全文获取类型
收费全文 | 1110篇 |
免费 | 19篇 |
国内免费 | 7篇 |
专业分类
化学 | 794篇 |
晶体学 | 11篇 |
力学 | 22篇 |
数学 | 69篇 |
物理学 | 240篇 |
出版年
2023年 | 9篇 |
2022年 | 6篇 |
2021年 | 8篇 |
2020年 | 8篇 |
2019年 | 8篇 |
2018年 | 8篇 |
2016年 | 10篇 |
2015年 | 13篇 |
2014年 | 22篇 |
2013年 | 37篇 |
2012年 | 49篇 |
2011年 | 54篇 |
2010年 | 28篇 |
2009年 | 35篇 |
2008年 | 67篇 |
2007年 | 59篇 |
2006年 | 62篇 |
2005年 | 46篇 |
2004年 | 49篇 |
2003年 | 48篇 |
2002年 | 30篇 |
2001年 | 35篇 |
2000年 | 25篇 |
1999年 | 8篇 |
1998年 | 7篇 |
1997年 | 8篇 |
1996年 | 8篇 |
1995年 | 14篇 |
1994年 | 20篇 |
1993年 | 19篇 |
1992年 | 35篇 |
1991年 | 19篇 |
1990年 | 19篇 |
1989年 | 10篇 |
1988年 | 15篇 |
1987年 | 20篇 |
1986年 | 24篇 |
1985年 | 29篇 |
1984年 | 18篇 |
1983年 | 13篇 |
1982年 | 19篇 |
1981年 | 20篇 |
1980年 | 12篇 |
1979年 | 19篇 |
1978年 | 15篇 |
1977年 | 11篇 |
1976年 | 9篇 |
1975年 | 6篇 |
1973年 | 5篇 |
1970年 | 4篇 |
排序方式: 共有1136条查询结果,搜索用时 15 毫秒
81.
The new molecule 1-phosphabut-3-ene-1-yne, CH2=CHCP, produced by pyrolyzing prop-1-ene-3-phosphorus dichloride, CH2=CHCH2PCl2, was detected by microwave spectroscopy. The analysis of the rotational transitions indicates that the molecule is planar with constants: A0 = 46 694(24), B0 = 2807.7100(21), and C0 = 2645.8356(21) MHz. These rotational constants indicate that the structure of the vinyl group is essentially the same as that in CH2=CHCN and CH2=CHCCH; r(C---C) = 1.432 Å and (C=C---C) = 123.9°. The dipole moment parameters are μA = 1.181(2), μB = 0.074(1), and μ = 1.183(2) D. The vibrational satellite spectra for the C---CP bending modes indicate that ν11(a′) = 184 ± 30 cm−1 and ν15(a″) = 263 ± 30 cm−1. 相似文献
82.
Hiroshi Kashiwagi Toshikazu Takada Shigeru Obara Eisaku Miyoshi Kimio Ohno 《International journal of quantum chemistry》1978,14(1):13-27
Ab initio LCAO SCF MO calculations are carried out on planar Co-porphine with a basis set of roughly double zeta quality for Co and N and of single zeta quality for C and H. The net charge on Co and N and the overlap population between them are 1.78, ?0.57, and 0.06, respectively, in the 2A1g, state, which is known to be the ground state by experiment. The bonding in this complex is thus largely ionic. The first and second calculated ionization potentials are 6.51 and 6.77 eV, respectively, and are in reasonable agreement with the observed ionization potentials of 6.44 and 6.62 eV for Ni-tetraphenylporphine. CI calculations within the framework of the ligand field theory are also performed. The calculated order of the five lowest states is 4B2g ≈ 4Eg, 4A2g, 2A1g, 4Eg from below and is not in agreement with the semiempirical order of 2A1g ≈ 4B2G, 4A2g, 2Eg, 4Eg determined by Lin. 相似文献
83.
In this Letter, we discuss the generation of magnetic field from cosmological perturbations. We consider the evolution of three component plasma (electron, proton, and photon) evaluating the collision term between electrons and photons up to the second order. The collision term is shown to induce electric current, which then generates magnetic field. There are three contributions, two of which can be evaluated from the first-order quantities, while the other one is fluid vorticity, which is purely second order. We estimate the magnitudes of the former contributions and show that the amplitude of the produced magnetic field is about approximately 10(-19) G at 10 Mpc comoving scale at the decoupling. Compared to astrophysical and inflationary mechanisms for seed-field generation, our study suffers from much less ambiguities concerning unknown physics and/or processes. 相似文献
84.
Effect of moisture on impact toughness of sugar-coated tablets manufactured by the dusting method 总被引:1,自引:0,他引:1
The purpose of this study was to clarify the effect of moisture on the impact toughness of sugar-coated tablets manufactured by the dusting method. We demonstrated that moisture plays an important role in the impact toughness of sugar-coated tablets. Moisturizing the sugar-coating layer resulted in enhancement of impact toughness of sugar-coated tablets, while reducing moisture in the sugar-coating layer resulted in weakening of the impact toughness. This was due to the characteristics of sucrose, the main ingredient of the sugar-coating layer, which is a soft and non-fragile material at high moisture levels, but hard and fragile at low moisture levels. We also demonstrated that friability as an indicator of impact toughness changed with time, and friability should be measured at 14 d after manufacture. This is due to moisture movement from outer sugar-coating layer into the inner sugar-coated tablets. Incorporating microcrystalline cellulose (MCC) in the subcoating layer resulted in sugar-coating layers with high resistance against impact even though moisture content of sugar-coated tablets was low. We confirmed the high impact toughness of the sugar-coated tablets with MCC whose moisture content was low from the results of both free fall and friability tests. We suggest that the dusting method using dusting powder containing MCC is a useful method for the production of sugar-coated tablets containing moisture sensitive drugs. 相似文献
85.
Ohno H Iwasaki H Eguchi T Tanaka T 《Chemical communications (Cambridge, England)》2004,(19):2228-2229
Intramolecular arylation of aryl radicals was mediated by SmI(2)/HMPA in the presence of i-PrOH to give spirocycles and/or reduced cine-cyclised products, while the reaction in the absence of i-PrOH gave the rearomatised fused rings. 相似文献
86.
87.
88.
Components and isolated points of the topological space of composition operators onH
in the uniform operator topology are characterized. Compact differences of two composition operators are also characterized. With the aid of these results, we show that a component inC(H
) is not in general the set of all composition operators that differ from the given one by a compact operator.Supported by the Grant-in-Aid for Scientific Research (C), the Ministory of Education, Science and Culture, No. 09640218, and the Nippon Institute of Technology No. 111Supported by the Japan Society for the Promotion of Science 相似文献
89.
Xue QZ Xue QK Kuwano S Sadowski JT Kelly KF Sakurai T Ohno T 《Physical review letters》2000,84(17):4015
90.
A novel X-band CW EPR imaging has been developed using magnetic-field-gradient (MFG) spinning to obtain spatial distributions of electron paramagnetic species. Spinning MFG EPR imaging for 65 projection spectra required just 55 s while conventional imaging took 11 min 40 s, that is, the acquisition time for the new system is one order of magnitude shorter than that for conventional EPR imaging. Spinning MFG EPR imaging allows one to measure reconstructed images in an interactive manner where resolution and condition can be changed quickly. 相似文献