全文获取类型
收费全文 | 580篇 |
免费 | 157篇 |
国内免费 | 54篇 |
专业分类
化学 | 207篇 |
晶体学 | 8篇 |
力学 | 181篇 |
综合类 | 1篇 |
数学 | 54篇 |
物理学 | 340篇 |
出版年
2024年 | 1篇 |
2023年 | 29篇 |
2022年 | 51篇 |
2021年 | 55篇 |
2020年 | 30篇 |
2019年 | 24篇 |
2018年 | 35篇 |
2017年 | 31篇 |
2016年 | 38篇 |
2015年 | 31篇 |
2014年 | 57篇 |
2013年 | 50篇 |
2012年 | 62篇 |
2011年 | 52篇 |
2010年 | 31篇 |
2009年 | 41篇 |
2008年 | 18篇 |
2007年 | 32篇 |
2006年 | 32篇 |
2005年 | 18篇 |
2004年 | 6篇 |
2003年 | 7篇 |
2002年 | 8篇 |
2001年 | 10篇 |
2000年 | 8篇 |
1999年 | 4篇 |
1998年 | 1篇 |
1997年 | 4篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1988年 | 2篇 |
1987年 | 5篇 |
1986年 | 11篇 |
1985年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有791条查询结果,搜索用时 15 毫秒
681.
空间机器人系统的柔性主要体现在空间机器人的臂杆和连接各臂杆之间的铰关节。由于空间机器人系统结构的复杂性,以往研究人员对同时具有柔性关节和柔性臂的系统关注不够。为此探讨了参数未知柔性关节-柔性臂空间机器人系统的动力学模拟、轨迹跟踪控制算法设计和关节、臂杆双重柔性振动的主动抑制问题。首先,采用多体动力学建模方法并结合漂浮基空间机器人固有的线动量和角动量守恒动力学特性,推导了系统的动力学方程。以此为基础,考虑到空间机器人实际应用中各关节铰具有较强柔性的情况,引入一种关节柔性补偿控制器解决了传统奇异摄动法应用受关节柔性限制问题,导出了适用于控制系统算法设计的数学模型。然后,利用该模型,基于反演思想在慢时标子系统中设计神经网络自适应控制算法来补偿系统参数未知和柔性关节引起的转动误差,实现系统运动轨迹跟踪性能;针对快时标子系统,设计了鲁棒最优控制算法抑制因柔性关节及柔性臂引起的系统双重弹性振动,保证系统的稳定性。最后,通过仿真对比实验验证了所设计控制算法的有效性。 相似文献
682.
The spin-Hamiltonian parameters (g factors g i and hyperfine structure constants A i , where i = x, y, z) of the rhombic Mo5+ center in Ca1?x Y x MoO4 crystal are calculated from the high-order perturbation formulas based on the two-mechanism model for the rhombic d1 tetrahedral clusters with the ground state |d z 2〉. In these formulas, besides the contributions due to the widely applied crystal-field (CF) mechanism concerning CF excited states, those due to the charge-transfer (CT) mechanism (which is omitted in CF theory) concerning CT excited states are considered. The calculated results are in reasonable agreement with the experimental values. The calculations show that because of the great relative importance of CT mechanism for the components of spin-Hamiltonian parameter along x and y axes, the accurate and complete calculations of spin-Hamiltonian parameters for Mo5+ and other high valence state dn ions in crystals should take account of both the CF and CT mechanisms. The defect model of the rhombic Mo5+ center is also confirmed from the calculations. 相似文献
683.
评估每个粒子的重要性是确保粒子滤波法跟踪目标准确性的重要因素。针对背景杂波和噪声干扰形成的大量虚警导致小弱目标跟踪识别的随机性和不确定性问题, 提出了一种基于粒子区别性稀疏表征的小弱目标跟踪方法。该方法根据红外图像信号自适应构建分类超完备字典, 即反映目标信号特征的目标字典和表示背景杂波的背景字典, 有利于突出目标粒子和背景粒子在联合分类字典的稀疏表征差异程度;建立基于目标粒子和背景粒子稀疏重构残差差异性的粒子滤波观测模型, 采用随机估计法对字典子空间进行在线更新, 实现对目标状态估计与跟踪。理论分析和试验结果表明, 该方法增强了随机粒子的状态估计能力, 提升了粒子稀疏表征对小弱运动目标的适应能力和跟踪识别准确度。 相似文献
684.
电磁驱动柱形固体套筒内爆加载技术是高能量密度物理实验研究的重要加载方式。由于固体金属具有一定的结合强度, 需外加载荷达到特定阈值才会发生塑性流动, 且在内爆过程中塑性做功会耗散部分电磁力做功而变成金属材料的内能, 进而对固体套筒的内爆过程产生影响。通过弹塑性力学平面轴对称问题的解, 给出了套筒发生塑性流动时外加电流(即屈服电流)与套筒参数的关系。利用考虑材料强度的零维不可压缩模型对铝套筒的内爆过程进行模拟, 并分别与简单零维模型和实验数据进行对比, 结果发现当电流峰值远大于(20倍于)屈服电流时, 金属材料强度的影响甚微;而当峰值电流只数倍于屈服电流时, 金属材料强度的影响便不能忽略。 相似文献
685.
