全文获取类型
收费全文 | 967篇 |
免费 | 14篇 |
国内免费 | 8篇 |
专业分类
化学 | 703篇 |
晶体学 | 12篇 |
力学 | 14篇 |
数学 | 138篇 |
物理学 | 122篇 |
出版年
2020年 | 12篇 |
2019年 | 11篇 |
2018年 | 6篇 |
2017年 | 6篇 |
2016年 | 7篇 |
2015年 | 13篇 |
2014年 | 6篇 |
2013年 | 34篇 |
2012年 | 36篇 |
2011年 | 58篇 |
2010年 | 17篇 |
2009年 | 18篇 |
2008年 | 39篇 |
2007年 | 49篇 |
2006年 | 75篇 |
2005年 | 52篇 |
2004年 | 62篇 |
2003年 | 42篇 |
2002年 | 55篇 |
2001年 | 11篇 |
2000年 | 15篇 |
1999年 | 13篇 |
1998年 | 10篇 |
1997年 | 17篇 |
1996年 | 13篇 |
1995年 | 10篇 |
1994年 | 17篇 |
1993年 | 9篇 |
1992年 | 15篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 8篇 |
1988年 | 11篇 |
1987年 | 8篇 |
1986年 | 11篇 |
1985年 | 9篇 |
1984年 | 18篇 |
1983年 | 9篇 |
1982年 | 18篇 |
1981年 | 18篇 |
1980年 | 22篇 |
1979年 | 15篇 |
1978年 | 15篇 |
1977年 | 12篇 |
1976年 | 9篇 |
1975年 | 15篇 |
1974年 | 15篇 |
1973年 | 5篇 |
1972年 | 6篇 |
1966年 | 5篇 |
排序方式: 共有989条查询结果,搜索用时 281 毫秒
101.
Enzymatic hydrolysis of ammonia-treated sugar beet pulp 总被引:2,自引:0,他引:2
Foster Brian L. Dale Bruce E. Doran-Peterson Joy B. 《Applied biochemistry and biotechnology》2001,91(1-9):269-282
Sugar beet pulp is a carbohydrate-rich coproduct generated by the table sugar industry. Beet pulp has shown promise as a feedstock
for ethanol production using enzymesto hydroly zepolymeric carbohydrates and engineered bacteria to ferment sugars to ethanol.
In this study, sugar beet pulp underwent an ammonia pressurization depressurization (APD) pretreatment in which the pulp was
exploded by the sudden evaporation of ammonia in a reactor vessel. APD was found to substantially increase hydrolysis efficiency
of the cellulose component, but when hemicellulose- and pectindegrading enzymes wereadded, treated pulp hydrolysis was no
better than the untreated control. 相似文献
102.
Zoran S. Petrović Maria J. Cevallos Ivan Javni Dale W. Schaefer Ryan Justice 《Journal of Polymer Science.Polymer Physics》2005,43(22):3178-3190
Segmented polyurethanes were prepared from soy polyol, diphenyl methane diisocyanate (MDI), and ethylene glycol or butane diol as chain extenders. Samples were prepared with true hard-segment concentrations (HSC) of about 0, 10, and 40%. Both the soft MDI–polyol and hard MDI/diol segments are glassy at room temperature. These samples were also crosslinked through the polyfunctional polyol soft segment. Partial crystallinity and phase separation were detected in samples with 40% HSC, on the basis of DSC data. Small-angle X-ray scattering shows the existence of phase separation with domain sizes of about 10 nm in the 40% HSC samples, but not in the others. The distribution of domain sizes is considerably broader for the ethylene-glycol extended system compared with that for the butane-diol case. Although the presence of hard segments lowers the crosslink density, samples with higher HSC had higher glass transition temperatures, higher strengths, higher moduli, lower swelling, lower elongation at break, and lower impact strengths. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3178–3190, 2005 相似文献
103.
