全文获取类型
收费全文 | 623篇 |
免费 | 35篇 |
专业分类
化学 | 535篇 |
晶体学 | 2篇 |
力学 | 13篇 |
数学 | 55篇 |
物理学 | 53篇 |
出版年
2023年 | 7篇 |
2022年 | 12篇 |
2021年 | 26篇 |
2020年 | 22篇 |
2019年 | 13篇 |
2018年 | 19篇 |
2017年 | 3篇 |
2016年 | 27篇 |
2015年 | 34篇 |
2014年 | 19篇 |
2013年 | 37篇 |
2012年 | 31篇 |
2011年 | 53篇 |
2010年 | 30篇 |
2009年 | 33篇 |
2008年 | 45篇 |
2007年 | 38篇 |
2006年 | 27篇 |
2005年 | 36篇 |
2004年 | 19篇 |
2003年 | 25篇 |
2002年 | 23篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 7篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1960年 | 1篇 |
1928年 | 4篇 |
1924年 | 2篇 |
排序方式: 共有658条查询结果,搜索用时 312 毫秒
71.
Apetrei CL Tuchilus C Aprotosoaie AC Oprea A Malterud KE Miron A 《Molecules (Basel, Switzerland)》2011,16(9):7773-7788
The chemical constituents and biological activity of Pinus cembra L. (Pinaceae), native to the Central European Alps and the Carpathian Mountains, are not well known. The aim of the present work was to examine the phenolic content, antioxidant and antimicrobial effects of hydromethanolic extracts of Pinus cembra L. bark and needles. Bark extract had higher concentrations of total phenolics (299.3 vs. 78.22 mg gallic acid equivalents/g extract), flavonoids (125.3 vs. 19.84 mg catechin equivalents/g extract) and proanthocyanidins (74.3 vs. 12.7 mg cyanidin equivalents/g extract) than needle extract and was more active as a free radical scavenger, reducing agent and antimicrobial agent. The EC?? values in the 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2'-azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid) diammonium salt (ABTS) and reducing power assays were 71.1, 6.3 and 26 mg/mL for bark extract and 186.1, 24 and 104 mg/mL for needle extract, respectively. In addition, needle extract showed ferrous ions chelating effects (EC?? = 1,755 μg/mL). The antimicrobial effects against Staphylococcus aureus, Sarcina lutea, Bacillus cereus, Escherichia coli, Pseudomonas aeruginosa and Candida albicans were assessed by the agar diffusion method. Both extracts (4 mg/well) were active against all the microorganisms tested; bark extract showed higher inhibition on all strains. These results indicate that Pinus cembra L. bark and needles are good sources of phytochemicals with antioxidant and antimicrobial activities. 相似文献
72.
Pecchia P Cammareri M Malafronte N Consiglio MF Gualtieri MJ Conicella C 《Natural product communications》2011,6(11):1665-1669
Several different classes of secondary metabolites, including flavonoids, triterpenoid saponins and quinic acid derivatives, are found in Aster spp. (Fam. Asteraceae). Several Aster compounds revealed biological as well as pharmacological activities. In this work, a phytochemical investigation of A. caucasicus evidenced the presence of quinic acid derivatives, as well as the absence of triterpene saponins. To combine in one species the production of different phytochemicals, including triterpenes, an Agrobacterium-mediated transformation of A. caucasicus was set up to introduce A. sedifolius beta-amyrin synthase (AsOXA1)-encoding gene under the control of the constitutive promoter CaMV35S. The quali-quantitative analysis of transgenic calli with ectopic expression of AsOXA1 showed, in one sample, a negligible amount of triterpene saponins combined with higher amount of quinic acid derivatives as compared with the wild type callus. 相似文献
73.
Geometriae Dedicata - We show that every plumbing of disc bundles over surfaces whose genera satisfy a simple inequality may be embedded as a convex submanifold in some closed hyperbolic... 相似文献
74.
Medium-ring olefinic ketone and lactone enolsilanes were subjected to palladium(II)-mediated cycloalkenylation conditions. Diverse bicyclic ring products were obtained in moderate to good yields. The effect of olefin geometry and ring size is discussed. 相似文献
75.
76.
Maribel Navarro Clara Hernández Flor Vásquez Helen Goitia Luis E. Ojeda Mait Velásquez Germán Fraile 《Transition Metal Chemistry》2008,33(7):893-898
Antimalarial drugs such as chloroquine are beneficial agents in systemic lupus and rheumatoid arthritis. In this work, two
new chloroquine diphosphate (CQDP) complexes containing Zn(II) and Au(III) of formula Zn(CQDP)(NO3)2 (1) and Au(CQDP)Cl3 (2), respectively, were synthesized and characterized by physico-chemical and spectroscopic methods. To examine their possible
anti-inflammatory properties, the new derivatives were tested in the range from 1 to 100 μM on the respiratory burst of isolated
human neutrophils (PMNs) as well as in whole blood. In isolated PMNs, complex 1 inhibited the isoluminol-enhanced chemiluminescence (IL-CL) only at the highest concentration tested, whereas in the whole
blood assay, 10 μM of this complex was sufficient to significantly inhibit the luminol-enhanced chemiluminescence (L-CL).
On the contrary, complex 2 dose-dependently inhibited the IL-CL but affected the L-CL only at 100 μM. In conclusion, both complexes are more active
than CQDP and may be useful for future treatment of diseases resulting from exacerbated neutrophil functions. 相似文献
77.
78.
Agustin Campos Rafael Gavara Roberto Tejero Clara Gomez Bernardo Celda 《Journal of Polymer Science.Polymer Physics》1989,27(8):1559-1597
The Flory–Huggins theory as modified by Pouchlý has been applied to calculate preferential (λ) and total (Y) sorption coefficients for a ternary polymer system. The ternary interaction function (?1?2?3GT(u1, ?3)) is described as the product of three independent binary functions. This expression allows prediction of λ and Y from binary interaction parameters χ, χ, g, g, and g12(?10). Three ternary polymer systems are used to check the validity of the expression. Moreover for polymer systems in which the parameters g and/or g are unknown, a procedure to evaluate them has been developed and verified on systems for which sufficient experimental information is available. 相似文献
79.
80.
The effect of a parallel magnetic field on the 10-mHz surface resistance of gallium single crystals is reported. We suggest that the observed structure can be interpreted in terms of an angular dependence of the probability of specular reflection of the electron at the crystal surface. This model allows a quantitative determination from the data of the temperature-dependent electron mean free path for electron wave vectors with a narrow range that is determined by the magnetic field and crystal orientation. 相似文献