全文获取类型
收费全文 | 4136篇 |
免费 | 508篇 |
国内免费 | 517篇 |
专业分类
化学 | 2756篇 |
晶体学 | 50篇 |
力学 | 150篇 |
综合类 | 95篇 |
数学 | 333篇 |
物理学 | 1777篇 |
出版年
2024年 | 6篇 |
2023年 | 33篇 |
2022年 | 92篇 |
2021年 | 114篇 |
2020年 | 116篇 |
2019年 | 108篇 |
2018年 | 144篇 |
2017年 | 164篇 |
2016年 | 185篇 |
2015年 | 122篇 |
2014年 | 243篇 |
2013年 | 739篇 |
2012年 | 234篇 |
2011年 | 223篇 |
2010年 | 186篇 |
2009年 | 235篇 |
2008年 | 284篇 |
2007年 | 302篇 |
2006年 | 230篇 |
2005年 | 224篇 |
2004年 | 192篇 |
2003年 | 178篇 |
2002年 | 164篇 |
2001年 | 88篇 |
2000年 | 96篇 |
1999年 | 77篇 |
1998年 | 92篇 |
1997年 | 40篇 |
1996年 | 33篇 |
1995年 | 43篇 |
1994年 | 25篇 |
1993年 | 41篇 |
1992年 | 17篇 |
1991年 | 16篇 |
1990年 | 11篇 |
1989年 | 18篇 |
1988年 | 10篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 10篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有5161条查询结果,搜索用时 875 毫秒
141.
This work describes the influence of silica fillers on the thermomechanical properties of diglycidyl ether of bisphenol A/triethylenetetramine (DGEBA/TETA) epoxy resins during ageing under electron beam irradiation. Whatever be the silica filler (pure micrometric ground and spherical silicas, nanometric silicas and coupling agent treated silicas), the glass transition temperature of the epoxy resins decreases with increasing irradiation dose, meaning that the main effect of the irradiation is chain scission. No influence of the silica fillers has been detected from the changes in the glass transition temperature with the increase in the irradiation dose. The disappearance of the cooperativity of the γ relaxation, the decrease of the α relaxation and the decrease of the elastic modulus at the rubbery plateau observed by dynamic mechanical analyses involve a decrease in the crosslink density of the epoxy resins. The occurrence of chemical reactions between the epoxy resin and the silica surface at high irradiation doses has been shown. Moreover, we show evidence that chemical reactions between the epoxy resin and the silica surface occur at high irradiation dose. 相似文献
142.
Norimah Yusof Ros Anita Ahmad Ramli Foziah Ali 《Radiation Physics and Chemistry》2007,76(11-12):1882-1884
A study was carried out to determine optimum decontamination dose for a locally manufactured coconut cream powder. Samples were gamma irradiated (0–15 kGy) and ageing process was achieved using GEER oven at 60 °C for 7 days, which is equivalent to one-year storage at room temperature. Iodine value (IV), ranging from 4.8 to 6.4, was not affected by radiation doses and storage, however peroxide value and thiobarbituric acid (TBA) generally increased with radiation doses. In most samples, peroxide value (meq/kg) reduced after storage, whilst the TBA (mg malonaldehyde/kg), indicator for product quality, slightly increased. The sensory evaluation conducted using 25 taste panellists indicated that scores on odour, creamy taste and overall acceptance for all irradiated samples at more than 5 kGy were significantly lower (P<0.05) than the control. However, the panellists could not detect any significant differences among the irradiation doses (P>0.05). All stored products were significantly different in colour, creamy taste, odour and overall acceptance (P<0.05) when compared to the non-stored non-irradiated control. Microbiological count of the samples prior to irradiation was in the range of 1×102–1.7×103 cfu/g with no detection of Salmonella sp. and Escherichia coli. No microbial colonies were detected after irradiation. Based on the TBA and overall sensory acceptance, gamma irradiation of 5 kGy was found to be the optimum dose and lower doses can be considered to decontaminate coconut cream powder. 相似文献
143.
The title compound (C25H24N4O3) has been prepared by the cyclocondensation of 5-amino-3-methyl-l-phenypyrazol, m-nitrobenaldehyde and dimedone in glycol under microwave irradiation without catalyst. The crystal structure was determined by single-crystal X-ray diffraction to be orthorhombic, space group Pbca with a=16.3331(10), b=13.8329(9), c=19.4163(12) A, V= 4386.8(5)A3, Z=8, Dc=1.298g/cm^3,μ=0.087 mm^-1, F(000)=1808, Mr=428.48, the final R=0.0519 and wR=0.1019. X-ray analysis revealed that the pyridine ring is of boat conformation and the six-membered ring fused with it adopts twist boat conformation. 相似文献
144.
