全文获取类型
收费全文 | 8912篇 |
免费 | 1864篇 |
国内免费 | 2119篇 |
专业分类
化学 | 6604篇 |
晶体学 | 264篇 |
力学 | 769篇 |
综合类 | 289篇 |
数学 | 1097篇 |
物理学 | 3872篇 |
出版年
2024年 | 23篇 |
2023年 | 138篇 |
2022年 | 315篇 |
2021年 | 350篇 |
2020年 | 390篇 |
2019年 | 344篇 |
2018年 | 339篇 |
2017年 | 403篇 |
2016年 | 398篇 |
2015年 | 485篇 |
2014年 | 604篇 |
2013年 | 715篇 |
2012年 | 784篇 |
2011年 | 806篇 |
2010年 | 644篇 |
2009年 | 717篇 |
2008年 | 701篇 |
2007年 | 596篇 |
2006年 | 566篇 |
2005年 | 531篇 |
2004年 | 437篇 |
2003年 | 330篇 |
2002年 | 346篇 |
2001年 | 383篇 |
2000年 | 306篇 |
1999年 | 219篇 |
1998年 | 163篇 |
1997年 | 106篇 |
1996年 | 117篇 |
1995年 | 86篇 |
1994年 | 97篇 |
1993年 | 91篇 |
1992年 | 66篇 |
1991年 | 51篇 |
1990年 | 39篇 |
1989年 | 33篇 |
1988年 | 37篇 |
1987年 | 19篇 |
1986年 | 24篇 |
1985年 | 20篇 |
1984年 | 14篇 |
1983年 | 14篇 |
1982年 | 12篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 9篇 |
1965年 | 2篇 |
1964年 | 2篇 |
1962年 | 2篇 |
1960年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
961.
962.
A series of lanthanide coordination polymers, [LnIII(mal)(ox)0.5(H2O)2]·2H2O (Ln = Pr ( 1 ), Nd ( 2 ), and La ( 3 ); H2mal= maleic acid; H2ox = oxalic acid), were synthesized firstly by the reaction of LnIII nitrate salts with maleic anhydrid and oxalic acid under hydrothermal conditions and were characterized by elemental analysis, IR spectroscopy, and single‐crystal X‐ray diffraction. X‐ray diffraction analyses reveal that they are crystallized in orthorhombic space group Fddd. Lanthanide metal center atom (Ln) and its corresponding centrosymmtric atom link through two chelating/bridging bidentate carboxyl groups of maleic acid ligands to form an infinite inorganic rod‐shaped building unit. These rod‐shaped building units were linked to each other through the carbon atoms of the maleate anions on the [110] plane to form lanthanide‐maleic acid layers. The oxalic acid pillared lanthanide‐maleic acid layers with intersected channels by free water molecules consist of a 3D framework structure. The thermogravimetric analyses of 1 – 3 were discussed in detail. The courses of the thermal decomposition of complexes are similar. 相似文献
963.
A convenient route for the synthesis of 3,4-dihydrocoumarin derivates from salicylaldehyde derivates and 1,3-dicarbonyl compounds under solvent-free microwave irradiation conditions was described. In this way, a range of compounds was obtained in moderate to good yields in a short reaction time. 相似文献
964.
取代芳烃对呆鲦鱼急性毒性的QSAR研究 总被引:4,自引:0,他引:4
用20种取代芳烃化合物DFT-B3LYP/6-31G**和B3LYP/6-311G**全优化计算结构参数:分子最高占用和最低空轨道能(EHOMO和ELUMO)、分子次最高占用和次最低空轨道能(ENHOMO和ENLUMO)、分子总能量(ET)、氢原子所带的最高正电荷(Q H)、最负原子的静电荷(Q-)、分子偶极矩(μ)和分子体积(V),对呆鲦鱼急性毒性(-lgLC50)分别进行定量构效关系研究.结果表明:取代芳烃对呆鲦鱼的毒性与ENLUMO和V的相关系数分别为0.986和0.621;建立了20种取代芳烃化合物对呆鲦鱼急性毒性的构效关系式,预测值与实验值基本吻合. 相似文献
965.
966.
967.
Novel CdClOH sub‐nanocone crystals were successfully synthesized on a large scale by a facile solution‐based method using polymers as crystal growth modifiers. The crystals showed cone‐like morphology. Some factors affecting the morphology and size of the product, such as reaction temperature, concentrations of polyacrylamide (PAM), and pH value of the solution, were systematically studied. Experiments implied that polymer PAM played a key role in the formation of CdClOH sub‐nanocones. A possible formation mechanism of CdClOH sub‐nanocones was suggested based on nucleation‐etching process‐recrystallization in a mild aqueous solution. Furthermore, the as‐prepared CdClOH sub‐nanocones could be further transformed into CdS hollow sub‐nanocones by an anion‐exchange reaction. 相似文献
968.
969.
应用固体经验电子理论,并联系 G.Inden 的有序转变温度与原子间作用能的关系式,计算了 CuZnAl 记忆合金的 A_2到 B_2,B_2到 DO_3两种有序转变温度随合金元素变化的规律。计算得出的变化趋势与实验结果符合得相当好,表明所采用的理论模型可以说明 CuZnAl 合金的记忆性能和用来指导探索新的记忆合金。 相似文献
970.
In recent years,low-dimensional materials have received extensive attention in the field of electronics and optoelectronics.Among them,photoelectric devices based on photoconductive effect in low-dimensional materials have a broad development space.In contrast to positive photoconductivity,negative photoconductivity(NPC)refers to a phenomenon that the conductivity decreases under illumination.It has novel application prospects in the field of optoelectronics,memory,and gas detection,etc.In this paper,we review reports about the NPC effect in low-dimensional materials and systematically summarize the mechanisms to form the NPC effect in existing low-dimensional materials. 相似文献