全文获取类型
收费全文 | 554篇 |
免费 | 46篇 |
国内免费 | 76篇 |
专业分类
化学 | 252篇 |
晶体学 | 9篇 |
力学 | 17篇 |
数学 | 71篇 |
物理学 | 90篇 |
无线电 | 237篇 |
出版年
2024年 | 8篇 |
2023年 | 26篇 |
2022年 | 27篇 |
2021年 | 22篇 |
2020年 | 17篇 |
2019年 | 22篇 |
2018年 | 16篇 |
2017年 | 20篇 |
2016年 | 17篇 |
2015年 | 21篇 |
2014年 | 25篇 |
2013年 | 36篇 |
2012年 | 46篇 |
2011年 | 123篇 |
2010年 | 30篇 |
2009年 | 28篇 |
2008年 | 15篇 |
2007年 | 20篇 |
2006年 | 23篇 |
2005年 | 14篇 |
2004年 | 15篇 |
2003年 | 7篇 |
2002年 | 12篇 |
2001年 | 1篇 |
2000年 | 18篇 |
1999年 | 17篇 |
1998年 | 10篇 |
1997年 | 11篇 |
1996年 | 11篇 |
1995年 | 4篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1992年 | 1篇 |
1990年 | 2篇 |
1979年 | 1篇 |
排序方式: 共有676条查询结果,搜索用时 140 毫秒
151.
152.
计算光度法同时测定人发中的锌铜铁 总被引:5,自引:0,他引:5
本文对5-溴-(二乙基氨基-2-(2-哟啶偶氮)苯显色剂,用多元线性回归或卡尔曼滤波法处理多波长测量数据数据,在pH5.11的30%乙醇介质中同时测定了人发中的锌、铜和铁。 相似文献
153.
不对称催化氢化制备(S)—(+)—萘普生:Ⅰ.不对称催化剂的合成及催化性能 总被引:6,自引:0,他引:6
全过程合成出手性双膦配体2,2’-双(二苯基膦)-6,6’-二甲基联苯,以金属钌为中心原子,制备出几种不对称催化剂。通过考察不对称氢化制备(S)-(+)-萘普生的反应光学收率,研究了催化剂的催化性能,并与联萘型双膦配体催化剂进行了比较。 相似文献
154.
适合低PH范围测量的新型中性载体膜PH电极的研究 总被引:2,自引:0,他引:2
本文设计合成了一种在低PH范围对氢离子有很好Nernst响应的新型中性载体-N,N-二辛基菸酰胺,并把它制成PVC膜PH电极,测试了该电极的线性范围、选择性、稳定、重现性和内阻等各项性能参数,并试验了电极抗氢氟酸腐蚀的能力,该该电极用于氢氟酸的电离常数测定时获得了满意的结果。 相似文献
155.
156.
Rune Møllegaard Friborg Brian VinterAuthor vitae 《Journal of computational science》2011,2(3):304-313
Scientific applications are often not written with multiprocessing, cluster computing or grid computing in mind. This paper suggests using Python and PyCSP to structure scientific software through Communicating Sequential Processes. Three scientific applications are used to demonstrate the features of PyCSP and how networks of processes may easily be mapped into a visual representation for better understanding of the process workflow. We show that for many sequential solutions, the difficulty in implementing a parallel application is removed. The use of standard multi-threading mechanisms such as locks, conditions and monitors is completely hidden in the PyCSP library. We show the three scientific applications: kNN, stochastic minimum search and McStas to scale well on multi-processing, cluster computing and grid computing platforms using PyCSP. 相似文献
157.
Jussi Kantola Antti Piirto Jarmo Toivonen Yoon Chang Hannu VanharantaAuthor vitae 《Journal of computational science》2011,2(3):207-215
The personal capabilities and intentions of employees indicate their performance within their organization. It is important for the organization to capture this kind of tacit knowledge since the workforce are the true experts in perceiving the organization's current reality and evaluating which assets require development – including themselves as knowledge assets. The collective inner voice of the workforce helps the organization's management to steer the company and its assets in a sustainable direction.This article presents how the collective inner voice of the workforce can be captured and how it can be used for the benefit of the organization and its employees. The objective is to support individuals’ personal aspirations, as well as to save the money, time and resources that an organization spends on personnel training.The focus of this article is on demonstrating a possible soft-computing method used for competency simulation. The process starts with a linguistic self-evaluation conducted by employees, where individuals’ own perception of current and target competence levels is captured. The self-evaluation is conducted with the help of fuzzy logic. Clusters are formed from the result dataset using an unsupervised neural network clustering method: self-organizing maps. A demonstrator tool is then used to perform a “what-if” type of analysis/simulation on the clusters in the results. With the demonstrator tool, employees can roughly test the impact of alternative training scenarios for themselves. For individuals this may open up new directions for self-development, and for organizations this may allow the efficient use of training resources. We tested the approach with a dataset from a real human resource development project among nuclear power plant operators.The case study reveals the potential of soft-computing based collective competency simulation as one part of personnel development projects in the future. Yet the techniques and the demonstrator tool used in this experiment are far from being products that employees could easily use as part of their training project. Possible benefits of the proposed approach are demonstrated in this article. 相似文献
158.
159.
Environmentally friendly method for the determination of acrylamide and trimethylolpropane in paper packaging materials by liquid chromatography with tandem mass spectrometry 下载免费PDF全文
Fei Yang Zhonghao Li Zhaoyang Bian Gangling Tang Ziyan Fan Ying Wang ShanShan Liu Hongfei Zhang 《Journal of separation science》2014,37(24):3625-3631
A simple, rapid, and environmentally friendly method was developed for the determination of acrylamide and trimethylolpropane in paper packaging materials. No organic solvent was used and the matrix effect was investigated. The extract was directly analyzed by liquid chromatography with tandem mass chromatography for quantification and confirmation. The chromatographic separations were performed on a ZORBAX HILIC Plus (2.1 mm × 150 mm, 3μm; Agilent, USA) column with only one mobile phase (100% water). Calibration curves for acrylamide and trimethylopropane were achieved with concentrations ranging from 0.4 to 20 mg/kg and the corresponding r2 values were 0.998 and 0.999, respectively. The recoveries were >85% with relative standard deviations <10%. The validated method was applied to the analysis of 50 real samples, and positive results were obtained for 30 samples. The result indicated that trimethylolpropane is associated with inks and printing activity and acrylamide is widely used as a papermaking additive in many paper packages. The concentrations of acrylamide and trimethylolpropane ranged from 0.41 to 7.5 and 0.50 to 8.8 mg/kg, respectively. The results of this study revealed that this method could be used accurately and precisely. 相似文献
160.