全文获取类型
收费全文 | 259篇 |
免费 | 13篇 |
国内免费 | 68篇 |
专业分类
化学 | 265篇 |
力学 | 11篇 |
综合类 | 4篇 |
数学 | 7篇 |
物理学 | 53篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 12篇 |
2021年 | 8篇 |
2020年 | 11篇 |
2019年 | 12篇 |
2018年 | 7篇 |
2017年 | 11篇 |
2016年 | 12篇 |
2015年 | 17篇 |
2014年 | 12篇 |
2013年 | 23篇 |
2012年 | 25篇 |
2011年 | 17篇 |
2010年 | 21篇 |
2009年 | 18篇 |
2008年 | 17篇 |
2007年 | 14篇 |
2006年 | 18篇 |
2005年 | 12篇 |
2004年 | 12篇 |
2003年 | 4篇 |
2002年 | 5篇 |
2001年 | 2篇 |
2000年 | 7篇 |
1999年 | 9篇 |
1998年 | 13篇 |
1997年 | 10篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1990年 | 3篇 |
1986年 | 1篇 |
排序方式: 共有340条查询结果,搜索用时 31 毫秒
201.
不同海藻吸附重金属镉离子的研究 总被引:14,自引:0,他引:14
本文采用6种分别属于褐藻门、绿藻门、红藻门的海边常见大型海藻对重金属镉离子进行吸附比较实验,镉离子浓度较低时,其吸附容量排列顺序为:海黍子>海带>孔石莼>节荚藻>刺松藻>内枝藻,海黍子的吸附量高达181mg/g,超出文献报道值,对3种吸附容量较高的海藻进行了较详细的研究,研究溶液的pH值、初始Cd^2 离子浓度等因素对Ca^2 的吸附特性的影响,对吸附机理进行了初步的探讨,发现镉离子与海藻中的钙离子发生离子交换作用,交换率占总吸附量的33-34%,得出了适宜的吸附等温线方程。 相似文献
202.
203.
Functionalization of platinum nanoparticles for electrochemical detection of nitrite 总被引:2,自引:0,他引:2
In this work, a novel electrochemical method for nitrite detection by using functionalized platinum nanoparticles (PtNPs)
is proposed. Firstly, a gold electrode is immobilized with 4-(2-aminoethyl)benzenamine. Then, PtNPs are modified with 5-[1,
2]dithiolan-3-yl-pentanoic acid [2-(naphthalene-1-ylamino)-ethyl]amide (DPAN). Consequently, in the presence of nitrite ions,
Griess reaction occurs between 4-(2-aminoethyl)benzenamine on the electrode and DPAN on PtNPs, thus PtNPs are localized onto
the electrode surface. So, PtNPs-electrocatalyzed reduction of H2O2 can be achieved to correlate the electrochemical signal with the concentration of nitrite ions. The linear concentration
range can be as wide as 10–1,000 μM, while the detection limit is as low as 5 μM. The proposed method has been also successfully
applied to the detection of nitrite with the local lake water, and the result is well consistent with that obtained by UV-visible
spectrophotometric method. So, this method has potential use for monitoring nitrite in drinking water supplies in the future. 相似文献
204.
The abundant fruit hulls of tea-oil tree (Camellia oleifera) are still underutilized and wastefully discaded to pollute the environment. In order to solve this problem and better utilize the fruit hulls of C. oleifera, a microwave-assisted extraction system was used to extract their polyphenols using water as the extraction solvent. A central composite design (CCD) was used to monitor the effects of three extraction processing parameters--liquid:solid ratio (mL/g), extraction time (min) and extraction temperature (°C)--on the polyphenol yield (%). The results showed that the optimal conditions were liquid:solid ratio of 15.33:1 (mL/g), extraction time of 35 min and extraction temperature of 76 °C. Validation tests indicated that under the optimized conditions the actual yield of polyphenols was 15.05 ± 0.04% with RSD = 0.21% (n = 5), which was in good agreement with the predicted yield. Phenolic compounds in the extracts were analysed by HPLC, and gallic acid was found to be the predominant constituent. The total flavonoid content in the extracts was determined and high total flavonoid content was revealed (140.06 mg/g dry material). 相似文献
205.
