全文获取类型
收费全文 | 16777篇 |
免费 | 2601篇 |
国内免费 | 2695篇 |
专业分类
化学 | 9626篇 |
晶体学 | 155篇 |
力学 | 1260篇 |
综合类 | 1361篇 |
数学 | 4086篇 |
物理学 | 5585篇 |
出版年
2024年 | 16篇 |
2023年 | 527篇 |
2022年 | 550篇 |
2021年 | 635篇 |
2020年 | 677篇 |
2019年 | 489篇 |
2018年 | 550篇 |
2017年 | 648篇 |
2016年 | 693篇 |
2015年 | 715篇 |
2014年 | 1122篇 |
2013年 | 1545篇 |
2012年 | 1699篇 |
2011年 | 1572篇 |
2010年 | 1286篇 |
2009年 | 1359篇 |
2008年 | 1194篇 |
2007年 | 1363篇 |
2006年 | 1369篇 |
2005年 | 847篇 |
2004年 | 496篇 |
2003年 | 346篇 |
2002年 | 331篇 |
2001年 | 264篇 |
2000年 | 319篇 |
1999年 | 237篇 |
1998年 | 210篇 |
1997年 | 162篇 |
1996年 | 115篇 |
1995年 | 89篇 |
1994年 | 72篇 |
1993年 | 102篇 |
1992年 | 89篇 |
1991年 | 77篇 |
1990年 | 61篇 |
1989年 | 35篇 |
1988年 | 18篇 |
1987年 | 35篇 |
1986年 | 28篇 |
1985年 | 34篇 |
1984年 | 16篇 |
1983年 | 9篇 |
1982年 | 17篇 |
1981年 | 13篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1976年 | 2篇 |
1971年 | 1篇 |
1959年 | 26篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
自20世纪70年代开始,随着计算复杂性理论的建立,近似算法逐渐成为组合优化的重要研究方向。作为第一批研究对象,装箱问题引起了组合优化领域学者的极大关注。装箱问题模型简单、拓展性强,广泛出现在各种带容量约束的资源分配问题中。除了在物流装载和材料切割等方面愈来愈重要的应用外,装箱算法的任何理论突破都关乎到整个组合优化领域的发展。直到今天,对装箱问题近似算法的研究仍如火如荼。本文主要针对一维模型,简述若干经典Fit算法的发展历程,分析基于线性规划松弛的近似方案的主要思路,总结当前的研究现状并对未来的研究提供一些参考建议。 相似文献
42.
An adaptive tracking design strategy based on quantized state feedback is developed for uncertain nonholonomic mobile robots with unknown wheel slippage effects. All state variables and control torques are assumed to be quantized by the state and input quantizers, respectively, in a network control environment. Thus, the quantized state feedback information is only available for the tracking control design. An approximation-based adaptive controller using quantized states is recursively designed to ensure the robust adaptive tracking against unknown wheel slippage effects where the quantized-states-based adaptive mechanism is derived to compensate for unknown wheel slippage effects, system nonlinearities, and quantization errors. The boundedness of the quantization errors and estimated parameters in the closed-loop system is analyzed by presenting some theoretical lemmas. Based on these lemmas, we prove the uniform ultimate boundedness of closed-loop signals and the convergence of the trajectory tracking error in the presence of wheel slippage effects. Simulations verify the effectiveness of the resulting tracking scheme. 相似文献
43.
Riccardo Adami Ugo Boscain Valentina Franceschi Dario Prandi 《Annales de l'Institut Henri Poincaré (C) Analyse Non Linéaire》2021,38(4):1095-1113
In this paper we show that, for a sub-Laplacian Δ on a 3-dimensional manifold M, no point interaction centered at a point exists. When M is complete w.r.t. the associated sub-Riemannian structure, this means that Δ acting on is essentially self-adjoint in . A particular example is the standard sub-Laplacian on the Heisenberg group. This is in stark contrast with what happens in a Riemannian manifold N, whose associated Laplace-Beltrami operator acting on is never essentially self-adjoint in , if . We then apply this result to the Schrödinger evolution of a thin molecule, i.e., with a vanishing moment of inertia, rotating around its center of mass. 相似文献
44.
