全文获取类型
收费全文 | 5400篇 |
免费 | 35篇 |
国内免费 | 15篇 |
专业分类
化学 | 2301篇 |
晶体学 | 72篇 |
力学 | 250篇 |
数学 | 697篇 |
物理学 | 2130篇 |
出版年
2022年 | 51篇 |
2021年 | 80篇 |
2020年 | 86篇 |
2019年 | 103篇 |
2018年 | 131篇 |
2017年 | 127篇 |
2016年 | 160篇 |
2015年 | 58篇 |
2014年 | 123篇 |
2013年 | 238篇 |
2012年 | 203篇 |
2011年 | 192篇 |
2010年 | 208篇 |
2009年 | 194篇 |
2008年 | 225篇 |
2007年 | 185篇 |
2006年 | 212篇 |
2005年 | 171篇 |
2004年 | 149篇 |
2003年 | 126篇 |
2002年 | 141篇 |
2001年 | 141篇 |
2000年 | 129篇 |
1999年 | 81篇 |
1998年 | 98篇 |
1997年 | 73篇 |
1996年 | 78篇 |
1995年 | 53篇 |
1994年 | 56篇 |
1993年 | 53篇 |
1992年 | 67篇 |
1991年 | 56篇 |
1990年 | 85篇 |
1989年 | 53篇 |
1988年 | 55篇 |
1987年 | 68篇 |
1986年 | 59篇 |
1985年 | 58篇 |
1984年 | 67篇 |
1983年 | 55篇 |
1982年 | 68篇 |
1980年 | 55篇 |
1979年 | 48篇 |
1978年 | 49篇 |
1977年 | 60篇 |
1976年 | 60篇 |
1975年 | 57篇 |
1974年 | 61篇 |
1973年 | 73篇 |
1969年 | 45篇 |
排序方式: 共有5450条查询结果,搜索用时 265 毫秒
141.
142.
B. E. Ivanov S. S. Krokhina T. V. Chichkanova A. B. Ageeva 《Russian Chemical Bulletin》1986,35(12):2535-2539
Conclusion N-Acetoxymethyldiethylamine reacts with tetraethyldiamidophenylphosphonite and diethylamidodiphenylphosphinite, and N-acetoxymethylbenzamide with tetraethyldiamidophenylphosphonite at the phosphorus atom only to form Arbuzov reaction products. The reaction of N-acetoxymethylacetamide with tetraethyldiamidophenylphosphonite and diethylamidodiphenylphosphinite, and the reaction of N-acetoxymethylbenzamide with diethylamidodiphenylphosphinite proceed at two reaction centers at the phosphorus atom to form the Arbuzov reaction products, and at the nitrogen atom to form acetoxyphosphinites (phosphonites) and N-diethylaminomethylamides.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2765–2769, December, 1986. 相似文献
143.
Ivanov AR Nazimov IV Baratova L Lobazov AP Popkovich GB 《Journal of chromatography. A》2001,913(1-2):315-318
The fast isocratic narrow-bore reversed-phase high-performance liquid chromatographic method employing fluorescence detection is described for the precise reproducible simultaneous measurement of total homocysteine, cysteine and glutathione in human blood. Sample preparation involves conversion of disulfides to free thiols with triphenylphosphine, precipitation of proteins with sulfosalicylic acid, and conjugation of thiols with monobromobimane. Optimized sample preparation conditions as well as chromatographic conditions allowed to obtain reliable quantitative results within the concentration range corresponding to the levels of these thiols in human blood in norm and pathology. The detection limit was approximately 70 amol for all labeled aminothiols. The proposed method for these compounds analysis includes simple sample preparation, high selectivity, good linearity (r2>0.998), high reproducibility (within-run precision for derivatized aminothiol peaks area RSD<1.8% for three times consequently injected sample); high reliability and the small sample volume (1 microl) required for analysis make it suitable for clinical studies. 相似文献
144.
B. E. Ivanov L. A. Valitova T. G. Bykova N. V. Yakimova 《Russian Chemical Bulletin》1978,27(7):1416-1418
Conclusions The reaction of 2,2-bis(4-hydroxy-3-N,N-diethylaminomethylphenyl)propane with triethyl phosphite gave 2,2-bis(4-ethoxy-3-diethylphosphonomethylphenyl)propane via the intermediate formation of a compound with a pentacovalent phosphorus atom. In the presence of acetic acid the reaction leads to 2,2-bis(4-hydroxy-3-diethylphosphonomethylphenyl)propane.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1621–1624, July, 1978. 相似文献
145.
