全文获取类型
收费全文 | 220篇 |
免费 | 50篇 |
国内免费 | 41篇 |
专业分类
化学 | 110篇 |
晶体学 | 1篇 |
力学 | 15篇 |
综合类 | 1篇 |
数学 | 42篇 |
物理学 | 142篇 |
出版年
2023年 | 2篇 |
2021年 | 3篇 |
2020年 | 3篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2016年 | 5篇 |
2015年 | 3篇 |
2014年 | 6篇 |
2013年 | 27篇 |
2012年 | 2篇 |
2011年 | 13篇 |
2010年 | 9篇 |
2009年 | 8篇 |
2008年 | 9篇 |
2007年 | 14篇 |
2006年 | 15篇 |
2005年 | 10篇 |
2004年 | 8篇 |
2003年 | 12篇 |
2002年 | 30篇 |
2001年 | 13篇 |
2000年 | 17篇 |
1999年 | 4篇 |
1998年 | 6篇 |
1997年 | 7篇 |
1996年 | 12篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1978年 | 4篇 |
1976年 | 1篇 |
1972年 | 2篇 |
1970年 | 1篇 |
1967年 | 1篇 |
1966年 | 1篇 |
1965年 | 5篇 |
1964年 | 2篇 |
1963年 | 3篇 |
1959年 | 3篇 |
1957年 | 1篇 |
1955年 | 1篇 |
1948年 | 3篇 |
1947年 | 3篇 |
排序方式: 共有311条查询结果,搜索用时 15 毫秒
251.
252.
LEE Youngu 《中国科学B辑(英文版)》2011,(2)
Charge transport through single molecular neutral monoand di-cobalt(II) complexes with π-conjugated macromolecular wire was investigated.Scanning tunnelling spectroscopy (STS) studies revealed that the mono-cobalt(II) complex showed a pronounced rectifying effect with a large rectification ratio and finely featured NDR peaks,while the di-cobalt(II) complex showed a relatively symmetric electron transport without clear NDR peaks.Th 相似文献
253.
In this paper,we consider the existence,nonexistence and multiplicity of positive solutions for two-point boundary value problems of p-Laplacian systems which have a singular indefinite weight and real multiparameters.For proofs,we mainly make use of the upper and lower solution method and the fixed point index theorem.To obtain a global multiplicity result,we construct a weighted space to benefit richer topology of the solution space than C 0-space. 相似文献
254.
The average static third-order polarizabilities (γ) have been computed for the bowls and cages having the same number of carbon atoms. The bowls have higher (γ) than their corresponding cages. The dependence of (γ) on the average pyrimidalized angle (Θp) and maximal length L can be deduced. Near cages, having one open window (C72 isomers), are capped with C6 to generate five isolated pentagon rule (IPR) isomers of C78 fullerenes following a circumscribing algorithm. The (γ) values for the C78's and C72′s are correlated with (Θp) and L. The change in (γ) from C72′s to C78′s are correlated with a local parameter like the capped angle (α). 相似文献
255.
ABSTRACT. Many anadromous salmonid stocks in the Pacific Northwest are at their lowest recorded levels, which has raised questions regarding their long‐term persistence under current conditions. There are a number of factors, such as freshwater spawning and rearing habitat, that could potentially influence their numbers. Therefore, we used the latest advances in information‐theoretic methods in a two‐stage modeling process to investigate relationships between landscape‐level habitat attributes and maximum recruitment of 25 index stocks of chinook salmon (Onocorhynchus tshawy‐tscha) in the Columbia River basin. Our first‐stage model selection results indicated that the Ricker‐type, stock recruitment model with a constant Ricker a, i.e., recruits‐per‐spawner at low numbers of fish) across stocks was the only plausible one given these data, which contrasted with previous unpublished findings. Our second‐stage results revealed that maximum recruitment of chinook salmon had a strongly negative relationship with percentage of surrounding subwatersheds categorized as predominantly containing U.S. Forest Service and private moderate‐high impact managed forest. That is, our model predicted that average maximum recruitment of chinook salmon would decrease by at least 247 fish for every increase of 33% in surrounding subwatersheds categorized as predominantly containing U.S. Forest Service and privately managed forest. Conversely, mean annual air temperature had a positive relationship with salmon maximum recruitment, with an average increase of at least 179 fish for every increase in 2°C mean annual air temperature. 相似文献
256.
257.
PiaoPingYANG JianFengYU TongHaoWU GuoZongLIU TaeSunCHANG DongKooLEE DeugHeeCHO 《中国化学快报》2004,15(1):90-92
The urea decomposition property at high temperature has been used to control the pH value in the synthesis of layer compounds. The hydrotalcites of Mg-Al and Ni-Al with high crystallinity were synthesized by using this property. 相似文献
258.
Abstract— Quantum yields for luminol (3-aminophthalic hydrazide) chemiluminescence reactions fall into two classes depending on oxidizing conditions. In aprotic solvents the quantum yield is high and the excitation yield which allows for the fluorescence quantum yield of the product, is 0·09 and is unaffected by changes in solution temperature or polarity, or the presence of quenchers. In aqueous solution under optimum pH conditions (11–13), hydrogen peroxide oxidation results in a high chemiluminescence quantum yield with an excitation yield of 0·04 again unaffected by temperature, viscosity or quenchers. Other oxidizing conditions produce lower quantum yields probably by the introduction of competing chemical pathways. The luminol chemiluminescence light standard has been used to calibrate a spectrofluoro-meter with results in good agreement with the quantum yields of the ferrioxalate actinometer and the fluorescence of quinine sulfate and diphenylanthracene. 相似文献
259.
CHUNG ILL-Min ALl Mohd CHUN Se-Chul LEE Sun-Joo SAN Ka-Yiu CHRISTIE A. M. Peebles AHMAD Ateeque 《中国化学》2007,25(11):1695-1699
Two new compounds cadin-2-en-1β-ol-1β-D-glucuronopyranoside (1), guaia-l,7-dien-3β,13-diol-13α-D- glucofuranoside (2) along with three known compounds have been isolated from the culture hairy roots of Catharanthus roseus. Their structures have been elucidated with the help of 500 MHz NMR using 1D and 2D spectral methods: viz: ^1H and ^13C NMR, ^1H-^1H COSY, ^1H-^13C HETCOR and DEPT aided by ELMS, FAB-MS, HR-FABMS and IR spectroscopy. 相似文献
260.