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   4493篇
  免费   824篇
  国内免费   497篇
化学   3396篇
晶体学   41篇
力学   220篇
综合类   51篇
数学   491篇
物理学   1615篇
  2024年   5篇
  2023年   81篇
  2022年   168篇
  2021年   124篇
  2020年   184篇
  2019年   203篇
  2018年   161篇
  2017年   127篇
  2016年   239篇
  2015年   203篇
  2014年   257篇
  2013年   301篇
  2012年   367篇
  2011年   373篇
  2010年   271篇
  2009年   293篇
  2008年   314篇
  2007年   274篇
  2006年   258篇
  2005年   226篇
  2004年   163篇
  2003年   144篇
  2002年   181篇
  2001年   152篇
  2000年   93篇
  1999年   103篇
  1998年   68篇
  1997年   60篇
  1996年   71篇
  1995年   45篇
  1994年   56篇
  1993年   36篇
  1992年   22篇
  1991年   43篇
  1990年   38篇
  1989年   29篇
  1988年   12篇
  1987年   13篇
  1986年   11篇
  1985年   19篇
  1984年   6篇
  1983年   6篇
  1982年   3篇
  1981年   5篇
  1970年   1篇
  1966年   1篇
  1964年   1篇
  1962年   1篇
  1959年   1篇
  1936年   1篇
排序方式: 共有5814条查询结果,搜索用时 15 毫秒
991.
赵元安  邵建达  刘晓凤  李大伟 《强激光与粒子束》2022,34(1):011004-1-011004-12
光学元件是各类激光系统不可或缺的光学功能实现部件,其性能决定了激光系统的输出能力和光束质量。光学元件的激光损伤问题从激光发明起就一直伴随着激光技术的发展,随着激光新技术的发展和激光新应用的牵引,激光的波段、脉冲宽度以及重复频率等参数不断拓宽,使得激光损伤问题更加复杂,但万变不离其宗,激光损伤问题的核心是光学元件或光学材料对激光的吸收机制问题。从激光与光学材料相互作用的基本原理出发,以惯性约束聚变(ICF)激光驱动器应用的典型光学材料和光学元件为研究对象,回顾了针对光学元件的激光损伤问题开展的科研工作,总结了在此期间形成的关键技术和里程碑进展,同时也对依然困扰该领域的几类光学元件存在的问题瓶颈以及进一步研究发展趋势进行了展望。  相似文献   
992.
Hao L  Du Y  Lv H  Chen X  Jiang H  Shao Y  Chi YR 《Organic letters》2012,14(8):2154-2157
The first N-Heterocyclic Carbene (NHC) mediated activation of stable carboxylate esters to generate enolate intermediates is disclosed. The catalytically generated arylacetic ester enolates undergo enantioselective reactions with α,β-unsaturated imines.  相似文献   
993.
The natural product curcumin is widely used in Asian countries for the treatment of several diseases. However, the clinical potential of curcumins remains limited due to their relatively poor bioavailability and no experimental data about their lipophilicity for bioavailability prediction. To evaluate the retention and lipophilicity of curcumin and its 31 newly synthesized analogues, they were subjected to 3D quantitative structure-retention relationship studies by RP-HPLC. Superior than the classical four-variant quantitative structure-retention relationship model (conventional r(2) =0.734), the 3D comparative molecular similarity index analysis model with combined steric, electrostatic, and H-bond donor fields, resulted in a robust structure-retention correlation (cross-validated q(2) =0.613 and r(2) =0.979). The statistical analyses indicate that the electrostatic and H-bond donor fields have a primary influence on the chromatographic retention of analytes. The predictive power and robustness of the derived comparative molecular similarity index analysis model was further confirmed by the test-set validation (q(2) =0.702, r(2) =0.905, and the slope K=1.016) and Y-randomization examination. Statistically significant and physically meaningful 3D-quantitative structure-retention relationship provided better insight into understanding the retention behaviors of curcumin and its analogues, and their separation mechanism in a given RP-HPLC system.  相似文献   
994.