Preparation and characterization of some unusually transparent poly(dimethylsiloxane) nanocomposites
Guru S. Rajan Gil S. Sur James E. Mark Dale W. Schaefer Gregory Beaucage 《Journal of Polymer Science.Polymer Physics》2003,41(16):1897-1901
A technique was developed for preparing poly(dimethylsiloxane) nanocomposites having unusually high transparencies as quantitatively judged by ultraviolet–visible spectroscopy. The method was the in situ generation of silica particles by a two‐step sol–gel procedure in which the required water of hydrolysis was simply absorbed from the air, and the catalyst was generated in situ from a tin salt. Electron microscopy showed that the phase‐separated silica domains were very small (30–50 nm in diameter) and well dispersed, as expected from the transparency of the composites. Stress‐strain measurements in tension indicated that the particles provide very good reinforcement. Ultra‐small‐angle X‐ray scattering data showed that the domain morphology depends strongly on catalyst, but weakly on loading level. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1897–1901, 2003 相似文献
104.
The oxidation of solid europium(II) sulphide under mild conditions has been examined by151Eu Mössbauer spectroscopy. The results show that europium(II) sulphide is remarkably stable to oxidation at 25°C and is only partially converted to Eu3+ after exposure to air for four days. Treatment in air at a temperature of 250°C for six hours induces a similar degree of oxidation. The mechanism and kinetics of oxidation of curopium(II) sulphide under mild conditions in the solid state are therefore non-trivial matters. 相似文献
105.
Bruce A. Kimball Rori K. Craver John J. Johnston Dale L. Nolte 《Journal of separation science》1995,18(4):221-225
In order to investigate the relationship between terpenoid content and black bear foraging preference, an analytical method was required to quantify mono- and sesquiterpenoids present in Douglas-fir sapwood. Sapwood samples were scraped from trees, immediately frozen in liquid nitrogen, and then homogenized. A simple extraction requiring no clean-up step was performed with ethyl acetate. Extracts were analyzed by gas chromatography with mass selective detection versus external standards. The recoveries of 22 terpenoids from fortified controls were approximately 90% with good precision (relative standard deviations of approximately 10%). 相似文献
106.
107.
108.
109.
Dale McMorrow Michon Irons Wyche Pi Tai Chou Michael Kasha 《Photochemistry and photobiology》2015,91(3):576-585
Trace quantities of hydrogen‐bonding impurities in otherwise highly purified and dried glassy hydrocarbon matrices at 77 K can modify the relative triplet state energy levels, and hence the photophysical properties of two aromatic ketones, xanthone and chromone, to the extent that the intrinsic spectroscopic properties are obscured. The intrinsic spectroscopic properties of each are revealed in multicrystalline n‐alkane Shpol'skii matrices, and also can be observed in rigorously purified and dried hydrocarbon glasses at 77 K. The extreme sensitivity to stoichiometric, and even substoichiometric quantities of hydrogen‐bonding impurities arises from the near‐degeneracy of the two lowest‐lying triplet states, and the sensitive nature of the n→π* blueshift phenomena to specific hydrogen‐bonding interactions. 相似文献
110.
Dale Magnar Ekrann Steinar Mykkeltveit Johannes Virnovsky George 《Transport in Porous Media》1997,26(3):229-260
The paper presents an analytical construction of effective two-phase parameters for one-dimensional heterogeneous porous media, and studies their properties. We base the computation of effective parameters on analytical solutions for steady-state saturation distributions. Special care has to be taken with respect to saturation and pressure discontinuities at the interface between different rocks. The ensuing effective relative permeabilities and effective capillary pressure will be functions of rate, flow direction, fluid viscosities, and spatial scale of the heterogeneities.The applicability of the effective parameters in dynamic displacement situations is studied by comparing fine-gridded simulations in heterogeneous media with simulations in their homogeneous (effective) counterparts. Performance is quite satisfactory, even with strong fronts present. Also, we report computations studying the applicability of capillary limit parameters outside the strict limit. 相似文献