全文获取类型
收费全文 | 3589篇 |
免费 | 524篇 |
国内免费 | 327篇 |
专业分类
化学 | 1784篇 |
晶体学 | 29篇 |
力学 | 200篇 |
综合类 | 7篇 |
数学 | 240篇 |
物理学 | 1075篇 |
综合类 | 1105篇 |
出版年
2024年 | 27篇 |
2023年 | 82篇 |
2022年 | 133篇 |
2021年 | 151篇 |
2020年 | 132篇 |
2019年 | 116篇 |
2018年 | 122篇 |
2017年 | 102篇 |
2016年 | 166篇 |
2015年 | 154篇 |
2014年 | 176篇 |
2013年 | 209篇 |
2012年 | 311篇 |
2011年 | 325篇 |
2010年 | 202篇 |
2009年 | 175篇 |
2008年 | 192篇 |
2007年 | 201篇 |
2006年 | 166篇 |
2005年 | 139篇 |
2004年 | 112篇 |
2003年 | 103篇 |
2002年 | 74篇 |
2001年 | 61篇 |
2000年 | 57篇 |
1999年 | 80篇 |
1998年 | 78篇 |
1997年 | 95篇 |
1996年 | 87篇 |
1995年 | 55篇 |
1994年 | 59篇 |
1993年 | 57篇 |
1992年 | 54篇 |
1991年 | 42篇 |
1990年 | 39篇 |
1989年 | 24篇 |
1988年 | 26篇 |
1987年 | 9篇 |
1986年 | 20篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1979年 | 1篇 |
1973年 | 1篇 |
1970年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有4440条查询结果,搜索用时 15 毫秒
111.
A new oligothiophene-based sensor 3 TH for monitoring Hg2+ has been designed and synthesized based on the intramolecular charge transfer (ICT) mechanism. The 3 TH shows the significant specificity toward Hg2+ through “naked-eye” colorimetric detection as well as via ratiometric fluorescence enhancement response with low detection limit of 62 nM. In addition, sensor 3 TH shows high selectivity and sensitivity for Hg2+ with fast response in a suitable pH range. Moreover, the 3 TH-based test strips was used to conveniently detect Hg2+ ions in water. Furthermore, considering its good ‘‘turn-on’’ fluorescent sensing behavior and low cell cytotoxicity, 3 TH was successfully applied to detect and image Hg2+ in real water samples and living cells, which shows great potentials for application in environmental and biological systems. 相似文献
112.
113.
Dian Niu Yuqian Jiang Lukang Ji Guanghui Ouyang Minghua Liu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(18):6007-6011
Multiple noncovalent interactions can drive self‐assembly through different pathways. Here, by coordination‐assisted changes in π‐stacking modes between chromophores in pyrene‐conjugated histidine (PyHis), a self‐assembly system with reversible and inversed switching of supramolecular chirality, as well as circularly polarized luminescence (CPL) is described. It was found that l ‐PyHis self‐assembled into nanofibers showing P‐chirality and right‐handed CPL. Upon ZnII coordination, the nanofibers changed into nanospheres with M‐chirality, as well as left‐handed CPL. The process is reversible and the M‐chirality can change to P‐chirality by removing the ZnII ions. Experimental and theoretical models unequivocally revealed that the cooperation of metal coordination and π‐stacking modes are responsible the reversible switching of supramolecular chirality. This work not only provides insight into how multiple noncovalent interactions regulate self‐assembly pathways. 相似文献
114.
<正>A new naphthoquinone compound named 7-hydroxyl-8-methoxyltrypethelone 3 together with two known compounds trypethelone 1 and trypethelone methyl ether 2 was isolated from cultured mycobiont of Astrothelium sp.The structures were elucidated by 1D and 2D NMR spectroscopic analysis as well as comparison with those reported in literatures.Compound 1 displayed significant antibacterial activity against Bacillus subtilis(ATCC 6633),and showed modest antibacterial activity against Staphylococcus aureus col(MRSA)(CGMCC 1.2465),while compounds 2 and 3 showed modest antibacterial activity against Enterococcus faecalis 850E(CGMCC 1.2135) and S.aureus col(MRSA)(CGMCC 1.2465). 相似文献
115.
NF3 decomposition in the absence of water over Al2O3, Fe2O3, Co3O4 and NiO, and transition metal oxides (Fe2O3, Co3O4 and NiO) coated Al2O3 reagents was investigated. The results show that Al2O3 is an active reagent for NF3 decomposition with 100% conversion lasting for 8.5 h at 400 ℃. Fe2O3, Co3O4 and NiO coated Al2O3 reagents are superior to bare Al2O3, and 5%Co3O4/Al2O3 has a high reactivity with NF3 full conversion maintaining for 10.5 h. It is suggested that the presence of transition metal oxide is beneficial to the reactivity of Al2O3, and results in a significant enhancement in the fluorination of Al2O3. 相似文献
116.
