全文获取类型
收费全文 | 11884篇 |
免费 | 2213篇 |
国内免费 | 1624篇 |
专业分类
化学 | 8370篇 |
晶体学 | 168篇 |
力学 | 824篇 |
综合类 | 118篇 |
数学 | 1288篇 |
物理学 | 4953篇 |
出版年
2024年 | 21篇 |
2023年 | 270篇 |
2022年 | 405篇 |
2021年 | 494篇 |
2020年 | 498篇 |
2019年 | 513篇 |
2018年 | 423篇 |
2017年 | 388篇 |
2016年 | 619篇 |
2015年 | 584篇 |
2014年 | 709篇 |
2013年 | 885篇 |
2012年 | 1087篇 |
2011年 | 1065篇 |
2010年 | 845篇 |
2009年 | 774篇 |
2008年 | 758篇 |
2007年 | 704篇 |
2006年 | 711篇 |
2005年 | 599篇 |
2004年 | 396篇 |
2003年 | 327篇 |
2002年 | 336篇 |
2001年 | 248篇 |
2000年 | 227篇 |
1999年 | 222篇 |
1998年 | 183篇 |
1997年 | 208篇 |
1996年 | 186篇 |
1995年 | 165篇 |
1994年 | 145篇 |
1993年 | 101篇 |
1992年 | 89篇 |
1991年 | 80篇 |
1990年 | 79篇 |
1989年 | 70篇 |
1988年 | 55篇 |
1987年 | 31篇 |
1986年 | 46篇 |
1985年 | 33篇 |
1984年 | 25篇 |
1983年 | 16篇 |
1982年 | 15篇 |
1981年 | 8篇 |
1980年 | 10篇 |
1975年 | 7篇 |
1973年 | 4篇 |
1972年 | 7篇 |
1965年 | 7篇 |
1964年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
A novel class of platinum-based initiating systems for the ring-opening polymerization of a wide variety of heterocyclic compounds including epoxides, oxetanes, and 1,3,5-trioxane have been discovered. In addition to a platinum complex as a catalyst, a cocatalyst, consisting of a compound or polymer containing silicon-hydrogen bonds must also be present. This article reports on a preliminary survey of the scope and limitations of these new initiator systems. Particular emphasis in this article has been placed on the ring-opening polymerization of epoxides which have been studied in some detail and which proceed rapidly and exothermically at room temperature. A number of mechanistic studies have been conducted and the best current evidence suggests that polymerization proceeds by a cationic mechanism. Evidence is also presented which suggests that platinum metal colloids may function as the active initiating species. 相似文献
82.
83.
叠层连续开口圆柱壳的精确解 总被引:2,自引:0,他引:2
抛弃任何有关位移和应力模式的假设,引入δ-函数,对正变异性连续开口圆柱壳建立状态方程.给出薄的、中厚的和强厚的叠层连续开口圆柱壳静力问题的统一的精确解.数值结果和SAPS解进行了对比. 相似文献
84.