An ethanol biosensor was fabricated based on a Methylobacterium organophilium-immobilized eggshell membrane and an oxygen(O2) electrode.A linear response for ethanol was obtained in the range of 0.050-7.5 mmol/L with a detection limit of 0.025 mmol/L(S/N= 3) and a R.S.D.of 2.1%.The response time was less than 100 s at room temperature and ambient pressure. The optimal loading of bacterial cells on the biosensor membrane is 40 mg(wet weight).The optimal working conditions for the microbial biosensor are pH 7.0 phosphate buffer(50 mmol/L) at 20-25℃.The interference test,operational and storage stability of the biosensor are studied in detail.Finally,the biosensor is applied to determine the ethanol contents in various alcohol samples and the results are comparable to that obtained by gas chromatographic method and the results are satisfactory.Our proposed biosensor provides a convenient,simple and reliable method to determine ethanol content in alcoholic drinks.  相似文献   
995.
A novel graft copolymer consisting of polyisoprene backbone and hydrophilic side chain with carbamic acid ester functional group was prepared via thiol-ene"click"reaction and alcohol-isocyanate reactions.Polyisoprene was synthesized by anionic polymerization using n-butyl lithium as initiator,and the pendant hydroxyl groups were introduced by the thiol-ene reaction of mercaptoethanol with the double bond of 1,2-addition units of PI backbone in the presence of radical initiator azobisisobutyronitrile. Isocyanate end group capped poly(ethylene glycol)(mPEG-NCO) was grafted onto the PI backbone through alcoholisocyanate reaction between the pendant hydroxyl groups and isocyanate group of mPEG-NCO.The structure of the graft copolymer were characterized and confirmed by means of size-exclusion chromatography,~1H NMR and FTIR spectroscopy.  相似文献   
996.
Zhang J  Li J  Shao D  Yao B  Jiang J 《色谱》2012,30(2):190-195
建立了同时测定食品塑料包装材料中9种紫外光稳定剂含量的高效液相色谱方法。样品用甲醇-乙酸乙酯混合溶剂超声提取,经固相萃取小柱净化后,以ZORBAX SB-C18柱(250 mm×4.6 mm, 5 μm)为分离色谱柱,甲醇和水为流动相,梯度洗脱,以310 nm为检测波长进行定性、定量分析。该方法前处理简单、易操作,9种紫外光稳定剂分离效果良好。9种紫外光稳定剂在0.2~10 mg/L范围内呈良好的线性关系,线性相关系数大于0.999;方法检出限为0.05~0.1 mg/L;实际样品中的加标回收率为70.2%~89.0%,相对标准偏差为0.4%~4.5%。该方法简单、准确,能够满足食品塑料包装材料中紫外光稳定剂的检测要求。  相似文献   
997.
粒度分析及粒度标准物质研究进展   总被引:1,自引:0,他引:1  
综述了当前粒度分析测试方法的研究进展,并简单介绍了各种测试方法的基本原理以及包括美国、欧洲、中国在内的国家和地区在粒度标准物质方面的研究概况。  相似文献   
998.
999.
Zeolitic Imidazolate Framework-8 (ZIF-8), for the first time for ZIFs, exhibits a remarkable capacity for the anticancer drug 5-fluorouracil (5-FU), around 660 mg of 5-FU/g of ZIF-8, and presents a pH-triggered controlled drug release property. These prove ZIF-8 to be a valuable candidate for delivery of anticancer agents and reveal its potential applications in the treatment of cancer.  相似文献   
1000.
A new organic-inorganic hybrid, [Cu(en)(2)](3){[Cu(en)(2)][H(6)SiNb(18)O(54)]}·22H(2)O (1, en = ethylenediamine) containing the crescent-shaped polyoxoanion [H(6)SiNb(18)O(54)](8-) and copper-organic cations has been successfully synthesized, and elemental analyses, IR spectra, thermogravimetric analyses and single-crystal X-ray diffraction were investigated.  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