全文获取类型
收费全文 | 172315篇 |
免费 | 5107篇 |
国内免费 | 3862篇 |
专业分类
化学 | 63562篇 |
晶体学 | 2304篇 |
力学 | 9787篇 |
综合类 | 237篇 |
数学 | 30524篇 |
物理学 | 52612篇 |
无线电 | 22258篇 |
出版年
2024年 | 124篇 |
2023年 | 785篇 |
2022年 | 1166篇 |
2021年 | 1415篇 |
2020年 | 1298篇 |
2019年 | 1311篇 |
2018年 | 11724篇 |
2017年 | 12777篇 |
2016年 | 6510篇 |
2015年 | 2759篇 |
2014年 | 2363篇 |
2013年 | 3331篇 |
2012年 | 8736篇 |
2011年 | 18621篇 |
2010年 | 11872篇 |
2009年 | 11893篇 |
2008年 | 15744篇 |
2007年 | 19739篇 |
2006年 | 3573篇 |
2005年 | 10933篇 |
2004年 | 6483篇 |
2003年 | 6029篇 |
2002年 | 3493篇 |
2001年 | 2216篇 |
2000年 | 1916篇 |
1999年 | 1434篇 |
1998年 | 1137篇 |
1997年 | 1076篇 |
1996年 | 1190篇 |
1995年 | 935篇 |
1994年 | 874篇 |
1993年 | 781篇 |
1992年 | 752篇 |
1991年 | 660篇 |
1990年 | 585篇 |
1989年 | 482篇 |
1988年 | 423篇 |
1987年 | 337篇 |
1986年 | 323篇 |
1985年 | 359篇 |
1984年 | 292篇 |
1983年 | 220篇 |
1982年 | 205篇 |
1981年 | 187篇 |
1980年 | 172篇 |
1979年 | 194篇 |
1978年 | 191篇 |
1976年 | 145篇 |
1974年 | 122篇 |
1973年 | 163篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Sh. M. Khaliullin V. D. Zhuravlev V. G. Bamburov L. V. Ermakova 《Physics of Atomic Nuclei》2015,78(12):1382-1388
Submicron CaZrO3 powder is obtained in combustion reactions (solution combustion synthesis—SCS) with glycine. It is found that SCS reduces the sintering temperature of CaZrO3 powders. The dielectric properties of calcium zirconate ceramics are studied by the electrochemical impedance method. It is shown that a ceramics of powders obtained by the SCS method has high dielectric characteristics. 相似文献
22.
Norbornene derivatives from a metal‐free,strain‐promoted cycloaddition reaction: New building blocks for ring‐opening metathesis polymerization reactions 下载免费PDF全文
Christopher E. Hobbs Binhong Lin Thomas Malinski 《Journal of polymer science. Part A, Polymer chemistry》2015,53(20):2357-2362
The preparation of new ring opening metathesis polymerization (ROMP) monomers using a 1,3‐dipolar cycloaddition between aryl azides and norbornadiene is described. Various norbornenetriazolines, obtained through a solvent‐and catalyst‐free reaction, can subsequently be incorporated into polymer backbones through ROMP reactions. Furthermore, thermal decomposition of the triazoline moiety can allow for further polymer functionalization. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2357–2362 相似文献
23.
V. G. Deibuk 《Semiconductors》2003,37(10):1151-1155
The miscibility gaps and the critical temperatures of spinodal decomposition of ternary semiconducting Ga-In-Sb, Ga-In-P, and In-As-Sb systems are calculated by taking into account the deformation energy and the effect of plastic relaxation caused by the misfit dislocations. It is shown that taking into consideration elastic energy narrows the ranges of spinodal decomposition and lowers its critical temperature. The introduction of the phenomenological parameter into Matthews-Blakeslee formula makes it possible to reach a satisfactory agreement between theoretically calculated values of critical thickness of epitaxial films and the experimental data. 相似文献
24.
