全文获取类型
收费全文 | 1705篇 |
免费 | 65篇 |
国内免费 | 103篇 |
专业分类
化学 | 1644篇 |
晶体学 | 9篇 |
力学 | 5篇 |
综合类 | 22篇 |
数学 | 5篇 |
物理学 | 188篇 |
出版年
2024年 | 9篇 |
2023年 | 31篇 |
2022年 | 87篇 |
2021年 | 78篇 |
2020年 | 69篇 |
2019年 | 44篇 |
2018年 | 26篇 |
2017年 | 52篇 |
2016年 | 75篇 |
2015年 | 66篇 |
2014年 | 54篇 |
2013年 | 96篇 |
2012年 | 123篇 |
2011年 | 99篇 |
2010年 | 80篇 |
2009年 | 92篇 |
2008年 | 75篇 |
2007年 | 99篇 |
2006年 | 66篇 |
2005年 | 77篇 |
2004年 | 74篇 |
2003年 | 64篇 |
2002年 | 49篇 |
2001年 | 45篇 |
2000年 | 38篇 |
1999年 | 25篇 |
1998年 | 32篇 |
1997年 | 14篇 |
1996年 | 26篇 |
1995年 | 24篇 |
1994年 | 7篇 |
1993年 | 14篇 |
1992年 | 15篇 |
1991年 | 9篇 |
1990年 | 9篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1982年 | 3篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有1873条查询结果,搜索用时 15 毫秒
91.
92.
丙烯酸盐喷膜防水材料在酸碱溶液浸润和冻融条件下的耐久性能是该类材料在工程应用中较难回避的实际问题,论文采用酸性介质(0.2%的H2SO4溶液)和碱性介质(0.1%NaOH+饱和Ca(OH)2溶液)对该材料进行饱和浸泡并进行冻融循环后,研究了该材料的吸水性、断裂拉伸强度和拉断伸长率的变化规律。试验结果表明:喷膜防水材料在侵蚀-冻融循环作用下,其拉断伸长率和断裂拉伸强度显著降低,且酸性介质对材料拉伸性能的影响较大;材料耐低温冰冻能力较强,耐高温能力较差。反映出丙烯酸盐喷膜防水材料在低温冰冻和碱性介质中耐久性较好,不建议在高温和酸性介质条件下使用。 相似文献
93.
密闭微波消解-冷原子荧光光谱法测定蔬菜中的痕量汞 总被引:1,自引:0,他引:1
采用硝酸和过氧化氢体系,密闭微波消解,冷原子荧光光谱法测定蔬菜中的痕量汞,选择0.3g/L硼氢化钾溶液为还原剂,硝酸溶液(1 99)为酸介质。测定结果表明汞浓度在0~1μg/L范围线性良好,相关系数大于0.9990,汞的加标回收率为90.2%~99.6%,测定结果的相对标准偏差均小于4%,检出限为0.0058μg/L。 相似文献
94.
为准确定量土壤硒总量,提出以逆王水(1+1)-石墨消解法消解土壤,氢化物原子荧光光谱法(HG-AFS)测定土壤总硒含量的方法.其中,对消解方式、消解时间和仪器条件进行了探讨,确定最优检测条件.称取0.2 g土壤样品加入5 mL逆王水(1+1),于石墨消解仪120℃消解1.5 h,冷却至室温后用超纯水定容至25 m L,... 相似文献
96.
97.
98.
Glutamic acid (H2glu) and its lithium, sodium
and ammonium monosalts were submitted to thermal analysis using thermogravimetry
(TG) and differential thermal analysis (DTA). The main goal of these studies
was to compare the relative thermal stability and to evaluate the effect of
the counter ion in the thermal decomposition pathways. Salts were obtained
by direct neutralization of the purified acid with LiOH, NaOH or NH4OH
and were characterized by elemental analysis (C, H and N) and IR spectroscopy.
Decomposition occurred after conversion to the pyroglutamic acid or the respective
pyroglutamates and ammonium salt loosing NH3 being
converted to H2glu before decomposition. 相似文献
99.
Evaluation of the aerobic composting process of winery and distillery residues by thermal methods 总被引:1,自引:0,他引:1
F.C. Marhuenda-Egea E. Martínez-Sabater A. Sánchez-Sánchez M.A. Bustamante M.D. Pérez-Murcia 《Thermochimica Acta》2007,454(2):135-143
The possibility of using thermal analysis for a quick characterization of chemical changes was tested in the organic matter from composting materials. Differential thermal analysis (DTA), thermogravimetry (TG) and the first derivative of the TG (DTG) were calculated in oxidizing conditions on compost samples obtained from three composting piles. The composting piles were made by mixing winery and distillery residues with sewage sludge (pile 1), with cow manure (pile 2) and hen droppings (pile 3). The temperature values in the pile 1 showed a different evolution during the thermophilic stage of the composting process in relation to the piles 2 and 3. The thermophilic stage for pile 1 was 17 days, meanwhile for the piles 2 and 3 were around 80 and 110 days, respectively, and probably pile 1 was not well composted. The curves of ion current of CO2 have been recorded in order to shed light on changes occurring in organic matter during composting. Particularly DTG curves allowed us to distinguish between well (piles 2 and 3) and poor (pile 1) stabilized organic matter. The energy released was calculated for each sample by integrating the DTA curves and these results are agreed with the previous hypothesis. Information deriving from weight losses, registered by the TG and DTG curves, enables to follow the evolution state of the organic matter and therefore changes in its stability. These data could determine the final point of the composting process of winery and distillery residues and then reduce the time for compost harvest. 相似文献
100.