全文获取类型
收费全文 | 5090篇 |
免费 | 1111篇 |
国内免费 | 539篇 |
专业分类
化学 | 5870篇 |
晶体学 | 39篇 |
力学 | 58篇 |
综合类 | 10篇 |
数学 | 60篇 |
物理学 | 703篇 |
出版年
2024年 | 19篇 |
2023年 | 193篇 |
2022年 | 165篇 |
2021年 | 201篇 |
2020年 | 339篇 |
2019年 | 239篇 |
2018年 | 245篇 |
2017年 | 186篇 |
2016年 | 334篇 |
2015年 | 346篇 |
2014年 | 387篇 |
2013年 | 550篇 |
2012年 | 341篇 |
2011年 | 325篇 |
2010年 | 266篇 |
2009年 | 273篇 |
2008年 | 314篇 |
2007年 | 262篇 |
2006年 | 212篇 |
2005年 | 211篇 |
2004年 | 187篇 |
2003年 | 152篇 |
2002年 | 105篇 |
2001年 | 99篇 |
2000年 | 100篇 |
1999年 | 103篇 |
1998年 | 79篇 |
1997年 | 82篇 |
1996年 | 71篇 |
1995年 | 55篇 |
1994年 | 32篇 |
1993年 | 38篇 |
1992年 | 40篇 |
1991年 | 28篇 |
1990年 | 18篇 |
1989年 | 17篇 |
1988年 | 10篇 |
1987年 | 13篇 |
1986年 | 8篇 |
1985年 | 15篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1982年 | 7篇 |
1981年 | 9篇 |
1980年 | 5篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1973年 | 3篇 |
1971年 | 4篇 |
排序方式: 共有6740条查询结果,搜索用时 15 毫秒
11.
Kinetic parameters of amino acid cations in an MK-40 ion-exchange membrane are calculated from the conductivity data. A theoretical quantum-chemical analysis of experimental activation energies for conduction suggests a mechanism of elementary act of transport of amino acid cations in the membrane. 相似文献
12.
13.
14.
A closed microwave digestion method followed by inductively coupled plasma spectrometric (ICP-MS) analysis was evaluated for the determination of trace impurities in photoresist. To optimize the digestion procedure, several digestion parameters such as acid, heating temperature and heating time were evaluated. Besides, the digestion efficiency of used photoresist material and the recovery of analyte elements obtained by the use of gravimetric method and ICP-MS measurement, individually, were also compared to clarify the completeness of digestion. According to our experiments, the gravimetric method was found to be not so relevant to the completeness of digestion, because the remaining sample matrix could cause suppression effect in the subsequent ICP-MS measurement. In view of minimizing blank value and working time, a simple single-step heating program was proposed to mineralize 0.25 ml of photoresist material with 5 ml of nitric acid at 180 °C for 10 min. Based on the comparative study of the analytical results obtained by instrumental neutron activation analysis (INAA) and proposed method, the reliability of proposed method for the determination of trace metallic impurities in photoresist material has been confirmed. 相似文献
15.
We herein report that PtCl4 has proven to be a hydroarylation catalyst with an efficiency and substrate scope superior to previously known methods. This catalyst demonstrated consistent performance with arene-yne substrates of diverse structural features, including propargyl ethers, propargylamines, and alkynoate esters, providing good to excellent yields of the 6-endo products (chromenes, dihydroquinolines, and coumarins). In contrast, Pt(II), Pd(II), and Ga(III) salts were shown to be sensitive to the substitution on the alkyne moiety. PtCl4 is compatible with both terminal and disubstituted alkynes, as well as with various functionalities on the arene ring, including methyl, methoxyl, hydroxyl, protected amine, and halide. 相似文献
16.
聚醚醚酮链结构与反应的模型化合物的量子化学研究 总被引:1,自引:1,他引:0
利用AM1方法对聚醚醚酮模型化合物全优化,结果为:芳环平均相互扭转角为33.0度,桥键角117.0-118.0度,其分子结构拓扑图形表明:所有苯环(核)为平面构型,但其内角扭曲;其氢原子对苯环构型无实质性贡献,在更长链的计算中,冻结苯核与氢原子也得出满意结果,根据Mulliken键序与电荷讨论了醚交换与磺化反应。 相似文献
17.
Enrique J. Baran 《Monatshefte für Chemie / Chemical Monthly》1991,122(6-7):479-481
Summary Mean amplitudes of vibration for OTeF
5
–
have been calculated from known spectroscopic and structural data in a wide temperature range. The results are briefly discussed in comparison with those of related species. 相似文献
18.
Tatiana B. Mikenas Vladimir A. Zakharov Lyudmila G. Echevskaya Mikhail A. Matsko 《Journal of polymer science. Part A, Polymer chemistry》2007,45(22):5057-5066
The effects of polymerization temperature, polymerization time, ethylene and hydrogen concentration, and effect of comonomers (hexene‐1, propylene) on the activity of supported catalyst of composition LFeCl2/MgCl2‐Al(i‐Bu)3 (L = 2,6‐bis[1‐(2,6‐dimethylphenylimino)ethyl] pyridyl) and polymer characteristics (molecular weight (MW), molecular‐weight distribution (MWD), molecular structure) have been studied. Effective activation energy of ethylene polymerization over LFeCl2/MgCl2‐Al(i‐Bu)3 has a value typical of supported Ziegler–Natta catalysts (11.9 kcal/mol). The polymerization reaction is of the first order with respect to monomer at the ethylene concentration >0.2 mol/L. Addition of small amounts of hydrogen (9–17%) significantly increases the activity; however, further increase in hydrogen concentration decreases the activity. The IRS and DSC analysis of PE indicates that catalyst LFeCl2/MgCl2‐Al(i‐Bu)3 has a very low copolymerizing ability toward propylene and hexene‐1. MW and MWD of PE produced over these catalysts depend on the polymerization time, ethylene and hexene‐1 concentration. The activation effect of hydrogen and other kinetic features of ethylene polymerization over supported catalysts based on the Fe (II) complexes are discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5057–5066, 2007 相似文献
19.
Push-pull dithiafulvenes with reduced bond length alternation (BLA) and high optical nonlinearities have been prepared. The interplay between the proaromaticity of the donor and the structural and optical properties of these merocyanines is discussed. The donor ability of dithiafulvenes can reach that of ferrocene or dialkylaminophenyl groups. 相似文献
20.