全文获取类型
收费全文 | 3349篇 |
免费 | 451篇 |
国内免费 | 165篇 |
专业分类
化学 | 2695篇 |
晶体学 | 29篇 |
力学 | 97篇 |
综合类 | 20篇 |
数学 | 232篇 |
物理学 | 892篇 |
出版年
2024年 | 15篇 |
2023年 | 57篇 |
2022年 | 90篇 |
2021年 | 96篇 |
2020年 | 139篇 |
2019年 | 134篇 |
2018年 | 103篇 |
2017年 | 89篇 |
2016年 | 153篇 |
2015年 | 160篇 |
2014年 | 175篇 |
2013年 | 210篇 |
2012年 | 248篇 |
2011年 | 277篇 |
2010年 | 184篇 |
2009年 | 167篇 |
2008年 | 206篇 |
2007年 | 157篇 |
2006年 | 167篇 |
2005年 | 150篇 |
2004年 | 135篇 |
2003年 | 131篇 |
2002年 | 112篇 |
2001年 | 62篇 |
2000年 | 66篇 |
1999年 | 64篇 |
1998年 | 41篇 |
1997年 | 37篇 |
1996年 | 45篇 |
1995年 | 37篇 |
1994年 | 35篇 |
1993年 | 17篇 |
1992年 | 21篇 |
1991年 | 22篇 |
1990年 | 15篇 |
1989年 | 11篇 |
1988年 | 14篇 |
1987年 | 13篇 |
1986年 | 9篇 |
1985年 | 12篇 |
1984年 | 12篇 |
1983年 | 8篇 |
1982年 | 7篇 |
1981年 | 13篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1977年 | 8篇 |
1976年 | 3篇 |
1974年 | 7篇 |
1973年 | 4篇 |
排序方式: 共有3965条查询结果,搜索用时 15 毫秒
81.
Phthalocyanines have been used as photodynamic therapy (PDT) agents because of their uniquely favorable optical properties and high photostability. They have been shown to be highly successful for the treatment of cancer through efficient singlet‐oxygen (1O2) production. However, due to their hydrophobic properties, the considerations of solubility and cellular location have made understanding their photophysics in vitro and in vivo difficult. Indeed, many quantitative assessments of PDT reagents are undertaken in purely organic solvents, presenting challenges for interpreting observations during practical application in vivo. With steady‐state and time‐resolved laser spectroscopy, we show that for axial ligated silicon phthalocyanines in aqueous media, both the water:lipophile ratio and the pH have drastic effects on their photophysics, and ultimately dictate their functionality as PDT drugs. We suggest that considering the presented photophysics for PDT drugs in aqueous solutions leads to guidelines for a next generation of even more potent PDT agents. 相似文献
82.
Chi Fang Ting Xiong Jie Hou Jing Wei Gu Mei Hu Sheng 《Journal of Dispersion Science and Technology》2013,34(4):604-610
Amidoxime (AO)/amine co-functionalized polypropylene fiber adsorbents were prepared. The all-polymeric structures were characterized by using Fourier transform infrared spectroscopy (FTIR), optical microscope, contact angle meter and electron spin resonance (ESR) analysis methods, confirming the grafting, modification, and amidoximation stages gravimetrically, spectroscopically, and visually. The properties for the removal of uranyl(VI) from aqueous solutions were investigated. For amidoxime (AO) fiber, high adsorption rate was observed within the first 30 minutes and the plateau value of 40.6% uranium loading (0.0812 mg/g) was reached at around 30 minutes. The adsorption equilibrium for AO/amine fiber was attained within 20 minutes, resulting in the adsorption of 92.6% uranium loading (0.185 mg/g). The percentage of adsorption increases with increasing pH value (2–6), reaches a maximum at pH 6.0 and then remains almost constant for AO/amine fiber, whereas reduces slightly for AO fiber. 相似文献
83.
Hyojin Lee Chi P. Huynh Stephen C. Hawkins Mustafa Musameh Dae Hyung Kim 《Liquid crystals》2013,40(3):322-327
We investigated the orientational and electro-optical properties of a nematic liquid crystal (LC) aligned with a directly spinnable carbon nanotube (CNT) web functioning both as an electrode and as an alignment layer. The LC molecules were uniformly oriented along the drawing direction of the CNT web and the spatially averaged birefringence was comparable to a rubbed polyimide sample. The CNT web sample also showed smaller residual DC and hysteresis compared to the polyimide sample. 相似文献
84.
Simon Giret Christophe Théron Audrey Gallud Dr. Marie Maynadier Dr. Magali Gary‐Bobo Dr. Marcel Garcia Dr. Michel Wong Chi Man Dr. Carole Carcel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(38):12806-12814
Two new prodrugs, bearing two and three 5‐fluorouracil (5‐FU) units, respectively, have been synthesized and were shown to efficiently treat human breast cancer cells. In addition to 5‐FU, they were intended to form complexes through H‐bonds to an organo‐bridged silane prior to hydrolysis‐condensation through sol–gel processes to construct acid‐responsive bridged silsesquioxanes (BS). Whereas 5‐FU itself and the prodrug bearing two 5‐FU units completely leached out from the corresponding materials, the prodrug bearing three 5‐FU units was successfully maintained in the resulting BS. Solid‐state NMR (29Si and 13C) spectroscopy show that the organic fragments of the organo‐bridged silane are retained in the hybrid through covalent bonding and the 1H NMR spectroscopic analysis provides evidence for the hydrogen‐bonding interactions between the prodrug bearing three 5‐FU units and the triazine‐based hybrid matrix. The complex in the BS is not affected under neutral medium and operates under acidic conditions even under pH as high as 5 to deliver the drug as demonstrated by HPLC analysis and confirmed by FTIR and 13C NMR spectroscopic studies. Such functional BS are promising materials as carriers to avoid the side effects of the anticancer drug 5‐FU thanks to a controlled and targeted drug delivery. 相似文献
85.
