全文获取类型
收费全文 | 1044篇 |
免费 | 46篇 |
国内免费 | 4篇 |
专业分类
化学 | 779篇 |
晶体学 | 2篇 |
力学 | 28篇 |
数学 | 129篇 |
物理学 | 156篇 |
出版年
2023年 | 3篇 |
2022年 | 10篇 |
2021年 | 9篇 |
2020年 | 19篇 |
2019年 | 15篇 |
2018年 | 10篇 |
2017年 | 17篇 |
2016年 | 31篇 |
2015年 | 24篇 |
2014年 | 30篇 |
2013年 | 44篇 |
2012年 | 77篇 |
2011年 | 91篇 |
2010年 | 43篇 |
2009年 | 27篇 |
2008年 | 69篇 |
2007年 | 60篇 |
2006年 | 43篇 |
2005年 | 43篇 |
2004年 | 44篇 |
2003年 | 41篇 |
2002年 | 32篇 |
2001年 | 12篇 |
2000年 | 16篇 |
1999年 | 13篇 |
1998年 | 17篇 |
1997年 | 12篇 |
1996年 | 17篇 |
1995年 | 20篇 |
1994年 | 11篇 |
1993年 | 13篇 |
1992年 | 11篇 |
1991年 | 12篇 |
1990年 | 15篇 |
1989年 | 16篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1985年 | 3篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 8篇 |
1976年 | 11篇 |
1975年 | 10篇 |
1974年 | 7篇 |
1973年 | 6篇 |
排序方式: 共有1094条查询结果,搜索用时 156 毫秒
91.
Replacing the backbone amide function by a heterocyclic bioisostere, [3+2] azide-alkyne cycloaddition has been applied for the construction of biologically relevant peptidomimetics. Starting from aminoalkynoates, triazole formation was accomplished by addition of hydrazoic acid. NMR studies displayed that the newly developed 4,5-triazolopeptides, which incorporate a biomimetic triazole NH-function as polar constraint element, showed a substantially higher tendency to form a cis-prolyl-geometry than a comparable native peptide sequence. 相似文献
92.
Regioselective halogen/metal exchange reactions using isopropylmagnesium chloride were studied on 3-substituted 1,2,5-tribromoarenes. Seven examples are given. 相似文献
93.
94.
95.
96.
Polymeric melaminium sulfate [(LH2)2(SO4)2]n has been synthesized by reaction of melamine L with sulfuric acid in aqueous solution. The compound was characterized by elemental analysis, 1H NMR, ESI MS and a single crystal X‐ray diffraction analysis. The architecture of the assembly formed is based on hydrogen bonded dimers of diprotonated melaminium cations (LH2)2+ which are linked by a hydrogen bonded network with sulfate ions forming 2D sheets. A 3D polymeric structure results from the presence of mutual hydrogen bonds between sulfate ions and melaminium cations in different sheets. Significant π‐π stacking is also present between the aromatic cations in this supramolecular arrangement. 相似文献
97.
98.
99.
100.
Sreenivasan Ramaswami Holger Gulyas Joachim Behrendt Ralf Otterpohl 《International journal of environmental analytical chemistry》2017,97(1):56-70
The presence of chloride ions in wastewaters in concentrations above 50 mg/L poses interference in several methods used for the measurement of nitrate-nitrogen. The aim of this study was to characterise the reliability and costs of some commonly available methods for the analysis of nitrate concentration in landfill leachate which contains high chloride levels. To investigate the effect of chloride interference, several widely used methods [ion chromatography (IC), continuous flow analysis (CFA), the German standard method (DIN), cuvette test (CUV), standard addition method (SAM) and reflectometric test (REF)] were used to measure the nitrate concentration in synthetic solutions containing varying concentrations of chloride and nitrate-nitrogen. Nitrate recoveries of the various methods were found to decrease in the following rank order: CUV (>95%) > IC (>90%) > CFA (89%) > DIN (88%) > REF (70%) > SAM (<80%). In the second part of the study, the same methods were used to measure nitrate concentrations in samples of biologically nitrified landfill leachate with and without chloride elimination. For leachate samples without chloride elimination, CUV results were well correlated (linear regression) with IC results (slope = 1.02/R2 = 0.99) but to lesser extents with results obtained by CFA (0.91/0.86), DIN (0.89/0.97) and REF (0.86/0.77), and not correlated with SAM (0.74/–1.3). The incurred measurement costs per sample (in Euros) for the methods were as follows: CFA (<0.1) < DIN (0.6) < REF (0.7) < SAM (3) < CUV (3.8) < IC (15). Cuvette tests are recommended as the method of choice due to their accuracy and lower cost than IC. 相似文献