全文获取类型
收费全文 | 5629篇 |
免费 | 105篇 |
国内免费 | 9篇 |
专业分类
化学 | 4080篇 |
晶体学 | 27篇 |
力学 | 91篇 |
数学 | 623篇 |
物理学 | 922篇 |
出版年
2020年 | 52篇 |
2018年 | 43篇 |
2017年 | 43篇 |
2016年 | 68篇 |
2015年 | 78篇 |
2014年 | 86篇 |
2013年 | 167篇 |
2012年 | 172篇 |
2011年 | 199篇 |
2010年 | 136篇 |
2009年 | 149篇 |
2008年 | 193篇 |
2007年 | 207篇 |
2006年 | 201篇 |
2005年 | 202篇 |
2004年 | 192篇 |
2003年 | 153篇 |
2002年 | 169篇 |
2001年 | 136篇 |
2000年 | 157篇 |
1999年 | 109篇 |
1998年 | 90篇 |
1997年 | 90篇 |
1996年 | 97篇 |
1995年 | 79篇 |
1994年 | 89篇 |
1993年 | 91篇 |
1992年 | 98篇 |
1991年 | 76篇 |
1990年 | 62篇 |
1989年 | 63篇 |
1988年 | 67篇 |
1987年 | 70篇 |
1986年 | 79篇 |
1985年 | 96篇 |
1984年 | 70篇 |
1983年 | 62篇 |
1982年 | 74篇 |
1981年 | 74篇 |
1980年 | 60篇 |
1979年 | 78篇 |
1978年 | 66篇 |
1977年 | 57篇 |
1976年 | 58篇 |
1975年 | 49篇 |
1974年 | 50篇 |
1973年 | 44篇 |
1972年 | 46篇 |
1971年 | 38篇 |
1967年 | 37篇 |
排序方式: 共有5743条查询结果,搜索用时 15 毫秒
981.
Kurt Begitt 《Nachrichten aus der Chemie》2002,50(11):1285-1285
982.
Phosphoraneiminato Acetate Cluster of Copper and Zinc. Crystal Structures of [Cu4(NPEt3)2(O2CCH3)6] and [Zn4(NPEt3)2(O2CCH3)6] The anhydrous acetates of copper(II) and zinc react with the silylated phosphaneimine Me3SiNPEt3 in dichloromethane at 20 °C forming the mixed phosphoraneiminato acetate clusters [Cu4(NPEt3)2(O2CCH3)6] ( 1 ), which forms emerald crystals, and colourless [Zn4(NPEt3)2 · (O2CCH3)6] ( 2 ). In spite of analogous composition the structures of 1 and 2 are completely different. In the asymmetric unit of 1 three copper atoms of an almost isosceles triangle are linked via two nitrogen atoms of the NPEt3– groups to form a trigonal bipyramidal aggregate. One of these three copper atoms is chelated by an acetate group, another one is connected with the fourth copper atom via three μ2‐O2C–CH3 groups. The asymmetric units are associated via a μ2‐O2C–CH3 group and a μ3‐OC(O)CH3 group at a time so that infinite chains result. In 2 two zinc atoms are linked via the nitrogen atoms of the two NPEt3– groups to form an almost centrosymmetric four‐membered ring. Both nitrogen atoms of the four‐membered ring are connected with another zinc atom each. These zinc atoms again are linked with the zinc atoms of the Zn2N2 four‐membered ring via two μ2‐O2C–CH3 groups each and additionally coordinated with a terminal acetate ligand each. 相似文献
983.
[ScCl2{N(SiMe3)2}(THF)2] – a Precursor for the Synthesis of Scandium Nitride [ScCl2{N(SiMe3)2}(THF)2] ( 1 ) has been prepared by the reaction of [ScCl3(THF)3] with the trisamide Sc[N(SiMe3)2]3 in tetrahydrofurane solution forming colourless moisture sensitive crystals, which were characterized by a crystal structure determination. Space group P 1, Z = 2, lattice dimensions at –50 °C: a = 841.4(1), b = 924.2(1), c = 1550.0(1) pm, α = 90.046(7)°, β = 95.671(9)°, γ = 106.066(6)°, R1 = 0.0329. In the molecular structure of 1 the scandium atom has a distorted trigonal‐bipyramidal coordination with the THF molecules in apical positions. At 400 °C 1 is converted into scandium nitride, ScN, by stepwise leaving of THF and ClSiMe3. 相似文献
984.
