全文获取类型
收费全文 | 16792篇 |
免费 | 1618篇 |
国内免费 | 936篇 |
专业分类
化学 | 16242篇 |
晶体学 | 337篇 |
力学 | 261篇 |
综合类 | 40篇 |
数学 | 148篇 |
物理学 | 2318篇 |
出版年
2024年 | 6篇 |
2023年 | 169篇 |
2022年 | 246篇 |
2021年 | 574篇 |
2020年 | 563篇 |
2019年 | 412篇 |
2018年 | 356篇 |
2017年 | 338篇 |
2016年 | 629篇 |
2015年 | 619篇 |
2014年 | 659篇 |
2013年 | 1278篇 |
2012年 | 802篇 |
2011年 | 764篇 |
2010年 | 838篇 |
2009年 | 827篇 |
2008年 | 851篇 |
2007年 | 884篇 |
2006年 | 851篇 |
2005年 | 803篇 |
2004年 | 857篇 |
2003年 | 753篇 |
2002年 | 1476篇 |
2001年 | 438篇 |
2000年 | 390篇 |
1999年 | 386篇 |
1998年 | 355篇 |
1997年 | 256篇 |
1996年 | 396篇 |
1995年 | 415篇 |
1994年 | 170篇 |
1993年 | 152篇 |
1992年 | 150篇 |
1991年 | 96篇 |
1990年 | 67篇 |
1989年 | 74篇 |
1988年 | 78篇 |
1987年 | 43篇 |
1986年 | 48篇 |
1985年 | 61篇 |
1984年 | 45篇 |
1983年 | 25篇 |
1982年 | 27篇 |
1981年 | 26篇 |
1980年 | 19篇 |
1979年 | 11篇 |
1978年 | 13篇 |
1975年 | 8篇 |
1972年 | 6篇 |
1966年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 47 毫秒
81.
The influence of humic substances on sorption and methylation processes for inorganic- and organotin species is presented. Four sediment samples from different locations of the Rivers Elbe, Mulde and Spittelwasser, Germany, with different organotin and humic contents were selected to extract the humic and fulvic acids. The various fractions—the original sediment, the humic acid, the fulvic acid and the residual sediment—were analysed for their organotin content. The individual buyltin species show quite different distribution patterns. Monobutyltin is found mostly associated with humic acids. Dibutyltin shows a nonunique behaviour. At low total organotin content, dibutyltin is found bonded to humic and fulvic acids, whereas at high organotin content dibutyltin is distributed more with the residual sediment. Most of the tributyltin remains in the sediment unextracted; only small quantities of it are in the fulvic acid fraction. Tetrabutyltin is only in the humic acid fraction when it binds to humic matter; it mostly remains in the sediment. General observations indicate that ionic butyltin species bind to fulvic acids whereas the non-polar tetrabutyltin is not found in the fulvic acid fractions in any of the samples. The appearance of monomethyl- and dimethyl-tin species in the humic and fulvic acid fractions after the alkaline extraction was surprising. There is a correlation between the humic content of the sample and the formation of methyltin species. Evidence is provided by experiments that humic substances act as methylation agents. 相似文献
82.
83.
Nianchen Zhou Wenjian Xu Yu Zhang Jian Zhu Xiulin Zhu 《Journal of polymer science. Part A, Polymer chemistry》2006,44(4):1522-1528
2,2,6,6‐Tetramethyl‐4‐[d‐(+)‐10‐camphorsulfonyl]‐1‐piperidinyloxy was synthesized and used as a chiral nitroxide for the bulk polymerizations of styrene initiated with benzoyl peroxide (BPO), tetraethylthiuram disulfide (TETD), and thermal initiation. The results showed that the polymerizations proceeded in a controlled/living way; that is, the kinetics presented approximately first‐order plots, and the number‐average molecular weights of the polymers with narrow molecular weight distributions (weight‐average molecular weight/number‐average molecular weight) increased with the monomer conversion linearly. The molecular weight distributions in the case of thermal initiation were narrower than those in the case of BPO and TETD, whereas the polymerization rate with BPO or TETD as an initiator was obviously faster than that with thermal initiation. In addition, successful chain‐extension reactions were carried out, and the structures of the obtained polymers were characterized by gel permeation chromatography and 1H NMR. The specific rotations of the polymers were also measured by polarimetric analysis. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1522–1528, 2006 相似文献
84.
Summary. The photocycloaddition of aldehydes and α-ketoesters to 2,5-dimethyl-4-isobutyloxazole leads to bicyclic oxetanes with high
to moderate (exo) diastereoselectivity that can be easily ring-opened to give α-amino-β-hydroxyketones. 相似文献
85.
M. G. Bettoli M. Ravanelli L. Tositti O. Tubertini L. Guzzi W. Martinotti G. Queirazza M. Tamba 《Radiation Physics and Chemistry》1998,52(1-6):327-331
Decomposition by ionizing radiations of p-chlorophenol and tetrachloroethylene in synthetic water samples at about 2 mg Cl L−1, has been studied on laboratory-scale experiments. Bicarbonate/carbonate and nitrate ions, at two concentration levels (20 and 200 mg HCO3−1 and 1 and 50 mg NO3−L−) were added to synthetic samples in order to evaluate their influence on decomposition yield. At 5 kGy γ dose level, a quantitative degradation of p-chlorophenol is obtained whereas only qualitative consideration can be drawn on tetracholoroethylene. Comparative study with respect to degradation of p-cholophenol solutions (about 2 mg Cl L−1) by γ-rays and electron beam irradiation treatment at 0.5 kGy dose level, are in progress; preliminary results indicate that irradiation with γ-rays seems to be more efficient in terms of removal efficiency respect to electron beams source. 相似文献
86.
高分子阳离子絮凝剂用于炼油废水处理研究 总被引:15,自引:0,他引:15
用聚二甲基二烯丙基氯化铵型高分子阳离子絮凝剂处理炼油废水考察了险油和化学耗氧量的动态变化规律。对产生的浮渣性质及滤饼的成份进行了研究。并且与聚合铝的处理效果进行对照。研究结果表明,HCA除油和化学耗管氧量的性能优于PAC,HCA产生的浮渣是PAC的三分之一,而浮渣中的含油量则是PAC的三倍。 相似文献
87.
R. B. King 《Russian Chemical Bulletin》1993,42(11):1772-1781
Reactions of disodium tetracarbonylferrate, Na2Fe(CO)4, with sterically hindered dialkylaminodichlorophosphines, R2NPCl2 (R2N=diisopropylamino, dicyclohexylamino, and 2,2, 6, 6-tetramethylpiperidino) in diethyl ether lead to the air-stable phosphorus-bridging carbonyl derivatives (R2NP)2COFe2(CO)6 as the major products. The phosphorus-bridging carbonyl group in (i-Pr2NP)2COFe2(CO)6 has been found to undergo the following types of reactions: 1)Reduction, 2)Acylation, 3)Extrusion of the carbonyl group. The mechanisms of the reactions have been considered.This work was presented at the Workshop «The Modern Problems of Heteroorganic Chemistry» held on the ship «Nikolai Bauman» during the period May 8–13, 1993.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1858–1867, November, 1993. 相似文献
88.
89.
90.