全文获取类型
收费全文 | 6977篇 |
免费 | 1380篇 |
国内免费 | 977篇 |
专业分类
化学 | 4229篇 |
晶体学 | 100篇 |
力学 | 108篇 |
综合类 | 53篇 |
数学 | 55篇 |
物理学 | 4789篇 |
出版年
2024年 | 4篇 |
2023年 | 68篇 |
2022年 | 172篇 |
2021年 | 205篇 |
2020年 | 269篇 |
2019年 | 232篇 |
2018年 | 227篇 |
2017年 | 330篇 |
2016年 | 350篇 |
2015年 | 322篇 |
2014年 | 463篇 |
2013年 | 586篇 |
2012年 | 510篇 |
2011年 | 459篇 |
2010年 | 379篇 |
2009年 | 428篇 |
2008年 | 525篇 |
2007年 | 507篇 |
2006年 | 438篇 |
2005年 | 353篇 |
2004年 | 352篇 |
2003年 | 317篇 |
2002年 | 288篇 |
2001年 | 251篇 |
2000年 | 181篇 |
1999年 | 174篇 |
1998年 | 139篇 |
1997年 | 130篇 |
1996年 | 114篇 |
1995年 | 118篇 |
1994年 | 101篇 |
1993年 | 57篇 |
1992年 | 62篇 |
1991年 | 31篇 |
1990年 | 36篇 |
1989年 | 36篇 |
1988年 | 24篇 |
1987年 | 20篇 |
1986年 | 15篇 |
1985年 | 14篇 |
1984年 | 8篇 |
1983年 | 3篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 4篇 |
排序方式: 共有9334条查询结果,搜索用时 15 毫秒
51.
Dr. Lenka Štacková Marina Russo Dr. Lucie Muchová Vojtěch Orel Prof. Libor Vítek Dr. Peter Štacko Prof. Petr Klán 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(58):13184-13190
Carbon monoxide (CO) is an endogenous signaling molecule that controls a number of physiological processes. To circumvent the inherent toxicity of CO, light-activated CO-releasing molecules (photoCORMs) have emerged as an alternative for its administration. However, their wider application requires photoactivation using biologically benign visible and near-infrared (NIR) light. In this work, a strategy to access such photoCORMs by fusing two CO-releasing flavonol moieties with a NIR-absorbing cyanine dye is presented. These hybrids liberate two molecules of CO in high chemical yields upon activation with NIR light up to 820 nm and exhibit excellent uncaging cross-sections, which surpass the state-of-the-art by two orders of magnitude. Furthermore, the biocompatibility and applicability of the system in vitro and in vivo are demonstrated, and a mechanism of CO release is proposed. It is hoped that this strategy will stimulate the discovery of new classes of photoCORMs and accelerate the translation of CO-based phototherapy into practice. 相似文献
52.
采用湿化学法合成了Eu原子掺量5%的Lu2O3陶瓷前驱体,通过SEM、XRD研究了煅烧前后前驱体和1 100 ℃煅烧4 h后粉体的形貌、结构以及物相。结果表明煅烧后的粉体为纳米类球形、高分散且结晶性良好的颗粒。颗粒尺寸为68.5 nm。使用煅烧后的粉体为原料,在1 650 ℃真空烧结30 h制备了高透过率的Eu:Lu2O3陶瓷,晶粒尺寸为46 μm,在611 nm处的直线透过率可以达到66.3%。此外对陶瓷的吸收曲线、光致激发和发射光谱特性以及X射线激发发射光谱进行研究。可观察到,Eu:Lu2O3陶瓷存在基质和激活离子两类吸收,光致发光光谱和X射线激发发射光谱均可以看出Eu:Lu2O3陶瓷存在极强的5D0→7F2跃迁发光,位于611 nm处。对比商业的BGO单晶的X射线发射光谱,可得本实验中制备的陶瓷的光输出为85 000 ph/MeV。Eu:Lu2O3陶瓷本身有着高X射线以及高能粒子的阻止能力,结合高光输出特性,表明Eu:Lu2O3陶瓷在X射线成像等领域具有巨大的潜在应用价值。 相似文献
53.
