全文获取类型
收费全文 | 8304篇 |
免费 | 959篇 |
国内免费 | 1525篇 |
专业分类
化学 | 6691篇 |
晶体学 | 45篇 |
力学 | 500篇 |
综合类 | 67篇 |
数学 | 1018篇 |
物理学 | 2467篇 |
出版年
2024年 | 47篇 |
2023年 | 151篇 |
2022年 | 306篇 |
2021年 | 381篇 |
2020年 | 554篇 |
2019年 | 358篇 |
2018年 | 315篇 |
2017年 | 304篇 |
2016年 | 402篇 |
2015年 | 344篇 |
2014年 | 488篇 |
2013年 | 654篇 |
2012年 | 466篇 |
2011年 | 510篇 |
2010年 | 434篇 |
2009年 | 482篇 |
2008年 | 480篇 |
2007年 | 507篇 |
2006年 | 435篇 |
2005年 | 392篇 |
2004年 | 333篇 |
2003年 | 383篇 |
2002年 | 363篇 |
2001年 | 219篇 |
2000年 | 176篇 |
1999年 | 154篇 |
1998年 | 140篇 |
1997年 | 117篇 |
1996年 | 121篇 |
1995年 | 88篇 |
1994年 | 96篇 |
1993年 | 78篇 |
1992年 | 77篇 |
1991年 | 44篇 |
1990年 | 53篇 |
1989年 | 39篇 |
1988年 | 52篇 |
1987年 | 37篇 |
1986年 | 47篇 |
1985年 | 41篇 |
1984年 | 21篇 |
1983年 | 9篇 |
1982年 | 29篇 |
1981年 | 15篇 |
1980年 | 8篇 |
1979年 | 10篇 |
1978年 | 8篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1973年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
1.
Dekun Wu Dr. Qing Xu Dr. Jing Qian Prof. Xiaopeng Li Prof. Yuhan Sun 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(12):3105-3111
Covalent organic frameworks (COFs) are a new class of crystalline porous polymers comprised mainly of carbon atoms, and are versatile for the integration of heteroatoms such as B, O, and N into the skeletons. The designable structure and abundant composition render COFs useful as precursors for heteroatom-doped porous carbons for energy storage and conversion. Herein, we describe a multifunctional electrochemical catalyst obtained through pyrolysis of a bimetallic COF. The catalyst possesses hierarchical pores and abundant iron and cobalt nanoparticles embedded with standing carbon layers. By integrating these features, the catalyst exhibits excellent electrochemical catalytic activity in the oxygen reduction reaction (ORR), with a 50 mV positive half-wave potential, a higher limited diffusion current density, and a much smaller Tafel slope than a Pt-C catalyst. Moreover, the catalyst displays superior electrochemical performance toward the hydrogen evolution reaction (HER), with overpotentials of −0.26 V and −0.33 V in acidic and alkaline aqueous solution, respectively, at a current density of 10 mA cm−2. The overpotential in the catalysis of the oxygen evolution reaction (OER) was 1.59 V at the same current density. 相似文献
2.
Plasma-assisted flow control is of high industrial interest, but practical applications at full scale require a large surface of interaction. Nanosecond pulsed Dielectric Barrier Discharge (DBD) have demonstrated promising results of flow control, but their interacting region is limited to only a few cm2. In this paper, the conditions to extend a surface nanosecond DBD are documented. It is shown that a sliding discharge regime can fully fill an inter-electrode distance of 40 mm. This discharge regime promotes the formation of two hemispheric pressure waves originating from both air-exposed electrodes while an horizontal region of pressure gradient is also observed. 相似文献
3.
托卡马克工程试验混合堆等离子体性能的等值线图分析 总被引:3,自引:3,他引:0
盛光昭 《核聚变与等离子体物理》1989,9(1):29-36
本文简要叙述托卡马克工程试验混合堆等离子体概念设计的物理基础,对等离子体性能进行了等值线图(Plasma Operation Contour)分析。根据工程试验混合堆的要求,得出一组等离子体参数。 相似文献
4.
Daisuke Matsuura 《Tetrahedron letters》2006,47(9):1371-1374
An efficient and stereodefined strategy is described for the asymmetric synthesis of a new styryllactone from the stem bark of Goniothalamus cardiopetalus, cardiobutanolide. The synthetic process is based on requisite manipulation of the functionalized bicyclic lactol-lactone intermediate incorporating the glucuronolactone-derived skeleton in a complete stereoselective manner. 相似文献
5.
Gregorio Falqui 《Reports on Mathematical Physics》2002,50(3):395
We formulate and discuss a reduction theorem for Poisson pencils associated with a class of integrable systems, defined on bi-Hamiltonian manifolds, recently studied by Gel'fand and Zakharevich. The reduction procedure is suggested by the bi-Hamiltonian approach to the separation of variables problem. 相似文献
6.
A Garcia-Quiroz David L AzevedoE.C da Silva 《Journal of Physics and Chemistry of Solids》2002,63(10):1863-1866
Properties of oxygenated carbon nitride films have attracted the attention of physics researchers due to their magnetic and physical properties, as well as for their usefulness in the industry. The free radicals were investigated using electron paramagnetic resonance applied in the study of spin concentration due to the different mechanism of preparation of carbon nitride films by RF-discharge with different kinds of plasma. Unpaired spin concentrations, in the order of 1020 per cm3, were measured and their time recombination dependency was important in those films. The films were grown by plasma enhanced chemical vapor deposition using mixtures of hydrocarbons, N2 and O2 in different proportions. 相似文献
7.
L. T. Ashchepkov 《Computational Mathematics and Mathematical Physics》2006,46(7):1168-1175
A general nonlinear programming problem with interval functions is considered. Two reductions of this problem to the deterministic nonlinear programming problem are proposed, and illustrative examples are discussed. 相似文献
8.
Baker‘s yeast mediated reduction of optically active diketone is described. The two keto groups are efficiently differentiated and the ee value of the recovered material is considerably raised. It affords highly optically active key intermediates efficiently for the synthesis of natural polyhydroxylated agarofuran products. 相似文献
9.
For three‐dimensional flows with one inhomogeneous spatial coordinate and two periodic directions, the Karhunen–Loeve procedure is typically formulated as a spatial eigenvalue problem. This is normally referred to as the direct method (DM). Here we derive an equivalent formulation in which the eigenvalue problem is formulated in the temporal coordinate. It is shown that this so‐called method of snapshots (MOS) has some numerical advantages when compared to the DM. In particular, the MOS can be formulated purely as a matrix composed of scalars, thus avoiding the need to construct a matrix of matrices as in the DM. In addition, the MOS avoids the need for so‐called weight functions, which emerge in the DM as a result of the non‐uniform grid typically employed in the inhomogeneous direction. The avoidance of such weight functions, which may exhibit singular behaviour, guarantees satisfaction of the boundary conditions. The MOS is applied to data sets recently obtained from the direct simulation of turbulence in a channel in which viscoelasticity is imparted to the fluid using a Giesekus model. The analysis reveals a steep drop in the dimensionality of the turbulence as viscoelasticity is increased. This is consistent with the results that have been obtained with other viscoelastic models, thus revealing an essential generic feature of polymer‐induced drag reduced turbulent flows. Published in 2006 by John Wiley & Sons, Ltd. 相似文献
10.