全文获取类型
收费全文 | 263篇 |
免费 | 6篇 |
国内免费 | 6篇 |
专业分类
化学 | 132篇 |
力学 | 9篇 |
数学 | 68篇 |
物理学 | 66篇 |
出版年
2022年 | 5篇 |
2021年 | 4篇 |
2020年 | 5篇 |
2018年 | 4篇 |
2017年 | 4篇 |
2014年 | 5篇 |
2013年 | 11篇 |
2012年 | 5篇 |
2011年 | 12篇 |
2010年 | 10篇 |
2009年 | 9篇 |
2008年 | 14篇 |
2007年 | 5篇 |
2006年 | 9篇 |
2005年 | 11篇 |
2004年 | 8篇 |
2003年 | 5篇 |
2002年 | 11篇 |
2001年 | 11篇 |
2000年 | 5篇 |
1999年 | 9篇 |
1998年 | 8篇 |
1997年 | 9篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1981年 | 3篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1973年 | 2篇 |
1971年 | 1篇 |
1970年 | 3篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1965年 | 2篇 |
1963年 | 1篇 |
1955年 | 1篇 |
1954年 | 1篇 |
1935年 | 2篇 |
排序方式: 共有275条查询结果,搜索用时 0 毫秒
1.
A succinct series expression is derived for describing the limit distribution of the number of times r consecutive elements are all records (in a sequence of independent and identically distributed random variables with a common continuous distribution) for all r ≥ 2. Previously, only the limit distributions for r = 1, 2, and 3 were known. © 2005 Wiley Periodicals, Inc. Random Struct. Alg., 2005 相似文献
2.
3.
The radiation-induced crosslinking and grafting of two aryloxy-substituted elastomeric polyphosphazenes have been carried out by both gamma and electron beam irradiation. The classic Charlesby–Pinner [1] plus a simpler approach were used to determine the G(X) values for the crosslinked elastomeric polymers. The apparent G(X) value for the same polymer depended on whether the gamma-ray or the E-beam results were used. The presence of 8.5% repeat units with allylic groups in the side chain increased the G(X) value by an order of magnitude when the irradiation was performed under vacuum with the gamma source. The extent of acrylic acid grafting was also higher for the polymer containing the allylic group. Nearly all the grafted polyphosphazene films were insoluble in THF, a good solvent for the ungrafted samples. 相似文献
4.
The reaction of 2,5-diamino-4-benzylamino-pyrimidin-6(III)-one (6) with benzoyl isothiocyanate furnished 2-amino-4-benzylamino-5-[1-(3-benzoylthioureido)]-pyrimidin-6(1H)-one (7) in good yield. The title compound I was synthesized from compound 7 via a cyclodesulfurative reaction with DCC in DMF at 80°C directly to form 8-benzoylamino-9-benzylguanine (9) which was subsequently treated with 1 N sodium hydroxide. 相似文献
5.
Meei-Shiou Chern 《Tetrahedron letters》2004,45(45):8323-8326
Isoquinolinone is a structural unit found in many natural products having various important biological activities. A traceless solid-phase synthetic approach has been developed to prepare isoquinolinone derivatives. This approach enables one to synthesize isoquinolinones having various moieties on benzene nuclei and also can produce derivatives with a proton on the amide nitrogen. 相似文献
6.
Chorng-Shyan Chern Gary W. Poehlein 《Journal of polymer science. Part A, Polymer chemistry》1987,25(2):617-635
Previous kinetic studies in emulsion polymerization have almost always involved an assumption of uniform distribution of free radicals in the latex particle. Such an assumption is not likely to reflect reality in many systems that employ water-soluble initiators because the hydrophilic end-group of the oligomeric free radical will preferentially stay in the surface layer of the particle. This constrained end-group location would result in nonuniform distribution of free radicals in the polymerizing latex particles. A Monte Carlo simulation of the growth of a single polymer chain within the latex particle supports this hypothesis. Such a nonuniform distribution of free radicals in the latex particle is expected to have an influence on reaction kinetics and product properties. The mechanism for transport of free radicals out of polymerizing latex particles is reexamined based on the proposed concept, and a modified expression for the desorption rate constant is presented. 相似文献
7.
