全文获取类型
收费全文 | 3871篇 |
免费 | 657篇 |
国内免费 | 410篇 |
专业分类
化学 | 2305篇 |
晶体学 | 40篇 |
力学 | 170篇 |
综合类 | 17篇 |
数学 | 243篇 |
物理学 | 1080篇 |
无线电 | 1083篇 |
出版年
2024年 | 24篇 |
2023年 | 107篇 |
2022年 | 145篇 |
2021年 | 201篇 |
2020年 | 187篇 |
2019年 | 192篇 |
2018年 | 167篇 |
2017年 | 151篇 |
2016年 | 215篇 |
2015年 | 241篇 |
2014年 | 232篇 |
2013年 | 322篇 |
2012年 | 332篇 |
2011年 | 333篇 |
2010年 | 228篇 |
2009年 | 216篇 |
2008年 | 281篇 |
2007年 | 203篇 |
2006年 | 194篇 |
2005年 | 145篇 |
2004年 | 118篇 |
2003年 | 93篇 |
2002年 | 103篇 |
2001年 | 68篇 |
2000年 | 50篇 |
1999年 | 73篇 |
1998年 | 46篇 |
1997年 | 34篇 |
1996年 | 40篇 |
1995年 | 31篇 |
1994年 | 34篇 |
1993年 | 21篇 |
1992年 | 23篇 |
1991年 | 14篇 |
1990年 | 21篇 |
1989年 | 18篇 |
1988年 | 13篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有4938条查询结果,搜索用时 8 毫秒
991.
Daoyong Zhu Zhiwei Jiao Yonggui Robin Chi Tho P. Gonalves Kuo‐Wei Huang Jianrong Steve Zhou 《Angewandte Chemie (International ed. in English)》2020,59(13):5341-5345
Substituted cyclohexylamines are becoming increasingly important in drug discovery. Asymmetric Heck insertion/amination of nonconjugated cyclodienes proceeds to give 5‐aryl cyclohexenylamines with good enantioselectivity and exclusive trans configurations. Primary and secondary anilines, indoline, and benzylamines are suitable amines. The weakly donating diphosphite Kelliphite forms a deep unsymmetrical pocket, which is essential for stereoselective anti attack of amines. 相似文献
992.
Pengfei Xie Jiao Wang Jianbo Li Qian Cheng Keyu Zhou Jie Ren 《Journal of polymer science. Part A, Polymer chemistry》2019,57(7):814-826
The miktoarm star‐shaped poly(lactic acid) (PLA) copolymer, (PLLA)2‐core‐(PDLA)2, was synthesized via stepwise ring‐opening polymerization of lactide with dibromoneopentyl glycol as the starting material. 1H NMR and FTIR spectroscopy proved the feasibility of synthetic route and the successful preparation of star‐shaped PLA copolymers. The results of FTIR spectroscopy and XRD showed that the stereocomplex structure of the copolymer could be more perfect after solvent dissolution treatment. Effect of chain architectures on crystallization was investigated by studying the nonisothermal and isothermal crystallization of the miktoarm star‐shaped PLA copolymer and other stereocomplexes. Nonisothermal differential scanning calorimetry and polarizing optical microscopy tests indicated that (PLLA)2‐core‐(PDLA)2 exhibited the fastest formation of a stereocomplex in a dynamic test due to its special structure. In isothermal crystallization tests, the copolymer exhibited the fast crystal growth rate and the most perfect crystal morphology. The results reveal that the unique molecular structure has an important influence on the crystallization of the miktoarm star‐shaped PLA copolymer. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 814–826 相似文献
993.
