全文获取类型
收费全文 | 591篇 |
免费 | 97篇 |
国内免费 | 124篇 |
专业分类
化学 | 674篇 |
晶体学 | 19篇 |
综合类 | 2篇 |
物理学 | 117篇 |
出版年
2024年 | 5篇 |
2023年 | 14篇 |
2022年 | 32篇 |
2021年 | 39篇 |
2020年 | 38篇 |
2019年 | 25篇 |
2018年 | 28篇 |
2017年 | 14篇 |
2016年 | 16篇 |
2015年 | 11篇 |
2014年 | 37篇 |
2013年 | 53篇 |
2012年 | 24篇 |
2011年 | 21篇 |
2010年 | 21篇 |
2009年 | 26篇 |
2008年 | 39篇 |
2007年 | 41篇 |
2006年 | 39篇 |
2005年 | 38篇 |
2004年 | 36篇 |
2003年 | 27篇 |
2002年 | 28篇 |
2001年 | 10篇 |
2000年 | 12篇 |
1999年 | 8篇 |
1998年 | 16篇 |
1997年 | 7篇 |
1996年 | 12篇 |
1995年 | 12篇 |
1994年 | 16篇 |
1993年 | 8篇 |
1992年 | 9篇 |
1991年 | 10篇 |
1990年 | 3篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1973年 | 4篇 |
1972年 | 1篇 |
排序方式: 共有812条查询结果,搜索用时 15 毫秒
91.
Reactions of SnCl2 with the complexes cis‐[PtCl2(P2)] (P2=dppf (1,1′‐bis(diphenylphosphino)ferrocene), dppp (1,3‐bis(diphenylphosphino)propane=1,1′‐(propane‐1,3‐diyl)bis[1,1‐diphenylphosphine]), dppb (1,4‐bis(diphenylphosphino)butane=1,1′‐(butane‐1,4‐diyl)bis[1,1‐diphenylphosphine]), and dpppe (1,5‐bis(diphenylphosphino)pentane=1,1′‐(pentane‐1,5‐diyl)bis[1,1‐diphenylphosphine])) resulted in the insertion of SnCl2 into the Pt? Cl bond to afford the cis‐[PtCl(SnCl3)(P2)] complexes. However, the reaction of the complexes cis‐[PtCl2(P2)] (P2=dppf, dppm (bis(diphenylphosphino)methane=1,1′‐methylenebis[1,1‐diphenylphosphine]), dppe (1,2‐bis(diphenylphosphino)ethane=1,1′‐(ethane‐1,2‐diyl)bis[1,1‐diphenylphosphine]), dppp, dppb, and dpppe; P=Ph3P and (MeO)3P) with SnX2 (X=Br or I) resulted in the halogen exchange to yield the complexes [PtX2(P2)]. In contrast, treatment of cis‐[PtBr2(dppm)] with SnBr2 resulted in the insertion of SnBr2 into the Pt? Br bond to form cis‐[Pt(SnBr3)2(dppm)], and this product was in equilibrium with the starting complex cis‐[PtBr2(dppm)]. Moreover, the reaction of cis‐[PtCl2(dppb)] with a mixture SnCl2/SnI2 in a 2 : 1 mol ratio resulted in the formation of cis‐[PtI2(dppb)] as a consequence of the selective halogen‐exchange reaction. 31P‐NMR Data for all complexes are reported, and a correlation between the chemical shifts and the coupling constants was established for mono‐ and bis(trichlorostannyl)platinum complexes. The effect of the alkane chain length of the ligand and SnII halide is described. 相似文献
92.
93.
Abstract Fourier transform infrared (4000-200 cm1) and Raman (3500-50 cm?1) spectra are reported for metal(II) halide 3,5-lutidine (3,5-dimethylpyridine) complexes of the following stoichiometries: M(3,5L)4X2 M=Co or Ni, X=C1 or Br; M=Mn or Cu, X=Br; M=Cd, X=I; M(3,5L)3X2 M=Fe, X=C1; M=Cu, X=Br; Hg(3,5L) X2 X=C1 or Br. Vibrational assignments are given for all the observed bands. Some structure- spectra correlations are found. For a given series of isomorphous complexes the sum of the difference between the liquid and ligand values of the vibrational modes of 3,5-lutidine is found to increase in the order of the second ionization potentials of the metals. The frequency shifts are also found to depend on the halogen. 相似文献
94.
Masami Kamigaito Mitsuo Sawamoto Toshinobu Higashimura 《Journal of polymer science. Part A, Polymer chemistry》1993,31(12):2987-2994
Phosphoric and phosphinic acid derivatives (R1R2PO2H; R1, R2 = OPh, OPh; OnBu, OnBu; Ph, Ph; Ph, H) in conjunction with zinc chloride (ZnCl2) led to living cationic polymerization of isobutyl vinyl ether (IBVE) in toluene below 0°C. The number-average molecular weights (M?n) of the polymers (M?n > 2 × 104) were directly proportional to monomer conversion and in excellent agreement with the calculated values assuming that one polymer chain forms per R1R2PO2H molecule. Throughout the reaction, the molecular weight distributions (MWDs) stayed narrow (M?w/M?n ? 1.1). A dibasic acid, PhOP (O) (OH)2, coupled with ZnCl2, also induced living cationic polymerization of IBVE where one molecule of the acid generated two living polymer chains. The polymerization by (PhO)2PO2H/ZnCl2 and its model reactions were directly analyzed by 31P and 1H-NMR spectroscopy. The analysis showed that the acid initially forms the adduct [CH3CH(OiBu)OP(O)(OPh)2], the phosphate linkage of which is in turn activated by ZnCl2 so as to initiate living propagation. The finding thus indicates that (PhO)2PO2H indeed acts as an initiator in the living polymerization. The NMR analysis also suggested that an exchange reaction occurs between the phosphate group at the polymer terminal and the chlorine in ZnCl2. The occurrence of living IBVE polymerization with these various R1R2PO2H/ZnCl2 systems shows that phosphoric and phosphinic acids are another general class of protonic acids which are effective initiators for the living cationic polymerization assisted by Lewis acids. © 1993 John Wiley & Sons, Inc. 相似文献
95.
