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   13561篇
  免费   2416篇
  国内免费   4074篇
化学   11117篇
晶体学   400篇
力学   806篇
综合类   441篇
数学   2020篇
物理学   5267篇
  2024年   23篇
  2023年   152篇
  2022年   360篇
  2021年   408篇
  2020年   504篇
  2019年   482篇
  2018年   460篇
  2017年   517篇
  2016年   561篇
  2015年   683篇
  2014年   873篇
  2013年   1047篇
  2012年   1149篇
  2011年   1165篇
  2010年   1113篇
  2009年   1116篇
  2008年   1209篇
  2007年   1080篇
  2006年   1024篇
  2005年   914篇
  2004年   848篇
  2003年   617篇
  2002年   700篇
  2001年   639篇
  2000年   596篇
  1999年   383篇
  1998年   210篇
  1997年   153篇
  1996年   152篇
  1995年   133篇
  1994年   115篇
  1993年   93篇
  1992年   102篇
  1991年   80篇
  1990年   66篇
  1989年   53篇
  1988年   57篇
  1987年   48篇
  1986年   34篇
  1985年   16篇
  1984年   26篇
  1983年   25篇
  1982年   9篇
  1981年   22篇
  1980年   7篇
  1979年   11篇
  1978年   2篇
  1974年   2篇
  1971年   2篇
  1965年   2篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Insomnia is a common clinical disease that can seriously damage the normal lives of sufferers. Suan‐Zao‐Ren decoction has been used to treat insomnia for a long time. However, the underlying molecular mechanism of Suan‐Zao‐Ren decoction is still not clear. In this study, the nontargeted metabolomics based on high‐resolution mass spectrometry and multiple statistical approaches were initially used to investigate the changes of potential serum and brain biomarkers and metabolic pathways in the insomnia model rat. Principal component analysis‐discriminate analysis indicated that the Suan‐Zao‐Ren decoction treatment improved the metabolic phenotype insomnia. Moreover, the heatmap analysis identified the most important biomarkers involved in insomnia. According to the pathway analysis, phenylalanine metabolism, tryptophan metabolism, and so on were recognized as the most affected metabolic pathways associated with insomnia disease. These findings provided a comprehensive understanding of the regulative effects of Suan‐Zao‐Ren decoction on the host metabolic phenotype of the insomnia rats. Our work demonstrated that the metabolomics approach is a promising tool that could help us to conduct the exploration of the therapeutic effects and mechanism of traditional Chinese medicines.  相似文献   
992.
Proton pump inhibitors, including omeprazole, rabeprazole, lansoprazole, and pantoprazole, achieved simultaneous enantioselective determination in the human plasma by chiral liquid chromatography–tandem mass spectrometry. The four corresponding stable isotope‐labeled proton pump inhibitors were adopted as the internal standards. Each enantiomer and the internal standards were extracted with acetonitrile containing 0.1% ammonia, then separated with a Chiralpak IC column (5 µm, 4.6 mm × 150 mm) within 10 min. The mobile phase was composed of acetonitrile–ammonium acetate (10 mM) containing 0.2% acetic acid (50:50, v/v). To quantify all enantiomers, an API 4000 tandem mass spectrometer was used, and multiple reaction monitoring transitions were performed on m/z 360.1→242.1, 384.1→200.1, 370.1→252.1, and 346.1→198.1, respectively. No significant matrix effect was observed for all analytes. The calibration curve for all enantiomers were linear from 1.25 to 2500 ng/mL. The precisions for intra‐ and inter‐run were < 14.2%, and the accuracy fell in the interval of –5.3 to 8.1%. Stability of samples was confirmed under the storage and processing conditions. The developed method was also suitable for separation and determination of ilaprazole enantiomers. The validated method combining the equilibrium dialysis method was applied to the protein binding ratio studies of four pairs proton pump inhibitor enantiomers in human plasma.  相似文献   
993.
Ma  Lijiao  Xu  Ye  Zu  Yunfei  Liao  Qing  Xu  Bowei  An  Cunbin  Zhang  Shaoqing  Hou  Jianhui 《中国科学:化学(英文版)》2020,63(1):21-27
In order to meet the requirements for making organic solar cells(OSCs) through solution printing techniques, great efforts have been devoted into developing high performance OSCs with relatively thicker active layers. In this work, a thick-film(300 nm)ternary OSC with a power conversion efficiency of 14.3% is fabricated by introducing phenyl-C_(61)-butyric-acid-methyl ester(PC_(61)BM) into a PBDB-T-2Cl:BTP-4 F host blend. The addition of PC_(61)BM is found to be helpful for improving the hole and electron mobilities, and thus facilitates charge transport as well as suppresses charge recombination in the active layers, leading to the improved efficiencies of OSCs with relatively thicker active layers. Our results demonstrate the feasibility of employing fullerene derivative PC_(61)BM to construct a high-efficiency thick-film ternary device, which would promote the development of thick layer ternary OSCs to fulfill the requirements of future roll to roll production.  相似文献   
994.
