全文获取类型
收费全文 | 1226篇 |
免费 | 157篇 |
国内免费 | 331篇 |
专业分类
化学 | 1280篇 |
晶体学 | 41篇 |
力学 | 5篇 |
综合类 | 9篇 |
数学 | 27篇 |
物理学 | 352篇 |
出版年
2023年 | 21篇 |
2022年 | 31篇 |
2021年 | 48篇 |
2020年 | 59篇 |
2019年 | 45篇 |
2018年 | 48篇 |
2017年 | 39篇 |
2016年 | 42篇 |
2015年 | 37篇 |
2014年 | 53篇 |
2013年 | 99篇 |
2012年 | 134篇 |
2011年 | 71篇 |
2010年 | 65篇 |
2009年 | 84篇 |
2008年 | 81篇 |
2007年 | 77篇 |
2006年 | 77篇 |
2005年 | 66篇 |
2004年 | 60篇 |
2003年 | 61篇 |
2002年 | 68篇 |
2001年 | 40篇 |
2000年 | 33篇 |
1999年 | 43篇 |
1998年 | 18篇 |
1997年 | 25篇 |
1996年 | 28篇 |
1995年 | 23篇 |
1994年 | 19篇 |
1993年 | 19篇 |
1992年 | 15篇 |
1991年 | 14篇 |
1990年 | 8篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 12篇 |
1984年 | 2篇 |
1982年 | 4篇 |
1981年 | 11篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 2篇 |
排序方式: 共有1714条查询结果,搜索用时 656 毫秒
971.
Jin-An Zhao Huai-Bin Yu Shuang-Cheng Zhi Rui-Na Mao Ji-Yong Hu Xiao-Xiao Wang 《中国化学快报》2017,28(7):1539-1546
In this study, novel mono/di-nuclear Cu(p-2-bmb)(OH)(ClO4) (1) and Co2(p-2-bmb)2Cl4 (2) (p-2-bmb=1- ((2-(pyridin-2-yl)-benzoimidazol-1-yl)methyl)-1H-benzotriazole) complexes with the nitrogen heterocyclic benzimidazole-based ligand were synthesized and characterized. The two complexes showed antiproliferative effects in various carcinoma cell lines, especially complex 1 in the SMMC7721 tumor cell line. Complex 1 was also able to pass through the cell membrane and enter the nucleus and mitochondrion. An analysis of in vitro chemical nuclease activity revealed that complex 1 partially intercalated to calf thymus DNA and exhibited strong unwinding activity against pBR322 superhelical plasmid DNA. The comet assay and flow cytometry analysis confirmed that 1 caused extensive DNA damage and arrested SMMC7721 tumor cells at G2/M phase of the cell cycle, leading to loss of mitochondrial membrane potential and apoptosis. These results suggest that these benzimidazole-based metal complexes could be potential anti-cancer agents. 相似文献
972.
Controllable Synthesis of Mesoporous Peapod‐like Co3O4@Carbon Nanotube Arrays for High‐Performance Lithium‐Ion Batteries
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Dong Gu Dr. Wei Li Fei Wang Hans Bongard Bernd Spliethoff Dr. Wolfgang Schmidt Dr. Claudia Weidenthaler Prof. Dr. Yongyao Xia Prof. Dr. Dongyuan Zhao Prof. Dr. Ferdi Schüth 《Angewandte Chemie (International ed. in English)》2015,54(24):7060-7064
Transition metal oxides are regarded as promising anode materials for lithium‐ion batteries because of their high theoretical capacities compared with commercial graphite. Unfortunately, the implementation of such novel anodes is hampered by their large volume changes during the Li+ insertion and extraction process and their low electric conductivities. Herein, we report a specifically designed anode architecture to overcome such problems, that is, mesoporous peapod‐like Co3O4@carbon nanotube arrays, which are constructed through a controllable nanocasting process. Co3O4 nanoparticles are confined exclusively in the intratubular pores of the nanotube arrays. The pores between the nanotubes are open, and thus render the Co3O4 nanoparticles accessible for effective electrolyte diffusion. Moreover, the carbon nanotubes act as a conductive network. As a result, the peapod‐like Co3O4@carbon nanotube electrode shows a high specific capacity, excellent rate capacity, and very good cycling performance. 相似文献
973.
Jibin Zhang Yanjun Zhong Xiaxing Shi Zhuo Zheng Weibo Hua Yanxiao Chen Wenyuan Liu Benhe Zhong 《中国化学》2015,33(11):1303-1309
Porous structure Li[Ni1/3Co1/3Mn1/3]O2 has been synthesized via a facile carbonate co‐precipitation method using Li2CO3 as template and lithium‐source. The physical and electrochemical properties of the materials were examined by many characterizations including TGA, XRD, SEM, EDS, TEM, BET, CV, EIS and galvanostatic charge‐discharge cycling. The results indicate that the as‐synthesized materials by this novel method own a well‐ordered layered structure α‐NaFeO2 [space group: R‐3m(166)], porous morphology, and an average primary particle size of about 150 nm. The porous material exhibits larger specific surface area and delivers a high initial capacity of 169.9 mAh·g?1 at 0.1 C (1 C=180 mA·g?1) between 2.7 and 4.3 V, and 126.4, 115.7 mAh·g?1 are still respectively reached at high rate of 10 C and 20 C. After 100 charge‐discharge cycles at 1 C, the capacity retention is 93.3%, indicating the excellent cycling stability. 相似文献
974.