Ab initio calculations using a molecular pseudopotential and an all-electron approximation have been carried out with various basis sets for Mg complexes and for dianions of malonic aldehyde and its imino and chloro derivatives. The valence levels are reproduced most adequately, whereas the atomic charges and bond characteristics depend heavily on the basis used. Employing a pseudopotential does not change the quality of the electronic characteristics of the system, slightly increasing the existing charge separation. The Cl atom in the -position is involved in -conjugation of the dicarbonyl cycle, causing antibonding in the dianion. Introduction of Mg considerably increases the mesomeric effect of Cl and electron density on the N and O atoms, slightly changing the charges on the carbon atoms. According to the calculations, the Mg–O and Mg–N bonds are slightly covalent. The metal AO is not included in the -system of the ring. 相似文献
146.
The nature of the reaction of a reagent with tetranitrodibenzo-18-crown-6 was found to depend on its basicity. This behavior was interpreted in the framework of the theory of hard and soft acids and bases.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 605–608, May, 1992. 相似文献
147.
M. N. Rimskaya-Korsakova A. V. Dubinin V. M. Ivanov 《Journal of Analytical Chemistry》2003,58(9):870-874
A procedure was developed for determining ultratrace rare-earth elements in sulfide minerals by inductively coupled plasma mass spectrometry with ion-exchange preconcentration. The concentration factor was 200. The found concentrations of rare-earth elements were 6–30 times lower than those in chondrites. For lanthanum and praseodymium, RSD < 10%; for other rare-earth elements, RSD < 6%. The accuracy of the results was verified by the addition of known amounts of Eu, Tb, Tm, and Lu to a chalcopyrite sample at the stage of decomposition with HCl and HNO3. The calculated yield of rare-earth elements was 94–96%. The detection limit was from 0.06 ng/g (6 × 10–9%) for lutetium to 5 ng/g (5 × 10–7%) for cerium. The procedure was used for the determination of rare-earth elements in chalcopyrites, pyrites, and sphalerites. 相似文献
148.
B. Constantinescu D. Galeriu E. A. Ivanov G. Pascovici D. Plostinaru 《Journal of Radioanalytical and Nuclear Chemistry》1988,128(1):15-21
Various samples from the south-east region of Roumania/greens, fodder, cheese/were analyzed for131I,134Cs and137Cs concentrations in May and July 1986 by -ray spectrometry. The concentrations are reported in nCi. kg–1 wet weight. For greens, a considerable decrease was observed for131I/to 3.0–7.0 nCi. kg–1/,134Cs/to 0.5–2.0 nCi.kg–1/ and137Cs /to 1.0–4.0 nCi. kg–1/ from the first half /5–15 May/ till the end of May 1986. For cheese, maximum values were measured between 5 and 15 May /sheep cottage cheese: 500–800 nCi.kg–1 for131I, 25–50 nCi. kg–1 for134Cs, 40–80 nCi. kg–1 for137Cs/; at the beginning of July a considerable decrease /to 5–10 nCi. kg–1 for131I, 1.2–2.0 nCi.kg–1 for134Cs, 2.2–3.0 nCi. kg–1 for137Cs/ was observed. In autumn 1986 a small increase up to 2.0–3.0 nCi. kg–1 for134Cs and 3.4–5.0 nCi. kg–1 for137Cs /in November/ was reported. The population's internal possible contamination was strongly limited by the authorities' severe control of the food-stuff. 相似文献
149.
The integral encounter theory (IET) has been extended to the reactions limited by diffusion along the reaction coordinate to the level crossing points where either thermal or hot electron transfer occurs. IET describes the bimolecular ionization of the instantaneously excited electron donor D* followed by the hot geminate backward transfer which precedes the ion pair equilibration and its subsequent thermal recombination. We demonstrate that the fraction of ion pairs which avoids the hot recombination is much smaller than their initial number when the electron tunneling is strong. 相似文献
150.
V. I. Terenin E. V. Kabanova N. A. Tselishcheva A. S. Ivanov N. V. Zyk 《Chemistry of Heterocyclic Compounds》2007,43(8):1038-1043
A study was carried out on the reaction of pyrrolo[1,2-a]pyrazines containing an alkyl, aryl, or aralkyl substituent at C-1
with trifluoroacetic anhydride. Trifluoroacetylation products may be formed either by reaction in the pyrrole ring or at the
aryl or aralkyl groups at C-1. Products of electrophilic substitution at C-6 are formed in the trifluoroacetylation of pyrrolo[1,2-a]pyrazines
containing at C-1 a substituent bulkier than a methyl group but lacking substituents at C-6 (the α-position of the pyrrole
ring).
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1226–1233, August, 2007. 相似文献