全文获取类型
收费全文 | 1783篇 |
免费 | 57篇 |
国内免费 | 9篇 |
专业分类
化学 | 1241篇 |
晶体学 | 26篇 |
力学 | 42篇 |
数学 | 208篇 |
物理学 | 332篇 |
出版年
2022年 | 20篇 |
2021年 | 30篇 |
2020年 | 34篇 |
2019年 | 30篇 |
2018年 | 24篇 |
2017年 | 16篇 |
2016年 | 52篇 |
2015年 | 40篇 |
2014年 | 38篇 |
2013年 | 115篇 |
2012年 | 100篇 |
2011年 | 131篇 |
2010年 | 61篇 |
2009年 | 67篇 |
2008年 | 83篇 |
2007年 | 100篇 |
2006年 | 80篇 |
2005年 | 66篇 |
2004年 | 63篇 |
2003年 | 53篇 |
2002年 | 47篇 |
2001年 | 25篇 |
2000年 | 19篇 |
1999年 | 23篇 |
1998年 | 23篇 |
1997年 | 15篇 |
1996年 | 18篇 |
1995年 | 18篇 |
1994年 | 25篇 |
1993年 | 25篇 |
1992年 | 20篇 |
1991年 | 18篇 |
1990年 | 18篇 |
1989年 | 12篇 |
1988年 | 21篇 |
1987年 | 15篇 |
1986年 | 16篇 |
1985年 | 23篇 |
1984年 | 19篇 |
1983年 | 19篇 |
1982年 | 28篇 |
1981年 | 22篇 |
1980年 | 17篇 |
1979年 | 13篇 |
1978年 | 16篇 |
1977年 | 13篇 |
1976年 | 16篇 |
1975年 | 14篇 |
1974年 | 12篇 |
1973年 | 14篇 |
排序方式: 共有1849条查询结果,搜索用时 15 毫秒
71.
Leendert Vergeynst Herman Van Langenhove Pieter Joos Kristof Demeestere 《Analytica chimica acta》2013
Uniform guidelines for the data processing and validation of qualitative and quantitative multi-residue analysis using full-spectrum high-resolution mass spectrometry are scarce. 相似文献
72.
Pieter Bouckenooge Oliver Bauer Kathrin Eckhard Herman Terryn 《Surface and interface analysis : SIA》2020,52(4):174-184
In this paper, the behaviour of the industrial applied Ti/Zr conversion coating (CC) pretreatment on rolled automotive aluminium samples (AA5182) is analysed. Due to its nanometre lateral and depth resolution, Auger electron spectroscopy (AES) is used to analyse the CC distribution at surface cathodic intermetallic particles. As a result of its high surface sensitivity, the AES technique is very susceptible to differences in the top contamination layer thickness. It is demonstrated that AES point measurements performed on aluminium model samples coated with 1.5 and 3 nm of Ti (oxide) layer cannot differentiate the two-layer thicknesses if a difference in the top contamination thickness is not taken into account. A data analysis methodology is introduced, based on the ratio of normalized peak areas (enrichment ratios), to eliminate the effect of the contamination layer thickness. The experimental validation of the methodology is performed on the model samples, demonstrating errors of 2% on the enrichment ratios on similar samples with different contamination layer thicknesses, while the conventional spectra quantification results in errors of 49%. The methodology is also theoretically substantiated within certain constraints. By the use of the AES methodology, an enriched Ti and Zr deposition is confirmed at the cathodic intermetallic particles at the surface of the industrial no-rinse CC sprayed automotive aluminium sheet samples. 相似文献
73.
Ribeiro Sabrina Dias Meneguin Andria Bagliotti Barud Hernane da Silva Silva Jhonatan Miguel Oliveira Rafael L. Asuno Rosana Maria Nascimento de Tormin Thiago Faria Muoz Rodrigo Alejandro Abarza Filho Guimes Rodrigues Ribeiro Clovis Augusto 《Journal of Thermal Analysis and Calorimetry》2022,147(13):7265-7275
Journal of Thermal Analysis and Calorimetry - Cellophane film production generates cellulosic residues from scraps, edges, and low-quality films. In this work, cellophane was used as a raw material... 相似文献
74.
