全文获取类型
收费全文 | 1398篇 |
免费 | 49篇 |
国内免费 | 2篇 |
专业分类
化学 | 960篇 |
晶体学 | 6篇 |
力学 | 28篇 |
数学 | 116篇 |
物理学 | 339篇 |
出版年
2023年 | 11篇 |
2022年 | 32篇 |
2021年 | 34篇 |
2020年 | 31篇 |
2019年 | 37篇 |
2018年 | 12篇 |
2017年 | 20篇 |
2016年 | 45篇 |
2015年 | 37篇 |
2014年 | 40篇 |
2013年 | 66篇 |
2012年 | 84篇 |
2011年 | 75篇 |
2010年 | 59篇 |
2009年 | 39篇 |
2008年 | 65篇 |
2007年 | 62篇 |
2006年 | 63篇 |
2005年 | 48篇 |
2004年 | 41篇 |
2003年 | 41篇 |
2002年 | 33篇 |
2001年 | 34篇 |
2000年 | 23篇 |
1999年 | 19篇 |
1998年 | 18篇 |
1997年 | 7篇 |
1996年 | 31篇 |
1995年 | 14篇 |
1994年 | 12篇 |
1993年 | 20篇 |
1992年 | 20篇 |
1991年 | 26篇 |
1990年 | 15篇 |
1989年 | 12篇 |
1988年 | 13篇 |
1987年 | 16篇 |
1986年 | 13篇 |
1985年 | 14篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 16篇 |
1977年 | 9篇 |
1976年 | 5篇 |
1975年 | 11篇 |
1974年 | 13篇 |
1973年 | 11篇 |
1971年 | 5篇 |
排序方式: 共有1449条查询结果,搜索用时 15 毫秒
71.
Jana Strišovská Veronika Drábová Jozef Kuruc 《Journal of Radioanalytical and Nuclear Chemistry》2013,298(2):1179-1183
The present work describes preparation of 239Np tracer from 243Am stock solution and the purification of this solution from ferric cation. The method of the preparation of tracer involves stabilization of Np(IV) by ascorbic acid and ferric nitrate, separation of 239Np from 243Am by extraction chromatography and determination of recoveries of 239Np by means of gamma spectroscopy. We used the commercially available sorbents TEVA®Resin for the 239Np preparation and DGA Resin for 243Am purification. All sorbents were purchased from Eichrom Industries, Inc. The first eluate from the column can be stored for a future preparation of the tracer and fraction with 239Np will be used to monitor radiochemical yield of 237Np. 相似文献
72.
Two new cesium thorium fluorides and three new rubidium thorium fluorides have been synthesized hydrothermally and structurally characterized. The structures of two polymorphs of CsTh(3)F(13) are described in space group P6/mmm with a = 8.2608(14) and c = 8.6519(17) and space group Pmc2(1) with a = 8.1830(16), b = 7.5780(15), and c = 8.6244(17). The analogous orthorhombic compound RbTh(3)F(13), with a = 8.1805(16), b = 7.4378(15), and c = 8.6594(17) in space group Pmc2(1), is also reported. Two other rubidium thorium fluorides are also described: RbTh(2)F(9) crystallizes in the space group Pnma where a = 8.9101(18), b = 11.829(2), and c = 7.4048(15), and Rb(7)Th(6)F(31) crystallizes in the space group R3 where a = 15.609(2) and c = 10.823(2). Comparison of these materials was made on the basis of their structures and synthesis conditions. The formation of these species in hydrothermal fluids appears to be dependent upon the concentration of the alkali fluoride mineralizer solution and, thus, the ratio of alkali ions to thorium in the system. 相似文献
73.
