全文获取类型
收费全文 | 61168篇 |
免费 | 1833篇 |
国内免费 | 166篇 |
专业分类
化学 | 37803篇 |
晶体学 | 376篇 |
力学 | 995篇 |
综合类 | 5篇 |
数学 | 11216篇 |
物理学 | 12772篇 |
出版年
2023年 | 394篇 |
2022年 | 604篇 |
2021年 | 828篇 |
2020年 | 885篇 |
2019年 | 910篇 |
2018年 | 1138篇 |
2017年 | 1073篇 |
2016年 | 2044篇 |
2015年 | 1712篇 |
2014年 | 1744篇 |
2013年 | 3775篇 |
2012年 | 3658篇 |
2011年 | 3670篇 |
2010年 | 2452篇 |
2009年 | 2181篇 |
2008年 | 3232篇 |
2007年 | 3040篇 |
2006年 | 2739篇 |
2005年 | 2676篇 |
2004年 | 2258篇 |
2003年 | 1918篇 |
2002年 | 1655篇 |
2001年 | 1283篇 |
2000年 | 1227篇 |
1999年 | 888篇 |
1998年 | 696篇 |
1997年 | 642篇 |
1996年 | 806篇 |
1995年 | 578篇 |
1994年 | 657篇 |
1993年 | 610篇 |
1992年 | 619篇 |
1991年 | 525篇 |
1990年 | 565篇 |
1989年 | 461篇 |
1988年 | 455篇 |
1987年 | 438篇 |
1986年 | 413篇 |
1985年 | 547篇 |
1984年 | 525篇 |
1983年 | 404篇 |
1982年 | 407篇 |
1981年 | 414篇 |
1980年 | 364篇 |
1979年 | 334篇 |
1978年 | 314篇 |
1977年 | 314篇 |
1976年 | 324篇 |
1974年 | 284篇 |
1973年 | 305篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
The electron impact ionization mass spectra of o-, m- and p-bis(1,4-dithiafulven-6-yl)benzenes were studied by means of accurate mass measurements, metastable analysis and collision-induced dissociation. Differences observed in the spectra of the ortho isomers are due to a cyclization reaction leading to molecular ions with the same structure as those generated from certain cyclic compounds, as confirmed by comparison of linked scans at constant B/E of metastable and collisionally activated molecular ions. Parallels of this cyclization of molecular ions with their electrochemical or acid-induced isomerization are also discussed. 相似文献
172.
Reduced charge montmorillonites (RCM) were prepared by the thermal treatment of lithiumsaturated montmorillonite. Samples prepared by mild thermal treatment with lithium contained more water sorbed than the original montmorrilonite. When RCMs were prepared, part of the lithium cations reacted with hydroxyl groups in the octahedral sheet and released protons, which reacted with the structure. Acid treatment probably enhanced the surface area. which was reflected in the amount of water sorbed. Deprotonation of hydroxyl groups was proved by the measurements of the ignition loss. The heating of lithium saturated montmorillonite at higher temperatures brough about the collapse of the interlayers and a decrease in the amount of water sorbed. 相似文献
173.
Oxyethylene macrocyclic compounds (crown-ethers) act as ligands of intracrystalline cations of certain layered silicates as montmorillonites. Stable intercalation materials are formed which are used to prepare organic-inorganic membranes by encapsulating these intercalation compounds with a poly-butadiene thin coating. Electrochemical Impedance Spectroscopy (EIS) is used to study the resulting composite membranes in contact with aqueous electrolytes. From the impedance plots, the ionic resistance of the membranes is obtained. The thickness of the polybutadiene coating is an important factor determining the ability of ions to pass across the membrane. Marked differences in the ionic resistance are observed as a function of the nature of the interlayer macrocyclic compound. For non-intercalated montmorillonite membranes, the ionic resistance is strongly reduced, whereas for some crown-ether intercalated materials such as 18-crown-6 and dibenzo 24-crown-8, iono-selective membranes are obtained. Concerning the nature of the electrolyte, cations exhibiting greater hydration energies show higher difficulties to pass through the membrane and, consequently, the ionic resistance increases. 相似文献
174.
175.
Tibor Cserháti 《Analytical and bioanalytical chemistry》1994,349(10-11):751-755
The interaction between 23 anticancer drugs and acetyl-β-cyclodextrin (acetyl-β-CD) was studied by reversed-phase charge-transfer thin-layer chromatography and the relative strength of interaction was calculated. Acetyl-β-CD formed inclusion complexes with 16 compounds, the complex always being more hydrophilic than the uncomplexed drug. The inclusion forming capacity of drugs differed considerably according to their chemical structure. The significant linear correlation between the hydrophobicity and specific hydrophobic surface area of anticancer drugs indicated that they can be considered as a homologous series of compounds, however, their chemical structures are highly different. 相似文献
176.
The Gaussian property of the Brownian bridge is characterized as an application of Ramachandran's theorem in terms of the independence of the random variables that appear in the Karhunen-Loéve expansion of the process. A reference about the construction of the Brownian bridge by means of functional transformations is also included. 相似文献
177.
Domokos Szász 《Communications in Mathematical Physics》1992,145(3):595-604
TheK-property is demonstrated for a class of planar billiards satisfying Wojtkowski's principles. Their boundary may consist of convex-scattering, concave and linear pieces. Earlier Wojtkowski showed that these billards had non-zero Lyapunov exponents. 相似文献
178.
Angla Schwartz Lszl Szab Katalin Pusztay-Szab Istvn Hermecz Zoltn Mszros 《Journal of heterocyclic chemistry》1987,24(3):655-660
Ultraviolet-visible spectra of 4-oxo 1 and 4-imino 2 quinolizines or their monocyclic tautomers 3, 4 have been studied in neutral, acidic and basic ethanolic solution as well as in dimethyl sulfoxide and chloroform. Ring B of 4-oxo and 6-unsubstituted 4-imino compounds can be cleaved by sodium ethanolate more or less easily. Ring B of 6-methyl-4-iminoquinolizines is very unstable and they are present mainly in the monocyclic form which are partly dissociated in ethanol and dimethyl sulfoxide especially in higher dilution or in the presence of sodium ethanolate. In dilute acidic ethanol or chloroform, the dissociation is suppressed and in the latter solvent and in some cases, absorption bands can be observed due to a small amount of the 4-imino-6-methylquinolizines. In acidic solution of compounds 3B=C, 3D, 4E, 4F=G having simultaneously cyano and ethoxycarbonyl groups in 1 and 3 position, not simple reprotonation occurs but irreversible changes can be observed. 相似文献
179.
Jürgen Kurths M. Carmen Romano Marco Thiel Grigory V. Osipov Mikhail V. Ivanchenko István Z. Kiss John L. Hudson 《Nonlinear dynamics》2006,44(1-4):135-149
We present two different approaches to detect and quantify phase synchronization in the case of coupled non-phase coherent
oscillators. The first one is based on the general idea of curvature of an arbitrary curve. The second one is based on recurrences
of the trajectory in phase space. We illustrate both methods in the paradigmatic example of the R?ssler system in the funnel
regime. We show that the second method is applicable even in the case of noisy data. Furthermore, we extend the second approach
to the application of chains of coupled systems, which allows us to detect easily clusters of synchronized oscillators. In
order to illustrate the applicability of this approach, we show the results of the algorithm applied to experimental data
from a population of 64 electrochemical oscillators. 相似文献
180.
Katalytische Epoxidierung und 1,2‐Dihydroxylierung von Olefinen mit Bispidin‐Eisen(II)/H2O2‐Systemen