全文获取类型
收费全文 | 7599篇 |
免费 | 237篇 |
国内免费 | 31篇 |
专业分类
化学 | 5850篇 |
晶体学 | 66篇 |
力学 | 125篇 |
数学 | 379篇 |
物理学 | 1447篇 |
出版年
2023年 | 28篇 |
2022年 | 49篇 |
2021年 | 77篇 |
2020年 | 71篇 |
2019年 | 89篇 |
2018年 | 60篇 |
2017年 | 68篇 |
2016年 | 138篇 |
2015年 | 137篇 |
2014年 | 166篇 |
2013年 | 372篇 |
2012年 | 389篇 |
2011年 | 469篇 |
2010年 | 251篇 |
2009年 | 252篇 |
2008年 | 436篇 |
2007年 | 441篇 |
2006年 | 419篇 |
2005年 | 388篇 |
2004年 | 348篇 |
2003年 | 319篇 |
2002年 | 298篇 |
2001年 | 191篇 |
2000年 | 189篇 |
1999年 | 124篇 |
1998年 | 104篇 |
1997年 | 111篇 |
1996年 | 108篇 |
1995年 | 78篇 |
1994年 | 87篇 |
1993年 | 100篇 |
1992年 | 89篇 |
1991年 | 64篇 |
1990年 | 70篇 |
1989年 | 74篇 |
1988年 | 66篇 |
1987年 | 65篇 |
1986年 | 53篇 |
1985年 | 129篇 |
1984年 | 117篇 |
1983年 | 40篇 |
1982年 | 63篇 |
1981年 | 67篇 |
1980年 | 70篇 |
1979年 | 104篇 |
1978年 | 71篇 |
1977年 | 75篇 |
1976年 | 65篇 |
1975年 | 50篇 |
1974年 | 49篇 |
排序方式: 共有7867条查询结果,搜索用时 15 毫秒
51.
52.
M Sugiyama T Sakamoto K Tabata K Endo K Ito M Kobayashi H Fukumi 《Chemical & pharmaceutical bulletin》1989,37(8):2122-2131
Thiazolo[3,2-a]thieno[3,2-d]-, [3,4-d]- and [2,3-d]pyrimidin-5-one derivatives (6, 11 and 16), and polymethylene condensed thieno[3,2-d]-, [3,4-d]- and [2,3-d]pyrimidin-5-one derivatives (19-21), in which the oxygen atom of the oxazolidine moiety in 3 was replaced by a sulfur atom or methylene groups, were synthesized and evaluated for gastric antisecretory activity in pylorus-ligated rats. The structure-activity relationships of these compounds are discussed. 相似文献
53.
54.
A mild one-pot method for the synthesis of acyclic N-(1-methoxyalkyl)amides starting from carboxylic acids and methyl imidates had been developed and applied to the total synthesis of the insect poison pederine . 相似文献
55.
56.
M. Takagaki K. Ono S-I. Masunaga Y. Kinashi Y. Sakurai T. Kobayashi S-I. Miyatake N. Hashimoto 《Journal of Radioanalytical and Nuclear Chemistry》2001,247(2):389-392
Quantitative determination of ppb-order 10B was carried out in a small number of cultured tumor cells by particle tracks by the 10B(n,)7Li reactions using solid state nuclear track detector (SSNTD) for boron neutron capture therapy research. The detection limit of 10B concentration in tumor cells is less than 1·10-3 ppm under our experimental conditions which permits the quantitative determination of 10B in a small number of boronated tumor cells (105/ml = ca. 0.1 mg). Boron quantities in tumor cells determined were well compatible with the tumor cell killing effects of boron neutron capture therapy. 相似文献
57.
58.
Junji Furukawa Eiichi Kobayashi Morio Nakamura 《Journal of polymer science. Part A, Polymer chemistry》1974,12(12):2789-2799
The effect of ultraviolet irradiation on the terpolymerization was investigated. In the terpolymerizations of sulfur dioxide–butene-1–acrylonitrile, sulfur dioxide–butene-1–n-butyl acrylate, and maleic anhydride–allyl chloride–acrylonitrile systems, the composition of the terpolymers prepared under ultraviolet irradiation was different from those prepared in the dark. The unit content of sulfur dioxide and butene-1 or of maleic anhydride and allyl chloride in the terpolymer increased under ultraviolet irradiation. The nature of the growing end under ultraviolet irradiation is supposed to be the same as that of the dark polymerization on the basis of the same solvent effect on the terpolymer composition, the rate of polymerization and the molecular weight of polymer. The experimental results suggest that the complex between sulfur dioxide and butene-1 or maleic anhydride and allyl chloride might be excited by ultraviolet light and the excited complex may participate in the terpolymerization. 相似文献
59.
The equilibrium constants, K
2, have been determined for the proton-transfer reactions of 1-phenacylquinolinium ion, PHQ+, with several amines {triethylamine (TEA), N,N,N′,N′-tetramethylethylenediamine (ED), N,N,N′, N′-tetramethylpropanediamine (PD), N,N,N′,N′-tetramethylbutanediamine (BD), and 1,8-bis(dimethylamino-naphthalene (DMAN)} in acetonitrile (AN), AN-tetrahydrofuran (THF)
and AN-ethanol (EtOH) mixtures. The reaction was followed spectrophotometrically using a stopped-flow technique. The K
2 value decreased for DMAN and increased for TEA with increasing vol-% of THF in AN-THF mixtures. The changes in the K
2 value for ED, PD and BD changed in the order: ED, PD and BD from a pattern similar to TEA to a pattern similar to DMAN. The
change in the K
2 value for DMAN with increasing vol-% of THF in AN-THF mixtures was explained by the effect of polarity on the stability of
P−Q+ (the deprotonated product of PHQ+). The effect of THF on the K
2 value is consistent with that of the peak wavelength of the absorption spectrum of P−Q+. The change in the K
2 value for TEA, ED, PD and BD depended on the structures of the protonated bases, one of the products for this reaction. The
effect of EtOH on the K
2 value for DMAN was examined in ternary EtOH-THF-AN mixtures that contain different amounts of EtOH and whose relative permittivities
were adjusted to that of EtOH. The K
2 value increased with increasing vol-% of EtOH because of the stabilization of P−Q+ upon the formation of the hydrogen-bonded complex with EtOH. The absorption spectrum of P−Q+ demonstrated a blue shift as the vol-% of EtOH increased. 相似文献
60.
Takeshi SatoSaburo Aimoto 《Tetrahedron letters》2003,44(44):8085-8087
Use of thiosulfonate for protecting thiol (-SH) groups in peptide ligation by the thioester method was examined. Thiosulfonate was introduced and was stable in the presence of silver ion, 4-dihydro-3-hydroxy-4-oxo-1,2,3-benzotriazine, and diisopropylethylamine. Based on these results, a strategy for using the thioester method and the native chemical ligation method in the synthesis of a single polypeptide is described. 相似文献