全文获取类型
收费全文 | 830篇 |
免费 | 42篇 |
国内免费 | 14篇 |
专业分类
化学 | 429篇 |
力学 | 28篇 |
数学 | 43篇 |
物理学 | 386篇 |
出版年
2023年 | 4篇 |
2022年 | 17篇 |
2021年 | 23篇 |
2020年 | 10篇 |
2019年 | 14篇 |
2018年 | 17篇 |
2017年 | 32篇 |
2016年 | 35篇 |
2015年 | 29篇 |
2014年 | 44篇 |
2013年 | 66篇 |
2012年 | 46篇 |
2011年 | 39篇 |
2010年 | 33篇 |
2009年 | 39篇 |
2008年 | 59篇 |
2007年 | 57篇 |
2006年 | 37篇 |
2005年 | 31篇 |
2004年 | 35篇 |
2003年 | 28篇 |
2002年 | 20篇 |
2001年 | 22篇 |
2000年 | 23篇 |
1999年 | 14篇 |
1998年 | 18篇 |
1997年 | 17篇 |
1996年 | 9篇 |
1995年 | 9篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 10篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有886条查询结果,搜索用时 31 毫秒
1.
《Electroanalysis》2004,16(9):748-756
A strategy for constructing a global multivariate calibration model that includes calibration samples measured over time on different days is developed and applied in electroanalysis. Both synthetic and real samples (tap, extracted and river water) are analyzed by differential‐pulse anodic stripping voltammetry, showing the suitability of the global model constructed that provides successful results similar to those of the usual multivariate calibration. In addition the capability of discrimination of this model is evaluated in prediction for the mean of three replicates with estimation of probability of false noncompliance, α, and false compliance, β, being found 3.1, 11.2, 6.7 and 64.7 nM for nominal concentrations of zinc, cadmium, lead and copper of 96.0, 40.4, 37.3 and 328.0 nM respectively when α=β=0.05. It has been proven that the use of the global calibration does not imply a loss of multivariate analytical sensitivity, using this parameter as quality index of the analytical procedure. The viability of using calibration maintenance strategies with electroanalytical techniques is shown, providing a way to save time and experimental effort when these techniques are used in routine analysis. 相似文献
2.
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
3.
P. Davies 《Accreditation and quality assurance》1996,1(6):240-246
Laboratory accreditation is becoming increasingly accepted around the world as a means of identifying technically competent
laboratories. It is also being used as a mechanism for the acceptance of test data both nationally and internationally. The
concept and mechanisms of accreditation have been developed over the past 50 years. The first national laboratory accreditation
system appeared in Australia in 1947. This organisation, known as the National Association of Testing Authorities (NATA),
has since taken a leading role in developing accreditation practices that are now used world-wide in evaluating testing, measurement
and calibration laboratories. This paper examines the development of the world's first and largest laboratory accreditation
system, and looks at the difficulties and triumphs in gaining acceptance and recognition by government and industry of the
benefits of laboratory accreditation.
Received: 24 June 1996 Accepted: 25 June 1996 相似文献
4.
5.
6.
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
7.
R. Hoelzl Christian Hoelzl Ludwig Kotz Lazlo Fabry 《Accreditation and quality assurance》1998,3(5):185-188
Inductively coupled plasma mass spectrometry (ICP-MS) and high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS)
are powerful methods of determining metallic impurities in the low- and sub-ppt level in process media such as ultra-pure
water used in semiconductor and wafer manufacturing. By using mass spectrometers for analysis, an isotope dilution analysis
(IDMS) is possible. The reproducibility of an IDMS is unmatched. For concentration levels near the instrument detection limit
a novel method is reported to find the optimal amount of isotopic spike solution. This optimal value can be derived by the
law of propagation of uncertainty combined with the Poisson statistics of the measured number of counts. Generally, an excess
of isotopic spike solution should be used to provide results of lowest possible uncertainty. The results are presented in
a diagram for easy practical use.
Received: 14 October 1997 · Accepted: 13 February 1998 相似文献
8.
Summary The concept of a diffusion-averaged molecular weight, Md is presented, and Md is defined for polydisperse samples. It is shown via oligostyrene mixtures that Md can be determined in 20 minutes with common chromatographic equipment. If Md is measured and Mn or Mw is known, the polydispersity can be obtained. 相似文献
9.
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
10.
Cuadros-Rodríguez L Almansa-López EM García-Campaña AM González-Casado A Egea-González FJ Garrido-Frenich A Martínez-Vidal JL 《Talanta》2005,66(4):1063-1072
The use of the recovery term has presented some confusion in Analytical Chemistry. Recent IUPAC recommendations propose to distinguish between two terms: recovery or recovery factor, ℜ, and apparent recovery, ℜ*. Apparent recovery includes recovery factor and a new recovery term proposed in this paper, named calibration recovery, ℜC, which depends of the type of systematic error due to the matrix effect (constant and/or proportional) and is related to the applied calibration methodology. This paper highlights the dependence of the calibration recovery on the sample analyte concentration and, for extension, of the apparent recovery, defines the recovery profile, and makes evident the need to determine a “fit for purpose” analyte concentration interval to comply with a regulated recovery requirements. An approach to estimate the calibration recovery and its associated uncertainty in relation to the above-mentioned dependence is presented. The usefulness of the proposed methodology has been shown in the quantification of a pesticide by GC-ECD for assessing dermal exposure. 相似文献