Kan‐Yi Pu Yi Chen Xiao‐Ying Qi Chun‐Yang Qin Qing‐Quan Chen Hong‐Yu Wang Yun Deng Qu‐Li Fan Yan‐Qin Huang Shu‐Juan Liu Wei Wei Bo Peng Wei Huang 《Journal of polymer science. Part A, Polymer chemistry》2007,45(16):3776-3787
In this contribution, we demonstrate a new effective methodology for constructing highly efficient and durable poly(p‐phenyleneethynylene) (PPE) containing emissive material with nonaggregating and hole‐facilitating properties through the introduction of hole‐transporting blocks into the PPE system as the grafting coils as well as building the energy donor–acceptor architecture between the grafting coils and the PPE backbone. Poly(2‐(carbazol‐9‐yl)ethyl methacrylate) (PCzEMA), herein, is chosen as the hole‐transporting blocks, and incorporated into the PPE system as the grafting coils via atom transfer radical polymerization. The chemical structure of the resultant copolymer, PPE‐g‐PCzEMA, was characterized by NMR and gel permeation chromatography, showing that the desirable copolymer was obtained with the narrow polydispersity. The increased thermal stability of PPE‐g‐PCzEMA was confirmed by thermogravimetric analysis and differential scanning calorimetry along with its macroinitiator. The optoelectronic properties of this copolymer were studied in detail by ultraviolet‐visible absorption, photoluminescence emission and excitation spectra, and cyclic voltammogram (CV). The results indicate that PPE‐g‐PCzEMA exhibits the solid‐state luminescent property dominated by individual lumophores, and also the energy transfer process from the PCzEMA blocks to the PPE backbone with a relatively higher energy transfer efficiency in the solid‐state compared to that of the solution state. Additionally, the hole‐injection property is greatly facilitated due to the presence of PCzEMA, as confirmed by CV profiles. All these data indicate that PPE‐g‐PCzEMA is a good candidate for use in optoelectronic devices. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3776–3787, 2007 相似文献
85.
86.
Kikue S. Burnham Robert Roth Faith Zhou Wenya Fan Emma Brouk Mehari Stifanos 《Journal of polymer science. Part A, Polymer chemistry》2006,44(24):6909-6925
In an attempt to develop a low‐k interlayer dielectric, adamantane‐diphenyldiethynyl moiety containing oligomer is prepared. Oligomerization of 1,3,5,7‐tetrakis[3/4‐ethynylphenyl]adamantane ( 4 ) is accomplished by a Glaser–Hay oxidative coupling with 1,3,5‐triethynylbenzene and phenylacetylene end‐capping agent. The CHCl3 soluble oligomer is then thermally treated by step‐curing at 200, 300, 380, and 450 °C for 30 min at each temperature under nitrogen flow to render a shiny void‐free black polymer. TGA analysis indicates that the polymer is stable under nitrogen up to 500 °C with a marginal decomposition up to 800 °C. Solid‐state 13C NMR, Raman scattering, and FTIR are used to characterize the structure of the polymer. The polymer consists of amorphous carbon networks with the adamantane moieties and nanosized graphitic regions (clusters), which are generated from the thermal crosslinking of the diphenyldiethynyl units. It shows a remarkably low linear coefficient of thermal expansion (~25 ppm/°C), presumably due to the presence of the disordered graphitic structure. Its high density (~1.21 g/cm3), refractive index (~1.80 at 632 nm), and Young's modulus (~17.0 GPa) are also consistent with the interpretation. This study reveals important details about the effect of microscopic structure on the macroscopic properties of the highly crosslinked polymer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6909–6925, 2006 相似文献
87.
88.
基于专家动态权重的群组AHP交互式决策方法 总被引:2,自引:0,他引:2
为了能在群组决策中得到更为客观和准确的决策结果,在把专家权重划分为静态权重和动态权重的基础上,研究了在交互式决策中专家动态权重的确定方法,给出了共识度的一个定义.在此基础上,研究了群组AHP交互式决策方法中的一致性和相容性检验,给出了基于专家动态权重的群组AHP交互式决策方法流程,最后用一个示例说明了该方法的应用步骤. 相似文献
89.
90.
The binding of lomefloxacin to bovine lactoferrin (BLf) in a dilute aqueous solution was studied using fluorescence spectra. The binding constant (K) and the number of binding sites (n) were obtained by a fluorescence quenching method. The binding distance (r) and energy-transfer efficiency (E) between lomefloxacin and bovine lactoferrin were also obtained according to the mechanism of Fo?rster-type dipole-dipole nonradiative energy-transfer. The effect of lomefloxacin on the conformation of bovine lactoferrin was also analyzed by synchronous fluorescence spectroscopy. The interaction between lomefloxacin and bovine lactoferrin is strong. Lomefloxacin can affect the conformation of bovine lactoferrin to some degree. 相似文献