种植沙生植物--沙棘改善内蒙古地区生态环境 总被引:2,自引:0,他引:2
结合内蒙古地区现状,对沙棘的生物学和生态学特性、沙棘属植物化学成分和微量元素及种植沙生植物——沙棘的重要性和必要性进行了详细的研究和探讨。研究表明,沙棘属植物具有极强的生态适应性并富含多种营养成分和生物活性物质,并以耐干旱、耐瘠薄、萌蘖及固氮能力强等特点被称为治理非宜林地水土流失、改善生态环境的先锋树种。种植沙棘是治理内蒙古脆弱生态环境最经济、最有效的措施,是贫瘠的不毛之地发展经济、增加收入的经济树种。另外.种植沙棘的技术简便,容易掌握,投资少,见效快。 相似文献
145.
A design of a combined ozone/electron beam irradiation process for treating a 50 m3/h waste water stream from a molasses processing is discussed. Moreover, a cost evaluation of such a process in comparison to a conventional ozonation/biology treatment process has been performed to assess the potential of the irradiation process for technical use. Although the result of this comparison is not bad for the irradiation process an implementation into a full scale plant would not seem to be the thing to do in the present case. 相似文献
146.
Chun-Long?Chen Andrea?M.?Goforth Mark?D.?Smith William?R.?Gemmill Cheng-Yong?Su Hans-Conrad?zur?LoyeEmail author 《Journal of Cluster Science》2005,16(4):477-487
A new flexible ligand, 1,5-bis(8-oxaquinoline)-3-methylpentane (C5MeOQ), was synthesized and used in the preparation of the
new dinuclear copper(II) complex 1: [Cu2(μ-OMe)2(μ-C5MeOQ)(NO3)2]. Single crystal X-ray analysis revealed that complex 1 contains dinuclear Cu(II) units with bridging methoxo groups. The ligand, C5MeOQ, takes on a bent conformation in order to
connect to and complete the square planar coordination environment of both copper centers; and one of the two Cu(II) centers
adopts a distorted square planar configuration as a result of the ligand conformation. The magnetic properties of complex
1 were investigated by variable-temperature magnetic susceptibility measurements in the 100–300 K range. Interestingly, the
susceptibility data for complex 1 reveals that the compound is diamagnetic, suggesting the presence of very strong antiferromagnetic coupling interactions
between the adjacent Cu(II) centers. 相似文献
147.
New optically active polyamides were synthesized according to two ways: using a microwave-assisted polycondensation of an optically active isosorbide-derived diacylchloride with different aromatic diamines in NMP and using interfacial polymerization from an isosorbide-derived diamine with different diacylchlorides. The polymers are obtained with inherent viscosities in the range from 0.11 to 1.05 dL/g. The DSC and TGA measurements clearly demonstrate the high thermal stability of these polymers when considering the range of the melting points from 200 °C to 300 °C and the absence of decomposition till 350 °C. 相似文献
148.
149.
A biocompatible surfactant-n-dodecylammonium α-glutamate (GDA) with biodegradable and biocompatible properties was synthesized, and the phase behavior
and the structural properties of GDA/n-pentanol/water system was studied by small-angle X-ray diffraction, electron spin resonance, and freeze-fracture transmission
electron microscopy (FF-TEM). In the ternary phase diagram of GDA/n-pentanol/water system, there exist three isotropic regions—O/W, bicontinuous, and W/O structures, and two anisotropic regions—hexagonal
liquid crystal (HEX), and lamellar liquid crystal (LLC) regions. UV irradiation causes the decrease in the interlayer space,
d, of lamellar liquid crystal and in the radius, r, of column aggregates of hexagonal liquid crystal, but it has little effect on the structure of O/W and W/O microemulsions. 相似文献
150.
A simple, efficient, and general method has been developed for the synthesis of bis-(α-hydroxyalkyl)phosphinic acids from hypophosphorous acid using microwave irradiation. Bis-(α-hydroxyalkyl)phosphinic acids were obtained in high yield under mild conditions by reaction of hypophosphorous acid with aldehydes under microwave irradiation. 相似文献