全文获取类型
收费全文 | 2141篇 |
免费 | 55篇 |
国内免费 | 6篇 |
专业分类
化学 | 1507篇 |
晶体学 | 33篇 |
力学 | 19篇 |
数学 | 43篇 |
物理学 | 600篇 |
出版年
2022年 | 18篇 |
2021年 | 14篇 |
2020年 | 23篇 |
2019年 | 24篇 |
2018年 | 20篇 |
2017年 | 11篇 |
2016年 | 38篇 |
2015年 | 32篇 |
2014年 | 46篇 |
2013年 | 85篇 |
2012年 | 72篇 |
2011年 | 79篇 |
2010年 | 47篇 |
2009年 | 52篇 |
2008年 | 122篇 |
2007年 | 98篇 |
2006年 | 119篇 |
2005年 | 115篇 |
2004年 | 132篇 |
2003年 | 100篇 |
2002年 | 73篇 |
2001年 | 54篇 |
2000年 | 38篇 |
1999年 | 48篇 |
1998年 | 20篇 |
1997年 | 22篇 |
1996年 | 36篇 |
1995年 | 40篇 |
1994年 | 28篇 |
1993年 | 23篇 |
1992年 | 52篇 |
1991年 | 42篇 |
1990年 | 26篇 |
1989年 | 32篇 |
1988年 | 21篇 |
1987年 | 32篇 |
1986年 | 33篇 |
1985年 | 31篇 |
1984年 | 20篇 |
1983年 | 17篇 |
1982年 | 26篇 |
1981年 | 22篇 |
1980年 | 30篇 |
1979年 | 20篇 |
1978年 | 17篇 |
1977年 | 17篇 |
1976年 | 13篇 |
1975年 | 20篇 |
1974年 | 20篇 |
1973年 | 25篇 |
排序方式: 共有2202条查询结果,搜索用时 15 毫秒
41.
A series of parallel reactions were carried out for the tandem Ugi/Diels-Alder reaction on our MPEG-O-CH2- platform. Ninety-six out of a 100 entries were successful to give complex heterotricycles. The stereoselectivity was found not to be influenced by the building blocks used for amine and carboxylic acid components. An unexpected side pathway was found but was suppressed by employing appropriate reaction conditions. The reaction was also performed on solid phase, by which a larger library is potentially realized by employing the split-pool method. 相似文献
42.
Ye S Zhou W Abe M Nishida T Cui L Uosaki K Osawa M Sasaki Y 《Journal of the American Chemical Society》2004,126(24):7434-7435
A highly selective ligand exchange reaction is realized in the self-assembled monolayer (SAM) of a triruthenium cluster on a gold electrode surface under precise electrochemical potential control. CO as well as NO molecules, which are known to play key roles in many chemical, biological, and environmental systems, can be efficiently introduced into the SAM by electrochemically tuning the electronic state of the Ru site. These unique surface reactions are more convenient and efficient than conventional ligand exchange reactions in solution and could be used for the elucidation of the electron-transfer mechanism in a biological system as well as in the development of molecular sensors and devices. 相似文献
43.
Takao K Yasui H Yamamoto S Sasaki D Kawasaki S Watanabe G Tadano K 《The Journal of organic chemistry》2004,69(25):8789-8795
The total syntheses of (+)-mycoepoxydiene and (-)-1893A have been completed. The present synthetic strategy features the use of one-pot ring-opening/cross metathesis (ROM/CM) followed by a ring-closing metathesis (RCM) reaction, allowing for the concise construction of the 9-oxabicyclo[4.2.1]nona-2,4-diene framework from a 7-oxabicyclo[2.2.1]hept-2-ene derivative and 1,3-butadiene. The sequential metathesis product was converted into (+)-mycoepoxydiene through the oxidative rearrangement of a furfuryl alcohol to a pyranone, thereby establishing its absolute stereochemistry. From the common intermediate, a structurally related natural product (-)-1893A was also synthesized via the vinylogous aldol reaction. 相似文献
44.
The synthesis and properties of novel anthracene-bridged porphyrin dimers having an oxomolybdenum(V) porphyrin unit, H(2)(DPA)[Mo(V)O(OMe)] (1) and (DPA)[Mo(V)O(OMe)][Zn(II)(MeOH)] (2), and the relevant monomer porphyrin complexes Mo(V)O(MPP)OMe (3) and Zn(II)(MPP) (4) are presented. An oxomolybdenum(V) unit was introduced into one of the two porphyrins in DPA to give 1, which has a free-base porphyrin unit. By introducing a zinc(II) ion to the free-base part, a mixed-metal complex of 2 was prepared and isolated. The structure of 2 was analyzed by X-ray crystallography (2.(7)/(6)CH(2)Cl(2), triclinic, P(-)1 (no. 2), a = 15.2854(12) A, b = 19.9640(15) A, c = 13.6915(12) A, alpha = 90.968(3), beta = 113.108(4), gamma = 96.501(4), Z = 2, R1 = 9.9, wR2 = 19.2). The structure of 2 demonstrated that a methanol is stably coordinated to the Zn(II) ion with the aid of a hydrogen bond to the methoxo ligand on the Mo(V) ion in the binding pocket of DPA. The electrochemical measurements of 2 suggested that the methanol was kept in the pocket of DPA in solution even at the reduced state of the molybdenum ion. 相似文献
45.
Actinide(III), (IV), (V) and (VI) ions were extracted by N,N-dimethyl-N,N-dihexyl-3-oxapentanediamide (DMDHOPDA) and thenoyltrifluoroacetone (HTTA). The extraction behaviors suggested the possibility of the mutual separation, and the convenient separation method of actinide ions (III), (IV), (V) and (VI) without reducing and oxidizing agents was studied. Th(IV) was extracted from the aqueous phase by HTTA (5 mM in toluene) in the first step. The Am(III) and U(VI) ions can be extracted by 1 and 20 mM DMDHOPDA in toluene, and the Np(V) ion can be extracted into nitrobenzene with 100 mM DMDHOPDA in the last step. The residual activities in the aqueous phase were much lower than the initial activities. These activities in the fractions were confirmed by the gamma- and the alpha-spectrometry. The one-through and rough separation is advanced, and in case of the fine isolation of actinide elements, each fraction should be purified in more detail. 相似文献
46.
47.
N,N-dimethyl-N,N-dihexyl-3-oxapentanediamide, DMDHOPDA, N,N-dihexyl-3-thiopentanediamide, DHTPDA and N,N-dihexyl-3-oxapentanediamide, DHOPDA were synthesized and tested for the synergistic extraction of Eu3+, Th4+, UO
2
2+
, NpO
2
+
and Am3+ with thenoyltrifluoroacetone (HTTA). Although Eu3+, Th4+, UO
2
2+
and Am3+ were not extracted by DHTPDA or DHOPDA alone, they were extracted synergistically when combined with HTTA. Analysis of the dependency of extraction on pH and extractant concentration indicated that the dominant extracted species were Eu(TTA)3(A), Th(TTA)3(A)(X), UO2(TTA)2(A) and Am(TTA)3(A) (where A is diamide, and X is chloroacetate or ClO
4
–
). 相似文献
48.
49.
50.