全文获取类型
收费全文 | 8855篇 |
免费 | 1345篇 |
国内免费 | 1322篇 |
专业分类
化学 | 6784篇 |
晶体学 | 144篇 |
力学 | 490篇 |
综合类 | 78篇 |
数学 | 880篇 |
物理学 | 3146篇 |
出版年
2024年 | 50篇 |
2023年 | 196篇 |
2022年 | 372篇 |
2021年 | 386篇 |
2020年 | 456篇 |
2019年 | 454篇 |
2018年 | 332篇 |
2017年 | 368篇 |
2016年 | 432篇 |
2015年 | 466篇 |
2014年 | 531篇 |
2013年 | 702篇 |
2012年 | 746篇 |
2011年 | 811篇 |
2010年 | 575篇 |
2009年 | 499篇 |
2008年 | 589篇 |
2007年 | 463篇 |
2006年 | 424篇 |
2005年 | 354篇 |
2004年 | 270篇 |
2003年 | 238篇 |
2002年 | 275篇 |
2001年 | 191篇 |
2000年 | 170篇 |
1999年 | 139篇 |
1998年 | 115篇 |
1997年 | 107篇 |
1996年 | 107篇 |
1995年 | 107篇 |
1994年 | 106篇 |
1993年 | 88篇 |
1992年 | 62篇 |
1991年 | 52篇 |
1990年 | 47篇 |
1989年 | 50篇 |
1988年 | 30篇 |
1987年 | 27篇 |
1986年 | 29篇 |
1985年 | 38篇 |
1984年 | 20篇 |
1983年 | 15篇 |
1982年 | 10篇 |
1981年 | 10篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1959年 | 2篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
972.
973.
The influences of pH and NaCl concentration of dipping solutions and the pH and NaCl concentration of disintegration solutions on the disintegration behaviors of poly(4-vinylpyridiniomethanecarboxylate) (PVPMC)/poly(sodium 4-styrenesulfonate) (PSS) (PVPMC/PSS) multilayer films were investigated by ultraviolet-visible spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FT-IR), quartz crystal microbalance (QCM) and atomic force microscopy (AFM). It was found that the disintegration rates and degrees of PVPMC/PSS multilayer films in neutral water could be well controlled by changing pH of dipping solutions and immersion time during the disintegration process. Furthermore, PVPMC/PSS multilayer films could be disintegrated completely and rapidly in pH 8 alkali solution or physiological condition (i.e., 0.15 M NaCl solution). The controllable disintegration of PVPMC/PSS multilayer films was then utilized to fabricate PEC/PSS free-standing multilayer films, in which PEC was a positively charged polyelectrolyte complex made from excessive poly(diallyldimethylammonium) (PDDA) and PSS. The experimental results indicated that the disintegration rates of PVPMC/PSS sacrificial sublayer strongly affected the integrity of the resultant PEC/PSS free-standing multilayer films. Only free-floating PEC/PSS was released from neutral water by disintegrating PVPMC/PSS multilayer sublayers. However, large size flat and tube-like PEC/PSS free-standing multilayer films with good mechanical properties were obtained facilely from pH 8 alkali solution and 0.15 M NaCl solution, respectively. The preparation of such free-standing films at physiological condition may be useful in the biological or medical application. 相似文献
974.
Dr. Xin Fang Ying Tong Di Yu Zhang Dr. Zhi Ping Xu Prof. Yang Lu Qian Qian Chen Prof. Qi Tai Zheng Prof. Dr. Xiao Jiang Hao 《Angewandte Chemie (International ed. in English)》2015,54(19):5592-5595
Perforalactone A ( 1 ), a new 20S quassinoid with a unique cagelike 2,4‐dioxaadamantane ring system and a migrated side chain, was isolated from the plant Harrisonia perforata together with two biosynthetically related new quassinoids. The structures of these natural products were elucidated by NMR spectroscopy, X‐ray diffraction analysis, computational modeling, and the CD excitation chirality method. The compounds exhibited notable biological properties, including insecticidal activity against Aphis medicaginis Koch and antagonist activity at the nicotinic acetylcholine receptor of Drosophila melanogaster. The structural features of these compounds may be related to their promising biological characteristics. Their biosynthesis and an alternative origin of quassinoid‐type natural products are also discussed. 相似文献
975.
