全文获取类型
收费全文 | 2860篇 |
免费 | 970篇 |
国内免费 | 261篇 |
专业分类
化学 | 912篇 |
晶体学 | 61篇 |
力学 | 168篇 |
综合类 | 67篇 |
数学 | 151篇 |
物理学 | 2732篇 |
出版年
2024年 | 3篇 |
2023年 | 16篇 |
2022年 | 63篇 |
2021年 | 72篇 |
2020年 | 106篇 |
2019年 | 78篇 |
2018年 | 88篇 |
2017年 | 128篇 |
2016年 | 147篇 |
2015年 | 127篇 |
2014年 | 186篇 |
2013年 | 221篇 |
2012年 | 252篇 |
2011年 | 246篇 |
2010年 | 234篇 |
2009年 | 216篇 |
2008年 | 208篇 |
2007年 | 204篇 |
2006年 | 199篇 |
2005年 | 187篇 |
2004年 | 169篇 |
2003年 | 124篇 |
2002年 | 97篇 |
2001年 | 128篇 |
2000年 | 111篇 |
1999年 | 52篇 |
1998年 | 70篇 |
1997年 | 48篇 |
1996年 | 46篇 |
1995年 | 44篇 |
1994年 | 23篇 |
1993年 | 33篇 |
1992年 | 25篇 |
1991年 | 23篇 |
1990年 | 17篇 |
1989年 | 10篇 |
1988年 | 24篇 |
1987年 | 9篇 |
1986年 | 10篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 5篇 |
排序方式: 共有4091条查询结果,搜索用时 0 毫秒
111.
Effects of Neutron Irradiation on Superconducting Properties of GdBa2Cu3O7-δ Single Domain Superconductor 下载免费PDF全文
The effects of neutron irradiation with a fluence of 1015 n/cm2 on the superconducting properties of GdBa2Cu3O7-δsingle domain sample were studied. The point and cascade defects produced by the neutron irradiation were observed by high-resolution transmission electron microscopy. The cascade defects were found to have the sizes of about 4-7 nm which is comparable to the coherence lengths of high temperature superconductors. The point defects disappear while the cascades still exist through thermal annealing. The temperature dependence of magnetization for the magnetic field parallel to the crystallographic c axis shows that the neutron irradiation leads to a dramatic degradation of uperconductivity for the as-irradiated sample, a decrease of critical current density (Jc), and the weakening of the fishtail effect in the Jc versus magnetic induction B curve. However, for the as-irradiated sample annealed in the flowing oxygen atmosphere, it shows that Jc under high magnetic fields is greatly enhanced, the fishtail shifts towards higher magnetic fields, and its superconductivity is partially recovered as well due to the remaining effecive pinning centers of the cascades. These results suggest a prospective application for such a treated GdBa2Cu3O7-δsuperconductor. 相似文献
112.
国内现有化学微课的整体水平可以从3个角度进行分析: 拍摄方式、拍摄内容和拍摄技术。分析精品化学微课, 主要有4个典型特征。关于微课使用, 提出了精品微课在“翻转课堂”中需要“自主任务学习单”支撑的观点。对于未来的微课创作与使用, 需要破除6大疑惑, 解决创作中的8大问题。 相似文献
113.
Ru-Ir-Ti氧化物阳极正反电流电解失效机理研究 总被引:2,自引:0,他引:2
应用热分解法制备适用于海水电解的钛基金属氧化物阳极.由SEM、EDX和XRD分析表征该阳极的形貌、成分及相结构,结果表明,烧结后阳极表面形成了固溶体结构,分别为(Ru,Ir,Ti)O2和(Ir,Ti)O2,失效后氧化物阳极的固溶体结构几乎完全消失,活性物质丧失.强化正反向电流寿命测试、循环伏安曲线和电化学阻抗谱等测试表明,失效后氧化物阳极表面的电化学活性点大大减少,同时膜电阻增加,这是由于活性物质脱落导致的,进一步说明正反向电流导致阳极表面活性物质脱落是氧化物阳极失效的根本原因. 相似文献
114.
115.