The structure, chemical composition, and magnetic properties of electrochemically deposited nanocrystalline Co-Ni-Fe films
were investigated using a number of techniques. A high saturation magnetic induction up to B
s
= 21 kG was attained. An enhancement of the saturation magnetization compared to the ideal anticipated one was revealed,
which correlated with the nonlinear behavior of the structural phase composition and lattice parameters with the change of
the composition.
The text was submitted by the authors in English. 相似文献
25.
N. I. Golovina G. N. Nechiporenko G. G. Nemtsev G. P. Dolganova V. P. Roshchupkin D. B. Lempert G. B. Manelis 《Russian Journal of Applied Chemistry》2007,80(1):24-30
Methods for phase stabilization of ammonium nitrate were sought for in order to considerably expand the application area of this oxidizing agent in various-purpose self-combustible formulations, including that in a new generation of gas-generating formulations for automobile air bags. New methods for stabilization of ammonium nitrate were studied and, in particular, a search was made for organic compounds that can stabilize ammonium nitrate even at their low content. The mechanism of phase state stabilization of ammonium nitrate by compounds of this kind was examined. 相似文献
26.
城域网的建设是今后光纤网络建设的一个热点,根据城域网的特点和系统技术要求选择光纤光缆是网络设计的重要组成部分。本根据城域网的特点和需求,对市场上现有的光纤光缆做了详细的分析和探讨,提出了城域网规划中光纤光缆选择的原则和具体的建议。 相似文献
27.
W. Shieh R. Hui X. Yi 《Photonics Technology Letters, IEEE》2006,18(10):1122-1124
We perform a systematic measurement of the degree-of-polarization (DOP) and eye-closure penalty for optical signals with orthogonal polarizations. We find that the symmetry of DOP is maintained for the orthogonal polarizations under both first and higher order polarization-mode dispersion (PMD), whereas the symmetry of eye-closure penalty is broken under second-order PMD. An orthogonal polarization pair can have large disparity of eye-closure penalty despite an identical DOP. We also demonstrate a novel approach to estimate the maximum eye-closure penalty asymmetry with three orthogonal polarizations on the Poincare/spl acute/ sphere. 相似文献
28.
Finite sample size effect on minimum variance beamformers: optimum diagonal loading factor for large arrays 总被引:6,自引:0,他引:6
Minimum variance beamformers are usually complemented with diagonal loading techniques in order to provide robustness against several impairments such as imprecise knowledge of the steering vector or finite sample size effects. This paper concentrates on this last application of diagonal loading techniques, i.e., it is assumed that the steering vector is perfectly known and that diagonal loading is used to alleviate the finite sample size impairments. The analysis herein is asymptotic in the sense that it is assumed that both the number of antennas and the number of samples are high but have the same order of magnitude. Borrowing some results of random matrix theory, the authors first derive a deterministic expression that describes the asymptotic signal-to-noise-plus-interference ratio (SINR) at the output of the diagonally loaded beamformer. Then, making use of the statistical theory of large observations (also known as general statistical analysis or G-analysis), the authors derive an estimator of the optimum loading factor that is consistent when both the number of antennas and the sample size increase without bound at the same rate. Because of that, the estimator has an excellent performance even in situations where the quotient between the number of observations is low relative to the number of elements of the array. 相似文献
29.
从做大到做强的主体是PCB企业(集团) 中国PCB工业如何从做大到做强!(6) 总被引:2,自引:2,他引:0
从做大到做强是中国PCB工业的唯一出路.而做强中国PCB工业的主体是中国的PCB企业(集团).只有大多数的中国PCB企业做大并做强了,中国PCB工业才能称得上是PCB强国. 相似文献
30.
A discussion about the quantum mechanical effects on noise properties of ballistic (phase-coherent) nanoscale devices is presented. It is shown that quantum noise can be understood in terms of quantum trajectories. This interpretation provides a simple and intuitive explanation of the origin of quantum noise that can be very salutary for nanoelectronic engineers. In particular, an injection model is presented that, coupled with a standard Monte Carlo algorithm, provides an accurate modeling of quantum noise. As a test, the standard results of noise in tunneling junction devices are reproduced within this approach. 相似文献