全文获取类型
收费全文 | 1028篇 |
免费 | 51篇 |
国内免费 | 2篇 |
专业分类
化学 | 743篇 |
晶体学 | 13篇 |
力学 | 13篇 |
数学 | 57篇 |
物理学 | 255篇 |
出版年
2024年 | 2篇 |
2023年 | 16篇 |
2022年 | 36篇 |
2021年 | 34篇 |
2020年 | 44篇 |
2019年 | 60篇 |
2018年 | 52篇 |
2017年 | 34篇 |
2016年 | 57篇 |
2015年 | 41篇 |
2014年 | 100篇 |
2013年 | 104篇 |
2012年 | 68篇 |
2011年 | 69篇 |
2010年 | 37篇 |
2009年 | 28篇 |
2008年 | 41篇 |
2007年 | 31篇 |
2006年 | 27篇 |
2005年 | 22篇 |
2004年 | 27篇 |
2003年 | 17篇 |
2002年 | 20篇 |
2001年 | 14篇 |
2000年 | 7篇 |
1999年 | 10篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 6篇 |
1995年 | 9篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 8篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 8篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1939年 | 1篇 |
排序方式: 共有1081条查询结果,搜索用时 46 毫秒
931.
Arshpreet Kaur Sapna Singla Anupam Dixit G. P. Kothiyal K. Krishnan 《Phase Transitions》2013,86(8):759-777
Lead silicate glasses containing 40–65?mol% of PbO were prepared at two melt-quenching rates and characterized by X-ray diffraction, UV-Visible absorption spectroscopy, density, microhardness, thermo-mechanical analysis, differential scanning calorimetry and Raman scattering studies. On increasing the PbO concentration, density increases, glass transition temperature decreases and the optical absorption edge shifts towards longer wavelength. An intense optical absorption band was observed just below the absorption edge in glasses with 55?mol% and higher concentration of PbO. Dilatometric measurements show an unusual property that glasses do not show any abrupt increase in volume near the glass transition temperature but transform directly into the liquid state. Raman spectroscopy confirmed that the concentration of SiO4 tetrahedra containing one or more NBOs increase with PbO mol%. Devitrification studies on lead silicate glasses found that samples with 40–45?mol% of PbO do not crystallize, whereas samples with higher PbO concentration produce multiple crystalline phases like PbSiO3, Pb33Si24O81, Pb2SiO4 and Pb3Si2O7 on heat treatment. 相似文献
932.
Asiya Nazir Rohit Soni H. S. Saini Amarjeet Kaur B. S. Chadha 《Applied biochemistry and biotechnology》2010,162(2):538-547
This study reports differential expression of endoglucanase (EG) and β-glucosidase (βG) isoforms of Aspergillus terreus. Expression of multiple isoforms was observed, in presence of different carbon sources and culture conditions, by activity
staining of poly acrylamide gel electrophoresis gels. Maximal expression of four EG isoforms was observed in presence of rice
straw (28 U/g DW substrate) and corn cobs (1.147 U/ml) under solid substrate and shake flask culture, respectively. Furthermore,
the sequential induction of EG isoforms was found to be associated with the presence of distinct metabolites (monosaccharides/oligosaccharides)
i.e., xylose (X), G1, G3 and G4 as well as putative positional isomers (G1/G2, G2/G3) in the culture extracts sampled at different time intervals, indicating specific role of these metabolites in the sequential
expression of multiple EGs. Addition of fructose and cellobiose to corn cobs containing medium during shake flask culture
resulted in up-regulation of EG activity, whereas addition of mannitol, ethanol and glycerol selectively repressed the expression
of three EG isoforms (Ia, Ic and Id). The observed regulation profile of βG isoforms was distinct when compared to EG isoforms,
and addition of glucose, fructose, sucrose, cellobiose, mannitol and glycerol resulted in down-regulation of one or more of
the four βG isoforms. 相似文献
933.
Sukhdeep Kaur Gurmeet Singh Virendra K. Gupta 《Journal of polymer science. Part A, Polymer chemistry》2009,47(8):2156-2162
Montmorillionite K10 powder presence during radically initiated copolymerization of methyl acrylate (M) and 1‐octene (O) gave copolymers with higher incorporation of alkene unit. Highly viscous and transparent copolymers showed alternation irrespective of the copolymer composition. Increasing the amount of K10 powder increased the total percentage conversion, as well as 1‐octene incorporation. The monomodal curves obtained in gel permeation chromatography (GPC) substantiated that true copolymers were formed. The alternation in the copolymers was authenticated through Heteronuclear Multiple Quantum Correlation (HMQC) experiments in conjugation with Total Correlated Spectroscopy (TOCSY). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2156–2162, 2009 相似文献
934.
935.
936.
