全文获取类型
收费全文 | 1520篇 |
免费 | 55篇 |
国内免费 | 26篇 |
专业分类
化学 | 789篇 |
晶体学 | 26篇 |
力学 | 23篇 |
数学 | 398篇 |
物理学 | 365篇 |
出版年
2022年 | 16篇 |
2021年 | 20篇 |
2020年 | 26篇 |
2019年 | 27篇 |
2018年 | 14篇 |
2017年 | 17篇 |
2016年 | 37篇 |
2015年 | 37篇 |
2014年 | 33篇 |
2013年 | 76篇 |
2012年 | 86篇 |
2011年 | 79篇 |
2010年 | 55篇 |
2009年 | 51篇 |
2008年 | 78篇 |
2007年 | 87篇 |
2006年 | 97篇 |
2005年 | 89篇 |
2004年 | 83篇 |
2003年 | 54篇 |
2002年 | 69篇 |
2001年 | 21篇 |
2000年 | 31篇 |
1999年 | 20篇 |
1998年 | 27篇 |
1997年 | 20篇 |
1996年 | 24篇 |
1995年 | 20篇 |
1994年 | 28篇 |
1993年 | 35篇 |
1992年 | 23篇 |
1991年 | 16篇 |
1990年 | 19篇 |
1989年 | 16篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1986年 | 10篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 11篇 |
1982年 | 10篇 |
1981年 | 11篇 |
1980年 | 9篇 |
1979年 | 5篇 |
1978年 | 11篇 |
1977年 | 8篇 |
1976年 | 6篇 |
1975年 | 14篇 |
1974年 | 6篇 |
1973年 | 9篇 |
排序方式: 共有1601条查询结果,搜索用时 15 毫秒
81.
Shyue-Tzoo Lin Steve K. Huang 《Journal of polymer science. Part A, Polymer chemistry》1996,34(5):869-884
Siloxane-modified sulfone-containing epoxy resins (ESBS) were prepared by polycondensation of PMPS and/or PDMS siloxane oligomers with EBS, the sulfone-containing epoxy resin. Structures were analyzed by IR, 1H-, and 13C-NMR. The siloxane content in the copolymers was determined by 1H-NMR with an integration technique. Epoxy equivalent weight (EEW) determination indicated that the oxirane ring of EBS was intact with this hot-melt procedure. The GPC measurement of these ESBS copolymers showed that molecular weight (MW) increased with increasing siloxane content in PMPS-modified copolymers. Evidence of siloxane incorporation in the copolymer was discussed. © 1996 John Wiley & Sons, Inc. 相似文献
82.
83.
Jim J. Lin Steve Harich Dennis W. Hwang Malcom S. Wu Yuan T. Lee Xueming Yang 《中国化学会会志》1999,46(3):435-444
Elimination of atomic hydrogen (H) and molecular hydrogen (H2) are important elementary chemical processes in photochemistry and combustion chemistry. Recently, unique and sensitive detection techniques for atomic and molecular hydrogen detection were developed in our laboratory. Using the advanced molecular beam methods, we have studied the photodissociation of a few typical hydrocarbons at 157 nm excitation, especially their atomic and molecular hydrogen elimination processes. In this report, we will briefly describe the results from photodissociation of propane, ethylene, propyne and methanol at 157 nm excitation. These molecules represent different classes of hydrocarbons such as alkane, alkene, alkyne and alcohol. Through careful studies on differently deuterated compounds, clear pictures of selective atomic and molecular hydrogen elimination processes can be constructed for all of the above compounds. These results will help us to understand the dissociation dynamics of the small hydrocarbon molecules. 相似文献
84.
Dr. Steve Y. Rhieu Dr. Aaron A. Urbas Dr. Daniel W. Bearden Dr. John P. Marino Dr. Katrice A. Lippa Dr. Vytas Reipa 《Angewandte Chemie (International ed. in English)》2014,53(2):447-450
Non‐invasive and real‐time analysis of cellular redox processes has been greatly hampered by lack of suitable measurement techniques. Here we describe an in‐cell nuclear magnetic resonance (NMR) based method for measuring the intracellular glutathione redox potential by direct and quantitative measurement of isotopically labeled glutathione introduced exogenously into living yeast. By using this approach, perturbations in the cellular glutathione redox homeostasis were also monitored as yeast cells were subjected to oxidative stress. 相似文献
85.
