全文获取类型
收费全文 | 411419篇 |
免费 | 4304篇 |
国内免费 | 1097篇 |
专业分类
化学 | 204474篇 |
晶体学 | 5920篇 |
力学 | 19436篇 |
综合类 | 7篇 |
数学 | 59494篇 |
物理学 | 127489篇 |
出版年
2020年 | 1983篇 |
2019年 | 1956篇 |
2018年 | 10974篇 |
2017年 | 11853篇 |
2016年 | 7907篇 |
2015年 | 4153篇 |
2014年 | 4549篇 |
2013年 | 14102篇 |
2012年 | 15026篇 |
2011年 | 25631篇 |
2010年 | 15521篇 |
2009年 | 15444篇 |
2008年 | 22726篇 |
2007年 | 26290篇 |
2006年 | 12388篇 |
2005年 | 18266篇 |
2004年 | 13570篇 |
2003年 | 12171篇 |
2002年 | 10044篇 |
2001年 | 10258篇 |
2000年 | 7980篇 |
1999年 | 6151篇 |
1998年 | 4935篇 |
1997年 | 4751篇 |
1996年 | 4915篇 |
1995年 | 4451篇 |
1994年 | 4191篇 |
1993年 | 4004篇 |
1992年 | 4492篇 |
1991年 | 4356篇 |
1990年 | 4071篇 |
1989年 | 3897篇 |
1988年 | 4199篇 |
1987年 | 3861篇 |
1986年 | 3736篇 |
1985年 | 5395篇 |
1984年 | 5484篇 |
1983年 | 4449篇 |
1982年 | 4824篇 |
1981年 | 4866篇 |
1980年 | 4621篇 |
1979年 | 4751篇 |
1978年 | 4763篇 |
1977年 | 4670篇 |
1976年 | 4651篇 |
1975年 | 4553篇 |
1974年 | 4399篇 |
1973年 | 4603篇 |
1972年 | 2594篇 |
1971年 | 1896篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
In this paper we propose time-optimal convex hull algorithms for two classes of enhanced meshes. Our first algorithm computes the convex hull of an arbitrary set ofn points in the plane inO (logn) time on a mesh with multiple broadcasting of sizen×n. The second algorithm shows that the same problem can be solved inO (1) time on a reconfigurable mesh of sizen×n. Both algorithms achieve time lower bounds for their respective model of computation.This work was supported by NASA under grant NCCI-99.Additional support by the National Science Foundation under grant CCR-8909996 is gratefully acknowledged. 相似文献
942.
943.
J.-M. Colmont B. Bakri G. Wlodarczak G. Cazzoli C. Puzzarini 《Journal of Molecular Spectroscopy》2005,231(2):171-187
For atmospheric purposes, the N2- and O2-, or Air-broadenings of selected transitions of ozone have been investigated in the 195-300 K temperature range. More precisely, the following 13 transitions in the 280-345 GHz frequency range have been studied: the 22,0 ← 21,1 (279.5 GHz), 242,22 ← 241,23 (286.2 GHz), 32,2 ← 31,3 (286.3 GHz), 52,4 ← 51,5 (293.2 GHz), 134,10 ← 143,11 (300.7 GHz), 140,14 ← 131,13 (301.8 GHz), 72,6 ← 71,7 (303.2 GHz), 262,24 ← 261,25 (315.9 GHz), 53,3 ← 62,4 (317.2 GHz), 201,19 ← 200,20 (320.0 GHz), 266,20 ← 275,23 (343.2 GHz), 262,24 ← 253,23 (343.2 GHz), and 43,1 ← 52,4 (343.5 GHz) lines. Systematic errors are known to be the principal error source and recent intercomparisons of line-broadening coefficients showed differences up to 20%, thus a large effort in minimizing systematic error sources has been taken and cross check measurements with different techniques have been carried out. The conclusion of the intercomparison performed indicates an excellent agreement of the results and that an uncertainty less than 3%, which also takes into account the systematic errors, can be claimed for the line-broadening parameters. 相似文献
944.
