全文获取类型
收费全文 | 10562篇 |
免费 | 1743篇 |
国内免费 | 1462篇 |
专业分类
化学 | 8451篇 |
晶体学 | 111篇 |
力学 | 496篇 |
综合类 | 103篇 |
数学 | 1294篇 |
物理学 | 3312篇 |
出版年
2024年 | 24篇 |
2023年 | 205篇 |
2022年 | 253篇 |
2021年 | 314篇 |
2020年 | 392篇 |
2019年 | 408篇 |
2018年 | 357篇 |
2017年 | 279篇 |
2016年 | 470篇 |
2015年 | 500篇 |
2014年 | 576篇 |
2013年 | 738篇 |
2012年 | 862篇 |
2011年 | 889篇 |
2010年 | 656篇 |
2009年 | 648篇 |
2008年 | 714篇 |
2007年 | 652篇 |
2006年 | 606篇 |
2005年 | 531篇 |
2004年 | 484篇 |
2003年 | 451篇 |
2002年 | 479篇 |
2001年 | 329篇 |
2000年 | 277篇 |
1999年 | 304篇 |
1998年 | 223篇 |
1997年 | 193篇 |
1996年 | 162篇 |
1995年 | 137篇 |
1994年 | 112篇 |
1993年 | 66篇 |
1992年 | 73篇 |
1991年 | 75篇 |
1990年 | 53篇 |
1989年 | 39篇 |
1988年 | 37篇 |
1987年 | 30篇 |
1986年 | 31篇 |
1985年 | 29篇 |
1984年 | 24篇 |
1983年 | 12篇 |
1982年 | 11篇 |
1981年 | 7篇 |
1980年 | 10篇 |
1979年 | 6篇 |
1976年 | 7篇 |
1975年 | 5篇 |
1974年 | 4篇 |
1968年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 937 毫秒
101.
Guey‐Sheng Liou Sheng‐Huei Hsiao Yi‐Kai Fang 《Journal of polymer science. Part A, Polymer chemistry》2006,44(21):6466-6483
Two new phenyl‐ and naphthyl‐substituted rigid‐rod aromatic dicarboxylic acid monomers, 2,2′‐diphenylbiphenyl‐4,4′‐dicarboxylic acid ( 4 ) and 2,2′‐di(1‐naphthyl)biphenyl‐4,4′‐dicarboxylic acid ( 5 ), were synthesized by the Suzuki coupling reaction of 2,2′‐diiodobiphenyl‐4,4′‐dicarboxylic acid dimethyl ester with benzeneboronic acid and naphthaleneboronic acid, respectively, followed by alkaline hydrolysis of the ester groups. Four new polyhydrazides were prepared from the dicarboxylic acids 4 and 5 with terephthalic dihydrazide (TPH) and isophthalic dihydrazide (IPH), respectively, via the Yamazaki phosphorylation reaction. These polyhydrazides were amorphous and readily soluble in many organic solvents. Differential scanning calorimetry (DSC) indicated that these hydrazide polymers had glass transition temperatures in the range of 187–234 °C and could be thermally cyclodehydrated into the corresponding oxadiazole polymers in the range of 300–400 °C. The resulting poly(1,3,4‐oxadiazole)s exhibited Tg's in the range of 252–283 °C, 10% weight‐loss temperature in excess of 470 °C, and char yield at 800 °C in nitrogen higher than 54%. These organo‐soluble polyhydrazides and poly(1,3,4‐oxadiazole)s exhibited UV–Vis absorption maximum at 262–296 and 264–342 nm in NMP solution, and their photoluminescence spectra showed maximum bands around 414–445 and 404–453 nm, respectively, with quantum yield up to 38%. The electron‐transporting properties were examined by electrochemical methods. Cyclic voltammograms of the poly(1,3,4‐oxadiazole) films cast onto an indium‐tin oxide (ITO)‐coated glass substrate exhibited reversible reduction redox with Eonset at ?1.37 to ?1.57 V versus Ag/AgCl in dry N,N‐dimethylformamide solution. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6466–6483, 2006 相似文献
102.
