全文获取类型
收费全文 | 36812篇 |
免费 | 6536篇 |
国内免费 | 4277篇 |
专业分类
化学 | 25292篇 |
晶体学 | 485篇 |
力学 | 2429篇 |
综合类 | 296篇 |
数学 | 4431篇 |
物理学 | 14692篇 |
出版年
2024年 | 34篇 |
2023年 | 758篇 |
2022年 | 818篇 |
2021年 | 1109篇 |
2020年 | 1475篇 |
2019年 | 1381篇 |
2018年 | 1233篇 |
2017年 | 1150篇 |
2016年 | 1726篇 |
2015年 | 1698篇 |
2014年 | 2075篇 |
2013年 | 2625篇 |
2012年 | 3215篇 |
2011年 | 3414篇 |
2010年 | 2332篇 |
2009年 | 2311篇 |
2008年 | 2498篇 |
2007年 | 2252篇 |
2006年 | 2151篇 |
2005年 | 1663篇 |
2004年 | 1335篇 |
2003年 | 1089篇 |
2002年 | 980篇 |
2001年 | 808篇 |
2000年 | 830篇 |
1999年 | 789篇 |
1998年 | 703篇 |
1997年 | 663篇 |
1996年 | 674篇 |
1995年 | 610篇 |
1994年 | 532篇 |
1993年 | 426篇 |
1992年 | 424篇 |
1991年 | 324篇 |
1990年 | 300篇 |
1989年 | 237篇 |
1988年 | 204篇 |
1987年 | 171篇 |
1986年 | 153篇 |
1985年 | 152篇 |
1984年 | 104篇 |
1983年 | 70篇 |
1982年 | 60篇 |
1981年 | 36篇 |
1980年 | 16篇 |
1979年 | 10篇 |
1977年 | 2篇 |
1971年 | 1篇 |
1959年 | 1篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Science China Mathematics - In this study, we propose nonparametric testing for heteroscedasticity in nonlinear regression models based on pairwise distances between points in a sample. The test... 相似文献
52.
Heat energy can transfer via convection, conduction, and radiation. Based on convection and conduction in microfluidics, people have designed and fabricated many novel devices. However, almost none of them has adaptivity, thus restricting practical applications under different conditions. To solve this problem, here we propose a passive approach to adaptive responses. That is,we consider the thermal convection-conduction process in microfluidic structures where Darcy’s law and Fourier’s law are both valid. By carefully designing two key parameters(i.e., tensorial thermal conductivity and tensorial permeability) of a metashell,we theoretically reveal that its effective properties(i.e., effective thermal conductivity and effective permeability) can adaptively change according to the inside object, thus yielding the "chameleonlike metashell". Further, this metashell is passive since it requires no prior knowledge of the inside object. We also report that the chameleonlike behavior can occur for anisotropic inside objects, nonuniform external fields, or even complex shapes. All theoretical analyses agree well with finite-element simulations.The chameleonlike metashell can act as an intelligent metamaterial in microfluidics for its adaptive responses, and it can also benefit other physical fields where convection plays a role, such as mass diffusion. 相似文献
53.
We fabricate Sm-doped Ca3Co4O9+δ(CCO)bulk materials in magnetic field during both processes of chemical synthesis and cold pressing.The structure and electrical performance of the samples are investigated.With the increasing Sm concentration,the electrical conductivity 1/ρ decreases and the Seebeck coefficientαincreases.As a result,the power factor(PF=α^2/ρ)is raised slightly.After applying magnetic field,the extent of texture,grain size and density of all the bulk materials are improved obviously,thereby an enhanced electrical conductivity can be gained.Additionally,the degeneracy of Co^4+ state in the CoO2 layer of CCO is also increased as the magnetic field is used in the preparing process,which results in an enhancedα.The Ca2.85Sm0.15Co4O9+δ prepared in magnetic field shows the largest power factor(0.20 mW·m^-1·K^-2 at 1073 K). 相似文献
54.
Artem Yakovliev Tymish Y. Ohulchanskyy Roman Ziniuk Tereza Dias Xin Wang Hao Xu Guanying Chen Junle Qu Anderson S. L. Gomes 《Particle & Particle Systems Characterization》2020,37(2):1900445
In this work, the application of near infrared (NIR)-emitting NaYbF4:1%Tm3+@NaLuF4:30%Nd3+ core–shell nanoparticles is reported for noninvasive probing and monitoring the temperature during photopolymerization of dental materials. When excited at 808 nm, the synthesized nanoparticles emit NIR photoluminescence (PL) with two distinctive peaks at 865 and 980 nm which correspond to radiative transitions from the doped Nd3+ and Yb3+ ions, respectively. Luminescence intensity ratio between these two bands is found to vary with temperature due to temperature-dependent electronic excitation energy transfer between Nd3+ and Yb3+ ions at the core/shell interface. This finding allows luminescence ratiometric evaluation of the in situ temperature during photopolymerization of resin cement (doped with nanoparticles) in a veneer placement procedure. In addition, the NIR emission also enables PL imaging of the distribution of the adhesive under the veneer. The results highlight that rare-earth ions–doped nanoparticles with both excitation and emission in the NIR spectral range are advantageous for both PL-based nanothermometry and imaging due to the reduced attenuation of NIR light by dental ceramics. 相似文献
55.
