全文获取类型
收费全文 | 38851篇 |
免费 | 9682篇 |
国内免费 | 1458篇 |
专业分类
化学 | 43395篇 |
晶体学 | 363篇 |
力学 | 580篇 |
综合类 | 2篇 |
数学 | 2292篇 |
物理学 | 3359篇 |
出版年
2023年 | 33篇 |
2022年 | 51篇 |
2021年 | 241篇 |
2020年 | 1290篇 |
2019年 | 2638篇 |
2018年 | 1065篇 |
2017年 | 694篇 |
2016年 | 3438篇 |
2015年 | 3601篇 |
2014年 | 3534篇 |
2013年 | 4232篇 |
2012年 | 3193篇 |
2011年 | 2464篇 |
2010年 | 3007篇 |
2009年 | 2955篇 |
2008年 | 2591篇 |
2007年 | 1909篇 |
2006年 | 1622篇 |
2005年 | 1839篇 |
2004年 | 1571篇 |
2003年 | 1460篇 |
2002年 | 2106篇 |
2001年 | 1453篇 |
2000年 | 1357篇 |
1999年 | 405篇 |
1998年 | 82篇 |
1997年 | 93篇 |
1996年 | 94篇 |
1995年 | 59篇 |
1994年 | 66篇 |
1993年 | 90篇 |
1992年 | 72篇 |
1991年 | 57篇 |
1990年 | 52篇 |
1989年 | 63篇 |
1988年 | 42篇 |
1987年 | 39篇 |
1986年 | 38篇 |
1985年 | 47篇 |
1984年 | 37篇 |
1983年 | 25篇 |
1982年 | 23篇 |
1981年 | 36篇 |
1980年 | 17篇 |
1979年 | 25篇 |
1978年 | 24篇 |
1977年 | 22篇 |
1976年 | 19篇 |
1975年 | 17篇 |
1974年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
141.
This paper proposes a model for the parametric representation of linguistic hedges in Zadeh’s fuzzy logic. In this model each linguistic truth-value, which is generated from a primary term of the linguistic truth variable, is identified by a real number r depending on the primary term. It is shown that the model yields a method of efficiently computing linguistic truth expressions accompanied with a rich algebraic structure of the linguistic truth domain, namely De Morgan algebra. Also, a fuzzy logic based on the parametric representation of linguistic truth-values is introduced. 相似文献
142.
Sung‐Fu Hsu Tzong‐Ming Wu Chien‐Shiun Liao 《Journal of Polymer Science.Polymer Physics》2006,44(23):3337-3347
Poly(3‐hydroxybutyrate) (PHB)/layered double hydroxides (LDHs) nanocomposites were prepared by mixing PHB and poly(ethylene glycol) phosphonates (PEOPAs)‐modified LDH (PMLDH) in chloroform solution. Both X‐ray diffraction data and TEM micrographs of PHB/PMLDH nanocomposites indicate that the PMLDHs are randomly dispersed and exfoliated into the PHB matrix. In this study, the effect of PMLDH on the isothermal crystallization behavior of PHB was investigated using a differential scanning calorimeter (DSC) and polarized optical microscopy. Isothermal crystallization results of PHB/PMLDH nanocomposites show that the addition of 2 wt % PMLDH into PHB induced more heterogeneous nucleation in the crystallization significantly increasing the crystallization rate and reducing their activation energy. By adding more PMLDH into the PHB probably causes more steric hindrance of the diffusion of PHB, reducing the transportation ability of polymer chains during crystallization, thus increasing the activation energy. The correlation among crystallization kinetics, melting behavior and crystalline structure of PHB/PMLDH nanocomposites can also be discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3337–3347, 2006 相似文献
143.
L. A. Gil‐Alana 《商业与工业应用随机模型》2006,22(4):385-395
This article examines the length of the cycles in the gross domestic product (GDP) real per capita series of 15 countries by means of new statistical techniques based on unit root cycles. We propose tests for unit root cycles at each of the frequencies of the process. Using this approach, we are able to approximate the number of periods per cycle. The results show that the cycles have a periodicity of approximately six years when the disturbances are white noise. However, if we permit autocorrelation, they may also occur at smaller intervals of time. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
144.
In this paper, we report that the phase transformation of Ni-B, Ni-P diffusion barriers deposited electrolessly on Cu, for the reason that the Ni-P layer is a more effective diffusion barrier than the Ni-B layer. The Ni3B crystallized was decomposed to Ni and B2O3 above 400 °C and the Ni3P crystallized was decomposed to Ni and P2O5 above 600 °C respectively in Ar atmosphere. Also, the Ni3B was decomposed to Ni and free B above 400 °C and the Ni3P was decomposed to Ni and free P above 600 °C respectively in H2 atmosphere. The decomposed Ni formed a solid solution with Cu. The Cu diffusion occurred above 400 °C for Ni-B layer and above 600 °C for Ni-P layer, respectively. Because the decomposition temperature of Ni-P layer is about 200 °C higher than that of Ni-B layer, the Ni-P layer is a more effective barrier for Cu than the Ni-B layer. 相似文献
145.
146.
Jian‐guo Tang 《Mathematical Methods in the Applied Sciences》2006,29(11):1327-1338
An implicit iterative method is applied to solving linear ill‐posed problems with perturbed operators. It is proved that the optimal convergence rate can be obtained after choosing suitable number of iterations. A generalized Morozov's discrepancy principle is proposed for the problems, and then the optimal convergence rate can also be obtained by an a posteriori strategy. The convergence results show that the algorithm is a robust regularization method. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
147.
This paper is devoted to the proof of almost global existence results for Klein‐Gordon equations on Zoll manifolds (e.g., spheres of arbitrary dimension) with Hamiltonian nonlinearities, when the Cauchy data are smooth and small. The proof relies on Birkhoff normal form methods and on the specific distribution of eigenvalues of the Laplacian perturbed by a potential on Zoll manifolds. © 2007 Wiley Periodicals, Inc. 相似文献
148.
149.
150.