Syntheses and Crystal Structures of the Nitrido‐chloro‐molybdates [Mg(THF)4{NMoCl4(THF)}2] · 4 CH2Cl2 and [Li(12‐Crown‐4)(NMoCl4)]2 · 2 CH2Cl2 Both the title compounds as well as [Li(12‐crown‐4)2]+MoNCl4– were made from MoNCl3 and the chlorides MgCl2 and LiCl, respectively, in dichloromethane suspensions in the presence of tetrahydrofuran and 12‐crown‐4, respectively. They form orange‐red moisture‐sensitive crystals, which were characterized by their IR spectra and partly by crystal structure analyses. [Mg(THF)4{NMoCl4(THF)}2] · 4 CH2Cl2 ( 1 ): space group C2/m, Z = 2, lattice dimensions at –50 °C: a = 1736.6(1), b = 1194.8(1), c = 1293.5(2) pm; β = 90.87(1)°; R1 = 0.037. In 1 the magnesium ion is coordinated octahedrally by the oxygen atoms of the four THF molecules and in trans‐position by the nitrogen atoms of the two [N≡MoCl4(THF)]– ions. [Li(12‐crown‐4)(NMoCl4)]2 · 2 CH2Cl2 ( 2 ): space group P 1, Z = 1, lattice dimensions at –70 °C: a = 930.4(1), b = 957.9(1), c = 1264.6(1) pm; α = 68.91(1)°, β = 81.38(1)°, γ = 63.84(1)°; R1 = 0.0643. 2 forms a centrosymmetric ion ensemble in the dimeric cation of which, i. e. [Li(12‐crown‐4)]22+, the lithium ions on the one hand are connected to the four oxygen atoms each of the crown ether molecules in a way not yet known; and in addition, each of the lithium ions enters into a intermolecular Li–O bond with neighboring crown ether molecules under formation of a Li2O2 four‐membered ring. The two N≡MoCl4– counterions are loosely coordinated to one oxygen atom each of the crown ether molecules with Mo–O distances of 320.2 pm. 相似文献
985.
Phosphoraneiminato Cluster of Iron. The Crystal Structures of [FeCl(NPEt3)]4, [Fe(C=C–SiMe3)(NPEt3)]4, and [Fe3Cl4{NP(NMe2)3}3] The reaction of iron dichloride with the silylated phosphaneimine Me3SiNPEt3 in the presence of potassium fluoride at 165 ?C leads to the phosphoraneiminato complex [FeCl(NPEt3)]4 ( 1 ). Compound 1 forms black, moisture and oxygen sensitive crystals. According to the crystal structure analysis 1 has a heterocubane structure, in which the iron and the nitrogen atoms of the NPEt3– groups occupy the corners of a distorted cube and form Fe–N–Fe bond angles of 83.1? and N–Fe–N angles of 96.5?. This results in significantly short Fe…Fe contacts of 272.9 pm. The results of magnetic susceptibility measurements in the range of temperatures from 1.8 to 293 K and the 57Fe‐Mössbauer spectra in the range of temperatures from 2 to 300 K are reported. Compound 1 reacts with the lithiated acetylenes LiC=C–CMe3 and LiC=C–SiMe3 in n‐hexane to form the iron‐organic derivatives [Fe(C=C–R)(NPEt3)]4 [R = CMe3 ( 2 a ), R = SiMe3 ( 2 b )] keeping the heterocubane structure. Compounds 2 a and 2 b form crystals which are very reactive and also black. According to the crystal structure analysis 2 b has a Fe4N4 heterocubane structure which is less distorted than that in 1 with bond angles Fe–N–Fe of 85.5? and N–Fe–N of 94.2?. This leads to the longer Fe…Fe contacts of 281.4 pm. With the dimethylamido derivative Me3SiNP(NMe2)3 iron dichloride reacts under conditions similar to those in the synthesis of 1 to form the dark green mixed‐valenced FeII/FeIII cluster [Fe3Cl4{NP(NMe2)3}3] ( 3 ). According to the crystal structure analysis the three iron atoms in 3 are connected via one μ3‐N atom of a NP(NMe2)3– ligand, via two μ‐N atoms of the two remaining phosphoraneiminato ligands, and via one μ‐Cl atom to form an incomplete heterocubane skeleton. 相似文献
986.