IntroductionFreeradicalformationfromhalogenatedhydrocarbonshasreceivedconsiderableattentionbecauseofitsscientif icandenvironmentalrelevance .1 6 Thisreactionseemstoplayanimportantroleinvariousprocesses .Bond break ingreactionisapowerfulsynthetictooltoprov… 相似文献
96.
The title compound (4,4′-H2bipy)[CdBr4]·H2O 1 has been synthesized via hydrothermal reaction and characterized by X-ray diffraction. The crystal belongs to monoclinic,space group P21/c with a=8.260(3),b=23.926(7),c=9.774(2),β=106.777(9)o,C10H12Br4CdN2O,Mr=608.26,V=1849.4(9)3,Z=4,Dc=2.185 g/cm3,S=1.005,μ(MoKα) =9.814 mm–1,F(000)=1128,R=0.0646 and wR=0.0989. The crystal structure analysis of 1 reveals that the title compound features an isolated structure,based on discrete 4,4′-H2bipy moieties and lattice water molecules which are linked by hydrogen bonds together with tetra-hedral cadmium atoms terminally coordinated by four bromine atoms. 相似文献
97.
Crystal Structure of the Monohydrates of Lithium Chloride and Lithium Bromide Using single crystal analysis and powder diffraction data the crystal structures of the monohydrates of lithium chloride and lithium bromide were solved. Both compounds crystallise isotypic in the space group Cmcm (LiCl·H2O: single crystal analysis; T = 100 K; a = 758, 35(2); b = 768, 07(2); c = 762, 35(2) pm; Z = 8; 1179 unique reflections; R1 = 0, 0196. LiBr·H2O: Rietveld‐refinement; T = 220 K; a = 806, 15(1); b = 799, 44(1) und c = 794, 61(1) pm; Z = 8; 157 unique reflections; Rp = 0, 0922; Rwp = 0, 0979; Rexp = 0, 0657). The structure derives from the perowskite structure according to the formula X(H2O)Li□2 (X = Cl, Br). The orientation of the water molecules is linked clearly to the distribution of the lithium cations and vice versa. The high level ionic conductivity in the cubic high temperature phase of LiBr·H2O is related to the initial rotation of the water molecules during the phase transformation. This motion favours the lithium ion hopping and the melting of the lithium substructure respectively. 相似文献
98.
Electron diffraction data have been used as a constraint in the determination of force field for Tl2F2 having planar rhombic structure. The L-F approximation method, recently given by us, has also been applied to evaluate force
constants for thallous halide dimers,e.g. T12F2 and T12Cl2. The results have been compared with the available experimental data in order to check the validity of the present work.
It is concluded that non-bond experimental mean amplitudeU
1...Tl for Tl2F2 is capable of fixing the force field and L-F approximation gives reasonably good force fields for the two thallous halide
dimers now under study. 相似文献
99.
Arnold V. Lesikar 《Journal of solution chemistry》1977,6(12):839-853
The glass-transition temperature (T
g) in binary mixtures of the primary alkanols with CBr
4
and CHBr
3
has been measured as a function of composition. The results are compared with earlier studies on alkanol solutions of organic chlorides. The initial molar slope (IMS) of theT
g vs. composition curve at the pure alkanol indicates formation of a 1:1 halide-alkanol complex stabilized by a specific halogen-oxygen interaction. The IMS values decrease in the order CBr
4
>CHBr
3
>CCl
4
>CHCl
3
>CH
2
Cl
2
, reflecting decreasing stability of the complex. 相似文献
100.
Precision densities and sound velocities for solutions of selected univalent electrolytes and nonelectrolytes in DMSO have been measured at 25°C, and apparent molar isentropic compressibilities and volumes evaluated. The data were extrapolated to infinite dilution to obtain standard state partial molar quantities, K
s,2
°
, and V
2
°
. Values of V
2
°
and K
s,2
°
for alkali metal halides in DMSO are very similar to those in water. The results confirm conclusions derived from data in water and other nonaqueous solvents that K
s,2
°
and V
2
°
for alkali metal halides are strongly dependent on solvent compressibility. K
s,2
°
becomes more negative and V
2
°
decreases as solvent compressibility increases. Attempts to determine ionic K
s,2
°
values suggest that a significant dissymmetry exists between 4P+ and 4B– in DMSO, whereas in water and MeOH, these large ions appear to behave similarly. Ionic V
2
°
values support this conclusion. Steric hindrance in the DMSO molecule is believed to be responsible for this dissymmetry. 相似文献