全文获取类型
收费全文 | 18103篇 |
免费 | 3140篇 |
国内免费 | 2094篇 |
专业分类
化学 | 12901篇 |
晶体学 | 184篇 |
力学 | 1046篇 |
综合类 | 107篇 |
数学 | 1815篇 |
物理学 | 7284篇 |
出版年
2024年 | 78篇 |
2023年 | 412篇 |
2022年 | 655篇 |
2021年 | 749篇 |
2020年 | 749篇 |
2019年 | 746篇 |
2018年 | 668篇 |
2017年 | 599篇 |
2016年 | 904篇 |
2015年 | 880篇 |
2014年 | 1038篇 |
2013年 | 1312篇 |
2012年 | 1627篇 |
2011年 | 1515篇 |
2010年 | 1056篇 |
2009年 | 982篇 |
2008年 | 1090篇 |
2007年 | 1023篇 |
2006年 | 940篇 |
2005年 | 852篇 |
2004年 | 607篇 |
2003年 | 514篇 |
2002年 | 508篇 |
2001年 | 397篇 |
2000年 | 357篇 |
1999年 | 425篇 |
1998年 | 345篇 |
1997年 | 337篇 |
1996年 | 319篇 |
1995年 | 276篇 |
1994年 | 225篇 |
1993年 | 198篇 |
1992年 | 156篇 |
1991年 | 136篇 |
1990年 | 157篇 |
1989年 | 111篇 |
1988年 | 76篇 |
1987年 | 54篇 |
1986年 | 59篇 |
1985年 | 60篇 |
1984年 | 30篇 |
1983年 | 30篇 |
1982年 | 30篇 |
1981年 | 19篇 |
1980年 | 10篇 |
1979年 | 3篇 |
1977年 | 3篇 |
1942年 | 2篇 |
1930年 | 2篇 |
1916年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
951.
Honying M Han H Qiao C Richardson NV Yue W Jianhua Z Haiyang L Pimo H Shining B 《The Journal of chemical physics》2004,121(14):6972-6977
The structure of perylene adsorbed on Ru(0001) surface has been studied by ultraviolet photoemission spectroscopy (UPS) and low-energy electron diffraction. An ordered p(4x4) structure is observed from a monolayer (about 4 A thickness) of the perylene on Ru(0001) surface. UPS measurements show the molecular features, from the perylene multiplayer, between 2 and 10 eV below the Fermi level. Angle-resolved ultraviolet photoemission spectroscopy measurements suggest that the perylene molecular plane is parallel to the substrate. Temperature dependent UPS measurements show that the perylene multilayer is stable on Ru(0001) surface up to 125 degrees C. The desorption of the multilayer and the decomposition of the monolayer are observed above 125 degrees C. 相似文献
952.
Infrared study of HDTMA+ intercalated montmorillonite 总被引:5,自引:0,他引:5
Hongping H Ray FL Jianxi Z 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2004,60(12):2853-2859
In this paper, FTIR spectroscopy using attenuated total reflection (ATR) and KBr pressed disk techniques has been used to characterize sorbed water and HDTMA+ in organo-clay. Sorbed water content decreases with the intercalation of HDTMA+. With the decrease of the sorbed water content, the position of the nu2 mode shifts to higher frequency dramatically while the stretching vibration shifts to lower frequency slightly, indicating that H2O is less strongly hydrogen bonded. This might be resulted from the polarization of H2O molecules by the changeable cations and HDTMA+. FTIR spectra show that both antisymmetric and symmetric CH2 stretching absorption bands shift to low frequencies with increase of amine concentration within the galleries of montmorillonite, elucidating the increase of ordered conformation. Furthermore, the present study demonstrates that the antisymmetric CH2 stretching mode is more sensitive to the conformational ordering than the symmetric stretching mode. When KBr pressed disk technique used, two well resolved absorption bands at 730 and 720 cm(-1), and at 1473 and 1463 cm(-1), corresponding to the methylene scissoring and rocking modes, respectively, could be observed in FTIR spectra of organo-clays with relative higher concentration of surfactant. However, the FTIR spectra using ATR technique only display singlets and they are independent of amine concentration and chain conformation. Our present study demonstrates that FTIR spectroscopy using KBr pressed disk technique is more suitable to probe the conformational ordering of surfactant in organo-clays than that suing ATR technique does. 相似文献
953.
Shu‐Mei Chen Can‐Zhong Lu Ya‐Qin Yu Quan‐Zheng Zhang Xiang He 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(11):m549-m550
The title compound, [NaLaMo8O26(C3H7NO)7]n, contains infinite chains of [Mo8O26]4− units supporting dimethylformamide‐coordinated LaIII cations and linked by Na+ cations. The lanthanum center adopts a nine‐coordinate geometry and the Na atom is sandwiched between two β‐[Mo8O26]4− units. 相似文献
954.
