全文获取类型
收费全文 | 16403篇 |
免费 | 1621篇 |
国内免费 | 3036篇 |
专业分类
化学 | 14764篇 |
晶体学 | 1250篇 |
力学 | 506篇 |
综合类 | 226篇 |
数学 | 1471篇 |
物理学 | 2843篇 |
出版年
2024年 | 18篇 |
2023年 | 206篇 |
2022年 | 365篇 |
2021年 | 964篇 |
2020年 | 880篇 |
2019年 | 709篇 |
2018年 | 629篇 |
2017年 | 655篇 |
2016年 | 900篇 |
2015年 | 770篇 |
2014年 | 858篇 |
2013年 | 1463篇 |
2012年 | 1159篇 |
2011年 | 1100篇 |
2010年 | 858篇 |
2009年 | 1013篇 |
2008年 | 1022篇 |
2007年 | 1019篇 |
2006年 | 896篇 |
2005年 | 759篇 |
2004年 | 684篇 |
2003年 | 571篇 |
2002年 | 665篇 |
2001年 | 344篇 |
2000年 | 381篇 |
1999年 | 327篇 |
1998年 | 290篇 |
1997年 | 256篇 |
1996年 | 181篇 |
1995年 | 175篇 |
1994年 | 160篇 |
1993年 | 124篇 |
1992年 | 106篇 |
1991年 | 107篇 |
1990年 | 71篇 |
1989年 | 85篇 |
1988年 | 66篇 |
1987年 | 30篇 |
1986年 | 29篇 |
1985年 | 30篇 |
1984年 | 28篇 |
1983年 | 16篇 |
1982年 | 21篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1978年 | 7篇 |
1976年 | 6篇 |
1975年 | 5篇 |
1973年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
101.
102.
Richards模型在蔬菜生长预测中的应用 总被引:6,自引:0,他引:6
本文从 Richards模型的数学表达出发 ,阐述了模型中各参数初始值的确定以及优化过程 .并利用菜花和菠菜的试验数据建立其“最优”生长模型 . 相似文献
103.
Jacquelyn A. Carioscia Lauren Schneidewind Casey O'Brien Robert Ely Caitlin Feeser Neil Cramer Christopher N. Bowman 《Journal of polymer science. Part A, Polymer chemistry》2007,45(23):5686-5696
The ability to prepare high Tg low shrinkage thiol–ene materials is attractive for applications such as coatings and dental restoratives. However, thiol and nonacrylated vinyl materials typically consist of a flexible backbone, limiting the utility of these polymers. Hence, it is of importance to synthesize and investigate thiol and vinyl materials of varying backbone chemistry and stiffness. Here, we investigate the effect of backbone chemistry and functionality of norbornene resins on polymerization kinetics and glass transition temperature (Tg) for several thiol–norbornene materials. Results indicate that Tgs as high as 94 °C are achievable in thiol–norbornene resins of appropriately controlled chemistry. Furthermore, both the backbone chemistry and the norbornene moiety are important factors in the development of high Tg materials. In particular, as much as a 70 °C increase in Tg was observed in a norbornene–thiol specimen when compared with a sample prepared using allyl ether monomer of analogous backbone chemistry. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5686–5696, 2007 相似文献
104.
资源有限网络计划的PRWI启发式优化方法 总被引:1,自引:0,他引:1
本文在综合考虑了有资源约束的网络计划结构特征、资源强度、时间约束等方面因素的基础上,提出了一种新的资源优化的启发式优化方法—PRWI方法,并通过分析证明了该方法处理问题的效果较现有的其它方法好。 相似文献
105.
ZHAO Yan-fang ZHAI Xin CHEN Jiao-yue GUO Shu-chun GONG Ping 《高等学校化学研究》2006,22(4):468-473
IntroductionAdenosine 3′,5′-cyclic monophosphate (cAMP)and guanosine 3′,5′-cyclic monophosphate(cGMP) areubiquitous second messengers that mediate biologicalresponses to a variety of extracellular cues, includinghormones, neurotransmitters, chemokines… 相似文献
106.
关于多项式系数微分方程复振荡理论的两个结果 总被引:2,自引:0,他引:2
本文证明了:如果ak-j(j=1,…,k)为多项式,degak-j=nk-j,存在某个ak-s(1≤s≤k)满足:当1≤j<s时,nk-j/j≤nk-s/s;当s<j≤k时,nk-j<nk-s-(j-s).如果F≠0是整函数且满足σ(F)=β<(nk-s+s)/s,那么微分方程f(k)+a 相似文献
107.
108.
István Szilágyi László. Horváth Imre Labádi Klara Hernadi István Pálinkó Tamás Kiss 《Central European Journal of Chemistry》2006,4(1):118-134
An imidazolate-bridged copper(II)-zinc(II) complex (Cu(II)-diethylenetriamino-μ-imidazolato-Zn(II)-tris(2-aminoethyl)amine perchlorate (denoted as “Cu,Zn complex”) and a simple copper(II) complex (Cu(II)-tris(2-aminoethyl)
amine chloride (“Cu-tren”) were prepared and immobilised on silica gel (by hydrogen or covalent bonds) and montmorillonite
(by ion exchange). The immobilised substances were characterised by FT-IR spectroscopy and their thermal characteristics were
also studied. The obtained materials were tested in two probe reactions: catalytic oxidation of 3,5-di-tert-butyl catechol (DTBC) (catecholase activity) and the decomposition of hydrogen peroxide (catalase activity). It was found
that the catecholase activity of the Cu,Zn complex increased considerably upon immobilization on silica gel via hydrogen bonds and intercalation by ion exchange among the layers of montmorillonite. The imidazolate-bridged copper(II)-zinc(II)
complex and its immobilised versions were inactive in hydrogen peroxide decomposition. The Cu(II)-tris(2-aminoethyl)amine
chloride complex displayed good catalase activity; however, immobilisation could not improve it. 相似文献
109.
Wei‐Lie Xiao Jian‐Xin Pu Rui‐Rui Wang Liu‐Meng Yang Xiao‐Li Li Sheng‐Hong Li Rong‐Tao Li Sheng‐Xiong Huang Yong‐Tang Zheng Han‐Dong Sun 《Helvetica chimica acta》2007,90(8):1505-1513
Seven new highly oxygenated nortriterpenoids, rubriflorins D–J ( 1 – 7 ), were isolated from the leaves and stems of Schisandra rubriflora, and their structures were elucidated on the basis of extensive analysis of spectroscopic data. These new compounds feature the opening of ring A compared with related known nortriterpenoids isolated from the genus Schisandra and showed weak activity against HIV‐1. 相似文献
110.