全文获取类型
收费全文 | 274篇 |
免费 | 12篇 |
国内免费 | 5篇 |
专业分类
化学 | 191篇 |
力学 | 5篇 |
数学 | 22篇 |
物理学 | 73篇 |
出版年
2023年 | 4篇 |
2022年 | 12篇 |
2021年 | 14篇 |
2020年 | 4篇 |
2019年 | 9篇 |
2018年 | 12篇 |
2017年 | 10篇 |
2016年 | 5篇 |
2015年 | 8篇 |
2014年 | 8篇 |
2013年 | 33篇 |
2012年 | 17篇 |
2011年 | 6篇 |
2010年 | 7篇 |
2009年 | 7篇 |
2008年 | 6篇 |
2007年 | 18篇 |
2006年 | 8篇 |
2005年 | 7篇 |
2004年 | 7篇 |
2003年 | 10篇 |
2002年 | 3篇 |
2001年 | 6篇 |
2000年 | 8篇 |
1999年 | 7篇 |
1998年 | 6篇 |
1997年 | 7篇 |
1996年 | 3篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有291条查询结果,搜索用时 15 毫秒
1.
德国夏洛滕堡物理技术研究所(The Physikallisch-Technische Reichanstalt,简称PTR)是世界上第一个国家级的物理技术研究所,它开创了科学研究和技术研究相结合,服务于工业和国家经济之先河。文章从PTR建立的历史背景、早期研究工作和所产生的影响等方面作较为全面的讨论。 相似文献
2.
Summary Six commercial hydrogen standards containing helium, oxygen, nitrogen, methane and carbon dioxide at trace levels were analyzed
by gas chromatography, for periods up to 105 days. The concentrations, in the range of 0–120 μmol mol−1, were stable (with the exception of oxygen) but often significantly different from the certified values provided by the suppliers,
especially for helium, oxygen and nitrogen. Concurrently, some experiments were carried out to verify the stability of gas
mixtures based on hydrogen stored in cylinders submitted to different chemical and physical treatments. The causes that led
to the deviations observed, as well as the decreases in oxygen, are discussed.
Presented at the 21st ISC held in Stuttgart, Germany, 15th–20th September, 1996. 相似文献
3.
Theodor H. G. Hehenkamp 《Mikrochimica acta》1992,107(3-6):273-277
In order to optimize the physical properties of HTSC small single crystals grown from a melt for basic studies of their physical properties the influence of the environment on their impurity content was investigated by EPMA. This requires quantitative analysis of all elements being present in the crystals. The accuracy of results was affected by problems with the choice and quality of standards, by contamination but also by malfunction of microprobe electronics. The HTSC materials were found to react with mills, milling balls, crucibles and the atmosphere. These problems are being discussed and some reactions being studied for Y1Ba2Cu3O6+x (0 < x < 1) HTSC in A12O3 and ZrO2 crucibles. The crystals grown contain reproducible amounts of impurities depending on boundary conditions and exhibit a zone structure in composition particularly for Y and Ba within their range of homogeneity. 相似文献
4.
高分辨等离子体质谱法直接测定高纯镓中的痕量元素 总被引:9,自引:0,他引:9
建立高分辨电感耦合等离子体质谱法(HR-ICP-MS)测定高纯镓样品中Be、Mg、A l、S i、Ti、V、Cr、Mn、Fe、Co、N i、Cu、Zn、Ge、As、Mo、Ag、Cd、In、Sb、Ba、Pb、B i等痕量元素的方法。样品用HNO3 HC l经微波消解后,试液直接进样用HR-ICP-MS法同时测定上述元素,在高分辨质谱测量模式下避免了大量的质谱干扰,详细地研究了HC l和高纯镓所产生的基体效应,以Sc、Rh、Tl作为内标元素校正了基体效应,讨论和确定了实验的最佳测定条件。结果表明,23种痕量元素的检出限在0.001~0.21μg/L之间;回收率在89.8%~111.6%之间,相对标准偏差(RSD)小于3.3%。 相似文献
5.
