全文获取类型
收费全文 | 66011篇 |
免费 | 4680篇 |
国内免费 | 2553篇 |
专业分类
化学 | 39251篇 |
晶体学 | 973篇 |
力学 | 3197篇 |
综合类 | 112篇 |
数学 | 7380篇 |
物理学 | 22331篇 |
出版年
2023年 | 601篇 |
2022年 | 1024篇 |
2021年 | 1239篇 |
2020年 | 1450篇 |
2019年 | 1401篇 |
2018年 | 1400篇 |
2017年 | 1226篇 |
2016年 | 2026篇 |
2015年 | 1655篇 |
2014年 | 2184篇 |
2013年 | 3566篇 |
2012年 | 4213篇 |
2011年 | 4636篇 |
2010年 | 3083篇 |
2009年 | 2950篇 |
2008年 | 3504篇 |
2007年 | 3318篇 |
2006年 | 3057篇 |
2005年 | 2653篇 |
2004年 | 2248篇 |
2003年 | 1841篇 |
2002年 | 1731篇 |
2001年 | 1824篇 |
2000年 | 1421篇 |
1999年 | 1321篇 |
1998年 | 1053篇 |
1997年 | 1050篇 |
1996年 | 989篇 |
1995年 | 855篇 |
1994年 | 773篇 |
1993年 | 649篇 |
1992年 | 720篇 |
1991年 | 696篇 |
1990年 | 647篇 |
1989年 | 577篇 |
1988年 | 556篇 |
1987年 | 556篇 |
1986年 | 484篇 |
1985年 | 547篇 |
1984年 | 532篇 |
1983年 | 405篇 |
1982年 | 435篇 |
1981年 | 412篇 |
1980年 | 348篇 |
1979年 | 426篇 |
1978年 | 398篇 |
1977年 | 405篇 |
1976年 | 410篇 |
1975年 | 364篇 |
1973年 | 350篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
通过反应磁控溅射过程中的等离子体发射光谱,研究了制备ZnO薄膜的沉积温度、氧气流量比例R=O2/(O2+Ar)对Zn和O原子发射光谱的影响,并结合ZnO薄膜的结构和物理性能,探讨了沉积温度在ZnO薄膜生长中的作用.研究结果显示:当R≥0.75%时, Zn的溅射产额随R的增加基本呈线性下降规律.当R介于10%—50%时,氧含量的变化相对平缓,有利于ZnO薄膜生长的稳定性控制.Zn原子发射光谱强度随沉积温度的变化可以分为三个阶段.当沉积温度低于250℃时,发射光谱强
关键词:
ZnO
薄膜生长
反应磁控溅射
等离子体发射光谱 相似文献
72.
文章提出了大学研究性物理实验与创新心理品质培养的主题,介绍了大学研究性物理实验的特点,论述了大学研究性物理实验对大学生创新心理品质的影响。 相似文献
73.
许多实验对用CsI(Tl)闪烁晶体作为探测器来寻找和探测暗物质的可行性进行了研究.本工作利用8MeV单能中子轰击CsI(Tl)晶体探测器来研究Cs核和I核的QuenchingFactor.在数据处理中,运用脉冲形状甄别(PSD)方法来分辨反冲核信号和本底信号.实验结果表明,在7keV到132keV的能区中,Quench ingFactor随着反冲核能量的减少而增加.在探测暗物质的实验中,这一性质对于CsI(Tl)晶体探测器获得较低的能量阈值是很有利的. 相似文献
74.
F. Chen L. Liu Z. Shen G.Q. Xu T.S.A. Hor 《Applied Physics A: Materials Science & Processing》2002,74(2):317-319
Free-standing and supported hydrogenated amorphous carbon films (a:C–H) were prepared upon pyrolysis of the polymer formed
by ethanolamine (EA) and citric acid (CA), under an ambient atmosphere at 300 °C. EA facilitates the formation of the macroscopic
films, while CA is essential for obtaining the a:C–H microstructure, which comprises a mixture of sp2 and sp3 carbon.
Received: 29 May 2001 / Accepted: 17 August 2001 / Published online: 20 December 2001 相似文献
75.
Q. Sun Q. Wang X.G. Gong V. Kumar Y. Kawazoe 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(1):77-81
We report results of the atomic and electronic structures of Al7C cluster using ab initio molecular dynamics with ultrasoft pseudopotentials and generalized gradient approximation. The lowest energy structure is
found to be the one in which carbon atom occupies an interstitial position in Al7 cluster. The electronic structure shows that the recent observation [Chem. Phys. Lett. 316, 31 (2000)] of magic behavior of Al7C- cluster is due to a large highest occupied and lowest unoccupied molecular orbital (HOMO-LUMO) gap which makes Al7C- chemically inert. These results have further led us to the finding of a new neutral magic cluster Al7N which has the same number of valence electrons as in Al7C- and a large HOMO-LUMO gap of 1.99 eV. Further, calculations have been carried out on (Al7N)2 to study interaction between magic clusters.
Received 28 July 2001 相似文献
76.
A three-dimensional molecular dynamics (MD) model is utilized to investigate the effect of tool geometry on the deformation process of the workpiece and the nature of deformation process at the atomic-scale. Results show that different states exist between the atomic force microscope (AFM) pin tool and the workpiece surface, i.e. the non-wear state, the ploughing state, the state in which ploughing is dominant and the state in which cutting plays a key role. A relationship between the deformation process of the workpiece and the potential energy variation is presented. The potential energy variation of atoms in different deformed regions in the workpiece such as plastically deformed region, elastically deformed region and the mixed deformation region is different. The features of variations of potential energy are discussed. 相似文献
77.
Huafei Sun 《Geometriae Dedicata》2002,90(1):63-75
We study minimal submanifolds in the locally symmetric and conformally flat Riemannian manifold and generalize Yau's result obtained in J. Amer. Math. 97 (1975), 76–100. 相似文献
78.
This paper is concerned with the implementation and testing of an algorithm for solving constrained least-squares problems. The algorithm is an adaptation to the least-squares case of sequential quadratic programming (SQP) trust-region methods for solving general constrained optimization problems. At each iteration, our local quadratic subproblem includes the use of the Gauss–Newton approximation but also encompasses a structured secant approximation along with tests of when to use this approximation. This method has been tested on a selection of standard problems. The results indicate that, for least-squares problems, the approach taken here is a viable alternative to standard general optimization methods such as the Byrd–Omojokun trust-region method and the Powell damped BFGS line search method. 相似文献
79.
孙文祥 《中国科学A辑(英文版)》2002,45(9):1147-1153
A Liao hyperbolic diffeomorphism has equal measure entropy and topological entropy to that of its induced systems on frame
bundles and Grassmann bundles. This solves a problem Liao posed in 1996 for Liao hyperbolic diffeomorphisms. 相似文献
80.
The revival of the nondiffracting vortex beam after its interaction with the 2D on axis obstacle is examined. We show that the phase topology and the spatial distribution of the orbital angular momentum of the beam transmitted through the obstacle regenerate to the initial form during further free propagation. We verify that the healing effect appears even if the interaction is accompanied by the exchange of the orbital angular momentum. 相似文献