全文获取类型
收费全文 | 10603篇 |
免费 | 1453篇 |
国内免费 | 1056篇 |
专业分类
化学 | 2154篇 |
晶体学 | 69篇 |
力学 | 774篇 |
综合类 | 70篇 |
数学 | 1219篇 |
物理学 | 3630篇 |
无线电 | 5196篇 |
出版年
2024年 | 30篇 |
2023年 | 193篇 |
2022年 | 160篇 |
2021年 | 228篇 |
2020年 | 310篇 |
2019年 | 218篇 |
2018年 | 220篇 |
2017年 | 383篇 |
2016年 | 421篇 |
2015年 | 414篇 |
2014年 | 681篇 |
2013年 | 809篇 |
2012年 | 714篇 |
2011年 | 822篇 |
2010年 | 639篇 |
2009年 | 771篇 |
2008年 | 815篇 |
2007年 | 819篇 |
2006年 | 711篇 |
2005年 | 565篇 |
2004年 | 519篇 |
2003年 | 388篇 |
2002年 | 330篇 |
2001年 | 326篇 |
2000年 | 283篇 |
1999年 | 195篇 |
1998年 | 192篇 |
1997年 | 147篇 |
1996年 | 131篇 |
1995年 | 107篇 |
1994年 | 102篇 |
1993年 | 74篇 |
1992年 | 81篇 |
1991年 | 51篇 |
1990年 | 34篇 |
1989年 | 33篇 |
1988年 | 49篇 |
1987年 | 16篇 |
1986年 | 22篇 |
1985年 | 19篇 |
1984年 | 16篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1981年 | 5篇 |
1980年 | 10篇 |
1979年 | 13篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 4篇 |
1974年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Maura Paterson 《Designs, Codes and Cryptography》2007,42(2):195-212
A sliding-window dynamic frameproof code is a scheme for discouraging the piracy of digital broadcasts through the use of
digital fingerprinting. In this paper, we formally define sliding-window dynamic frameproof codes and provide optimal constructions
for a certain class of these schemes. We also discuss bounds on the number of users such schemes can support.
相似文献
992.
《Electroanalysis》2005,17(2):148-154
The determination of leucoindigo adsorbed on the surface of pretreated carbon paste electrodes has been performed by cyclic (CV) and alternating current voltammetry (ACV). The water‐soluble compound called leucoindigo is obtained through the reduction of water insoluble indigo in an alkaline media and in presence of a dithionite salt (Na2S2O4) as a reducing agent. Cyclic voltammograms of leucoindigo show two reversible electrodic processes, in the aqueous 0.1 M Tris‐HCl pH 7.2, at the formal potential of ?0.4 V and +0.3 V (vs. Ag/AgCl/sat. KCl). In a batch protocol, leucoindigo was quantified by CV with a change of medium between accumulation and detection steps. Reversible voltammetric processes of leucoindigo were greatly enhanced by other voltammetric technique like alternating current voltammetry. Limit of detection in the nanomolar range was achieved for a 2 min accumulation time by ACV in a batch procedure. A flow system was also employed, with adsorptive voltammetric detection of leucoindigo, since this automates the methodology and decreases analysis time. Parameters related to the electrochemical technique are optimized and calibration plots obtained are reported. These data provide useful information about the suitability of using leucoindigo in the detection system of alkaline phosphatase (AP) and horseradish peroxidase (HRP) based affinity devices, in which indigo is generated by the enzymatic hydrolysis of the 3‐indoxyl phosphate substrate. 相似文献
993.
I. Tamayo J. Belana J. C. Caadas M. Mudarra J. A. Diego J. Sellars 《Journal of Polymer Science.Polymer Physics》2003,41(12):1412-1421
With thermally stimulated depolarization currents, we researched the relaxations of crosslinked polyethylene as it is used in medium‐voltage cable insulation. Through conventional polarization two heteropolar peaks stand up in the spectra, at 80 and 105 °C. As the sample is annealed, a homopolar peak is developed at about 99 °C. With window polarization, our results indicated that the 80 °C peak is a structured peak related to polar crosslinking subproducts and impurities. The 105 and 99 °C peaks are fitted to the general kinetic‐order model because the 105 °C peak is related to free‐charge detrapping at the crystalline phase, in the bulk and maybe at the amorphous‐crystal interphases, and the peak that is observed at 99 °C is due to injected charge. Annealing at high temperatures promotes the creation of traps in the material. Charge trapping at T < 70 °C seems to be related to the increased insulator resistivity with annealing time. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1412–1421, 2003 相似文献
994.
