全文获取类型
收费全文 | 403篇 |
免费 | 45篇 |
国内免费 | 9篇 |
专业分类
化学 | 184篇 |
力学 | 10篇 |
综合类 | 5篇 |
数学 | 152篇 |
物理学 | 106篇 |
出版年
2024年 | 1篇 |
2023年 | 12篇 |
2022年 | 31篇 |
2021年 | 35篇 |
2020年 | 29篇 |
2019年 | 16篇 |
2018年 | 21篇 |
2017年 | 16篇 |
2016年 | 14篇 |
2015年 | 19篇 |
2014年 | 24篇 |
2013年 | 47篇 |
2012年 | 20篇 |
2011年 | 28篇 |
2010年 | 16篇 |
2009年 | 20篇 |
2008年 | 20篇 |
2007年 | 12篇 |
2006年 | 9篇 |
2005年 | 16篇 |
2004年 | 5篇 |
2003年 | 9篇 |
2002年 | 13篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 8篇 |
1996年 | 2篇 |
1994年 | 1篇 |
1991年 | 1篇 |
排序方式: 共有457条查询结果,搜索用时 31 毫秒
1.
分析学生对二氧化碳的3个典型学科认知障碍,以“二氧化碳的捕捉”为情境,通过“尝试捕捉二氧化碳”“谁在捕捉二氧化碳”“捕捉背后的原理”等3个主要环节,实现对学科认知障碍的突破,展示了一种新的中考复习教学思路。 相似文献
2.
Addition of aqueous hydrogen peroxide significantly accelerates the substitution reactions of hydroxide salts with haloarenes bearing electron withdrawing substituents. A similar effect is observed in the reactions of hydroxide salts with halogenated heteroarenes. Reactions are carried out in water or water-THF at ambient temperature or at 50-60 °C. 相似文献
3.
Philippe Bénilan 《Journal of Differential Equations》2004,196(2):301-315
In this paper, we study the singular limit of the Porous Medium equation ut=Δum+g(x,u), as m→∞, in a bounded domain with Neumann boundary condition. 相似文献
4.
The efficiency of 3,5-bis(n-pyridyl)-1,3,4-oxadiazole (n-POX, n = 1, 2, 3), as corrosion inhibitors for mild steel in 1 M perchloric acid (HClO4) have been determined by weight loss measurements and electrochemical studies. The results show that these inhibitors revealed a good corrosion inhibition even at very low concentrations. Comparison of results among those obtained by the studied oxadiazoles shows that 3-POX was the best inhibitor. Polarisation curves indicate that n-pyridyl substituted-1,3,4-oxadiazoles are mixed type inhibitors in 1 M HClO4. The adsorption of these inhibitors follows a Langmuir isotherm model. The electronic properties of n-POX, obtained using the AM1 semi-empirical quantum chemical approach, were correlated with their experimental efficiencies using the linear resistance model (LR). 相似文献
5.
In this paper, we proved the global existence and uniqueness of the strong, weak and mild solutions for one-dimensional Burgers equation perturbed by a Poisson form process, a Poisson form and Q-Wiener process with the Dirichlet bounded condition. We also proved the existence of the invariant measure of these models. 相似文献
6.
A selective cleavage of acetals of 1,2- and 1,3-diols has been achieved under mild conditions using ZnBr2 in dichloromethane at room temperature. Acetal types cleavable by this procedure include benzylidene, isopropylidene and cyclohexylidene acetals. This method is compatible with several other types of hydroxyl protecting groups such as Bn, Bz, TBDPS, TIPS and TBDMS. 相似文献
7.
Meng Wang Weiyue Feng Junwen Shi Fang Zhang Bing Wang Motao Zhu BaiLi Yuliang Zhao Zhifang Chai 《Talanta》2007,71(5):2034-2039
A mild, efficient and convenient extraction method of using 2-mercaptoethanol contained extractant solution combined with an incubator shaker for determination of mercury species in biological samples by HPLC–ICP-MS has been developed. The effects of the concentration of 2-mercaptoethanol, the composition of the extractant solution and the shaking time on the efficiency of mercury extraction were evaluated. The optimization experiments indicated that the quantitative extraction of mercury species from biological samples could be achieved by using 0.1% (v/v) HCl, 0.1% (v/v) 2-mercapoethanol and 0.15% (m/v) KCl extractant solution in an incubator shaker for shaking overnight (about 12 h) at room temperature. The established method was validated by analysis of various biological certified reference materials, including NRCC DOLT-3 (dogfish liver), IAEA 436 (tuna fish), IAEA MA-B-3/TM (garfish filet), IAEA MA-M-2/TM (mussel tissue), GBW 08193 (bovine liver) and GBW 08572 (prawn). The analytical results of the reference materials were in good agreement with the certified or reference values of both methyl and total mercury, indicating that no distinguishable transformation between mercury species had occurred during the extraction and determination procedures. The limit of detection (LOD) for methyl (CH3Hg+) and inorganic mercury (Hg2+) by the method are both as 0.2 μg L−1. The relative standard deviation (R.S.D.s) for CH3Hg+ and Hg2+ are 3.0% and 5.8%, respectively. The advantages of the developed extraction method are that (1) it is easy to operate in HPLC–ICP-MS for mercury species determination since the extracted solution can be directly injected into the HPLC column without pH adjustment and (2) the memory effect of mercury in the ICP-MS measurement system can be reduced. 相似文献
8.
Ajay K. Bose Subhendu N. Ganguly Maghar S. Manhas Vaidyanathan Srirajan Ashoke Bhattacharjee Sochanchingwung Rumthao Anju H. Sharma 《Tetrahedron letters》2004,45(6):1179-1181
A novel dinitro secondary metabolite, 2-nitro-4-(2′-nitroethenyl)phenol from a marine source, has been prepared via highly accelerated, microwave assisted, nitration reactions using mild reagents. ipso-Substitution of a carboxy group by a nitro group is discussed. 相似文献
9.
Sara Mattsson 《Tetrahedron letters》2007,48(14):2497-2499
When treated with amine bases such as triethylamine and various lithium salts in wet solvents, esters are efficiently hydrolyzed to the corresponding acids in good yields. Esters incorporating an α- or β-heteroatom with respect to the ester carbonyl group are hydrolyzed rapidly even at room temperature. To further demonstrate the usefulness of this method, one example is provided where hydrolysis of acetylated camphorsultam is mediated by LiBr. 相似文献
10.
Rémy Lartia 《Tetrahedron letters》2004,45(31):5949-5952
We report here a novel, simple reagent enabling the chemical incorporation of a thiophosphate or a phosphate group at the 5′-end of oligonucleotides using very mild basic deprotection conditions. This method can be useful in the case of alkali sensitive modified oligonucleotides. This reagent also gives access to the preparation of bifunctional oligonucleotides with either a thiophosphate group at the 5′-end and a phosphate at the 3′-end, or two thiophosphate groups at both the 5′- and the 3′-ends, or a 5′-thiophosphate group and a 3′-amino-containing linker. 相似文献