全文获取类型
收费全文 | 1579篇 |
免费 | 69篇 |
国内免费 | 9篇 |
专业分类
化学 | 1021篇 |
晶体学 | 12篇 |
力学 | 54篇 |
数学 | 110篇 |
物理学 | 460篇 |
出版年
2024年 | 2篇 |
2023年 | 6篇 |
2022年 | 28篇 |
2021年 | 26篇 |
2020年 | 23篇 |
2019年 | 30篇 |
2018年 | 20篇 |
2017年 | 24篇 |
2016年 | 50篇 |
2015年 | 45篇 |
2014年 | 55篇 |
2013年 | 110篇 |
2012年 | 122篇 |
2011年 | 105篇 |
2010年 | 88篇 |
2009年 | 64篇 |
2008年 | 118篇 |
2007年 | 114篇 |
2006年 | 105篇 |
2005年 | 99篇 |
2004年 | 62篇 |
2003年 | 69篇 |
2002年 | 70篇 |
2001年 | 34篇 |
2000年 | 33篇 |
1999年 | 14篇 |
1998年 | 18篇 |
1997年 | 11篇 |
1996年 | 23篇 |
1995年 | 26篇 |
1994年 | 7篇 |
1993年 | 11篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1974年 | 4篇 |
1973年 | 1篇 |
1970年 | 1篇 |
1968年 | 2篇 |
1963年 | 1篇 |
1961年 | 1篇 |
排序方式: 共有1657条查询结果,搜索用时 203 毫秒
991.
Jung-Hoon Pyun Byeong-Yun Ahn Tuan Anh Vuong Su Woo Kim Yunju Jo Jaehyung Jeon Seung Ho Baek Jaewon Kim Sungsu Park Gyu-Un Bae Jun-Hyuk Choi Jae-Ryong Kim Dongryeol Ryu Sang-Jin Lee Jong-Sun Kang 《Experimental & molecular medicine》2021,53(10):1569
Vascular smooth muscle cells (VSMCs) have remarkable plasticity in response to diverse environmental cues. Although these cells are versatile, chronic stress can trigger VSMC dysfunction, which ultimately leads to vascular diseases such as aortic aneurysm and atherosclerosis. Protein arginine methyltransferase 1 (Prmt1) is a major enzyme catalyzing asymmetric arginine dimethylation of proteins that are sources of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase. Although a potential role of Prmt1 in vascular pathogenesis has been proposed, its role in vascular function has yet to be clarified. Here, we investigated the role and underlying mechanism of Prmt1 in vascular smooth muscle contractility and function. The expression of PRMT1 and contractile-related genes was significantly decreased in the aortas of elderly humans and patients with aortic aneurysms. Mice with VSMC-specific Prmt1 ablation (smKO) exhibited partial lethality, low blood pressure and aortic dilation. The Prmt1-ablated aortas showed aortic dissection with elastic fiber degeneration and cell death. Ex vivo and in vitro analyses indicated that Prmt1 ablation significantly decreased the contractility of the aorta and traction forces of VSMCs. Prmt1 ablation downregulated the expression of contractile genes such as myocardin while upregulating the expression of synthetic genes, thus causing the contractile to synthetic phenotypic switch of VSMCs. In addition, mechanistic studies demonstrated that Prmt1 directly regulates myocardin gene activation by modulating epigenetic histone modifications in the myocardin promoter region. Thus, our study demonstrates that VSMC Prmt1 is essential for vascular homeostasis and that its ablation causes aortic dilation/dissection through impaired myocardin expression.Subject terms: Epigenetics, Cardiovascular diseases 相似文献
992.
