全文获取类型
收费全文 | 2779篇 |
免费 | 350篇 |
国内免费 | 303篇 |
专业分类
化学 | 581篇 |
晶体学 | 6篇 |
力学 | 156篇 |
综合类 | 72篇 |
数学 | 2105篇 |
物理学 | 512篇 |
出版年
2024年 | 7篇 |
2023年 | 26篇 |
2022年 | 59篇 |
2021年 | 66篇 |
2020年 | 82篇 |
2019年 | 77篇 |
2018年 | 88篇 |
2017年 | 95篇 |
2016年 | 87篇 |
2015年 | 77篇 |
2014年 | 135篇 |
2013年 | 219篇 |
2012年 | 150篇 |
2011年 | 170篇 |
2010年 | 146篇 |
2009年 | 208篇 |
2008年 | 227篇 |
2007年 | 206篇 |
2006年 | 211篇 |
2005年 | 147篇 |
2004年 | 142篇 |
2003年 | 122篇 |
2002年 | 110篇 |
2001年 | 79篇 |
2000年 | 76篇 |
1999年 | 75篇 |
1998年 | 60篇 |
1997年 | 45篇 |
1996年 | 52篇 |
1995年 | 33篇 |
1994年 | 30篇 |
1993年 | 19篇 |
1992年 | 10篇 |
1991年 | 11篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 10篇 |
1985年 | 4篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有3432条查询结果,搜索用时 250 毫秒
41.
IntroductionSincethespecialsuperiorityofartificialneuralnetworkstechnologyinvariousengineeringtechniquesfields,suchasoptimization ,associativememories,patternrecognition ,signalprocessingandautomaticcontrol,therehasbeenincreasinginterestintheinvestigati… 相似文献
42.
为了揭示地形变化对连续档输电线动态特性的影响,本文提出了基于任意高差角的动刚度理论.首先将单档导线视为连续档导线的子结构,构建了两悬挂点不等高的单档导线振动方程,并在该理论方程中引入了二次项,能够考虑重力沿弦向分量的影响,推导出绝缘子串绕其悬挂点转动的动刚度计算方法,通过动刚度理论研究连续档导线横向振动模态和频率,并应用有限元软件ABAQUS 验证理论模态和频率公式的准确性.所得结果表明,动刚度的计算方法具有较高的精度,理论模态与有限元输出结果吻合较好,同时获得的频率和模态可为山地高压输电线路防舞技术的研究提供依据. 相似文献
43.
Yunzhi Ling Yuqiong Luo Jiwen Luo Xiaoying Wang Runcang Sun 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(12):1194-1200
The optimal conditions for synthesizing quaternized chitosan (QCS) via microwave irradiation were explored. The microwave temperature, time, power, mole ratio between chitosan and 2,3-epoxypropyltrimethyl ammonium chloride (ETA), volume ratio between isopropanol and water, and pH value of the reaction system were studied to evaluate the effect on the degree of substitution (DS). The structure of QCS was characterized by means of FT-IR, NMR, XPS and XRD. TGA and DTG were used to measure its thermal stability. At last, QCS acted as a reducing and stabilizing agent to greenly synthesize gold nanoparticles without adding any other chemical reagent. 相似文献
44.
45.
Nonstationarity and related measures for time‐dependent hartree–fock and multiconfigurational models
Anatoliy V. Luzanov 《International journal of quantum chemistry》2013,113(23):2489-2505
Based on an earlier article (Eberly and Singh, Phys. Rev. D 1973 , 7, 359) and related works on short‐time evolution, this article proposes a many‐electron formulation for the nonstationarity degree which can be assigned to quantum system at each time point. The key measure introduced, , is a nonstationarity index that can be thought of as an inverse nominal lifetime at each instance of time. The index is directly computed from the time derivative of one‐electron density matrix and is a size‐consistent quantity. In this article, the approach is developed for the time‐dependent Hartree–Fock (TDHF), single‐excitation (TDCIS), and time‐dependent full configuration interaction (TDFCI) models. As a rule, nonstationarity effects are more pronounced in correlated electron systems, and a joint analysis of and the multiconfigurational character of wave functions apparently provide a deeper insight into dynamical molecular processes. The performed calculations on small molecules in laser fields show a preference for the TDCIS model when comparing TDCIS and TDHF with the “exact” TDFCI model. © 2013 Wiley Periodicals, Inc. 相似文献
46.
The degree distribution has attracted considerable attention from network scientists in the last few decades to have knowledge of the topological structure of networks. It is widely acknowledged that many real networks have power-law degree distributions. However, the deviation from such a behavior often appears when the range of degrees is small. Even worse, the conventional employment of the continuous power-law distribution usually causes an inaccurate inference as the degree should be discrete-valued. To remedy these obstacles, we propose a finite mixture model of truncated zeta distributions for a broad range of degrees that disobeys a power-law behavior in the range of small degrees while maintaining the scale-free behavior. The maximum likelihood algorithm alongside the model selection method is presented to estimate model parameters and the number of mixture components. The validity of the suggested algorithm is evidenced by Monte Carlo simulations. We apply our method to five disciplines of scientific collaboration networks with remarkable interpretations. The proposed model outperforms the other alternatives in terms of the goodness-of-fit. 相似文献
47.
48.
49.
《Discrete Mathematics》2019,342(7):1956-1965
50.
Gallai’s path decomposition conjecture states that the edges of any connected graph on vertices can be decomposed into at most paths. We confirm that conjecture for all graphs with maximum degree at most five. 相似文献