通过引入参数,构造了一个全平面上的、含双曲函数的非齐次核函数。利用正切函数的有理分式展开,建立了最佳常数因子与正切函数高阶导数相关联的Hilbert型积分不等式。 作为应用,通过赋予参数不同的值,建立了一些有意义的特殊结果。 相似文献
45.
46.
将一种人工合成的无机聚合物——蒙脱石皂石黏土(smectite,Sm)应用于基质辅助激光解吸电离飞行时间质谱分析(matrix-assisted laser desorption/ionization time of flight mass spectrometry, MALDI-TOF-MS),以检测糖类化合物。 将传统的有机基质2,4,6-三羟基苯乙酮(trihydroxyacetophenone, THAP)与阳离子交换后的皂石黏土混合制备成新型复合基质,应用于糖类化合物的检测。通过比较不同的制样方法,测定不同分子直径的糖类化合物,发现由于受复合基质晶面间距的限制,只有小分子糖类化合物能进入晶面间隙充分接触有机基质并被离子化,从而实现对小分子糖类化合物的选择性检测。 相似文献
47.
Ma Ji Chen Jinjin Chen Liye Zhou Xingjian Qin Xujia Tang Ying Sun Guodao Chen Jiazhou 《显形杂志》2021,24(3):545-563
Journal of Visualization - Effective extraction and visualization of complex target features from volume data are an important task, which allows the user to analyze and get insights of the complex... 相似文献
48.
The acoustic radiation force resulting from acoustic waves have been extensively studied for the contact-free generation of organized patterning arrays. The precise arrangement of microscopic objects clustered at the pressure nodes is critical to the development of functional structures and patterned surfaces. However, the size of the clusters is restricted by the saturation limit of the acoustic nodes. Here, we present a bulk acoustic wave (BAW) platform, which employs a two-dimensional acoustic wave to propel particles of various sizes. Experimentally, when particles are large, significant acoustic energy is scattered and partly absorbed by the matched layers in front of the sensors. The acoustic radiation force from a convergent acoustic pressure field agglomerates the large polystyrene (PS) particles towards the central region instead of the pressure nodes. The parametric analysis has been performed to assess the transition in the particles from clustering at the organized nodal arrays to agglomerating in the central region, which is a function of particle size, particle concentration, and load voltage. Statistically, the particles can agglomerate with a cluster ratio greater than 70%, and this ratio can be improved by increasing the load power/voltage supplied to the transducers. With its ability to perform biocompatible, label-free, and contact-free self-assembly, this concept offers a new possibility in the fabrication of colloidal layers, the recreation of tissue microstructure, the development of organoid spheroid cultures, the migration of microorganisms, and the assembly of bioprinting materials. 相似文献
49.
文章从超冷原子研究的视角出发,回顾了用"从下到上"的方案来开展量子模拟研究的历史。超冷原子作为宏观量子态,各个自由度精确可控,是量子模拟的绝佳平台。光晶格将冷原子物理和凝聚态物理融合起来,是其中最重要的技术之一,为超冷原子量子模拟提供了一个扎实的落脚点。近年来,关于拓扑量子模拟的研究日益兴起,成为超冷原子量子模拟新的重要方向。文章介绍这方面近期的一些工作进展。最后分享作者对超冷原子量子模拟的一些思考。 相似文献
50.
Hao Hongmiao Huang Sumei Chen Aixi 《International Journal of Theoretical Physics》2021,60(8):2766-2777
The strong coupling between a macroscopic mechanical oscillator and a cavity field is essential for many quantum phenomena in a cavity optomechanical system. In this work, we discuss the normal mode splitting in a cavity optomechanical system with a cubic nonlinear movable mirror. We study how the mechanical nonlinearity affects the normal-mode splitting behavior of the movable mirror and the output field. We find that the mechanical nonlinearity can increase the peak separation in the spectra of the movable mirror and the output field. We also find that the heights and linewidths of the two peaks are very sensitive to the mechanical nonlinearity.
相似文献