全文获取类型
收费全文 | 442137篇 |
免费 | 5754篇 |
国内免费 | 2539篇 |
专业分类
化学 | 225947篇 |
晶体学 | 6864篇 |
力学 | 21282篇 |
综合类 | 77篇 |
数学 | 59138篇 |
物理学 | 137122篇 |
出版年
2019年 | 2567篇 |
2018年 | 11428篇 |
2017年 | 12340篇 |
2016年 | 8739篇 |
2015年 | 4727篇 |
2014年 | 5232篇 |
2013年 | 15365篇 |
2012年 | 15510篇 |
2011年 | 26188篇 |
2010年 | 16280篇 |
2009年 | 16301篇 |
2008年 | 23067篇 |
2007年 | 26419篇 |
2006年 | 12346篇 |
2005年 | 18260篇 |
2004年 | 13714篇 |
2003年 | 12137篇 |
2002年 | 10018篇 |
2001年 | 10826篇 |
2000年 | 8513篇 |
1999年 | 6589篇 |
1998年 | 5078篇 |
1997年 | 5041篇 |
1996年 | 5126篇 |
1995年 | 4603篇 |
1994年 | 4366篇 |
1993年 | 4141篇 |
1992年 | 4838篇 |
1991年 | 4701篇 |
1990年 | 4378篇 |
1989年 | 4406篇 |
1988年 | 4351篇 |
1987年 | 4296篇 |
1986年 | 4009篇 |
1985年 | 5667篇 |
1984年 | 5671篇 |
1983年 | 4665篇 |
1982年 | 4987篇 |
1981年 | 4818篇 |
1980年 | 4690篇 |
1979年 | 4810篇 |
1978年 | 5087篇 |
1977年 | 4830篇 |
1976年 | 4741篇 |
1975年 | 4582篇 |
1974年 | 4406篇 |
1973年 | 4577篇 |
1972年 | 2821篇 |
1968年 | 2588篇 |
1967年 | 2762篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
The magnified cross-section of the LDV probe volume fringe field created on a far screen (image plane) with an imaging lens is examined both analytically and experimentally. It is shown that measurements of the image plane fringe field can be used to quantitatively determine the fringe field existing within the probe volume. Because the fringe spacing in the magnified image is more accessible experimentally, both longitudinal- and lateral-coordinate variations in fringe spacing can be determined, permitting a complete mapping of the fringe field. The detailed knowledge of the fringe field thus obtained allows beam quality, alignment, and fringe uniformity to be evaluated with greater precision than is possible with other techniques.The authors would like to acknowledge C. F. Edwards and R. L. Schmitt for the loan of the beam profiler and for many helpful discussions. This work was performed at the Combustion Research Facility, Sandia National Laboratories, and was supported by the U.S. Department of Energy, Office of Industrial Technologies, Advanced Industrial Concepts Division. 相似文献
962.
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
963.
P. C. Morais A. C. Oliveira V. K. Garg M. L. Silva E. F. C. Alcântara F. Q. Soares D. Rabelo 《Hyperfine Interactions》2007,177(1-3):51-56
We have used time-differential perturbed angular correlation (PAC) spectroscopy with 181Ta-probes to study the electric field gradient at Zr-sites in synthetic zircon and hafnon between room temperature and 1,200°C. PAC spectra are similar to those obtained from naturally occurring zircons. In particular, a change in slope of the quadrupole coupling vs. temperature is observed in the synthetic zircon at the same temperature as seen in natural zircons from the Mud Tank carbonatite (Australia). The synthetic hafnon data also shows this feature but at somewhat higher temperature. Low-temperature PAC spectra of both synthetic zircon and hafnon have a clearly reduced anisotropy. We believe that the cause for this is a electronic defect, possibly created during the β-decay of the probe parent nucleus. 相似文献
964.
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
965.
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
966.
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
967.
Jean-Marc Hérard 《Comptes Rendus Mathematique》2006,342(10):779-784
We introduce a hyperbolic entropy-consistent model to describe three-phase flows, which ensures that void fractions, mass fractions and pressures remain positive through single waves occurring in the one dimensional solution of the Riemann problem. To cite this article: J.-M. Hérard, C. R. Acad. Sci. Paris, Ser. I 342 (2006). 相似文献
968.
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
969.
We fabricated high-quality InAlN/GaN heterostructures by metal–organic vapor phase epitaxy (MOVPE). X-ray diffraction measurements revealed that InAlN/GaN heterostructures grown under optimal conditions have flat surfaces and abrupt heterointerfaces. Electron mobility from 1200 to 2000 cm2/V s was obtained at room temperature. To our knowledge, this mobility is the highest ever reported for InAlN/GaN heterostructures. We also investigated the relationship between the Al composition and sheet electron density (Ns) for the first time. Ns increased from 1.0×1012 to 2.7×1013 cm−2 when the Al composition increased from 0.78 to 0.89. 相似文献
970.