Jan Tauchen Lukas Huml Ludvik Bortl Ivo Doskocil Veronika Jarosova Petr Marsik 《Natural product research》2019,33(18):2718-2721
Plants mentioned in this study have numerous records in traditional Peruvian medicine being used in treatment of cancer and other diseases likely to be associated with oxidative stress. Amongst the eight plant species tested, only Dysphania ambrosioides exhibited combinatory antioxidant and anti-proliferative effect on a broad spectrum of cancer cells (DPPH and ORAC values = 80.6 and 687.3 μg TE/mg extract, respectively; IC50 against Caco-2, HT-29 and Hep-G2 = 129.2, 69.9 and 130.6, respectively). Alkaloids and phenolic compounds might significantly contribute to anticancer/antioxidant activity of this plant. The results justify the traditional medicinal use of this plant. Our findings further suggest that D. ambrosioides might serve as a prospective material for further development of novel plant-based antioxidant and/or anti-proliferative agents. Detailed analysis of chemical composition together with toxicology assessments and in vivo antioxidant/anti-proliferative activity of this plant should be carried out in order to verify its potential practical use. 相似文献
74.
Florian A. Mann Zhiyi Lv Jrg Großhans Felipe Opazo Sebastian Kruss 《Angewandte Chemie (International ed. in English)》2019,58(33):11469-11473
Fluorescent nanomaterials such as single‐walled carbon nanotubes (SWCNTs) have many advantages in terms of their photophysics, but it is difficult to target them to specific locations in living systems. In contrast, the green fluorescent protein (GFP) has been genetically fused to proteins in many cells and organisms. Therefore, GFP can be seen not only as a fluorophore but as a universal target/handle. Here, we report the conjugation of GFP‐binding nanobodies to DNA‐wrapped SWCNTs. This approach combines the targeting capabilities of GFP‐binding nanobodies and the nonbleaching near‐infrared fluorescence (850–1700 nm) of SWCNTs. These conjugates allow us to track single Kinesin‐5‐GFP motor proteins in developing embryos of Drosophila melanogaster. Additionally, they are sensitive to the neurotransmitter dopamine and can be used for targeted sensing of dopamine in the nm regime. 相似文献
75.
Edit Csapó Péter Buglyó Nóra Veronika Nagy M. Amélia Santos Alma Corona Etelka Farkas 《Polyhedron》2010
Two histidinehydroxamic acid derivatives (N-methyl-histidinehydroxamic acid, N-Me-Hisha and Z-histidinehydroxamic acid, Z-Hisha) have been synthesized and their complexation with Cu2+-, Ni2+- and Zn2+-ions has been studied by using pH-potentiometric, UV–Vis, CD, 1H NMR, EPR and ESI-MS methods. Both of the two new derivatives contain one donor atom less compared to the histidinehydroxamic acid (Hisha). In the case of N-Me-Hisha the hydroxamate-N as donor is eliminated, while the coordination of the amino-N of Z-Hisha is not possible at all. 相似文献
76.
Pavel Jandera Jiří Urban Veronika Škeříková Pavel Langmaier Romana Kubíčková Josef Planeta 《Journal of chromatography. A》2010,1217(1):22-33
We prepared hybrid particle-monolithic polymethacrylate columns for micro-HPLC by in situ polymerization in fused silica capillaries pre-packed with 3–5 μm C18 and aminopropyl silica bonded particles, using polymerization mixtures based on laurylmethacrylate–ethylene dimethacrylate (co)polymers for the reversed-phase (RP) mode and [2-(methacryloyloxy)ethyl]-dimethyl-(3-sulfopropyl) zwitterionic (co)polymers for the hydrophilic interaction (HILIC) mode. The hybrid particle-monolithic columns showed reduced porosity and hold-up volumes, approximately 2–2.5 times lower in comparison to the pure monolithic columns prepared in the whole volume of empty capillaries. The elution volumes of sample compounds are also generally lower in comparison to packed or pure monolithic columns. The efficiency and permeability of the hybrid columns are intermediate in between the properties of the reference pure monolithic and particle-packed columns. The chemistries of the embedded solid particles and of the interparticle monolithic moiety in the hybrid capillary columns contribute to the retention to various degrees, affecting the selectivity of separation. Some hybrid columns provided improved separations of proteins in comparison to the reference particle-packed columns in the reversed-phase mode. Zwitterionic hybrid particle-monolithic columns show dual mode retention HILIC/RP behaviour depending on the composition of the mobile phase and allow separations of polar compounds such as phenolic acids in the HILIC mode at lower concentrations of acetonitrile and, often in shorter analysis time in comparison to particle-packed and full-volume monolithic columns. 相似文献
77.
