全文获取类型
收费全文 | 554篇 |
免费 | 44篇 |
国内免费 | 5篇 |
专业分类
化学 | 416篇 |
晶体学 | 3篇 |
力学 | 15篇 |
数学 | 62篇 |
物理学 | 107篇 |
出版年
2023年 | 3篇 |
2022年 | 6篇 |
2021年 | 11篇 |
2020年 | 13篇 |
2019年 | 13篇 |
2018年 | 15篇 |
2017年 | 11篇 |
2016年 | 35篇 |
2015年 | 21篇 |
2014年 | 24篇 |
2013年 | 29篇 |
2012年 | 41篇 |
2011年 | 56篇 |
2010年 | 21篇 |
2009年 | 24篇 |
2008年 | 30篇 |
2007年 | 28篇 |
2006年 | 37篇 |
2005年 | 28篇 |
2004年 | 21篇 |
2003年 | 19篇 |
2002年 | 11篇 |
2001年 | 14篇 |
2000年 | 7篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1996年 | 4篇 |
1995年 | 7篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1979年 | 2篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1975年 | 3篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1957年 | 2篇 |
1955年 | 1篇 |
1954年 | 1篇 |
1941年 | 2篇 |
排序方式: 共有603条查询结果,搜索用时 420 毫秒
41.
42.
43.
Over the past 50 years, pentafluorobenzaldehyde has received much attention due to its unique chemical and physical properties as well as its real or potential applications in chemistry of porphyrines, additives, drug delivery and in analytical chemistry. Pentafluorobenzaldehyde is multifunctional aromatic compound containing five atoms of fluorine and one aldehydic function. That is why it can provide nucleophilic substitutions of all or some atoms of fluorine, nucleophilic additions of aldehydic function, “haloform reaction” and some cyclization reactions. This year, it is being the 50th year, since the first synthesis of this compound was published. 相似文献
44.
Within a lattice model describing a binary mixture with fixed concentrations of the species we discuss the relationship between the surface tension of the mixture and the concentrations. 相似文献
45.
46.
W. W. Shdanow H. Hollings M. S. Gerschenowitsch G. F. Daletzki N. S. Kotelkow P. W. Putschkow R. M. Lilly N. P. Chesnutt Sol Smith A. M. Crowell und H. P. Guest 《Fresenius' Journal of Analytical Chemistry》1941,121(7-8):292-294
Ohne Zusammenfassung 相似文献
47.
Hyung Suk Chung Sung-Woo Kim Han Sol Lee Md. Musfiqur Rahman Md. Humayun Kabir 《International journal of environmental analytical chemistry》2017,97(2):99-111
The present study was carried out to develop an analytical method for simultaneously detecting and quantifying sulfoxaflor and its metabolites (X11721061, X11719474) in brown rice and rice straw using liquid chromatography–tandem mass spectrometry. The parent compound and its metabolites were extracted and purified using original ‘QuEChERS’ method with modification. The matrix-matched calibration curve of sulfoxaflor and its metabolites in both matrices achieved good linearity with determination coefficients (R2) ≥0.9944. The overall recoveries of sulfoxaflor at two fortification levels (rice: 0.2 and 1.0 mg/kg; rice straw: 0.4 and 2.0 mg/kg) ranged from 97.37% to 107.71% with relative standard deviations (RSDs) <5%. On the other hand, the recoveries of both metabolites (X11721061 and X11719474) at 0.1 and 0.5 mg/kg (rice) and 0.2 and 1.0 mg/kg (rice straw) were satisfactory with values ranging from 83.70 % to 112.60% with RSDs <8%. During storage at ?20°C, the analyte and its metabolites were stable for up to 87 days. The limits of quantification of 0.02 mg/kg were lower than the maximum residue limit (0.2 mg/kg) set by the Korean Ministry of Food and Drug Safety for brown rice. The method was successfully applied to paddy field treated with different programme schedules and a preharvest interval of 7 days was proposed based upon the current study. In sum, the developed method is accurate and reproducible for ensuring the reliable determination of sulfoxaflor (and its metabolites) in harvested rice grain and straw samples from the field. The residual level of parent compound does not seem to pose any hazardous effect and treated rice could be safely used for consumption. 相似文献
48.
