全文获取类型
收费全文 | 24262篇 |
免费 | 4406篇 |
国内免费 | 3738篇 |
专业分类
化学 | 18913篇 |
晶体学 | 351篇 |
力学 | 1377篇 |
综合类 | 239篇 |
数学 | 2751篇 |
物理学 | 8775篇 |
出版年
2024年 | 20篇 |
2023年 | 413篇 |
2022年 | 625篇 |
2021年 | 749篇 |
2020年 | 968篇 |
2019年 | 1082篇 |
2018年 | 898篇 |
2017年 | 899篇 |
2016年 | 1210篇 |
2015年 | 1337篇 |
2014年 | 1531篇 |
2013年 | 1930篇 |
2012年 | 2366篇 |
2011年 | 2345篇 |
2010年 | 1647篇 |
2009年 | 1735篇 |
2008年 | 1881篇 |
2007年 | 1600篇 |
2006年 | 1462篇 |
2005年 | 1310篇 |
2004年 | 1050篇 |
2003年 | 758篇 |
2002年 | 750篇 |
2001年 | 644篇 |
2000年 | 488篇 |
1999年 | 412篇 |
1998年 | 338篇 |
1997年 | 311篇 |
1996年 | 246篇 |
1995年 | 226篇 |
1994年 | 194篇 |
1993年 | 171篇 |
1992年 | 146篇 |
1991年 | 128篇 |
1990年 | 112篇 |
1989年 | 69篇 |
1988年 | 75篇 |
1987年 | 50篇 |
1986年 | 48篇 |
1985年 | 44篇 |
1984年 | 22篇 |
1983年 | 27篇 |
1982年 | 10篇 |
1981年 | 12篇 |
1980年 | 8篇 |
1979年 | 9篇 |
1977年 | 7篇 |
1975年 | 6篇 |
1965年 | 4篇 |
1936年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
1.
In this article,we study the initial boundary value problem of coupled semi-linear degenerate parabolic equations with a singular potential term on manifolds with corner singularities.Firstly,we introduce the corner type weighted p-Sobolev spaces and the weighted corner type Sobolev inequality,the Poincare′inequality,and the Hardy inequality.Then,by using the potential well method and the inequality mentioned above,we obtain an existence theorem of global solutions with exponential decay and show the blow-up in finite time of solutions for both cases with low initial energy and critical initial energy.Significantly,the relation between the above two phenomena is derived as a sharp condition.Moreover,we show that the global existence also holds for the case of a potential well family. 相似文献
2.
The row iterative method is popular in solving the large‐scale ill‐posed problems due to its simplicity and efficiency. In this work we consider the randomized row iterative (RRI) method to tackle this issue. First, we present the semiconvergence analysis of RRI method for the overdetermined and inconsistent system, and derive upper bounds for the noise error propagation in the iteration vectors. To achieve a least squares solution, we then propose an extended version of the RRI (ERRI) method, which in fact can converge in expectation to the solution of the overdetermined or underdetermined, consistent or inconsistent systems. Finally, some numerical examples are given to demonstrate the convergence behaviors of the RRI and ERRI methods for these types of linear system. 相似文献
3.
Zheng Xinyan Hu Po Yao Ruxian cheng Jinhe Chang Yiheng Wu Haitao Mei Hongying Sun Shuxiang Chen Qingtai liu Fang Chen Shujing Wen Hua 《Journal of Radioanalytical and Nuclear Chemistry》2022,331(5):2217-2226
Journal of Radioanalytical and Nuclear Chemistry - Enhancement of U(VI) biomineralization by Saccharomyces cerevisiae through addition of inorganic phosphorus was studied in this work. The addition... 相似文献
4.
合成了一种多级孔芳香骨架材料(PAF-70); 使用由氨基修饰过的单体, 应用该合成策略得到了同样具有窄分布介孔的含有氨基活性位点的PAF材料, 并通过硫脲单体与其氨基活性位点的反应, 将硫脲基团引入PAF-70材料中, 获得了含有硫脲催化位点的材料(PAF-70-thiourea). 氮气吸附-脱附测试结果显示, PAF-70存在孔径分布较窄的介孔, 介孔孔径为3.8 nm, 与模拟计算值(约3.7 nm)吻合. 热重分析结果表明, PAF-70具有很高的热稳定性. PAF-70在大多数溶剂中可以稳定存在, 具有良好的化学稳定性. 将PAF-70-thiourea作为催化剂, 应用在N-溴代琥珀酰亚胺(NBS)氧化醇类的反应中, 其表现出较高的催化活性、 较高的稳定性和广泛的底物适用性. 与含有相同硫脲催化位点的金属有机框架(MOF)材料(IRMOF-3-thiourea)作为催化剂对比, 进一步证实PAFs材料非常适合作为催化有机反应的固载平台. 相似文献
5.
Yongjing Liu Qiang Chen Suxia Zhang Hua Zhang Wei Xu 《Biomedical chromatography : BMC》2022,36(3):e5293
Deep eutectic solvents (DESs) were applied as eco-friendly solvents in this study for the extraction of alkaloids from lotus leaf, including O-nornuciferine, N-nornuciferine, nuciferine and roemerine. A series of hydrophilic and hydrophobic DESs with different hydrogen bond donors and a acceptors were synthesized and screened for a suitable DESs for extraction of alkaloids from lotus leaf. The study results showed that the hydrophilic DES with choline chloride and propanediol had the highest extraction yield. The main factors affecting the extraction efficiency—choline chloride–propanediol ratio, water content in deep eutectic solvents, solid–liquid ratio and extraction time—were investigated via a single-factor experiment. The optimized extraction conditions were 30% of water in choline chloride–propanediol (1:4) for heated extraction for 30 min and solid–liquid ratio 1:100 g/ml. Under optimum conditions, the extraction yields of O-nornuciferine, N-nornuciferine, nuciferine and roemerine were 0.069, 0.152, 0.334 and 0.041 g/100 g respectively, which were higher than those of methanol in acidified aqueous solution. This study suggests considerable potential for DESs as promising materials for the green and efficient extraction solvents for bioactive alkaloids from natural sources. 相似文献
6.
7.
Huo Guang-Hua Cui Chao-Yu He Tian Yan Jun-Qing Peng Wen-Wen 《Chemistry of Natural Compounds》2022,58(3):468-470
Chemistry of Natural Compounds - A new carotane sesquiterpenoid, methyl gymnabloate (1), was isolated from the fermentation broth of the wild macrofungus Gymnopus sp. 0612-9. Its structure was... 相似文献
8.
Li Quanxin Li Zheng He Cheng Sun Huilin Tan Shengheng Zhang Hua 《Journal of Radioanalytical and Nuclear Chemistry》2022,331(5):2105-2115
Journal of Radioanalytical and Nuclear Chemistry - The simplified 8-oxide system (SiO2-B2O3-Na2O-Al2O3-CaO-TiO2-MoO3-La2O3) has been prepared under two types of cooling methods, and analyzed with... 相似文献
9.
10.
Liu Wei Li Kehong Deng Hao Wang Jing Zhao Peng Liao Wei Zhuo Liangang Wei Hongyuan Yang Xia Chen Yue 《Journal of Radioanalytical and Nuclear Chemistry》2022,331(2):747-754
Journal of Radioanalytical and Nuclear Chemistry - There is an urgent need to develop more specific targeted therapies for lung cancer treatment due to the its low survival rate. EGFR is a... 相似文献