全文获取类型
收费全文 | 1541篇 |
免费 | 72篇 |
国内免费 | 15篇 |
专业分类
化学 | 909篇 |
晶体学 | 17篇 |
力学 | 35篇 |
数学 | 379篇 |
物理学 | 288篇 |
出版年
2024年 | 3篇 |
2023年 | 14篇 |
2022年 | 36篇 |
2021年 | 43篇 |
2020年 | 32篇 |
2019年 | 43篇 |
2018年 | 43篇 |
2017年 | 51篇 |
2016年 | 60篇 |
2015年 | 43篇 |
2014年 | 97篇 |
2013年 | 141篇 |
2012年 | 109篇 |
2011年 | 95篇 |
2010年 | 83篇 |
2009年 | 64篇 |
2008年 | 97篇 |
2007年 | 80篇 |
2006年 | 81篇 |
2005年 | 53篇 |
2004年 | 62篇 |
2003年 | 49篇 |
2002年 | 41篇 |
2001年 | 19篇 |
2000年 | 19篇 |
1999年 | 19篇 |
1998年 | 7篇 |
1997年 | 6篇 |
1996年 | 9篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1993年 | 9篇 |
1992年 | 10篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 11篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1982年 | 15篇 |
1981年 | 1篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有1628条查询结果,搜索用时 15 毫秒
51.
The present work describes the synthesis, characterization and application of functionalized surfactants derived through simple organic reaction steps. These surfactants have been particularly tailor made to resist hardness due to calcium ions in water. It is unique of its kind because here the surfactants have an analogous hydrophobic chain but differ structurally in the composition of the head groups in terms of the position of attachment of the chain. The effect of this small variability in the head group on the surfactant property, adsorption, self assembly and calcium tolerance behaviour has been studied in detail. This kind of phenol–keto surfactants has not been reported before. It was also found that one of the surfactants was more tolerant towards Ca2+ ion than the other. The individual packing behaviour of the surfactants at the air–water interface has been projected to cause this difference which is very interesting. 相似文献
52.
The indolones nucleus is the central core to develop new effective anticancer agents and its substitution at the 3-position can affect antitumor activity, 3-spirocyclopropyl-2-oxindoles have attracted the scientist's community to design and develop expedition's strategies towards their construction and explore the potential of this useful scaffold with their newer derivatives in medicinal world. The present paper describes the synthesis of 3-spirocyclopropyl-2-indolone derivatives in three steps via synthesis of ylide leading to methylene-indolinones followed by the formation of the final product spirocyclopropyl oxindole derivatives with improved yields. In this milieu we considered motivating to advance exploration the biological potencies and computational studies of our newly synthesized molecules. The aimed target molecules were screened for antimicrobial and anticancer activities where they exhibited substantial effective antimicrobial activities. Amongst them, potent compound, bromospirocyclopropyl indolone, 6d displayed encouraging MIC ranging from 0.007 to 0.49 μg/mL for gram positive microbes and also substantial anticancer activity with an IC50 of 11.5 μg/mL. Finally, the computational modelling studies were performed to explore structure-activity relationship analysis. Active site of receptor protein shows docking scores of these molecules as - 5.78 kcal/mol and ?5.097 kcal/mol for the docked target proteins. The binding energy of the best score is found to be ?41.67 kcal/mol to ?44.67 kcal/mol. Thus, the present paper efficaciously validated spirocyclopropyl indolone framework for drug candidates as potent anticancer as well as antimicrobial compounds. 相似文献
53.
54.
Tripathi Ravi P. Alvi M. A. Khan Shamshad A. 《Journal of Thermal Analysis and Calorimetry》2021,146(5):2261-2272
Journal of Thermal Analysis and Calorimetry - In our present research work, we have investigated the different thermal, optical and electrical properties of Se85In15?xBix alloys in bulk and... 相似文献
55.
Dr. Bhupendra Goswami Dr. Thomas J. Feuerstein Dr. Ravi Yadav Dr. Ralf Köppe Dr. Sergei Lebedkin Prof. Dr. Manfred M. Kappes Prof. Dr. Peter W. Roesky 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(13):4401-4411
The synthesis of calcium complexes ligated by three different chiral iminophosphonamide ligands, L- H ( L =[Ph2P{N(R)CH(CH3)Ph}2]), L′ -H ( L′ =[Ph2P{NDipp}{N(R)CH(CH3)Ph}]), (Dipp=2,6-iPr2C6H3), and L′′ -H ( L′′ =[Ph2P{N(R)CH(CH3)naph}2]), (naph=naphthyl) is presented. The resulting structures [ L 2Ca], [ L′ 2Ca], and [ L′′ 2Ca] represent the first examples of enantiopure homoleptic calcium complexes based on this type of ligands. The calcium complexes show blue–green photoluminescence (PL) in the solid state, which is especially bright at low temperatures. Whereas the emission of [ L′′ 2Ca] is assigned to the fluorescence of naphthyl groups, the PL of [ L 2Ca] and [ L′ 2Ca] is contributed by long-lived phosphorescence and thermally activated delayed fluorescence (TADF), with a strong variation of the PL lifetimes over the temperature range of 5–295 K. Furthermore, an excellent catalytic activity was found for these complexes in hydroboration of ketones at room temperature, although no enantioselectivity was achieved. 相似文献
56.