Vasily L. Morgunov 《Pramana》2007,69(6):1097-1100
A new calorimeter energy calibration method was developed for the proposed ILC detectors. The method uses the center-of-mass
energy of the accelerator as the reference. It has been shown that using the energy conservation law it is possible to make
ECAL and HCAL cross calibration to reach a good energy resolution for the simple calorimeter energy sum.
相似文献
945.
F. Rubio F. García H. D. Burrows A. A. C. C. Pais A. J. M. Valente M. J. Tapia J. M. García 《Journal of polymer science. Part A, Polymer chemistry》2007,45(9):1788-1799
The interaction between trivalent lanthanide ions and poly(1,4,7,10,13‐pentaoxacyclopentadecan‐2‐yl‐methyl methacrylate), PCR5, in aqueous solution and in the solid state have been studied. In aqueous solution, evidence of a weak interaction between the lanthanides and PCR5 comes from the small red shift of the Ce(III) emission spectra and the slight broadening of the Gd(III) EPR spectra. From the Tb(III) lifetimes in the presence of H2O and D2O the loss of one or two water coordinated molecules is confirmed when Tb(III) is bound to PCR5. An association constant of the order of 200 M?1 was obtained for a 1:1 (lanthanide:15‐crown‐5) complex from the shift of the polymer NMR signals induced by Tb(III). A similar association constant is obtained from the differences of the molar conductivity of Ce(III) solution at various concentrations in presence and absence of PCR5. When Tb(III) is adsorbed on PCR5 membranes, lifetime experiments in H2O and D2O confirm the loss of 5 or 6 water coordinated molecules indicating that in solid state the lanthanide(III)‐PCR5 interaction is stronger than in solution. The adsorption of Ce(III) in PCR5 membranes shows a Langmuir type isotherm, from which an equilibrium constant of 39 M?1 has been calculated. SEM shows that the membrane morphology is not much affected by lanthanide adsorption. Support for lanthanide ion–crown interactions comes from ab initio calculations on 15‐crown‐5/La(III) complex. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1788–1799, 2007 相似文献
946.
947.
I. V. Gaishun 《Proceedings of the Steklov Institute of Mathematics》2006,255(2):S47-S53
For a linear nonautonomous system with one output, the existence conditions for an identifier that estimates the current state with exponential rate are established. An algorithm for constructing such an identifier is described and its dependence on small perturbations of coefficients is studied. 相似文献
948.
This Note deals with optimal control problems with only one control variable and one state constraint, of arbitrary order. We consider the case of finitely many boundary arcs and touch times. We obtain a no-gap theory of second-order conditions, allowing us to characterize second-order quadratic growth. To cite this article: J.F. Bonnans, A. Hermant, C. R. Acad. Sci. Paris, Ser. I 343 (2006). 相似文献
949.
J.H. Sung J.Y. Park T. Imran Y.S. Lee C.H. Nam 《Applied physics. B, Lasers and optics》2006,82(1):5-8
Optical pulses with 1.1-mJ energy and 5.5-fs duration have been generated at 1-kHz repetition rate from a chirped pulse amplification
Ti:Sapphire laser incorporating a differentially pumped hollow-fiber chirped-mirror compressor. The effects of self-focusing
and multi-photon ionization during the beam propagation were minimized by differentially pumping the hollow fiber filled with
neon. The spectral broadening at the hollow-fiber compressor was optimized by adjusting gas pressure, laser intensity, and
laser chirp, covering from 540 nm to 950 nm.
PACS 42.65.Jx; 42.65.Re 相似文献
950.
Christopher Batchelor-McAuley Craig E Banks Andrew O Simm Timothy G J Jones Richard G Compton 《Chemphyschem》2006,7(5):1081-1085
The benefits of using nanoparticle-modified electrodes are exemplified through the electrochemical detection of protons and/or hydrogen. It is shown that a palladium-nanoparticle-modified boron-doped diamond allows voltammetric information relating to the relative roles played by the surface and the bulk metal to be obtained for the proton-hydrogen system at palladium surfaces which is not accessible using palladium macroelectrodes or microelectrodes. 相似文献