全文获取类型
收费全文 | 19657篇 |
免费 | 3394篇 |
国内免费 | 3472篇 |
专业分类
化学 | 15632篇 |
晶体学 | 355篇 |
力学 | 1024篇 |
综合类 | 293篇 |
数学 | 2197篇 |
物理学 | 7022篇 |
出版年
2024年 | 22篇 |
2023年 | 328篇 |
2022年 | 448篇 |
2021年 | 654篇 |
2020年 | 810篇 |
2019年 | 805篇 |
2018年 | 683篇 |
2017年 | 706篇 |
2016年 | 886篇 |
2015年 | 1031篇 |
2014年 | 1161篇 |
2013年 | 1521篇 |
2012年 | 1698篇 |
2011年 | 1905篇 |
2010年 | 1450篇 |
2009年 | 1372篇 |
2008年 | 1517篇 |
2007年 | 1364篇 |
2006年 | 1202篇 |
2005年 | 1079篇 |
2004年 | 815篇 |
2003年 | 696篇 |
2002年 | 749篇 |
2001年 | 654篇 |
2000年 | 493篇 |
1999年 | 381篇 |
1998年 | 304篇 |
1997年 | 237篇 |
1996年 | 243篇 |
1995年 | 233篇 |
1994年 | 198篇 |
1993年 | 152篇 |
1992年 | 116篇 |
1991年 | 139篇 |
1990年 | 85篇 |
1989年 | 82篇 |
1988年 | 66篇 |
1987年 | 55篇 |
1986年 | 34篇 |
1985年 | 35篇 |
1984年 | 20篇 |
1983年 | 20篇 |
1982年 | 21篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1979年 | 8篇 |
1978年 | 5篇 |
1976年 | 6篇 |
1975年 | 3篇 |
1971年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
991.
范宇航 孙丽萍 霍丽华 赵辉 Jean-Marc Bassat Aline Rougier Sbastien Fourcade Jean-Claude Grenier 《无机化学学报》2013,29(18)
采用EDTA-柠檬酸法合成了中温固体氧化物燃料电池阴极材料Sr1.5La0.5Mn1-xCoxO4(SLMCOx),并利用粉末X射线衍射(XRD)、X射线光电子能谱(XPS)以及电化学交流阻抗谱(EIS)进行表征。结果表明,该材料与Ce0.9Gd0.1O1.95(CGO)在1 200℃烧结12 h不发生化学反应。随着Co掺入量的增加,氧化物中Mn3+和Co2+含量增多,晶格氧含量降低,晶格畸变率增大。交流阻抗谱(EIS)测试结果显示,钴的掺杂明显降低电极的极化电阻,其中Sr1.5La0.5Mn0.7Co0.3O4阴极在700℃空气中的极化电阻为0.62 Ω·cm2,明显小于Sr1.5La0.5MnO4阴极在750℃的极化电阻(1.5 Ω·cm2),表明钴掺杂的Sr1.5La0.5Mn1-xCoxO4是一种潜在的IT-SOFC阴极材料。 相似文献
992.
基于一系列二氰根铬与[Cu(cyclam)](ClO4)2反应合成了3个氰根桥联CrⅢ-CuⅡ-CrⅢ三核配合物[Cu(cyclam)][Cr(bpmb)(CN)2]2·4H2O(1)(cyclam=1,4,8,11-四氮杂环十四,bpmb2-=1,2-二(2-吡啶甲酰胺基)-4-甲基苯),[Cu(cyclam)][Cr(bpdmb)(CN)2]2(2)(bpdmb2-=1,2-二(2-吡啶甲酰胺基)-4,5-二甲基苯)和[Cu(cyclam)][Cr(bpClb)(CN)2]2·4H2O(3)(bpClb2-=1,2-二(2-吡啶甲酰胺基)-4-氯苯)。单晶衍射结果表明:3个化合物是结构类似的中性三核配合物,均含有氰根桥联的Cr(Ⅲ)-CN-Cu(Ⅱ)-NC-Cr(Ⅲ)连接;磁性研究表明:氰根桥在CrⅢ和CuⅡ离子间传递弱的铁磁耦合作用,基于自旋哈密顿算符Ĥ=-2JCrCuŜCu(ŜCr1+ŜCr2)拟合得到它们的磁耦合常数分别是JCrCu=1.53(2) cm-1(1),0.45(1) cm-1(2)和0.73(2) cm-1(3)。 相似文献
993.
以三苯甲烷-4,4’,4"-三羧酸(H3TCOPM)为主配体,以含氮二齿配体4,4’-bipyridine(4,4’-bipy)为辅助配体,与Co(NO3)2·6H2O通过溶剂热反应得到了2个配位聚合物{[Co2(α-OH-TCOPM)(OH)(H2O)4]·DMF}n(1)(α-OH-H3TCOPM=三苯甲醇-4,4’,4"-三羧酸)和{[Co3(α-OH-TCOPM)2(4,4’-bipy)3(H2O)6]·2H2O}n(2)。晶体结构分析表明,配合物1为四边形的二维层状结构,而配合物2为二维网状结构。采用红外光谱、粉末X射线衍射对配合物进行了表征,用热重分析仪研究了其热稳定性。 相似文献
994.
采用EDTA-柠檬酸盐法制备了(Pr0.9La0.1)2(Ni0.74Cu0.21Ga0.05)O4+δ(PLNCG),并与Ce0.9Gd0.1O2-δ(CGO)形成复合阴极PLNCG-CGO。XRD和SEM分析结果表明PLNCG与CGO在1 000℃具有较好的化学相容性。电化学阻抗测试结果表明PLNCG-30% CGO复合阴极在700℃的极化电阻为0.092 Ω·cm2;过电位为39.3 mV时,电流密度达到113.3 mA·cm-2。氧分压分析表明电极反应的速率控制步骤为电荷转移过程。阳极支撑单电池(Ni-CGO/CGO/PLNCG-30% CGO)在700℃的最大输出功率密度达到569 mW·cm-2,开路电压(OCV)为0.76 V。综上结果预示PLNCG-30% CGO复合阴极是一种有发展前景的电极材料。 相似文献
995.