A comprehensive study on the efficient one‐pot synthesis of polyhedral octaphenylsilsesquioxane (OPS) is reported via the hydrolytic condensation of phenyltrimethoxysilane (PTMS) in the presence of basic catalyst to investigate the specific synthesis mechanism. The synthetic reactions are monitored with real time infrared (RTIR) spectroscopy. Then RTIR coupled with 29Si nuclear magnetic resonance spectroscopy (NMR) and matrix‐assisted laser desorption/ionization time of flight mass spectrometry (MALDI‐TOF‐MS) are used to monitor the reactions and identify the intermediary species during the reaction. The rapid hydrolysis of PTMS is detected by RTIR. Contrary to previous reports, the ladder‐like structured species are identified as intermediates during the reaction process. It is suggested that formation of caged T8 OPS is realized through the chain break and rearrangement of the ladder‐like phenyltrimethoxysilanes. Accordingly, a scheme from hydrolysis of the PTMS to formation of the OPS is provided. 相似文献
994.
995.
996.
Wu Ke-Han Wang Yu Yu-Jiang Zhang Guo-Hua Jiao Shu-Qiang Chou Kuo-Chih 《Journal of nanoparticle research》2019,21(5):1-14
Journal of Nanoparticle Research - In this work, impact of synthesized silica nanotubes (SNTs) on morphology and performance of polyvinylidene fluoride (PVDF) nanocomposite membrane was studied.... 相似文献
997.
Regulating PdC3/PtC3···thiophene interaction by small molecule doping (AgOTf,CuBr, CuI,CuBr2, PdCl2)
Structural Chemistry - The influences of small molecule doping on PdC3/PtC3···thiophene interaction have been investigated by atoms in molecules (AIM) theory, electron location... 相似文献
998.
Huan Yang Ying Zhou Pingtian Yu Yaya Yang Zhaoqun Jiao James P. Tam 《Natural product research》2019,33(9):1251-1256
A novel PCR technology was developed to detect short DNA fragments using species-specific primers for rapid and non-sequencing authentication of Bombyx batryticatus based on differences in the mitochondrial genome. Three specifically designed primer reactions were established to target species for the reliable identification of their commercial products. They were confirmed to have a high inter-species specificity and intra-species stability. The limit of detection was estimated as 1 ng of genomes for Beauveria bassiana and 100 pg for Bombyx mori and Metarhizium anisopliae. Furthermore, validation results demonstrated that raw materials and their processed products can be conveniently authenticated with good sensitivity and precision using this newly proposed approach. In particular, when counterfeits were assayed, these primer sets performed well, whereas COI barcoding technology did not. These could also assist in the discrimination and identification of adulterates of other animal-derived medicines in their pulverized and processed forms and even in complexes. 相似文献
999.
Two stable heterometal‐organic frameworks, {Na[LnCo(DATP)2(Ac)(H2O)](NO3)?DMA?11 H2O}n (Ln=Er( 1 ) and Yb( 2 )), have been prepared with H2DATP (4′‐(3,5‐dicarboxyphenyl)‐2,2′:6′,2′′′‐terpyridine) as organic building block. These two isostructural compounds featuring two‐dimensional layer architectures possess outstanding thermal stabilities and excellent chemical stabilities in common organic solvents and different acid/base solutions with pH range changing from 1 to 13. Moreover, compounds 1 and 2 serving as heterogeneous catalysts can efficiently catalyse the CO2 fixation reaction with various aziridines to result in corresponding oxazolidinones at 70 °C. Importantly, a good recyclable performance of 1 for at least 10 cycles is observed based on the experimental results, which are further confirmed by PXRD, TGA and ICP analyses. 相似文献
1000.
以NiFeNb为种子层,制备(Ni79Fe21)1-xNbx(5nm)/(Ni79Fe21) (20nm)/Ta(3nm)系列膜,并对其颗粒大小、 磁滞回线及表面粗糙度等进行测量,探讨种子层中Nb含量x对坡莫合金磁滞回线的影响.结果 表明,以NiFeNb作种子层能更好地改善坡莫合金的微结构. Nb含量为23%时的磁滞回线有最 小的最大磁能积、矫顽力.种子层影响坡莫合金磁滞回线的一个重要原因是脱附激活能等因 素造成种子层具有不同的表面粗糙度,进而使坡莫合金具有不同的微结构和磁性能.
关键词:
NiFeNb种子层
坡莫合金
磁滞回线
粗糙度 相似文献