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   100859篇
  免费   5344篇
  国内免费   4572篇
化学   56923篇
晶体学   1368篇
力学   5701篇
综合类   327篇
数学   11908篇
物理学   34548篇
  2023年   880篇
  2022年   1824篇
  2021年   2345篇
  2020年   2604篇
  2019年   2830篇
  2018年   2918篇
  2017年   2836篇
  2016年   3558篇
  2015年   2417篇
  2014年   3490篇
  2013年   4940篇
  2012年   5060篇
  2011年   5371篇
  2010年   4258篇
  2009年   4257篇
  2008年   4458篇
  2007年   4177篇
  2006年   3813篇
  2005年   3383篇
  2004年   3056篇
  2003年   2714篇
  2002年   2827篇
  2001年   2548篇
  2000年   1986篇
  1999年   1601篇
  1998年   1539篇
  1997年   1332篇
  1996年   1294篇
  1995年   1078篇
  1994年   1157篇
  1993年   1095篇
  1992年   1063篇
  1991年   1124篇
  1990年   1120篇
  1989年   1041篇
  1988年   921篇
  1987年   916篇
  1986年   882篇
  1985年   925篇
  1984年   917篇
  1983年   828篇
  1982年   801篇
  1979年   802篇
  1978年   812篇
  1977年   806篇
  1976年   919篇
  1975年   812篇
  1974年   844篇
  1973年   847篇
  1972年   752篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
A diruthenium complex with a redox‐active amine bridge has been designed, synthesized, and studied by single‐crystal X‐ray analysis and DFT and TDDFT calculations. It shows three well‐separated redox processes with exclusive near‐infrared (NIR) absorbance at each redox state. The electropolymerized film of a related vinyl‐functionalized complex displays multistate NIR electrochromism with low operational potential, good contrast ratio, and long retention time. Flip‐flop, flip‐flap‐flop, and ternary memories have been realized by using the obtained film (ca. 15–20 nm thick) with three electrochemical inputs and three NIR optical outputs that each displays three levels of signal intensity.  相似文献   
42.
The ability to supply suitable blood vessel system is a major challenge for artificial thick tissue engineering. Angiogenesis is a key point during the process of microvascular formation. Many bioactive molecules such as extra cellular matrix(ECM) proteins and adhesion peptides derived from the ECM are applied to promote angiogenesis. In this work, two adhesion peptides, YIGSR and REDV, were selected to modify sodium alginate(ALG) to obtain YIGSR- and REDV-alginate conjugates(ALG-YIGSR, and ALG-REDV, respectively). We mixed the two peptide-conjugates together in a series of concentration ratios to prepare bioactive surfaces for in vitro studies and hydrogel scaffolds for in vivo studies. In vitro studies showed that surfaces modified with 1.09 pmol/mm2 peptide had the best affinity to human umbilical vein endothelial cells(HUVECs) than that with high or low concentrations of peptides. In addition, surfaces modified with dual peptides could significantly promote HUVECs proliferation, where ALG-YIGSR:ALG-REDV at a mole ratio of 5:1 exhibited the best enhancement ability. Furthermore, the in vivo angiogenesis results demonstrated that hydrogel scaffolds composed of mixed ALG-YIGSR and ALG-REDV at the 5:1 ratio had angiogenic induction potential by stimulating new blood vessel formation, and showed higher blood vessel density than scaffolds composed of a single peptide. These results demonstrated that a mixed combination of peptide alginate conjugates could be a potential scaffold to stimulate and induce angiogenesis in tissue engineering applications.  相似文献   
43.
Structure–function correlations are a central theme in heterogeneous (photo)catalysis. In this study, the geometric and electronic structure of perovskite ferroelectric KNbO3 nanowires with respective orthorhombic and monoclinic polymorphs have been systematically addressed. By virtue of aberration-corrected scanning transmission electron microscopy, we directly visualize surface photocatalytic active sites, measure local atomic displacements at an accuracy of several picometers, and quantify ferroelectric polarization combined with first-principles calculations. The photoreactivity of the as-prepared KNbO3 nanowires is assessed toward aqueous rhodamine B degradation under UV light. A synergy between the ferroelectric polarization and electronic structure in photoreactivity enhancement is uncovered, which accounts for the prominent reactivity order: orthorhombic > monoclinic. Additionally, by identifying new photocatalytic products, rhodamine B degradation pathways involving N-deethylation and conjugated structure cleavage are proposed. Our findings not only provide new insights into the structure–photoreactivity relationships in perovskite ferroelectric photocatalysts, but also have broad implications in perovskite-based water splitting and photovoltaics, among others.  相似文献   
44.
Russian Journal of Applied Chemistry - Pt/Sup catalysts with SiO2, MCM-48, and Al2O3 supports (Sup) were prepared. The catalysts were studied by methods of low-temperature nitrogen adsorption,...  相似文献   
45.
Russian Chemical Bulletin - Nucleophilic substitution of the chlorine atom in 4,5-dichloro-1,2-dithiol-3-one using 1-thio-β-d-glucopyranose and its 2,3,4,6-tetra-O-acetyl derivative in...  相似文献   
46.
Russian Journal of Electrochemistry - The reduction of zinc oxide in a limited volume of the alkaline electrolyte is studied. Methods of chronopotentiometry, chronoamperometry, and...  相似文献   
47.
Russian Journal of General Chemistry - Acylation of 5,7-di(tert-butyl)-2-{5,8-dimethyl-4-[(3,5-dimethylphenyl)amino]quinolin-2-yl}-3-[(3,5-dimethylphenyl)amino]tropone leads to...  相似文献   
48.
Russian Journal of General Chemistry - Azomethines were synthesized from 2,4,6-trimethylaniline, salicylaldehyde, and its 3(5)-halogen derivatives, as well as their complexes with zinc(II) (ZnL2)....  相似文献   
49.
Russian Chemical Bulletin - The method of one-stage catalytic polycyclocondensation according to the B4 + AB scheme was used to synthesize new tetraarm star-shaped oligoimides (SOIs) with terminal...  相似文献   
50.
Russian Chemical Bulletin - Two new D—π—A chromophores with the tricyanofuranyl acceptor (A), an amphi-divinyl quinoxaline π-electron conjugated bridge, and the carbazole or...  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