全文获取类型
收费全文 | 42607篇 |
免费 | 9703篇 |
国内免费 | 1445篇 |
专业分类
化学 | 45732篇 |
晶体学 | 353篇 |
力学 | 772篇 |
综合类 | 1篇 |
数学 | 3522篇 |
物理学 | 3375篇 |
出版年
2022年 | 79篇 |
2021年 | 255篇 |
2020年 | 1298篇 |
2019年 | 2669篇 |
2018年 | 1081篇 |
2017年 | 720篇 |
2016年 | 3509篇 |
2015年 | 3645篇 |
2014年 | 3582篇 |
2013年 | 4395篇 |
2012年 | 3298篇 |
2011年 | 2635篇 |
2010年 | 3097篇 |
2009年 | 3055篇 |
2008年 | 2737篇 |
2007年 | 2098篇 |
2006年 | 1826篇 |
2005年 | 2007篇 |
2004年 | 1782篇 |
2003年 | 1605篇 |
2002年 | 2277篇 |
2001年 | 1446篇 |
2000年 | 1378篇 |
1999年 | 440篇 |
1998年 | 156篇 |
1997年 | 171篇 |
1996年 | 161篇 |
1995年 | 112篇 |
1994年 | 128篇 |
1993年 | 106篇 |
1992年 | 100篇 |
1991年 | 70篇 |
1990年 | 73篇 |
1989年 | 64篇 |
1988年 | 64篇 |
1987年 | 63篇 |
1986年 | 58篇 |
1985年 | 82篇 |
1984年 | 88篇 |
1983年 | 72篇 |
1982年 | 87篇 |
1981年 | 97篇 |
1980年 | 96篇 |
1979年 | 114篇 |
1978年 | 116篇 |
1977年 | 108篇 |
1976年 | 98篇 |
1975年 | 92篇 |
1974年 | 92篇 |
1973年 | 63篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
We show the existence of monotone in time solutions for
a semilinear parabolic equation with memory. The blow-up rate
estimate of the solution is known to be a consequence of the
monotonicity property. 相似文献
162.
C. Vaca‐Garcia G. Gozzelino W. G. Glasser M. E. Borredon 《Journal of Polymer Science.Polymer Physics》2003,41(3):281-288
The main transitions of cellulose fatty esters with different degrees of substitution (DSs) were investigated with dynamic mechanical thermal analysis. Two distinct main relaxations were observed in partially substituted cellulose esters (PSCEs). They were attributed to the glass‐transition temperature and to the chain local motion of the aliphatic substituents. The temperatures of both transitions decreased when DS or the number of carbon atoms (n) of the acyl substituent increased. Conversely, all the transitions of fully substituted cellulose esters occurred within a narrow temperature range, and they did not vary significantly with n. This phenomenon was explained by the formation of a crystalline phase of the fatty substituents. The presence of few residual OH groups in PSCEs was responsible for a large increase in the storage bending modulus, and it eliminated the effect of n on damping. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 281–288, 2003 相似文献
163.
164.
We establish gradient estimates for bounded solutions of semilinear parabolic equations, where the nonlinearity only satisfies one-sided quadratic upper growth assumptions, instead of the classical (two-sided) Bernstein's condition. This extends a recent work of Al. and Ar. Tersenov (Indiana Univ. Math. J. 50 (2001) 1899–1913), where results of this kind were obtained for radial solutions in a ball, by a different technique. To cite this article: J.-Ph. Bartier, Ph. Souplet, C. R. Acad. Sci. Paris, Ser. I 338 (2004). 相似文献
165.
166.
For solutions of (inviscid, forceless, one dimensional) Burgers equation with random initial condition, it is heuristically shown that a stationary Feller–Markov property (with respect to the space variable) at some time is conserved at later times, and an evolution equation is derived for the infinitesimal generator. Previously known explicit solutions such as Frachebourg–Martin's (white noise initial velocity) and Carraro–Duchon's Lévy process intrinsic-statistical solutions (including Brownian initial velocity) are recovered as special cases. 相似文献
167.
An m‐covering of a graph G is a spanning subgraph of G with maximum degree at most m. In this paper, we shall show that every 3‐connected graph on a surface with Euler genus k ≥ 2 with sufficiently large representativity has a 2‐connected 7‐covering with at most 6k ? 12 vertices of degree 7. We also construct, for every surface F2 with Euler genus k ≥ 2, a 3‐connected graph G on F2 with arbitrarily large representativity each of whose 2‐connected 7‐coverings contains at least 6k ? 12 vertices of degree 7. © 2003 Wiley Periodicals, Inc. J Graph Theory 43: 26–36, 2003 相似文献
168.
Klai Nadia Berredjem Malika Khettache Nawel Belghit Med Yazid Rgaïnia Zine Nour‐Eddine Aouf 《Journal of heterocyclic chemistry》2004,41(1):57-60
Dedicated to the memory of Pr. Ladjama Daif A series of chiral cyclosulfamides have been synthesized by alkaline cyclisation starting from N‐benzoylamino acids (Ala, Val, Leu, Phe) derivatives and chlorosulfonyl isocyanate. A simplified and regioselective deprotection of the cyclic compounds (cyclosulfamides) containing the tert‐butyloxycarbonyl group (Boc) has been achieved in good yield by fusion under reduced pressure. 相似文献
169.
Andrew Bach Xinglong Jiang Joseph Mckenna Kapa Prasad Oljan Repic Wen‐Chung Shieh 《Journal of heterocyclic chemistry》2004,41(4):637-640
An efficient approach has been developed for the synthesis of an isofervenulin analogue 1 employing a one‐pot condensation‐substitution reaction of a chlorocarboethoxytriazine (electrophile) with a urea (nucleophile). The resulting cyclization reaction resulted in the synthesis of a pyrimido‐heterocycle in good yield in either acidic or basic media. The former was assisted by utilizing trimethylsilyl chloride. 相似文献
170.
Crystal Structure of the Zinc Amide Zn[N(SiMe3)2]2 X‐ray quality crystals of Zn[N(SiMe3)2]2 (monoclinic, P21/c) are obtained by sublimation of the zinc amide Zn[N(SiMe3)2]2 at —30 °C in vacuo (300 torr). According to the result of the X‐ray structural analysis, Zn[N(SiMe3)2]2 contains an almost linear N‐Zn‐N unit with two short N‐Zn bonds. 相似文献