以巯基乙酸为稳定剂合成水溶性CdTe量子点(QDs),利用CdTe QDs荧光猝灭-恢复技术,建立了一种测定青霉素的新方法。考察了不同缓冲溶液、pH值、Co2+浓度等因素对体系的影响。结果表明,在pH=10的硼砂缓冲溶液中,Co2+能猝灭CdTe QDs的荧光,体系中加入青霉素后,CdTe QDs的荧光得到恢复且恢复强度与青霉素的浓度呈良好的线性关系,方法的线性范围为2.0×10-5~1.0×10-4 mol/L,检出限为2.2×10-6 mol/L,应用于实际样品测定,结果较好。 相似文献
975.
É. B. Coropceanu A. P. Rija V. N. Shafranskii O. A. Bologa M. Gdaniec S. T. Malinovskii 《Journal of Structural Chemistry》2007,48(6):1110-1117
The complexes [Co(DH)2(Sam)2]2[ZrF6]·5H2O (I) and [Co(DH)2(Sam)2][BF4]·H2O (II), where DH? is the dimethylglyoxime monoanion, and Sam is para-aminobenzenesulfamide (sulfanilamide, white streptocid), were synthesized, and their crystal structures were determined by X-ray diffraction analysis. The coordination polyhedron of the Co3+ atom is an N6 octahedron formed by four nitrogen atoms of the two dimethylglyoxime residues and two nitrogen atoms of the Sam fragments. The latter are realized in virtually parallel orientation relative to the polyhedron of the metal atom and its equatorial plane; the average value of the dihedral angles is 26.8(1)°, and there is π-π interaction between the benzene rings of the Sam fragments and the π delocalized equatorial metallocycle. The deviation of the cobalt atom from the four-angle plane is up to 0.009(1) Å. The (Co-N)DH? and (Co-N)Sam distances in the [Co(DH)2(Sam)2]+ complex cations vary from 1.892(2) Å to 1.907(3) Å and from 2.000(2) Å to 2.012(2) Å, respectively. The [ZrF6]2? and [BF4]? complex anions play the major role in crystal formation; they produce a substantial effect on the formation of a complex system of hydrogen bonds. 相似文献
976.
Chandra S Kumar A 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2007,68(5):1410-1415
Co(II), Ni(II) and Cu(II) complexes were synthesized with thiosemicarbazone (L(1)) and semicarbazone (L(2)) derived from 2-acetyl furan. These complexes were characterized by elemental analysis, molar conductance, magnetic moment, mass, IR, electronic and EPR spectral studies. The molar conductance measurement of the complexes in DMSO corresponds to non-electrolytic nature. All the complexes are of high-spin type. On the basis of different spectral studies six coordinated geometry may be assigned for all the complexes except Co(L)(2)(SO(4)) and Cu(L)(2)(SO(4)) [where L=L(1) and L(2)] which are of five coordinated square pyramidal geometry. 相似文献
977.
The synthesis, characterization and catalytic activity of a series of tetra-halo-dimethyl salen and di-halo-tetramethyl-salen ligands are reported in this paper: α,α′-dimethyl-Salen (dMeSalen) (L1); 3,3′,5,5′-tetrachloro-α,α′-dimethyl-Salen, (tCldMeSalen) (L2); 3,3′-dibromo-5,5′-dichloro-α,α′-dimethyl-Salen, (dCldBrdMeSalen) (L3); 3,3′,5,5′-tetrabromo-α,α′-dimethyl-Salen, (tBrdMeSalen) (L4); 3,3′,5,5′-tetraiodo-α,α′-dimethyl-salen, (tIdMeSalen) (L5); 3,3′-dichloro-5,5′,α,α′-tetramethyl-Salen (dCltMeSalen) (L6); 3,3′-dibromo-5,5′,α,α′-tetramethyl-Salen (dBrtMeSalen) (L7); and 3,3′-diiodo-5,5′,α,α′-tetramethyl-Salen (dItMeSalen) (L8) (Salen = bis(salicylaldehyde)ethylenediamine). Upon reaction with Co(II) ions, these ligands form complexes with square planar geometry that have been characterized by elemental analysis, cyclic voltammetry, UV–Vis, IR and EPR spectroscopies. In the presence of pyridine the obtained Co(II) complexes were found able to bind reversibly O2, which was shown by EPR spectroscopy and cyclic voltammetry. They were also found able to catalyze the oxidation of 2,6-di-tert-butylphenol (DtBuP) (9) with formation of 2,6-di-tert-butyl-1,4-benzoquinone (DtBuQ) (10) and 2,6,2′,6′-tetra-tert-butyl-1,1′-diphenobenzoquinone (TtBuDQ) (11). These properties are first influenced by the coordination of pyridine in axial position of the Co(II) ion that causes an increase of the electronic density on the cobalt ion and as a consequence a decrease in the E1/2 value and an increase of the reducing power of the Co(II) complex. It is noteworthy that, under those conditions the complexes also show a remarkable quasi-reversible behaviour. Second, complex properties are also influenced by the substituents (methyl and halogen) grafted on the aromatic ring and on the azomethynic groups. The donating methyl substituent on the azomethynic groups causes a decrease in the E1/2 value, whereas the halogen substituents on the aromatic rings have two effects: a mesomeric donating effect that tends to lower the redox potential of the complex, and a steric effect that tends to decrease the conjugation of the ligand and then to increase the redox potential of the Co(II) complex. In pyridine, the steric effect predominates, which causes both an increase of the redox potential and a decrease of the selectivity of the oxidation of phenol 9. As a result of all these effects, it then appears that the best catalysts to realize the selective oxidation of 2,6-di-tert-butyl-phenol (9) by O2 are the Co complexes of ligands bearing CH3 donating substituents, Co(dMeSalen) 1 (2CH3 substituents), and Co-di-halo-tetra-methyl-salen complexes 6, 7 and 8 (4CH3 substituents), in the presence of pyridine. 相似文献
978.