Stephen J. Elliott 《ETRI Journal》2004,26(6):641-646
As the use of signatures for identification purposes is pervasive in society and has a long history in business, dynamic signature verification (DSV) could be an answer to authenticating a document signed electronically and establishing the identity of that document in a dispute. DSV has the advantage in that traits of the signature can be collected on a digitizer. The research question of this paper is to understand how the individual variables vary across devices. In applied applications, this is important because if the signature variables change across the digitizers this will impact performance and the ability to use those variable. Understanding which traits are consistent across devices will aid dynamic signature algorithm designers to create more robust algorithms. 相似文献
995.
The system of equations describing ion transport in a binary electrolyte z
a-z
c with allowance for the linear dependence of the diffusion coefficients on the concentration was analyzed in the framework
of the phenomenological Nernst-Planck approach. The expressions are obtained that define concentration profiles of ions and
conditions favorable for the limiting current caused by the achievement of the concentration of a saturated solution (in the
case of the anodic reaction) and depletion of the near-electrode region in electroactive cations (in the case of the cathodic
reaction). The revealed theoretical dependence of the limiting current on the volume concentration of the salt agrees with
published experimental data. The voltammetric characteristics of the corresponding systems were calculated. The role of the
migrational component of the ion flow is discussed.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 638–642, April, 2006. 相似文献
996.
An analytical model is developed for the response of clamped monolithic and sandwich beams subjected to impulse loading over a central loading patch. A number of topologies of sandwich core are investigated, including the honeycomb core, pyramidal core, prismatic diamond core and metal foam. The various cores are characterised by their dependencies of through-thickness compressive strength and longitudinal tensile strength upon relative density. Closed-form expressions are derived for the deflection of the beam when the ratio r of length of loading patch to the beam span exceeds 0.5. In contrast, an ordinary differential equation needs to be solved numerically for the choice r<0.5. Explicit finite element calculations show that most practical shock loadings can be treated as impulsive and the accuracy of the impulsive analytical predictions is confirmed. The analytical formulae are employed to determine optimal geometries of the sandwich beams that maximise the shock resistance of the beams for a given mass. The optimisation reveals that sandwich beams have a superior shock resistance relative to monolithic beams of the same mass, with the prismatic diamond core sandwich beam providing the best performance. Further, the optimal sandwich beam designs are only mildly sensitive to the length of the loading patch. 相似文献
997.
D. P. Webb Y. C. Chan C. K. H. Wong Y. W. Lam K. M. Leung D. S. Chrp 《Journal of Electronic Materials》1997,26(5):470-473
Thermally stimulated current (TSC) measurements have been performed on a xerographic photoreceptor which has been treated
with ultraviolet (UV) radiation. The charge transport layer of the photoreceptor consists of a polyester molecularly doped
with an arylamine substituted hydrazone which was observed to undergo UV induced rearrangement to an indazole derivative.
The indazole derivative is transparent to the wavelength component inducing the photo-reaction so that the depth of converted
material gradually extends farther into the CTL with UV exposure time. The xerographic residual potential variation with irradiation
time is attributed to the formation of a potential barrier to transfer of charge from hydrazone hopping states to indazole
hopping states. The mobility activation energy obtained from TSC measurements is 0.22 eV for unirradiated material, which
decreases to 0.12 eV after 1200 s of irradiation. The latter energy is identified as a signature of the potential barrier.
This identification is corroborated by the correlation between the decrease of the residual potential and the increase of
the TSC activation energy after 3600 s of irradiation. 相似文献
998.
Magnetic field measurements above type-II superconductor films in a remanent magnetization state have been used to determine
two dimensional surface current distributions. Using the Biot-Savart law for the surface current density, integral equations
(of 2-D convolution type) for two components of current have been obtained. These equations have been solved by employing
Tikhonov's method of generalized discrepancy, and the surface current pattern in superconductors as well as the magnetic field
distribution on the film surface have been obtained. Current peculiarities related to various kinds of inhomogeneities, specific
character of the film form, and a laser pulse effect have been observed. In particular, it was discovered that a laser pulse
can signficantly redistribute the film currents without changing the total number of current vortices in the film. 相似文献
999.
1000.