Nonlinear Dynamics - This paper describes the chaos behavior of an in-plane tethered satellite system induced by atmospheric drag and the Earth’s oblateness. A commonly used model, the... 相似文献
56.
Dr. Feifan Wang Jie Tian Dr. Mengzhu Li Dr. Weizhen Li Dr. Lifang Chen Xiaozhi Liu Dr. Jian Li Aidaer Muhetaer Prof. Dr. Qi Li Prof. Dr. Yuan Wang Prof. Dr. Lin Gu Prof. Dr. Ding Ma Prof. Dr. Dongsheng Xu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(21):8280-8286
Fully utilizing solar energy for catalysis requires the integration of conversion mechanisms and therefore delicate design of catalyst structures and active species. Herein, a MOF crystal engineering method was developed to controllably synthesize a copper–ceria catalyst with well-dispersed photoactive Cu-[O]-Ce species. Using the preferential oxidation of CO as a model reaction, the catalyst showed remarkably efficient and stable photoactivated catalysis, which found practical application in feed gas treatment for fuel cell gas supply. The coexistence of photochemistry and thermochemistry effects contributes to the high efficiency. Our results demonstrate a catalyst design approach with atomic or molecular precision and a combinatorial photoactivation strategy for solar energy conversion. 相似文献
57.
核电池具有能量密度高、工作稳定可靠、无需人工干预等优点,在需要长期稳定供电的场合具有独特优势,其中热转换式核电池(RTG)是技术最为成熟且应用最早的一类,而β辐射伏特效应核电池已有商业化案例。目前,在β辐射伏特效应核电池研究中存在着放射源自吸收效应浪费能量、转化效率低、换能器件辐射损伤严重等问题,而对于一个实际的核电池,由于放射源自身不断衰变的属性,导致源的成分及其活度随着时间而发生变化,最终影响核电池的电学性能,其影响程度需要加以深入研究。本文以时间轴的形式对核电池的发展进行了全面回顾,简要介绍多种主流类型核电池的原理和应用范围;对于β辐射伏特效应核电池,指出放射源的自吸收是其中的关键科学问题。对于使用63Ni和TiT2放射源的核电池,给出了其电学性能随时间变化的规律;指出对于某一特定结构的β辐射伏特效应核电池设计,在前期的模拟优化环节中,精细计算是至关重要的;最后提出了将放射源与换能材料相结合、使用含有较重同位素的换能器件的设想,这些设想有利于解决放射源自吸收问题、提高核电池输出功率和减轻辐射损伤的影响。 相似文献
58.
Potapenko O. Potapenko A. Zhou Changji Zhang Lili Xu Jun Gu Zhuowei 《Russian Journal of Electrochemistry》2020,56(12):1043-1050
Russian Journal of Electrochemistry - The electrochemical properties of batteries consist of LiFePO4 (LFP) with the NV-1A binder were studied in depth. It was shown that SEI layer for NV-1A formed... 相似文献
59.
Motor Imagery Electroencephalography (MI-EEG) has shown good prospects in neurorehabilitation, and the entropy-based nonlinear dynamic methods have been successfully applied to feature extraction of MI-EEG. Especially based on Multiscale Fuzzy Entropy (MFE), the fuzzy entropies of the τ coarse-grained sequences in τ scale are calculated and averaged to develop the Composite MFE (CMFE) with more feature information. However, the coarse-grained process fails to match the nonstationary characteristic of MI-EEG by a mean filtering algorithm. In this paper, CMFE is improved by assigning the different weight factors to the different sample points in the coarse-grained process, i.e., using the weighted mean filters instead of the original mean filters, which is conductive to signal filtering and feature extraction, and the resulting personalized Weighted CMFE (WCMFE) is more suitable to represent the nonstationary MI-EEG for different subjects. All the WCMFEs of multi-channel MI-EEG are fused in serial to construct the feature vector, which is evaluated by a back-propagation neural network. Based on a public dataset, extensive experiments are conducted, yielding a relatively higher classification accuracy by WCMFE, and the statistical significance is examined by two-sample t-test. The results suggest that WCMFE is superior to the other entropy-based and traditional feature extraction methods. 相似文献
60.
Numerical Algorithms - A singularly perturbed Volterra integro-differential equation with an integrable singularity in the integral term is considered. The upwind difference method is used to... 相似文献