Maria Jo?o Carrilho Plancha Carmen Mireya Rangel César Augusto Correia de Sequeira 《Journal of Solid State Electrochemistry》2012,16(2):665-671
The (PEO)4ZnCl2 electrolyte (PEO, polyethylene oxide) was studied in view of its potential application in a solid-state rechargeable zinc
cell. The electrochemical stability window was established, and decomposition voltage values between 3.19 (20 °C) and 1.44 V
(150 °C) were estimated. Cyclic voltammetry studies using a Pt/(PEO)4ZnCl2/Pt cell indicated reversibility of the Zn2+/Zn couple at the electrode/electrolyte interface. Laboratory cells Zn(−)/(PEO)4ZnCl2/Nb2O5(+) were assembled and studied at 55 °C, under various discharge current densities. Results of cell discharge profiles, capacity
values, charge–discharge cycles and cell stabilities are reported. 相似文献
75.
76.
77.
Adriana Predoi−Cross Michel Herman Luciano Fusina Gianfranco Di Lonardo 《Journal of Quantitative Spectroscopy & Radiative Transfer》2012,113(11):1134-1137
The far infrared spectrum of HCOOH was recorded at a high resolution (0.0009 cm?1) and long path length (72 m) at the far-infrared beamline, Canadian Light Source. Spectra were recorded in the region 62–300 cm?1, showing transitions from the trans-isomer.Ground state rotational transitions with Ka up to 30, were identified up to 175 cm?1, extending the observation reported in the literature. A total of 3321 transitions were assigned and fitted together with previous (4149) published data. An improved set of rotational parameters was obtained adopting the symmetric top (A) reduction of the rotational Hamiltonian in the Ir representation. The newly measured far infrared transitions allowed the determination of all diagonal and off diagonal 8th order parameters L and of some of the diagonal 10th order parameters P. 相似文献
78.
Electrohydrodyamic (EHD) heat transfer enhancement and flow control methods are becoming increasingly popular in engineering
science and applications both in terrestrial and low gravity applications. The correct choice of the working fluid is essential
for the design and performance of EHD hardware and can pose challenge because some working fluids with favorable EHD properties
can be unstable or hazardous. In this paper key properties and criteria for the selection of working fluids for single-phase
(liquid) as well as gas–liquid and vapor–liquid two-phase electrohydrodynamic experiments and applications are discussed.
Key physical and electrical properties as well as environmental and safety issues are reviewed for the sample fluids PF-5052,
FC-72, R141b, cyclohexane and pure water. Microgravity experiments impose additional demands on the selection of the working
fluids. Some of these demands are addressed by contrasting bubble dimensions and shapes at detachment, estimated using a simple
thermodynamic model, in terrestrial and microgravity conditions with and without electric fields. Data are obtained using
a simplified analytical model and verified experimentally. 相似文献
79.
Larisa G. Shaidarova Larisa G. Popesku Nikolay A. Ulakhovich Herman C. Budnikov Nail G. Zabirov 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1)
Abstract Crown-containing N-(thio)phosphoryl(thio)ureas are related to a class of NH-acids due to the presence of two acceptor-groups: (thio)phosphorylic and (thio)acylic. In agreement with structure of lariat ether, it was observed a stage corresponding to the step ejection of two H* ion on the potentiometric titration curve of ligand by alkaline. Calculated step ionization constants demonstrate that these compounds are weak acids with relative values of pK1 and pK2. 相似文献
80.
Bruno M. Soares Ederson R. Pereira Juliana V. Maciel Augusto A. Vieira Fabio A. Duarte 《Journal of separation science》2013,36(20):3411-3418
This work reports the development of a dispersive liquid – liquid microextraction method for the simultaneous extraction, preconcentration, and derivatization of Hg2+ and CH3Hg+ species from water samples for further determination by GC – MS. Some parameters of the proposed method, such as volume and type of disperser and extraction solvent, and Na[B(C6H5)4] concentration were investigated using response surface methodology. Suitable recoveries were obtained using 80 μL C2Cl4 (as extraction solvent), 1000 μL ethanol (as disperser solvent), and 300 μL 2.1 mmol/L Na[B(C6H5)4] (as derivatizing agent). Accuracy was evaluated in terms of recovery and ranged from 87 to 99% with RSD values <7%. In addition, a certified reference material of water (NIST 1641d) was analyzed and agreed with the certified value about 107% (for Hg2+), with RSD values <8.5%. LODs were 0.3 and 0.2 μg/L, with enrichment factors of 112 and 115 for Hg2+ and CH3Hg+, respectively. The optimized method was applied for the determination of Hg2+ and CH3Hg+ in tap, well, and lake water samples. 相似文献