Zimcik P Novakova V Kopecky K Miletin M Uslu Kobak RZ Svandrlikova E Váchová L Lang K 《Inorganic chemistry》2012,51(7):4215-4223
Magnesium(II), zinc(II), and metal-free phthalocyanines (Pcs) and azaphthalocyanines (AzaPcs) containing alkylsulfanyl, aryloxy, and dialkylamino peripheral substituents have been synthesized. The complexation of magnesium(II) by metal-free Pcs and AzaPcs has been studied in detail to determine the optimal reaction conditions necessary to ensure a complete conversion. Photophysical and photochemical measurements in tetrahydrofuran showed that magnesium(II) AzaPcs with aryloxy and alkylsulfanyl substituents have excellent fluorescent properties (Φ(F) up to 0.73) and that the corresponding zinc(II) Pcs are efficient singlet oxygen producers (Φ(Δ) up to 0.68). The presence of dialkylamino substituents causes intramolecular charge transfer within the molecule that competes with fluorescence and singlet oxygen formation. Alkylsulfanyl MgAzaPc and ZnAzaPc were the most photostable compounds among the series of studied derivatives. In addition, high molar absorption coefficients (ε ~ 300,000 M(-1) cm(-1)), absorption (λ(max) ~ 650 nm), and emission (λ(em) ~ 660 nm, high Φ(F)) in the red region suggest that these molecules are potential fluorescent probes that are superior to the commercial red cyanine dye Cy5. MgAzaPc, when incorporated into lipidic bilayers of liposomes, maintains excellent fluorescence properties (Φ(F) = 0.64). Water-soluble MgAzaPc with quaternary ammonium peripheral substituents retained a high fluorescence quantum yield even in water (Φ(F) = 0.25). The described properties show that magnesium(II) AzaPcs are excellent red-emitting fluorophores with potential applications as fluorescent probes in sensing or in vitro imaging applications. 相似文献
78.
Novakova V Roh J Gela P Kuneš J Zimcik P 《Chemical communications (Cambridge, England)》2012,48(36):4326-4328
The presented work deals with synthesis and isolation of constitutional isomers of triazolo-fused azaphthalocyanines. Distribution of the isomers did not follow the statistical calculations due to steric effects of the substituents preferring the least sterically stressed C(4h) isomer. 相似文献
79.
Mann AK Steinmiller EM Skrabalak SE 《Dalton transactions (Cambridge, England : 2003)》2012,41(26):7939-7945
Polycrystalline microspheres and single-crystalline microplates of Bi(2)WO(6) have been synthesized by ultrasonic spray pyrolysis. Herein, these materials are evaluated as photocatalysts for the visible light mediated degradation of rhodamine B, a model pollutant, and the results compared to those obtained with Bi(2)WO(6) prepared by traditional methods. The microplates, which displayed the best crystallinity and highest surface area, were anticipated to facilitate the greatest rate of dye photodegradation. However, the polycrystalline microspheres outperformed both the Bi(2)WO(6) microplates and traditional samples. To understand the origin of this result, the local and macroscale structures of the Bi(2)WO(6) samples were comprehensively characterized by spectroscopy techniques (diffuse reflectance, fluorescence, Raman, and X-ray photoelectron spectroscopy) as well as electron microscopy and diffraction. This analysis found that the enhanced performance of the Bi(2)WO(6) microspheres results from the expression of a hydrophilic surface, a low concentration of point defects, and a moderate surface area. This finding highlights the significant role synthesis plays in imparting structure and functionality to solid materials. 相似文献