全文获取类型
收费全文 | 77636篇 |
免费 | 10931篇 |
国内免费 | 7796篇 |
专业分类
化学 | 52201篇 |
晶体学 | 747篇 |
力学 | 5276篇 |
综合类 | 604篇 |
数学 | 9477篇 |
物理学 | 28058篇 |
出版年
2024年 | 242篇 |
2023年 | 1530篇 |
2022年 | 2455篇 |
2021年 | 2693篇 |
2020年 | 2790篇 |
2019年 | 2667篇 |
2018年 | 2368篇 |
2017年 | 2160篇 |
2016年 | 3327篇 |
2015年 | 3358篇 |
2014年 | 4008篇 |
2013年 | 5337篇 |
2012年 | 6500篇 |
2011年 | 6585篇 |
2010年 | 4552篇 |
2009年 | 4429篇 |
2008年 | 4645篇 |
2007年 | 4176篇 |
2006年 | 3945篇 |
2005年 | 3457篇 |
2004年 | 2790篇 |
2003年 | 2198篇 |
2002年 | 2047篇 |
2001年 | 1844篇 |
2000年 | 1647篇 |
1999年 | 1795篇 |
1998年 | 1504篇 |
1997年 | 1316篇 |
1996年 | 1385篇 |
1995年 | 1189篇 |
1994年 | 1122篇 |
1993年 | 948篇 |
1992年 | 828篇 |
1991年 | 728篇 |
1990年 | 588篇 |
1989年 | 502篇 |
1988年 | 397篇 |
1987年 | 365篇 |
1986年 | 323篇 |
1985年 | 319篇 |
1984年 | 211篇 |
1983年 | 188篇 |
1982年 | 153篇 |
1981年 | 121篇 |
1980年 | 85篇 |
1979年 | 51篇 |
1978年 | 56篇 |
1977年 | 52篇 |
1975年 | 57篇 |
1973年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Three-dimensional time-dependent quantum wave packet calculation for the O((1)D)+HBr reaction has been carried out using an accurate ab initio global potential energy surface [K. A. Peterson, J. Chem. Phys. 113, 4598 (2000)]. The calculations show that the initial state-selected reaction probabilities are dominated by resonance structures, and the lifetime of the resonance is generally in the subpicosecond time scale. The energy dependence of the reaction cross section is computed, which manifests still resonance structures, and is a decreasing function of the translational energy. The thermal rate constants are also computed, which are nearly independent on the temperature. The calculation results are discussed and compared to similar reaction with deep well. 相似文献
103.
A novel compound, [Co(phen)3][V10O26]·H2O, was hydrothermally synthesized and characterized by single-crystal X-ray diffraction. This compound crystallizes in the orthorhombic space group Ccca with a=13.447(3), b=29.936(6), c=23.252(5) Å, V=9360(3) Å3, Z=8 and R=0.0285. Data were collected on a Rigaku R-AXIS RAPID IP diffractometer at 293 K in the range of 1.36<θ<24.99°. The structure of the compound consists of vanadium oxide layers, which are built up from the infinite VO4 chains by corners and edges sharing. The [Co(phen)3]2+ complexes occupy the interlayer space and contact each other via π−π stacking interactions of the phen groups to form infinite one-dimensional chains. 相似文献
104.
The 2-methyloxazol-5-on-2-yl radical (3) and its deuterium labeled analogs were generated in the gas-phase by femtosecond electron-transfer and studied by neutralization-reionization mass spectrometry and quantum chemical calculations. Radical 3 undergoes fast dissociation by ring opening and elimination of CO and CH(3)CO. Loss of hydrogen is less abundant and involves hydrogen atoms from both the ring and side-chain positions. The experimental results are corroborated by the analysis of the potential energy surface of the ground electronic state in 3 using density functional, perturbational, and coupled-cluster theories up to CCSD(T) and extrapolated to the 6-311 ++ G(3df,2p) basis set. RRKM calculations of radical dissociations gave branching ratios for loss of CO and H that were k(CO)/k(H) > 10 over an 80-300 kJ mol(-1) range of internal energies. The driving force for the dissociations of 3 is provided by large Franck-Condon effects on vertical neutralization and possibly from involvement of excited electronic states. Calculations also provided the adiabatic ionization energy of 3, IE(adiab) = 5.48 eV and vertical recombination energy of cation 3(+), RE(vert) = 4.70 eV. The present results strongly indicate that oxazolone structures can explain fragmentations of b-type peptide ions upon electron capture, contrary to previous speculations. 相似文献
105.
A solution-phase synthesis of bicyclic prolines containing four points of diversity has been developed by a two-step synthesis involving 1,3-dipolar cycloaddition of perfluoroalkylsulfonyl-protected hydroxybenzaldehydes followed by Pd-catalyzed Suzuki coupling reaction of fluorous sulfonates with boronic acids. Both reactions are conducted under microwave irradiation and reaction mixtures are purified by solid-phase extractions without performing chromatography. 相似文献
106.
A novel micro-injector has been fabricated for capillary electrophoresis (CE). It was successfully used for the determination of some indole derivatives for example melatonin (MT), serotonin (5-HT), tryptophan (Trp), and 5-hydroxy-tryptophane (5-HTrp) in the rat pineal gland by capillary electrophoresis with electrochemical detection (CE-EC). CE was performed in 0.20 mol L(-1) phosphate buffer (pH 8.0). The compounds investigated can be well separated and detected within 15 min. The working electrode used was a 300-microm diameter carbon electrode positioned opposite the outlet of the capillary. The relationship between peak current and analyte concentration was highly linear in the range from 0.10 to 500 micromol L(-1); detection limits (S/N = 3) were 0.03-0.13 micromol L(-1). The proposed method has been successfully used to analyze real biological samples. 相似文献
107.
In this paper, we deal with the nonlinear second-order differential equation with damped vibration term involving p-Laplacian operator. Of particular interest is the resolution of an open problem. An interesting outcome from our result is that we can obtain the fast homoclinic solution with general superlinear growth assumption in suitable Sobolev space. To our knowledge, our theorems appear to be the first such result about damped vibration problem with p-Laplacian operator. 相似文献
108.
Hu Wentao Chen Cuixia Shi Yufeng Chen Ze 《Methodology and Computing in Applied Probability》2022,24(2):831-874
Methodology and Computing in Applied Probability - Risk measures for tail risk have an important application in the dynamic portfolio insurance strategies. We propose a new risk measure called... 相似文献
109.
In this paper, we prove the global well-posedness of the 3-D magnetohydrodynamics(MHD) equations with partial diffusion in the periodic domain when the initial velocity is small and the initial magnetic field is close to a background magnetic field satisfying the Diophantine condition. 相似文献
110.
Liang Chen 《Communications in Mathematical Physics》1995,167(2):431-469
A class of differential operator Lie algebras on the unit circle is introduced and discussed. They are the natural generalizations of the Witt algebra and the Virasoro algebra. Among them are the higher-spin algebrasW
1+ andW
which occur in the physics literature. 相似文献