A new approach to a CD45 protein tyrosine phosphatase inhibitor, pulchellalactam, is described. The key step of the sequence involves addition and elimination of an enolic lactam in a single step and 70% yield, employing an organocuprate reagent. The resulting alpha,beta-unsaturated lactam could be condensed with isobutyraldehyde to produce Z-pulchellalactam or converted into siloxypyrrole, which was subjected to the BF(3) x Et(2)O-promoted coupling reaction with isobutyraldehyde to afford E-pulchellalactam after E1-cB elimination and TFA deprotection. This first total synthesis afforded Z-pulchellalactam in six steps and 32% overall yield from Boc-glycine. The same sequence of reactions could also be applied to the liquid- or solid-phase synthesis of trifunctionalized pulchellalactam derivatives. 相似文献
8.
To measure the hydrophobic character of the ribose moiety of doridosine on the adenosine receptors, 2′,3′-didehydro-2′,3′-dideoxydoridosine (2) and 2′,3′-dideoxydoridosine (3) were prepared. Initial treatment of doridosine with N,N-dimethylformamide diethylacetal, and subsequently with tert-butyldimethylsilyl chloride gave 5. Compound 5 was then reacted with 1,1′-thiocarbonyldiimidazole and the resulting thionocarbonate 6 was heated with triethyl phosphite at 135°C to afford 7. Treatment of compound 7 with tetrabutylammonium fluoride and methanolic ammonia furnished compound 2 in good yield. Compound 2 was subjected to catalytic hydrogenation affording compound 3 in 85% yield. 相似文献
9.
High-resolution solid-state 29Si NMR has been applied to the study of partially exchanged Li, K, and Cs NaY zeolites. The order of the 29Si chemical shifts of dehydrated samples is Li, Na-Y < Na-Y < K, Na-Y. The correlation between the 29Si chemical shift and the Li or K loading on Li, Na-Y or K, Na-Y was rationalized in terms of the interaction between the framework and the cations inside the small cages. Because of the restrictive migration of large Cs+ ions from the supercages to the small cages, the 29Si chemical shift of Cs, Na-Y was found to be similar to that of Na-Y. 相似文献
10.
Ji-Wang Chern Ching-Po Ho Ying-Hwa Wu Jiann-Gwo Rong Kang-Chien Liu Ming-Chu Cheng Yu Wang 《Journal of heterocyclic chemistry》1990,27(7):1909-1915
Reactions of 2-aminobenzenesulfonamide ( 1 ) with allyl, methyl, 2-chloroethyl aor 3-chloropropyl isocyanates gave 2-(methylureido)-, 2-(allylureido)-, 2-(2′-chloroethylureido)- and 2-(3′-chloropropylureido)-benzene sulfonamides 3a,b and 7a,b in excellent yields. Treatment of 3a,b at refluxing temperature of DMF afforded 2H-1,2,4-benzothiadiazin-3(4H)-one 1,1-dioxide ( 4 ) in good yield. However, when compounds 7a,b were refluxed in 2-propanol, 3-(2′-aminoethoxy)-2H-1,2,4-benzothiadiazine 1,1-dioxide ( 11a ) and 3-(3′-aminopropoxy)-2H-1,2,4-benzothiadiazine 1,1-dioxide ( 11b ) were obtained in a form of the hydrochloride salts 10a,b in 87% and 78% yields respectively. Heating 11b in ethanol gave a dimeric form of 2H-1,2,4-benzothiadiazin-3(4H)-one 1,1-dioxide and 3-(3′-aminopropoxy)-2H-1,2,4-benzothiadiazine 1,1-dioxide ( 12 ) in 55% yield. Treating of 7a,b or 11a,b with triethylamine at the refluxing temperature of 2-propanol afforded 3-(2′-hydroxyethylamino)-2H-1,2,4-benzothiadiazine 1,1-dioxide ( 2a ) and 3-(3′-hydroxypropylamine)-2H-1,2,4-benzothiadiazine 1,1-dioxide ( 2b ) via a Smiles rearrangement. 相似文献