网格生成技术是CFD复杂工程应用的重要环节, 网格质量的好坏直接影响计算结果的精准度, 因此其已成为CFD的重要研究领域.在张涵信院士的指导下, 作者自20世纪90年代初开始开展非结构网格、混合网格技术和相应的计算方法研究, 并逐步发展至动态混合网格技术及非定常计算方法.在张涵信院士80华诞之际, 对近年来作者及团队在网格生成技术及应用方面所取得的进展进行了简要的综述, 分别介绍了静动态混合网格生成、定常/非定常计算方法、网格技术的应用等方面的进展情况.最后, 就网格生成技术目前还存在的问题, 展望了未来的发展方向.作者谨以此文表达对张涵信院士25年来的培养、关怀和帮助的崇高敬意. 相似文献
686.
《中国化学快报》2023,34(8):108102
The threat to public health from bacterial infections has led to an urgent need to develop simpler, faster and more reliable bacterial detection methods. In this work, we developed a universal dual-recognition based sandwich fluorescence resonance energy transfer (FRET) sensor by using specific aptamer-modified quantum dots (Aptamer-QDs) as energy donor and lectin concanavalin A (Con A) modified gold nanoparticles (Con A-AuNPs) as energy acceptor to achieve rapid and sensitive detection of Escherichia coli (E. coli) within 0.5 h. In the presence of the target E. coli, the energy donor of Aptamer-QDs and acceptor of Con A-AuNPs were close to each other, causing changes of FRET signals. Based on the constructed FRET sensor, a linear detection range of from 102 cfu/mL to 2 × 108 cfu/mL with the detection limit of 45 cfu/mL for E. coli was achieved. Furthermore, the FRET sensor was applied to detect E. coli in the milk and orange juice with the detection limit of 300 cfu/mL and 200 cfu/mL, respectively and recovery rate from 83.1% to 112.5%. The strategy holds great promise in pathogenic bacteria detection due to its rapid and sensitivity. 相似文献
687.
《中国化学快报》2023,34(8):107897
Hydrocarbons are promising products for CO2 electroreduction (CRR) while is impeded by the low selectivity. Turning the curvature of the active site is an effective strategy to change the adsorption properties and further regulate the product distribution and reactivity. Herein, we have designed a novel V single atom catalyst (SAC) based on rolled two-dimensional (2D) BC3N2 substrate with different curvatures. The results have demonstrated that increased curvature can enhance the adsorption strength of CRR intermediates, which follows different mechanisms for systems with low and high curvature. This character eventually leads to the deviation away from the scaling line between Ead[CO]∼Ead[COOH] based on transition metals for V@2D-BC3N2 systems. 3-3 system is screened as the optimal candidate for hydrocarbons production due to the enhanced binding ability of adsorbates, which can increase the reactivity for hydrocarbons production and hinder the production of H2 and HCOOH simultaneously. 相似文献
688.
《中国化学快报》2023,34(8):107885
Aqueous zinc ion batteries (AZIBs) have attracted much attention in recent years due to their high safety, low cost, and decent electrochemical performance. However, the traditional electrodes development process requires tedious synthesis and testing procedures, which reduces the efficiency of developing high-performance battery devices. Here, we proposed a high-throughput screening strategy based on first-principles calculations to aid the experimental development of high-performance spinel cathode materials for AZIBs. We obtained 14 spinel materials from 12,047 Mn/Zn-O based materials by examining their structures and whether they satisfy the basic properties of electrodes. Then their band structures and density of states, open circuit voltage and volume expansion rate, ionic diffusion coefficient and energy barrier were further evaluated by first-principles calculations, resulting in five potential candidates. One of the promising candidates identified, Mg2MnO4, was experimentally synthesized, characterized and integrated into an AZIB based cell to verify its performance as a cathode. The Mg2MnO4 cathode exhibits excellent cycling stability, which is consistent with the theoretically predicted low volume expansion. Moreover, at high current density, the Mg2MnO4 cathode still exhibits high reversible capacity and excellent rate performance, indicating that it is an excellent cathode material for AZIBs. Our work provides a new approach to accelerate the development of high-performance cathodes for AZIBs and other ion batteries. 相似文献
689.
《中国化学快报》2023,34(8):108079
Current clinical treatments cannot effectively delay the progression of osteoarthritis (OA). Consequently, joint replacement surgery is required for late-stage OA when patients cannot tolerate pain and joint dysfunction. Therefore, the prevention of OA progression in the early and middle stages is an urgent clinical problem. In a previous study, we demonstrated that NDRG3-mediated hypoxic response might be closely related to the development and progression of OA. In this study, an injectable thermosensitive hydrogel was established by cross-linking Pluronic F-127 and hyaluronic acid (HA) for the sustained release of hypoxia-induced exosomes (HExos) derived from adipose-derived mesenchymal stem cells. We demonstrated that for OA at the early and middle stages, the HExos-loaded HP hydrogel could maintain the chondrocyte phenotype by enhancing chondrocyte autophagy, reducing chondrocyte apoptosis, and promoting chondrocyte activity and proliferation through the NDRG3-mediated hypoxic response. This novel composite hydrogel, which could activate the NDRG3-mediated hypoxic response, may provide new ideas and a theoretical basis for the treatment of early- and mid-stage OA. 相似文献
690.