全文获取类型
收费全文 | 1192篇 |
免费 | 63篇 |
国内免费 | 11篇 |
专业分类
化学 | 772篇 |
晶体学 | 31篇 |
力学 | 65篇 |
综合类 | 2篇 |
数学 | 174篇 |
物理学 | 222篇 |
出版年
2023年 | 8篇 |
2022年 | 19篇 |
2021年 | 44篇 |
2020年 | 43篇 |
2019年 | 35篇 |
2018年 | 44篇 |
2017年 | 30篇 |
2016年 | 61篇 |
2015年 | 44篇 |
2014年 | 60篇 |
2013年 | 117篇 |
2012年 | 94篇 |
2011年 | 98篇 |
2010年 | 60篇 |
2009年 | 54篇 |
2008年 | 53篇 |
2007年 | 71篇 |
2006年 | 55篇 |
2005年 | 43篇 |
2004年 | 25篇 |
2003年 | 26篇 |
2002年 | 26篇 |
2001年 | 10篇 |
2000年 | 2篇 |
1999年 | 10篇 |
1998年 | 9篇 |
1997年 | 5篇 |
1996年 | 13篇 |
1995年 | 9篇 |
1994年 | 7篇 |
1993年 | 13篇 |
1992年 | 7篇 |
1990年 | 3篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 9篇 |
1982年 | 10篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1975年 | 2篇 |
1974年 | 4篇 |
1973年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1964年 | 2篇 |
1962年 | 1篇 |
排序方式: 共有1266条查询结果,搜索用时 15 毫秒
1.
Background
The aim of the present study was to characterize the activation profiles of 15 opioid ligands in transfected human embryonic kidney cells expressing only δ opioid receptors. Activation profiles of most of these ligands at δ opioid receptors had not been previously characterized in vitro. Receptor activation was assessed by measuring the inhibition of forskolin-stimulated cAMP production. 相似文献2.
Danny E. Akin W. Herbert Morrison III Luanne L. Rigsby Franklin E. Barton II David S. Himmelsbach Kevin B. Hicks 《Applied biochemistry and biotechnology》2006,129(1-3):104-116
Information is presented on structure, composition, and response to enzymes of corn stover related to barriers for bioconversion
to ethanol. Aromatic compounds occurred in most tissue cell walls. Ferulic acid esterase treatment before cellulase treatment
significantly improved dry weight loss and release of phenolic acids and sugars in most fractions over cellulase alone. Leaf
fractions were considerably higher in dry weight loss and released sugars with esterase treatment, but stem pith cells gave
up the most phenolic acids. Results help identify plant fractions more appropriate for coproducts and bioconversion and those
more suitable as residues for soil erosion control. 相似文献
3.
Efficient synthesis of ferrocenylenones using a Friedel-Crafts acylation reaction is described. Acryloyl, methacryloyl, crotonoyl, cinnamoyl, and β-methylcrotonoyl chlorides react with ferrocene in the presence of a Lewis acid (EtAlCl2 or EtAlCl2-Me3Al) to give the corresponding ferrocenylenones (acryloyl, methacryloyl, crotonoyl, cinnamoyl, and methylcrotonoylferrocenes) in good isolated yields. Besides ferrocenylenones, chloroactylferrocene is also synthesised by this method. 相似文献
4.
S. Akin S. Isikli F. Korkusuz M. Ungan A. Senkoylu 《Journal of Radioanalytical and Nuclear Chemistry》2004,259(2):361-364
The aim of this study was to investigate the relationship between BMD and age at lumbar spine and proximal femur in Turkish
males. Two hundred ninety healthy males (aged 20-59 years) were investigated. BMD of the lumbar spine had its peak at ages
30-39, however, the peak for the proximal femur was between the ages of 20 and 29. There was a significant decrease in BMD
at proximal femur after these peak values with increasing age. In conclusion, there was a significant correlation between
age and the proximal femoral BMD in males and age has a strong predictive power on proximal femur BMD score.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
5.
We show that a theorem of Shchepin and Repovš concerning the smoothness of compacta follows from the theory of semicontinuous relations. 相似文献
6.
A. Konjhodzic A. Adamczyk F. Vagizov Z. Hasan E E. Alp W. Sturhahn Jiyong Zhao J J. Carroll 《Hyperfine Interactions》2006,170(1-3):83-89
With the decrease in size of devices, rapid characterization of nano-devices is an inevitable necessity. It is shown that Mössbauer spectroscopy using synchrotron radiation from the advanced photon source provides such a tool of investigation. Results are presented and compared for conventional Mössbauer and Nuclear Forward Scattering for 151Eu-doped magnesium sulfide as an example, especially at low concentrations. 相似文献
7.
Sk. Asrof Ali Yunusa Umar B. F. Abu‐Sharkh Hasan A. Al‐Muallem 《Journal of polymer science. Part A, Polymer chemistry》2006,44(19):5480-5494
The cycloterpolymerizations of single‐, twin‐, and triple‐tailed hydrophobes with hydrophilic monomer N,N‐diallyl‐N‐carboethoxymethylammonium chloride and sulfur dioxide afforded a series of cationic polyelectrolytes (CPEs) in excellent yields. These CPEs, upon the acidic hydrolysis of the pendent ester groups, gave the corresponding pH‐responsive cationic acid salts, which, upon a treatment with sodium hydroxide, were converted to polybetaines (PBs), anionic polyelectrolytes (APEs), and PB/APE polymers containing various proportions of zwitterionic (PB) and anionic fractions (APE) in the polymer chain. At a shear rate of 0.36 s−1 at 30 °C, salt‐free water solutions of the CPEs (2 g/dL) containing 8, 4, and 2.67 mol % of the single‐, twin‐, and triple‐tailed hydrophobes (all having 8 mol % octyloxy tails) had apparent viscosity values of 70, 2800, and 396,000 cps, respectively. The PB/APE polymer with a ratio of 33:67 for the zwitterionic and anionic fractions in the polymer chain gave the highest viscosity value. The superior viscosity behavior of the polymers containing the triple‐tailed hydrophobe was attributed to the blocky nature of the comonomer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5480–5494, 2006 相似文献
8.
This paper proves that any set of n points in the plane contains two points such that any circle through those two points encloses at least
points of the set. The main ingredients used in the proof of this result are edge counting formulas for k-order Voronoi diagrams and a lower bound on the minimum number of semispaces of size at most k.Work on this paper by the first author has been supported by Amoco Fnd. Fac. Dev. Comput. Sci. 1-6-44862 and by the National Science Foundation under Grant CCR-8714565, by the second author has been partially supported by the Digital Equipment Corporation, by the fourth author has been partially supported by the Office of Naval Research under Grant N00014-86K-0416. 相似文献
9.
10.
Viktor Kettmann Jan Lokaj Viktor Milata Jozef Salo Mohamed Mahmoud Mohamed Hasan 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(6):o365-o366
The title compound, C11H10N3+·Cl?·H2O, belongs to the N1‐methyl‐substituted imidazo[4,5‐f]quinoline family, in which the heterocyclic ring is protonated at the pyridine rather than at the imidazole N atom. The molecule as a whole is almost exactly planar. The molecular structure has been compared with that of the 2‐amino analogue described in the literature, and it was found that the extra amino group of the latter is involved in conjugation with the adjacent double bond, i.e. the conjugation does not extend over the entire heterocyclic system. The cation of the title compound forms a strong hydrogen bond with the Cl? anion and the anions are interconnected by the water solvent molecule. 相似文献