976.
977.
本用提高样品蒸发速率的方法提高氧化钪中难熔杂质光谱分析灵敏度。采用一种特殊的阴极设计,配合使用N2+Ar气氛控制,在旋流气室中放电激发,取样仅5mg的条件下,光谱测定氧化钪中难烷质Ti,Zr,Mo,W,V灵敏度可达(1-3)×10^-4%。测定的相对标准偏差为9%-27%。 相似文献
978.
FeO/RGO复合材料的制备及其电化学性能研究 《燃料化学学报》2017,45(3):362-369
以改进Hummers法合成的氧化石墨烯(GO)为前驱体,通过水热法结合烧结工艺制备了四氧化三铁/还原氧化石墨烯(Fe_3O_4/RGO)复合材料。利用X射线衍射(XRD)、拉曼光谱(Raman)、扫描电镜(SEM)、透射电镜(TEM)等手段对复合材料的理化性能进行表征;通过充放电测试、循环伏安(CV)和电化学阻抗谱(EIS)等技术,综合考察了材料的储锂性能及电化学性能增强机制。结果表明,在200和600 m A/g电流密度下,Fe_3O_4/RGO复合负极循环60次后的放电比容量分别保持在709和479 mAh/g,表现出良好的倍率性能;相较于纯Fe_3O_4负极,复合负极呈现出更优异的锂电性能,其电化学性能的改善得益于RGO能增强材料的电导性和结构稳定性。 相似文献
979.
Dongxia Nie Ying Liang Tianshu Zhou Qian Sun Litong Jin 《International journal of environmental analytical chemistry》2013,93(7):832-843
FDU-15 is a hexagonal mesoporous material with nanometer-sized, highly ordered arrays and large special surface area. In this work, FDU-15-Pt with 2.0%, 5.0% and 8.0% Pt loading were synthesised and used for electrochemical detection of trace nitroaromatic compounds (NACs). The FDU-15-Pt samples were characterised by CO Chemisorption, transmission electron microscopy (TEM) and X-ray diffraction (XRD). It has been demonstrated that FDU-15-Pt with 2.0% Pt loading has the smallest Pt particle size of 2.9?nm, highest Pt metal dispersion of 37.7% and largest Pt metal surface area of 21.36?m2?g?1. The FDU-15-Pt/PDDA modified electrode were assembled by electrostatic adsorption of Poly (diallyldimethylammonium chloride) (PDDA) and FDU-15-Pt. The 2.0% FDU-15-Pt modified sensor showed higher selectivity for NACs than those of 5.0% and 8.0% FDU-15-Pt, which were verified by electrochemical experiments. A linear response over TNT concentration ranging from 8.8?×?10?9?M to 1.2?×?10?5 M was exhibited with a low detection limit of 2.9?×?10?9?M (S/N?=?3). Moreover, the proposed 2.0% FDU-15-Pt/PDDA modified sensor has been applied to the detection of NACs in spiked environmental water samples and shows promise for fast and accurate determination of trace NACs in real samples. 相似文献
980.
CdS/石墨烯纳米复合物的可见光催化效率和抗光腐蚀行为 总被引:1,自引:0,他引:1
制备了一系列CdS纳米晶/石墨烯(CdS/GR)复合物,并在可见光照条件下评价了其光催化降解亚甲基蓝的光催化效率和抗光腐蚀行为. 研究表明,石墨烯的引入加速了CdS纳米晶(NCs)光生电子的迁移速率,抑制了其光生电子-空穴的复合,有效改善了其光催化降解有机污染物的性能. CdS/GR复合物中的石墨烯含量显著影响其光催化效率,其中石墨烯含量为4.6%的光催化剂效率最高,其光电流是CdS NCs的2.3倍. 利用光电化学和X射线衍射技术进一步证实,石墨烯的引入抑制了CdS NCs光腐蚀的发生,提高了CdS/GR复合物的光催化稳定性. 相似文献