The aromaticity of metal-metal quintuple bonded complexes of the type M2L2 (M=Cr, Mo, and W; L=amidinate) are studied employing gauge including magnetically induced ring current (GIMIC) analysis and electron density of delocalized bonds (EDDB). It is found that the complexes possess two types of aromaticity: i) Hückel aromaticity through delocalization of ligand π electrons with metal-metal δ-bond-forming 6 conjugated electrons (4π and 2δ) ring; ii) Craig-Möbius aromaticity through delocalization of π electrons of both the ligands with metal d-orbitals in Craig type orientation forming 10π electrons ring with a double twist. Extended transition state natural orbital chemical valence (ETS-NOCV) and canonical molecular orbital natural chemical shielding (CMO-NCS) analysis confirm the Craig-Möbius type arrangement of the orbitals. Furthermore, the unprecedented Hückel and Möbius type aromaticity is confirmed from the plot of the current pathways using 3D line integral convolution (3D-LIC) plots. The metal-metal bond order also increases down the group as justified from the complete active space self-consistent field (CASSCF) analysis. Due to an increase in the π and δ electron conjugation, both the Hückel and Möbius aromaticity increase down the group. 相似文献
116.
Milivoj Lovrić 《Electroanalysis》2021,33(11):2372-2380
A model of cyclic staircase voltammetry of enzymatic reactions on the rotating disk electrode is developed and the inhibition by the product is investigated. The responses are mostly time – dependent current – potential curves with maxima in the forward but not in the backward branch. If the maxima appear in both branches, the inhibition is potential – dependent either directly or indirectly. The source of the second maximum is explained. 相似文献
117.
《Journal of computational chemistry》2017,38(3):144-151
An increasing number of observations show that non‐classical isomers may play an important role in the formation of fullerenes and their exo‐ and endo‐derivatives. A quantum‐mechanical study of all classical isomers of C58, C60, and C62, and all non‐classical isomers with at most one square or heptagonal face, was carried out. Calculations at the B3LYP/6‐31G* level show that the favored isomers of C58, C60, and C62 have closely related structures and suggest plausible inter‐conversion and growth pathways among low‐energy isomers. Similarity of the favored structures is reinforced by comparison of calculated ring currents induced on faces of these polyhedral cages by radial external magnetic fields, implying patterns of magnetic response similar to those of the stable, isolated‐pentagon C60 molecule. © 2016 Wiley Periodicals, Inc. 相似文献
118.
采用循环伏安、线性扫描、交流阻抗等技术研究了Ce3+/Ce4+电对在混酸(硫酸与甲磺酸)中的电化学行为,并对该体系在间接有机电合成中的应用进行了探索.结果表明:当硫酸和甲磺酸(MSA)浓度分别为0.8和1.0 mol·L-1时,Ce3+/Ce4+电对具有最佳的电化学活性;在上述配比的混酸介质中,铈盐的溶解度得到了大幅提高,同时电解氧化铈(III)离子的电流效率较高(92.1%),与纯硫酸体系中的电流效率接近(92.8%),明显高于纯甲磺酸体系(78.5%);该混酸介质中Ce4+在氧化茴香醚生成茴香醛这一过程中也表现出很好的氧化能力. 相似文献
119.
A comprehensive study was performed for the design of ABX3 perovskites, (A = Li, K, Na, B = Ge, Sn, Pb, X = F, Cl, Br, I) and organic hole transfer materials, HTMs (Fu-2a, Fu-2b, Fu-2c, and Dm-Q) for efficient perovskite solar cells (PSCs) through quantum chemistry calculations. Photovoltaic characteristics of the investigated perovskites are strongly affected by the halide anions. The results reveal that reducing the exciton binding energy of perovskites enhances the rate of the formation/dissociation of holes and electrons so F-based perovskites are superior from this viewpoint. Additionally, the electron and hole injection processes are more favorable in the case of the F-based perovskites in comparison with other studied perovskites. Moreover, spectroscopic properties of the perovskites demonstrate that KSnCl3, NaSnCl3, and F-based perovskites exhibit a greater ability of the light-harvesting and incident photon to current conversion efficiency. Ultimately, based on diverse analyses, F-based perovskites, KSnCl3 and NaSnCl3 are the preferred candidates to be applied in the PSCs due to an excellent incident photon to current conversion efficiency, light-harvesting efficiency, short circuit current, and solar cell final efficiency. 相似文献
120.
C. Durot 《Mathematical Methods of Statistics》2008,17(4):327-341
In this paper we study the nonparametric least squares estimator of a regression function in a random design setting under
the constraint that this function is monotone, say, nonincreasing. The errors are not assumed conditionally i.i.d. given the
observation points. In particular, this includes the case of conditional heteroscedasticity and the case of the current status
model. The -error is shown to be of order n
−p/3 and asymptotically Gaussian with explicit asymptotic mean and variance.
相似文献