全文获取类型
收费全文 | 23283篇 |
免费 | 4343篇 |
国内免费 | 3323篇 |
专业分类
化学 | 16790篇 |
晶体学 | 378篇 |
力学 | 1610篇 |
综合类 | 255篇 |
数学 | 2509篇 |
物理学 | 9407篇 |
出版年
2024年 | 38篇 |
2023年 | 463篇 |
2022年 | 598篇 |
2021年 | 794篇 |
2020年 | 1034篇 |
2019年 | 975篇 |
2018年 | 833篇 |
2017年 | 806篇 |
2016年 | 1170篇 |
2015年 | 1176篇 |
2014年 | 1406篇 |
2013年 | 1766篇 |
2012年 | 2241篇 |
2011年 | 2265篇 |
2010年 | 1574篇 |
2009年 | 1495篇 |
2008年 | 1639篇 |
2007年 | 1392篇 |
2006年 | 1349篇 |
2005年 | 1132篇 |
2004年 | 891篇 |
2003年 | 719篇 |
2002年 | 699篇 |
2001年 | 565篇 |
2000年 | 457篇 |
1999年 | 524篇 |
1998年 | 349篇 |
1997年 | 335篇 |
1996年 | 380篇 |
1995年 | 328篇 |
1994年 | 288篇 |
1993年 | 224篇 |
1992年 | 201篇 |
1991年 | 169篇 |
1990年 | 144篇 |
1989年 | 121篇 |
1988年 | 109篇 |
1987年 | 68篇 |
1986年 | 62篇 |
1985年 | 50篇 |
1984年 | 33篇 |
1983年 | 31篇 |
1982年 | 15篇 |
1981年 | 18篇 |
1980年 | 11篇 |
1979年 | 2篇 |
1966年 | 1篇 |
1957年 | 5篇 |
1936年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Inside Cover: An Extra‐Large‐Pore Zeolite with 24×8×8‐Ring Channels Using a Structure‐Directing Agent Derived from Traditional Chinese Medicine (Angew. Chem. Int. Ed. 22/2018) 下载免费PDF全文
992.
Linghan Xiao Xin Zheng Tianyi Zhao Liying Sun Fengqi Liu Ge Gao Alideertu Dong 《Colloid and polymer science》2013,291(10):2359-2364
A novel route was introduced to synthesize dense polyacrylamide (PAM) onto the glass slide surface. To investigate the surface chemistry of the PAM on the glass slides, X-ray photoelectron spectroscopy (XPS) was utilized to obtain detailed chemical state information on the PAM layer constituents. The XPS peak data were consistent with the presented model of the PAM on the glass slide surface. Scanning electron microscopy and atomic force microscope data indicated the presence of PAM on the glass slides, which consist of nodules. The results showed that PAM was successfully immobilized onto glass slides with a two-tier structure under aqueous condition and a monolayer structure under anhydrous condition. Compared with those under aqueous condition, the controllability of the molecular layer on glass slides and the reproducibility under anhydrous condition were much better, which makes anhydrous condition an advisable condition for the study of the reaction mechanisms of glass slides modified by PAM. 相似文献
993.
A palladium-based catalyst (Fe3O4/SiO2/HPG–OPPh2–PNP) supported on chlorodiphenylphosphine-functionalized magnetic nanoparticles was successfully prepared from Fe3O4/SiO2 with sequential attachment of glycerol and chlorodiphenylphosphine, followed by treatment of an ethanolic solution of palladium chloride with hydrazine. The as-prepared catalyst was characterized by ICP-AES, FTIR, XRD, SEM, and TEM. The Fe3O4/SiO2/HPG–OPPh2–PNP was found as a magnetically separable and highly active catalyst for Suzuki coupling reactions of aryl iodides, bromides, and chlorides as well as Heck reactions of aryl iodides and bromides. Under appropriate conditions, all reactions afforded the desired products in moderate to excellent yields. Moreover, this catalyst can be easily recovered by using a magnetic field and directly reused for at least six cycles without significant loss of its activity. 相似文献
994.
995.
Dr. Heng Liao Dr. Liu Zhong Dr. Zefan Xiao Dr. Ting Zheng Prof. Haiyang Gao Prof. Qing Wu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(39):14048-14055
A series of novel α‐diamine nickel complexes, (ArNH‐C(Me)‐(Me)C‐NHAr)NiBr2, 1 : Ar=2,6‐diisopropylphenyl, 2 : Ar=2,6‐dimethylphenyl, 3 : Ar=phenyl), have been synthesized and characterized. X‐ray crystallographic analysis showed that the coordination geometry of the α‐diamine nickel complexes is markedly different from conventional α‐diimine nickel complexes, and that the chelate ring (N‐C‐C‐N‐Ni) of the α‐diamine nickel complex is significantly distorted. The α‐diamine nickel catalysts also display different steric effects on ethylene polymerization in comparison to the α‐diimine nickel catalyst. Increasing the steric hindrance of the α‐diamine ligand by substitution of the o‐methyl groups with o‐isopropyl groups leads to decreased polymerization activity and molecular weight; however, catalyst thermal stability is significantly enhanced. Living polymerizations of ethylene can be successfully achieved using 1 /Et2AlCl at 35 °C or 2 /Et2AlCl at 0 °C. The bulky α‐diamine nickel catalyst 1 with isopropyl substituents can additionally be used to control the branching topology of the obtained polyethylene at the same level of branching density by tuning the reaction temperature and ethylene pressure. 相似文献
996.
Optimizing Optoelectronic Properties of Pyrimidine‐Based TADF Emitters by Changing the Substituent for Organic Light‐Emitting Diodes with External Quantum Efficiency Close to 25 % and Slow Efficiency Roll‐Off 下载免费PDF全文
Kailong Wu Tao Zhang Lisi Zhan Dr. Cheng Zhong Prof. Shaolong Gong Prof. Nan Jiang Prof. Zheng‐Hong Lu Prof. Chuluo Yang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(31):10860-10866
A series of green butterfly‐shaped thermally activated delayed fluorescence (TADF) emitters, namely PXZPM , PXZMePM , and PXZPhPM , are developed by integrating an electron‐donor (D) phenoxazine unit and electron‐acceptor (A) 2‐substituted pyrimidine moiety into one molecule via a phenyl‐bridge π linkage to form a D –π–A–π–D configuration. Changing the substituent at pyrimidine unit in these emitters can finely tune their emissive characteristics, thermal properties, and energy gaps between the singlet and triplet states while maintaining frontier molecular orbital levels, and thereby optimizing their optoelectronic properties. Employing these TADF emitters results in a green fluorescent organic light‐emitting diode (OLED) that exhibits a peak forward‐viewing external quantum efficiency (EQE) close to 25 % and a slow efficiency roll‐off characteristic at high luminance. 相似文献
997.
The study toward the total synthesis of (R)‐(+)‐harmicine is reported in this paper. The enantioselective synthesis of pyrrolidinone, the main backbone of of (R)‐(+)‐harmicine, has been completed by the methodology based on photo‐induced Wolff rearrangement of α‐diazo‐β‐carbonyl compounds. 相似文献
998.
Inside Back Cover: Stepwise Assembly of MII7 Clusters Revealed by Mass Spectrometry,EXAFS, and Crystallography (Chem. Eur. J. 51/2016) 下载免费PDF全文
999.
1000.