全文获取类型
收费全文 | 1488篇 |
免费 | 214篇 |
国内免费 | 287篇 |
专业分类
化学 | 1200篇 |
晶体学 | 9篇 |
力学 | 98篇 |
综合类 | 21篇 |
数学 | 281篇 |
物理学 | 380篇 |
出版年
2024年 | 1篇 |
2023年 | 11篇 |
2022年 | 23篇 |
2021年 | 41篇 |
2020年 | 38篇 |
2019年 | 37篇 |
2018年 | 48篇 |
2017年 | 27篇 |
2016年 | 64篇 |
2015年 | 51篇 |
2014年 | 87篇 |
2013年 | 108篇 |
2012年 | 115篇 |
2011年 | 103篇 |
2010年 | 98篇 |
2009年 | 85篇 |
2008年 | 100篇 |
2007年 | 80篇 |
2006年 | 83篇 |
2005年 | 99篇 |
2004年 | 95篇 |
2003年 | 86篇 |
2002年 | 113篇 |
2001年 | 117篇 |
2000年 | 48篇 |
1999年 | 37篇 |
1998年 | 38篇 |
1997年 | 17篇 |
1996年 | 24篇 |
1995年 | 11篇 |
1994年 | 12篇 |
1993年 | 8篇 |
1992年 | 16篇 |
1991年 | 10篇 |
1990年 | 16篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 9篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有1989条查询结果,搜索用时 15 毫秒
991.
n the past decades, photoconductive polymers have received much attention either from atlindamental standpoint or for their potential uses ]' 2. The photoconductivities of manypolymers have been reported, such as phenylmethylpolysilane, poly(pphenylenevinylene ), N-poly(vinylcarbazole ), and so on.Recently we have synthesized a novel polyphosphazene that contains chargetransporting agent for photoconductive application. Polyphosphazene was selectedbecause of its photochemical stability, the go… 相似文献
992.
993.
一类二次特征值反问题的中心对称解及其最佳逼近 总被引:1,自引:0,他引:1
1引言给定n阶实矩阵M,C和K,二次特征值问题:求数λ和非零向量x使得Q(λ)x=0, (1.1)其中Q(λ)=λ2M λC K称为二次束.数λ和相应的非零向量x分别称为二次束Q(λ)的特征值和特征向量.Tisseur和Meerbergen概述了二次特征值问题的各种应用、数学理论和数值方法.在工程技术,特别是结构动力模型修正技术领域经常遇到与二次特征值问题相反的问题(称之为二次特征值反问题).对阻尼结构进行动力分析时,应用有限元方法可得到系统的质量矩阵M,阻尼矩阵C和刚度矩阵K,从而可求得二次特征值问题的特征值(频率)和特征向量(振型).但是有限元模型毕竟是实际结构系统的离散化,并且 相似文献
994.
Organicthinfilmelectr0luminescentdisplay(OTFELD)hasgoneintothestageofpracticalstudy'sincePioneerC0.reportedthefirstc0mmercialproductoforganicgreenELdispla}'usingSma1lm0lecules1.AsOTFELDhasmanyadvantagessuchasactiveemission-highbrightness.l0wdrivingv0ltage,wideviewingangle,Iightweight,andpotentiall0wcost,itisat-tractingmuchattenti0nasacandidatef0rnewflatpaneldisplay.However.therearemanysubjectst0realizethefullcol0rdisplays.The0rganicredandbIueELdisplaysarethebasicessentialt0reaIizefull… 相似文献
995.
We derive the influence function and the effective dynamics of a quantum systems coupled to a chaotic environment, using very
general parametric and banded random matrices to describe the quantum properties of a chaotic bath. We find that only in certain
limits the thermalization can result from the environment. We study the general transport problems including escape, fusion
and tunneling (fission).
Presented by D. Kusnezov at the International Conference on “Atomic Nuclei and Metallic Clusters”, Prague, September 1–5,
1997. 相似文献
996.
997.
We consider those subsets of the self‐affine Sierpinski carpets that are the union of an uncountable number of sets each of which consists of the points with their location codes having prescribed group frequencies. It is proved that their Hausdorff dimensions equal to the supremum of the Hausdorff dimensions of the sets in the union. The main advantage is that we treat these subsets in a unified manner and the value of the Hausdorff dimensions do not need to be guessed a priori. 相似文献
998.
Prenylated Indole Alkaloid Derivatives from Marine Sediment‐Derived Fungus Penicillium paneum SD‐44 下载免费PDF全文
Three new prenylated indole alkaloids, including two β‐carbolines, penipalines A and B ( 1 and 2 , resp.), and one indole carbaldehyde derivative, penipaline C ( 3 ), as well as two known indole derived analogs, 4 and 5 , were isolated from the deep‐sea‐sediment derived fungus Penicillium paneum SD‐44 cultured in a 500‐l bioreactor. The structures of the new compounds were determined on the basis of 1D‐ and 2D‐NMR spectroscopy, as well as by high‐resolution mass spectrometry. The new compounds 2 and 3 showed potent cytotoxic activities against A‐549 and HCT‐116 cell lines. 相似文献
999.
A Pd-catalyzed decarboxylative coupling of substituted benzoic acids with phenylboronic acid has been developed. Under the optimized conditions, a variety of substituted benzoic acids were found to undergo decarboxylative coupling with various phenylboronic acids to give the desired unsymmetrical biaryls in good yields.
[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.] 相似文献
1000.
Excellent Capacitive Performance of a Three‐Dimensional Hierarchical Porous Graphene/Carbon Composite with a Superhigh Surface Area 下载免费PDF全文
Xue Jin Li Prof. Wei Xing Prof. Jin Zhou Prof. Gui Qiang Wang Prof. Shu Ping Zhuo Prof. Zi Feng Yan Prof. Qing Zhong Xue Prof. Shi Zhang Qiao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(41):13314-13320
Three‐dimensional hierarchical porous graphene/carbon composite was successfully synthesized from a solution of graphene oxide and a phenolic resin by using a facile and efficient method. The morphology, structure, and surface property of the composite were investigated intensively by a variety of means such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption, Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR). It is found that graphene serves as a scaffold to form a hierarchical pore texture in the composite, resulting in its superhigh surface area of 2034 m2g?1, thin macropore wall, and high conductivity (152 S m?1). As evidenced by electrochemical measurements in both EMImBF4 ionic liquid and KOH electrolyte, the composite exhibits ideal capacitive behavior, high capacitance, and excellent rate performance due to its unique structure. In EMImBF4, the composite has a high energy density of up to 50.1 Wh kg?1 and also possesses quite stable cycling stability at 100 °C, suggesting its promising application in high‐temperature supercapacitors. In KOH electrolyte, the specific capacitance of this composite can reach up to an unprecedented value of 186.5 F g?1, even at a very high current density of 50 A g?1, suggesting its prosperous application in high‐power applications. 相似文献