全文获取类型
收费全文 | 922篇 |
免费 | 34篇 |
国内免费 | 27篇 |
专业分类
化学 | 142篇 |
晶体学 | 2篇 |
力学 | 87篇 |
综合类 | 3篇 |
数学 | 40篇 |
物理学 | 83篇 |
综合类 | 626篇 |
出版年
2024年 | 3篇 |
2023年 | 5篇 |
2022年 | 5篇 |
2021年 | 9篇 |
2020年 | 8篇 |
2019年 | 11篇 |
2018年 | 14篇 |
2017年 | 21篇 |
2016年 | 14篇 |
2015年 | 21篇 |
2014年 | 31篇 |
2013年 | 35篇 |
2012年 | 44篇 |
2011年 | 55篇 |
2010年 | 31篇 |
2009年 | 42篇 |
2008年 | 49篇 |
2007年 | 50篇 |
2006年 | 91篇 |
2005年 | 56篇 |
2004年 | 43篇 |
2003年 | 56篇 |
2002年 | 53篇 |
2001年 | 36篇 |
2000年 | 29篇 |
1999年 | 26篇 |
1998年 | 24篇 |
1997年 | 18篇 |
1996年 | 20篇 |
1995年 | 9篇 |
1994年 | 18篇 |
1993年 | 13篇 |
1992年 | 7篇 |
1991年 | 8篇 |
1990年 | 8篇 |
1989年 | 10篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有983条查询结果,搜索用时 31 毫秒
1.
郑健儿 《浙江万里学院学报》2002,15(2):58-60
儿童文学是快乐的文学。但稚嫩柔弱的孩子要想通过儿童文学之门,变为堂堂正正的硬汉,也得在拥抱危难、感受不幸之时一步步走向成熟。 相似文献
2.
采用氟离子选择电极法测定氟含量,具有简便、快速、灵敏、选择性好等优点,最低检出浓度为0.05mg/L,适用浓度范围宽,在测定牙膏含氟量中取得良好效果。 相似文献
3.
4.
The bi(anthracene‐9,10‐dimethylene) photoisomer has remarkably long C–C single bonds. To examine the lengthening of the C–C bond, we propose a novel procedure for quantitatively analyzing orbital interactions in a molecule at the level of the ab initio molecular orbital method. In this procedure, we can cut off the specific through‐space/bond interactions in a molecule by artificially increasing the absolute magnitude of the exponents in a Gaussian function. Then, the spatial orbital interactions were perfectly cut off, and, each term that makes up the total energy, that is, the nuclear–electron attractions, the electron–electron repulsions, and the nuclear–nuclear repulsions cancel each other. Several model molecules of the photoisomer were analyzed by this procedure. It was found that the orbital interaction between the p orbital on the benzene ring and the σ* orbital on the C–C bond in question, σ→σ* electron transfer through π orbital, weakens the C–C bond efficiently when these orbitals were located in the “periplanar” conformation. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001 相似文献
5.
试验研究了废黄河竖井双层涵洞输送水流和泥沙运动特性。试验表明:竖井进口段过水断面呈渐趋收缩状,涵洞泄流能力增大;在通过小流量时,下层涵洞流速大,有利于依靠水力输沙;双层涵洞中间隔层具有随上下层涵洞流速差减小、脉动压力影响趋于微弱的性质。提出了轮换开启部分闸门,使开启涵洞内平均流速大于泥沙不淤流速的调控方法,解决了双层涵洞安全输送泥沙的工程措施问题。 相似文献
6.
Surowiec I Baena JR Frank J Laurell T Nilsson J Trojanowicz M Lendl B 《Journal of chromatography. A》2005,1080(2):132-139
A flow-through microdispenser has been coupled to a micro HPLC separation system and used as a solvent elimination interface for Fourier transform infrared (FTIR) and Raman spectroscopic detection of the separated compounds. Using the microdispenser picoliter sized droplets can be generated and deposited on an appropriate target placed on a computerized x, y-stage. Evaporation of volatile solvent and buffer is rapid and allows analysis of the obtained dry deposits by various techniques. Due to the destruction free character of Raman and FTIR spectroscopy they can be applied sequentially to interrogate the same deposit. In the reported application five phenolic acids typically present in wine have been separated on a C-18 column technique using a mixture of water, methanol and acetic acid as mobile phase. For spectrum acquisition infrared and Raman microscopes have been used. The spectra recorded from the dried deposits of the separated compounds agreed well with the reference spectra of corresponding components. 相似文献
7.
A method has been developed for the preparation of modified silica plates for high performance thin-layer chromatography (HPTLC). Some typical organosilanes were thus allowed to react in situ with the silica of Merck HPTLC-plates. This method was found to be highly reproducible, simple and cheap. Non-polar plates were prepared and compared with commercial plates from Merck, Whatman and Macherey-Nagel. Modification with cyanodecyltrichlorosilane resulted in plates that showed good coverage, efficiency and low residual silica activity. Silica modified with a multifunctional silane has different properties in different organic solvents. It will appear to be non-polar in a polar solvent and vice versa. New advantageous separation systems are thus made feasible by the presence of cyano groups on the plate. The utility of modified thin-layer plates is demonstrated by the separation of some homologues of p-hydroxybenzoic acid esters and of some polycyclic aromatic hydrocarbons. 相似文献
8.
Kaupp M Patrakov A Reviakine R Malkina OL 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(9):2773-2782
The characteristic dependence of J(31P,31P) spin-spin coupling constants of alkali metal tetraphosphane-1,4-diides on structure and composition has been analyzed by density functional methods. The computations confirm that the structure of the contact ion pairs is conserved in solution. Calculations on model systems M2P4H4, on naked P4H4(2-) anions, and on models including point charges, show that the role of the cations is mainly structural and to a smaller extent electrostatic. Three of the four J(P,P) coupling constants depend characteristically on the conformation of the anion, which in turn is determined by the substituents R and by cation-anion interactions. Several couplings exhibit a large through-space component and are thus strongly dependent on the relative orientation of nonbonding electron pairs on the phosphorus atoms involved. This is shown by visualization of coupling pathways using the recently introduced coupling energy density (CED), in combination with the electron localization function (ELF). 相似文献
9.
为研究含穿透裂纹悬臂方板的振动辐射声场,根据有限元模态分析理论,提取了含人工斜向和十字形穿透裂纹的悬臂方薄板各单元的相关物理参数,同时将瑞利积分离散化,进而计算出裂纹悬臂方薄板辐射声场的空间分布,并通过实验测定了含裂纹悬臂方薄板辐射声场的功率谱。结果表明,斜向裂纹越长,二、四、六阶模态的频率降低越多,而一、三、五阶模态频率随斜向裂纹长度的增大表现为先增大再减小的规律;十字裂纹越长,各阶模态的频率降低越多。穿透裂纹的出现不仅使悬臂板的模态频率有明显的变化,而且声场在空间的分布特征也有显著的变化。 相似文献
10.
黄东东 《重庆三峡学院学报》2003,19(1):5-9
开发性移民方针的提出是我国水库移民理论的一次重大创新,开发性移民是对补偿性移民的发展.从法律角度来看,开发性移民的实质是遵循市场经济的基本规律,运用法制手段,以移民补偿和库区开发为基础,对国家、集体、个人利益关系的一种平衡和协调,以实现库区经济社会的可持续发展. 相似文献