全文获取类型
收费全文 | 2000篇 |
免费 | 48篇 |
国内免费 | 6篇 |
专业分类
化学 | 1198篇 |
晶体学 | 10篇 |
力学 | 36篇 |
数学 | 198篇 |
物理学 | 612篇 |
出版年
2022年 | 13篇 |
2021年 | 21篇 |
2020年 | 24篇 |
2019年 | 12篇 |
2018年 | 19篇 |
2016年 | 28篇 |
2015年 | 27篇 |
2014年 | 36篇 |
2013年 | 74篇 |
2012年 | 91篇 |
2011年 | 132篇 |
2010年 | 49篇 |
2009年 | 47篇 |
2008年 | 95篇 |
2007年 | 95篇 |
2006年 | 104篇 |
2005年 | 105篇 |
2004年 | 100篇 |
2003年 | 91篇 |
2002年 | 86篇 |
2001年 | 56篇 |
2000年 | 50篇 |
1999年 | 16篇 |
1998年 | 18篇 |
1997年 | 20篇 |
1996年 | 39篇 |
1995年 | 23篇 |
1994年 | 41篇 |
1993年 | 40篇 |
1992年 | 47篇 |
1991年 | 39篇 |
1990年 | 27篇 |
1989年 | 23篇 |
1988年 | 14篇 |
1987年 | 14篇 |
1986年 | 20篇 |
1985年 | 23篇 |
1984年 | 18篇 |
1983年 | 20篇 |
1982年 | 10篇 |
1981年 | 11篇 |
1980年 | 15篇 |
1979年 | 13篇 |
1978年 | 12篇 |
1977年 | 9篇 |
1976年 | 10篇 |
1975年 | 14篇 |
1974年 | 11篇 |
1973年 | 23篇 |
1967年 | 10篇 |
排序方式: 共有2054条查询结果,搜索用时 15 毫秒
91.
Dash AK Jensen TR Stern CL Marks TJ 《Journal of the American Chemical Society》2004,126(39):12528-12540
Single-site polymerization catalysts generated in situ via activation of Cp*MMe(3) (Cp* = C(5)Me(5); M = Ti, Zr), (CGC)MMe(2) (CGC = C(5)Me(4)SiMe(2)NBu(t)(); M = Ti, Zr), and Cp(2)ZrMe(2) with Ph(3)C(+)B(C(6)F(5))(4)(-) catalyze alkylation of aromatic molecules (benzene, toluene) with alpha-chloronorbornene at room temperature, to regioselectively afford the 1:1 addition products exo-1-chloro-2-arylnorbornane (aryl = C(6)H(5) (1a), C(6)H(4)CH(3) (1b)) in good yields. Analogous deuterium-labeled products exo-1-chloro-2-aryl-d(n)-norbornane-7-d(1) (aryl-d(n) = C(6)D(5) (1a-d(6)), C(6)D(4)CD(3) (1b-d(8))) are obtained via catalytic arylation of alpha-chloronorbornene in either benzene-d(6) or toluene-d(8). Isolated ion-pair complexes such as (CGC)ZrMe(toluene)(+)B(C(6)F(5))(4)(-) and Cp(2)ThMe(+)B(C(6)F(5))(4)(-) also catalyze the reaction of alpha-chloronorbornene in toluene-d(8) to give 1b-d(8) in good yields, respectively. Small quantities of the corresponding bis(1-chloronorbornyl)aromatics 2 are also obtained from preparative-scale reactions. These reactions exhibit turnover frequencies exceeding 120 h(-1) (for the Cp*TiMe(3)/Ph(3)C(+)B(C(6)F(5))(4)(-)-catalyzed system), and chlorine-free products are not observed. Compounds 1 and 2 were characterized by (1)H, (2)H, (13)C, and 2D NMR, GC-MS, and elemental analysis. The aryl group exo-stereochemistry in 1a and 1b is established using (1)H-(1)H COSY, (1)H-(13)C HMBC, and (1)H-(1)H NOESY NMR, and is further corroborated by X-ray analysis of the product 1,4-bis(exo-1-chloro-2-norbornyl)benzene (2a). Control experiments and reactivity studies on each component step suggest a mechanism involving participitation of the metal electrophiles in the catalytic cycle. 相似文献
92.
The vibrational frequencies and corresponding normal mode assignments of urazole are examined theoretically using the Gaussian98 set of quantum chemistry codes. All normal modes were successfully assigned to one of eight types of motion (N--H stretch, C=O stretch, C--N stretch, N--N stretch, N--H bend, C=O bend, N--C--N bend, ring torsion) utilizing the C2 symmetry of the molecule. The molecular orbitals of urazole are examined. The simultaneous double inversion of the amine groups in urazole is also examined. 相似文献
93.
Jensen JO 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2004,60(11):2561-2566
The normal mode frequencies and corresponding vibrational assignments of Triethynylmethylstannane (SnCH(3)(CCH)(3)) are examined theoretically using the Gaussian 98 set of quantum chemistry codes. Each of the vibrational modes was assigned to one of nine types of motion predicted by a group theoretical analysis (Sn-C stretch, C[triple bond]C stretch, C-H stretch, C[triple bond]C-H bend, Sn-C[triple bond]C bend, C-Sn-C bend, H-C-H bend, CH(3) wag, and CH(3) twist) utilizing the C(3v) symmetry of the molecule. A set of uniform scaling factors was derived for each type of motion. Predicted infrared and Raman intensities are reported. 相似文献
94.
95.
96.
97.
98.
99.
100.