全文获取类型
收费全文 | 3146篇 |
免费 | 555篇 |
国内免费 | 358篇 |
专业分类
化学 | 2276篇 |
晶体学 | 33篇 |
力学 | 245篇 |
综合类 | 12篇 |
数学 | 333篇 |
物理学 | 1160篇 |
出版年
2024年 | 8篇 |
2023年 | 73篇 |
2022年 | 100篇 |
2021年 | 125篇 |
2020年 | 150篇 |
2019年 | 140篇 |
2018年 | 127篇 |
2017年 | 122篇 |
2016年 | 177篇 |
2015年 | 154篇 |
2014年 | 174篇 |
2013年 | 215篇 |
2012年 | 321篇 |
2011年 | 338篇 |
2010年 | 217篇 |
2009年 | 167篇 |
2008年 | 177篇 |
2007年 | 191篇 |
2006年 | 171篇 |
2005年 | 120篇 |
2004年 | 105篇 |
2003年 | 99篇 |
2002年 | 66篇 |
2001年 | 47篇 |
2000年 | 52篇 |
1999年 | 49篇 |
1998年 | 47篇 |
1997年 | 54篇 |
1996年 | 48篇 |
1995年 | 29篇 |
1994年 | 26篇 |
1993年 | 32篇 |
1992年 | 27篇 |
1991年 | 22篇 |
1990年 | 18篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1987年 | 5篇 |
1986年 | 16篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1973年 | 1篇 |
1970年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有4059条查询结果,搜索用时 31 毫秒
971.
The binding specificity of silver cations to abasic (AP) site-containing DNA was electrochemically investigated by comparison with the fully matched DNA without the AP site. AP site-containing DNA is designed in a way that only the nucleotide opposite the AP site is variable to allow for coexistence of an unpaired nucleotide and a number of DNA base pairs. The surface of a gold electrode was modified by AP site-containing DNA duplex on which Ag+ binding specificity was evaluated. Electrochemical investigations on the AP-DNA-modified electrodes reveal that Ag+ preferentially associates to the unpaired nucleotides instead of the coexisted base pairs and shows sequence-dependant binding, especially stronger for purines than for pyrimidines. Additionally, the hydrogen bond pattern moieties of the unpaired nucleotides should be involved in Ag+ binding evidenced by a decrease of the redox signal when introducing a ligand with its hydrogen bond moiety complementary to the nucleotide deoxycytidine. This is the first attempt to make a comparison in one DNA molecule for metal ion binding to coexisted unpaired nucleotide and DNA base pairs. The present method demonstrates an easy way for investigating binding specificity of heavy metal ions to AP site in the presence of coexisted DNA base pairs. 相似文献
972.
973.
974.
In this paper, we consider a discrete Lotka–Volterra competitive system with feedback control. Assuming that the coefficients in the system are almost periodic sequences, we obtain the existence and uniqueness of the almost periodic solution which is uniformly asymptotically stable. 相似文献
975.
Haibo Gu Haijun Jiang Zhidong Teng 《Journal of Applied Mathematics and Computing》2009,30(1-2):151-170
In this paper, we consider a class of stochastic impulsive high-order neural networks with time-varying delays. By using Lyapunov functional method, LMI method and mathematics induction, some sufficient conditions are derived for the globally exponential stability of the equilibrium point of the neural networks in mean square. It is believed that these results are significant and useful for the design and applications of impulsive stochastic high-order neural networks. 相似文献
976.
Huang K Zhang Y Long Y Yuan J Han D Wang Z Niu L Chen Z 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(20):5314-5319
One-dimensional gold/polyaniline (Au/PANI-CSA) coaxial nanocables with an average diameter of 50-60 nm and lengths of more than 1 mum were successfully synthesized by reacting aniline monomer with chlorauric acid (HAuCl(4)) through a self-assembly process in the presence of D-camphor-10-sulfonic acid (CSA), which acts as both a dopant and surfactant. It was found that the formation probability and the size of the Au/PANI-CSA nanocables depends on the molar ratio of aniline to HAuCl(4) and the concentration of CSA, respectively. A synergistic growth mechanism was proposed to interpret the formation of the Au/PANI-CSA nanocables. The directly measured conductivity of a single gold/polyaniline nanocable was found to be high (approximately 77.2 S cm(-1)). Hollow PANI-CSA nanotubes, with an average diameter of 50-60 nm, were also obtained successfully by dissolving the Au nanowire core of the Au/PANI-CSA nanocables. 相似文献
977.
Surface-enhanced Raman scattering (SERS) spectra of single-walled carbon nanotubes (SWCNTs) on metal-coated filter paper are reported for the first time. Experimental results show that the metal-coated filter paper is very effective and active. The SERS spectrum not only shows that all Raman bands of SWCNTs in normal Raman scattering have been generally enhanced, but also shows many new bands, which characterize the structure of SWCNTs and the interaction between SWCNTs and silver/gold nanoparticles, arising from symmetry lowering and selection rule relaxing of SWCNTs induced by the silver/gold surface. In our case, it is difficult to separate the contributions of the electromagnetic and chemical mechanisms to the great enhancement of the Raman signal. The analysis shows that the SERS spectra of SWCNTs on the metal-coated filter paper provide convenience for probing the sample molecules with fine structures related to defects of SWCNTs, the diameter of SWCNTs, and the SERS mechanism of SWCNTs deposited on metal-coated filter paper. Moreover, this can be used as a probe technique for monitoring the synthesis quality of SWCNTs with significant higher sensitivity than other methods, which has promise of being a new technique for monitoring synthesis quality of SWCNTs. 相似文献
978.
979.
We report the experimental verification of the predicted chaotic mixing characteristics for a polydimethylsioxane microfluidic chip, based on the mechanism of multistage cross-channel flows. While chaotic mixing can be achieved within short passage distances, there is an optimal side channel flow pulsation frequency beyond which the mixing becomes ineffective. Based on the physical understanding of a Poincaré section analysis, we propose the installation of passive flow baffles in the main microfluidic channel to facilitate high-frequency mixing. The combined hybrid approach enables chaotic mixing at enhanced frequency and reduced passage distance in two-dimensional flows. 相似文献
980.
Harry Joe Haijun Li Aristidis K. Nikoloulopoulos 《Journal of multivariate analysis》2010,101(1):159-270
Tail dependence and conditional tail dependence functions describe, respectively, the tail probabilities and conditional tail probabilities of a copula at various relative scales. The properties as well as the interplay of these two functions are established based upon their homogeneous structures. The extremal dependence of a copula, as described by its extreme value copulas, is shown to be completely determined by its tail dependence functions. For a vine copula built from a set of bivariate copulas, its tail dependence function can be expressed recursively by the tail dependence and conditional tail dependence functions of lower-dimensional margins. The effect of tail dependence of bivariate linking copulas on that of a vine copula is also investigated. 相似文献