全文获取类型
收费全文 | 1232篇 |
免费 | 154篇 |
国内免费 | 64篇 |
专业分类
化学 | 1033篇 |
晶体学 | 14篇 |
力学 | 40篇 |
综合类 | 2篇 |
数学 | 97篇 |
物理学 | 264篇 |
出版年
2024年 | 3篇 |
2023年 | 17篇 |
2022年 | 30篇 |
2021年 | 32篇 |
2020年 | 58篇 |
2019年 | 52篇 |
2018年 | 26篇 |
2017年 | 16篇 |
2016年 | 46篇 |
2015年 | 51篇 |
2014年 | 55篇 |
2013年 | 80篇 |
2012年 | 110篇 |
2011年 | 120篇 |
2010年 | 78篇 |
2009年 | 52篇 |
2008年 | 75篇 |
2007年 | 49篇 |
2006年 | 87篇 |
2005年 | 62篇 |
2004年 | 41篇 |
2003年 | 46篇 |
2002年 | 44篇 |
2001年 | 28篇 |
2000年 | 26篇 |
1999年 | 31篇 |
1998年 | 12篇 |
1997年 | 13篇 |
1996年 | 11篇 |
1995年 | 14篇 |
1994年 | 8篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 20篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1976年 | 1篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有1450条查询结果,搜索用时 85 毫秒
961.
Victor Udo Nna Ainul Bahiyah Abu Bakar Zaida Zakaria Zaidatul Akmal Othman Nur Asyilla Che Jalil Mahaneem Mohamed 《Molecules (Basel, Switzerland)》2021,26(11)
Diabetic nephropathy is reported to occur as a result of the interactions between several pathophysiological disturbances, as well as renal oxidative stress and inflammation. We examined the effect of Malaysian propolis (MP), which has anti-hyperglycemic, antioxidant and anti-inflammatory properties, on diabetes-induced nephropathy. Diabetic rats were either treated with distilled water (diabetic control (DC) group), MP (300 mg/kg b.w./day), metformin (300 mg/kg b.w./day) or MP + metformin for four weeks. We found significant increases in serum creatinine, urea and uric acid levels, decreases in serum sodium and chloride levels, and increase in kidney lactate dehydrogenase activity in DC group. Furthermore, malondialdehyde level increased significantly, while kidney antioxidant enzymes activities, glutathione level and total antioxidant capacity decreased significantly in DC group. Similarly, kidney immunoexpression of nuclear factor kappa B, tumor necrosis factor-α, interleukin (IL)-1β and caspase-3 increased significantly, while IL-10 immunoexpression decreased significantly in DC group relative to normal control group. Histopathological observations for DC group corroborated the biochemical data. Intervention with MP, metformin or both significantly mitigated these effects and improved renal function, with the best outcome following the combined therapy. MP attenuates diabetic nephropathy and exhibits combined beneficial effect with metformin. 相似文献
962.
经颅磁刺激(TMS)是一种采用电磁线圈在大脑指定区域产生磁场的刺激方式. TMS的治疗原理是通过电磁感应产生作用于神经元的外加电场进而影响神经元编码. 然而目前TMS感应外电场改变神经元编码的内在机理尚不清楚.研究表明, 神经元编码由神经元的放电起始动态机理决定. 本文建立了TMS感应外电场作用下的最小神经元模型, 采用相平面分析和分岔分析方法, 研究了外电场作用下神经元放电起始动态的动力学机理, 并从阈下电位的不同动力学特性离子电流竞争角度揭示了TMS感应外电 场作用下神经元放电起始动态的生理学机理. 相似文献
963.
Liu L Bruhn T Guo L Götz DC Brun R Stich A Che Y Bringmann G 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(9):2604-2613
Chloropupukeanolides C–E ( 8 – 10 ), three highly functionalized secondary metabolites featuring a novel spiroketal skeleton derived from the chlorinated tricyclo‐[4.3.1.03, 7]‐decane (pupukeanane) and the 2,6‐dihydroxy‐4‐methylbenzoic acid moieties, were isolated from the scale‐up fermentation extract of the plant endophytic fungus Pestalotiopsis fici. The constitutions of compounds 8 – 10 were elucidated primarily by NMR experiments. Their relative configurations were deduced by analogy to metabolites 4 – 6 , which were previously isolated from the same fungus. The absolute configuration of 8 was assigned by X‐ray crystallography and those of 9 and 10 by quantum‐chemical CD calculations. Biogenetically, chloropupukeanolides C–E ( 8 – 10 ) are presumably derived from the same oxidation‐induced Diels–Alder reaction pathway as compounds 1 and 4 – 7 , via the putative biosynthetic precursors 2 and 3 . The opposite configurations of the complete “Southern parts” of 8 and 9 suggests that this Diels–Alder reaction is stereochemically not very selective. Compounds 8 – 10 showed significant cytotoxicity against a small panel of human tumor cell lines and weak activities against the pathogens of tropical diseases. 相似文献
964.
