全文获取类型
收费全文 | 6860篇 |
免费 | 1160篇 |
国内免费 | 580篇 |
专业分类
化学 | 3032篇 |
晶体学 | 74篇 |
力学 | 136篇 |
综合类 | 23篇 |
数学 | 130篇 |
物理学 | 3336篇 |
综合类 | 1869篇 |
出版年
2024年 | 31篇 |
2023年 | 99篇 |
2022年 | 224篇 |
2021年 | 258篇 |
2020年 | 354篇 |
2019年 | 237篇 |
2018年 | 197篇 |
2017年 | 265篇 |
2016年 | 289篇 |
2015年 | 274篇 |
2014年 | 339篇 |
2013年 | 523篇 |
2012年 | 439篇 |
2011年 | 501篇 |
2010年 | 382篇 |
2009年 | 384篇 |
2008年 | 386篇 |
2007年 | 417篇 |
2006年 | 398篇 |
2005年 | 344篇 |
2004年 | 295篇 |
2003年 | 251篇 |
2002年 | 223篇 |
2001年 | 190篇 |
2000年 | 195篇 |
1999年 | 127篇 |
1998年 | 148篇 |
1997年 | 137篇 |
1996年 | 124篇 |
1995年 | 94篇 |
1994年 | 79篇 |
1993年 | 75篇 |
1992年 | 71篇 |
1991年 | 53篇 |
1990年 | 45篇 |
1989年 | 47篇 |
1988年 | 34篇 |
1987年 | 16篇 |
1986年 | 11篇 |
1985年 | 10篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 2篇 |
排序方式: 共有8600条查询结果,搜索用时 0 毫秒
81.
微波等离子体炬发射光谱法去溶系统性能的研究 总被引:7,自引:0,他引:7
用微波等离子体矩(MPT)作激发光源,等离子体的工作气体为氩气,研究了气动雾化进样去溶系统的工作参数对分析性能的影响,探讨了水冷凝与浓硫酸吸收二者协同去溶的相关性,结果表明,OH (Q1带,带头谱线为308.520nm)的发射强度即可判别样品去溶效果。 相似文献
82.
83.
阐述了ICP-AES专家系统中AES电离和激发模型的基本原理,研究了模拟中应用non-LTE理论的正确性以及所需的支持数据库。利用Boltzmann曲线,讨论了Boltzmann温度的测量值随能级激发能变化的现象,并与类似条件下的经验Boltzmann曲线进行对比,证明了专家系统中AES电脑和激发模型可靠性。 相似文献
84.
Robert S. Pomeroy Jeffrey D. Kolczynski Jonathan V. Sweedler M. Bonner Denton 《Mikrochimica acta》1989,99(3-6):347-353
A unique simultaneous emission spectrograph is utilized to perform qualitative and quantitative analysis on trace quantities of solid particulates. The atomic emission spectroscopic system consists of a direct current plasma source and an echelle spectrograph with a charge injection device detector, enabling the system to simultaneously measure the wavelength range from 220 nm to 520 nm with 0.02 nm resolution at 300 nm. Monitoring all wavelengths simultaneously allows the qualitative and quantitative determination of most major and minor constituent in a trace quantity of sample with little prior knowledge about the sample. The ability to perform qualitative and quantitative analysis on particulates is demonstrated by evaluating NBS certified coal fly ash, as well as a sample taken from the respirator air filter at an acute care unit in a hospital.Presented in part at the 1989 European Winter Conference on Plasma Spectrochemistry, Reutte, Austria 相似文献
85.
A. Greiner H. Hou A. Reuning A. Thomas J.H. Wendorff S. Zimmermann 《Cellulose (London, England)》2003,10(1):37-52
Cholesteric materials display unique optical properties which can be exploited in opto-electronic applications such as light emitting diodes. The key feature is the position of the wavelength of the emitted light relative to the one of the selective reflection band. We have synthesized a set of cellulose derivatives displaying the cholesteric phase with the aim to investigate the correlation between chemical structure and properties. Phase transition temperatures, the chain packing, the wavelength of selective reflection but also absorption and fluorescence spectra were investigated as a function of the degree of substitution (DS), the nature of lateral substituents, the composition of doped systems and blends of different cellulose derivatives. Investigated were furthermore the degree of circular polarization of the emitted light for guest–host systems and for cellulose systems with chromophores linked by covalent bonds to the cellulose backbone as well as their performance in light emitting diodes. The conclusion is that the optical properties can be accounted for on the basis of the model of a one-dimensional photonic crystal. The limiting factor with respect to opto-electronic applications is the poor control of the uniformity of the helix formation and orientation. 相似文献
86.
