篇 |
1983年 | 30篇 |
1982年 | 36篇 |
1981年 | 33篇 |
1980年 | 32篇 |
1979年 | 44篇 |
1978年 | 39篇 |
1977年 | 27篇 |
1976年 | 29篇 |
1975年 | 24篇 |
1974年 | 17篇 |
排序方式: 共有6243条查询结果,搜索用时 426 毫秒
31.
Cam Nguyen 《Journal of Infrared, Millimeter and Terahertz Waves》1993,14(5):969-985
A theoretical analysis of general multiple parallel coupled transmission lines in an inhomogeneous medium is presented. The analysis is based on the generalized telegraphists' equation. It is relatively simple and has the advantage of giving explicit solutions for the properties of the coupled-line system. Considerations are also given to a coupled-line structure whose lines have the same characteristic impedance. Results for two and three coupled lines are found in agreement with those published previously. 相似文献
32.
A systematic study of the upper semicontinuity and the lower semicontinuity of the solution map in parametric affine variational
inequalities is given in this paper. Several examples are constructed to analyze the results.
This work was supported by Korea Research Foundation Grant (KRF 2001-015-DP0049), the APEC Postdoctoral Fellowships Program,
and the KOSEF Brain Pool Program. 相似文献
33.
T. Ramanathan S. Stankovich D. A. Dikin H. Liu H. Shen S. T. Nguyen L. C. Brinson 《Journal of Polymer Science.Polymer Physics》2007,45(15):2097-2112
Mechanical, thermal, and electrical properties of graphite/PMMA composites have been evaluated as functions of particle size and dispersion of the graphitic nanofiller components via the use of three different graphitic nanofillers: “as received graphite” (ARG), “expanded graphite,” (EG) and “graphite nanoplatelets” (GNPs) EG, a graphitic materials with much lower density than ARG, was prepared from ARG flakes via an acid intercalation and thermal expansion. Subsequent sonication of EG in a liquid yielded GNPs as thin stacks of graphitic platelets with thicknesses of ~10 nm. Solution‐based processing was used to prepare PMMA composites with these three fillers. Dynamic mechanical analysis, thermal analysis, and electrical impedance measurements were carried out on the resulting composites, demonstrating that reduced particle size, high surface area, and increased surface roughness can significantly alter the graphite/polymer interface and enhance the mechanical, thermal, and electrical properties of the polymer matrix. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2097–2112, 2007 相似文献
34.
We use the PCP-SAFT equation of state, which is of the Van der Waals type and has a sound physical basis, to predict mixture properties, such as vapor–liquid and liquid–liquid equilibria, as well as excess enthalpies. We use molecular properties, such as dipole moment, quadrupole moment, polarizability and dispersion interaction coefficients, that have been determined quantum mechanically in Part I of this publication and adjust the remaining three pure compound parameters to pure compound data. We finally present a new combination rule for the dispersion energy parameter ? that is based on the quantum mechanically determined data. The predictions based on quantum mechanically determined pure compound properties along with the new combination rule show an improved performance compared to the original PCP-SAFT combination rule. 相似文献
35.
Ngo Quang Huy Trinh Thi Bich Nguyen Van Suc 《Journal of Radioanalytical and Nuclear Chemistry》2006,269(1):129-133
Summary The paper presents a procedure to prepare soil samples for U and Th isotope measurement by alpha-spectrometry after coprecipitation
with LaF3. In this procedure the reduction of U(VI) to U(IV) was performed by Zn metal in 4M HCl solution. The recoveries of chemical
separation equal to eU-chemistry = 78±4% for uranium and eTh-chemistry = 82±4% for thorium. Canberra alpha-spectrometer was used with PIPS detectors of A-1200-37-AM Model of 1200 mm2 active area. The counting efficiency of the measuring system equals to ecounting = 18% and the total efficiencies were eU = ecounting .eU-chemistry = 14.0±0.7% for uranium and eTh = ecounting .eTh-chemistry = 14.7±0.7% for thorium. The recoveries of chemical separation were rather high (about 80%), that leads to the use of a small
weight of soil sample (about 0.5 g). The efficiencies were also stable, that allows analyzing the soil sample without using
radiotracers. They are advantages of the sample preparation procedure of this work. 相似文献
36.
