全文获取类型
收费全文 | 2765篇 |
免费 | 152篇 |
国内免费 | 19篇 |
专业分类
化学 | 2049篇 |
晶体学 | 44篇 |
力学 | 69篇 |
数学 | 175篇 |
物理学 | 599篇 |
出版年
2024年 | 4篇 |
2023年 | 28篇 |
2022年 | 72篇 |
2021年 | 76篇 |
2020年 | 63篇 |
2019年 | 77篇 |
2018年 | 58篇 |
2017年 | 48篇 |
2016年 | 100篇 |
2015年 | 104篇 |
2014年 | 122篇 |
2013年 | 182篇 |
2012年 | 221篇 |
2011年 | 277篇 |
2010年 | 145篇 |
2009年 | 147篇 |
2008年 | 199篇 |
2007年 | 164篇 |
2006年 | 163篇 |
2005年 | 151篇 |
2004年 | 110篇 |
2003年 | 87篇 |
2002年 | 87篇 |
2001年 | 39篇 |
2000年 | 47篇 |
1999年 | 26篇 |
1998年 | 22篇 |
1997年 | 15篇 |
1996年 | 15篇 |
1995年 | 15篇 |
1994年 | 14篇 |
1993年 | 11篇 |
1992年 | 8篇 |
1991年 | 12篇 |
1990年 | 12篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1982年 | 1篇 |
排序方式: 共有2936条查询结果,搜索用时 15 毫秒
991.
Plasma surface functionalization of poly[bis(2,2,2-trifluoroethoxy)phosphazene] films and nanofibers 总被引:1,自引:0,他引:1
Allcock HR Steely LB Kim SH Kim JH Kang BK 《Langmuir : the ACS journal of surfaces and colloids》2007,23(15):8103-8107
Polyphosphazenes are a class of hybrid organic-inorganic macromolecules with high thermo-oxidative stability and good solubility in many solvents. Fluoroalkoxy phosphazene polymers also have high surface hydrophobicity. A method is described to tune this surface property while maintaining the advantageous bulk materials characteristics. The polyphosphazene single-substituent polymer, poly[bis(2,2,2-trifluoroethoxy)phosphazene], with flat film, fiber mat, or bead mat morphology was surface functionalized using an atmospheric plasma treatment with oxygen, nitrogen, methane, or tetrafluoromethane/hydrogen gases. Surface chemistry changes were detected by static water contact angle (WCA) measurements as well as X-ray photon spectroscopy (XPS). It was found that changes in the WCA of as much as 150 degrees occurred, accompanied by shifts in the ratio of elements on the polymer surface as detected by XPS. Overall this plasma technique provides a convenient method for the generation of specific surface characteristics while maintaining the hydrophobicity of the bulk material. 相似文献
992.
993.
994.
Ligand-dependent particle size control of PbSe quantum dots 总被引:1,自引:0,他引:1
Baek IC Seok SI Pramanik NC Jana S Lim MA Ahn BY Lee CJ Jeong YJ 《Journal of colloid and interface science》2007,310(1):163-166
Colloidal solutions of monodisperse PbSe quantum dots (QDs) were synthesized by a hot solution chemical method from a reaction mixture of lead oleate and TOPSe (TOP: tri-n-octylphosphine). The synthesis was carried out at a fixed temperature (170 degrees C) and time, while the particle sizes of the PbSe QDs were controlled by using two different kinds of organic ligands with varied chain length. It was seen that the tuning of PbSe QDs are possible by using the proper molar ratio of the co-ligands, such as acetic acid or hexanoic acid, at a fixed reaction temperature and time, verified by TEM and XRD as well as NIR absorption analysis. The effects of different organic acids were studied and the role of additional organic acids might be due to the extent of ligand exchange efficiency between the Pb oleate and acetic/hexanoic acid in the initial stage, which is caused by the steric hindrance effects of the acids. 相似文献
995.