Brajagopal Samanta Joy Chakraborty R.K. Bhubon Singh Manas K. Saha Stuart R. Batten Paul Jensen M. Salah El. Fallah Samiran Mitra 《Polyhedron》2007
Two new cyano bridged Cu–Co and Cu–Fe trinuclear bimetallic assemblies, [(CuL)[Co(CN)6](CuL)]ClO4 · 3.5H2O (1) and [(CuL)[Fe(CN)6](CuL)] · 13H2O (2) where [L = (3E,5E)-N1,N4-bis((pyridin-2-yl)methylene)butane-1,4-diamine] have been prepared using cyanometallates as anion precursors and characterised by elemental analyses, spectroscopic studies, single crystal X-ray diffraction and cryomagnetic susceptibility measurements. Magneto-structural correlations have been drawn from cryomagnetic susceptibility measurements over a wide temperature range (2–300 K) under 0.5 T magnetic fields. Weak antiferromagnetic interactions with J = −0.81 and −0.73 cm−1 are found for 1 and 2, respectively, showing a very weak coupling, as expected from the diamagnetic long chain –NC–Co–CN–CN– and –NC–Fe–CN–CN– bridges revealed from the single crystal X-ray diffraction studies. 相似文献
979.
Raul Cardoso Gil Wilder Carrillo‐Cabrera Martin Schultheiss Karl Peters Hans Georg von Schnering Yuri Grin 《无机化学与普通化学杂志》1999,625(2):285-293
The compounds Ba4Ag2Si6, Eu4Ag2Si6, and Ca4Ag2Si6, prepared from the elements at 1273 K (the components in inner corundum crucibles are enclosed in sealed quartz ampoules), are brittle semiconductors with silvery luster. They react slowly with acids liberating hydrogen. Ba4Ag2[Si6] and Eu4Ag2[Si6] crystallize like Ba4Li2[Si6] (space group Fddd (No. 70); a = 8.613 Å, b = 14.927 Å, c = 19.639 Å, and a = 8.420 Å, b = 14.585 Å, c = 17.864 Å, respectively), whereas Ca4Ag2[Si6] represents a new structure type (space group Fmmm (No. 69); a = 8.315 Å, b = 14.391 Å, c = 8.646 Å). The three compounds are Zintl phases with the formal charges M2+, Ag+ and [Si6]10–. The mean bond lengths d(Si–Si) = 2.335–2.381 Å in the 10π‐Hückel arene [Si6]10– as well as d(Ag–Si) = 2.464–2.595 Å vary with the size of the M2+ cations. The chemical bonding was analyzed in terms of the Electron Localization Function (ELF) and compared with the bonding in related systems (Ce4Co2Si6). 相似文献
980.
Co3O4 nanorods have been synthesized at 160℃ for 10 h in the solution of oleic and n-cetane by an emulsion-solvothermal method using Co(NO3)2·6H2O as starting materials. The as-prepared product was characterized by X-ray powder diffraction(XRD),transmission electron microscope(TEM),and vibrating sample magnetometer(VSM). The formation mechanism of the prepared product was analyzed based on formation of rod-like micelles of oleic acid. Cobalt ions can migrate into the micelle core for the nucleation and growth of Co3O4 . The results show that the as-prepared Co3O4 nanorods are with the average size 25×100 nm and in the cubic phase. The magnetic susceptibility meets about linearly with the applied magnetic field at room temperature,and the coercivity (Hc)and remanent magnetization(Ms)values of the product at room temperature are 353 Oe and 0.4 emu/g,respectively. This simple route is also expanded to synthesize other materials with the rod-like morphology. 相似文献