首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2165篇
  免费   234篇
  国内免费   175篇
化学   1617篇
晶体学   23篇
力学   94篇
综合类   8篇
数学   216篇
物理学   616篇
  2023年   39篇
  2022年   36篇
  2021年   51篇
  2020年   77篇
  2019年   96篇
  2018年   68篇
  2017年   50篇
  2016年   88篇
  2015年   78篇
  2014年   105篇
  2013年   144篇
  2012年   177篇
  2011年   197篇
  2010年   123篇
  2009年   106篇
  2008年   141篇
  2007年   133篇
  2006年   118篇
  2005年   112篇
  2004年   67篇
  2003年   53篇
  2002年   68篇
  2001年   43篇
  2000年   30篇
  1999年   32篇
  1998年   28篇
  1997年   29篇
  1996年   32篇
  1995年   32篇
  1994年   21篇
  1993年   18篇
  1992年   29篇
  1991年   12篇
  1990年   21篇
  1989年   16篇
  1988年   14篇
  1987年   14篇
  1986年   6篇
  1985年   10篇
  1984年   14篇
  1983年   9篇
  1982年   6篇
  1981年   7篇
  1980年   4篇
  1979年   5篇
  1978年   3篇
  1975年   3篇
  1962年   1篇
  1961年   1篇
  1954年   1篇
排序方式: 共有2574条查询结果,搜索用时 15 毫秒
1.
Anh  Pham Ngoc  Tu  Ho Phi 《Numerical Algorithms》2021,86(1):55-74
Numerical Algorithms - In this paper, by basing on the inexact subgradient and projection methods presented by Santos et al. (Comput. Appl. Math. 30: 91–107, 2011), we develop subgradient...  相似文献   
2.
Structural health monitoring (SHM) is recognized as an efficient tool to interpret the reliability of a wide variety of infrastructures. To identify the structural abnormality by utilizing the electromechanical coupling property of piezoelectric transducers, the electromechanical impedance (EMI) approach is preferred. However, in real-time SHM applications, the monitored structure is exposed to several varying environmental and operating conditions (EOCs). The previous study has recognized the temperature variations as one of the serious EOCs that affect the optimal performance of the damage inspection process. In this framework, an experimental setup is developed in current research to identify the presence of fatigue crack in stainless steel (304) beam using EMI approach and estimate the effect of temperature variations on the electrical impedance of the piezoelectric sensors. A regular series of experiments are executed in a controlled temperature environment (25°C–160°C) using 202 V1 Constant Temperature Drying Oven Chamber (Q/TBXR20-2005). It has been observed that the dielectric constant ε33T which is recognized as the temperature-dependent constant of PZT sensor has sufficiently influenced the electrical impedance signature. Moreover, the effective frequency shift (EFS) approach is optimized in term of significant temperature compensation for the current impedance signature of PZT sensor relative to the reference signature at the extended frequency bandwidth of the developed measurement system with better outcomes as compared to the previous literature work. Hence, the current study also deals efficiently with the critical issue of the width of the frequency band for temperature compensation based on the frequency shift in SHM. The results of the experimental study demonstrate that the proposed methodology is qualified for the damage inspection in real-time monitoring applications under the temperature variations. It is capable to exclude one of the major reasons of false fault diagnosis by compensating the consequence of elevated temperature at extended frequency bandwidth in SHM.  相似文献   
3.
Xiao  Yang  He  Chong  Yang  Zi-Fan  Chen  Er-Qiang  Lu  Huan-Jun  Li  Xiao-Hong  Tu  Ying-Feng 《高分子科学》2022,40(6):584-592

We demonstrate here a novel method for the design of liquid crystals (LCs) via the cyclization of mesogens by flexible chains. For two azobenzene-4,4′-dicarboxylate derivatives, the cyclic dimer, cyclic bis(tetraethylene glycol azobenzene-4,4′-dicarboxylate) (CBTAD), shows LC properties with smectic A phase, while its linear counterpart, bis(2-(2′-hydroxyethyloxy)ethyl azobenzene-4,4′-dicarboxylate (BHAD), has no LC phase. The difference is ascribed to the shackling effect from the cyclic topology, which leads to the much smaller entropy change during phase transitions and increases the isotropic temperature greatly for cyclics. In addition, the trans-to-cis isomerization of azobenzene groups under UV-light is also limited in CBTAD. With the reversible isomerization of azobenzene groups, CBTAD showed interesting isothermal phase transition behaviors, where the LC phase disappeared upon photoirradiation of 365 nm UV-light, and recovered when the UV-light was off. Combined with the smectic LC nature, a novel UV-light tuned visible light regulator was designed, by simply placing CBTAD in two glass plates. The scattered phase of smectic LC was utilized as the “OFF” state for light passage, while the UV-light induced isotropic phase was utilized as the “ON” state. The shackling effect outlined here should be applicable for the design of cyclic LC oligomers/polymers with special properties.