Guadalupe Fortuño 《Plasma Chemistry and Plasma Processing》1988,8(1):19-34
A parametric study of the etching of Si and SiO2 by reactive ion etching (RIE) was carried out to gain a better understanding of the etching mechanisms. The following fluorocarbons (FCs) were used in order to study the effect of the F-to-Cl atom ratio in the parent molecule to the plasma and the etching properties: CF4, CF3Cl, CF2Cl2, and CFCl3 (FC-14, FC-13, FC-12, and FC-11 respectively). The Si etch rate uniformity across the wafer as a function of the temperature of the wafer and the Si load, the optical emission as a function of the temperature of the load, the etch rate of SiO2 as a function of the sheath voltage, and the mass spectra for each of the FCs were measured. The temperature of the wafer and that of the surrounding Si load strongly influence the etch rate of Si, the uniformity of etching, and the optical emission of F, Cl, and CF2. The activation energy for the etching reaction of Si during CF4 RIE was measured. The etch rate of Si depends more strongly on the gas composition than on the sheath voltage; it seems to be dominated by ion-assisted chemical etching. The etching of photoresist shifted from chemical etching to ion-assisted chemical etching as a function of the F-to-Cl ratio and the sheath voltage. The etch rate of SiO2 depended more strongly on the sheath voltage than on the F-to-Cl ratio. 相似文献
87.
Julieta Marrero Griselda Polla Raúl Jiménez Rebagliati Rita Plá Darío Gómez Patricia Smichowski 《Spectrochimica Acta Part B: Atomic Spectroscopy》2007
Different techniques were selected for comprehensive characterization of seven samples of fly ashes collected from the electrostatic precipitator of the San Nicolás thermal power plant (Buenos Aires, Argentina). Particle size was measured using laser based particle size analyzer. X-ray diffraction powder (XRD) analysis and scanning electron microscopy (SEM) were used to characterize the mineral phase present in the matrix consisting basically of aluminosilicates and large amounts of amorphous material. The predominant crystalline phases were mullite and quartz. Major and minors elements (Al, Ca, Cl, Fe, K, Mg, Na, S, Si and Ti) were detected by energy dispersive X-ray analysis (EDAX). Trace elements (As, Cd, Co, Cr, Cu, Mn, Ni, Pb, Se, V and Zn) content was quantified by inductively coupled plasma optical emission spectrometry (ICP OES). Different acid mixtures and digestion procedures were compared for subsequent ICP OES measurements of the dissolved samples. The digestion procedures used were: i) a mixture of FH + HNO3 + HClO4 (open system digestion); ii) a mixture of FH + HNO3 (MW-assisted digestion); iii) a mixture of HF and aqua regia (MW-assisted digestion). Instrumental neutron activation analysis (INAA) was employed for the determination of As, Ba, Co, Cr, Ce, Cs, Eu, Fe, Gd, Hf, La, Lu, Rb, Sb, Sc, Sm, Ta, Tb, Th, U and Yb. The validation of the procedure was performed by the analysis of two certified materials namely, i) NIST 1633b, coal fly ash and ii) GBW07105, rock. Mean elements content spanned from 41870 μg g− 1 for Fe to 1.14 μg g− 1 for Lu. The study showed that Fe (41870 μg g− 1) ? V (1137 μg g− 1) > Ni (269 μg g− 1) > Mn (169 μg g− 1) are the main components. An enrichment, with respect to crustal average, in many elements was observed especially for As, V and Sb that deserve particular interest from the environmental and human health point of view. 相似文献
88.
Emission and absorption polarization spectra as well as emission lifetimes between room temperature and 5 °K have been measured of [Cr urea6]X3 single crystals, where X stands for ClO
4
–
, J–, NO
3
–
, Br–, Cl–, F–, and X3 for JSO
4
3–
. The strong temperature dependence of the fluorescence/phosphorescence-ratios, and of the emission lifetimes is discussed. The differences between the spectra as well as the emission lifetimes of the various salts can be attributed to an anion dependent trigonal perturbation.
Die Autoren danken dem Verband der Chemischen Industrie für finanzielle Unterstützung dieser Arbeit. 相似文献
89.
Inductively coupled plasma optical emission spectrometry (ICP-OES) was applied to the analysis of major and minor elements of Ni-Nb alloys obtained by aluminothermic reduction process. Digestion of samples was made using a mixture of HF+HNO3. Minor and trace elements were determined without matrix separation. The precision for all constituents was <3%. Recoveries for the analyte-spiked samples were 95%. 相似文献
90.
Thieo E. Hogen‐Esch 《Journal of polymer science. Part A, Polymer chemistry》2006,44(7):2139-2155
The synthesis and characterization by size exclusion chromatography, liquid chromatography, NMR, matrix‐assisted laser desorption/ionization, thermal analysis, and other techniques of well‐defined and narrow molecular weight distribution macrocyclic polystyrene (PS), poly(2‐vinylpyridine), poly(α‐methylstyrene), poly (2‐vinyl‐naphthalene) (P2VN), and poly(9,9‐dimethyl‐2‐vinylfluorene) (PDMVF) containing a single 1,4‐benzylidene, methylidene, or 9,10‐anthracenylidene unit are reviewed. The absorption and emission spectroscopy of PS, P2VN, and PDMVF is also discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2139–2155, 2006 相似文献