Peter Ferenc Peter Solár Ján Kleban Jaromír Mikeš Peter Fedoročko 《Journal of photochemistry and photobiology. B, Biology》2010,98(1):25-34
Presented experiment considers combination of genistein and photodynamic therapy with hypericin with a view to achieve higher therapeutic outcome in human breast adenocarcinoma cell lines MCF-7 and MDA-MB-231, both identified in our conditions as photodynamic therapy resistant. Since genistein is known to suppress Bcl-2 expression, we predicted that photodynamic therapy with hypericin might benefit from mutual therapeutic combination. In line with our expectations, combined treatment led to down-regulation of Bcl-2 and up-regulation of Bax in both cell lines as well as to suppression of Akt and Erk1/2 phosphorylation induced by photoactivated hypericin in MCF-7 cells. Although Akt and Erk1/2 phosphorylation was not stimulated by photodynamic therapy with hypericin in MDA-MB-231 cells, it was effectively suppressed in combination. Variations in cell death signaling favoring apoptosis were indeed accompanied by cell cycle arrest in G2/M-phase, activation of caspase-7, PARP cleavage and increased occurrence of cells with apoptotic morphology of nucleus. All these events corresponded with suppression of proliferation and significantly lowered clonogenic ability of treated cells. In conclusion, our results indicate that pre-treatment with tyrosine kinase inhibitor genistein may significantly improve the effectiveness of photodynamic therapy with hypericin in MCF-7 and MDA-MB-231 breast cancer cells. 相似文献
49.
Casitas A Poater A Solà M Stahl SS Costas M Ribas X 《Dalton transactions (Cambridge, England : 2003)》2010,39(43):10458-10463
Well-defined aryl-Cu(III)-halide species undergo reductive elimination upon acid addition resulting in the formation of strong aryl-halide bonds. The computationally studied mechanism points towards ligand protonation as the rate-determining step, in agreement with previous experimental data. 相似文献
50.
Enikö Kádár David M. Lowe Montserrat Solé Andrew S. Fisher Awadhesh N. Jha James W. Readman Thomas H. Hutchinson 《Analytical and bioanalytical chemistry》2010,396(2):657-666
Nano-Fe particle uptake was experimentally examined in vitro using excised gills and blood cells of the edible blue mussel
Mytilus sp. Whole gills were exposed to both Fe2O3 nanoparticles and a solution of the hydrated FeCl3 salt, for up to 12 h, and blood cells for 30 min. Equimolar Fe+3 in the nano- and the soluble form was estimated under the assumption of dense spherical particles accommodating the same
number of Fe+3 as in the dissolved salt solution, namely: 1,000 μg L−1 Fe2O3 equivalent to 100 μg L−1 FeCl3·6H2O. Putative toxic impact of nano-Fe in gill epithelia and blood cells was assessed by an array of techniques including light-
and electron microscopy, biomarkers for oxidative stress (lipid peroxidation levels), neurotoxic effects (acetylcholinesterase
activity) and cytotoxicity (neutral red retention). Total and filtered fractions (20 and 200 nm, respectively) of Fe were
analysed by ICP-OES. Our results provide evidence for the following: (1) much of both the soluble (95%) and the nano-Fe (90%)
were removed from the water column within 12 h; (2) dissolved- and nano-Fe seemed to follow different routes of uptake within
the gill epithelium; (3) both nano-Fe and soluble FeCl3 caused similar impairment of lysosomal stability in circulating blood cells; (4) lipid peroxidation in gills exposed to the
two distinct forms of Fe was increased, while acetylcholinesterase activity was unaffected. In these short-term in vitro studies,
there appears to be little difference in toxic response between exposure to the Fe salt and the nano-Fe indicating that, in
this case, the nanoparticles do not invoke special properties affecting biological function in gills. However, with the use
of nano-Fe as a food additive, clearly longer-term in vivo studies are warranted. 相似文献