Wangdong Zeng Dr. Masatoshi Ishida Sangsu Lee Young Mo Sung Dr. Zebing Zeng Yong Ni Prof. Chunyan Chi Prof. Dongho Kim Prof. Jishan Wu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(49):16814-16824
A p‐quinodimethane (p‐QDM)‐bridged porphyrin dimer 1 has been prepared for the first time. An unexpected Michael addition reaction took place when we attempted to synthesize compound 1 by reaction of the cross‐conjugated keto‐linked porphyrin dimers 8 a and 8 b with alkynyl/aryl Grignard reagents. Alternatively, compound 1 could be successfully prepared by intramolecular Friedel–Crafts alkylation of the diol‐linked porphyrin dimer 14 with concomitant oxidation in air. Compound 1 shows intense one‐photon absorption (OPA, λmax=955 nm, ε=45400 M ?1 cm?1) and a large two‐photon absorption (TPA) cross‐section (σ(2)max=2080 GM at 1800 nm) in the near‐infrared (NIR) region due to its extended π‐conjugation and quinoidal character. It also exhibits a short singlet excited‐state lifetime of 25 ps. The cyclic voltammogram of 1 displays multiple redox waves with a small electrochemical energy gap of 0.86 eV. The ground‐state geometry, electronic structure, and optical properties of 1 have been further studied by density functional theory (DFT) calculations and compared with those of the keto‐linked dimer 8 b . This research has revealed that incorporation of a p‐QDM unit into the porphyrin framework had a significant impact on its optical and electronic properties, leading to a novel NIR OPA and TPA chromophore. 相似文献
86.
87.
Dr. Junwu Zhu Chi Cheng Xiaowei Yang Yufei Wang Ling Qiu Prof. Dan Li 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(9):3082-3089
Restacking of graphene sheets to a graphite‐like structure is a prevailing problem that is known to compromise the performance of individual graphene sheets in an assembled bulk form. To address this common problem efficiently and monitor the structure and quality of graphene products comprehensively, it is highly desirable to develop reliable metrology techniques for characterising graphene‐based materials on a bulk assembly level and in a quantitative manner. Here, by revisiting the physicochemical principle of electrosorption, we propose a simple electrochemical approach, namely dynamic electrosorption analysis (DEA), as an easily accessible and effective technique for evaluation of the self‐stacking behaviour of graphene. Taking multilayered chemically converted graphene films as a model, we demonstrate that the DEA technique can effectively reveal very subtle variation in accessible surface area and pore size of graphene assemblies in the liquid phase and thus can provide useful insights to the experimental design relating to restacking control. This work also reveals the huge effect some routine processing conditions, such as heat treatment and drying, can have on the structure and performance of graphene‐based bulk materials, providing useful guidance for future manufacturing of this class of materials. 相似文献
88.
89.
Wenjuan Cheng Lu‐Tao Weng Yongjie Li Arthur Lau Chak Chan Chi‐Ming Chan 《Surface and interface analysis : SIA》2014,46(7):480-488
Size‐segregated particles were collected with a ten‐stage micro‐orifice uniform deposit impactor from a busy walkway in a downtown area of Hong Kong. The surface chemical compositions of aerosol samples from each stage were analyzed using time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) operated in the static mode. The ToF‐SIMS spectra of particles from stage 2 (5.6–10 µm), stage 6 (0.56–1 µm), and stage 10 (0.056–0.1 µm) were compared, and the positive ion spectra from stage 2 to stage 10 were analyzed with principal component analysis (PCA). Both spectral analysis and PCA results show that the coarse‐mode particles were associated with inorganic ions, while the fine particles were associated with organic ions. PCA results further show that the particle surface compositions were size dependent. Particles from the same mode exhibited more similar surface features. Particles from stage 2 (5.6–10 µm), stage 6 (0.56–1 µm), and stage 10 (0.056–0.1 µm) were further selected as representatives of the three modes, and the chemical compositions of these modes of particles were examined using ToF‐SIMS imaging and depth profiling. The results reveal a non‐uniform chemical distribution from the outer to the inner layer of the particles. The coarse‐mode particles were shown to contain inorganic salts beneath the organics surface. The accumulation‐mode particles contained sulfate, nitrate, ammonium salts, and silicate in the regions below a thick surface layer of organic species. The nucleation‐mode particles consisted mainly of soot particles with a surface coated with sulfate, hydrocarbons, and, possibly, fullerenic carbon. The study demonstrated the capability of ToF‐SIMS depth profiling and imaging in characterizing both the surface and the region beneath the surface of aerosol particles. It also revealed the complex heterogeneity of chemical composition in size and depth distributions of atmospheric particles. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
90.