Xiaofan Zhang 《中国物理 B》2022,31(11):114209-114209
We theoretically investigate the yield enhancement of elliptical high harmonics in the interaction of molecules with bicircular laser pulses by solving the time-dependent Schrödinger equation. It is shown that by adjusting the relative intensity ratio of the two bicircular field components in specific ranges the yield of the molecular high harmonics for the plateau and cutoff regions can be respectively enhanced. To analyze this enhancement phenomenon, we calculate the weights of the electron classical trajectories. Additionally, we also study the ellipticity distribution of harmonics for different intensity ratios. We find that these enhanced harmonics are elliptically polarized, which we mainly attribute to the recombination dipole moment of the major weighted trajectories. These enhanced elliptical extreme ultraviolet and soft x-ray radiations may serve as essential tools for exploring the ultrafast dynamics in magnetic materials and chiral media. 相似文献
54.
Yoshino Katsurayama Prof. Yasuhiro Ikabata Prof. Hajime Maeda Prof. Masahito Segi Prof. Hiromi Nakai Prof. Taniyuki Furuyama 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(2):e202103223
The high penetration of near-infrared (NIR) light makes it effective for use in selective reactions under light-shielded conditions, such as in sealed reactors and deep tissues. Herein, we report the development of phthalocyanine catalysts directly activated by NIR light to transform small organic molecules. The desired photocatalytic properties were achieved in the phthalocyanines by introducing the appropriate peripheral substituents and central metal. These phthalocyanine photocatalysts promote cross-dehydrogenative-coupling (CDC) under irradiation with 810 nm NIR light. The choice of solvent is important, and a mixture of a reaction-accelerating (pyridine) and -decelerating (methanol) solvents was particularly effective. Moreover, we demonstrate photoreactions under visible-light-shielded conditions through the transmission of NIR light. A combined experimental and computational mechanistic analysis revealed that this NIR reaction does not involve a photoredox-type mechanism with electron transfer, but instead a singlet-oxygen-mediated mechanism with energy transfer. 相似文献
55.
56.
Meihong Zhang Yuqian Fang Shuai Yuan Liyi Shi Zhuyi Wang Yi Wang Jiefang Zhu Yin Zhao 《Surface and interface analysis : SIA》2023,55(1):63-70
The graphitic carbon nitride (g-C3N4) materials with many intriguing properties have attracted much attention in photocatalysis. The photocatalytic activity of g-C3N4 is hindered by serious aggregation and limited exposed active sites. Herein is shown that nanosized g-C3N4 can be simply obtained by a superfast high-pressure homogenization approach. The high-pressure homogenization treatment can provide strong force to cut and/or to exfoliate the bulk g-C3N4 into nanosized g-C3N4 with good dispersion. Moreover, choosing different solvents during treatment can cause a different surface structure of as-prepared nanosized g-C3N4. In addition, the narrow bandgap properties, the high photogenerated charge carrier separation, and the transport abilities are achieved in as-prepared nanosized g-C3N4 because of the retaining conjugated C3N4 system. Specifically, the photocatalytic activities of as-prepared nanosized g-C3N4 have been significantly enhanced in terms of degradation of organic dye Rhodamine B (RhB) under visible light irradiation (10 times higher than that of bulk g-C3N4). These findings can provide a promising and simple approach to the exfoliation, nanonization, and surface functionalization of 2D layered materials. 相似文献
57.
《Mendeleev Communications》2023,33(1):130-132
A glass with CdS nanoparticles was used simultaneously as a matrix for Ce-doped garnet and a yellow-red phosphor to prepare luminescent glass ceramics for the sources of white light. CdS nanoparticles compensate for the unbalanced Ce3+ emission spectrum of the composite material due to the addition of a red component. The synthesized composite material can be a tunable light converter due to altered luminescence spectra by changing the sintering conditions and excitation wavelength 相似文献
58.