Aromatic helical receptors P- 1 and P- 2 were slightly modified by aerobic oxidation to afford new receptors P- 7 and P- 8 with right-handed helical cavities. This subtle modification induced significant changes in the binding properties for chiral guests. Specifically, P- 1 was reported to bind d -tartaric acid (Ka=35500 M−1), used as a template, much strongly than l -tartaric acid (326 M−1). In contrast, its modified receptor P- 7 exhibited significantly reduced affinities for d -tartaric acid (3600 M−1) and l -tartaric acid (125 M−1). More dramatic changes in the affinities and selectivities were observed for P- 2 and P- 8 upon binding of polyol guests. P- 2 was determined to selectively bind d -sorbitol (52000 M−1) over analogous guests, but P- 8 showed no binding selectivity: d -sorbitol (1890 M−1), l -sorbitol (3330 M−1), d -arabitol (959 M−1), l -arabitol (4970 M−1) and xylitol (4960 M−1) in 5% (v/v) DMSO/CH2Cl2 at 25±1 °C. These results clearly demonstrate that even subtle post-modifications of synthetic receptors may significantly alter their binding affinities and selectivities, in particular for guests of long and flexible chains. 相似文献
996.
Ga-Ram Kim Eun-Nam Kim Kyoung Jin Park Ki Hyun Kim Gil-Saeng Jeong 《Molecules (Basel, Switzerland)》2021,26(6)
Osteoblasts and osteoclasts play a pivotal role in maintaining bone homeostasis, of which excessive bone resorption by osteoclasts can cause osteoporosis and various bone diseases. However, current osteoporosis treatments have many side effects, and research on new treatments that can replace these treatments is ongoing. Therefore, in this study, the roles of ligustroside (LGS) and oleoside dimethylester (ODE), a natural product-derived compound isolated from Syringa oblata subsp. dilatata as a novel, natural product-derived osteoporosis treatments were investigated. In the results of this study, LGS and ODE inhibited the differentiation of receptor activator of nuclear factor kappa-Β ligand (RANKL)-induced RAW264.7 cells into osteoclasts without cytotoxicity, and down-regulated the activity of TRAP, a specific biomarker of osteoclasts. In addition, it inhibited bone resorption and actin ring formation, which are important functions and features of osteoclasts. Also, the effects of LGS and ODE on the mitogen-activated protein kinase (MAPK) and nuclear factor kappa-light-chain-enhancer of activated B (NF-κB) and phosphoinositide 3-kinases (PI3K)/ protein kinase B (Akt)/mechanistic target of rapamycin (mTOR) signaling pathways that play important roles in osteoclast differentiation were evaluated. In the results, LGS and ODE downregulated the phosphorylation of RANKL-induced MAPK and PI3K/Akt/mTOR proteins in a concentration-dependent manner, translocation of NF-κB into the nucleus was inhibited. As a result, the compounds LGS and ODE isolated from S. oblate subsp. dilatata effectively regulated the differentiation of RANKL-induced osteoclasts and inhibited the phosphorylation of signaling pathways that play a pivotal role in osteoclast differentiation. Therefore, these results suggest the possibility of LGS and ODE as new natural product treatments for bone diseases caused by excessive osteoclasts. 相似文献
997.
Seok-In Jang Han Young Eom Jeong Ho Hwang Lila Kim Jong-Hwa Lee 《Molecules (Basel, Switzerland)》2021,26(4)
Sialyllactose (SL), an acidic oligosaccharide, has immune-protective effects against pathogens and helps with the development of the immune system and intestinal microorganisms. To elucidate the pharmacokinetic characterization after oral administration to rats, the simultaneous quantification method for 3′-SL and 6′-SL in rat plasma was validated, using liquid chromatography-tandem mass spectrometry (LC-MS/MS) in an electrospray ionization (ESI) mode. Several types of columns [C18, amide, and hydrophilic interaction liquid chromatography (HILIC) phase] were used to separate the peaks of 3′-SL and 6′-SL, which improved chromatographic selectivity. Ultimately, the HILIC phase column had a good peak shape and quick resolution, with a mobile phase comprising ammonium acetate buffer and acetonitrile obtained by gradient elution. In addition, the simultaneous quantification of 3′-SL and 6′-SL in rat plasma samples were adequately applied to pharmacokinetic study. 相似文献
998.