Summary Cold neutrons at the external neutron guide laboratory (ELLA) of the KFA Jülich are used to demonstrate their profitable application
for multielement characterization of biological materials. The set-up and experimental conditions of the Prompt Gamma Cold
Neutron Activation Analysis (PGCNAA) device is described in detail. Results for C, H, N, S, K, B, and Cd using synthetic standards
and the “ratio” technique for calculation are reported for several reference materials and prove the method to be reliable
and complementary with respect to the elements being determined by INAA.
IAEA fellow at the KFA from 6. 3. 91 to 2. 9. 91 on contract No. VIE/9016R. 相似文献
37.
A new miniature bandpass filter, comprising three-conductor short-circuited spurline resonators of approximately a quarter-wavelength long, with a very wide bandwidth approaching multioctaves is reported for the first time. The chain matrix of the filter resonator is derived. The new filter has been developed using microstrip line with less than 1 dB insertion loss over a passband from 2 to 8 GHz. Reasonably good agreement between the measured and calculated results is observed 相似文献
38.
Hayden J.D. Taft R.C. Kenkare P. Mazure C. Gunderson C. Nguyen B.-Y. Woo M. Lage C. Roman B.J. Radhakrishna S. Subrahmanyan R. Sitaram A.R. Pelley P. Lin J.-H. Kemp K. Kirsch H. 《Electron Devices, IEEE Transactions on》1994,41(12):2318-2325
An advanced, high-performance, quadruple well, quadruple polysilicon BiCMOS technology has been developed for fast 16 Mb SRAM's. A split word-line bitcell architecture, using four levels of polysilicon and two self-aligned contacts, achieves a cell area of 8.61 μm2 with conventional I-line lithography and 7.32 μm2 with I-line plus phase-shift or with deep UV lithography. The process features PELOX isolation to provide a 1.0 μm active pitch, MOSFET transistors designed for a 0.80 μm gate poly pitch, a double polysilicon bipolar transistor with aggressively scaled parasitics, and a thin-film polysilicon transistor to enhance bitcell stability. A quadruple-well structure improves soft error rate (SER) and allows simultaneous optimization of MOSFET and bipolar performance 相似文献
39.
Parasitic bipolar gain in fully depleted n-channel SOI MOSFET's 总被引:3,自引:0,他引:3
Ver Ploeg E.P. Nguyen C.T. Wong S.S. Plummer J.D. 《Electron Devices, IEEE Transactions on》1994,41(6):970-977
Fully depleted SOI MOSFET's include an inherent parasitic lateral bipolar structure with a floating base. We present here the first complete physically based explanation of the bipolar gain mechanism, and its dependence on bias and technological parameters. A simple, one-dimensional physical model, with no fitting parameters, is constructed, and is shown to agree well with simulations and measurements performed on a new type of SOI MOSFET structure. It is shown that parameters which affect the gain, such as SOI layer thickness, body doping concentration and gate and drain voltages, do so primarily by affecting the concentration of holes in the body region. Thus, current gain falls dramatically with increasing drain voltage due to the associated impact ionization driven increase in the hole concentration. Gummel plots of this parasitic bipolar indicate an apparent ideality factor of 0.5 for the hole current, due to the body hole concentration's dependence on drain voltage 相似文献
40.
Sanghera J.S. Nguyen V.Q. Pureza P.C. Kung F.H. Miklos R. Aggarwal I.D. 《Lightwave Technology, Journal of》1994,12(5):737-741
Improved purification and processing techniques have been utilized to fabricate Ge30As10Se30Te30 glass fibers with a minimum loss of O.11 dB/m at 6.6 μm. This is the lowest loss reported for any telluride glass fiber in the infrared region. Furthermore, the fibers exhibit less than 1 dB/m loss between 5.25 and 9.5 μm 相似文献