全文获取类型
收费全文 | 12637篇 |
免费 | 778篇 |
国内免费 | 779篇 |
专业分类
化学 | 13173篇 |
晶体学 | 138篇 |
力学 | 7篇 |
综合类 | 27篇 |
数学 | 277篇 |
物理学 | 572篇 |
出版年
2023年 | 92篇 |
2022年 | 173篇 |
2021年 | 299篇 |
2020年 | 423篇 |
2019年 | 341篇 |
2018年 | 284篇 |
2017年 | 275篇 |
2016年 | 368篇 |
2015年 | 265篇 |
2014年 | 332篇 |
2013年 | 752篇 |
2012年 | 1322篇 |
2011年 | 506篇 |
2010年 | 446篇 |
2009年 | 626篇 |
2008年 | 704篇 |
2007年 | 855篇 |
2006年 | 660篇 |
2005年 | 611篇 |
2004年 | 595篇 |
2003年 | 502篇 |
2002年 | 413篇 |
2001年 | 364篇 |
2000年 | 357篇 |
1999年 | 337篇 |
1998年 | 294篇 |
1997年 | 288篇 |
1996年 | 309篇 |
1995年 | 315篇 |
1994年 | 211篇 |
1993年 | 187篇 |
1992年 | 157篇 |
1991年 | 104篇 |
1990年 | 63篇 |
1989年 | 50篇 |
1988年 | 52篇 |
1987年 | 43篇 |
1986年 | 37篇 |
1985年 | 30篇 |
1984年 | 31篇 |
1983年 | 12篇 |
1982年 | 26篇 |
1981年 | 14篇 |
1980年 | 18篇 |
1979年 | 12篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1975年 | 5篇 |
1974年 | 3篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
采用缓慢挥发法合成了2个烟酰腙类Schiff碱配合物[Cu(Py)(HL1)]2 (1)和[Ni(L2)2] (2), 其中, H3L1=2, 4-二羟基苯甲醛缩烟酰腙, HL2=2-乙酰基吡啶缩烟酰腙。采用元素分析、红外光谱、紫外光谱、荧光光谱和热重分析以及X-射线单晶衍射分析进行 了表征。结果表明, 1和2的晶体均属单斜晶系, P21/c空间群;1的晶胞参数a=0.739 86(12) nm, b=1.903 7(3) nm, c=1.154 86(19) nm, β=105.090(3)°, V=1.570 5(4) nm3;该化合物是中心对称的双核配合物, 每个Cu(Ⅱ)离子都处于畸变四方锥配位环境;结构基 元通过π-π相互作用和O-H…N氢键形成三维超分子。2的晶胞参数a=2.034 0(5) nm, b=1.183 2(3) nm, c=1.020 7(3) nm, V=2.456 1(11) nm3;中心离子Ni(Ⅱ)的配位数为6, 它处于畸变八面体配位环境。配合物有很高的热稳定性, 分解温度分别为315 ℃ (1)和358 ℃ (2)。 相似文献
992.
《Tetrahedron letters》2014,55(52):7233-7235
The α-alkylation of ketones with primary alcohols was realized by CC cross-coupling with iridium–CNP complexes as catalyst. This reaction proceeds via dehydrogenation reactions, aldol condensation, and hydrogenation using the borrowed hydrogen atoms from alcohols. The pyridyl methanols and other heterocyclic substituted methanols, especially alkyl alcohols, were also suitable for this transformation. 相似文献
993.
994.
The metathetical reactions between SnBr4 and Li2[E'C(PPh2E)2] in toluene produce the homoleptic tin(IV) complexes Sn[E′C(PPh2E)2]2 [E = E′ = S ( 1b ); E = S, E′ = Se ( 1c )], which were isolated as red crystals and structurally characterized by X‐ray crystallography. The metrical parameters of these octahedral complexes are compared with those of the all‐selenium analog Sn[E′C(PPh2E)2]2 (E = E′ = Se, 1a ), which was prepared previously by a different route. 相似文献
995.
The quadruply bonded Mo24+ complex Mo2(DAniF)3(OOCC6F5) ( 1 ) [DAniF = N,N′‐bis(4‐methoxyphenyl)formamidinate] was synthesized. The solvate Mo2(DAniF)3(OOCC6F5) · (C6H6) ( 2 ) and co‐crystal Mo2(DAniF)3(OOCC6F5) · (C10H8) ( 3 ) complexes were obtained by self‐assembly of crystals of 1 with benzene and naphthalin, respectively. Compounds 1 , 2 , and 3 were structurally characterized by single‐crystal X‐ray diffraction. In monomer 1 , the Mo–Mo bond length of 2.0874(6) Å is typical for dimolybdenum quadruple bonds. The solvate complex 2 was stabilized by weak π–π stacking interactions between the benzene molecule and the pentafluorophenyl ring (as indicated by a center‐to‐center distance of 3.838(10) Å and a center‐to‐plane distance of 3.712(4) Å between phenyl and pentafluorophenyl ring) and intermolecular C–H ··· F–C interactions (the shortest F ··· H distance is 2.560(2) Å). In complex 3 , a one‐dimensional chain was formed by C–H ··· F–C interactions between the hydrogen atoms in naphthalin and the fluorine atoms in the monomer (H ··· F distances of 2.582(2) Å). Information on the structures in solution of the three crystals was obtained by 1H NMR spectroscopy. 相似文献
996.
