全文获取类型
收费全文 | 66234篇 |
免费 | 9589篇 |
国内免费 | 18364篇 |
专业分类
化学 | 45678篇 |
晶体学 | 2217篇 |
力学 | 5159篇 |
综合类 | 1828篇 |
数学 | 10386篇 |
物理学 | 28919篇 |
出版年
2023年 | 519篇 |
2022年 | 1901篇 |
2021年 | 1973篇 |
2020年 | 1976篇 |
2019年 | 1958篇 |
2018年 | 1943篇 |
2017年 | 2756篇 |
2016年 | 2172篇 |
2015年 | 2679篇 |
2014年 | 3447篇 |
2013年 | 4431篇 |
2012年 | 4304篇 |
2011年 | 4659篇 |
2010年 | 4837篇 |
2009年 | 4979篇 |
2008年 | 5504篇 |
2007年 | 5109篇 |
2006年 | 4788篇 |
2005年 | 4146篇 |
2004年 | 3294篇 |
2003年 | 2426篇 |
2002年 | 2515篇 |
2001年 | 2545篇 |
2000年 | 2587篇 |
1999年 | 1489篇 |
1998年 | 907篇 |
1997年 | 712篇 |
1996年 | 673篇 |
1995年 | 667篇 |
1994年 | 619篇 |
1993年 | 675篇 |
1992年 | 630篇 |
1991年 | 516篇 |
1990年 | 555篇 |
1989年 | 554篇 |
1988年 | 401篇 |
1987年 | 427篇 |
1986年 | 371篇 |
1985年 | 392篇 |
1984年 | 421篇 |
1983年 | 349篇 |
1982年 | 356篇 |
1979年 | 380篇 |
1978年 | 355篇 |
1976年 | 420篇 |
1975年 | 365篇 |
1974年 | 400篇 |
1973年 | 401篇 |
1972年 | 369篇 |
1971年 | 343篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The stability and convergence of the solutions of perturbed and regularized variational inequality to the solutions of the primary (unstable a priori) variational inequality with proper monotone operator are investigated. All the objects of inequality: the operatorA, the right-hand partf and the set of constrains are to be perturbed. At the same time no assumptions of boundedness and smoothness of the operatorA are used. The connection between the parameters of perturbations, which guarantees strong convergence of approximate solutions, is established. It is proved that the existence of the solution to the unperturbed variational inequality is necessary and sufficient condition for convergence of the regularized perturbed inequality solutions.This research was supported in part by the Ministry of Science Grant 3481-1-91 and by the Ministry of Absorption Center for Absorption in Science. 相似文献
992.
Condensation of fluorine-containing anilines with paraldehyde gave quinaldine derivatives with CF3, CF3S, and CF3SO2 groups in the 6 position, from which carbocyanine, merocyanine, and styryl dyes were synthesized. Fluorine-containing groups lower the basicity of quinaldine by 0.7–2.0 pKa units and lead to deepening of the color of the dyes.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 76–78, January, 1978. 相似文献
993.
ZrO2在合成甲醇催化剂CuO-ZnO-ZrO2中的作用 总被引:1,自引:0,他引:1
采用并流共沉淀法制备了一系列ZrO2的原子比不同的CuO-ZnO-ZrO2甲醇合成催化剂.在固定床反应器中进行合成气制甲醇的研究,考察了ZrO2在催化剂中的作用.结果表明,ZrO2的加入能显著提高催化剂的性能,当ZrO2的原子比达到0.10时,催化剂的活性最高并且耐热性能最强;过量的ZrO2会降低催化剂的活性.利用TPR、XRD、BET技术对催化剂进行了表征,发现适量ZrO2的加入不仅有助于提高Cu活性组分在催化剂表面的分散,提高催化剂的比表面积,使催化剂不容易高温烧结,而且有利于促进催化剂还原. 相似文献
994.
995.
Conclusions Both the extent of C2H4 hydropolymerization, initiated by 0.01% CO, on Co zeolites at a temperature below 100°C, and the initiating effect increase symbatically with increase in the ratio of SiO2/Al2O3 in the zeolite in the investigated limits (from 2 to 10).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 894–896, April, 1974. 相似文献
996.
The infrared spectra of naphthalene and anthracene anion-radicals and their completely deuterated analogs have been studied. The most intense bands have been assigned, and it has been shown that the frequencies of the bending and stretching vibrations of the ring and the C-H (D) bond are less than the corresponding frequencies for the hydrocarbons. The decrease in the frequencies has been attributed to the fact that the unpaired electron of the anionradical, present in an antibonding orbital, decreases the force constants of the bonds; this is analogous to an excited state of the hydrocarbon molecule. A product rule has been proposed for the anion-radicals and their original hydrocarbons. 相似文献
997.
Zhi Qiang Shi Ya Qing Feng Bing Zhao Wen Xiang Wang 《中国化学快报》2007,18(12):1493-1495
A novel series of N-alkylphthalimidylaminocarbonylmethoxylcalix[4]arenes with the reaction between 4-(N-bromoacetyla- mino)-phthalimide derivatives and calix[4]arene has been synthesized and structurally characterized by IR,~1HNMR and MS.From their analysis data,it was found that compounds 7a-7d adopted a cone conformation. 相似文献
998.
A radical mechanism of the reaction of molybdenum carbonyl complexes with bis(triethylgermyl)mercury
M. I. Sykhrannova A. N. Tatarnikov S. Ya. Khorshev E. N. Gladyshev 《Russian Chemical Bulletin》1993,42(9):1585-1587
The reaction of [Cp(CO)3Mo]2 with (Et3Ge)2Hg occurs in toluene and THF by a radical mechanism. The interaction between [Cp(CO)3Mo]2Hg and (Et3Ge)2Hg has a radical character only in THF. The formation of Cp(CO)3MoH at the first stage of these reactions substantially affects the further course of the process.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1648–1650, September, 1993. 相似文献
999.
The synthesis has been achieved of the hexadecyl -glycosides of N-acetylmur-amoyl-L-alanyl-D-glutamic acid and N-acetyl-nor-muramoyl-L-alanyl-D-glutamic acid and of the -octadecylamide of N-acetylmuramoyl-L-alanyl-D-glutamic acid — lipophilic glycopeptides of differing hydrophilic-lipophilic balance.M. V. Frunze Simferopol' State University. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 553–557, July–August, 1991. 相似文献
1000.