全文获取类型
收费全文 | 8209篇 |
免费 | 426篇 |
国内免费 | 44篇 |
专业分类
化学 | 5726篇 |
晶体学 | 21篇 |
力学 | 204篇 |
数学 | 1465篇 |
物理学 | 1263篇 |
出版年
2023年 | 76篇 |
2022年 | 90篇 |
2021年 | 135篇 |
2020年 | 189篇 |
2019年 | 192篇 |
2018年 | 115篇 |
2017年 | 115篇 |
2016年 | 359篇 |
2015年 | 320篇 |
2014年 | 299篇 |
2013年 | 475篇 |
2012年 | 557篇 |
2011年 | 655篇 |
2010年 | 381篇 |
2009年 | 322篇 |
2008年 | 519篇 |
2007年 | 469篇 |
2006年 | 444篇 |
2005年 | 411篇 |
2004年 | 352篇 |
2003年 | 317篇 |
2002年 | 293篇 |
2001年 | 174篇 |
2000年 | 129篇 |
1999年 | 125篇 |
1998年 | 95篇 |
1997年 | 105篇 |
1996年 | 106篇 |
1995年 | 90篇 |
1994年 | 68篇 |
1993年 | 70篇 |
1992年 | 55篇 |
1991年 | 41篇 |
1990年 | 39篇 |
1989年 | 31篇 |
1988年 | 38篇 |
1987年 | 28篇 |
1986年 | 32篇 |
1985年 | 27篇 |
1984年 | 24篇 |
1983年 | 15篇 |
1982年 | 24篇 |
1981年 | 20篇 |
1980年 | 19篇 |
1979年 | 14篇 |
1978年 | 23篇 |
1977年 | 15篇 |
1976年 | 10篇 |
1975年 | 14篇 |
1974年 | 15篇 |
排序方式: 共有8679条查询结果,搜索用时 31 毫秒
61.
62.
H. M. Ortner H. H. Xu J. Dahmen K. Englert H. Opfermann W. Görtz 《Fresenius' Journal of Analytical Chemistry》1996,355(5-6):657-664
Surface characterization of new unused PTFE, PFA and PVDF labware has been carried out by light microscopy, scanning electron microscopy, profilometry and atomic force microscopy. It has been found that in spite of higher micro-roughness, PFA exhibits the lowest nano-roughness and hence seems best suited as vessel material for relatively mild pressureless chemical operations for sample preparation of ultrapure substances, as container material for storage of ultrapure liquids, and for transport of such liquids, e.g., from the producer in the chemical to the end user in the microelectronics industry. This suitability refers only to the surface quality of the investigated materials. PTFE-surfaces, due to the sintering process of production, exhibit the most unfavourable surface quality of the investigated fluorinated polymers. 相似文献
63.
64.
65.
Gáti T Simon A Tóth G Magiera D Moeller S Duddeck H 《Magnetic resonance in chemistry : MRC》2004,42(7):600-604
Adducts of four phosphine chalcogenides with the chiral dirhodium complex ([Rh-Rh]) were investigated by variable-temperature 1H and 31P NMR spectroscopy in order to compare their properties as axial ligands. Whereas the selenide (1) and the sulfide (2) are strong ligands with electrostatic attraction and, in addition, a significant orbital (HOMO-LUMO) interaction, the phosphine oxide compounds (P=O) bind primarily via electrostatic attraction and are relatively weak donors. Moreover, the overall bond strength in these adducts depends on steric congestion around the P=O group. 相似文献
66.
67.
68.
A liquid membrane electrode prepared with moclobemide-dipicrylamine ion-pair complex, dissolved in nitrobenzene as solvent, was studied for analytical performance. The linear response covers the range 10(-3)-10(-6) M moclobemide solution, with a slope of 50.7 mV decade(-1) (pH range 3.5-8). The detection limit is 3 x 10(-7) M. The electrode shows stability, good reproducibility and fast response. The selectivity of the electrode is good. There are two important interfering ions: mianserin and thiamine (Vitamin B(1)). The compression excipients (such as Mg(2+), starch, talcum powder) do not interfere. These characteristics of the electrode enabled it to be used for the determination of moclobemide in drugs and as an active substance, via indirect and direct potentiometric methods. Via an indirect potentiometric method moclobemide, as an active substance, can be determined with an average recovery of 99.96% and a relative standard deviation of 0.85%, and this method can also be used for its determination in drugs with a relative standard deviation of < 2%. The electrode is useful for the determination of the dissolution rate of moclobemide tablets. The physical processes are numerically simulated by typical equations. The apparent first-order rate constants for disintegration and dissolution were calculated. 相似文献
69.
70.
Stefan Berger 《Tetrahedron》1977,33(13):1587-1589
The pH dependence of the 13C chemical shifts of ascorbic acid has been measured and interpreted in terms of protonation sites. The transition of the dimer of dehydroascorbic acid into the hydrated monomer form is monitored by 13C spectroscopy. 相似文献