全文获取类型
收费全文 | 114367篇 |
免费 | 31934篇 |
国内免费 | 28716篇 |
专业分类
化学 | 57711篇 |
晶体学 | 1352篇 |
力学 | 6016篇 |
综合类 | 441篇 |
数学 | 11592篇 |
物理学 | 58453篇 |
无线电 | 39452篇 |
出版年
2024年 | 864篇 |
2023年 | 1718篇 |
2022年 | 2054篇 |
2021年 | 2096篇 |
2020年 | 2393篇 |
2019年 | 3543篇 |
2018年 | 3327篇 |
2017年 | 4248篇 |
2016年 | 4852篇 |
2015年 | 5792篇 |
2014年 | 5786篇 |
2013年 | 7689篇 |
2012年 | 8322篇 |
2011年 | 9173篇 |
2010年 | 11989篇 |
2009年 | 12004篇 |
2008年 | 5996篇 |
2007年 | 5448篇 |
2006年 | 5091篇 |
2005年 | 4778篇 |
2004年 | 5551篇 |
2003年 | 4431篇 |
2002年 | 4369篇 |
2001年 | 4393篇 |
2000年 | 3519篇 |
1999年 | 3122篇 |
1998年 | 2607篇 |
1997年 | 2347篇 |
1996年 | 2687篇 |
1995年 | 2989篇 |
1994年 | 3043篇 |
1993年 | 3174篇 |
1992年 | 2725篇 |
1991年 | 2381篇 |
1990年 | 1918篇 |
1989年 | 2039篇 |
1988年 | 1940篇 |
1987年 | 1182篇 |
1986年 | 1226篇 |
1985年 | 882篇 |
1984年 | 990篇 |
1982年 | 902篇 |
1981年 | 755篇 |
1980年 | 781篇 |
1979年 | 543篇 |
1978年 | 542篇 |
1977年 | 636篇 |
1976年 | 1043篇 |
1972年 | 540篇 |
1971年 | 444篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Ingrid Lukkari Jaromir Ruzicka Gary D. Christian 《Fresenius' Journal of Analytical Chemistry》1993,346(6-9):813-818
Summary Automated methods for the determination of ammonium and ammonia are reviewed, and techniques based on gas diffusion using a semi-permeable membrane were selected for the determination of both total ammonium-nitrogen and free ammonia in fermentation samples. A simple and robust instrument based on sequential injection analysis (SIA) consisting of a piston pump and two selector valves was used. Two different methods of ammonia detection, the Berthelot method and detection using pH-indicators, have been evaluated and compared. The indicator method showed higher reproducibility and the range of determination could easily be adjusted to match the concentrations of the samples. The range of determination could be adjusted from 0.05 mmol/l to 350 mmol/l, depending on choice of acceptor solution. This method has been evaluated with fermentation medium samples and tested on-line in a yeast fermentation process.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday 相似文献
62.
Graham A. Jullien Wenzhe Luo Neil M. Wigley 《The Journal of VLSI Signal Processing》1996,14(2):207-220
This paper discusses strategies for implementing DSP systems using residue replication. The theory, recently introduced by two of the authors, uses formal polynomial ring mappings, from binary representations, to direct product ring implementation of integer processing arrays. The mapping produces completely independent computational arrays each computing over the same ring. This paper describes an architecture and processing array to implement, and take advantage of, the special computational ring structures that result from the mapping. A brief review of the theory and mapping techniques, is followed by the discussion of the architecture and VLSI design of an efficient inner product processing array using Fermat Primes. 相似文献
63.
Dynamic Programming (DP) applies to many signal and image processing applications including boundary following, the Viterbi algorithm, dynamic time warping, etc. This paper presents an array processor implementation of generic dynamic programming. Our architecture is a SIMD array attached to a host computer. The processing element of the architecture is based on an ASIC design opting for maximum speed-up. By adopting a torus interconnection network, a dual buffer structure, and a multilevel pipeline, the performance of the DP chip is expected to reach the order of several GOPS. The paper discusses both the dedicated hardware design and the data flow control of the DP chip and the total array.This work was supported in part by the NATO, Scientific and Environmental Affairs Division, Collaborative Research Grant SA.5-2-05(CRG.960201)424/96/JARC-501. 相似文献
64.
65.
The Mathematical Intelligencer encourages comments about the material in this issue. Letters to the editor should be sent
to either of the editors-in-chief, Chandler Davis or Marjorie Senechal. 相似文献
66.
Q. Gong R. N tzel P.J. van Veldhoven T.J. Eijkemans J.H. Wolter 《Journal of Crystal Growth》2005,280(3-4):413-418
We report on the shape transition from InAs quantum dashes to quantum dots (QDs) on lattice-matched GaInAsP on InP(3 1 1)A substrates. InAs quantum dashes develop during chemical-beam epitaxy of 3.2 monolayers InAs, which transform into round InAs QDs by introducing a growth interruption without arsenic flux after InAs deposition. The shape transition is solely attributed to surface properties, i.e., increase of the surface energy and symmetry under arsenic deficient conditions. The round QD shape is maintained during subsequent GaInAsP overgrowth because the reversed shape transition from dot to dash is kinetically hindered by the decreased ad-atom diffusion under arsenic flux. 相似文献
67.
68.
69.
Tensile impact experiments of EC8.0−24×7 glass fiber bundles at different low temperaturesT(14°C, −40°C and −10°C) and strain rates ɛ were carried out, and complete stress-strain curves were obtained. Within the range
of the experiment temperatures and strain rates, it is found that the initial modulusE, the ultimate strength σmax and the unstable strain ɛ
b
of the glass fiber bundles all increase with ɛ at an identicalT. At an identical ɛ, with the decrease ofT, E and σmax increase; but ɛ
b
increases when 10°C>T>−40°C and decreases when −40°C>T>−100°C. The strain-rate- and temperature-dependent bimodal Weibull statistical constitutive theory was adopted for the statistical
analysis of the experimental results, and the Weibull parameters of single fiber were obtained. The results show that the
bimodal Weibull distribution function is suitable to represent the strength distribution of the glass fiber at low temperature
and different strain rates. The differences in the mechanical properties between EC8.0−24×7 and EC5.5−12 ×14 glass fiber bundles
were also discussed.
Project supported by the National Natural Science Foundation of China (No. 19772058). 相似文献
70.
Sung‐Fu Hsu Tzong‐Ming Wu Chien‐Shiun Liao 《Journal of Polymer Science.Polymer Physics》2006,44(23):3337-3347
Poly(3‐hydroxybutyrate) (PHB)/layered double hydroxides (LDHs) nanocomposites were prepared by mixing PHB and poly(ethylene glycol) phosphonates (PEOPAs)‐modified LDH (PMLDH) in chloroform solution. Both X‐ray diffraction data and TEM micrographs of PHB/PMLDH nanocomposites indicate that the PMLDHs are randomly dispersed and exfoliated into the PHB matrix. In this study, the effect of PMLDH on the isothermal crystallization behavior of PHB was investigated using a differential scanning calorimeter (DSC) and polarized optical microscopy. Isothermal crystallization results of PHB/PMLDH nanocomposites show that the addition of 2 wt % PMLDH into PHB induced more heterogeneous nucleation in the crystallization significantly increasing the crystallization rate and reducing their activation energy. By adding more PMLDH into the PHB probably causes more steric hindrance of the diffusion of PHB, reducing the transportation ability of polymer chains during crystallization, thus increasing the activation energy. The correlation among crystallization kinetics, melting behavior and crystalline structure of PHB/PMLDH nanocomposites can also be discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3337–3347, 2006 相似文献