全文获取类型
收费全文 | 463篇 |
免费 | 30篇 |
国内免费 | 32篇 |
专业分类
化学 | 370篇 |
晶体学 | 1篇 |
力学 | 9篇 |
综合类 | 1篇 |
数学 | 24篇 |
物理学 | 120篇 |
出版年
2022年 | 2篇 |
2021年 | 4篇 |
2019年 | 15篇 |
2018年 | 5篇 |
2017年 | 3篇 |
2016年 | 10篇 |
2015年 | 6篇 |
2014年 | 11篇 |
2013年 | 19篇 |
2012年 | 29篇 |
2011年 | 17篇 |
2010年 | 13篇 |
2009年 | 19篇 |
2008年 | 20篇 |
2007年 | 9篇 |
2006年 | 14篇 |
2005年 | 18篇 |
2004年 | 20篇 |
2003年 | 9篇 |
2002年 | 15篇 |
2001年 | 19篇 |
2000年 | 24篇 |
1999年 | 23篇 |
1998年 | 18篇 |
1997年 | 8篇 |
1996年 | 9篇 |
1995年 | 12篇 |
1994年 | 13篇 |
1993年 | 15篇 |
1992年 | 19篇 |
1991年 | 13篇 |
1990年 | 9篇 |
1989年 | 12篇 |
1988年 | 8篇 |
1987年 | 5篇 |
1986年 | 11篇 |
1985年 | 9篇 |
1982年 | 3篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1958年 | 1篇 |
1943年 | 1篇 |
1937年 | 2篇 |
1936年 | 4篇 |
排序方式: 共有525条查询结果,搜索用时 31 毫秒
31.
32.
信息的不确定性是由于模糊性、随机性、不完全性、不精确性等因素造成的,不确定性信息在现实世界中广泛存在.关于这方面的研究主要集中在模糊性这种不确定性上.我们课题组在此领域的研究已经持续20余年,概括起来讲,早期的研究兴趣在于模糊(非可加)测度与积分的理论建立,主要研究了传统的可加测度与积分理论到非可加情况的推广;尔后的兴趣转向为如何用数值方法确定非可加测度;近期的研究兴趣在于从已有数据中获取模糊控制规则以及具有模糊表示的归纳学习问题.近10年的研究曾得到了多项基金项目资助,出版专著3部,发表学术论文100余篇,30余篇被SCI收录,20余篇被EI收录,省级以上奖励3项.以下是我们近期研究工作的一个总结,主要包括模糊决策树归纳;基于模糊信息的决策表简化;产生模糊规则的扩张矩阵算法;模糊归纳学习在其他领域中的应用;基于示例学习的模糊控制等. 相似文献
33.
Zakir Murtaza Leah Tolosa Peter Harms Joseph R. Lakowicz 《Journal of fluorescence》2002,12(2):187-192
We describe a new approach to optical sensing of glucose based on the competitive interactions between a ruthenium metal ligand complex, a boronic acid derivative and glucose. The metal-ligand complex [Ru(2,2-bipyridine)2(5,6-dihydroxy-1,10-phenanthroline)](PF6)2 at pH 8 forms a reversible complex with 2-toluylboronic acid or 2-methoxyphenyl boronic acid. Complexation is accompanied by a several-fold increase in the luminescent intensity of the ruthenium complex. Addition of glucose results in decreased luminescent intensity, which appears to be the result of decreased binding between the metal-ligand complex and the boronic acid. Ruthenium metal-ligand complexes are convenient for optical sensing because their long luminescent decay times allow lifetime-based sensing with simple instrumentation. 相似文献
34.
The N-alkoxycarbonyl substituted 2,3-dihydropyrroles 3 and 8 are converted to 2-benzyl-3-pyrrolidinols by the Paternò - Büchi reaction followed by hydrogenolysis. Since the addition of the photoexcited benzaldehyde at the unsaturated heterocycle proceeds in a syn fashion, the benzyl group at C-2 and the hydroxy group at C-3 of the product are cis oriented. The simple and facial diastereoselectivities of the Paternò-Büchi reaction were studied more closely and the relative configuration of the products was elucidated. The thermodynamically less stable endo product is formed as a result of simple diastereoselection. The face differentiation in 2-substituted 2,3-dihydropyrroles is presumably due to the nonplanarity of these heterocycles, which forces attack of the carbonyl group on the face with the existing substituent. All-cis-pyrrolidinols are consequently formed after hydrogenolysis. Following this route, a total synthesis of the pyrrolidinol alkaloid (+)-preussin (1) was conducted, which yielded the target compound in a total yield of 11% over nine steps starting from L-pyroglutaminol (11). 相似文献
35.
