全文获取类型
收费全文 | 22571篇 |
免费 | 4150篇 |
国内免费 | 4386篇 |
专业分类
化学 | 13543篇 |
晶体学 | 527篇 |
力学 | 816篇 |
综合类 | 175篇 |
数学 | 326篇 |
物理学 | 8934篇 |
无线电 | 6786篇 |
出版年
2024年 | 52篇 |
2023年 | 255篇 |
2022年 | 469篇 |
2021年 | 671篇 |
2020年 | 765篇 |
2019年 | 667篇 |
2018年 | 662篇 |
2017年 | 885篇 |
2016年 | 1057篇 |
2015年 | 1025篇 |
2014年 | 1231篇 |
2013年 | 1862篇 |
2012年 | 1599篇 |
2011年 | 1645篇 |
2010年 | 1336篇 |
2009年 | 1538篇 |
2008年 | 1514篇 |
2007年 | 1635篇 |
2006年 | 1555篇 |
2005年 | 1349篇 |
2004年 | 1281篇 |
2003年 | 1074篇 |
2002年 | 968篇 |
2001年 | 801篇 |
2000年 | 796篇 |
1999年 | 621篇 |
1998年 | 540篇 |
1997年 | 523篇 |
1996年 | 454篇 |
1995年 | 403篇 |
1994年 | 340篇 |
1993年 | 299篇 |
1992年 | 271篇 |
1991年 | 198篇 |
1990年 | 150篇 |
1989年 | 118篇 |
1988年 | 112篇 |
1987年 | 60篇 |
1986年 | 48篇 |
1985年 | 38篇 |
1984年 | 33篇 |
1983年 | 25篇 |
1982年 | 35篇 |
1981年 | 18篇 |
1980年 | 20篇 |
1979年 | 24篇 |
1978年 | 23篇 |
1977年 | 12篇 |
1976年 | 22篇 |
1975年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
81.
Fe2(CO)6(μ-S2) was used as a single source precursor in attempt to produce FeS film via MOCVD. Pyrolysis of Fe2(CO)6(μ-S2) at temperature below 500℃ produced Fe1-xS or Fe7S8 powder as indicated by its powder X-ray spectra. At 750 ℃, polycrystalline FeS powder was obtained. In film deposition, polycrystalline Fe1-xS or Fe7Ss films were obtained on Si(100) and Ag/Si(100) substrates below 500 ℃. SEM micrographs showed the film on Si(100) substrate containing whisker like grains. However, pillar like grains were obtained on Ag/Si(100) substrate.Deposition rates are also different for different substrates as evaluated by the thickness of the films, which were obtained by SEM micrographs of the cross section of the films. At 750℃, similar polycrystalline Fe1-xS or Fe7S8 film was obtained. 相似文献
82.
83.
In this paper, we examine, both experimentally and theoretically, the kinetics of formation and microstructure of product
phases in thin film reactions, using the Nb/Al and Ti/Al systems as our prototypes. The results of calorimetry and microscopy
studies are interpreted using simple kinetic and morphology models. In particular, the kinetic models employed here focus
on the nucleation and growth components of the phase formation process and the morphology models provide a starting point
for the classification of product grain structures.
An erratum to this article is available at . 相似文献
84.
Chihiro J. Uchibori Y. Ohtani T. Oku Naoki Ono Masanori Murakami 《Journal of Electronic Materials》1997,26(4):410-414
Significant reduction of the contact resistance of In0.7Ga0.3As/Ni/W contacts (which were previously developed by sputtering in our laboratory) was achieved by depositing a W2N barrier layer between the Ni layer and W layer. The In0.7Ga0.3 As/Ni/W2N/W contact prepared by the radio-frequency sputtering technique showed the lowest contact resistance of 0.2 Ωmm after annealing
at 550°C for 10 s. This contact also provided a smooth surface, good reproducibility, and excellent thermal stability at 400°C.
The polycrystalline W2N layer was found to suppress the In diffusion to the contact surface, leading to improvement of the surface morphology and
an increase in the total area of the InxGa−As between metal and the GaAs substrate. These improvements are believed to reduce the contact resistance. 相似文献
85.
含三正辛胺微胶囊对六价铬的富集 总被引:5,自引:0,他引:5
本文将对六价铬有效的萃取剂TOA(三正辛胺)微胶囊化,制成填充柱型的酸性体系六价铬的富集分离装置。实验结果表明,微胶囊填充柱中每毫升TOA对六价铬的最大萃取容量为158.0g/mL,为纯TOA液相萃取的4.9倍。微胶囊经碱/水洗涤后,可再生使用。 相似文献
86.
87.
Kurt M. Anstreicher 《Mathematical Programming》1997,76(1):245-263
We consider the construction of small step path following algorithms using volumetric, and mixed volumetric-logarithmic, barriers.
We establish quadratic convergence of a volumetric centering measure using pure Newton steps, enabling us to use relatively
standard proof techniques for several subsequently needed results. Using a mixed volumetric-logarithmic barrier we obtain
an O(n
1/4
m
1/4
L) iteration algorithm for linear programs withn variables andm inequality constraints, providing an alternative derivation for results first obtained by Vaidya and Atkinson. In addition,
we show that the same iteration complexity can be attained while holding the work per iteration to O(n
2
m), as opposed to O(nm
2), operations, by avoiding use of the true Hessian of the volumetric barrier. Our analysis also provides a simplified proof
of self-concordancy of the volumetric and mixed volumetric-logarithmic barriers, originally due to Nesterov and Nemirovskii.
This paper was first presented at the 1994 Faculty Research Seminar “Optimization in Theory and Practice”, at the University
of Iowa Center for Advanced Studies. 相似文献
88.
89.
L.-H. Tang P. Smilauer D.D. Vvedensky 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(3):409-412
Two types of mechanisms are proposed for mound coarsening during unstable epitaxial growth: stochastic, due to deposition
noise, and deterministic, due to mass currents driven by surface energy differences. Both yield the relation H=(RWL)2 between the typical mound height W, mound size L, and the film thickness H. An analysis of simulations and experimental data shows that the parameter R saturates to a value which discriminates sharply between stochastic () and deterministic () coarsening. We derive a scaling relation between the coarsening exponent 1/z and the mound-height exponent which, for a saturated mound slope, yields .
Received: 11 November 1997 / Revised in final form: 28 November 1997 /
Accepted: 28 November 1997 相似文献
90.