全文获取类型
收费全文 | 23687篇 |
免费 | 4942篇 |
国内免费 | 6747篇 |
专业分类
化学 | 18151篇 |
晶体学 | 829篇 |
力学 | 1490篇 |
综合类 | 836篇 |
数学 | 2916篇 |
物理学 | 11154篇 |
出版年
2024年 | 33篇 |
2023年 | 369篇 |
2022年 | 735篇 |
2021年 | 887篇 |
2020年 | 1041篇 |
2019年 | 1040篇 |
2018年 | 940篇 |
2017年 | 1108篇 |
2016年 | 1104篇 |
2015年 | 1334篇 |
2014年 | 1648篇 |
2013年 | 2139篇 |
2012年 | 2215篇 |
2011年 | 2390篇 |
2010年 | 1962篇 |
2009年 | 1964篇 |
2008年 | 2195篇 |
2007年 | 1945篇 |
2006年 | 1729篇 |
2005年 | 1403篇 |
2004年 | 1123篇 |
2003年 | 827篇 |
2002年 | 842篇 |
2001年 | 800篇 |
2000年 | 792篇 |
1999年 | 554篇 |
1998年 | 320篇 |
1997年 | 208篇 |
1996年 | 224篇 |
1995年 | 184篇 |
1994年 | 191篇 |
1993年 | 188篇 |
1992年 | 156篇 |
1991年 | 118篇 |
1990年 | 99篇 |
1989年 | 103篇 |
1988年 | 80篇 |
1987年 | 68篇 |
1986年 | 69篇 |
1985年 | 53篇 |
1984年 | 42篇 |
1983年 | 36篇 |
1982年 | 28篇 |
1981年 | 23篇 |
1980年 | 7篇 |
1979年 | 19篇 |
1976年 | 5篇 |
1959年 | 6篇 |
1957年 | 5篇 |
1936年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
High‐Nuclear Organometallic Copper(I)–Alkynide Clusters: Thermochromic Near‐Infrared Luminescence and Solution Stability 下载免费PDF全文
Hong‐Yan Zhuo Dr. Hai‐Feng Su Zhao‐Zhen Cao Wei Liu Prof. Shu‐Ao Wang Lei Feng Dr. Gui‐Lin Zhuang Dr. Shui‐Chao Lin Prof. Mohamedally Kurmoo Prof. Chen‐Ho Tung Dr. Di Sun Prof. Lan‐Sun Zheng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(49):17619-17626
Cu(CF3COO)2 reacts with tert‐butylacetylene (tBuC≡CH) in methanol in the presence of metallic copper powder to give two air‐stable clusters, [CuI15(tBuC≡C)10(CF3COO)5]?tBuC≡CH ( 1 ) and [CuI16(tBuC≡C)12(CF3COO)4(CH3OH)2] ( 2 ). The assembly process involves in situ comproportionation reaction between Cu2+ and Cu0 and the formation of two different clusters is controlled by reactants concentration. The clusters consist of Cu15 and Cu16 cores co‐stabilized by strong by σ‐ and π‐bonded tert‐butylethynide and CF3COO? (together with methanol molecule in 2 ). Their stabilities in solution were confirmed using electrospray ionization mass spectrometry in which the cluster core remains intact for 1 in chloroform and acetone, and for 2 in acetonitrile. Strong thermochromic luminescence in the near infrared (NIR) region was observed in the solid‐state. Of particular interest, the emission maximum of 1 is red‐shifted from 710 nm at 298 K to 793 nm at 93 K, along with a 17‐fold fluorescence enhancement. In contrast, 2 exhibits red shift from 298 to 123 K followed by blue shift from 123 to 93 K. The emission wavelength was correlated with the structural parameters using variable‐temperature X‐ray single‐crystal analyses. The rich cuprophilic interaction plays a significant role in the formation of 3LMCT (tBuC≡C→Cux) excited state mixed with cluster‐centered (3CC) characters, which can be considerably influenced by temperature, leading to thermochromic luminescence. The present work provides 1) a new synthetic protocol for the high‐nuclear CuI–alkynyl clusters; 2) a comprehensive insight into the mechanism of thermochromic luminescence; 3) unusual emissive materials with the characters of NIR and thermochromic luminescence simultaneously. 相似文献
83.
84.
85.
86.
Is PdII‐Promoted σ‐Bond Metathesis Mechanism Operative for the PdPEPPSI Complex‐Catalyzed Amination of Chlorobenzene with Aniline? Experiment and Theory 下载免费PDF全文
Feiqun Wang Lei Zhu Yunfei Zhou Prof. Xiaoguang Bao Prof. Henry F. Schaefer III 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(10):4153-4161
Reduction of the Pd?PEPPSI precatalyst to a Pd0 species is generally thought to be essential to drive Buchwald–Hartwig amination reactions through the well‐ documented Pd0/PdII catalytic cycle and little attention has been paid to other possible mechanisms. Considered here is the Pd?PEPPSI‐catalyzed aryl amination of chlorobenzene with aniline. A neat reaction system was used in new experiments, from which the potentially reductive roles of the solvent and labile ligand of the PEPPSI complex in leading to Pd0 species are ruled out. Computational results demonstrate that anilido‐containing PdII intermediates involving σ‐bond metathesis in pathways leading to the diphenylamine product have relatively low barriers. Such pathways are more favorable energetically than the corresponding reductive elimination reactions resulting in Pd0 species and other putative routes, such as the PdII/PdIV mechanism, single electron transfer mechanism, and halide atom transfer mechanism. In some special cases, if reactants/additives are inadequate to reduce a PdII precatalyst, a PdII‐involved σ‐bond metathesis mechanism might be feasible to drive the Buchwald–Hartwig amination reactions. 相似文献
87.
88.
分别在有机碱三乙胺、三丙胺和三丁胺的作用下,使用2-羟基喹啉-4-羧酸(H2hqc)与EuCl3·6H2O反应制备了3种配合物Eu(Hhqc)3(TEL)、Eu(Hhqc)3(TPL)和Eu(Hhqc)3(TBL)。通过元素分析、热重分析、摩尔电导率、紫外光谱、荧光光谱、荧光寿命和量子产率等对配合物进行了表征。所有配合物均在580,592,613,654,702 nm附近产生5条谱带,为Eu3+的特征发射,归属为5D0→7FJ(J=0,1,2,3,4)能级间的跃迁,荧光寿命分别为2.22,3.29,3.31 ms,量子产率分别为0.011,0.019,0.028。随着有机胺碳链长度的增加,配合物的荧光强度依次增大,表明有机碱参与了配合物的分子组成。 相似文献
89.
90.
�� ������Է����� �������¾�������ƽ���� �� 《核聚变与等离子体物理》2015,35(3):233-239
The performance of the four strap ion cyclotron range of frequency (ICRF) antenna in EAST was studied by three dimensional electromagnetic code CST MWS. The coupling impedance with various frequencies, the distribution of current on straps and the power spectra for the three types of phases were calculated. The voltage breakdown and ICRF-related impurity were also studied. Simulation results show that the coupling impedance and power spectrum of the antenna design were reasonable, however, highest electric field, which is 3.61MV•m−1 for (0, 0, 0, 0) toroidal phasing at the local area, exceeds the empirical value of breakdown. After the structure size was optimized, the maximum of E-field was below the breakdown value, the results also show that the high radio frequency (RF) potential was close to the antenna limiter, the RF potential along total B-field in front of Faraday screens 10mm for (0, π, π, 0) phasing was one-third of that for (0, 0, π, π) phasing. 相似文献