全文获取类型
收费全文 | 39711篇 |
免费 | 6588篇 |
国内免费 | 4098篇 |
专业分类
化学 | 27401篇 |
晶体学 | 451篇 |
力学 | 2591篇 |
综合类 | 337篇 |
数学 | 4719篇 |
物理学 | 14898篇 |
出版年
2024年 | 67篇 |
2023年 | 790篇 |
2022年 | 1131篇 |
2021年 | 1287篇 |
2020年 | 1598篇 |
2019年 | 1448篇 |
2018年 | 1246篇 |
2017年 | 1195篇 |
2016年 | 1854篇 |
2015年 | 1737篇 |
2014年 | 2092篇 |
2013年 | 2751篇 |
2012年 | 3476篇 |
2011年 | 3553篇 |
2010年 | 2441篇 |
2009年 | 2313篇 |
2008年 | 2624篇 |
2007年 | 2247篇 |
2006年 | 2269篇 |
2005年 | 1756篇 |
2004年 | 1411篇 |
2003年 | 1172篇 |
2002年 | 1007篇 |
2001年 | 833篇 |
2000年 | 837篇 |
1999年 | 939篇 |
1998年 | 806篇 |
1997年 | 715篇 |
1996年 | 722篇 |
1995年 | 626篇 |
1994年 | 561篇 |
1993年 | 508篇 |
1992年 | 427篇 |
1991年 | 368篇 |
1990年 | 351篇 |
1989年 | 256篇 |
1988年 | 198篇 |
1987年 | 152篇 |
1986年 | 156篇 |
1985年 | 107篇 |
1984年 | 73篇 |
1983年 | 72篇 |
1982年 | 59篇 |
1981年 | 38篇 |
1980年 | 24篇 |
1979年 | 9篇 |
1976年 | 11篇 |
1975年 | 10篇 |
1973年 | 8篇 |
1957年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
91.
Density functional method (DFT) (B3p86) of Gaussian98 has been used to optimize the structure of the Tc_2 molecule. The result shows that the ground state for Tc_2 molecule is an 11-multiple state and its electronic configuration is {}^{11}Σ_g^-, which shows the spin polarization effect of Tc_2 molecule of a transition metal element for the first time. Meanwhile, we have not found any spin pollution because the wavefunction of the ground state does not mingle with wavefunctions of higher energy states. So, that the ground state for Tc_2 molecule is an 11-multiple state is indicative of the spin polarization effect of Tc_2 molecule of a transition metal element: that is, there exist 10 parallel spin electrons. The non-conjugated electron is greatest in number. These electrons occupy different spacious tracks, so that the energy of Tc_2 molecule is minimized. It can be concluded that the effect of parallel spin of the Tc_2 molecule is larger than the effect of the conjugated molecule, which is obviously related to the effect of electron d delocalization. In addition, the Murrell--Sorbie potential functions with the parameters for the ground state {}^{11}Σ_g^- and other states of Tc_2 molecule are derived. Dissociation energy D_e for the ground state of T_{c2} molecule is 2.266eV, equilibrium bond length R_e is 0.2841nm, vibration frequency ω_e is 178.52cm^{-1}. Its force constants f_2, f_3, and f_4 are 0.9200aJ·nm^{-2}, --3.5700aJ·nm^{-3}, 11.2748aJ·nm^{-4} respectively. The other spectroscopic data for the ground state of Tc_2 molecule ω_eχ_e, B_e, α_e are 0.5523cm^{-1}, 0.0426cm^{-1}, 1.6331×10^{-4}cm^{-1} respectively. 相似文献
92.
Shujiang Tu Fang Fang Tuanjie Li Songlei Zhu Xiaojing Zhang 《Journal of heterocyclic chemistry》2005,42(4):707-710
A series of pyrimidoquinoline derivatives were synthesized through one‐pot condensation of 2,6‐diaminopyrimidin‐4‐one, aldehyde and cyclic a 1,3‐dicarbonyl compound in glycol under microwave irradiation without catalyst. The protocol in the absence of catalyst has the advantage of good yield (87‐95%), short reaction time (4‐7 min) and an environmentally friendly technique. 相似文献
93.
