全文获取类型
收费全文 | 726篇 |
免费 | 18篇 |
国内免费 | 26篇 |
专业分类
化学 | 434篇 |
晶体学 | 20篇 |
力学 | 21篇 |
综合类 | 1篇 |
数学 | 59篇 |
物理学 | 235篇 |
出版年
2022年 | 23篇 |
2021年 | 9篇 |
2020年 | 11篇 |
2019年 | 7篇 |
2018年 | 4篇 |
2017年 | 7篇 |
2016年 | 14篇 |
2015年 | 8篇 |
2014年 | 32篇 |
2013年 | 28篇 |
2012年 | 40篇 |
2011年 | 59篇 |
2010年 | 37篇 |
2009年 | 25篇 |
2008年 | 37篇 |
2007年 | 31篇 |
2006年 | 27篇 |
2005年 | 30篇 |
2004年 | 24篇 |
2003年 | 15篇 |
2002年 | 16篇 |
2001年 | 12篇 |
2000年 | 12篇 |
1999年 | 7篇 |
1998年 | 7篇 |
1997年 | 6篇 |
1996年 | 12篇 |
1995年 | 11篇 |
1994年 | 15篇 |
1993年 | 19篇 |
1992年 | 24篇 |
1991年 | 14篇 |
1990年 | 13篇 |
1989年 | 15篇 |
1988年 | 8篇 |
1987年 | 10篇 |
1986年 | 3篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 3篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1976年 | 9篇 |
1975年 | 7篇 |
1974年 | 4篇 |
1937年 | 4篇 |
排序方式: 共有770条查询结果,搜索用时 31 毫秒
171.
Thomas J. Barloon William T. C. Yuh Frances L. Chiang Simon C. S. Kao Yutaka Sato Mark Mehringer 《Magnetic resonance imaging》1989,7(6):635-642
A retrospective review of 21 patients with lesions involving the fourth ventricle was performed to determine the relative capability of computed tomography (CT) and MR for detection, characterization, localization, and diagnosis. Lesions involving the fourth ventricle included ependymoma (three), subependymoma (one), glioma (five), cysticercosis cyst (three), medulloblastoma (three), bleeding into the fourth ventricle (two), epidermoid cyst (two), “trapped” fourth ventricle (one), and lymphomatoid granuloma (one). Posterior fossa lesions that displaced but did not invade the fourth ventricle were excluded. Lesion detectability on CT was judged excellent in ten, good in 8, and fair or poor in 3. Detectability of lesions by MR was judged excellent in 16 and good in 5. There was complete agreement on lesion extension between CT and MR in 6 lesions, mild disagreement in 4, and moderate to significant disagreement in 11. Preoperatively, MR alone correctly diagnosed seven lesions, and CT alone correctly diagnosed three lesions. A review of the combined scans (after the correct diagnosis was given) showed both CT and MR were equal in the diagnosis of 14 lesions, MR better than CT in six, and CT better in one. There was complete agreement on both CT and MR with the surgical/pathologic findings in three lesions. Both studies proved disappointing in their ability to make the correct histologic diagnosis, probably because CT and MR characteristics may not always offer a definitive diagnosis and because of the wide spectrum of pathologic processes that may involve the fourth ventricle. 相似文献
172.
The multiple scattering Xα(R) method with the scaling parameter α expressed as a function of the internuclear distance is applied to the Li2, N2, and F2 molecules. Compared with the results obtained by the Xα method, the calculated Xα(R) equilibrium distances are smaller, the total energies are lower, and the dissociation energies are larger. 相似文献
173.
Decomposition of H2O2 with Fe2+ was studied with SnO2 electrodes. By chronoamperometric and voltammetric techniques, the diffusion coefficients of Fe3* and H 2O2 were estimated to be 5 × 10-6 and 2 × 10?5 cm2/s, respectively; the rate of decomposition of H2O2 with Fe2+ was proportional to [H2O2]1/2·[Fe2+]2 at a smaller concentration of Fe2+, but to [H2O2]1/2·[Fe2+] when [Fe2+] was increased, indicating the formation of ferryl ion and the electron exchange between it and Fe2+ playing important roles. This catalytic decomposition. was dependent on pH; the maximum rate was observed to occur about pH = 1.5. 相似文献
174.
Chi-Chyuang Lin Cheng-Yu Fang Dah-Yu Kao Jenn-Shing Chen 《Journal of solution chemistry》1997,26(8):817-832
We describe a novel graphical method which, in conjunction with the previously proposed graphical determination of monomer
shift, dimer shift, and dimerization constant for self-association, allows us to determine the complex shift and equilibrium
constant for a hetero-association, A + B ⇌ AB, accompanying self-associations, A + A ⇌ A2, and B + B ⇌ B2. The merit of the new method includes the removal of the restrictions imposed on the conventional Benesi-Hildebrand (B-H)
plot: (1) that the concentration of one component must be much less than that of the other; (2) that there be no accompanying
self-association. The simultaneous equilibrium of the self-association of 2-pyrrolidone (A) and that of 4-methyl-α-pyrrolidone
(B) and the hetero-association between A and B in acetonitrile-d3 at 25‡C is studied. The inappropriateness of the B-H plot in dealing with this case is also pointed out. 相似文献
175.
A superconducting oxide with a stoichiometry La3CaBa3Cu7O15.5+x, in which x = 0.75, was prepared. It had a tetragonal triple-perovskite structure with lattice parameters a = 3.879 Å and c = 11.637 Å. According to resistivity measurements, a sharp superconducting transition, ΔTc(10-90%) = 1.5 K, and Tc(zero) = 80 K were observed. When it was measured at a small magnetic field (10-20 gauss) with field cooling, the sintered pellet showed a positive magnetic susceptibility, but the powdered sample exhibited (he diamagnetism of a typical superconductor. However, no peculiar shielding effect was found in both the sintered and powdered samples. 相似文献
176.
177.
178.
179.
180.