大豆中蛋白质含量的示波滴定 总被引:1,自引:1,他引:0
1 引言大豆中蛋白质含量的测定,国内外标准方法是采用凯达尔法,作者研究了用示波滴定的方法进行测定,样品用H_2SO_4-Na_2SO_4-CuSO_4消化处理,N以NH_4~+的形式存在于试液中.在pH5~6用四苯硼钠(Na-TPB)沉淀NH_4~+,过量的TPB,在pH10~12的NaOH-NaAc碱性底液中有明显的示波图,用四乙基氯化铵标准溶液反滴定至TPB示波图下切口突然消失为终点,据此计算出N含量,再换算为蛋白质的含量.2 实验部分2.1 仪器与试剂 LS-1A型示波滴定仪(山东电讯七厂);磁力搅拌器;钨电极;汞膜电极;PHS-3C型酸度计.N标准溶液:1.000×10~3mg/L,用优级纯NH_4CI配制;Na-TPB溶液:0.05mol/L;30%NaOH溶液;无水Na_2SO_4;CuSO_4-5H_2O;H_2SO_4相对密度1.84g/ml;HAc-NaAc缓冲溶液:pH=5.5,取2mol/LNaAc溶液,滴加HAc调节,用酸度计测量;四乙基氯化铵标准溶液:0.02mol/L,用示波滴定法标定. 相似文献
206.
207.
208.
压力机焊接残余应力的状态分析 总被引:2,自引:0,他引:2
对 2000k N 及 1500k N 压力机焊后残余应力状态进行了测试分析,并对用振动法和热处理两种方法进行消除残余应力的效果进行了现场测试及对比分析。 相似文献
209.
A facile synthesis method for SePSe-containing macrocycles was developed. The macrocycles were obtained by one-pot reaction. The powder selenium was reduced by potassium borohydride in absolute alcohol to produce potassium diselenide,which reacted with bis(o-bromomethylphenyl)phenylphosphine oxide 1 to give the intermediate, 1-phenyl-2,3:8,9-dibenzo-5,6-diselena-1-phosphacyclononadiene 1-oxide 2, and its oligomer. Without isolation, the mixture was treated with potassium borohydride and sodium hydroxide to produce diselenide anion, then allowed to react with alkyl dibromide to give SePSe-containing macrocycles (shown as Scheme 1). A medium-sized eight-membered heterocycle, l-phenyl-2,3:7,8-dibenzo-5-selena-1-phosphacyclooctadiene 1-oxide 4 was obtained surprisingly. The formation of heterocycle 4 was due to the presence of potassium selenide when selenium was reduced by potassium borohydride. The attempts to isolate the intermediate 2 were totally unsuccessful. When the alkyl dibromide was the 1,2-dibromoethane, the expected macrocycle was not obtained, with deposition of red selenium and extrusion of ethylene. The similar case was reported by Pinto B. M. in 1989. 相似文献
210.
氯化氢(HCl)是在各种工业过程中释放的有毒有害气体,但气相HCl中的氯、氢资源可以用于合成许多化工产品,这对副产HCl的资源化利用提供了思路。当前,气相HCl的综合利用主要集中在制氯气和其他含氯产品。通过综述气相HCl资源化的研究进展,分析了相关过程和机理,讨论了影响HCl资源化的因素,并强调了气体成分是影响副产HCl综合利用的主要因素,重点是其他气体成分对反应过程的影响。最后针对目前存在的资源化方式少、系统研究不足等问题,提出未来研究方向包括开发利用方式和模拟多组分气体条件等。 相似文献