For an arbitrary bounded closed set E in the complex plane with complement Ω of finite connectivity, we study the degree of convergence of the lemniscates in Ω. 相似文献
94.
95.
5-Perfluorophenyl 4,5-dihydro-1H-pyrazoles were synthesized from 1,3-dipolar cycloaddition reaction of perfluorobenyl 2,4,6-triisopropylbenzenesulfonylhydrazone and α,β-unsaturated carbonyl compounds or acrylonitrile in THF or water. It was worthy to note that better results were obtained when water was employed as the solvent, which was considered as an effective, economic and environmentally friendly method to synthesize these pyrazole derivatives. 相似文献
96.
Zhengmao Zhu 《Applied Surface Science》2005,252(2):303-310
The reactivity of the surface of poly(ethylene terephthalate) (PET) film under 172 nm UV irradiation (xenon excimer lamp) towards nitrogen-borne 1-octene, n-nonane and heptafluorodecene vapor was investigated. Materials receiving from 0 to 24 J/cm2 of UV were examined by X-ray photoelectron spectroscopy (XPS), time of flight secondary ion mass spectroscopy (ToF/SIMS), water and mineral oil contact angle measurement and atomic force microscopy (AFM). A uniform nanoscale layer developed on PET surface attributed to the grafting reaction between photolytically-produced polymer radicals and vapor phase molecules. 相似文献
97.
从现有的PCDFs分子的正辛醇 /水分配系数 (logKow)实验数据出发 ,建立定量结构 性质关系方程(QSPR) .采用G98W程序包中的PM3方法对 13 5个多氯代二苯并呋喃 (PCDFs)分子和二苯并呋喃进行了优化计算 ,作业命令为 #pPM3optfreqscf(conver =9) ,以计算所得的分子轨道能量、碳原子电荷作为PCDFs分子结构描述符 ,运用多元线性回归技术建立了PCDFs的logKow与分子结构描述符的四元方程 ,最优相关系数为 0 .95 0 7,标准偏差为 0 .173 7,经检验该模型的稳健性好 ,并对未有实验数据的 85个PCDFs的logKow进行预测 相似文献
98.
Liang Liao Yi Pang Liming Ding Frank E. Karasz 《Journal of polymer science. Part A, Polymer chemistry》2003,41(20):3149-3158
A soluble cyano‐substituted poly[(1,3‐phenylene vinylene)‐alt‐(1,4‐phenylene vinylene)] derivative ( 9 ) was synthesized and characterized. Comparison between 9 and its model compound ( 10 ) showed that the chromophore in 9 remained to be well defined as a result of a π‐conjugation interruption at adjacent m‐phenylene units. The attachment of a cyano substituent only at the β position of the vinylene allowed the maximum electronic impact of the cyano group on the optical properties of the poly(p‐phenylene vinylene) material. At a low temperature (?108 or ?198 °C), the vibronic structures of 9 and 10 were partially resolved. The absorption and emission spectra of a film of 9 were less temperature‐dependent than those of a film of 10 , indicating that the former had a lower tendency to aggregate. A light‐emitting diode (LED) based on 9 emitted yellow light (λmax ≈ 578 nm) with an external quantum efficiency of 0.03%. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3149–3158, 2003 相似文献
99.
报道了硅基有机微腔的电致发光(EL).该微腔由上半透明金属膜、中心有源多层膜和多孔硅分布Bragg反射镜(PS DBR)组成.半透明金属膜由Ag(20nm)构成,充当发光器件的负电极和微腔的上反射镜.有源多层膜由Al (1 nm) / LiF(05 nm) /Alq3/Alq3:DCJTB/NPB/CuPc/ITO/SiO2组成,其中的Al/LiF为电子注入层,ITO为正电极,SiO2为使正、负电极电隔离的介质层.该PS DBR是采用设备简单、成本低廉且非常省时的电化学腐蚀法用单晶Si来制备的;该PS
关键词:
电化学腐蚀
电致发光
窄峰发射
硅基有机微腔 相似文献
100.