Xiao-Qian Xu Dr. Li-Hui Cao Yan Yang Xiang-Tian Bai Fang Zhao Dr. Zhen-Hong He Dr. Zheng Yin Prof. Dr. Yang-Min Ma 《化学:亚洲杂志》2021,16(2):142-146
Over the past two decades, progress in chemistry has generated various types of porous materials for removing iodine (129I or 131I) that can be formed during nuclear energy generation or nuclear waste storage. However, most studies for iodine capture are based on the weak host-guest interactions of the porous materials. Here, we present two cationic nonporous macrocyclic organic compounds, namely, MOC-1 and MOC-2 , in which 6I- and 8I− were as counter anions, for highly efficient iodine capture. MOC-1 and MOC-2 were formed by reacting 1,1′-diamino-4,4′-bipyridylium di-iodide with 1,2-diformylbenzene or 1,3-diformylbenzene, respectively. The presence of a large number of I− anions results in high I2 affinity with uptake capacities up to 2.15 g ⋅ g−1 for MOC-1 and 2.25 g ⋅ g−1 for MOC-2 . 相似文献
955.
956.
Wenjie?Jing Yuexiang?Lu Feiyang?Wang Liuying?He Jingwei?Sun Yueying?LiuEmail authorView authors OrcID profile 《Mikrochimica acta》2018,185(6):298
A time-resolved phosphorescence (TRP) is applied to the highly sensitive determination of Fe(II) ions. The method is based on the use of a phosphorescent probe consisting of cysteine-bridged Mn-doped ZnS quantum dots (Mn/ZnS QDs). The presence of cysteine enhances the phosphorescence of the QDs and also increases the efficiency of quenching caused by Fe(II) ions. This results in strongly improved selectivity for Fe(II). The linear response is obtained in the concentration range of 50–1000 nM with a 19 nM detection limit. Phosphorescence is recorded at excitation/emission peaks of 301/602 nm. The interference of short-lived fluorescent and scattering background from the biological fluids is eliminated by using the TRP mode with a delay time of 200 μs. The determination of Fe(II) in human serum samples spiked at a 150 nM level gave a 92.4% recovery when using the TRP mode, but only 52.4% when using steady-state phosphorescence. This demonstrates that this probe along with TRP detection enables highly sensitive and accurate determination of Fe(II) in serum. 相似文献
957.
958.
X. L. Zhou F. Q. Dong C. L. Hong D. K. Chen F. He 《Russian Journal of Coordination Chemistry》2018,44(3):179-182
A new cyanide-bridged neutral centrosymmetric cluster [Cu(En)2][(PzTp)Fe(CN)3]2 (I), where En = ethylenediamine, PzTp = tetra(pyrazol-1-yl)borate) was synthesized by a programmed self-assembly of preformed building blocks. Characterization with single crystal X-ray diffraction (CIF file CCDC no. 1555334) showed that the Cu2+ center was located in a large distorted octahedral environment due to the obvious Jahn–Teller effect, which was demonstrated by continuous shape measures with the SHAPE program. Furthermore, no coordinated or free solvent molecules existed in the clusters, showing good roomtemperature stability. In addition, in vitro anticancer activity of compound I on three human cancer cells (SKOV3, A2780, and OVCAR) was further determined. 相似文献
959.
A novel hyperbranched conjugated chemosensor with bipyridyl groups as periphery groups(BPY-HPV) was synthesized.BPY-HPV was highly sensitive to metal ions(Cu2+,Ni2+) for the strong coordination interaction(Ksv at the order of 107 mol-1 L) monitored by fluorescence spectroscopy.Moreover,by hydrogen bonds and charge transfer interaction,BPY-HPV shows strong interaction with 1,1,2,2-tetrachloroethane whatever in CH2Cl2(Ksv~106 mol-1 L) or film. 相似文献
960.
采用低温固相反应法合成了NiFe2O4纳米粉体,并通过浸渍法在其表面修饰La2O3及Y2O3,通过X射线衍射分析(XRD)和扫描电镜(SEM)研究了修饰前后粉体的结构及形貌,并对修饰不同含量La2O3及Y2O3的旁热式气敏元件的气敏性进行了测试.结果表明:La2O3及Y2O3以无定形结构附着于NiFe2O4颗粒表面,当表面修饰为4%(质量分数)的La2O3时,NiFe2O4气敏元件的最佳工作温度为150℃,对1000ppm的乙醇及丙酮气体具有较高的灵敏度.有望开发出一种低温下工作的新型气敏元件.当表面修饰2%Y2O3(质量分数)时,对1000ppm的乙醇气体的灵敏度要高于对丙酮气体的灵敏度,达到33.5,最佳工作温度为250℃. 相似文献