Yun‐Hi Kim Byeong‐Kwan Ahn Dong‐Cheol Shin Han‐Seong Yu Woo‐Hong Kim Soon‐Ki Kwon 《Macromolecular Symposia》2000,154(1):171-176
Poly[4,4′‐biphenylene‐α‐(9”,9”‐dihexyl‐2‐fluorenyl)vinylene] (PBPHFV) was synthesized by nickel catalyzed coupling reaction of 1,2‐bis(bromophenyl)‐1‐(9”,9”‐dihexyl‐2‐fluorenyl)ethene and characterized by spectroscopic methods and elemental analysis. PBPHFV is soluble in common organic solvents. The weight average molecular weight (Mw) of PBPHFV is about 15000. PBPHFV showed good thermal stability as weight loss was less than 5 % on heating to 420 C under nitrogen atmosphere. The polymer film showed maximum absorption and emission at 370 nm and 485 nm, respectively. A bright blue electroluminescence (λmax = 465nm, maximum intensity = 4116 cd/m²) was obtained when the device was fabricated with the structure of ITO/PEDOT/PBPHFV/LiF/Al. The turn on voltage of the device was 4.3 V and the maximum efficiency was 0.22 lm/W. When the blend with PVK (PBPHFV : PVK = 1:5) was used as an emitting layer, the maximum brightness and efficiency of the device were 9342 cd/m² and 1.66 lm/W, respectively. 相似文献
993.
Lei Wang Hyun-Soo Kim Jun-Geon Je Xiaoting Fu Caoxing Huang Ginnae Ahn Jae-Young Oh K. K. Asanka Sanjeewa Jiachao Xu Xin Gao In-Kyu Yeo You-Jin Jeon 《Molecules (Basel, Switzerland)》2021,26(22)
Skin is the largest organ of humans. Overexposure to ultraviolet (UV) is the primary environmental factor that causes skin damage. The compound, (-)-loliode, isolated from the brown seaweed Sargassum horneri, showed strong antioxidant and anti-inflammatory activities in in vitro and in vivo models. To further explore the potential of (-)-loliode in cosmetics, in the present study, we investigated the photoprotective effect of (-)-loliode in vitro in skin cells and in vivo in zebrafish. The results indicated that (-)-loliode significantly reduced intracellular reactive oxygen species (ROS) level, improved cell viability, and suppressed apoptosis of UVB-irradiated human keratinocytes. In addition, (-)-loliode remarkably attenuated oxidative damage, improved collagen synthesis, and inhibited matrix metalloproteinases expression in UVB-irradiated human dermal fibroblasts. Furthermore, the in vivo test demonstrated that (-)-loliode effectively and dose-dependently suppressed UVB-induced zebrafish damage displayed in decreasing the levels of ROS, nitric oxide, lipid peroxidation, and cell death in UVB-irradiated zebrafish. These results indicate that (-)-loliode possesses strong photoprotective activities and suggest (-)-loliode may an ideal ingredient in the pharmaceutical and cosmeceutical industries. 相似文献
994.
Geoffrey R. Mitchell Philip M.S Roberts Kyung-hwa Ahn Frederick J. Davis Craig Hasson Harald Hirschmann John A. Pople 《Macromolecular Symposia》1997,117(1):21-31
The polymer backbone of a side-chain liquid crystal polymer exhibits an anisotropic shape due to the coupling of the liquid crystal orientational order of the mesogenic side-chains to the backbone. The magnitude and sign of this coupling may be controlled by chemical design. The introduction of chemical cross-links in to such a system provides both a memory of the anisotropic organisation and a mechanism by which the microscopic anisotropy can be realised at a macroscopic level. We show how this anisotropic network structure yields new phenomena when electric or mechanical fields are applied. 相似文献
995.
Arlette Solladi-Cavallo Ahn Diep-Vohuule Thomas Isarno 《Angewandte Chemie (International ed. in English)》1998,37(12):1689-1691
Only the axial diastereomer of sulfonium salts 2 are formed upon alkylation of 1 . Deprotonation of 2 results in ylides, which allow the highly enantioselective cyclopropanation of Michael systems. The chiral auxiliary 1 is recovered and can be reused. 相似文献
996.
997.
