全文获取类型
收费全文 | 3251篇 |
免费 | 340篇 |
国内免费 | 289篇 |
专业分类
化学 | 1380篇 |
晶体学 | 10篇 |
力学 | 721篇 |
综合类 | 26篇 |
数学 | 381篇 |
物理学 | 1362篇 |
出版年
2024年 | 3篇 |
2023年 | 53篇 |
2022年 | 57篇 |
2021年 | 67篇 |
2020年 | 85篇 |
2019年 | 77篇 |
2018年 | 76篇 |
2017年 | 63篇 |
2016年 | 78篇 |
2015年 | 63篇 |
2014年 | 135篇 |
2013年 | 218篇 |
2012年 | 162篇 |
2011年 | 178篇 |
2010年 | 185篇 |
2009年 | 239篇 |
2008年 | 250篇 |
2007年 | 235篇 |
2006年 | 255篇 |
2005年 | 193篇 |
2004年 | 212篇 |
2003年 | 146篇 |
2002年 | 121篇 |
2001年 | 95篇 |
2000年 | 77篇 |
1999年 | 68篇 |
1998年 | 80篇 |
1997年 | 63篇 |
1996年 | 58篇 |
1995年 | 51篇 |
1994年 | 43篇 |
1993年 | 22篇 |
1992年 | 29篇 |
1991年 | 28篇 |
1990年 | 26篇 |
1989年 | 17篇 |
1988年 | 16篇 |
1987年 | 10篇 |
1986年 | 9篇 |
1985年 | 11篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有3880条查询结果,搜索用时 31 毫秒
81.
Ohshima H 《Journal of colloid and interface science》2003,260(2):339-343
A set of coupled equations is given which determines the distributions of the electric potential and counterions in a system of two interacting identical ion-penetrable membranes of thickness d at separation h immersed in a salt-free medium containing only counterions. The solution to these coupled equations also gives the electrostatic repulsive force between the membranes. It is shown that the interaction force remains finite at h-->0, unlike the case of the interaction between two planar charged surfaces (d-->0), and that the interaction force becomes independent of the membrane fixed charge and membrane thickness d at very large h. Finally, an approximate single transcendental equation giving the solution to the coupled equations is derived. 相似文献
82.
《Arabian Journal of Chemistry》2022,15(4):103712
Although recent decades have witnessed the synthesis of 1,3,4-thiadiazoles via phosphorus POCl3-promoted cyclization reaction, simultaneous access to 2-amino-1,3,4-thiadiazole and 2-amino-1,3,4-oxadiazole analogs remains unexpected and elusive. Herein, a detailed regiocontrolled synthesis of 2-amino-1,3,4-thiadiazoles in good to high yields with good regioselectivities from readily available thiosemicarbazides using POCl3 was disclosed. Meantime, to establish a comprehensive structure–activity relationship, 2-amino-1,3,4-oxadiazole derivatives as single regioisomers were prepared via EDCI·HCl-triggered cyclization of the thiosemicarbazide intermediates. The in vitro anti-influenza assays proved that the selected compounds with the pyrazine/pyridine ring exhibited certain inhibitory activities against influenza A virus strains A/HK/68 (H3N2) and A/PR/8/34 (H1N1) in MDCK cells. Among them, N-(adamantan-1-yl)-5-(5-(azepan-1-yl)pyrazin-2-yl)-1,3,4-thiadiazol-2-amine (4j) was the most active compound, and exhibited favorable activity with EC50 values of 3.5 μM and 7.5 μM, respectively. In addition, the molecular docking results explained the reason why compound 4j had dual inhibitory activity and revealed the reasonable binding mode of this compound with the M2-S31N and M2-WT ion channels. This compound had the potential to be further developed as an anti-influenza drug. 相似文献
83.
Cang Li 《Journal of solid state chemistry》2004,177(12):4569-4575
Reaction of an aqueous slurry of an Mg2Al-NO3 layered double hydroxide with a four-fold excess of Na[Eu(EDTA)] gives a material which analyses for Mg0.68Al0.32(OH)2[Eu(EDTA)]0.10(CO3)0.11·0.66H2O. The interlayer spacing of the material is 13.8 Å, corresponding to a gallery height of 9.0 Å, which accords with the maximal dimensions (9-10 Å) of the anion in metal-EDTA complex salts as determined by single crystal X-ray diffraction. Geometrical considerations show that the charge density on the layered double hydroxide layers is too high to be balanced by intercalation of [Eu(EDTA)]− alone, necessitating the co-intercalation of carbonate ions which have a much higher charge density. 相似文献
84.
