全文获取类型
收费全文 | 7444篇 |
免费 | 200篇 |
国内免费 | 22篇 |
专业分类
化学 | 4654篇 |
晶体学 | 46篇 |
力学 | 176篇 |
数学 | 863篇 |
物理学 | 1927篇 |
出版年
2021年 | 64篇 |
2020年 | 87篇 |
2019年 | 72篇 |
2018年 | 64篇 |
2017年 | 60篇 |
2016年 | 159篇 |
2015年 | 138篇 |
2014年 | 145篇 |
2013年 | 303篇 |
2012年 | 321篇 |
2011年 | 329篇 |
2010年 | 185篇 |
2009年 | 182篇 |
2008年 | 284篇 |
2007年 | 278篇 |
2006年 | 258篇 |
2005年 | 250篇 |
2004年 | 208篇 |
2003年 | 207篇 |
2002年 | 191篇 |
2001年 | 159篇 |
2000年 | 155篇 |
1999年 | 109篇 |
1998年 | 109篇 |
1997年 | 111篇 |
1996年 | 128篇 |
1995年 | 123篇 |
1994年 | 96篇 |
1993年 | 105篇 |
1992年 | 91篇 |
1991年 | 79篇 |
1990年 | 68篇 |
1989年 | 92篇 |
1988年 | 85篇 |
1987年 | 78篇 |
1986年 | 74篇 |
1985年 | 118篇 |
1984年 | 105篇 |
1983年 | 82篇 |
1982年 | 98篇 |
1981年 | 100篇 |
1979年 | 87篇 |
1978年 | 82篇 |
1977年 | 86篇 |
1976年 | 75篇 |
1975年 | 86篇 |
1973年 | 73篇 |
1968年 | 89篇 |
1967年 | 98篇 |
1966年 | 98篇 |
排序方式: 共有7666条查询结果,搜索用时 359 毫秒
11.
12.
Jan Schmidt 《Mathematische Semesterberichte》2007,54(2):261-301
Ohne Zusammenfassung 相似文献
13.
14.
Richard Kotek Kyeong Pang Ben Schmidt Alan Tonelli 《Journal of Polymer Science.Polymer Physics》2004,42(23):4247-4254
Poly(ethylene isophthalate) (PEI) was synthesized for this research with essentially a condensation polymerization of isophthalic acid and ethylene glycol catalyzed by zinc acetate and antimony trioxide. Several samples were obtained, and their characteristics were observed and compared with poly(ethylene terephthalate) (PET). The synthesized PEI samples were chemically identified by 1H NMR. Thermal analysis with differential scanning calorimetry (DSC) yielded results that indicate the samples were primarily amorphous, with a glass‐transition temperature of 55–60 °C. Molecular weights of these PEI samples were also obtained through intrinsic viscosity measurements (Mark–Houwink equation). Molecular weights varied with conditions of the polymerization, and the highest molecular weight achieved was 21,000 g/mol. Finally, the diffusion coefficient, solubility, and permeability of CO2 gas in PEI were measured and found to be substantially lower than in PET, as anticipated from their isomeric chemical structures. This is because in PET the phenyl rings are substituted in the para (1,4) positions, which allows for their facile flipping, effectively permitting gases to pass through. However, the meta‐substituted phenyl rings in PEI do not permit such ring flipping, and thus PEI may be more suitable for barrier applications. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4247–4254, 2004 相似文献
15.
16.
Mass distributions of fragments in the low-energy fission of nuclei from 187Ir to 213At have been analysed. This analysis has shown that shell effects in symmetric-mode fragment mass yields from the fission of pre-actinide nuclei could be described if one assumes the existence of two strongly deformed neutron shells in the arising fragments with neutron numbers N1 ≈ 52 and N2 ≈ 68. A new method has been proposed for quantitatively describing the mass distributions of the symmetric fission mode for pre-actinides with A ≈ 180–220. 相似文献
17.
18.
19.
Ohne ZusammenfassungDiese Arbeit wurde während eines Aufenthaltes von Schmidt in der Bundesrepublik Deutschland als Preisträger der Alexander von Humboldt-Stiftung geschrieben. 相似文献
20.
J. C. Raines J. P. Schmidt J. P. Burelbach H. K. Fauske 《Journal of Thermal Analysis and Calorimetry》2006,85(1):53-55
Hydrogen
peroxide is a very versatile oxidizing agent, and it is also environmentally
compatible considering that the products of its exothermic decomposition are
oxygen and water.When kept in a clean temperature-controlled environment,
the self-reaction (decomposition) rate is extremely low. However, it is well
known that even a small amount of contamination will dramatically increase
the reaction rate. This paper describes the use of the fast thermal activity
interpreter (FTAI) instrument to examine the chemical reactivity of commercially
available 50% hydrogen peroxide at two different temperatures (30 and 40°C)
both with and without contamination. The results show that at 30°C a small
amount of rust (330 ppm) increases the reaction rate of 50% hydrogen peroxide
by a factor of 50. When the temperature is increased to 40°C, the reaction
rate is further increased by almost a factor of four. The implication for
reactivity management is that at this contamination level most practical vessel
sizes would require emergency venting capability.
An evaluation
was then performed to determine the emergency venting requirement for the
safe transportation or storage of the contaminated hydrogen peroxide. It was
determined that for quantities of the material less than 5 gallons, conventional
breather vents would be sufficient to accommodate the gas evolved. However,
for larger quantities, a safety relief device would be needed. For example,
for a 400-gallon tote bin at 40°C the required minimum vent area is estimated
to be 4.3 in2, corresponding to a minimum vent
diameter of 2.3 inches. 相似文献