全文获取类型
收费全文 | 343777篇 |
免费 | 3832篇 |
国内免费 | 1684篇 |
专业分类
化学 | 189315篇 |
晶体学 | 5246篇 |
力学 | 14302篇 |
综合类 | 64篇 |
数学 | 36934篇 |
物理学 | 103432篇 |
出版年
2020年 | 2745篇 |
2019年 | 2953篇 |
2018年 | 3853篇 |
2017年 | 3898篇 |
2016年 | 5744篇 |
2015年 | 3768篇 |
2014年 | 5527篇 |
2013年 | 14086篇 |
2012年 | 11639篇 |
2011年 | 14201篇 |
2010年 | 10079篇 |
2009年 | 9973篇 |
2008年 | 13505篇 |
2007年 | 13444篇 |
2006年 | 12825篇 |
2005年 | 11742篇 |
2004年 | 10454篇 |
2003年 | 9440篇 |
2002年 | 9289篇 |
2001年 | 11234篇 |
2000年 | 8386篇 |
1999年 | 6275篇 |
1998年 | 4799篇 |
1997年 | 4860篇 |
1996年 | 4726篇 |
1995年 | 4255篇 |
1994年 | 4296篇 |
1993年 | 4026篇 |
1992年 | 4729篇 |
1991年 | 4848篇 |
1990年 | 4544篇 |
1989年 | 4428篇 |
1988年 | 4345篇 |
1987年 | 4304篇 |
1986年 | 4126篇 |
1985年 | 5352篇 |
1984年 | 5399篇 |
1983年 | 4440篇 |
1982年 | 4668篇 |
1981年 | 4292篇 |
1980年 | 4088篇 |
1979年 | 4509篇 |
1978年 | 4771篇 |
1977年 | 4814篇 |
1976年 | 4766篇 |
1975年 | 4371篇 |
1974年 | 4487篇 |
1973年 | 4540篇 |
1972年 | 3367篇 |
1971年 | 2679篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
L. A. Oparina O. V. Vysotskaya A. V. Stepanov I. V. Rodionova G. F. Myachina N. K. Gusarova B. A. Trofimov 《Russian Journal of Organic Chemistry》2008,44(1):120-123
2-Hydroxymethylfuran reacted with acetylene in superbasic catalytic systems MOH-DMSO (M = Na, K) under mild temperature conditions (75–85°C, 1–2 h), yielding 80% of 2-vinyloxymethylfuran. The product, as well as acetaldehyde acetals derived therefrom, turned out to be promising as modifiers for electrolyte in lithium-sulfur rechargeable batteries. 相似文献
992.
993.
G. I. Nikishin L. L. Sokova V. D. Makhaev N. I. Kapustina 《Russian Chemical Bulletin》2008,57(1):118-123
The solid-phase oxidation of cinnamic, 4-methoxy- and 3,4-dimethoxycinnamic acids with Ce(NH4)2(NO3)6—MHal system leads to β-halostyrenes. Similar procedure in the absence of a metal halide results in a cleavage of the C=C
bond giving the corresponding benzaldehydes.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 114–118, January, 2008. 相似文献
994.
M. Yu. Berezkin E. G. Polyakov V. V. Turygin L. V. Kaabak A. V. Khudenko A. P. Tomilov 《Russian Journal of Applied Chemistry》2008,81(8):1360-1363
Anodic dissolution of ferroniobium in anhydrous methanol in the presence of sodium methylate was studied. The possibility of recovering pure hexamethoxyniobate from the electrolyzate and its conversion into niobium methylate with an iron content not exceeding 0.01% was analyzed. 相似文献
995.
P.R. Willmott R. Herger M.C. Falub L. Patthey M. Döbeli C.V. Falub M. Shi M. Schneider 《Applied Physics A: Materials Science & Processing》2004,79(4-6):1199-1201
A new ablation target geometry is presented that was used to produce thin films of La1-xSrxMnO3 grown heteroepitaxially on SrTiO3 by pulsed reactive crossed-beam laser ablation. The films were grown in order to perform angle-resolved photoelectron spectroscopy, which demands that the surface be atomically flat. In situ and ex situ analysis shows that this condition was met, even after depositing to a thickness of over 100 nm. PACS 61.10.-i; 61.18.Bn; 68.47.Gh; 71.27.+a; 81.15.Fg 相似文献
996.
In the present paper we determine the oscillator strength of two-dimensional (2D) D− ions under the influence of a static magnetic field. The results are important for the analysis of the optical transitions observed in semiconductor quantum wells. We have applied the ab initio procedure Hyperspherical Adiabatic Approach, based on the use of hyperspherical coordinates. This approach uses an adiabatic separation of the total wave function that allows accurate energies determination from molecular-like potential curves. The convergence is obtained in a systematic way by the inclusion of non-adiabatic couplings without the need of adjustable parameters. 相似文献
997.
B. Y. Myung J. S. Kim J. J. Kim T. H. Yoon 《Journal of polymer science. Part A, Polymer chemistry》2003,41(21):3361-3374
2,2‐Bis[4(4‐aminophenoxy)phenyl]phthalein‐3′,5′‐bis(trifluoromethyl)anilide (6FADAP), containing fluorine and phthalimide moieties, was synthesized via the Williamson ether condensation reaction from 1‐chloro‐4‐nitrobenzene and phenolphthalein‐3′,5′‐bis(trifluoromethyl)anilide, which was followed by hydrogenation. Monomers such as 2,2‐bis[4(4‐aminophenoxy)phenyl]phthalein‐anilide containing phthalimide groups and 2,2‐bis[4(4‐aminophenoxy)phenyl]phthalein containing only phthalein moieties were also synthesized for comparison. The monomers were first characterized by Fourier transform infrared (FTIR), 1H NMR, 19F NMR, elemental analysis, and titration and were then used to prepare polyimides with 2,2‐bis(3,4‐dicarboxyphenyl)hexafluoropropane dianhydride. The polyimides were designed to have molecular weights of 20,000 g/mol via off‐stoichiometry and were characterized by FTIR, NMR, gel permeation chromatography (GPC), differential scanning calorimetry, and thermogravimetric analysis. Their solubility, water absorption, dielectric constant, and refractive index were also evaluated. The polyimides prepared with 6FADAP, containing fluorine and phthalimide moieties, had excellent solubility in N‐methylpyrrolidinone, N,N‐dimethylacetamide, tetrahydrofuran, CHCl3, tetrachloroethane, and acetone, and GPC analysis showed a molecular weight of 18,700 g/mol. The polyimides also exhibited a high glass‐transition temperature (290 °C), good thermal stability (~500 °C in air), low water absorption (1.9 wt %), a low dielectric constant (2.81), a low refractive index, and low birefringence (0.0041). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3361–3374, 2003 相似文献
998.
In this paper an automatic technique for handling discontinuous IVPs when they are solved by means of adaptive Runge–Kutta codes is proposed. This technique detects, accurately locates and passes the discontinuities in the solution of IVPs by using the information generated by the code along the numerical integration together with a continuous interpolant of the discrete solution. A remarkable feature is that it does not require additional information on the location of the discontinuities. Some numerical experiments are presented to illustrate the reliability and efficiency of the proposed algorithms. 相似文献
999.
1000.
H. Bungener L. Fries und C. O'Sullivan 《Fresenius' Journal of Analytical Chemistry》1885,24(1):116-119
Ohne Zusammenfassung 相似文献