全文获取类型
收费全文 | 145881篇 |
免费 | 25353篇 |
国内免费 | 15053篇 |
专业分类
化学 | 114678篇 |
晶体学 | 1586篇 |
力学 | 7064篇 |
综合类 | 837篇 |
数学 | 16106篇 |
物理学 | 46016篇 |
出版年
2024年 | 391篇 |
2023年 | 2293篇 |
2022年 | 4116篇 |
2021年 | 4493篇 |
2020年 | 5553篇 |
2019年 | 6506篇 |
2018年 | 4911篇 |
2017年 | 4373篇 |
2016年 | 8428篇 |
2015年 | 8476篇 |
2014年 | 9652篇 |
2013年 | 12118篇 |
2012年 | 12613篇 |
2011年 | 12247篇 |
2010年 | 9765篇 |
2009年 | 9443篇 |
2008年 | 9317篇 |
2007年 | 8060篇 |
2006年 | 7399篇 |
2005年 | 6496篇 |
2004年 | 5306篇 |
2003年 | 4393篇 |
2002年 | 4913篇 |
2001年 | 3764篇 |
2000年 | 3433篇 |
1999年 | 2642篇 |
1998年 | 1972篇 |
1997年 | 1738篇 |
1996年 | 1716篇 |
1995年 | 1499篇 |
1994年 | 1390篇 |
1993年 | 1118篇 |
1992年 | 991篇 |
1991年 | 897篇 |
1990年 | 762篇 |
1989年 | 565篇 |
1988年 | 448篇 |
1987年 | 380篇 |
1986年 | 378篇 |
1985年 | 315篇 |
1984年 | 210篇 |
1983年 | 182篇 |
1982年 | 143篇 |
1981年 | 91篇 |
1980年 | 66篇 |
1979年 | 35篇 |
1978年 | 30篇 |
1976年 | 29篇 |
1975年 | 30篇 |
1957年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
A series of heat energy storage microcapsules was prepared using melamine-formaldehyde resin as the shell material and the mechanical properties of the shell were investigated. A phase change material whose melting point was 24 °C was used as core and the quantity of heat involved in phase transition was 225.5 J/g. Average diameter of the microcapsules varied from 5 to 10 μm, and the globular surface was smooth and compact. The mechanical properties of the shell were evaluated by observing the surface morphological structure change after application of pressure by means of scanning electron microscopy. When the mass ratio of the core and shell material is 3:1, a yield point of about 1.1×105 Pa was found and when the compression was increased beyond this point the microcapsules showed plastic behavior. This has been attributed to the cross-link density and to the high degree of reaction of the shell material. Different yield points subsequently reflected differences in the mechanical behavior. It was also found that the mechanical intensity of double-shell microcapsules was better than that of single shelled ones. 相似文献
992.
GuoXiangCHENG GuangLingPEI LingGangZENG LiYongZHANG ChaoLIU 《中国化学快报》2004,15(2):242-245
In this paper, the surface imprinted cross-linked polystyrene beads were prepared via suspension polymerization with styrene (St), divinylbezene (DVB), polyvinyl alcohol (PVA1788),the mixture of Span 85 and xylene or the mixture of Span 85 and paraffin as monomer,cross-linking agent, dispersion stabilizer and templates, respectively. The results indicate that there are dense cavities on the surface of beads, and the diameter and density of cavity are related with the composition and amount of emulsion template. The forming mechanism of cavity from thermodynamics and dynamics was proposed. 相似文献
993.
994.
In this review, we check out the number of published literature in the field of ECL biosensors trends during nearly a decade, and compare the research status of four different types of biosensors; summarize the application forms of nanomaterials in ECL biosensor. We have an overview of the building patterns and application example of the four main types of biosensors in the paper. 相似文献
995.
Xin Sheng Li Yao Jun Zhang Qin Xin Chun Xin Ji Yan Fen Miao Li Wang 《Reaction Kinetics and Catalysis Letters》1996,57(1):177-182
Volumetric H2-uptake measurements on an Mo2N (79 m2g–1) sample reduced at 673 K have been carried out and the uptake isotherms in the temperature range of 308–623 K have been determined. Both the total and reversible hydrogen uptake increased with the uptake temperature. The irreversible hydrogen uptake increased abruptly when the uptake temperature was raised up to 423 K. The maximum of irreversible hydrogen uptake was measured at 473 K. The HIR/Mo ratio calculated from the uptakes obtained in the temperature range of 308–623 K varies in the range of 0.0010–0.0202. One possible mechanism for hydrogen adsorption is proposed to be heterolytic dissociation on Mo-N paris, in which the molybdenum atoms are in unsaturated coordination. 相似文献
996.
用ab initio能量解析梯度法,在UHF(RHF)/3-21G水平上优化得到AlCn,AlCn+(n=1~3)的四十三个构型,在RHF(UHF)/3-21G水平上优化得到AlC4,AlC4+的二十六个构型,CISD能量.从能量角度所研究的AlCn,AlCn+(n=1~4)构型中,最稳定的构型均是线性构型,且Al全都在端点上,同文献报导的理论和实验结果相一致.此外,还研究了原子簇的离子化能,原子平均结合能以及原子簇的碎片化通道和碎片化能,并计算了上述最稳定构型的谐振动光谱常数. 相似文献
997.
三溴偶氮胂催化光度法测定痕量铁 总被引:19,自引:2,他引:19
本文研究了硫酸介质中痕量 Fe(Ⅲ)催化加速抗坏血酸、溴酸钾和三溴偶氮胂之间的褪色反应及动力学条件,建立了动力学光度法测定痕量Fe(Ⅲ)的新方法.方法灵敏度为1.82×10~(-12)g·ml~(-1).测定范围为Fe(Ⅲ)0~30ng/25ml.已用于人发和食品中痕量铁的测定.结果满意. 相似文献
998.
999.
本文报导的方法是在南京大学高鸿教授研究的K_3Fe(CN)_6示波极谱滴定法(在PH8的K_2HPO_4—KH_2PO_4—KBr底液中,用0.04660mol/LK_3Fe(CN)_6标准溶液对纯抗坏血酸测定)的基础上,考虑到L—抗坏血酸(以下简称V_e)在碱性、中性介质中稳定性差,如用于V_e含量很微的果蔬测定,对结果影响大。本文改为H_2C_2O_4—KBr的酸性介质作底液,用 相似文献
1000.
Wei Luo Xiang Kai Fu Li Hua Ma 《中国化学快报》2007,18(7):883-886
The high quality TiO2, MoO3-doped WO3 electrochromic film was prepared by the sol–gel method for the first time. The sol, which has hydrogen peroxide (H2O2) and oxalic acid (H2C2O4), was very stable at room temperature and quite suitable for the deposition of films. The WO3 electrochromic film prepared from this doped sol had excellent performance, such as short response time, no cracks, good adhesion to the substrate, high coloring efficiency and longevity of service. 相似文献