Sang‐Soo Lee Han Mo Jeong Jae Young Jho Tae Oan Ahn 《Journal of Polymer Science.Polymer Physics》2000,38(5):803-811
Blends of poly(butylene terephthalate) (PBT) and polyestercarbonate (PEC), copolyesters consisting of polycarbonate (PC) and polyarylate (PAr), have been studied by thermal analysis to determine miscibility. The PBT blends with PAr and PEC containing 30 wt % of carbonate unit or less appeared to be miscible, and the tendency for stable single‐phase was observed to decrease as the content of carbonate unit in PEC copolymer increased. As determined with the crystalline phase behavior, the miscibility of PEC with PBT appeared to have a maximum around 10 ∼ 30 wt % of carbonate content in PEC copolymer, and this result was attributed to the internal repulsion effect between ester and carbonate repeating units in PEC copolymer. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 803–811, 2000 相似文献
998.
Kim J Kim SH Lee SU Ha GH Kang DG Ha NY Ahn JS Cho HY Kang SJ Lee YJ Hong SC Ha WS Bae JM Lee CW Kim JW 《Electrophoresis》2002,23(24):4142-4156
Hepatocellular carcinoma (HCC) is a common malignancy worldwide and is a leading cause of death. To contribute to the development and improvement of molecular markers for diagnostics and prognostics and of therapeutic targets for the disease, we have largely expanded the currently available human liver tissue maps and studied the differential expression of proteins in normal and cancer tissues. Reference two-dimensional electrophoresis (2-DE) maps of human liver tumor tissue include labeled 2-DE images for total homogenate and soluble fraction separated on pH 3-10 gels, and also images for soluble fraction separated on pH 4-7 and pH 6-9 gels for a more detailed map. Proteins were separated in the first dimension by isoelectric focusing on immobilized pH gradient (IPG) strips, and by 7.5-17.5% gradient sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) gels in the second dimension. Protein identification was done by peptide mass fingerprinting with delayed extraction-matrix assisted laser desorption/ionization-time of flight-mass spectrometry (DE-MALDI-TOF-MS). In total, 212 protein spots (117 spots in pH 4-7 map and 95 spots in pH 6-9) corresponding to 127 different polypeptide chains were identified. In the next step, we analyzed the differential protein expression of liver tumor samples, to find out candidates for liver cancer-associated proteins. Matched pairs of tissues from 11 liver cancer patients were analyzed for their 2-DE profiles. Protein expression was comparatively analyzed by use of image analysis software. Proteins whose expression levels were different by more than three-fold in at least 30% (four) of the patients were further analyzed. Numbers of protein spots overexpressed or underexpressed in tumor tissues as compared with nontumorous regions were 9 and 28, respectively. Among these 37 spots, 1 overexpressed and 15 underexpressed spots, corresponding to 11 proteins, were identified. The physiological significance of the differential expressions is discussed. 相似文献
999.
O. A. Usov K. Yu. Pogrebitskii B. T. Melekh Yu. N. Yur’ev Se Ahn Song 《Physics of the Solid State》1999,41(5):811-813
The fine structure in the titanium x-ray K-edge absorption has been measured in Ti1−x
NbxO2 mixed dioxides (x=0–0.1) with rutile structure in a laboratory-type spectrometer by total electron quantum-yield measurement. The position
of the XANES lines is shown to be in good agreement with classical x-ray absorption spectra obtained in transmission. The
structure and main features of the XANES spectra, including the effects of impurities and manyelectron excitations, are discussed.
It is suggested that the intensity of the B peak characteristic of the titanium K edge depends on the Nb concentration and correlates with the charge state of titanium ions.
Fiz. Tverd. Tela (St. Petersburg) 41, 894–896 (May 1999) 相似文献
1000.
Lee Sang-Hak Lee Yoon-Hee Ahn Jung-Mi Son Bum-Mok Yang Moon-Yul Nam Jae-Jak 《高等学校化学学报》1999,20(Z1):36
Several trivalent lanthanide ions are known to exhibit excellent luminescence characteristics when they are coordinated with appropriate organic ligands. Various analytical methods have been developed to determine lanthanide ions or organic compounds by taking advantage of these luminescence characteristics. The luminescence enhancement of the lanthanide ions by complexation with organic ligands has been explained on the basis of a ligand to metal energy transfer process. 相似文献