全文获取类型
收费全文 | 47468篇 |
免费 | 8547篇 |
国内免费 | 6526篇 |
专业分类
化学 | 34514篇 |
晶体学 | 704篇 |
力学 | 3031篇 |
综合类 | 437篇 |
数学 | 5038篇 |
物理学 | 18817篇 |
出版年
2024年 | 97篇 |
2023年 | 1024篇 |
2022年 | 1611篇 |
2021年 | 1867篇 |
2020年 | 2126篇 |
2019年 | 2008篇 |
2018年 | 1705篇 |
2017年 | 1639篇 |
2016年 | 2432篇 |
2015年 | 2391篇 |
2014年 | 2908篇 |
2013年 | 3560篇 |
2012年 | 4512篇 |
2011年 | 4600篇 |
2010年 | 3253篇 |
2009年 | 3017篇 |
2008年 | 3267篇 |
2007年 | 2805篇 |
2006年 | 2702篇 |
2005年 | 2207篇 |
2004年 | 1671篇 |
2003年 | 1367篇 |
2002年 | 1276篇 |
2001年 | 1015篇 |
2000年 | 880篇 |
1999年 | 947篇 |
1998年 | 705篇 |
1997年 | 660篇 |
1996年 | 700篇 |
1995年 | 587篇 |
1994年 | 545篇 |
1993年 | 412篇 |
1992年 | 381篇 |
1991年 | 321篇 |
1990年 | 266篇 |
1989年 | 235篇 |
1988年 | 194篇 |
1987年 | 121篇 |
1986年 | 142篇 |
1985年 | 104篇 |
1984年 | 58篇 |
1983年 | 47篇 |
1982年 | 38篇 |
1981年 | 29篇 |
1980年 | 17篇 |
1975年 | 9篇 |
1972年 | 7篇 |
1965年 | 6篇 |
1964年 | 5篇 |
1957年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
161.
A Bayesian approach is used to analyze the seismic events with magnitudes at least 4.7 on Taiwan. Following the idea proposed
by Ogata (1988,Journal of the American Statistical Association,83, 9–27), an epidemic model for the process of occurrence times given the observed magnitude values is considered, incorporated
with gamma prior distributions for the parameters in the model, while the hyper-parameters of the prior are essentially determined
by the seismic data in an earlier period. Bayesian inference is made on the conditional intensity function via Markov chain
Monte Carlo method. The results yield acceptable accuracies in predicting large earthquake events within short time periods. 相似文献
162.
Precise measurement of magnetic moment of short-lived β-emitting nuclei12B ( I π=1+, T 1/2=20.18 ms)
Zhou Dongmei Zheng Yongnan Du Enpeng Xu Yongjun Zhu Jiazheng Yuan Daqing Wang Zhiqiang Luo Hailong Zuo Yi Ma Ruigang Duan Xiao M. Mihara M. Fukuda K. Matsuta T. Minamisono Zhu Shengyun 《中国科学G辑(英文版)》2004,47(5):531-539
The spin polarized β-emitting nuclei12B (I
π=1+,T
1/2=20.18 ms) were produced by the nuclear reaction11B(d, p)12B and by the selection technique of the incident deuteron energy and the12B recoil angle following the nuclear reaction. The nuclear magnetic moment of the short-lived nuclei12B was measured by β-NMR with the β-NMR and β-NQR setup established for the first time in China. The nuclear magnetic moment
of12B was determined to be μ=0.99993±0.00048 nm org=0.99993±0.00048 after the precise correction of the Knight shift. 相似文献
163.
An analytical approach for vibration response analysis of a beam with single passive constrained layer damping (PCLD) patch is presented. The governing equation of motion of the beam is firstly derived on the basis of an energy approach and the Lagrange equation. The noval contribution is that a third admissible function is introduced to represent the longitudinal displacements of the constraining layer in the PCLD patch when the assumed-modes method is applied for discretizing the governing equation. In conventional analytical approaches, only two admissible functions are used together with a longitudinal static equilibrium equation of a section of base beam or constraining layer. Comparison of the computational results from the proposed analytical approach and the conventional analytical approach as well as a commercial FEM code reveals that the proposed analytical approach can describe the vibration responses of the damped beam more accurately for commonly used viscoelastic material (VEM) layer in the PCLD patch while the conventional analytical approach, in general, overestimates the damping effects of the PCLD patch. The advantages and disadvantages of the proposed analytical approach and conventional analytical approach are discussed through some case studies. 相似文献
164.
将稀土配合物Eu(asprin)_3phen掺杂到导电聚合物PVK中,制成结构分别为ITO/PVK:RE配合物/LiF/AI(1),ITO/PVK:RE配合物/PBD/LiF/AI(2)的电致发光(EL)器件。发现二者的电致发光谱存在着较大的差别:在器件(1)中,来自Eu~(3 )的位于594nm(~5D_0→~7F_1)和614nm(~5D_0→~7F_2)处的发光强度大致相当,而在器件(2)中,EL主要来自Eu~(3 )位于614nm的发光,594nm处的发光很弱,与薄膜状态下的光致发光谱(PL)一致。并针对此现象进行了初步讨论。 相似文献
165.
166.
167.
Fan Chung 《Annals of Combinatorics》2005,9(1):1-19
We consider Laplacians for directed graphs and examine their eigenvalues. We introduce a notion of a circulation in a directed graph and its connection with the Rayleigh quotient. We then define a Cheeger constant and establish the Cheeger inequality for directed graphs. These relations can be used to deal with various problems that often arise in the study of non-reversible Markov chains including bounding the rate of convergence and deriving comparison theorems.Received September 8, 2004 相似文献
168.
A new fluorescent chemosensor with imidazole as ionophore was synthesized by the selective derivation of calixarene, which can effectively recognize Cu2+ and Zn2+ leading to different fluoroscopic behaviors in CH3OH-H2O. This system could be considered as a molecular switch. By modulating the pH of the solution, on-off-on fluorescent switching is carried out upon combinatory addition of acid, base and Cu2+. 相似文献
169.
Shui Cao ZHENG Huo Nan LIN Di He HU 《数学学报(英文版)》2005,21(5):1137-1148
In this paper, we investigate the Hausdorff measure for level sets of N-parameter Rd-valued stable processes, and develop a means of seeking the exact Hausdorff measure function for level sets of N-parameter Rd-valued stable processes. We show that the exact Hausdorff measure function of level sets of N-parameter Rd-valued symmetric stable processes of index α is Ф(r) = r^N-d/α (log log l/r)d/α when Nα 〉 d. In addition, we obtain a sharp lower bound for the Hausdorff measure of level sets of general (N, d, α) strictly stable processes. 相似文献
170.
Jianhu Yang Shixun Dai Nengli Dai Lei Wen Lili Hu Zhonghong Jiang 《Journal of luminescence》2004,106(1):9-14
Nonradiative decay of 4I13/2→4I15/2 transition of Er3+ has been investigated in a series of oxide glasses. For Er3+-doped glass samples, the Judd-Ofelt analysis on absorption spectra was performed and the fluorescence lifetime was determined by extrapolating to zero Er3+ concentration limit. Infrared spectra were measured in order to investigate the influence of OH− groups in different glasses. The effects of glass matrix on the decay rate were discussed from the viewpoint of phonon energy, variations of effective fields, and OH− groups. Compared to other glasses, phosphate glass presents low quantum efficiency and large nonradiative decay rate due to its high phonon energy and hygroscopic behavior. 相似文献