以Mg-Al-NO3水滑石(LDHs)为载体,将5-氟尿嘧啶(5-FU)通过离子交换法插入其层间,得5-FU/LDHs缓释材料。并对水滑石表面进行弱酸预处理改性,利用XRD、FTIR、TG-DSC、SEM和零电荷点(pHPZC)等表征手段,考察酸预处理对水滑石表面化学性质及微观结构的影响。结果表明,5-FU/LDHs的层间距从0.858nm扩大到1.064nm,层间5-FU2阴离子与主体层板通过氢键与静电作用,以呈一定角度单层交替排列于层间。酸预处理的水滑石粒径变小,层板正电荷密度增大。5-FU的释放机理是物理扩散、离子交换和药物溶解等协同作用,酸预处理可提高水滑石的缓释性能和稳定性。 相似文献
996.
Wei Sun Linjie Tian Hui Qi Dan Jiang Ying Wang Song Li Junhai Xiao Xiaohong Yang 《中国化学》2013,(9):1144-1152
A series of tri-substituted chiral pyrrolidin-2-one derivatives have been designed and synthesized as CC chemokine receptor 4 (CCR4) antagonists. The structure of CCR4 was built by homology modeling. Asymmetric synthesis was applied to synthesize the R,R configuration chiral pyrrolidin-2-one scaffold. The stereoisomeric con- figurations of the compounds were identified by 2D I H-~H COSY spectroscopy and 1D NOESY spectroscopy. This method was more economical and convenient than traditional X-ray single crystal diffraction. In addition, the inter- actions between these compounds and the N-terminal extracellular tail of CCR4 were studied using capillary zone electrophoresis. The CCR4 chemotaxis inhibition effect was tested in CCR4-transfected HEK293 cells. Several compounds showed potent activities as CCR4 antagonists. Among these compounds, lc is the most active one. Its apparent binding constant of CZE experiment result is (1.569±0.11)× 10s L·mol ^-1, and its percentage inhibition of the HEK293/CCR4 cells migration with the concentration of I gmol·L ^-1 in DMSO is 59%. And compound If has slightly higher affinity to N-terminal of CCR4 according to its apparent binding constant than lb because of the in- troduced ester linkage. Further studies on the mechanism of these compounds are in progress. 相似文献
997.
Hui Tang Can-Hui Zheng Xiao-Hui Ren Jia Liu Na Liu Jia-Guo Lv Ju Zhu You-Jun Zhou 《中国化学快报》2013,24(3):219-222
A series of 1-(benzylamino)-2-(2,4-difluorophenyl)-3-(1H-1,2,4-triazol-l-yl)propan-2-ols compounds were synthesized and evaluated for their antifungal activities in vitro.The results showed that compounds 6A and 6B exhibited good antifungal activity.Compound 6A8 showed the strongest antifungal activity,which was significantly higher than that of the lead compounds and positive-control drugs Fluconazole and Itraconazole.In particular,the antifungal activity of compound 6A8 against Candida albicans and Candida krusei(MIC80 both at 0.00097μg/mL) was 515 and 64 times that of Fluconazole,respectively.The structure-activity relationships of the synthesized compounds were discussed,and the docking model of the target compounds with fungal lanosterol 14α-demethylase (CYP51) was analyzed. 相似文献
998.
You-An Xiao Zhi-Qiang Wang Xue-Min Wang Yi Hui Yong Ling Xin-Yang Wang Li-Qin He 《中国化学快报》2013,24(8):727-730
Novel 2-aminoimidazolone derivatives were synthesized.Most compounds displayed strong anticancer activities against human carcinoma cells in vitro.Compounds 8a,8b and 8j exhibited optimal activity superior to 5-FU in most cancer cells tested.Especially,the lC50s of 8b(12.6-21.5μmol/L) against five tumor cells were 1 -4 fold less than those of 5-FU(18.4-56.1μmol/L) in vitro.Furthermore,comp以ound 8b could induce SMMC-7721 cell apoptosis in a dose-dependent manner.Therefore,our novel findings may provide a new framework for the design of new 2-aminoimidazolone derivatives for the treatment of cancer. 相似文献
999.
A clean and safe synthesis method of 5-(4’-methylbiphenyl-2-yl)-1H-tetrazole was found:under hydrothermal conditions,1.2 equiv.of 4’-methylbiphenyl-2-carbonitrile react with 1 equiv.of sodium azide in a mixed solvent of propane-1,2-diol/H2O,with 1.5 equiv.of ammonium chloride and 0.2 equiv.of ammonium fluoride as catalyst.After simple post-processing,the yield can be improved to 95%,and the purity of the product is 99%without further recrystallization. 相似文献
1000.
A method for fast determination of the component in complex samples by using gas chromatography‐mass spectrometry (GC‐MS) was developed and used for quantitative analysis of phenanthrene in soils. In the method, window independent component analysis (WICA) was used for resolving the mass spectrum and non‐negative immune algorithm (NNIA) was employed for obtaining the chromatographic profile. Therefore, spectral and chromatographic information of a specific component can be obtained from the measured GC‐MS data of overlapping and high background. Six soil samples collected from different places were analyzed. The tedious pretreatments in preparing the samples and the elution in the separation were simplified for speeding up the analysis. Due to the complexity of the matrix, standard addition method was adopted for the final quantification. The applicability of the method was validated with a spiked sample and the results of the six samples are reasonable. 相似文献