全文获取类型
收费全文 | 46277篇 |
免费 | 3439篇 |
国内免费 | 3743篇 |
专业分类
化学 | 24869篇 |
晶体学 | 685篇 |
力学 | 2361篇 |
综合类 | 223篇 |
数学 | 10743篇 |
物理学 | 14578篇 |
出版年
2024年 | 58篇 |
2023年 | 471篇 |
2022年 | 750篇 |
2021年 | 835篇 |
2020年 | 955篇 |
2019年 | 991篇 |
2018年 | 1964篇 |
2017年 | 2190篇 |
2016年 | 1621篇 |
2015年 | 1547篇 |
2014年 | 1598篇 |
2013年 | 2048篇 |
2012年 | 4699篇 |
2011年 | 3859篇 |
2010年 | 3002篇 |
2009年 | 2663篇 |
2008年 | 1738篇 |
2007年 | 1618篇 |
2006年 | 1563篇 |
2005年 | 5307篇 |
2004年 | 4597篇 |
2003年 | 2892篇 |
2002年 | 1128篇 |
2001年 | 882篇 |
2000年 | 531篇 |
1999年 | 527篇 |
1998年 | 344篇 |
1997年 | 237篇 |
1996年 | 254篇 |
1995年 | 190篇 |
1994年 | 191篇 |
1993年 | 154篇 |
1992年 | 266篇 |
1991年 | 247篇 |
1990年 | 204篇 |
1989年 | 156篇 |
1988年 | 134篇 |
1987年 | 86篇 |
1986年 | 74篇 |
1985年 | 63篇 |
1984年 | 45篇 |
1983年 | 50篇 |
1976年 | 80篇 |
1975年 | 37篇 |
1974年 | 41篇 |
1973年 | 51篇 |
1972年 | 39篇 |
1969年 | 38篇 |
1968年 | 36篇 |
1966年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
利用一维拉格朗日流体动力学程序Med103详细研究了产生类镍Ag,Cd,In,Sn, Sb离子和类氖Fe,Co,Ni,Cu,Zn离子的等离子体状态.通过对电子温度、离子丰度、离子数密度等状态参量的分析比较,得到了这两类等离子体状态之间的对应关系.即类镍银的等离子体状态与类氖铁 的相近,类镍镉的与类氖钴的相近,依次类推.利用这一对应关系可以方便地由类氖机理x射线激光的等离子体状态来对相应元素的类镍x射线激光的等离子体状态进行判断.
关键词:
类氖
类镍
等离子体状态
x射线激光 相似文献
92.
The reaction of a new fluorinated unsymmetrical allenylazine with dimethyl acetylenedicarboxylate and phenylacetylene affords the combined intra-intermolecular criss-cross cycloaddition products, 2,3-disubstituted-1,10-diazatricyclo[5.2.1.04,10]deca-2,6-diene derivatives. The products contain three fused five-membered rings with two nitrogen atoms within an unsaturated heterocyclic system. The structures were assigned using 2D NMR correlations and in the case of the phenylacetylene adduct by X-ray structure analysis. 相似文献
93.
Ewa Stró?yna 《Journal of Differential Equations》2003,193(1):239-259
We solve completely the problem of classification of germs of complex planar vector fields with nilpotent singularity with respect to formal orbital equivalence. 相似文献
94.
A one-pot procedure for the conversion of mono-substituted arenes and heteroarenes into the ortho-cyano derivatives was achieved through directed lithiation followed by electrophilic cyanation with phenyl cyanate. This reaction method proved to be applicable to halogen-lithium exchanged intermediates, so especially useful for the synthesis of benzonitriles. The scope of the reaction sequence was explored using a number of substrates. 相似文献
95.
报道Ar^q Ne(q=8,9,11,12)碰撞体系中多电子转移过程,得到了多组实验测量电荷交换截面数据,讨论入射离子电荷交换截面、反冲离子产生截面与入射离子电荷态、能量以及散射离子电荷态的关系,并且将实验结果与Ar^q Ar碰撞体系进行对比研究。在修正分子库仑过垒模型的基础上,对实验现象做了合理的解释。 相似文献
96.
Parameters of Gaussian multivariate models are often estimated using the maximum likelihood approach. In spite of its merits, this methodology is not practical when the sample size is very large, as, for example, in the case of massive georeferenced data sets. In this paper, we study the asymptotic properties of the estimators that minimize three alternatives to the likelihood function, designed to increase the computational efficiency. This is achieved by applying the information sandwich technique to expansions of the pseudo-likelihood functions as quadratic forms of independent normal random variables. Theoretical calculations are given for a first-order autoregressive time series and then extended to a two-dimensional autoregressive process on a lattice. We compare the efficiency of the three estimators to that of the maximum likelihood estimator as well as among themselves, using numerical calculations of the theoretical results and simulations. 相似文献
97.
In this paper, by using elementary analysis, we establish some new Lyapunov-type inequalities for nonlinear systems of differential equations, special cases of which contain the well-known equations such as Emden-Fowler-type and half-linear equations. The inequalities obtained here can be used as handy tools in the study of qualitative behaviour of solutions of the associated equations. 相似文献
98.
99.
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
100.
E. Beinrohr M. Németh P. Tsch?pel G. T?lg 《Fresenius' Journal of Analytical Chemistry》1992,344(3):93-99
Summary Flow-through electrochemical cells with porous working electrodes made of crushed reticulated vitreous carbon and plated with mercury were used for absolute analysis of trace amounts of lead by anodic stripping coulometry with collection (ASCWC) in a flow system. The role of mercury coating, flow rate and pH were investigated. The coulombic content of the collection peak corresponded to the theoretical values calculated by Faraday's law in a concentration range from about 10–9 to 10–6 mol/l. The relative error and the relative standard deviation was +0.15% and 0.8%, respectively for 2×10–6 mol/l analyte concentration. The absolute detection limit (3 s) was 0.1 ng of Pb, the linear response range 7×104.
One leave from: Department of Analytical Chemistry, Slovak Technical University, CS-812 37 Bratislava, Czechoslovakia 相似文献