  相似文献   
4.
5.
Li  Jie  Tu  Siming 《中国科学 数学(英文版)》2022,65(6):1247-1266

In 2018, Petersen and Wilson introduced the notion of dynamical intricacy and average sample complexity for dynamical systems of ?-action, based on the past works on the notion of intricacy in the research of brain network and probability theory. If one wants to take into account underlying system geometry in applications, more general group actions may need to be taken into consideration. In this paper, we consider this notion in the case of amenable group actions. We show that many basic properties in the ?-action case remain true. We also show that their suprema over covers or partitions are equal to the amenable topological entropy and the measure entropy, using the quasitiling technique in the theory of the amenable group.

  相似文献   
6.
Bacterial biofilms are difficult to eradicate because they are less susceptible to antibiotics and more easily develop resistance. Therefore, there is an urgent need for new materials that can combat planktonic bacteria and disrupt established biofilms. To tackle this challenge, we design a multifunctional zwitterionic pillar[5]arene, which can self‐assemble into weakly positively charged nanoaggregates that exhibit antibacterial activity against Gram‐negative Escherichia coli (DH5α) and Gram‐positive Staphylococcus aureus (SH1000) bacterial strains in solution. In addition, the zwitterionic pillar[5]arene can efficiently disrupt pre‐existing Escherichia coli (DH5α) biofilms and kill the biofilm‐enclosed bacteria without rapid generation of resistance.  相似文献   
7.
Metal–organic frameworks (MOFs) enable the design of host–guest systems with specific properties. In this work, we show how the confinement of anthracene in a well‐chosen MOF host leads to reversible yellow‐to‐purple photoswitching of the fluorescence emission. This behavior has not been observed before for anthracene, either in pure form or adsorbed in other porous hosts. The photoresponse of the host–guest system is caused by the photodimerization of anthracene, which is greatly facilitated by the pore geometry, connectivity, and volume as well as the structural flexibility of the MOF host. The photoswitching behavior was used to fabricate photopatternable and erasable surfaces that, in combination with data encryption and decryption, hold promise in product authentication and secure communication applications.  相似文献   
8.
Tao  Wenyan  Tu  Xinman  Chen  Jian  Zhu  Qian  Zhu  Yongqian 《Journal of Solid State Electrochemistry》2019,23(5):1613-1619
Journal of Solid State Electrochemistry - Here, a nanoporous gold electrode (NAu) was reported with a unique cone-shape nanohole structure for electrochemical sensing of nitric oxide (NO), which...  相似文献   
9.
Over the past years, the metal‐catalyzed dearomative cycloaddition of 3‐nitroindoles and 2‐nitrobenzofurans have emerged as a powerful protocol to construct chiral fused heterocyclic rings. However, organocatalytic dearomative reaction of these two classes of heteroarenes has become a long‐standing challenging task. Herein, we report the first example of phosphine‐catalyzed asymmetric dearomative [3+2]‐cycloadditio of 3‐nitroindoles and 2‐nitrobenzofurans, which provide a new, facile, and efficient protocol for the synthesis of chiral 2,3‐fused cyclopentannulated indolines and dihydrobenzofurans by reacting with allenoates and MBH carbonates, respectively through a dearomative [3+2]‐cycloaddition.  相似文献   
10.
In this work, we report an efficient method to produce pure hollow silica spheres (HSS) using phenyltrimethoxysilane (PTMS) compound. The production of HSS was carried out via hydrolysis of PTMS in the aqueous media and followed by a condensation reaction to form silica spheres with phenyl groups. The product was then calcined to remove phenyl groups and obtain pure silica spheres with >95% fine structure. The chemical nature of pure silica was confirmed by Fourier transforms infrared spectroscopy. The calcined HSS were stable beyond the temperature of 900 °C as confirmed by thermal gravimetric analysis (TGA). The calcined spheres preserved their spherical appearance and hollow core as shown by SEM and TEM micrographs. Interestingly, the average size of the spheres was reduced significantly after calcination from 760 to 510 nm, confirming further the removal of phenyl groups. The calcined HSS offered much higher surface area (As) when analysed by BET; As for calcined product was ~406 and mere ~4.8 m2/g for uncalcined HSS. Finally, drug release study of cisplatin/HSS showed over 45% of steady cumulative release for 72 h. The prepared HSS can be dispersed in water opening the possibility of many novel bio/non-bio applications.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号