Identification of selenium species in urine by ion-pairing HPLC–ICP–MS using laboratory-synthesized standards 总被引:1,自引:0,他引:1
Wrobel K Wrobel K Kannamkumarath SS Caruso JA 《Analytical and bioanalytical chemistry》2003,377(4):670-674
This study focused on the detection/identification of possible selenium metabolites in human urine. Organoselenium compounds not commercially unavailable were synthesized and characterized by electrospray mass spectrometry. Separation of selenomethionine, methylselenomethionine, trimethylselonium, selenoethionine, and selenoadenosylmethionine was achieved by ion-pairing HPLC with a mobile phase of 2 mmol L–1 hexanesulfonic acid, 0.4% acetic acid, 0.2% triethanolamine (pH 2.5), and 5% methanol. The column effluent was introduced on-line to inductively coupled plasma–mass spectrometry for selenium-specific detection (77Se and 78Se). For selenium speciation in urine, solid-phase extraction was carried out using C18 cartridges modified with hexanesulfonic acid. Selective retention of cationic species was observed from acidified urine (perchloric acid, pH 2.0). After elution with methanol, evaporation, and dissolution in the mobile phase, the sample was introduced to the HPLC–ICP–MS system and the chromatographic peaks were assigned by adding standards. The species identified in urine were selenomethionine, trimethylselonium ion, and selenoadenosylmethionine. The last species was detected for the first time and our results suggest that selenomethionine might enter the metabolic pathway of its sulfur analog in the activated methylation cycle.Kazimierz Wrobel and Katarzyna Wrobel are on the leave from the Institute of Scientific Research, University of Guanajuato, L. de Retana No. 5, 36000 Guanajuato, Gto., Mexico 相似文献
6.
Standardising quality of measurements at both the national and international level results in a unity in measurement that
may be regarded a synonym of traceability. In gas analysis, the key issue in achieving this aim is production of gaseous reference
materials. Establishing a network of secondary measurement standards at gaseous CRM producers’ sites in Ukraine might be interesting
for those involved in gas analysis activities. Inevitably, problems concerning the recognition of measuring capabilities of
both national metrological institutes and local CRM producers are now an international issue. Thus, the problems of national
adoption of international standards, as well as harmonisation between different international documents are currently relevant,
and Ukrainian experience may be useful to others in this field.
Presented at the 3rd International Conference on Metrology, November 2006, Tel Aviv, Israel. 相似文献
7.
Emil Völkert 《Accreditation and quality assurance》2004,9(4-5):237-238
Manufacturers support the concept of traceability. However, only a small number of the medically relevant measurands can be traced to the highest metrological order. In many cases, the measured substances are heterogeneous mixtures where traceability can be established only to either an international conventional reference measurement procedure or to a manufacturers own in-house reference system. The traceability concept needs to be seen in the context that the results of medical laboratories are not an aim per se, but are meant to provide useful medical information to clinicians, and that pre- and post-analytical steps may also contribute significantly to errors. There is a need for the further development of suitable reference measurement systems, but in view of the multitude of tasks and limited resources, priorities need to be set.Presented at BERM-9 – 9th International Symposium on Biological and Environmental Reference Materials, 15–19 June 2003, Berlin, Germany 相似文献
8.
混合溶剂火焰原子吸收法直接测定原油中的镍刘广东袁存光张丙华刘文钦(石油大学(华东),山东东营257062)彭力(中国石油天然气总公司环保处,北京100724)关键词原油,混合溶剂,无机盐标准,原子吸收法,镍测定原油中,微量元素镍、钒、铁、铜的存在对... 相似文献
9.
M. Gastel J.S. Becker G. Küppers H.-J. Dietze 《Spectrochimica Acta Part B: Atomic Spectroscopy》1997,52(14):105-2059
A laser ablation system using a Nd:YAG laser was coupled both to a quadrupole inductively coupled plasma (ICP) mass spectrometer and to a double-focusing sector field ICP mass spectrometer. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was applied for the determination of long-lived radionuclides in a concrete matrix. The investigated samples were two laboratory standards with a concrete matrix, which we doped with different long-lived radionuclides (e.g. 99Tc, 232Th, 233U, 237Np) from the ng g−1 to μ g−1 concentration range and an undoped concrete material (blank). Detection limits for long-lived radionuclides in the 10 ng g−1 range are reached for LA-ICP-MS using the quadrupole mass spectrometer. With double-focusing sector field ICP-MS, the limits of detection are in general one order of magnitude lower and reach the sub ng g−1 range for 233U and 237Np. A comparison of mass spectrometric results with those of neutron activation analysis on undoped concrete sample indicates that a semiquantitative determination of the concentrations of the minor and trace elements in the concrete matrix is possible with LA-ICP-MS without using a standard reference material. 相似文献
10.
A homologous series of 2,4-dichlorobenzyl alkyl ethers (DCBEs) have been synthesized and purified for use as retention index calibrants and internal standards. They are stable, sensitive to ECD and FID and ideal for GC-MS, with base peaks at m/z 159/161. The retention index calibration against the n-alkanes for a linear temperature program (LTP) series is given and recommendations made for the most suitable members of the DCBE series for use as internal standards in organochlorine (OC) residue analysis. 相似文献