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   689篇
  免费   74篇
  国内免费   36篇
化学   522篇
晶体学   9篇
力学   24篇
综合类   1篇
数学   23篇
物理学   220篇
  2024年   3篇
  2023年   15篇
  2022年   31篇
  2021年   42篇
  2020年   33篇
  2019年   23篇
  2018年   21篇
  2017年   24篇
  2016年   46篇
  2015年   32篇
  2014年   44篇
  2013年   49篇
  2012年   61篇
  2011年   53篇
  2010年   36篇
  2009年   20篇
  2008年   36篇
  2007年   30篇
  2006年   34篇
  2005年   20篇
  2004年   12篇
  2003年   17篇
  2002年   16篇
  2001年   6篇
  2000年   5篇
  1999年   2篇
  1998年   5篇
  1997年   2篇
  1996年   9篇
  1995年   8篇
  1994年   4篇
  1993年   5篇
  1992年   3篇
  1991年   10篇
  1990年   1篇
  1989年   6篇
  1988年   5篇
  1986年   2篇
  1985年   8篇
  1984年   7篇
  1983年   3篇
  1982年   4篇
  1980年   2篇
  1978年   2篇
  1977年   1篇
  1968年   1篇
排序方式: 共有799条查询结果,搜索用时 0 毫秒
781.
黄可龙  张戈  刘素琴  杨赛 《无机化学学报》2006,22(11):2075-2079
以柠檬酸钠为配位剂、NaBH4为还原剂,将Sn(Ⅱ)和Sb(Ⅲ)盐在水溶液中共还原制得Sn-SnSb合金。X射线衍射和扫描电镜的测试结果表明:所得合金为多相合金,颗粒大小约200 nm。将该合金粉和石墨按质量比4∶1经机械球磨形成Sn-SnSb/石墨复合材料,将其作为锂离子电池阳极材料进行电化学性能测试,结果表明,该复合材料可逆容量超过600 mAh·g-1,具有良好的循环性能,15次循环内的稳定比容量为461 mAh·g-1,而纯Sn-SnSb合金粉15次循环后充电比容量为337 mAh·g-1。  相似文献   
782.
Impregnated and co-precipitated, promoted and unpromoted, bulk and supported iron catalysts were prepared, characterized, and subjected to hydrogenation of CO2 at various pressures (1–2 MPa) and temperatures (573–673 K). Potassium, as an important promoter, enhanced the CO2 uptake and selectivity towards olefins and long-chain hydrocarbons. Al2O3, when added as a structural promoter during co-precipitation, increased CO2 conversion as well as selectivity to C2+ hydrocarbons. Among V, Cr, Mn and Zn promoters, Zn offered the highest selectivity to C2–C4 alkenes. The different episodes involved in the transformation of the catalyst before it reached steady-state were identified, on the co-precipitated catalyst. Using a biomass derived syngas (CO/CO2/H2), CO alone took part in hydrogenation. When enriched with H2, CO2 was also converted to hydrocarbons. The deactivation of impregnated Fe–K/Al2O3 catalyst was found to be due to carbon deposition, whereas that for the precipitated catalyst was due to increase in crystallinity of iron species. The suitability of SiO2, TiO2, Al2O3, HY and ion exchanged NaY as supports was examined for obtaining high activity and selectivity towards light olefins and C2+ hydrocarbons and found Al2O3 to be the best support. A comparative study with Co catalysts revealed the advantages of Fe catalysts for hydrocarbon production by F–T synthesis.  相似文献   
783.
784.
V. Sai Sudhir 《Tetrahedron》2010,66(6):1327-2694
This work reports the synthesis of a wide range of ferrocenyl-amino acids and other derivatives in excellent yield. Diverse amino acid containing azides were synthesized and ligated to ferrocene employing click reaction to access ferrocenyl amino acids. Chiral alcohols, esters, diols, amines containing azido group were tagged to ferrocene via click reaction to generate ferrocene derived chiral derivatives. A novel strategy for direct incorporation of ferrocene into a peptide and a new route to 1, 1′disubstituted ferrocene amino acid derivative are reported.  相似文献   
785.