Zusammenfassung Spuren der Elemente Bi, Cd, Cu, Co, In, Ni, Pb, Tl und Zn können aus Wasserproben (Seewasser, Mineralwasser, Trinkwasser u.a.) nach Komplexierung mit APDTC durch einen einfachen Filtationsschritt über ein mit Aktivkohle beschichtetes Filter aus 100 ml bis 10l Probevolumen abgetrennt und angereichert werden. Bei der Bestimmung der angereicherten Elementspuren mit der Flammen-AAS oder der ICP/OES werden Nachweisgrenzen < 1 g/l erhalten. Die relativen Standardabweichungen betragen für Elementspuren-Konzentrationen im unteren g/l-Bereich für das Gesamtverfahren mit beiden Bestimmungsmethoden im allgemeinen weniger als 4%.
Herrn Prof. Dr. H. Monien zum 60. Geburtstag gewidmet. 相似文献
Multielement trace preconcentration from water on activated carbon for the sample pretreatment for atomic spectroscopy (flame-AAS, ICP/OES)
Summary It is possible to separate traces of the elements Bi, Cd, Cu, Co, In, Ni, Pb, Tl and Zn from water samples (sea water, mineral water, drinking water) of 100 ml–10 lsample volume, by employing the complexing agent APDTC and a simple filtration step via an activated carbon-lined filter. On determination of the preconcentrated element traces with flame-AAS or ICP/OES techniques, detection limits of <1 g/l are obtained. Generally, relative standard deviations with respect to the entire analysis are for both determination methods 4% when element trace concentrations in the lower 1 g/l range are concerned.
Herrn Prof. Dr. H. Monien zum 60. Geburtstag gewidmet. 相似文献
36.
G. Alexander L. Criegee H.C. Dehne K. Derikum R. Devenish G. Flügge G. Franke Ch. Gerke E. Hackmack P. Harms G. Horlitz Th. Kahl G. Knies E. Lehmann R. Schmitz U. Timm P. Waloschek K. Wacker 《Physics letters. [Part B]》1978,78(1):162-166
The decay of the heavy lepton τ into πv has been established using the magnetic detector PLUTO. The branching ratio is determined to be BR(τ→πv)=(9.0 ± 2.9)% with an additional systematic uncertainty of 2.5%. This value is in good agreement with the theoretical prediction. 相似文献
37.
38.
39.
E. Michalski J. Pieper J. Harms K. F. Jahr O. Tomiek und J. Feldmann 《Fresenius' Journal of Analytical Chemistry》1936,104(1-2):39-40
Ohne Zusammenfassung 相似文献
40.
JEONG-HAN KANG SEUNG-YEAL HA KYUNGKEUN KANG EUNHEE JEONG 《The Journal of mathematical sociology》2014,38(1):47-71
When cultural tastes are not neutral but hierarchically matched to social status, people assimilate themselves to higher status by consuming cultural goods while distinguishing themselves from lower status by developing new tastes. Extending the Cucker-Smale model for mutual influence among agents, we examine when and how many cultural classes emerge from continuous distributions of tastes and what conditions those classes satisfy, through the assimilation-distinction mechanism. We simulate the models with different initial distributions of tastes (uniform, normal, and chi-square), given various ranges of 2 parameters: (a) the strength and (b) the range of distinction relative to assimilation. Tastes are flocking and cultural classes emerge when the range of assimilation is much larger than that of distinction. The number of classes increases with the strength of distinction, whereas the distance between classes equals the range of distinction. Some properties of emergent classes are mathematically proved. First, in a two-class system, the stronger distinction, the larger the upper class. Second, in a three-class system, the middle class is necessarily larger than the lower class and likely larger than the upper class. Third, a 3-class system cannot emerge if distinction is weaker than assimilation. These properties are universal and do not depend on the initial distribution of cultural tastes. This independence predicts homogeneous cultural classes emerging across different social conditions. Also, the cultural middle class as the largest group may explain why subjective class consciousness is often higher than objective position. Unless assimilating efforts can reach an infinite range, there emerges a cultural outcast at the lowest end of the cultural hierarchy. 相似文献