Fang  Yuanxing  Zheng  Yun  Fang  Tao  Chen  Yong  Zhu  Yaodong  Liang  Qing  Sheng  Hua  Li  Zhaosheng  Chen  Chuncheng  Wang  Xinchen 《中国科学:化学(英文版)》2020,63(2):149-181
Photocatalysis,which is the catalyzation of redox reactions via the use of energy obtained from light sources,is a topic that has garnered a lot of attention in recent years as a means of addressing the environmental and economic issues plaguing society today.Of particular interest are photosynthesis can potentially mimic a variety of vital reactions,many of which hold the key to develop sustainable energy economy.In light of this,many of the technological and procedural advancements that have recently occurred in the field are discussed in this review,namely those linked to:(1)photocatalysts made from metal oxides,nitride,and sulfides;(2)photocatalysis via polymeric carbon nitride(PCN);and(3)general advances and mechanistic insights related to TiO2-based catalysts.The challenges and opportunities that have arisen over the past few years are discussed in detail.Basic concepts and experimental procedures which could be useful for eventually overcoming the problems associated with photocatalysis are presented herein.  相似文献   
995.
Three hydrogen bonding complexes of the gauche‐1PA dimer (GG), trans‐1PA dimer (TT) and mixed dimer (GT) have been calculated for the geometry conformations and excited‐state energies. The electron distribution at the site of C‐O of H‐donor moiety in HOMO transfers to the direction of O‐H of H‐acceptor moiety in LUMO. The hydrogen bond between two 1PAs is the bridge of the intermolecular charge transfer. By the Zhao and Han's excited‐state hydrogen bonding dynamics rule, the first excited‐state hydrogen bonding change has been discussed without optimizing the excited‐state geometry conformations. According to the distinct difference between GT and GG (TT), we concluded that two gauche‐1PA monomers of one dimer are transformed at the same time to two trans‐1PA monomers.  相似文献   
996.
During the 1st and 2nd stages of the commissioning of the upgrade project of the Beijing Electron Positron Collider(BEPC Ⅱ),which started on Nov.12,2006 and Oct.24,2007,respectively,we got the luminosity one tenth of its design value,provided beams to synchrotron radiation users for about 4 months,and studied beam dynamics as well.In this paper,some beam dynamics studies on the storage rings and their preliminary results are given.  相似文献   
997.
998.
以掺杂4mol%Hf4+的LiNbO3:Fe:Hf系列晶体([Li]/[Nb]比变化)为研究对象,研究了系列晶体的可见吸收光谱,在632.8nm的写入光下晶体的衍射效率、灵敏度和抗光散射能力在不同[Li]/[Nb]下的变化规律.研究发现Hf4+的浓度达到阈值浓度后,随着[Li]/[Nb]比的增大,晶体的可见吸收边会发生红移,而且晶格中[Fe2+]/[Fe3+]也会增加,这就导致随着[Li]/[Nb]比的增加,样品的衍射效率逐渐减小,写入时间缩短,灵敏度增大.同时,在晶体中,随着[Li]/[Nb]的增大,陷阱中心Fe2Li+数量增大会使得晶体抗光散射能力减弱.  相似文献   
999.
An ambient aerosol concentration enrichment system coupled with ICP-MS for real-time monitoring of airborne radioactive particles is now under development. ICP-MS is very sensitive to sample introduction conditions, so it is necessary to develop an easy-use calibration method for on-line quantitative analysis in field application. In this paper, a calibration method using standard solution instead of monodisperse particles was established and validated preliminarily. First of all, four parameters for the method were determined experimentally, including: uptake flow rate and nebulisation efficiency of the Microconcentric nebuliser, nebulisation/transport efficiency of Aridus Desolvating Sample Introduction System, and Relative Sensitivity Factor between 159?Tb and 174?Yb. Then, monodisperse terbium nitrate particles were generated by a commercial Vibrating Orifice Aerosol Generator. Continuous aerosols of ytterbium nitrate droplets were nebulised from standard solution. They were mixed together, desolvated through the membrane dryer and introduced into ICP-MS for on-line analysis of terbium nitrate particles. The air sampled from nuclear environment was also introduced into ICP-MS to investigate the effect of flow rate on instrument responses. Finally, atom numbers of 159?Tb in discrete terbium nitrate particles were determined using the calibration method and compared to the calculated value. Results show that when air flow rate increase from 10?mL?min?1 to 100?mL?min?1, the ratio of 159?Tb ion count to 174?Yb ion intensity keeps constant although instrument sensitivity decreases by a factor of 25. The relative standard deviation of 159?Tb atom number measured is better than 18%. The discrepancy with the calculated value could be attributed to the over-estimation of atom number in the particles generated by VOAG because there was some liquid leakage in the VOAG.  相似文献   
1000.
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