Sheng‐Hsiung Yang Hsing‐Chuan Li Chien‐Kai Chen Chain‐Shu Hsu 《Journal of polymer science. Part A, Polymer chemistry》2006,44(23):6738-6749
Two series of poly(2,3‐diphenyl‐1,4‐phenylenevinylene) (DP‐PPV) derivatives containing multiple bulky substituents were synthesized. In the first series, two different groups were incorporated on C‐5,6 positions of the phenylene moiety to increase steric hindrance and to obtain blue‐shifted emissions. In the second series, bulky fluorenyl groups with two hexyl chains on the C‐9 position were introduced on two phenyl pendants to increase the solubility as well as steric hindrance to prevent close packing of the main chain. Polymers with high molecular weights and fine‐tuned electro‐optical properties were obtained by controlling the feed ratio of different monomers during polymerization. The maximum photoluminescent emissions of the thin films are located between 384 and 541 nm. Cyclic voltammetric analysis reveals that the band gaps of these light‐emitting materials are in the range from 2.4 to 3.3 eV. A double‐layer EL device with the configuration of ITO/PEDOT/P4/Ca/Al emitted pure green light with CIE′1931 at (0.24, 0.5). Using copolymer P6 as the emissive layer, the maximum luminescence and current efficiency were both improved when compared with the homopolymer P4. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6738–6749, 2006 相似文献
103.
Two novel dithienylethenes with ferrocene units were synthesized by Wittig reaction. The structure of 2a has been established by X‐ray diffraction studies. They could reversibly interconvert between two thermally stable forms, an open and a closed one, using light of different wavelengths as triggers. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
104.
Sheng Xu Zuo-Feng Feng Ji-Ling Huang 《Journal of molecular catalysis. A, Chemical》2006,250(1-2):35-39
Five new double silylene-bridged binuclear titanium complexes were synthesized by the reaction of RCpTiCl3 and Li2[μ,μ-(SiMe2)2 (C5H3)2] in toluene. They were all well characterized. These complexes activated with methylaluminoxane (MAO) are highly active catalysts (2.33 × 105 g PE/mol Cat h) for the polymerization of ethylene even at low Al/Ti (Al/Ti = 300). The molecular weight distribution of the polymer indicates broad or bimodal (MWD = 26.76) distribution. 相似文献
105.
我们定义了(H,λ)求和法,它含有(N,pn),(R^rn)和(Vmn)求和法。讨论了函数f(x)∈C^r[-1,1](r∈N0)以及f(x)∈W^rH^a(r∈N0,0<a<1)的切比晓夫-富里埃级数的逼近阶。 相似文献
106.
卡尔曼滤波法用于ICP-AES分析时,在白色噪音情况下能给出准确的分析结果,当试样的某些组分未知时,测量噪音将不是白色的,分析结果将不准确。本文提出了一种加权增量卡尔曼滤波法来解决这个问题。 相似文献
107.
激光二极管泵浦的高重复频率Nd:YAG激光器 总被引:2,自引:1,他引:1
报道两个1.5W连续激光二极管端面泵浦的声光调QNd:YAG激光器,输出激光脉冲的最高重复频率为30kHz重复频率1kHz时,最窄脉宽为12ns,最高峰值功率为12.1kW。 相似文献
108.
报道了采用真空蒸镀的方法制备的MnBiDy(Sm)永磁膜的结构和磁性.Mn:Bi:Dy(Sm)的投料比为2:1:0.10.薄膜经过退出处理(350—425℃,保温4h)后,具有NiAs型hcp结构,C轴垂直膜面,剩余磁感应强度B=3.4-6.5kG,内禀矫顽力_MH_c≈3-8kOe,最大磁能积(BH)_(max)=13.39MG·Oe.实验发现,薄膜厚度对MnBiDy(Sm)永磁膜的结构和磁性具有很大的影响.
关键词: 相似文献
109.
We give a Euclidean wormhole solution in the vacuum Bergmann-Wagoner scalar-tensor gravitational theory. We show that this wormhole, unlike others, has complex charge and is a baby universe (half a wormhole). 相似文献
110.
实验研究表明,SnO2薄膜经过退火处理后其光致发光谱有明显的变化。在氧和氮两种不同气氛中进行热处理,其变化也有差异。这种变化主要是由于SnO2膜中氧空位和自由载流于浓度变化所致。 相似文献