全文获取类型
收费全文 | 2380篇 |
免费 | 150篇 |
国内免费 | 139篇 |
专业分类
化学 | 483篇 |
晶体学 | 6篇 |
力学 | 54篇 |
综合类 | 21篇 |
数学 | 104篇 |
物理学 | 212篇 |
综合类 | 1789篇 |
出版年
2024年 | 12篇 |
2023年 | 25篇 |
2022年 | 69篇 |
2021年 | 88篇 |
2020年 | 64篇 |
2019年 | 52篇 |
2018年 | 32篇 |
2017年 | 75篇 |
2016年 | 61篇 |
2015年 | 71篇 |
2014年 | 112篇 |
2013年 | 129篇 |
2012年 | 138篇 |
2011年 | 157篇 |
2010年 | 114篇 |
2009年 | 118篇 |
2008年 | 137篇 |
2007年 | 172篇 |
2006年 | 132篇 |
2005年 | 135篇 |
2004年 | 121篇 |
2003年 | 97篇 |
2002年 | 78篇 |
2001年 | 74篇 |
2000年 | 65篇 |
1999年 | 50篇 |
1998年 | 36篇 |
1997年 | 38篇 |
1996年 | 36篇 |
1995年 | 31篇 |
1994年 | 37篇 |
1993年 | 13篇 |
1992年 | 28篇 |
1991年 | 16篇 |
1990年 | 14篇 |
1989年 | 11篇 |
1988年 | 18篇 |
1987年 | 6篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 3篇 |
排序方式: 共有2669条查询结果,搜索用时 31 毫秒
71.
72.
木结构建筑的回归与发展 总被引:6,自引:0,他引:6
介绍了木结构建筑的环保、节能、高效等特点,对木结构的发展现状进行了分析,认为木结构建筑在我国的发展前景十分广阔· 相似文献
73.
刘引鸽 《宝鸡文理学院学报(自然科学版)》2004,24(3):223-227
采用宝鸡9个站点30 年(1971~2000年)气温资料,利用相关统计和模糊聚类等方法,分析了宝鸡地区气温的空间分布,并将宝鸡分成北部丘陵和渭河川原2个区域,探讨了气温的季节变化和年际变化特征,为宝鸡地区农业生产提供了重要依据. 相似文献
74.
高等教育行政体制改革,是我国高等教育改革的首要环节和关键因素.集权与分权、政府与学校的关系、职能转换是贯穿于历次高等教育行政体制改革的主要问题.在新世纪,我国高等教育行政体制改革的趋势是:在转换政府职能的基础上逐步建成与社会主义市场经济相适应,以统一领导、分级管理和自主办学为基本特征的高等教育行政体制. 相似文献
75.
重庆三大经济区城镇化发展趋势及模式思考 总被引:1,自引:1,他引:1
文章通过对重庆市城镇化现状特征与存在问题的分析,总结出在新形势下重庆城镇化进程必将呈现出梯度推进、快速发展的趋势.鉴于此,当前重庆市在引导城镇化发展的进程中,就必须充分利用现有的一切优势条件,根据三大经济区的现有基础,选择切实可行的发展模式,以引导重庆城镇化进程朝着快速、健康、有序的方向发展. 相似文献
76.
77.
P. K. Kamweru F. G. Ndiritu T. K. Kinyanjui Z. W. Muthui R. G. Ngumbu P. M. Odhiambo 《Journal of Macromolecular Science: Physics》2013,52(7):1338-1349
Plastic bags mostly made of polyethylene (PE) cause pollution as solid waste due to their non-degradability nature. Initiation of a degradative process by enhanced photo-oxidation is a possible method for an accelerated degradation. This paper presents temperature treatment effects on PE films where photodegradation was initiated using ultraviolet (UV) irradiation in the ranges of 200–300 nm and 300–400 nm for 2 hr. Effects of temperature of 40°C and 55°C on non-UV-irradiated and UV-irradiated PE films processed by conventional methods were investigated and evaluated after 50 hr, 150 hr, and 350 hr of temperature exposure. The effects of UV wavelength range irradiation on the degradation were deduced. Measuring the dynamic moduli using a dynamic mechanical analyzer monitored the degradation. The decrease in average storage modulus was 62% with treatment at 55°C, higher than the 16% drop at 40°C for unirradiated samples after 350-hr exposure. Cross-linking in UV-exposed samples, characterized by an increase in dynamic modulus (stiffening), was observed followed by a reduction of storage modulus. Temperature treatment at 55°C together with 300–400-nm UV range irradiation resulted in the largest increase, i.e., 22% after 150 hr, followed by the largest reduction of storage modulus, i.e., 74.6% for a cumulative 350-hr exposure. 相似文献
78.
Jon E. Carlé Martin Helgesen Natalia K. Zawacka Morten V. Madsen Eva Bundgaard Frederik C. Krebs 《Journal of Polymer Science.Polymer Physics》2014,52(13):893-899
Two low‐band gap polymer series based on benzo[1,2‐b:4,5‐b′]dithiophene (BDT) and dithienylbenzothiadiazole, with different numbers of fluorine substituents on the 2,3,1‐benzothiadiazole unit, have been synthesized and explored in a comparative study of the photochemical stability and operational lifetime in flexible large area roll‐coated bulk heterojunction solar cells. The two polymer series have different side chains on the BDT unit, namely 2‐hexyldecyloxy (BDTHDO) ( P1–P3 ) or 2‐hexyldecylthiophene (BDTTHD) ( P4–P6 ). The photochemical stability clearly shows that the stability enhances along with the number of fluorine atoms incorporated on the polymer backbone. Fabrication of the polymer solar cells based on the materials was carried out in ambient atmosphere on a roll coating/printing machine employing flexible and indium‐tin‐oxide‐free plastic substrates. Solar cells based on the P4–P6 series showed the best performance, reaching efficiencies up to 3.8% for an active area of 1 cm2, due to an enhanced current compared to P1–P3 . Lifetime measurements, carried out according to international summit on OPV stability (ISOS), of encapsulated devices reveals an initial fast decay for P1–P6 in the performance followed by a much slower decay rate, still retaining 40–55% of their initial performance after 250 h of testing under ISOS‐L‐1 conditions. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 893–899 相似文献
79.
综述了温度对生命体寿命的作用,包括温度参与调节特定基因表达和细胞信号传导通路,温度对能量代谢、氧化还原水平、免疫功能和热量限制的影响。介绍了一种将温度系数引入死亡率定律的假设,以此计算温度与寿命之间的关系,为探究温度对寿命的直接影响提供参考和依据。 相似文献
80.
Jared M. Schwartz Oluwadamilola Phillips Anthony Engler Alexandra Sutlief Jihyun Lee Paul A. Kohl 《Journal of polymer science. Part A, Polymer chemistry》2017,55(7):1166-1172
Low ceiling temperature, thermodynamically unstable polymers have been troublesome to synthesize and keep stable during storage. In this study, stable poly(phthalaldehyde) has been synthesized with BF3‐OEt2 catalyst. The role of BF3 in the polymerization is described. The interaction of BF3 with the monomer is described and used to maximize the yield and molecular weight of poly(phthalaldehyde). Various Lewis acids were used to investigate the effect of catalyst acidity on poly(phthalaldehyde) chain growth. In situ nuclear magnetic resonance was used to identify possible interactions formed between BF3 and phthalaldehyde monomer and polymer. The molecular weight of the polymer tracks with polymerization yield. The ambient temperature stability of poly(phthalaldehyde) was investigated and the storage life of the polymer has been improved. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 55, 1166–1172 相似文献