全文获取类型
收费全文 | 776篇 |
免费 | 17篇 |
国内免费 | 4篇 |
专业分类
化学 | 516篇 |
晶体学 | 3篇 |
力学 | 6篇 |
数学 | 170篇 |
物理学 | 102篇 |
出版年
2023年 | 4篇 |
2020年 | 9篇 |
2019年 | 5篇 |
2018年 | 8篇 |
2017年 | 10篇 |
2016年 | 7篇 |
2015年 | 18篇 |
2014年 | 10篇 |
2013年 | 41篇 |
2012年 | 45篇 |
2011年 | 77篇 |
2010年 | 26篇 |
2009年 | 27篇 |
2008年 | 54篇 |
2007年 | 45篇 |
2006年 | 39篇 |
2005年 | 42篇 |
2004年 | 24篇 |
2003年 | 21篇 |
2002年 | 26篇 |
2001年 | 12篇 |
2000年 | 18篇 |
1999年 | 10篇 |
1998年 | 15篇 |
1997年 | 9篇 |
1996年 | 6篇 |
1995年 | 17篇 |
1994年 | 18篇 |
1993年 | 10篇 |
1992年 | 12篇 |
1991年 | 11篇 |
1990年 | 13篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 14篇 |
1984年 | 11篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1978年 | 5篇 |
1976年 | 7篇 |
1975年 | 5篇 |
1974年 | 3篇 |
1973年 | 5篇 |
1969年 | 2篇 |
1942年 | 3篇 |
1929年 | 2篇 |
1863年 | 2篇 |
排序方式: 共有797条查询结果,搜索用时 390 毫秒
61.
62.
63.
Ugo Morin 《Annali di Matematica Pura ed Applicata》1942,21(1):113-155
Sunto Delle varietà algebriche a3 dimensioni (non coni o luoghi di ∞1 piani) a curve sezioni di genere π=3 si danno i tipi proiettivamente distinti. Questi, ad eccezione dellaV
3
(4)
dell'S
4, sono razionali. I loro sistemi rappresentativi forniscono tutti i sistemi lineari di superficie dell'S
3, cremonianamente distinti, a curva caratteristica di genere3, semplici e di grado >4. 相似文献
64.
Jane S. Murray Pat Lane Anian Nieder Thomas M. Klapötke Peter Politzer 《Theoretical chemistry accounts》2010,127(4):345-354
Si-pentaerythritol tetranitrate (PETN), Si[CH2ONO2]4, is a silicon analog of the widely used explosive PETN, C[CH2ONO2]4. Si-PETN is extremely sensitive to impact, much more so than PETN. This was attributed by Liu et al. to Si-PETN having a
much lower activation barrier to decomposition, via a facile rearrangement that is not as readily available to PETN, and which
releases considerable energy that can promote further steps. We have investigated computationally why the barrier to the rearrangement
is so much lower for Si-PETN than for PETN, using 5, (H3C)3C–CH2ONO2, and 6, (H3C)3Si–CH2ONO2, as models for PETN and Si-PETN. Reaction force analysis shows that most of the difference between the rearrangement barriers
for 5 and 6 comes about in the initial (reactant) stages of the processes, in which 6 benefits from a 1,3 electrostatic interaction involving a positive σ–hole on the silicon and the negative linking oxygen.
The analogous interaction is weaker in 5, since the central carbon does not have positive σ–holes; furthermore, this carbon is less able than silicon to temporarily
expand its coordination sphere. A similar explanation involving a positive silicon σ–hole and a linking oxygen is proposed
for Si-PETN. The greater exothermicity of the rearrangement of 6 (and also Si-PETN) can be rationalized, following Liu et al., in terms of the formation of the strong Si–O bond. 相似文献
65.
66.
Determination of organometallic compounds in surface water and sediment samples with SPME-CGC-ICPMS 总被引:5,自引:0,他引:5
Organometal compounds of tin, mercury and lead were simultaneously determined in environmental water and sediment samples by CGC-ICPMS. Instead of classical liquid/liquid extractions, solid phase microextraction was used as sampling technique. In this method, the organometallic compounds arein situ derivatised in the aqueous phase and simultaneously extracted onto a polydimethylsiloxane fiber, so that organic solvents are no longer necessary. The sorbed organometals are subsequently released from the fiber in the GC injection liner by thermal desorption. By sampling from the headspace, only the species of interest are sampled and no interfering matrix components are coextracted. With this new method, derivatisation, extraction, preconcentration and injection into the GC takes only 10 min with a minimum of handling steps. Owing to the very low detection limits (0.13–3.7 ng/1 as metal) only small sample amounts (25 ml of water, 0.5 g of sediment) are needed for one analysis. Finally, SPME is an inexpensive sampling technique that can be used with standard split/splitless injection systems. 相似文献
67.
Ugo Morin 《Annali di Matematica Pura ed Applicata》1940,19(1):257-288
Sunto. Si assegnano i tipi cremonianamente distinti di sistemi lineari completi, semplici, irriducibili di superficie algebriche
dello spazioS
3 a curva-caratteristica (variabile) di genereπ=2. Questi si distribuiscono in25 famiglie, delle quali si danno la dimensione, l'ordine minimo, ecc. e la rappresentazione analitica. 相似文献
68.
69.
70.
Abderrahim A?t Adoubel Christophe J. Morin Nadine Mofaddel Georges Dupas Paul-Louis Desbène 《Analytical and bioanalytical chemistry》2009,394(2):597-608
Enantiomer separations of underivatised amino acids were carried out by using ligand exchange capillary electrophoresis (LECE).
Chiral discrimination is based on the formation of ternary complexes between copper(II), a chiral selector (L-proline or trans-4-hydroxy-L-proline) and an amino acid. All amino acids containing aromatic moieties or not were detected at 214 nm because
of their interactions with copper(II). In order to reduce copper(II) adsorption onto capillary walls, we used hexadimethrine
bromide to reverse the electroosmotic flow. Using this original strategy, the studied enantiomers migrated in the opposite
direction of the anodic electroosmosis. After optimising the analytical conditions taking into account the chiral resolution
and the detection sensitivity, we performed very satisfactory enantioseparations not only of aromatic amino acids (tryptophan,
tyrosine, phenylalanine and histidine) but also of aliphatic amino acids (threonine, serine, isoleucine and valine). These
enantioseparations were performed in a short analysis time at 35 °C. In order to rationalise the obtained results, we evaluated
the complexation constants corresponding to the formed ternary complexes by capillary electrophoresis and we used molecular
mechanics modelling. 相似文献