全文获取类型
收费全文 | 8697篇 |
免费 | 1405篇 |
国内免费 | 1258篇 |
专业分类
化学 | 6693篇 |
晶体学 | 145篇 |
力学 | 472篇 |
综合类 | 77篇 |
数学 | 877篇 |
物理学 | 3096篇 |
出版年
2024年 | 50篇 |
2023年 | 198篇 |
2022年 | 369篇 |
2021年 | 386篇 |
2020年 | 452篇 |
2019年 | 449篇 |
2018年 | 326篇 |
2017年 | 364篇 |
2016年 | 423篇 |
2015年 | 461篇 |
2014年 | 517篇 |
2013年 | 692篇 |
2012年 | 744篇 |
2011年 | 806篇 |
2010年 | 568篇 |
2009年 | 493篇 |
2008年 | 583篇 |
2007年 | 461篇 |
2006年 | 420篇 |
2005年 | 353篇 |
2004年 | 272篇 |
2003年 | 234篇 |
2002年 | 270篇 |
2001年 | 189篇 |
2000年 | 169篇 |
1999年 | 135篇 |
1998年 | 103篇 |
1997年 | 103篇 |
1996年 | 103篇 |
1995年 | 105篇 |
1994年 | 97篇 |
1993年 | 81篇 |
1992年 | 56篇 |
1991年 | 48篇 |
1990年 | 44篇 |
1989年 | 50篇 |
1988年 | 29篇 |
1987年 | 25篇 |
1986年 | 28篇 |
1985年 | 36篇 |
1984年 | 19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 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
A structure and kinetic stability study on some complexes with the general formula MN5, where M are the alkali-metal atoms, Li, Na, K, and Rb, has been carried by using hybrid density functional methods. Complex B (C2v) with two points of attachment to the N5 ring is the most energetically favored for all metals considered here. Pyramidal structures A (C5v) are kinetically unstable and they rapidly rearrange to the most stable planar structures B. At the QCISD(T)/6-311 + G*//B3LYP/6-311 + G* + ZPE (B3LYP/6-311 + G*) level, the decomposition barrier heights of LiN5-B, NaN5–B, KN5-B, and RbN5-B are predicted to be 19.9, 22.0, 22.5, and 23.0 kcal/mol, respectively. In addition, the rate constants of the decomposition reaction MN5-B MN3 + N2 (M + Li, Na, K, and Rb) are also predicted using conventional transition state theory and canonical variational transition state theory, respectively. 相似文献
152.
High-energy-density batteries are in urgent need to solve the ever-increasing energy storage demand for portable electronic devices, electric vehicles, and renewable solar and wind energy systems. Alkali metals, typically lithium(Li), sodium(Na) and potassium(K), are considered as the promising anode materials owing to their low electrochemical potential, low density, and high theoretical gravimetric capacities. However, the problem of dendrite growth of alkali metals during their plating/stripping process will lead to low Coulombic efficiencies, a short lifespan and huge volume expansion, eventually hindering their practical commercialization. To resolve this issue, a very effective approach is engineering the anodes on structured current collectors. This review summarizes the development of the alkali metal batteries and discusses the recent advances in rational design of anode current collectors. First, the challenges and strategies of suppressing alkali-metal dendrite growth are presented. Then the special attention is paid to the novel current collector design for dendrite-free alkali metal anodes. Finally, we give conclusions and perspective on the current challenges and future research directions toward advanced anode current collectors for alkali metal batteries. 相似文献
153.
LiLi Liu WanHong Ma WenJing Song ChunCheng Chen Jun Lin JinCai Zhao XinHua Qian ShiBo Zhang 《中国科学:化学(英文版)》2007,50(6):770-775
This study investigated the visible-light catalysis mediated by zeolite NaY on the oxidation of dyes with H2O2. The results demonstrated that zeolite NaY acts as a sink for the electron from the photo-excited dye in the heterogeneous catalysis. Furthermore, the electron can effectively activate H2O2 to produce ·OH radical that is a powerful oxidant for the oxidation of dye at room temperature. The effects of the framework topology, Si/Al ratio, and exchangeable cation of the zeolite on the oxidation of various dyes were also shown. 相似文献
154.
