全文获取类型
收费全文 | 628篇 |
免费 | 5篇 |
国内免费 | 3篇 |
专业分类
化学 | 436篇 |
晶体学 | 6篇 |
力学 | 19篇 |
数学 | 57篇 |
物理学 | 118篇 |
出版年
2016年 | 6篇 |
2015年 | 7篇 |
2014年 | 6篇 |
2013年 | 12篇 |
2012年 | 15篇 |
2011年 | 16篇 |
2010年 | 6篇 |
2009年 | 7篇 |
2008年 | 12篇 |
2007年 | 17篇 |
2006年 | 20篇 |
2005年 | 15篇 |
2004年 | 16篇 |
2003年 | 18篇 |
2002年 | 15篇 |
2001年 | 15篇 |
2000年 | 20篇 |
1999年 | 11篇 |
1998年 | 7篇 |
1997年 | 15篇 |
1996年 | 16篇 |
1995年 | 7篇 |
1994年 | 6篇 |
1993年 | 15篇 |
1992年 | 5篇 |
1991年 | 10篇 |
1990年 | 7篇 |
1989年 | 5篇 |
1988年 | 9篇 |
1987年 | 8篇 |
1986年 | 14篇 |
1985年 | 12篇 |
1984年 | 13篇 |
1983年 | 6篇 |
1982年 | 12篇 |
1981年 | 14篇 |
1980年 | 18篇 |
1979年 | 15篇 |
1978年 | 16篇 |
1977年 | 12篇 |
1976年 | 10篇 |
1975年 | 16篇 |
1974年 | 22篇 |
1973年 | 18篇 |
1972年 | 6篇 |
1971年 | 5篇 |
1930年 | 5篇 |
1928年 | 4篇 |
1925年 | 6篇 |
1924年 | 7篇 |
排序方式: 共有636条查询结果,搜索用时 15 毫秒
1.
2.
Ksenia Pumpor Elisabeth Windeisen Klaus Burger 《Journal of heterocyclic chemistry》2003,40(3):435-442
The synthesis of heterocyclic α‐mercapto acids starting from (RS)‐thiomalic acid using hexafluoroacetone as protecting and activating agent is described. The new compounds are useful building blocks for peptide and depsipeptide modification as well as for drug design. 相似文献
3.
The Fourier transform infrared spectrum of monoisotopic SC80Se has been investigated in the ν2, ν3, 2ν2, 2ν3, and ν1 regions with a resolution between 3 and 4 × 10−3 cm−1. In addition, the millimeter-wave spectrum has been studied in the region 150 to 320 GHz, and ground and ν2 = 1 excited state transitions have been measured. Ground state constants, B0 = 2043.285 4(4) MHz and D0 = 146.53(5) Hz, have been determined from a merge of millimeter-wave data and ground state combination differences spanning J values up to 77 and 143, respectively. The band centers ν2 = 352.341 075(9) cm−1 and ν3 = 505.480 06(5)cm−1 have been determined. The rovibrational parameters of numerous overtone and combination levels (ν1νl22ν3) = 0200, 0220, 0310, 0330, 0400, 0420, 0002, and 0003 have been obtained from polynomial analyses whose standard deviations ranged from 0.7 to 3.5 × 10−4 cm−1. The 1000 level, νeff 1435.840 cm−1, is anharmonically perturbed by the 0400 level, with an avoided crossing at J = 55, and W12222 = 0.963 09(1) cm−1. Transitions to both the upper (E+) and lower (E−) sublevels of the dyad were observed for 1 ≤ J′ ≤ 117 and 4 ≤ J′ ≤ 171, respectively, and the deperturbed wavenumbers ν1 = 1435.542 76(2) and 4ν02 = 1432.725 00(3) cm−1 were derived. Furthermore, a local crossing of the E− and 0420 levels involving l-type resonance was observed at J = 91. 相似文献
4.
5.
6.
7.
Conclusion We have considered allNN-partial waves simultaneously. The central part of the one gluon exchange is always repulsive, the tensor part can be neglected and the spin-orbit part is too weak for this choice of parameters. An additional colourless VMEP potential allows us to reproduce the experimental data. However, this potential cannot be related to a long range one-pion exchange potential.Presented at the symposium Mesons and Light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985. 相似文献
8.
A new, simple and rapid method of determination of ascorbic acid in amounts of 45-360 mug is described. The ascorbic acid is determined spectrophotometrically at 420 nm from the decrease in absorbance it causes in 1 x 10(-3)M hexacyanoferrate(III) in McIlvaine buffer at pH 5.2. The proposed method is suitable for the determination of ascorbic acid in pharmaceutical preparations and probably natural products. 相似文献
9.
High-performance liquid chromatography separated successively and quantitatively the food flavoring agents pyrimidines, purines and nucleosides, followed by nucleotides, then by polyphenols and finally by pyrazines with a reversed-phase octadecylsilica (μBondapak C18) column and various proportions of methanol, water, acetic acid and tetrabutylammonium phosphate (PIC A). The polar solvent (solvent A) was water—acetic acid—PIC A (97.5:1.5:1.0) and the relatively non-polar solvent (solvent B) was methanol—acetic acid—PIC A (97.5:1.5:1.0). Purines, pyrimidines, and nucleosides were eluted with solvent A. Nucleotides were eluted with a mixture of solvents A and B (9:1). Polyphenols were separated with a gradient starting at 10% solvent B and finishing at 25% solvent B, and finally the pyrazines were removed successively from the column with a gradient starting at 25% solvent B and finishing at 45% solvent B. The resolution and reproducibility were excellent for more than 50 compounds. By this method beverages could be analyzed directly, without solvent extraction, for flavoring compounds. 相似文献
10.
Alexander S GolubevNatalia N Sergeeva Lothar HennigAlexey F Kolomiets Klaus Burger 《Tetrahedron》2003,59(9):1389-1394
An efficient synthesis of trifluoromethyl-containing 2,3-allenols via carbonyl-yne reaction of 3,3,3-trifluoropyruvates with acetylenes is described. In the presence of MgBr2·Et2O the reaction of methyl trifluoropyruvate with hex-1-yne proceeds diastereoselectively. Trifluoromethyl-substituted 2,3-allenols can be stereoselectively transformed into trifluoromethyl-substituted 2,5-dihydrofurans on treatment with AgNO3. 相似文献