全文获取类型
收费全文 | 91643篇 |
免费 | 17412篇 |
国内免费 | 9042篇 |
专业分类
化学 | 78118篇 |
晶体学 | 1296篇 |
力学 | 4060篇 |
综合类 | 625篇 |
数学 | 8619篇 |
物理学 | 25379篇 |
出版年
2024年 | 195篇 |
2023年 | 1074篇 |
2022年 | 1845篇 |
2021年 | 2132篇 |
2020年 | 3205篇 |
2019年 | 4466篇 |
2018年 | 2805篇 |
2017年 | 2463篇 |
2016年 | 5713篇 |
2015年 | 5959篇 |
2014年 | 6415篇 |
2013年 | 7857篇 |
2012年 | 7788篇 |
2011年 | 7200篇 |
2010年 | 6427篇 |
2009年 | 6361篇 |
2008年 | 6264篇 |
2007年 | 5224篇 |
2006年 | 4834篇 |
2005年 | 4378篇 |
2004年 | 3662篇 |
2003年 | 3179篇 |
2002年 | 3836篇 |
2001年 | 2858篇 |
2000年 | 2648篇 |
1999年 | 1595篇 |
1998年 | 1045篇 |
1997年 | 911篇 |
1996年 | 875篇 |
1995年 | 776篇 |
1994年 | 707篇 |
1993年 | 562篇 |
1992年 | 497篇 |
1991年 | 431篇 |
1990年 | 360篇 |
1989年 | 278篇 |
1988年 | 247篇 |
1987年 | 198篇 |
1986年 | 180篇 |
1985年 | 194篇 |
1984年 | 128篇 |
1983年 | 88篇 |
1982年 | 74篇 |
1981年 | 53篇 |
1980年 | 31篇 |
1979年 | 23篇 |
1978年 | 7篇 |
1977年 | 9篇 |
1957年 | 7篇 |
1936年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
Xian Xu 《Journal of Mathematical Analysis and Applications》2004,291(2):673-689
In this paper, some multiplicity results for positive solutions of some singular semi-positone three-point boundary value problem be obtained by using the fixed point index method. 相似文献
152.
KANG Zihua WANG Mingwei QIAN Jiamei RAO Jun LI Xiujuan ZHENG Tieliu WANG Xuehua 《核工业西南物理研究院年报(英文版)》2004,(1):73-76
Lower hybrid wave (LHW), electro cyclotron (EC) and neutral beam injection (NBI) etc. are the important methods of auxiliary heating. They would be devoted to the HL-2A tokamak step by step. In order to satisfy the debug of each system and the need of the experiment, the system should be equipped with high voltage pulse power (HVPP) according to the requirement. 相似文献
153.
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
154.
Shu Fen Wang Wen Guo Zou Su Wen Liu Dong Xu Duo Rong Yuan Guang Jun Zhou 《Journal of Physics and Chemistry of Solids》2004,65(7):1243-1245
The photoluminescence properties of the Bi3+ in sol-gel derived ZnTiO3 nanocrystals have been investigated. An ultra-violet emission at 360 nm and a visible emission band at 506 nm have been observed, originating from two kinds of emission centers. The former is ascribed to the 3P1-1S0 transition of Bi3+ and the latter to the recombination of the electrons with the photo-generated holes trapped in the zinc vacancies. In all cases the latter contribution is predominant. 相似文献
155.
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
156.
157.
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
158.
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
159.
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
160.
HaiHuiXIE XiaoYiWEI JiDongWANG MeiFangLIU RenZhouYANG 《中国化学快报》2003,14(6):588-590
A New Annonaceous acetogenin,squamostolide(1),was isolated from the seeds of Annona squamosa.Its structure was elucidated based on spectroscopic methods and comparison with known compounds.It is the first example of Annonaceous acetogenin with each of the two ends of the aliphatic chain bearing a γ-lactone.Thenew compound exhibited cytotoxic activity in vitro against bel-7402 and CNE2 human tumor cell lines. 相似文献