采用水热法合成了一种新的三维配位聚合物[Zn6(bta)4(2,2′-bipy)3](H3bta=1,3,5-苯三乙酸;2,2′-bipy=2,2′-二联吡啶),并通过X射线单晶结构分析、红外光谱、元素分析和热重分析对该配合物进行了表征.结构分析数据表明,该配合物属单斜晶系,Cc空间群,晶胞参数a=1·7714(4)nm,b=2·4391(5)nm,c=1·7120(3)nm,β=104·39(3)°,Z=4,V=7·165(2)nm3,Dc=1·722g/cm3,μ=2·065mm-1,F(000)=3768,R1=0·0645,wR2=0·1424.荧光光谱结果表明,配合物具有良好的荧光性质. 相似文献
155.
IntroductionItiswellknownthatmetallocenesactivatedwithmethylaluminoxane (MAO)arehighlyactivehomogeneousZiegler Nattacatalyststhatproducepolyolefinwithcon trolledstereoregularityandnarrowmolecularweightdistri bution ,1 4 however,themolecularweightofthepolym… 相似文献
156.
157.
HUA Guo-Pinga ZHU Xiao-Tongb ZHANG Jin-Pengb XU Jia-Ningb WANG Qianb JI Shun-Junc ZHANG Yongc TU Shu-Jiangb② a 《结构化学》2006,25(5):599-603
1 INTRODUCTION Various quinolone derivatives are known to dis- play interesting biological properties ranging from microbial activity to cytotoxicity[1]. They have been reported as antiviral (HIV-1)[2] and antitumor agents[3] as well as used as tubulin[4], topoisomerase[5] and thrombocyte inhibitors[6]. As a member of the quino- lone family, substituted N-phenyl-2-quinolones re-present the structural basis of many biologically active compounds, such as protein kinase inhibitors, immunodu… 相似文献
158.
159.
Shan Qian Li Hai Lei Tang Jin Cheng Yang Yong Wu 《中国化学快报》2007,18(3):261-262
An optically active intermediate 5 for A-ring of 19-nor-1a,25-dihydroxyvitamin D3 2 has been synthesized in five steps, starting from readily available, inexpensive D( )-xylose 6 with good yield. 相似文献
160.
A very sensitive electroanalytical method was employed to determine bergenin in phosphate buffer with a pH of 6.0, bergenin was accumulated at a 4-(2-pyridylazo)-resorcinol (PAR) polymer film modified glassy carbon electrode (GCE) surface under the condition of open-circuit. In the following anodic sweep from −0.4 to 0.8 V, bergenin adsorbed at the PAR polymer film modified electrode surface, was oxidized and yielded a sensitive oxidation peak at 0.595 V. Due to its unique structure and extraordinary properties, the PAR polymer film shows higher accumulation efficiency toward bergenin compared with a bare GCE. Hence, the amount of bergenin at the PAR polymer film modified GCE surface increases significantly, and finally the oxidation peak current improves greatly. The experimental conditions, such as supporting electrolyte, pH value, accumulation time and scan rate, were optimized for the measurement of bergenin, and a sensitive electroanalytical method was proposed for bergenin determination. The oxidation peak current varies linearly with the concentration of bergenin over the range of 2.0 × 10−7 to 1.2 × 10−5 mol/L, and the detection limit is 2.0 × 10−8 mol/L after 3 min open-circuit accumulation. The relative standard deviation of the same electrode in 10 successive scans is 1.8% for 1.0 × 10−6 mol/L bergenin and 2.1% for interelectrodes, indicating excellent reproducibility. This new method was successfully demonstrated with bergenin tablets and diluted urine. 相似文献