Sabine Schlecht Dirk V. Deubel Gernot Frenking Gertraud Geiseler Klaus Harms Jrg Magull Kurt Dehnicke 《无机化学与普通化学杂志》1999,625(6):887-891
Phosphoraneiminato Complexes of Rhenium(VII). Syntheses and Crystal Structures of [ReO3(NPR3)] (R = Ph, Et) and of [ReO(OSiMe3)3(Me3SiNPEt3)] The phosphoraneiminato complexes [ReO3(NPR3)] with R = Ph ( 1 ) and R = Et ( 2 ) are made from dirhenium heptaoxide and the silylated phosphoraneimines Me3SiNPR3. The complexes 1 and 2 as well as the red silanolate [ReO(OSiMe3)3(Me3SiNPEt3)] ( 3 ), which is formed as a by‐product in the synthesis of 2 , are characterized crystallographically. 1 and 2 are monomeric molecules, in which the phosphoraneiminato ligands NPR3– realize short ReN bonds of 179.3 pm ( 1 ) and 178.6 pm ( 2 ), respectively, with large ReNP bond angles of 162.0° ( 1 ) and 160.6° ( 2 ), respectively. In the rhenium(V) complex 3 the oxoligand occupies the apical position of the tetragonal pyramidal coordination of the rhenium atom, while the oxygen atoms of the Me3SiO– groups take the basic positions along with the nitrogen atom of the phosphaneimine molecule. 相似文献
987.
Roland Lang Arno Schrwerth Kurt Polborn Walter Ponikwar Wolfgang Beck Theodor Severin Kay Severin 《无机化学与普通化学杂志》1999,625(8):1384-1390
Organometallic Compounds with N -substituted 3-Hydroxy-2-methyl-4-pyridone Ligands: square planar Rhodium(I), Iridium(I), and Palladium(II) Complexes Reactions of [(OC)2MCl]2 (M = Rh, Ir) or [(cod)RhCl]2 with the anions of N-Aryl or N-Alkyl substituted 3-hydroxy-2-methyl-4-pyridones (O–O′) yield complexes of the general formula [L2M(O–O′)]. Compounds of this type are also available from reactions of [(OC)2Rh(acac)] with the corresponding neutral ligands. Substitution of one carbonyl-ligand of the N-phenyl complex [(OC)2Rh(C12H10NO2)] ( 2 ) with cyclooctene affords [(OC)(C8H14)Rh(C12H10NO2)] ( 8 ). The palladium complexes [(R3P)Pd(O–O′)Cl] (R = Et, Bu), [(C6H4CH2NMe2) · Pd(O–O′)] and [(Et3P)2Pd(O–O′)]BF4 ( 9 – 12 ) were synthesized from [(R3P)PdCl2]2, [(C6H4CH2NMe2)PdCl]2 or [(Et3P)PdCl2]. The structures of the N-methyl compounds [(OC)2Rh(C7H8NO2)] ( 1 ) and [(Ph3P)Pd(C7H8NO2)Cl] ( 9 ) were determined by single crystal X-ray diffraction. 相似文献
988.
