全文获取类型
收费全文 | 1531篇 |
免费 | 40篇 |
国内免费 | 7篇 |
专业分类
化学 | 1101篇 |
晶体学 | 6篇 |
力学 | 13篇 |
数学 | 258篇 |
物理学 | 200篇 |
出版年
2020年 | 16篇 |
2019年 | 15篇 |
2017年 | 11篇 |
2016年 | 23篇 |
2015年 | 30篇 |
2014年 | 32篇 |
2013年 | 62篇 |
2012年 | 26篇 |
2011年 | 37篇 |
2010年 | 37篇 |
2009年 | 37篇 |
2008年 | 76篇 |
2007年 | 54篇 |
2006年 | 68篇 |
2005年 | 54篇 |
2004年 | 44篇 |
2003年 | 57篇 |
2002年 | 54篇 |
2001年 | 40篇 |
2000年 | 31篇 |
1999年 | 30篇 |
1998年 | 27篇 |
1997年 | 26篇 |
1996年 | 29篇 |
1995年 | 27篇 |
1994年 | 43篇 |
1993年 | 37篇 |
1992年 | 51篇 |
1991年 | 22篇 |
1990年 | 14篇 |
1989年 | 17篇 |
1988年 | 21篇 |
1987年 | 31篇 |
1986年 | 24篇 |
1985年 | 22篇 |
1984年 | 23篇 |
1983年 | 28篇 |
1982年 | 21篇 |
1981年 | 16篇 |
1980年 | 21篇 |
1979年 | 21篇 |
1978年 | 28篇 |
1977年 | 17篇 |
1976年 | 12篇 |
1975年 | 17篇 |
1974年 | 25篇 |
1973年 | 20篇 |
1972年 | 16篇 |
1971年 | 21篇 |
1970年 | 12篇 |
排序方式: 共有1578条查询结果,搜索用时 156 毫秒
951.
952.
953.
Gerd Mannebach Ruth Bieringer Roman Morschhuser Reimund Stadler 《Macromolecular Symposia》1998,132(1):245-248
The anionic copolymerization of 5-(N,N-dialkylamino)isoprenes and 1,3 -butadiene was investigated in hexane. We found that basicity and increasing amount of the polar monomer has a strong influence on the microstructure of polybutadiene. All tested 5-(N,N-dialkylamino)isoprenes were incorporated much faster into the copolymer than butadiene. Depending on the alkyl substituents the resulting copolymer is either a nearly perfect diblock or shows a considerable tapered structure. 相似文献
954.
Crystal Structure of BaGdCl5 Colourless single crystals of BaGdCl5 are obtained from a 1 : 2 molar mixture of BaCl2 and GdCl3. It crystallizes with the monoclinic space group C2/c with a = 552.1(2), b = 1925.7(5), c = 687.4(2) pm, β = 93.25(4)° in a new structure. Ba2+ and Gd3+ have coordination numbers of 8 + 2 and 8, respectively. 相似文献
955.
Transverse deuterium (2H) nuclear spin relaxation experiments have been performed on a 2H labelled main chain liquid crystal polymer. Relaxation rates are determined as a function of temperature and pulse frequency using a modified Carr-Purcell-Meiboom-Gill pulse train. The results are analysed in terms of a hydrodynamic model for fluctuations of the liquid crystal director. Analytic expressions are employed which relate the transverse spin relaxation rate to the anisotropic viscoelastic parameters of the polymer and allow estimates to be obtained for the effective viscosity and average elastic constant of the polymer. The molecular weight dependence of the viscoelastic parameters has been investigated and is found to be consistent with theoretical predictions for highly extended liquid crystal polymers. 相似文献
956.
Metal Ampoules as Mini‐Autoclaves: Syntheses and Crystal Structures of [Al(NH3)4Cl2][Al(NH3)2Cl4] and (NH4)2[Al(NH3)4Cl2][Al(NH3)2Cl4]Cl2 The salts [Al(NH3)4Cl2]+[Al(NH3)2Cl4]–≡AlCl3 · 3 NH3 ( 1 ) and (NH4+)2[Al(NH3)4Cl2]+[Al(NH3)2Cl4]–(Cl–)2≡ AlCl3 · 3 NH3 · (NH4)Cl ( 2 ) have been obtained as single crystals during the reactions of aluminum and aluminum trichloride, respectively, with ammonium chloride in sealed Monel metal containers. The crystal structure of 1 was determined again [triclinic, P‐1; a = 574.16(10); b = 655.67(12); c = 954.80(16) pm; α = 86.41(2); β = 87.16(2); γ = 84.89(2)°], that of 2 for the first time [monoclinic, I2/m; a = 657.74(12); b = 1103.01(14); c = 1358.1(3) pm; β = 103.24(2)°]. 相似文献
957.
958.
Cp2YbCl(THF) crystallizes in the orthorhombic space group Pnma (Z = 4, a = 13.109(5), b = 11.851(4), c = 9.377(3) Å, R1 = 0.0412, wR2 = 0.0482), while Cp2YbBr(THF) is monoclinic (P21/n, Z = 4, a = 8.149(2), b = 12.997(2), c = 14.388(3) Å, β = 105.73(2)°, R1 = 0.0425, wR2 = 0.0436). The ligand arrangements around the formally eight coordinate Yb atoms are pseudo tetrahedral. These two determinations complete the first series of [Cp2LnX(L)] (X = F, Cl, Br, I) structures covering all halogens for one lanthanoid and cyclopentadienyl group. 相似文献
959.
Uwe Dieckbreder Gerd‐Volker Rschenthaler Alexander A. Kolomeitsev 《Heteroatom Chemistry》2002,13(7):650-653
Bis(trifluoromethyl)phosphines RP(CF3)2 (R = Me, NEt2) were methylated by MeOSO2CF3, yielding the respective phosphonium salts [RP(CF3)2Me]+ and CF3SO3−. Deprotonation using MeNP(NEt2)3 led to the phosphorus ylides RP(CF3)2CH2, stable in solution at ambient temperature, which could be converted into 1,2λ5σ5‐oxaphosphetanes by adding hexafluoroacetone. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:650–653, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10061 相似文献
960.
Gerd Schfer Wilder Carrillo‐Cabrera Walter Schnelle Horst Borrmann Rüdiger Kniep 《无机化学与普通化学杂志》2002,628(1):289-294
A borophosphate hydrate with general composition {(NH4)xCo((3–x)/2)}(H2O)2[BP2O8] · (1 – x) H2O (x ≈ 0.5) was prepared under mild hydrothermal conditions (T = 170 °C). The crystal structure of the purple title compound was refined in space group P65 (no. 170) as a merohedric twin (a = 949.14 pm, c = 1558.25 pm, R1 = 0.037, wR2 = 0.092 for all data). According to preliminary X‐ray investigations, vis‐spectra, and magnetic susceptibility measurements, a second blue coloured variant exhibits a superstructure of the title compound with a change in coordination numbers around cobalt from six and five to six and four. Both phases show reversible de‐/rehydration properties. 相似文献