全文获取类型
收费全文 | 38449篇 |
免费 | 359篇 |
国内免费 | 291篇 |
专业分类
化学 | 16054篇 |
晶体学 | 491篇 |
力学 | 1599篇 |
综合类 | 13篇 |
数学 | 10378篇 |
物理学 | 10564篇 |
出版年
2022年 | 131篇 |
2021年 | 214篇 |
2020年 | 169篇 |
2019年 | 199篇 |
2018年 | 1372篇 |
2017年 | 1620篇 |
2016年 | 1035篇 |
2015年 | 807篇 |
2014年 | 799篇 |
2013年 | 1410篇 |
2012年 | 3561篇 |
2011年 | 2830篇 |
2010年 | 2158篇 |
2009年 | 1887篇 |
2008年 | 1031篇 |
2007年 | 1052篇 |
2006年 | 983篇 |
2005年 | 4718篇 |
2004年 | 4195篇 |
2003年 | 2566篇 |
2002年 | 739篇 |
2001年 | 494篇 |
2000年 | 274篇 |
1999年 | 303篇 |
1998年 | 235篇 |
1997年 | 172篇 |
1996年 | 149篇 |
1995年 | 173篇 |
1994年 | 131篇 |
1993年 | 99篇 |
1992年 | 260篇 |
1991年 | 212篇 |
1990年 | 233篇 |
1989年 | 201篇 |
1988年 | 185篇 |
1987年 | 134篇 |
1986年 | 131篇 |
1985年 | 159篇 |
1984年 | 167篇 |
1983年 | 115篇 |
1982年 | 107篇 |
1981年 | 124篇 |
1980年 | 117篇 |
1979年 | 104篇 |
1978年 | 112篇 |
1977年 | 108篇 |
1976年 | 165篇 |
1975年 | 115篇 |
1974年 | 103篇 |
1973年 | 98篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
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
72.
A closed microwave digestion method followed by inductively coupled plasma spectrometric (ICP-MS) analysis was evaluated for the determination of trace impurities in photoresist. To optimize the digestion procedure, several digestion parameters such as acid, heating temperature and heating time were evaluated. Besides, the digestion efficiency of used photoresist material and the recovery of analyte elements obtained by the use of gravimetric method and ICP-MS measurement, individually, were also compared to clarify the completeness of digestion. According to our experiments, the gravimetric method was found to be not so relevant to the completeness of digestion, because the remaining sample matrix could cause suppression effect in the subsequent ICP-MS measurement. In view of minimizing blank value and working time, a simple single-step heating program was proposed to mineralize 0.25 ml of photoresist material with 5 ml of nitric acid at 180 °C for 10 min. Based on the comparative study of the analytical results obtained by instrumental neutron activation analysis (INAA) and proposed method, the reliability of proposed method for the determination of trace metallic impurities in photoresist material has been confirmed. 相似文献
73.
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
74.
75.
Formation of p-type ZnO film on InP substrate by phosphor doping 总被引:3,自引:0,他引:3
Kyu-Hyun Bang Deuk-Kyu Hwang Min-Chul Park Young-Don Ko Ilgu Yun Jae-Min Myoung 《Applied Surface Science》2003,210(3-4):177-182
ZnO thin film was initially deposited on InP substrate by radio frequency (rf) magnetron sputtering and the diffusion process was performed using the closed ampoule technique where Zn3P2 was used as the dopant source. To verify the junction formation of ZnO thin films, the electrical properties were measured, and the effects of Zn3P2 diffusion on ZnO thin films were investigated. It is observed that the electrical property of the film is changed from n-type to p-type by dopant diffusion effect. Based on the results, it is confirmed that ZnO thin films can be a potential candidate for ultraviolet (UV) optical devices. 相似文献
76.
We characterize Poisson and Jacobi structures by means of complete lifts of the corresponding tensors: the lifts have to be
related to canonical structures by morphisms of corresponding vector bundles. Similar results hold for generalized Poisson
and Jacobi structures (canonical structures) associated with Lie algebroids and Jacobi algebroids. 相似文献
77.
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
78.
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
79.
80.
The existence of a Nash equilibrium in the undiscounted repeated two-person game of incomplete information on one side is
established. The proof depends on a new topological result resembling in some respect the Borsuk-Ulam theorem. 相似文献