全文获取类型
收费全文 | 6264篇 |
免费 | 815篇 |
国内免费 | 1552篇 |
专业分类
化学 | 6037篇 |
晶体学 | 46篇 |
力学 | 458篇 |
综合类 | 68篇 |
数学 | 988篇 |
物理学 | 1034篇 |
出版年
2024年 | 42篇 |
2023年 | 145篇 |
2022年 | 293篇 |
2021年 | 365篇 |
2020年 | 537篇 |
2019年 | 326篇 |
2018年 | 286篇 |
2017年 | 257篇 |
2016年 | 355篇 |
2015年 | 291篇 |
2014年 | 417篇 |
2013年 | 578篇 |
2012年 | 370篇 |
2011年 | 373篇 |
2010年 | 293篇 |
2009年 | 337篇 |
2008年 | 355篇 |
2007年 | 349篇 |
2006年 | 322篇 |
2005年 | 288篇 |
2004年 | 253篇 |
2003年 | 316篇 |
2002年 | 302篇 |
2001年 | 181篇 |
2000年 | 141篇 |
1999年 | 118篇 |
1998年 | 107篇 |
1997年 | 78篇 |
1996年 | 96篇 |
1995年 | 70篇 |
1994年 | 67篇 |
1993年 | 46篇 |
1992年 | 57篇 |
1991年 | 25篇 |
1990年 | 23篇 |
1989年 | 19篇 |
1988年 | 24篇 |
1987年 | 17篇 |
1986年 | 22篇 |
1985年 | 30篇 |
1984年 | 16篇 |
1983年 | 6篇 |
1982年 | 17篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1975年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有8631条查询结果,搜索用时 15 毫秒
61.
N. S. Arutyunyan L. A. Akopyan G. A. Gevorgyan G. M. Snkhchyan G. A. Panosyan 《Chemistry of Heterocyclic Compounds》2005,41(4):437-441
A preparative method was developed for the synthesis of ethyl furfurylidenecyanoacetate. Its condensation with phenylmagnesium bromide gave ethyl α-cyano-β-(2-furyl)hydrocinnamate, the decarboxylation of which led to β-(2-furyl)hydrocinnamonitrile. Reduction of this nitrile with lithium aluminum hydride gave 2-(3-amino-1-phenylpropyl)furan. Some of its transformations were studied.__________Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 517–521, April, 2005. 相似文献
62.
ZheLi DangLi WeiHuang KechangXie 《天然气化学杂志》2005,14(2):115-118
The Cu-Mo/ZSM-5 catalysts with different Cu/Mo ratios were prepared by wet impregnation method, and their catalytic performance for selective catalytic reduction of NOx was studied. The results showed that Cu-Mo/ZSM-5 is a very effective catalyst for NOx catalytic reduction with ammonia, especially when Cu/Mo molar ratio is about 1.5. It not only exhibited the extremely high catalytic activity, but also showed good stability for 02. The bulk phase structure of Cu-Mo/ZSM-5 catalysts was determined by XRD technique, and the results indicated that there is a maximum dispersion for Cu species when Cu/Mo molar ratio is 1.5, and an interaction between Cu and Mo along with HZSM-5 may be present in Cu-Mo/ZSM-5, which may possibly result in a special structure favorable for the catalytic reduction of NOx over Cu-Mo/ZSM-5 catalyst. 相似文献
63.
I. E. Karpeiskaya L. F. Godunova E. S. Levitina M. R. Lyubeznova E. I. Klabunovskii E. S. Shpiro G. N. Baeva E. D. Lubuzh L. B. Krentsel' A. D. Litmanovich N. A. Plate 《Russian Chemical Bulletin》1992,41(10):1858-1867
Pd complexes have been obtained from linear and cross-linked copolymers ofR,S-, R-, andS-1-(4-vinylphenyl)ethylamine (1) with styrene and divinylbenzene. Reduction of these compounds gave catalysts which were active in the reductive solvolysis of -acetaminocinnamic acid azlactone (2) and hydrogenation of the solvolysis products -acetamidocinnamic acid (ACA), its esters, and its 1-phenylethylamide. The catalysts showed no enantioselective properties in the reductive hydrolysis, but were more active than the catalyst obtained in the absence of the polymer (the monomeric analog). The use of polymeric catalysts has shown that, in reductive aminolysis, the chiral nucleophile plays the dominant part in determining the stereoselectivity of the reaction, rather than the chiral ligand of the catalytic complex. The polymer matrix stabilizes the low-valent state of the palladium in the complex. In the hydrogenation of ACA and its esters, the catalyst on the cross-linked polymer is much more active than its monomeric analog, but showed no enantioselectivity. Hydrogenation of acetamidocinnamic acidR-andS-1-phenylethylamides on a chiral Pd-polymer catalyst occurred with double asymmetric induction.Deceased.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. A. V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, 117912 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 10, pp. 2368–2380, October, 1992. 相似文献
64.
65.
66.
We have obtained novel photosensitive materials containing a semiconductor photocatalyst and a dye sensitizer. We have studied the activity of the latter in the reaction of photoreduction of methylene blue, and we consider possible mechanisms for the photocatalytic effect. 相似文献
67.
68.
69.
A thermal analysis study on the reduction of iron oxide rich slags under different conditions is presented in this paper. The effects of important process variables such as time, temperature, lime-silica ratio, FeO level in slag etc. are discussed. It is shown that the mechanism of reduction by externally added graphite is different from that by a carbon saturated bath although the activation energy values are similar. 相似文献
70.