全文获取类型
收费全文 | 4415篇 |
免费 | 124篇 |
国内免费 | 25篇 |
专业分类
化学 | 3673篇 |
晶体学 | 47篇 |
力学 | 47篇 |
综合类 | 1篇 |
数学 | 203篇 |
物理学 | 593篇 |
出版年
2023年 | 24篇 |
2022年 | 25篇 |
2021年 | 48篇 |
2020年 | 68篇 |
2019年 | 56篇 |
2018年 | 37篇 |
2017年 | 35篇 |
2016年 | 72篇 |
2015年 | 91篇 |
2014年 | 98篇 |
2013年 | 212篇 |
2012年 | 229篇 |
2011年 | 299篇 |
2010年 | 161篇 |
2009年 | 159篇 |
2008年 | 336篇 |
2007年 | 272篇 |
2006年 | 314篇 |
2005年 | 281篇 |
2004年 | 260篇 |
2003年 | 235篇 |
2002年 | 210篇 |
2001年 | 67篇 |
2000年 | 85篇 |
1999年 | 67篇 |
1998年 | 42篇 |
1997年 | 51篇 |
1996年 | 54篇 |
1995年 | 48篇 |
1994年 | 38篇 |
1993年 | 43篇 |
1992年 | 46篇 |
1991年 | 31篇 |
1990年 | 33篇 |
1989年 | 22篇 |
1988年 | 22篇 |
1987年 | 30篇 |
1986年 | 16篇 |
1985年 | 41篇 |
1984年 | 37篇 |
1983年 | 17篇 |
1982年 | 26篇 |
1981年 | 32篇 |
1980年 | 34篇 |
1979年 | 17篇 |
1978年 | 22篇 |
1976年 | 17篇 |
1975年 | 20篇 |
1974年 | 13篇 |
1973年 | 14篇 |
排序方式: 共有4564条查询结果,搜索用时 15 毫秒
41.
42.
Dehydration of zinc biladienone was catalyzed by zinc acetate, while the reverse reaction was catalyzed by triethylamine. The transformation can be performed thermally without catalyst, and the ratio of the hydrated form to the dehydrated form depended on the solvents: the dehydrated form is favored in CHCl3 and CH2Cl2, while the hydrated form is favored in hexane, pyridine, and DMF. Kinetic studies on the thermal transformation of zinc biladienone from its hydrated blue form to the dehydrated yellow-brown form were performed in toluene and THF. The rate law was half order with respect to the zinc biladienone concentration in toluene, while first order in THF, leading to a slow transformation in concentrated solution in toluene. 相似文献
43.
Kinetics of chemiluminescence reactions of 2-methyl-6-phenylimidazo[1,2-a]pyrazin-3(7H)-one (1c, Cypridina luciferin analogue) and substituent effects of the 6-aryl group of derivatives 1 strongly suggest that the rate-determining step is a single electron transfer from an anion derived from 1 to a triplet molecular oxygen (O2) in the oxygenation process. 相似文献
44.
Pyrene-azacrown ether hybrid: cation-π interaction 总被引:1,自引:0,他引:1
A pyrene-modified lariat ether was synthesized in order to observe the cation-π interaction in solution. 相似文献
45.
Hiroyuki Ohno Yoshitaka Ogata Eishun Tsuchida 《Journal of polymer science. Part A, Polymer chemistry》1986,24(11):2959-2969
Small unilamellar liposomes were prepared in an aqueous medium by the sonication of phospholipids containing diene or triene groups in their hydrocarbon acyl chains. These liposomes were polymerized by gamma-ray irradiation. Conversion of polymerization was successively followed by UV spectrometry. Diene-type lipid liposomes were revealed for which a gamma-ray dose of 0.8 Mrad was required for complete polymerization and which were polymerized more easily than triene-type lipid liposomes. Triene-type lipids required 2.3 Mrad gamma ray to polymerize them completely. Contrary to UV-irradiation polymerization, there was no concentration dependence on the polymerization. Structure of the polymerized liposomes were confirmed by electron microscopy as small unilamellar liposomes. Study on the leakage of fluorescein from inner aqueous phase of the polymerized liposomes revealed that polymerized triene-type liposomes were relatively more stable than the polymerized diene-type liposomes. 相似文献
46.
Hiroyuki Nakazumi Takashi Endo Hikaru Sonoda Teijiro Kitao 《Journal of heterocyclic chemistry》1985,22(3):821-824
3-Substituted 2-phenyl-4H-1-benzothiopyran-4-ones (thioflavones) were prepared to test antimicrobial activity. It was found that 3-(phenyl)thiochromone derivatives (isothioflavones) were prepared by the Meerwein reaction of thiochromone with p-nitrobenzenediazonium ion. 3-(Formyl)thioflavone exhibits weak antimicrobial activity against Trichophytons and Candida. 相似文献
47.
Y. Miyamoto Y. Saito M. Magara S. Usuda 《Journal of Radioanalytical and Nuclear Chemistry》2003,255(3):553-557
To clarify the magnitude of wash-out effect of rain on the elemental composition of airborne dust and the possible origin of the dust, the dust samples were collected with a high-volume air sampler at the JAERI-Tokai. The dust suspended in rain was also collected from rain by filtration. Up to 20 elements in both types of the dust were determined by instrumental neutron activation analysis. It was found that the elements determined could be classified into 3 groups from the elemental composition and the elemental correlation in both types of the dust samples. 相似文献
48.
Akira Okubo Hiroyuki Kawai Toshiro Matsunaga Tatsuji Chuman Sunao Yamazaki Shozo Toda 《Tetrahedron letters》1980,21(42):4095-4096
T1 gives a clue to assign cis- and trans-methyl carbons in 2-methyl-1-propenyl moiety. 相似文献
49.
Nishiura M Hou Z Wakatsuki Y Yamaki T Miyamoto T 《Journal of the American Chemical Society》2003,125(5):1184-1185
Various terminal alkynes have been cleanly dimerized into the corresponding head-to-head (Z)-enynes by use of the half-metallocene lutetium alkyl complexes Me2Si(C5Me4)(NAr)Lu(CH2SiMe3)(THF) (Ar = Ph, C6H3Me2-2,6, C6H2Me3-2,4,6) as catalysts. Aromatic C-Cl, C-Br, and C-I bonds, which are known to be extremely susceptible to reductive cleavage by transition metals, survived in the present reactions. The corresponding dimeric alkynide species [Me2Si(C5Me4)(NAr)Lu(mu-CCR)]2 are thought to be the true catalysts, some of which have been isolated and structurally characterized. These alkynide species were thermally stable and soluble at the reaction temperatures (80-110 degrees C), but they precipitated upon cooling to room temperature after completion of the reaction. Therefore, this catalyst system works homogeneously but can be separated and reused, thus constituting the first example of a recyclable catalyst system for the dimerization of terminal alkynes and also the first example of (Z)-selective head-to-head dimerization of aromatic terminal alkynes. 相似文献
50.
Hiroshi Harada Kanichi Kamiya Hiroyuki Nasu Jun Matsuoka 《Journal of Sol-Gel Science and Technology》1997,10(3):291-300
The sodium dititanate, Na2O·2TiO2 glass was prepared by the sol-gel method. The structure of the glass, especially local environment of Ti4+ ions was examined using X-ray diffraction and X-ray absorption fine structure (XAFS) analyses, and was compared with that of the melt-derived glass with the same composition. It was found that Ti4+ ions are rather in five-fold coordination state, forming TiO5 pyramids with one doubly bonded Ti=O in the gel-glass, while they were in lower coordination state or four-fold coordination in the melt-derived glass. 相似文献