全文获取类型
收费全文 | 277835篇 |
免费 | 3869篇 |
国内免费 | 2161篇 |
专业分类
化学 | 149880篇 |
晶体学 | 4301篇 |
力学 | 12556篇 |
综合类 | 103篇 |
数学 | 30802篇 |
物理学 | 86223篇 |
出版年
2020年 | 2434篇 |
2019年 | 2728篇 |
2018年 | 3472篇 |
2017年 | 3423篇 |
2016年 | 5008篇 |
2015年 | 3260篇 |
2014年 | 4899篇 |
2013年 | 11443篇 |
2012年 | 8953篇 |
2011年 | 10776篇 |
2010年 | 7793篇 |
2009年 | 7545篇 |
2008年 | 10016篇 |
2007年 | 10081篇 |
2006年 | 9384篇 |
2005年 | 8550篇 |
2004年 | 7857篇 |
2003年 | 7127篇 |
2002年 | 7156篇 |
2001年 | 7737篇 |
2000年 | 5919篇 |
1999年 | 4579篇 |
1998年 | 4042篇 |
1997年 | 3974篇 |
1996年 | 3696篇 |
1995年 | 3435篇 |
1994年 | 3572篇 |
1993年 | 3255篇 |
1992年 | 3718篇 |
1991年 | 3723篇 |
1990年 | 3635篇 |
1989年 | 3484篇 |
1988年 | 3589篇 |
1987年 | 3479篇 |
1986年 | 3294篇 |
1985年 | 4368篇 |
1984年 | 4645篇 |
1983年 | 3883篇 |
1982年 | 4009篇 |
1981年 | 3944篇 |
1980年 | 3914篇 |
1979年 | 3883篇 |
1978年 | 4193篇 |
1977年 | 4108篇 |
1976年 | 4175篇 |
1975年 | 3851篇 |
1974年 | 3898篇 |
1973年 | 4052篇 |
1972年 | 2851篇 |
1971年 | 2380篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Gábor Dörnyei Marietta Bárczai-Beke Gábor Blaskó Péter Péchy Csaba Szántay 《Tetrahedron letters》1982,23(28):2913-2916
Regioselective demethylation of 3,4-dihydropapaveraldine (a) at 7 and 3' positions affords a properly substituted diphenolic key intermidiate (d) for the synthesis of reticuline and N-norreticuline. 相似文献
82.
F. G. Gerasimato 《Journal of Mathematical Sciences》1991,57(5):3381-3383
We propose a simplified method of determining the integral characteristics of the opening of a parachute which makes it possible to compute the maximal stress on a parachute and the trajectory parameters of the motion of the load in the region of the opening of the parachute, and to determine the size of the portion of the canopy at the time of maximal stress.Translated fromDinamicheskie Sistemy, No. 6, 1987, pp. 38–41. 相似文献
83.
E. G. Tarakanova 《Journal of Applied Spectroscopy》1991,54(4):357-362
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 4, pp. 581–587, April, 1991. 相似文献
84.
E. V. Gromachevskaya A. G. Sakhabutdinov V. G. Kul'nevich I. S. Arustamova R. B. Valeev B. A. Bazhenov 《Chemistry of Heterocyclic Compounds》1991,27(5):502-503
It was shown that the reaction of o-hyroxyphenyldiphenylmethanol with benzaldehyde labeled with 17O and 18O isotopes proceeds in such a way that oxygen atoms of the starting phenoloalcohol are retained.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 632–633, May, 1991. 相似文献
85.
Wen Zhang Hui Huang Yu Ding Margherita Gavagnin Ernesto Mollo Guido Cimino Yue‐Wei Guo 《Helvetica chimica acta》2006,89(4):813-820
Three new polyoxygenated steroids, muricesteroid ( 1 ), and menellsteroids A ( 2 ) and B ( 3 ), were isolated from two species of the South China Sea gorgonian Muricella flexuosa and Menella verrucosa Brundin , respectively. The structures of these new compounds were elucidated on the basis of extensive spectroscopic analysis, chemical methods and comparison with known related compounds. 相似文献
86.
It is proved that the variety of relevant disjunction lattices has the finite embeddability property. It follows that Avron's relevance logic RMI min has a strong form of the finite model property, so it has a solvable deducibility problem. This strengthens Avron's result that RMI min is decidable. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
87.
Kurenkov V. F. Zaitseva O. A. Kirdyashova G. N. 《Russian Journal of Applied Chemistry》2002,75(4):641-644
The kinetics of radical copolymerization of acrylamide with lithium, sodium, and potassium 2-acrylamido-2-methylpropanesulfonates in concentrated aqueous solutions in the presence of potassium persulfate as initiating agent at pH 9 and 50°C was studied by dilatometry. 相似文献
88.
In this paper we suggest a unique model for estimating the operating cost of each of three waste-collection systems. Under the traditional system, which is widely used, waste is typically collected in plastic bags and a three-man crew is needed on each vehicle. The other two systems require a one-man crew for vehicle collecting street containers. The side-loader system with fixed body automatically empties street containers into the vehicle body and empties the load at the disposal site. The side-loader system with demountable body allows the separation of the waste collection phase from transport to the disposal site, since the vehicle body can be demounted. We also present two case studies and show how the estimation of operating costs is a critical issue in decisions regarding the type of system to be used for waste collection. 相似文献
89.
Shunin D. G. Filippova A. G. Okhotina N. A. Liakumovich A. G. Samuilov Ya. D. 《Russian Journal of Applied Chemistry》2002,75(6):1020-1023
Procedures are discussed for production of rubber-bitumen compounds based on spent rubber items. A possibility of using these binders for paving is studied experimentally. 相似文献
90.
In this paper necessary and sufficient conditions of null-controllability and approximate null-controllability are obtained for the wave equation on a half-axis. Controls solving these problems are found explicitly. Moreover, bang-bang controls solving the approximate null-controllability problem are constructed with the aid of solutions of a frequency extinguishing problem in the restricted band (−a,a) for this equation and the Markov power moment problem. 相似文献