Noah Schwarz Xiaofei Sun Dr. Ravi Yadav Dr. Ralf Köppe Dr. Thomas Simler Prof. Dr. Peter W. Roesky 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(50):12857-12865
Divalent lanthanide and alkaline-earth complexes supported by N-heterocyclic carbene (NHC) ligands have been accessed by redox-transmetalation between air-stable NHC-AgI complexes and the corresponding metals. By using the small ligand 1,3-dimethylimidazol-2-ylidene (IMe), two series of isostructural complexes were obtained: the tetra-NHC complexes [LnI2(IMe)4] (Ln=Eu and Sm) and the bis-NHC complexes [MI2(IMe)2(THF)2] (M=Yb, Ca and Sr). In the former, distortions in the NHC coordination were found to originate from intermolecular repulsions in the solid state. Application of the redox-transmetalation strategy with the bulkier 1,3-dimesitylimidazol-2-ylidene (IMes) ligand yielded [SrI2(IMes)(THF)3], while using a similar procedure with Ca metal led to [CaI2(THF)4] and uncoordinated IMes. DFT calculations were performed to rationalise the selective formation of the bis-NHC adduct in [SrI2(IMe)2(THF)2] and the tetra-NHC adduct in [SmI2(IMe)4]. Since the results in the gas phase point towards preferential formation of the tetra-NHC complexes for both metal centres, the differences between both arrangements are a result of solid-state effects such as slightly different packing forces. 相似文献
57.
58.
Lay-Koon Goh Ravi Kiran Purama Kumar Sudesh 《Applied biochemistry and biotechnology》2014,172(3):1585-1598
Poly(3-hydroxybutyrate) [P(3HB)], a polymer belonging to the polyhydroxyalkanoate (PHA) family, is accumulated by numerous bacteria as carbon and energy storage material. The mobilization of accumulated P(3HB) is associated with increased stress and starvation tolerance. However, the potential function of accumulated copolymer such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] remained unknown. In this study, Delftia acidovorans DS 17 was used to evaluate the contributions of P(3HB) and P(3HB-co-3HV) granules during simulated exogenous carbon deprivation on cell survival by transferring cells with PHAs to carbon-free mineral salt medium supplemented with 1 % (w/v) nitrogen source. By mobilizing the intracellular P(3HB) and P(3HB-co-3HV) at 11 and 40 mol% 3HV compositions, the cells survived starvation. Surprisingly, D. acidovorans containing P(3HB-co-94 mol% 3HV) also survived although the mobilization was not as effective. Similarly, recombinant Escherichia coli pGEM-T::phbCAB Cn (harboring the PHA biosynthesis genes of Cupriavidus necator) containing P(3HB) granules had a higher viable cell counts compared to those without P(3HB) granules but without any P(3HB) mobilization when exposed to oxidative stress by photoactivated titanium dioxide. This study provided strong evidence that enhancement of stress tolerance in PHA producers can be achieved without mobilization of the previously accumulated granules. Instead, PHA biosynthesis may improve bacterial survival via multiple mechanisms. 相似文献
59.
Debabrata Chatterjee Swapan Kumar Moulik Lingamallu Giribabu Ravi Kumar Kanaparthi 《Transition Metal Chemistry》2014,39(6):641-646
The Fe(III) complex, [FeIII(HQS)3] (HQS = 8-hydroxyquinoline-5-sulfonic acid), is found to effect sensitization of the large band gap semiconductor, TiO2. The role of interfacial electron transfer in sensitization of TiO2 nanoparticles by surface adsorbed [FeIII(HQS)3] was studied using femtosecond time scale transient absorption spectroscopy. Electron injection has been confirmed by direct detection of the electron in the conduction band. A TiO2-based dye-sensitized solar cell (DSSC) was fabricated using [FeIII(HQS)3] as a sensitizer, and the resulting DSSC exhibited an open-circuit voltage value of 425 mV. The value of the short-circuit photocurrent was found to be 2.5 mA/cm2. The solar to electric power conversion efficiency of the [FeIII(HQS)3] sensitized TiO2-based DSSC device was 0.75 %. The results are discussed in the context of sensitization of TiO2 by other Fe(II)-dye complexes. 相似文献
60.
Jagjeet Kaur Ravi Shrivastava Vikas Dubey Beena Jaykumar 《Research on Chemical Intermediates》2014,40(8):2599-2604
This paper reports thermoluminescence glow curves of Eu3+, Dy3+-doped Ba2MgSi2O7 phosphor for different UV exposure times. Kinetic data were evaluated by the peak-shape method. The glow curves shift toward higher intensity with increasing exposure time to UV at 365 nm. When the heating rate was 5 °C s?1, peaks were observed at 101.76, 109.69, 102.67, and 104.05 °C, respectively, after UV exposure for 5, 10, 15, and 20 min. The glow peaks are indicative of second-order kinetics. Different kinetic data, i.e. trap depth, order of kinetics, activation energy, and frequency factor were also calculated. To evaluate the persistence characteristics of the luminescence of the phosphor, the lifetime of the charge in the trap was calculated; it was 348, 660, 368, and 428 s for UV exposure of 5, 10, 15, and 20 min, which indicates the luminescence of the phosphor is persistent. 相似文献