Zerihun Assefa Jie Ling Thomas E. Albrecht-Schmitt 《Journal of solid state chemistry》2006,179(12):3653-3663
The reaction of Lu3+ or Yb3+ and H5IO6 in aqueous media at 180 °C leads to the formation of Yb(IO3)3(H2O) or Lu(IO3)3(H2O), respectively, while the reaction of Yb metal with H5IO6 under similar reaction conditions gives rise to the anhydrous iodate, Yb(IO3)3. Under supercritical conditions Lu3+ reacts with HIO3 and KIO4 to yield the isostructural Lu(IO3)3. The structures have been determined by single-crystal X-ray diffraction. Crystallographic data are (MoKα, λ=0.71073 Å): Yb(IO3)3, monoclinic, space group P21/n, a=8.6664(9) Å, b=5.9904(6) Å, c=14.8826(15) Å, β=96.931(2)°, V=766.99(13), Z=4, R(F)=4.23% for 114 parameters with 1880 reflections with I>2σ(I); Lu(IO3)3, monoclinic, space group P21/n, a=8.6410(9), b=5.9961(6), c=14.8782(16) Å, β=97.028(2)°, V=765.08(14), Z=4, R(F)=2.65% for 119 parameters with 1756 reflections with I>2σ(I); Yb(IO3)3(H2O), monoclinic, space group C2/c, a=27.2476(15), b=5.6296(3), c=12.0157(7) Å, β=98.636(1)°, V=1822.2(2), Z=8, R(F)=1.51% for 128 parameters with 2250 reflections with I>2σ(I); Lu(IO3)3(H2O), monoclinic, space group C2/c, a=27.258(4), b=5.6251(7), c=12.0006(16) Å, β=98.704(2)°, V=1818.8(4), Z=8, R(F)=1.98% for 128 parameters with 2242 reflections with I>2σ(I). The f elements in all of the compounds are found in seven-coordinate environments and bridged with monodentate, bidentate, or tridentate iodate anions. Both Lu(IO3)3(H2O) and Yb(IO3)3(H2O) display distinctively different vibrational profiles from their respective anhydrous analogs. Hence, the Raman profile can be used as a complementary diagnostic tool to discern the different structural motifs of the compounds. 相似文献
85.
Vítězslav Zima Jan Svoboda Klára Melánová Ji?í Dybal 《Journal of solid state chemistry》2007,180(3):929-939
Several new strontium 4-carboxyphenylphosphonates, i.e., two modifications of Sr(HOOCC6H4PO3H)2, SrH(OOCC6H4PO3)·H2O, Sr3(OOCC6H4PO3)2·4H2O and Sr3(OOCC6H4PO3)2·5.7H2O were prepared and characterized by elemental analysis, thermogravimetry, X-ray powder diffraction and infrared spectroscopy. It was found that the compositions of these compounds depend on the acidity of the reaction medium. In addition, the presented compounds are interconvertible in dependence on pH. The position of the acid hydrogen atom in SrH(OOCC6H4PO3)·H2O was determined from the IR spectra of the studied compounds.The structure of the β modification of Sr(HOOCC6H4PO3H)2 was solved from its X-ray powder diffraction pattern using an ab initio method (the FOX program) with subsequent Rietveld refinement in the FULLPROF program. The compound is monoclinic, with the space group P21/c (No. 14), a=49.88(2), b=7.867(2), c=5.602(3) Å, β=128.68(2)°, and Z=4. It has a one-dimensional structure with an inorganic part built of SrO8 distorted tetragonal antiprisms. 相似文献
86.
Hydrothermal reaction of copper(II) acetate, 2,2′-bipyridine (bipy) and NH4VO3 at 170 °C lead to a new layered polyoxovanadate with organically covalent-bonded copper(II) complex, Cu2(bipy)2V6O17 (1). Cu2(bipy)2V6O17 (1) is a new copper(II) vanadium(V) oxide featuring a new layered architecture, in which the V2O7 dimeric units and the cyclic tetranuclear V4O12 cluster units are interconnected via corner sharing into a unique one-dimensional {V6O17}4− anionic chain, such chains are further bridged by {Cu(bipy)}2+ complex cations into a 010 organic–inorganic hybrid layer. 相似文献
87.