Cellulose synthesis in maize: isolation and expression analysis of the cellulose synthase (CesA) gene family 总被引:7,自引:0,他引:7
Laura Appenzeller Monika Doblin Roberto Barreiro Haiyin Wang Xiaomu Niu Krishna Kollipara Lori Carrigan Dwight Tomes Mike Chapman Kanwarpal S. Dhugga 《Cellulose (London, England)》2004,11(3-4):287-299
Stalk lodging in maize results in significant yield losses. We have determined that cellulose per unit length of the stalk is the primary determinant of internodal strength. An increase in cellulose concentration in the wall might allow simultaneous improvements in stalk strength and harvest index. Cellulose formation in plants can be perturbed by mutations in the genes involved in cellulose synthesis, post-synthetic cellulose alteration or deposition, N-glycosylation, and some other genes with as yet unknown functions. We have isolated 12 members of the cellulose synthase (CesA) gene family from maize. The genes involved in primary wall formation appear to have duplicated relatively independently in dicots and monocots. The deduced amino acid sequences of three of the maize genes, ZmCesA10–12, cluster with the Arabidopsis CesA sequences that have been shown to be involved in secondary wall formation. Based on their expression patterns across multiple tissues, these three genes appear to be coordinately expressed. The remaining genes show overlapping expression to varying degrees with ZmCesA1, 7, and 8 forming one group, ZmCesA3 and 5 a second group, and ZmCesA2 and 6 exhibiting independent expression of any other gene. This suggests that the varying levels of coexpression may just be incidental except in the case of ZmCesA10–12, which may interact with each other to form a functional enzyme complex. Isolation of the expressed CesA genes from maize and their association with primary or secondary wall formation has made it possible to test their respective roles in cellulose synthesis through mutational genetics or transgenic approaches. This information would be useful in improving stalk strength. 相似文献
117.
Two new sesquiterpenes (1–2), along with one known sesquiterpene (3), were isolated from cultures of the higher fungus Pholiota nameko. The structures of new compounds were elucidated by extensive spectroscopic methods. The known compound was identified by comparing its spectroscopic data with those reported in the literature. All compounds were evaluated for their cytotoxicities against five human cancer cell lines. 相似文献
118.
Zhenchuan Wen Xuejian Ma Xiaoyu Yang Pengqing Bi Mengsi Niu Kangning Zhang Lin Feng Xiaotao Hao 《中国化学快报》2019,30(5):995-999
In this work, the donor:acceptor ratio effected photophysical properties of non-fullerene organic solar cells are comparatively investigated. Effective transportation of the photo-generated charge carriers can be obtained with the PDBD-T:ITIC ratio variation. There is no significant energy loss variation exists in the process of changing the D:A ratio. 相似文献
119.
Q Zhang Z Gao F Xu S Tai X Liu S Mo F Niu 《Langmuir : the ACS journal of surfaces and colloids》2012,28(33):11979-11987
A series of novel cationic gemini surfactants with diethylammonium headgroups and a diamido spacer were synthesized, and their surface and bulk properties were investigated by surface tension, electrical conductivity, fluorescence, viscosity, dynamic light scattering (DLS), and transmission electron microscopy (TEM) measurements. An interesting phenomenon, that is, the obvious decline in surface tension upon increasing concentration above the critical micelle concentration (cmc), was found in these gemini surfactant solutions, and two explanations were proposed. This surface tension behavior could be explained by the rapid increase in the counterion activity in the bulk phase or the continued filling of the interface with increasing surfactant concentration above the cmc. More interestingly, not only vesicles but also the surfactant-concentration-induced vesicle to larger aggregate (spongelike aggregate) transition and the salt-induced vesicle and spongelike aggregate to micelle transition were found in the aqueous solutions of these gemini surfactants. The spongelike aggregate that is first reported in the cationic gemini surfactant-water binary system is probably caused by the adhesion and fusion of vesicles at high surfactant concentration. 相似文献
120.
Fimetarone A (1), a metabolite with the new spiro[chroman-3,7'-isochromene]-4,6'(8'H)-dione skeleton, was isolated from cultures of the Cordyceps-colonizing fungus Fimetariella sp. Compound 1 was a 1:1 atropdiastereomeric mixture in NMR data, and aS,9S and aR,9R enantiomers were found and confirmed by X-ray crystallography. Compound 1 could be derived from the hypothetical precursors 3,4,5-trihydroxy-2-(2-methylene-3,5-dioxohexanoyl)benzoic acid (5) and lapidosin (6). 相似文献