Benjamin L. Solomon Christopher P. Landee Jan L. Wikaira 《Journal of Coordination Chemistry》2014,67(23-24):3953-3971
Using 2-amino-5-chloro-3-fluoropyridine, two new copper halide coordination complexes and two new salts have been synthesized: [(3,5-FCAP)2CuCl2] (1), [(3,5-FCAP)2CuBr2](2), (3,5-FCAPH)2[CuCl4] (3) and (3,5-FCAPH)2[CuBr4] (4) [3,5-FCAP?=?2-amino-5-chloro-3-fluoropyridine; 3,5-FCAPH?=?2-amino-5-chloro-3-fluoropyridinium]. These complexes have been analyzed through single-crystal X-ray diffraction and temperature-dependent magnetic susceptibility. Compounds 1 and 2 crystallize in the triclinic space group P-1, while 3 and 4 crystallize in the monoclinic space group P21/c. All structures were distinct, with 1 giving a bihalide bridged chain, 2 yielding a halide bridged dimer, 3 forming a two-halide bridged chain via short Cl???Cl contacts, and 4 producing a rectangular sheet via short Br???Br contacts. All four compounds exhibit anti-ferromagnetic interactions and were fit to linear chain (1 and 3), dimer (2), and rectangular 2-D sheet (4) models. The resulting J/kB values are ?3.4(1), ?31.3(8), ?0.9(1), and ?9.46(6)?K with an α value (α?=?J?/J) of 0.06(2), respectively. 相似文献
997.
998.
Pablo Fuentealba Lorenzo Serón Camila Sánchez Jorge Manzur Verónica Paredes-Garcia Nancy Pizarro 《Journal of Coordination Chemistry》2014,67(23-24):3894-3908
A family of macrocyclic complexes [M2LnCl2] have been synthesized and characterized (M: CuII or ZnII; Ln: macrocyclic ligand derived from 2-hydroxy-5-methyl-1,3-benzenedicarbaldehyde and different aliphatic diamines and o-phenylenediamine). The influence of the aromaticity of the ligand and the metal center on the spectroscopic properties of the complexes (absorption and emission) has been studied. Making use of the weak interactions between hydrated potassium ions and the layers of the K0.4Mn0.8PS3 precursor, the obtained macrocyclic complexes have been intercalated in the interlamellar space by a microwave assisted cationic exchange reaction. The optical properties of the obtained hybrid materials are reported. The absorption edge, recorded by solid state reflectance spectroscopy for CuII and the ZnII macrocycle-based composites, is 1.67–1.76 eV, both shifted to lower energy compared with that of the pristine MnPS3. 相似文献
999.
Mariela M. Nolasco Patrícia M. Vaz Pedro D. Vaz Rute A.S. Ferreira 《Journal of Coordination Chemistry》2014,67(23-24):4076-4089
The α-substituted β-diketonate [Ln(3Cl-acac)3(H2O)2] [Ln = Tb, Gd] complexes (with 3Cl-acac– being 3-chloro-2,4-pentanedionate) were characterized by elemental analysis, infrared, ultraviolet (UV)-visible and photoluminescence spectroscopies. For comparison purposes regarding photoluminescence, the well-known [Tb(acac)3(H2O)2] complex was also synthesized. By considering the phosphorescence spectra of [Gd(3Cl-acac)3(H2O)2], the effect of chloride replacement of hydrogen on the triplet state energy of the 3Cl-acac ligand was revealed. To support the interpretation and rationalization of the experimental results, Time-dependent DFT calculations were performed on Tb(3Cl-acac)3(H2O)2. Additionally, the possibility of Tb(3Cl-acac)3(H2O)2 to be used as potential green-emitting phosphor material for solid-sate light emitting diodes was evaluated. A prototype was successfully fabricated coating a near-UV LED (370 nm) with the Tb(3Cl-acac)3(H2O)2 complex. 相似文献
1000.
Henry A. Nkabyo D. Hannekom Jean McKenzie 《Journal of Coordination Chemistry》2014,67(23-24):4039-4060
Irradiation cis-[M(Ln-S,O)2] complexes (M = PtII, PdII) derived from N,N-dialkyl-N′-benzoylthioureas (HLn) with various sources of intense visible polychromatic or monochromatic light with λ < 500 nm leads to light-induced cis?→?trans isomerization in organic solvents. In all cases, white light derived from several sources or monochromatic blue-violet laser 405 nm light, efficiently results in substantial amounts of the trans isomer appearing in solution, as shown by 1H NMR and/or reversed-phase HPLC separation in dilute solutions at room temperature. The extent and relative rates of cis/trans isomerization induced by in situ laser light (λ = 405 nm) of cis-[Pd(L2-S,O)2] was directly monitored by 1H NMR and 195Pt NMR spectroscopy of selected cis-[Pt(L-S,O)2] compounds in chloroform-d; both with and without light irradiation allows the δ(195Pt) chemical shifts cis/trans isomer pairs to be recorded. The cis/trans isomers appear to be in a photo-thermal equilibrium between the thermodynamically favored cis isomer and its trans counterpart. In the dark, the trans isomer reverts back to the cis complex in what is probably a thermal process. The light-induced cis/trans process is the key to preparing and isolating the rare trans complexes which cannot be prepared by conventional synthesis as confirmed by the first example of trans-[Pd(L-S,O)2] characterized by single-crystal X-ray diffraction, deliberately prepared after photo-induced isomerization in acetonitrile solution. 相似文献