全文获取类型
收费全文 | 17727篇 |
免费 | 2777篇 |
国内免费 | 2535篇 |
专业分类
化学 | 13548篇 |
晶体学 | 181篇 |
力学 | 879篇 |
综合类 | 223篇 |
数学 | 2127篇 |
物理学 | 6081篇 |
出版年
2024年 | 19篇 |
2023年 | 241篇 |
2022年 | 295篇 |
2021年 | 480篇 |
2020年 | 567篇 |
2019年 | 615篇 |
2018年 | 482篇 |
2017年 | 450篇 |
2016年 | 719篇 |
2015年 | 757篇 |
2014年 | 940篇 |
2013年 | 1252篇 |
2012年 | 1526篇 |
2011年 | 1663篇 |
2010年 | 1300篇 |
2009年 | 1193篇 |
2008年 | 1398篇 |
2007年 | 1302篇 |
2006年 | 1241篇 |
2005年 | 959篇 |
2004年 | 800篇 |
2003年 | 715篇 |
2002年 | 676篇 |
2001年 | 541篇 |
2000年 | 414篇 |
1999年 | 364篇 |
1998年 | 277篇 |
1997年 | 209篇 |
1996年 | 236篇 |
1995年 | 200篇 |
1994年 | 153篇 |
1993年 | 136篇 |
1992年 | 136篇 |
1991年 | 114篇 |
1990年 | 121篇 |
1989年 | 81篇 |
1988年 | 62篇 |
1987年 | 59篇 |
1986年 | 44篇 |
1985年 | 43篇 |
1984年 | 26篇 |
1983年 | 32篇 |
1982年 | 23篇 |
1980年 | 13篇 |
1979年 | 24篇 |
1978年 | 20篇 |
1977年 | 23篇 |
1976年 | 13篇 |
1975年 | 17篇 |
1973年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Hyun Chul Choi Min Kyu Lee Hyun Joon Shin Seung Bin Kim 《Journal of Electron Spectroscopy and Related Phenomena》2003,130(1-3):85-96
To investigate the formation of a solid electrolyte interface (SEI) on the Li1+xV3O8 electrode surface in the thermodynamic stability range of the organic electrolyte, we applied scanning photoelectron microscopy (SPEM) to a pristine electrode and to an electrode after ten cycles. The F K-edge absorption spectrum of the cycled electrode showed that LiF forms on the electrode surface during the lithium insertion–extraction process in the Li1+xV3O8/Li cell. The photoelectron spectrum for the cycled electrode showed intense spectral features corresponding to Li 1s, F 2s, F 2p, and P 2p electron signals, whereas these spectral features were of negligible intensity for the pristine electrode. The above results give strong support for the formation of an SEI that consists of LiF and compounds containing phosphorus during operation of the battery. The SPEM images also revealed that the fluorine distribution on the surface of the cycled electrode was inhomogeneous. 相似文献
92.
Properties of excitons in vertically coupled GaAs/AlGaAs quantum dots were investigated using the variational method within the envelope function and effective mass approximations. It was found that when the thickness of the spacer layer becomes less than about one exciton Bohr radius, both the exciton binding energy and the fundamental optical transition energy are reduced compared to those in isolated quantum dots. This is a result of increased space extension of exciton due to the penetration of carrier wave functions into the spacer layer and corresponding reduction in confinement energy which dominates over the Coulomb interaction between the electron and the hole. 相似文献
93.
94.
KunHuaLIN MaoPingSONG ChenXiaDU QiaoHongZHANG YangJieWU 《中国化学快报》2003,14(7):673-676
The cyclomercurated ferrocenylimines containing heterocyclic ring were prepared by the condensation of cyclomercuration of acylferrocene with the appropriate heterocyclic amine.This procedure provides an efficient method for the synthesis of cyclomerucurated ferrocenylimines containing heterocyclic ring which are difficultly synthesized by the conventional method.The reaction mechanism is proposed. 相似文献
95.
96.
Using the theoretically calculated point-defect total-energy values of Baraff and Schlüter in GaAs, anamphoteric-defect model has been proposed by Walukiewicz to explain a large number of experimental results. The suggested amphoteric-defect system consists of two point-defect species capable of transforming into each other: the doubly negatively charged Ga vacancyV
Ga
2–
and the triply positively charged defect complex (ASGa+V
As)3+, with AsGa being the antisite defect of an As atom occupying a Ga site andV
As being an As vacancy. When present in sufficiently high concentrations, the amphoteric defect systemV
Ga
2–
/(AsGa+V
As)3+ is supposed to be able to pin the GaAs Fermi level at approximately theE
v
+0.6 eV level position, which requires that the net free energy of theV
Ga/(AsGa+V
As) defect system to be minimum at the same Fermi-level position. We have carried out a quantitative study of the net energy of this defect system in accordance with the individual point-defect total-energy results of Baraff and Schlüter, and found that the minimum net defect-system-energy position is located at about theE
v
+1.2 eV level position instead of the neededE
v
+0.6 eV position. Therefore, the validity of the amphoteric-defect model is in doubt. We have proposed a simple criterion for determining the Fermi-level pinning position in the deeper part of the GaAs band gap due to two oppositely charged point-defect species, which should be useful in the future. 相似文献
97.
BAHADURASYMPTOTICEFFICIENCYINASEMIPARAMETRICREGRESSIONMODEL¥LIANGHUA;CHENGPINGAbstract:TheauthorSgiveMLEθ1MLofθ1inthemodelY=θ... 相似文献
98.
以陆地棉(冀棉20)下胚轴为外植体,在含KT0.3mg/L和2,4-D0.08mg/L的MS培养基上,诱导产生了胚性愈伤组织,继代培养不需要添加激素,胚性愈伤组织即分化为胚状体,并萌发出小芽,胚状体萌发过程与合子胚相似,但出现了一些畸形胚,解剖学方法观察发现,这些畸形胚的维管束系统不明显或形态异常,以农杆菌介导法对冀棉20胚状体及胚性愈伤组织进行了雪花莲凝集素(GNA)基因的遗传转化条件探索,并以GUS基域瞬间进行检测加以证实,得出农杆菌的浓度为O.D600=0.8时,浸染时间为5min,共培养时间为3d,筛选培养基中卡那霉素浓度为75mg/L,对冀棉20胚状体及胚性愈伤组织转化是较为适合的。 相似文献
99.
100.
Thin films of polystyrene (PS), poly(methyl methacrylate) (PMMA) and polystyrene-polyacrylonitrile copolymer (PS-AN), containing various embedded transition-metal complexes, have been studied by FTIR microscopy. The spatial distributions of the transition-metal carbonyl complexes throughout the thin organic polymer films have been determined by a two-dimensional IR mapping procedure. The spectral variations observed in the distribution of the metal carbonyls throughout the different polymer films are discussed. The IR data show that the technique used to prepare the organometallic-embedded thin films (viz. freeze-drying of solutions followed by hot mechanical pressing of the residues) does in general lead to homogeneous films which may eventually find industrial application, e.g. as membrane sensors for small molecules. 相似文献