Periodontitis is a set of chronic inflammatory diseases caused by the accumulation of Gram-negative bacteria on teeth, resulting in gingivitis, pocket formation, alveolar bone loss, tissue destruction, and tooth loss. In this study, the contents of ginsenosides isolated from Panax ginseng fruit extract were quantitatively analyzed, and the anti-inflammatory effects were evaluated in human periodontal ligament cells. The major ginsenosides, Re, Ra8, and Rf, present in ginseng fruit were simultaneously analyzed by a validated method using high-performance liquid chromatography with a diode-array detector; Re, Ra8, and Rf content per 1 g of P. ginseng fruit extract was 1.01 ± 0.03, 0.33 ± 0.01, and 0.55 ± 0.04 mg, respectively. Ginsenosides-Re, -Ra8, and -Rf inhibited the production of pro-inflammatory factors and the expression of important cytokines in periodontitis by inducing the expression of heme oxygenase 1 (HO-1), promoting osteoblast differentiation of periodontal ligament cells, suppressing alveolar bone loss, and promoting the expression of osteoblast-specific genes, such as alp, opn, and runx2. An inhibitory effect of these ginsenosides on periodontitis and alveolar bone loss was observed via the regulation of HO-1 and subsequent epidermal growth factor receptor (EGFR) signaling. Silencing EGFR with EGFR siRNA confirmed that the effect of ginsenosides on HO-1 is mediated by EGFR. In conclusion, this study evaluated the contents of ginsenosides-Re, -Ra8, and -Rf isolated from P. ginseng fruit extract. Therefore, these results provide important basic data for future P. ginseng fruit component studies and suggest that ginsenosides Re, Ra8, and Rf have potential as future treatment options for periodontitis. 相似文献
999.
Jeong Han Kim Jae Hong Kim Jun-Pil Jang Jae-Hyuk Jang Deuk-Hee Jin Yong Soo Kim Hyung-Joo Jin 《Molecules (Basel, Switzerland)》2021,26(9)
Coffee has been shown to attenuate sarcopenia, the age-associated muscle atrophy. Myostatin (MSTN), a member of the TGF-β growth/differentiation factor superfamily, is a potent negative regulator of skeletal muscle mass, and MSTN-inhibition increases muscle mass or prevents muscle atrophy. This study, thus, investigated the presence of MSTN-inhibitory capacity in coffee extracts. The ethanol-extract of coffee silverskin (CSE) but not other extracts demonstrated anti-MSTN activity in a pGL3-(CAGA)12-luciferase reporter gene assay. CSE also blocked Smad3 phosphorylation induced by MSTN but not by GDF11 or Activin A in Western blot analysis, demonstrating its capacity to block the binding of MSTN to its receptor. Oral administration of CSE significantly increased forelimb muscle mass and grip strength in mice. Using solvent partitioning, solid-phase chromatography, and reverse-phase HPLC, two peaks having MSTN-inhibitory capacity were purified from CSE. The two peaks were identified as βN-arachinoyl−5-hydroxytryptamide (C20−5HT) and βN-behenoyl−5-hydroxytryptamide (C22−5HT) using mass spectrometry and NMR analysis. In summary, the results show that CSE has the MSTN-inhibitory capacity, and C20−5HT and C22−5HT are active components of CSE-suppressing MSTN activity, suggesting the potential of CSE, C20−5HT, and C22−5HT being developed as agents to combat muscle atrophy and metabolic syndrome. 相似文献
1000.
Jihyun Hwang Heeju Jun Seoye Roh Seong Jae Lee Jeong Min Mun Seung Wook Kim Min-Yu Chung In-Hwan Kim Byung Hee Kim 《Molecules (Basel, Switzerland)》2021,26(11)
Herein, we prepared 1,3-dipalmitoyl-2-oleoyl glycerol (POP)-rich fats with reduced levels of diacylglycerols (DAGs), adversely affecting the tempering of chocolate, via two-step hexane fractionation of palm stearin. DAG content in the as-prepared fats was lower than that in POP-rich fats obtained by previously reported conventional two-step acetone fractionation. Cocoa butter equivalents (CBEs) were fabricated by blending the as-prepared fats with 1,3-distearoyl-2-oleoyl glycerol (SOS)-rich fats obtained by hexane fractionation of degummed shea butter. POP-rich fats achieved under the best conditions for the fractionation of palm stearin had a significantly lower DAG content (1.6 w/w%) than that in the counterpart (4.6 w/w%) prepared by the previously reported method. The CBEs fabricated by blending the POP- and SOS-rich fats in a weight ratio of 40:60 contained 63.7 w/w% total symmetric monounsaturated triacylglycerols, including 22.0 w/w% POP, 8.6 w/w% palmitoyl-2-oleoyl-3-stearoyl-rac-glycerol, 33.1 w/w% SOS, and 1.3 w/w% DAGs, which was not substantially different from the DAG content in cocoa butter (1.1 w/w%). Based on the solid-fat content results, it was concluded that, when these CBEs were used for chocolate manufacture, they blended with cocoa butter at levels up to 40 w/w%, without distinctively altering the hardness and melting behavior of cocoa butter. 相似文献