Ulrike Riese Naim Faza Werner Massa Klaus Harms Thees Breyhan Paul Knochel Jürgen Ensling Vadim Ksenofontov Philipp Gütlich Kurt Dehnicke 《无机化学与普通化学杂志》1999,625(9):1494-1499
The phosphoraneiminato complexes [MnBr(NPEt3)]4 ( 1 ) and [M4Br5{NP(NMe2)3}3] with M = Mn ( 2 ) and M = Co ( 3 ) are prepared by melting reactions from the anhydrous metal dibromides with the silylated phosphaneimines Me3SiNPR3 (R = Et, NMe2) in the presence of potassium fluoride. All complexes are characterized by crystal structure analyses. 1 forms an only slightly distorted Mn4N4 heterocubane skeleton with an approximate Td symmetry and short Mn…Mn distances of average 295.7 pm. In the structures of 2 and 3 one μ3-NPEt3 ligand of 1 is replaced by one bromine atom with μ3-function. This leads to the novel heterocubane type M4N3Br with approximate C3 symmetry. The deformation of the cubic skeleton leads to metal-metal distances of different lengths, i. e. 292.7 and 323.6 pm in 2 and 274.4 and 306.2 pm in 3 . Temperature dependent magnetic susceptibility measurements between 300 and 5 K on 1 have shown that strong antiferromagnetic coupling exists between the Mn(II) ions with S = 5/2, with a large negative Weiss constant of Θ = –694 K. 相似文献
989.
Marc Karl Klaus Harms Gerd Seybert Werner Massa Stefan Fau Gernot Frenking Kurt Dehnicke 《无机化学与普通化学杂志》1999,625(12):2055-2063
Deprotonation Reactions of Silylated Amido Complexes of Rare Earth Elements The deprotonation of the rare earth element-tris(bistrimethylsilyl)amides Ln[N(SiMe3)2]3 of scandium, ytterbium, and lutetium with sodium-bis(trimethylsilyl)amide in THF leads to the complexes [Na(THF)3LnCH2SiMe2NSiMe3{N(SiMe3)2}2] [Ln = Sc ( 1 ), Yb ( 2 ), and Lu ( 3 )]. According to crystal structure analyses of 1 and 2 the metal atoms Sc and Yb are constituents of planar LnCSiN four-membered rings. At the same time, the C atom of the CH2 group is coordinated with the sodium ion in a linear axis Ln–C–Na; the sodium ion obtains a distorted tetrahedral arrangement by three THF molecules. The equatorial positions of the methylene-C atom, which is coordinated in a trigonal bipyramidal fashion, are occupied by the two H atoms and the Si atom of the four-membered ring. 2.6-dimethylbenzoisonitrile can be inserted into the Yb–CH2 bond of 2 and the new five-membered heterocylce YbNCSiN originates, the exocyclic CH2 group of which enters into a C–C coupling with the centrosymmetric dimer 4 while the ytterbium undergoes reduction. At the same time, sodium-7-methyl indolate is formed, which together with [NaN(SiMe3)2(THF)2] forms the centrosymmetric dimeric molecular aggregate [NaN(SiMe3)2(THF)2Na(C9H16N)]2 ( 5 ). 1 : Space group P21/n, Z = 8, lattice dimensions at –80 °C: a = 2941.4(2), b = 1205.5(1), c = 2952.4(3) pm; β = 113.455(8)°; R1 = 0.0625. 2 : Space group P21/n, Z = 8, lattice dimensions at –80 °C: a = 2943.9(1), b = 1219.5(1), c = 2944.3(1) pm; β = 113.372(4)°; R1 = 0.0361. 4 : Space group P 1, Z = 4, lattice dimensions at –80 °C: a = 1117.0(1), b = 1207.5(1), c = 1614.3(2) pm; α = 73.634(10)°, β = 82.091(10)°, γ = 74.391(10)°; R1 = 0.0525. 5 : Space group P21/n, Z = 2, lattice dimensions at –80 °C: a = 1126.7(1), b = 1459.3(1), c = 1741.1(1) pm; β = 96.461(8)°; R1 = 0.0458. Quantum chemical DFT calculations of the scandium model compound [Na(Me2O)3ScCH2SiMe2NSiH3{N(SiH3)2}2] ( 1 M ) give a very large negative charge at the pentacoordinated carbon atom of the four-membered ring that is concentrated in a lone-pair orbital which has mainly p character. The carbon atom interacts with the positively charged scandium atom mainly by Coulombic interactions. 相似文献
990.