Determination of dissolved organic nitrogen in natural waters using high-temperature catalytic oxidation 总被引:5,自引:0,他引:5
El-Sayed A. Eric P. Alan D. Steve J. Charlotte B. 《Trends in analytical chemistry : TRAC》2003,22(11):819-827
Studies on nitrogen in natural waters have generally focussed on dissolved inorganic nitrogen (DIN), primarily because of relative ease of analysis and the important influence of DIN on water quality. Advances in analytical techniques now permit the systematic study of dissolved organic nitrogen (DON), and this work has shown that DON is quantitatively significant in many waters. This article describes the sampling and analytical protocols required for rapid, precise and reliable determinations of DON, involving high-temperature catalytic oxidation (HTCO), coupled to chemiluminescence detection. This approach simultaneously determines dissolved organic carbon (DOC) and total dissolved nitrogen (TDN), and DON is derived by subtraction of DIN measured by colorimetry. The DON determination is simple to perform, exhibits excellent precision (<1% for C and 1.5% for N) and is applicable to a wide range of natural waters. 相似文献
86.
Polymer brushes via surface-initiated polymerizations 总被引:2,自引:0,他引:2
Polymer brushes produced by controlled surface-initiated polymerization provide a route to surfaces coated with well-defined thin polymer films that are covalently bound to the substrate. All of the major controlled polymerization techniques have been applied to the synthesis of polymer brushes and examples of each are presented here. Many examples of brush synthesis in the literature have used the living atom transfer radical polymerization (ATRP) system, and in this tutorial review a particular focus is given to examples of this technique. 相似文献
87.
Photoactivation of silver-exchanged zeolite A 总被引:1,自引:0,他引:1
88.
Nick A. Thomburg Ihab M. Abdelrehim Steve Pullins Donald P. Land 《Journal of the American Society for Mass Spectrometry》1994,5(6):583-587
A method for deflecting ions, such as K+, produced outside a Fourier-transform mass spectrometer cell during laser-induced thermal desorption, is described. This technique has been shown to deflect laser-generated K and Ti ions from two Ti foil samples (biomedical implant model surfaces), yielding mass spectra of coadsorbed organic species. Further studies characterizing the laser desorption/deflection parameters have shown that ion deflection improves with higher deflection voltages and greater sample to Fourier-transform mass spectrometry cell separation. Higher laser power densities resulted in greater surface ion production; hence higher deflection voltages were necessary. A 6% increase in laser power necessitated a fourfold increase in deflection voltage for the Ti sample. 相似文献
89.
The following article describes an advanced dense wavelength division multiplexing (DWDM) Optical Network developed by L-3 Photonics. The network, configured as an amplified optical bus, carries traffic simultaneously in both directions, using multiple wavelengths. As a result, data distribution is of the form peer-to-multi-peer, it is protocol independent, and it is scalable. The network leverages the rapid growth in commercial optical technologies, including wavelength division multiplexing (WDM), and when applied to military and commercial platforms such as aircraft, ships, unmanned and other vehicles, provides a cost-effective, low-weight, high-speed, and high noise-immune data distribution system. 相似文献
90.
Jacqueline L. Stroud Steve P. McGrath 《International journal of environmental analytical chemistry》2013,93(2):222-236
Selenium (Se) speciation in soil affects its bioavailability to crops. An analytical procedure for the determination of inorganic Se species (selenite and selenate) in soil extracts by anion-exchange liquid chromatography (LC) with ICP-MS detection has been developed, with 10-fold higher sensitivity than existing HGAAS-based soil Se measurements. A comparison of phosphate extraction solutions on agricultural soils amended with 20?µg?kg–1 selenate or selenite was carried out, and a 0.016?M?KH2PO4 extraction solution is recommended. Recovery of selenate was >91%; however, selenite recovery ranged between 18.5% and 46.1%, due to rapid binding to the soil. Soil preparation did not have a significant (p?>?0.05) effect on the extractability of the selenate or selenite amendments. The stability of Se species in the phosphate extracts was variable, depending on temperature and storage time. Therefore, immediate (<1?h) analysis of the soil extracts is preferable. The method developed was applied to the determination of extractable Se from six arable soils in the UK. Extractable Se levels in these soils ranged between 6 and 13?µg?kg–1 consisting of selenite and some soluble organic Se. 相似文献