全文获取类型
收费全文 | 29816篇 |
免费 | 872篇 |
国内免费 | 37篇 |
专业分类
化学 | 19539篇 |
晶体学 | 215篇 |
力学 | 616篇 |
综合类 | 1篇 |
数学 | 4828篇 |
物理学 | 5526篇 |
出版年
2023年 | 204篇 |
2022年 | 344篇 |
2021年 | 483篇 |
2020年 | 485篇 |
2019年 | 492篇 |
2018年 | 611篇 |
2017年 | 560篇 |
2016年 | 1146篇 |
2015年 | 887篇 |
2014年 | 931篇 |
2013年 | 1914篇 |
2012年 | 1915篇 |
2011年 | 1948篇 |
2010年 | 1249篇 |
2009年 | 1159篇 |
2008年 | 1730篇 |
2007年 | 1730篇 |
2006年 | 1500篇 |
2005年 | 1358篇 |
2004年 | 1212篇 |
2003年 | 973篇 |
2002年 | 824篇 |
2001年 | 629篇 |
2000年 | 578篇 |
1999年 | 423篇 |
1998年 | 315篇 |
1997年 | 276篇 |
1996年 | 370篇 |
1995年 | 267篇 |
1994年 | 287篇 |
1993年 | 243篇 |
1992年 | 241篇 |
1991年 | 222篇 |
1990年 | 206篇 |
1989年 | 180篇 |
1988年 | 171篇 |
1987年 | 156篇 |
1986年 | 160篇 |
1985年 | 237篇 |
1984年 | 230篇 |
1983年 | 145篇 |
1982年 | 147篇 |
1981年 | 160篇 |
1980年 | 168篇 |
1979年 | 111篇 |
1978年 | 119篇 |
1977年 | 112篇 |
1976年 | 101篇 |
1975年 | 102篇 |
1973年 | 86篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Rafael López 《Annals of Global Analysis and Geometry》1997,15(3):201-210
In this paper we study constant mean curvature compact surfaces with two Jordan curves in parallel planes as boundary and we investigate the point at which the surface inherits the symmetries of its boundary. 相似文献
2.
3.
V. Palyok I.A. Szabó D.L. Beke A. Kikineshi 《Applied Physics A: Materials Science & Processing》2002,74(5):683-687
Surface relief formation at holographic recording on amorphous selenium films was demonstrated and investigated. The presence
of this optical phase modulation component is essential for ensuring significant, stable and erasable optical recording in
a-Se films at 290–320 K temperatures, where conventional photodarkening was known as insignificant and unstable. Photocrystallization
can only be observed in super-exposed a-Se films at the given experimental conditions of hologram recording. Erasing behavior
of surface relief gratings under heat treatment was also investigated in order to reveal further details of the mechanism.
Photoinduced structural transformations within the amorphous phase, connected to local ordering under the condition of light-induced
fluidity, are proposed as an explanation for the relief formation and erasing. The observed reversible optical recording process
may be useful for the various optoelectronic applications of photoconductive a-Se layers.
Received: 12 June 2000 / Accepted: 6 June 2001 / Published online: 30 August 2001 相似文献
4.
Alcindo A. Dos Santos Renan S. Ferrarini Jefferson L. Princival João V. Comasseto 《Tetrahedron letters》2006,47(50):8933-8935
A masked lithium homoenolate, generated by tellurium/lithium exchange, was reacted with epoxides. The lithium compound was also converted into other organometallics such as Grignard, and cuprates and the reactivity of those organometallics with epoxides was evaluated. The same building block was employed in the synthesis of (+/−)-frontalin. 相似文献
5.
Gábor Dörnyei Marietta Bárczai-Beke Gábor Blaskó Péter Péchy Csaba Szántay 《Tetrahedron letters》1982,23(28):2913-2916
Regioselective demethylation of 3,4-dihydropapaveraldine (a) at 7 and 3' positions affords a properly substituted diphenolic key intermidiate (d) for the synthesis of reticuline and N-norreticuline. 相似文献
6.
Sauer, Shelah, Vapnik and Chervonenkis proved that if a set system on n vertices contains many sets, then the set system has full trace on a large set. Although the restriction on the size of the
groundset cannot be lifted, Frankl and Pach found a trace structure that is guaranteed to occur in uniform set systems even
if we do not bound the size of the groundset. In this note we shall give three sequences of structures such that every set
system consisting of sufficiently many sets contains at least one of these structures with many sets. 相似文献
7.
G. Tóth 《Journal of Radioanalytical and Nuclear Chemistry》1989,137(4):259-264
The distribution of mono- poly- and unlabelled protein molecules in the radiolabelling mixture was calculated from probability point of view as a function of the radioiodine/protein ratio. 相似文献
8.
In order to study the influence of seeded impurities on ITER like reactor operation the COREDIV code has been extended to include the transport of several sputtered and/or injected impurities. In the COREDIV code the core plasma is treated in the frame of 1D radial transport model whereas in the edge the 2D multifluid code EPIT is used. The EPIT code solves in the slab geometry the MHD equations for densities and velocities for all ions species as well as for electron and ion temperatures. The iteration scheme in the code leads to steady state solution of coupled core and SOL system. The numerical results for Carbon and Nickel plate and seeded impurities Silicon and Neon are presented. 相似文献
9.
Ana Luísa Daniel‐da‐Silva João Carlos Moura Bordado José Miguel Martín‐Martínez 《Journal of Polymer Science.Polymer Physics》2007,45(22):3034-3045
The degree of phase separation in several moisture‐cured poly(urethane urea)s (PUUs) was studied by FTIR spectroscopy, wide angle X‐ray diffraction (WAXD), and temperature‐modulated differential scanning calorimetry (TMDSC). This latter technique was shown to be particularly useful in analysing the degree of phase separation in PUU polymers. Both phase mixing and phase segregation coexisted in the PUUs and the degree of phase separation increased as the urea hard segment (HS) content in the PUU increased. The maximum solubility of urea HSs into the polyol soft segments (SSs) was achieved for 50 wt % urea HS content in diol‐based PUUs, whereas for triol‐based PUUs the highest solubility between HS and SS was reached for lower urea HS amount. Finally, the higher the urea HS content the higher the extent of phase separation in the PUU. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3034–3045, 2007 相似文献
10.
In order to reduce infant mortality in the municipality of Rio de Janeiro it is desired to encourage all mothers-to-be to attend the appropriate health care facilities. A 3-level hierarchical prenatal–neonatal health care system is described together with a basic model for optimising accessibility to facilities. A genetic algorithm to solve the basic model is developed and some numerical experience reported. Extensions to the basic model and planned future research are briefly indicated. 相似文献