Richard E. Sykora Thomas E. Albrecht-Schmitt 《Journal of solid state chemistry》2004,177(10):3729-3734
The hydrothermal reaction of UO3, WO3, and CsIO4 leads to the formation of Cs6[(UO2)4(W5O21)(OH)2(H2O)2] and UO2(IO3)2(H2O). Cs6[(UO2)4(W5O21)(OH)2(H2O)2] is the first example of a hydrothermally synthesized uranyl tungstate. It's structure has been determined by single-crystal X-ray diffraction. Crystallographic data: tetragonal, space group I4 cm, , , Z=4, MoKα, , R(F)=2.84% for 135 parameters with 2300 reflections with I>2σ(I). The structure is comprised of two-dimensional anionic layers that are separated by Cs+ cations. The coordination polyhedra found in the novel layers consist of UO7 pentagonal bipyramids, WO6 distorted octahedra, and WO5 square pyramids. The UO7 polyhedra are formed from the binding of five equatorial oxygen atoms around a central uranyl, UO22+, unit. Both bridging and terminal oxo ligands are employed in forming the WO5 square pyramidal units, while oxo, hydroxo, and aqua ligands are found in the WO6 distorted octahedra. In the layers, four (UO2)O5 polyhedra corner share with equatorial oxygen atoms to form a U4O24 tetramer entity with a square site in the center; a tungsten atom populates the center of each of these sites to form a U4WO25 pentamer unit. The pentamer units that result are connected in two dimensions by edge-shared dimers of WO6 octahedra to form the two-dimensional [(UO2)4(W5O21)(OH)2(H2O)2]6- layers. The lack of inversion symmetry in Cs6[(UO2)4(W5O21)(OH)2(H2O)2] can be directly contributed to the WO5 square pyramids found in the pentamer units. In the structure, all of these polar polyhedra align their terminal oxygens in the same orientation, along the c axis, thus resulting in a polar compound. 相似文献
88.
《Arabian Journal of Chemistry》2022,15(4):103707
Alsophila spinulosa is a tree-like fern, and many evidences suggested that plant polyphenols had the potential therapeutic for Alzheimer s disease (AD). Herein, polyphenols (ASP) was isolated from A. spinulosa leaves and its major constituent were isoorientin and vitexin. ASP displayed excellent antioxidant activity and obvious anti-lipid peroxidation capacity in vitro. ASP improved the survival rate of C. elegans under high temperature by enhancing the antioxidant enzymes activities and decreasing the lipid peroxidation level. Moreover, ASP alleviated β-amyloid (Aβ) induced paralysis and reduced Aβ deposition, decreased reactive oxygen species (ROS) accumulation and improved the level of skn-1 mRNA. In addition, ASP decreased the levels of pdk-1 and akt-1 mRNA in P13K/AKT signaling pathway. In conclusion, ASP may be a potential ingredient for the alleviation of AD. 相似文献
89.
Hydrothermal reactions of cadmium(II) chloride with three amino-diphosphonic acids, C6H5CH2N(CH2PO3H2)2 (H4L1), C6H5CH2CH2N(CH2PO3H2)2 (H4L2) and 4-CH3-C6H4CH2N (CH2PO3H2)2) (H4L3) resulted in three new metal amino-diphosphonates, namely, Cd(H3L1)2, 1 Cd(H3L2)2·2H2O 2 and Cd(H3L3)23. In all three complexes, the Cd(II) ion is octahedrally coordinated by six phosphonate oxygen atoms from six ligands. Complexes 1 and 3 have a similar structure in which the CdO6 octahedra are cross-linked by bridging ligands into a double chain along the c-axis, such double chains are further interlinked via hydrogen bonds between non-coordinated phosphonate oxygen atoms to form 〈100〉 and 〈200〉 layers with the phenyl groups of the ligands orientated toward the interlayer space. The structure of complex 2 features a 〈100〉 cadmium(II) diphosphonate layer. The effects of the substitute groups attached to the amine groups on the structures of the metal phosphonates are also discussed. 相似文献
90.
Xingang Kong Jiarui Zhang Jianfeng Huang Jiayin Li Yi Qin Ting Zhao Qi Feng 《中国化学快报》2019,30(3):771-774
SnNb2O6 and Sn2Nb2O7 nanosheets were synthetized via microwave assisted hydrothermal method, and innovatively employed as anode materials for lithium-ion battery. Compared with Sn2Nb2O7 and the previously reported pure Sn-based anode materials, the SnNb2O6 electrode exhibited outstanding cycling performance. 相似文献