Salwinder Singh Dhaliwal Vivek Sharma Arvind Kumar Shukla Vibha Verma Sanjib Kumar Behera Prabhjodh Singh Sandhu Kamaljit Kaur Ahmed Gaber Yusuf S. Althobaiti Abdelhadi A. Abdelhadi Akbar Hossain 《Molecules (Basel, Switzerland)》2021,26(21)
To achieve the nutritional target of human food, boron (B) has been described as an essential mineral in determining seed and theoretical oil yield of Sesamum indicum L. The research to increase its cultivation is garnering attention due to its high oil content, quality and its utilization for various purposes, which include human nutrition as well as its use in the food industry. For this, a two-year field experiment was performed at PAU, Punjab, India to determine the effect of different concentrations of foliar-applied B (20, 30 and 40 mg L−1) and different growth stages of crop, i.e., we measured the effects on agroeconomic indicators and certain quality parameters of sesame using different concentrations of B applied at the flowering and capsule formation stages as compared to using water spray and untreated plants. Water spray did not significantly affect the studied parameters. However, B application significantly increased the yield, uptake, antioxidant activity (AOA) and theoretical oil content (TOC) compared to those of untreated plants. The maximum increase in seed yield (26.75%), B seed and stover uptake (64.08% and 69.25%, respectively) as well as highest AOA (69.41%) and benefit to cost ratio (B:C ratio 2.63) was recorded when B was applied at 30 mg L−1 at the flowering and capsule formation stages. However, the maximum sesame yield and B uptake were recorded when B was applied at a rate of 30 mg L−1. A significant increase in TOC was also recorded with a B application rate of 30 mg L−1. For efficiency indices, the higher values of boron agronomic efficiency (BAE) and boron crop recovery efficiency (BCRE) were recorded when B was applied at 20 mg L−1 (5.25 and 30.56, respectively) and 30 mg L−1 (4.96 and 26.11, respectively) at the flowering and capsule formation stages. In conclusion, application of B @ 30 mg L−1 at the flowering and capsule formation stages seemed a viable technique to enhance yield, B uptake and economic returns of sesame. 相似文献
937.
Amandeep Kaur Sra Marius Andruh Olivier Kahn Stphane Golhen Lahcne Ouahab J. V. Yakhmi 《Angewandte Chemie (International ed. in English)》1999,38(17):2606-2609
Long-range ferromagnetic ordering at 3 K is observed for the title compound, which may be considered as a fully localized mixed-valence species (Mo3+ and Mo4+) as well as a mixed-spin species (low-spin and high-spin Mn2+ ions). Its two-dimensional structure consists of heart-shaped 48-membered rings, and each ring contains 16 metal centers (see picture). 相似文献
938.
939.
Reem Smoum Christeene Haj Shira Hirsch Alina Nemirovski Zhannah Yekhtin Benny Bogoslavsky Gaganjyot Kaur Bakshi Mukesh Chourasia Ruth Gallily Joseph Tam Raphael Mechoulam 《Molecules (Basel, Switzerland)》2022,27(4)
A series of novel cannabinoid-type derivatives were synthesized by the coupling of (1S,4R)-(+) and (1R,4S)-(−)-fenchones with various resorcinols/phenols. The fenchone-resorcinol derivatives were fluorinated using Selectfluor and demethylated using sodium ethanethiolate in dimethylformamide (DMF). The absolute configurations of four compounds were determined by X-ray single crystal diffraction. The fenchone-resorcinol analogs possessed high affinity and selectivity for the CB2 cannabinoid receptor. One of the analogues synthesized, 2-(2′,6′-dimethoxy-4′-(2″-methyloctan-2″-yl)phenyl)-1,3,3-trimethylbicyclo[2.2.1]heptan-2-ol (1d), had a high affinity (Ki = 3.51 nM) and selectivity for the human CB2 receptor (hCB2). In the [35S]GTPγS binding assay, our lead compound was found to be a highly potent and efficacious hCB2 receptor agonist (EC50 = 2.59 nM, E(max) = 89.6%). Two of the fenchone derivatives were found to possess anti-inflammatory and analgesic properties. Molecular-modeling studies elucidated the binding interactions of 1d within the CB2 binding site. 相似文献
940.
Jasmeet Kaur Md. Khalid Anwer Ali Sartaj Bibhu Prasad Panda Abuzer Ali Ameeduzzafar Zafar Vinay Kumar Sadaf Jamal Gilani Chandra Kala Mohamad Taleuzzaman 《Molecules (Basel, Switzerland)》2022,27(4)
The objective of the current research is to develop ZnO-Manjistha extract (ZnO-MJE) nanoparticles (NPs) and to investigate their transdermal delivery as well as antimicrobial and antioxidant activity. The optimized formulation was further evaluated based on different parameters. The ZnO-MJE-NPs were prepared by mixing 10 mM ZnSO4·7H2O and 0.8% w/v NaOH in distilled water. To the above, a solution of 10 mL MJE (10 mg) in 50 mL of zinc sulfate was added. Box–Behnken design (Design-Expert software 12.0.1.0) was used for the optimization of ZnO-MJE-NP formulations. The ZnO-MJE-NPs were evaluated for their physicochemical characterization, in vitro release activity, ex vivo permeation across rat skin, antimicrobial activity using sterilized agar media, and antioxidant activity by the DPPH free radical method. The optimized ZnO-MJE-NP formulation (F13) showed a particle size of 257.1 ± 0.76 nm, PDI value of 0.289 ± 0.003, and entrapment efficiency of 79 ± 0.33%. Drug release kinetic models showed that the formulation followed the Korsmeyer–Peppas model with a drug release of 34.50 ± 2.56 at pH 7.4 in 24 h. In ex vivo studies ZnO-MJE-NPs-opt permeation was 63.26%. The antibacterial activity was found to be enhanced in ZnO-MJE-NPs-opt and antioxidant activity was found to be highest (93.14 ± 4.05%) at 100 µg/mL concentrations. The ZnO-MJE-NPs-opt formulation showed prolonged release of the MJE and intensified permeation. Moreover, the formulation was found to show significantly (p < 0.05) better antimicrobial and antioxidant activity as compared to conventional suspension formulations. 相似文献