全文获取类型
收费全文 | 22303篇 |
免费 | 813篇 |
国内免费 | 16篇 |
专业分类
化学 | 14686篇 |
晶体学 | 170篇 |
力学 | 372篇 |
数学 | 3795篇 |
物理学 | 4109篇 |
出版年
2023年 | 148篇 |
2022年 | 148篇 |
2021年 | 235篇 |
2020年 | 328篇 |
2019年 | 349篇 |
2018年 | 457篇 |
2017年 | 408篇 |
2016年 | 836篇 |
2015年 | 649篇 |
2014年 | 685篇 |
2013年 | 1463篇 |
2012年 | 1419篇 |
2011年 | 1423篇 |
2010年 | 867篇 |
2009年 | 799篇 |
2008年 | 1254篇 |
2007年 | 1299篇 |
2006年 | 1150篇 |
2005年 | 1060篇 |
2004年 | 955篇 |
2003年 | 740篇 |
2002年 | 646篇 |
2001年 | 495篇 |
2000年 | 463篇 |
1999年 | 341篇 |
1998年 | 229篇 |
1997年 | 222篇 |
1996年 | 292篇 |
1995年 | 207篇 |
1994年 | 236篇 |
1993年 | 197篇 |
1992年 | 195篇 |
1991年 | 179篇 |
1990年 | 171篇 |
1989年 | 153篇 |
1988年 | 143篇 |
1987年 | 139篇 |
1986年 | 134篇 |
1985年 | 196篇 |
1984年 | 198篇 |
1983年 | 124篇 |
1982年 | 131篇 |
1981年 | 141篇 |
1980年 | 140篇 |
1979年 | 96篇 |
1978年 | 95篇 |
1977年 | 104篇 |
1976年 | 83篇 |
1975年 | 86篇 |
1973年 | 71篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Manuel Fernández-López Eduardo García-Río Demir N. Kupeli 《Annals of Global Analysis and Geometry》2002,21(1):1-13
A characterization of time functions on a spacetime is made by using theMöbius equation. It is shown that a time function characterized in this wayyields past timelike geodesic incompleteness and local Lorentzian warpedproduct decomposition of spacetime, provided that the stress-energy tensoris a fluid. Also, by imposing additional assumptions on the stress-energytensor and global analytic structure of the spacetime, more restrictivedecompositions closer to Robertson–Walker spacetimes are obtained. 相似文献
92.
R. López-Martens J. Mauritsson P. Johnsson K. Varjú A. L’Huillier W. Kornelis J. Biegert U. Keller M. Gaarde K. Schafer 《Applied physics. B, Lasers and optics》2004,78(7-8):835-840
We characterize the temporal structure of high-order harmonic radiation on both the femtosecond and attosecond time scales. The harmonic emission is characterized by mixed-color two-photon ionization with an infrared femtosecond laser using a Mach–Zehnder interferometer where both pump and probe arms travel completely separate paths. In a first experiment, we measure the duration and chirp of individual harmonics. In a second experiment, we resolve, for the first time with this type of setup, the attosecond beating of several harmonics generated under conditions similar to the first experiment. We suggest that the results of both measurements can be combined to determine the full attosecond time structure of the harmonic emission. PACS 32.80.Rm; 42.65.Ky 相似文献
93.
L. Barral J. Cano A. J. López J. López P. Nogueira C. Ramírez 《Journal of Thermal Analysis and Calorimetry》1995,45(5):1167-1174
Using dynamic mechanical analysis (DMA) we have studied thermal degradation for a system containing a diglycidyl ether of bisphenol A (DGEBA) and 1,3-bisaminomethylcylohexane (1,3-BAC). The changes of dynamic mechanical properties during thermal degradation indicated a shift of the glass transition temperature (T g) to higher temperatures and a decrease in the peak value of the dynamic loss factor (tan δ) with an increasing of aging time. The value of dynamic storage modulus (E′) at the rubbery state showed an increase with aging time, whiteE′ at the glassy state only underwent a moderate change with increased thermal degradation. From these results it can be argued that thermal degradation during the stage prior to the onset of the severe degradation involves structural changes in the epoxy system, as further crosslinking and loss of dangling chains in the crosslinked network. 相似文献
94.
Gianpiero Cattaneo Giuseppe Nisticó 《International Journal of Theoretical Physics》1992,31(10):1873-1898
We give a criterion to compare the physical content of different mathematical structures derived from a preparation-question structure. Then this criterion is used in order to compare the physical content of the (Jauch-Piron's) property lattice with the physical content of the poset of testable properties. We prove that for complete preparation-question structures these two structures carry the same physical content; moreover the set of testable properties has the algebraic structure of the Brouwer-Zadeh lattice. For more general preparation-question structures the physical content of the poset of testable property can be larger than that of the property lattice. Physically relevant examples of the possible cases are given. 相似文献
95.
96.
József Kaizer József Pap Gábor Speier Marius Réglier Michel Giorgi 《Transition Metal Chemistry》2004,29(6):630-633
The preparation, spectroscopic properties, and crystal structure of [Cu(ind)(mco)] [ind is the anion of 1,3-bis(2-pyridylimino)isoindoline and mco is the anion of 3-hydroxy-(4H)-benzopyran-4-one] are reported. The complex exhibits a distorted square pyramidal geometry. The oxygenation of the title compound results in oxidative cleavage of the heterocyclic ring to give the (acetylsalicylato)copper(II) complex [Cu(asp)(ind)] (asp is the anion of acetylsalicylic acid) and CO as primary products, which reaction resembles the enzymatic reaction of quercetinase. 相似文献
97.
98.
99.
Dávid Szegvári Romána Zelkó Péter Horváth András Gergely 《Journal of inclusion phenomena and macrocyclic chemistry》2007,57(1-4):169-172
Enantioselective solubility of rac-norgestrel was found in the presence of γ-cyclodextrin or hydroxypropyl-γ-cyclodextrin.
In both cases the efficacious enantiomer was dissolved in greater extent. Calculating the molar absorptivity and molar ellipticity
spectra of the γ- and hydroxypropyl-γ-cyclodextrin aqueous complexes, a simple and rapid direct circular dichroism (CD) spectrometric
method was obtained for the determination of the enantiomer ratio in aqueous solutions. 相似文献
100.
Perdigón-Melón J. A. Auroux A. Bonnetot B. 《Journal of Thermal Analysis and Calorimetry》2003,72(2):443-451
As supported palladium oxide catalysts present the best performances in methane combustion in lean conditions, microcalorimetric
studies of the interaction between methane and palladium oxide or metallic palladium supported on Al2O3, ZrO2 and BN have been performed at 673 K. At this temperature methane reduced the palladium oxide, and the heat of reduction of
palladium oxide was shown to depend on the dispersion and on the support. The lowest heats of reduction corresponded to the
highest rates of methane combustion. Moreover methane reforming occurred on metallic palladium, producing hydrogen, and again
methane decomposition was shown to depend on the support.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献