Luteolin is reported to have antioxidant and anti-inflammatory properties. In this study, we investigated the protective effect of luteolin against the renal damage induced by d-galactose (d-gal). The levels of creatinine (Cr) and urea nitrogen (BUN) were evaluated in plasma, kidney sections were stained with haematoxylin–eosin, followed by assessment of the antioxidant and anti-inflammatory activity. Furthermore, we also investigated the expression of the p38 mitogen-activated protein kinase (p38 MAPK) and its phosphorylated activation. The results of luteolin treatment showed that the renal damages were attenuated. Luteolin could significantly ameliorate d-gal-induced oxidative damage and suppress the inflammatory response. Moreover, the result also shows that luteolin could significantly inhibit the p38 MAPK phosphorylation in the kidneys from the model of d-gal-treated mice. Therefore, our research suggests that luteolin might be involved in the attenuated oxidative stress and inflammatory responses, hence the protective effects against d-gal-induced renal damage.  相似文献   
786.
A simple, unique and selective HPLC‐PDA method was developed and validated for the simultaneous estimation of aliskiren (ALS) and amlodipine (AML) in human plasma. Extraction of the sample was accomplished by protein precipitation. Plasma proteins were precipitated by employing acetonitrile containing hydrochlorothiazide as internal standard. The compounds were analyzed by HPLC by using PDA detector on a Hibar C18 (250 × 4.6 mm) column with a mobile phase comprising acetonitrile and phosphate buffer (pH 4.2 and 25 mm ; 60:40 v/v) with a flow rate of 0.8 mL/min. Different sample pretreatment techniques were evaluated but protein precipitation was found to be satisfactory, offering good recovery values of 97.11–98.45% for ALS and 97.5–99.12% for AML. The within‐day precisions for ALS were 96.66, 99.16 and 99.41% at 90, 240 and 480 ng/mL, respectively, and for AML they were 97.27, 99.54 and 99.31% at 3.3, 8.8 and 17.6 ng/mL, respectively. The between‐day precisions for ALS were 96.66, 99.16 and 99.41% at 90, 240 and 480 ng/mL, respectively and the between‐day precisions for AML were 98.18, 99.20 and 99.40% at 3.3, 8.8 and 17.6 ng/mL, respectively. The limit of quantitation was 30 and 1.0 ng/mL for ALS and AML respectively. Different constituents of plasma proteins did not interfere with the absolute recovery of ALS and AML. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
787.
Iodination of certain aromatic amines and phenols are triggered by the oxidation of KI by peroxy compounds such as tert‐butyl hydroperoxide (tBuOOH) under liquid‐phase and solvent‐free conditions by grinding the reactants in a mortar with a pestle. The reactions afforded corresponding iodo derivatives in good yield with high regioselectivity (Table 1).  相似文献   
788.
曹靖 《高分子科学》2015,33(11):1618-1624
The anionic polymerization of N-vinylcarbazole(NVC) by using optically active anionic initiators such as the lithium salts of(S)-1-(9H-fluoren-2-yl)-4-isopropyl-4,5-dihydrooxazole((S)-1-FIDH) and(S)-2-(9H-fluoren-2-yl)-4-isopropyl-4,5-dihydrooxazole((S)-2-FIDH) and complexes of(-)-Sparteine with n-butylithium(n-Bu Li-(-)-Sp) or fluorenyl lithium(FILi-(-)-Sp) was achieved. The yield and specific rotation of poly(N-vinylcarbazole)s(poly(NVC)s) were considerably affected by the molar ratio of(S)-FIDH to NVC. The highest yield and specific rotation were obtained with Li-(S)-1-FIDH as an initiator, with a molar ratio of monomer and initiator [M]/[I] = 10/1. The effects of the chiral initiators, type of solvent and the polymerization temperature were investigated. The obtained optical activity of polymers was attributed to asymmetric induction of the chiral initiators.  相似文献   
789.
790.
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