全文获取类型
收费全文 | 6496篇 |
免费 | 873篇 |
国内免费 | 463篇 |
专业分类
化学 | 2357篇 |
晶体学 | 5篇 |
力学 | 583篇 |
综合类 | 112篇 |
数学 | 2634篇 |
物理学 | 2141篇 |
出版年
2024年 | 25篇 |
2023年 | 98篇 |
2022年 | 158篇 |
2021年 | 146篇 |
2020年 | 195篇 |
2019年 | 197篇 |
2018年 | 200篇 |
2017年 | 253篇 |
2016年 | 236篇 |
2015年 | 242篇 |
2014年 | 279篇 |
2013年 | 533篇 |
2012年 | 404篇 |
2011年 | 406篇 |
2010年 | 329篇 |
2009年 | 358篇 |
2008年 | 417篇 |
2007年 | 444篇 |
2006年 | 368篇 |
2005年 | 355篇 |
2004年 | 287篇 |
2003年 | 282篇 |
2002年 | 263篇 |
2001年 | 182篇 |
2000年 | 216篇 |
1999年 | 171篇 |
1998年 | 112篇 |
1997年 | 109篇 |
1996年 | 107篇 |
1995年 | 78篇 |
1994年 | 55篇 |
1993年 | 44篇 |
1992年 | 53篇 |
1991年 | 56篇 |
1990年 | 34篇 |
1989年 | 26篇 |
1988年 | 15篇 |
1987年 | 21篇 |
1986年 | 14篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 11篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1977年 | 2篇 |
1971年 | 2篇 |
1957年 | 2篇 |
1936年 | 2篇 |
排序方式: 共有7832条查询结果,搜索用时 15 毫秒
11.
Boris Goldfarb 《Topology and its Applications》2004,140(2-3):267-294
New compactifications of symmetric spaces of noncompact type X are constructed using the asymptotic geometry of the Borel–Serre enlargement. The controlled K-theory associated to these compactifications is used to prove the integral Novikov conjecture for arithmetic groups. 相似文献
12.
高智民 《纯粹数学与应用数学》1994,10(2):1-5
本文证明了:若X是K-半分层空间,f是闭映射,则f(X)是K-半分层空间,这一结果推广改进了Lutzer与高国士的有关结果。 相似文献
13.
On‐line coupling of LC and ICP‐MS has been used for fractionation and detection of species of Cu, Fe, I, Se and Zn in human serum. It has been shown that anion exchange chromatography provided better separation capability (both intra‐ and inter‐element) than size‐exclusion chromatography. The mobile phases for ion exchange chromatography consisted of Tris–HNO3 buffer and ammonium salt (nitrate, acetate or formate). Formate was found to be the best mobile phase counter ion, enabling good chromatographic separation, and is acceptable for mass spectrometry too. The quantitative evaluation of element concentrations adhering to individual fractions was performed by the peak area normalization method. The repeatability of results ranged from 3 to 15% (depending on the element concentration level) and represented the main part of the result uncertainty. The accuracy of Cu and Zn fraction determinations was confirmed by comparison with the isotope dilution technique. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
14.
Frank H.G.M. Wijnands Charles G. Crookes Paul M. Charles Richard M. Ash Ian F. Lealman Michael J. Robertson Anthony E. Kelly Kevin A. Williams Aeneas B. Massara Richard V. Penty Ian H. White 《Optical and Quantum Electronics》2002,34(10):959-973
An anomalous modulation in the wavelength spectrum has been observed in lasers with spot-size converters. This intensity modulation is shown to be caused by beating between the fundamental lasing mode and radiation modes in the taper. This results in a periodic modulation in the net gain spectrum, which causes wavelength jumps between adjacent net gain maxima, and a drive current dependent spectral width that is expected to affect system performance. The amplitude of this spectral modulation is reduced significantly by either using an angled rear-facet which reflects the beating radiation modes away from the laser axis, or by using a nonlinear, adiabatic taper. 相似文献
15.
16.
A planar map is a 2-cell embedding of a connected planar graph, loops and parallel edges allowed, on the sphere. A plane map is a planar map with a distinguished outside (“infinite”) face. An unrooted map is an equivalence class of maps under orientation-preserving homeomorphism, and a rooted map is a map with a distinguished oriented edge. Previously we obtained formulae for the number of unrooted planar n-edge maps of various classes, including all maps, non-separable maps, eulerian maps and loopless maps. In this article, using the same technique we obtain closed formulae for counting unrooted plane maps of all these classes and their duals. The corresponding formulae for rooted maps are known to be all sum-free; the formulae that we obtain for unrooted maps contain only a sum over the divisors of n. We count also unrooted two-vertex plane maps. 相似文献
17.
We propose iteration methods for solving the Dirichlet problem in domains with involved geometry. Such problems arise in relation to the problem of optimizing quantum dot and antidot infrared detectors. We estimate the deviation of an approximate solution from the exact solution. 相似文献
18.
Let X be a metric space, B the σ-algebra of Borel subsets of X, and μ a probability measure on (X,B). In this note, for a measure-preserving map T (respectively a measure-preserving semi-flow φ) on (X,B,μ), we prove that if suppμ=X, and T (respectively φ) is weak-mixing, then T (respectively φ) has sensitive dependence. 相似文献
19.
20.
Uptake of trace elements into fish otoliths is governed by several factors such as life histories and environment in addition to stock and species differences. In an attempt to elucidate the elemental signatures of rare earth elements (REEs) in otoliths, a solid phase extraction (SPE) protocol was used in combination with electrothermal vaporization (ETV) as a sample introduction procedure for the determinations by inductively coupled plasma quadrupole mass spectrometry (ICP-MS). Effects of various parameters, such as carrier gas flow rate, atomization temperature and chemical modification, were examined for optimization of the conditions by ETV-ICP-MS. Atomization was achieved at 2800 °C. Lower temperatures (i.e. 2600 °C) resulted in severe memory problems due to incomplete atomization. Palladium was used as a chemical modifier. It was found that an increase in Pd concentration up to 0.5 μg in the injection volume (70 μl) led up to four-fold enhancement in the integrated signals. This phenomenon is attributed to the carrier effect of Pd rather than the stabilization since no significant losses were observed for high temperature drying around 700 °C even in the absence of Pd. Preconcentration was performed on-line at pH 5 by using a mini-column of Toyopearl AF-Chelate 650M chelating resin, which also eliminated the calcium matrix of otolith solutions. After preconcentration of 6.4 ml of solution, the concentrate was collected in 0.65 ml of 0.5% (v/v) HNO3 in autosampler cups, and then analyzed by ETV-ICP-MS. The method was validated with the analysis of a fish otolith certified reference material (CRM) of emperor snapper, and then applied to samples. Results obtained from otoliths of fish captured in the same habitat indicated that otolith rare earth element concentrations are more dependent on environmental conditions of the habitat than on species differences. 相似文献