Prof. Dr. Toshiyuki Itoh Dr. Shuichi Hayase Prof. Dr. Toshiki Nokami 《Chemical record (New York, N.Y.)》2023,23(9):e202300028
The incorporation of fluorine atoms into an organic compound can alter the chemical reactivity or biological activity of the resulting compound due to the strong electron withdrawing nature of the fluorine atom. We have synthesized many original gem-difluorinated compounds and described the results in four sections. The first section describes the synthesis of optically active-gem-difluorocyclopropanes via the chemo-enzymatic reaction; we applied these compounds to liquid crystalline molecules, then further discovered a potent DNA cleavage activity for the gem-difluorocyclopropane derivatives. The second section describes the synthesis of selectively gem-difluorinated compounds via a radical reaction; we synthesized fluorinated analogues of a sex pheromone of the male African sugarcane borer, Eldana saccharina, and used the compounds as proof for investigating the origin of pheromone molecule recognition on the receptor protein. The third involves the synthesis of 2,2-difluorinated-esters by visible light-driven radical addition of 2,2-difluoroacetate with alkenes or alkynes in the presence of an organic pigment. The last section describes the synthesis of gem-difluorinated compounds via the ring-opening of gem-difluorocyclopropanes. We further developed a novel method of synthesizing gem-difluorohomoallylic alcohols via the ring-opening of gem-difluorocyclopropane and aerobic oxidation by photo-irradiation in the presence of an organic pigment. Since gem-difluorinated compounds that were prepared by the present method have two olefinic moieties with a different reactivity at the terminal position, we accomplished the synthesis of four types of gem-difluorinated cyclic alkenols via the ring-closing-metathesis (RCM) reaction. 相似文献
59.
Xiaoxuan Han Ruijie Zhao Yong Tian Yutong Li Xu-Wei Chen Jiping Ma Weiliang Wang Yanfeng Zhang Song Geng Menglin Liu 《Journal of separation science》2023,46(11):2300006
A high-performance liquid chromatography-ultraviolet method was developed for rapidly and simultaneously analyzing novel and typical bisphenols in building materials, including bisphenol S, diphenolic acid, bisphenol F, bisphenol E, bisphenol A, bisphenol B, bisphenol AF, bisphenol AP, bisphenol C, bisphenol FL, bisphenol Z, bisphenol BP, bisphenol M, and bisphenol P. By using a Kromasil 100–5 C18 column, these bisphenols were completely separated in 40 min via gradually increasing the concentration of methanol in the mobile phase from 45 to 80% during the elution process. In particular, this method achieved the synchronous analysis of bisphenol S, diphenolic acid, bisphenol FL, bisphenol BP, and bisphenol M through HPLC, which were difficult to separate and had to be identified and detected through mass spectrometry. The limits of detection of the method ranged from 0.002 to 0.040 mg/L for these 14 bisphenols, with a precision of less than 4.9% (n = 7, c = 0.05 mg/L). The analytical results for five types of building materials (phenolic, epoxy, polycarbonate, polyester, and polysulfone resins) indicated that the proposed method is appropriated for the rapid measurement of bisphenols in real samples. 相似文献
60.
Anna Szabó Rolando Pasquariello Pedro F. Costa Radmila Pavlovic Indi Geurs Koen Dewettinck Chris Vervaet Tiziana A. L. Brevini Fulvio Gandolfi Sandra Van Vlierberghe 《Macromolecular bioscience》2023,23(10):2300016
To provide prominent accessibility of fishmeal to the European population, the currently available, time- and cost-extensive feeding trials, which evaluate fish feed, should be replaced. The current paper reports on the development of a novel 3D culture platform, mimicking the microenvironment of the intestinal mucosa in vitro. The key requirements of the model include sufficient permeability for nutrients and medium-size marker molecules (equilibrium within 24 h), suitable mechanical properties (G' < 10 kPa), and close morphological similarity to the intestinal architecture. To enable processability with light-based 3D printing, a gelatin-methacryloyl-aminoethyl-methacrylate-based biomaterial ink is developed and combined with Tween 20 as porogen to ensure sufficient permeability. To assess the permeability properties of the hydrogels, a static diffusion setup is utilized, indicating that the hydrogel constructs are permeable for a medium size marker molecule (FITC-dextran 4 kg mol−1). Moreover, the mechanical evaluation through rheology evidence a physiologically relevant scaffold stiffness (G' = 4.83 ± 0.78 kPa). Digital light processing-based 3D printing of porogen-containing hydrogels results in the creation of constructs exhibiting a physiologically relevant microarchitecture as evidenced through cryo-scanning electron microscopy. Finally, the combination of the scaffolds with a novel rainbow trout (Oncorhynchus mykiss) intestinal epithelial cell line (RTdi-MI) evidence scaffold biocompatibility. 相似文献