Luminescent Palladium(II) Complexes with π‐Extended Cyclometalated [RC^N^NR′] and Pentafluorophenylacetylide Ligands: Spectroscopic,Photophysical, and Photochemical Properties
下载免费PDF全文
![点击此处可从《化学:亚洲杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A series of cyclometalated PdII complexes that contain π‐extended R? C^N^N? R′ (R? C^N^N? R′=3‐(6′‐aryl‐2′‐pyridinyl)isoquinoline) and chloride/pentafluorophenylacetylide ligands have been synthesized and their photophysical and photochemical properties examined. The complexes with the chloride ligand are emissive only in the solid state and in glassy solutions at 77 K, whereas the ones with the pentafluorophenylacetylide ligand show phosphorescence in the solid state (λmax=584–632 nm) and in solution (λmax=533–602 nm) at room temperature. Some of the complexes with the pentafluorophenylacetylide ligand show emission with λmax at 585–602 nm upon an increase in the complex concentration in solutions. These PdII complexes can act as photosensitizers for the light‐induced aerobic oxidation of amines. In the presence of 0.1 mol % PdII complex, secondary amines can be oxidized to the corresponding imines with substrate conversions and product yields up to 100 and 99 %, respectively. In the presence of 0.15 mol % PdII complex, the oxidative cyanation of tertiary amines could be performed with product yields up to 91 %. The PdII complexes have also been used to sensitize photochemical hydrogen production with a three‐component system that comprises the PdII complex, [Co(dmgH)2(py)Cl] (dmgH=dimethylglyoxime; py=pyridine), and triethanolamine, and a maximum turnover of hydrogen production of 175 in 4 h was achieved. The excited‐state electron‐transfer properties of the PdII complexes have been examined. 相似文献
965.
966.
A polynomial algorithm for no-wait cyclic hoist scheduling in an extended electroplating line 总被引:1,自引:0,他引:1
Ada Che 《Operations Research Letters》2005,33(3):274-284
This paper addresses cyclic hoist scheduling in a no-wait electroplating line where a part visits some processing tanks more than once and multiple duplicate tanks are used at some production stages. We prove that such an extended problem can be solved in polynomial time. 相似文献
967.
Haiyang Li Yanjun Shi Guangchao Han Jie Liu Jing Zhang Chunlei Li Jie Liu Yuanping Yi Tao Li Xike Gao Chongan Di Jia Huang Yanke Che Dong Wang Wenping Hu Yunqi Liu Lang Jiang 《Angewandte Chemie (International ed. in English)》2020,59(11):4380-4384
The sensitivity of conventional thin‐film OFET‐based sensors is limited by the diffusion of analytes through bulk films and remains the central challenge in sensing technology. Now, for the first time, an ultrasensitive (sub‐ppb level) sensor is reported that exploits n‐type monolayer molecular crystals (MMCs) with porous two‐dimensional structures. Thanks to monolayer crystal structure of NDI3HU‐DTYM2 (NDI) and controlled formation of porous structure, a world‐record detection limit of NH3 (0.1 ppb) was achieved. Moreover, the MMC‐OFETs also enabled direct detection of solid analytes of biological amine derivatives, such as dopamine at an extremely low concentration of 500 ppb. The remarkably improved sensing performances of MMC‐OFETs opens up the possibility of engineering OFETs for ultrasensitive (bio)chemical sensing. 相似文献
968.
The synthesis of a new sterically highly hindered 7‐membered alkoxyamine, 2,2,7,7‐tetraethyl‐1‐(1‐phenylethoxy)‐1,4‐diazepan‐5‐one ( 4 ), starting from known 2,2,6,6‐tetraethyl‐1‐(1‐phenylethoxy)piperidin‐4‐one ( 3 ) via a Beckmann‐type rearrangement is presented. It is shown that ring‐enlargement by insertion of an NH moiety in going from 3 to 4 leads to a more efficient regulator for nitroxide‐mediated controlled living radical styrene (= ethenylbenzene) and butyl acrylate (= butyl prop‐2‐enoate) polymerization. In addition to the polymerization experiments, kinetic data on the reversible C? O bond homolysis of alkoxyamines 3 and 4 are presented. 相似文献
969.
Zhongyuan Che 《Discrete Mathematics》2008,308(24):6104-6110
The concept of a k-pairable graph was introduced by Z. Chen [On k-pairable graphs, Discrete Mathematics 287 (2004), 11-15] as an extension of hypercubes and graphs with an antipodal isomorphism. In the present paper we generalize further this concept of a k-pairable graph to the concept of a semi-pairable graph. We prove that a graph is semi-pairable if and only if its prime factor decomposition contains a semi-pairable prime factor or some repeated prime factors. We also introduce a special class of k-pairable graphs which are called uniquely k-pairable graphs. We show that a graph is uniquely pairable if and only if its prime factor decomposition has at least one pairable prime factor, each prime factor is either uniquely pairable or not semi-pairable, and all prime factors which are not semi-pairable are pairwise non-isomorphic. As a corollary we give a characterization of uniquely pairable Cartesian product graphs. 相似文献
970.
The nonlinear optical properties of a new organic material, N-vinylcarbazole tricarbonyl chromium, are reported. The large two-photon absorption (TPA) coefficient and nonlinear refraction index are measured by an open-aperture Z-scan technique and closed-aperture Z-scan technique, respectively. The sample solution shows excellent optical limiting response. 相似文献