全文获取类型
收费全文 | 13214篇 |
免费 | 2212篇 |
国内免费 | 1415篇 |
专业分类
化学 | 9092篇 |
晶体学 | 122篇 |
力学 | 884篇 |
综合类 | 88篇 |
数学 | 1613篇 |
物理学 | 5042篇 |
出版年
2024年 | 45篇 |
2023年 | 280篇 |
2022年 | 474篇 |
2021年 | 518篇 |
2020年 | 532篇 |
2019年 | 474篇 |
2018年 | 461篇 |
2017年 | 400篇 |
2016年 | 575篇 |
2015年 | 636篇 |
2014年 | 734篇 |
2013年 | 979篇 |
2012年 | 1123篇 |
2011年 | 1148篇 |
2010年 | 796篇 |
2009年 | 735篇 |
2008年 | 818篇 |
2007年 | 764篇 |
2006年 | 684篇 |
2005年 | 563篇 |
2004年 | 415篇 |
2003年 | 348篇 |
2002年 | 320篇 |
2001年 | 280篇 |
2000年 | 235篇 |
1999年 | 278篇 |
1998年 | 262篇 |
1997年 | 192篇 |
1996年 | 214篇 |
1995年 | 213篇 |
1994年 | 183篇 |
1993年 | 160篇 |
1992年 | 129篇 |
1991年 | 142篇 |
1990年 | 143篇 |
1989年 | 108篇 |
1988年 | 92篇 |
1987年 | 78篇 |
1986年 | 59篇 |
1985年 | 62篇 |
1984年 | 28篇 |
1983年 | 33篇 |
1982年 | 26篇 |
1981年 | 20篇 |
1980年 | 13篇 |
1979年 | 10篇 |
1978年 | 8篇 |
1977年 | 10篇 |
1974年 | 6篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Tang K Green MM Cheon KS Selinger JV Garetz BA 《Journal of the American Chemical Society》2003,125(24):7313-7323
Helical polymers appended with paired structurally different enantiomers, which have opposing helical sense preferences, yield a new kind of relationship between optical activity and temperature, and also reveal unusual details of the nature of chiral interactions. Consistent with a statistical physical theory developed for these experiments, the proportion of the competing chiral groups, determined by synthesis, fixes the compensation temperature at which the helical senses are equally populated. The lyotropic liquid crystal state formed by these polymers yields therefore a nematic state at any chosen temperature over a very wide range, with a cholesteric state arising with tightening pitch as temperature deviates from this point. Far from the nematic temperature, the pitch reaches the nanometer scale and therefore the reflection of visible light. Before crossing zero at the nematic temperature, the optical activity becomes so large that it may be observed with the unaided eye through crossed polarizers. 相似文献
92.
本文报导的方法是在南京大学高鸿教授研究的K_3Fe(CN)_6示波极谱滴定法(在PH8的K_2HPO_4—KH_2PO_4—KBr底液中,用0.04660mol/LK_3Fe(CN)_6标准溶液对纯抗坏血酸测定)的基础上,考虑到L—抗坏血酸(以下简称V_e)在碱性、中性介质中稳定性差,如用于V_e含量很微的果蔬测定,对结果影响大。本文改为H_2C_2O_4—KBr的酸性介质作底液,用 相似文献
93.
The fluorimetric determination of mercury ions with o-vanillin-8-aminoquinoline (OVAQ) in aqueous solutions was investigated. Hg(II) could react with the fluorescent reagent OVAQ
(λex/em = 278/314 nm) to form a nonfluorescent complex in an ethanol-water medium of pH 6.00. The linear range of the proposed method
was from 2.5 to 80 μg/L, and the detection limit was 0.80 μg/L. The interferences of 24 foreign ions were also studied. The
method was successfully applied to the determination of Hg(II) in sludge.
The text was submitted by the authors in English. 相似文献
94.
Tang Y 《The Journal of chemical physics》2004,121(21):10605-10610
The first-order mean-spherical approximation (FMSA) [Y. Tang, J. Chem. Phys., 118, 4140 (2003)] is extended to the studies of inhomogeneous fluids by combining with Rosenfeld's perturbative method [Y. Rosenfeld, J. Chem. Phys. 98, 8126 (1993)]. In the extension, the key input-direct correlation function of FMSA-is applied to constructing the free energy density functional. Preserving its high fidelity at the bulk limit, the FMSA shows satisfactory performance for Yukawa fluids near hard and attractive walls. The results are better than or comparable to several other theories reported before for the geometry. The FMSA is found, in particular, more satisfactory than the traditional mean-field theory for predicting density profiles around hard walls. The FMSA is also compared with the full MSA for inhomogeneous fluids, showing no appreciable differences. The inhomogeneous FMSA goes successfully through the self-consistency test for reproducing the radial distribution function of the bulk Yukawa fluid. As far as the computation is concerned, the FMSA can be executed much faster than any nonmean-field theories, and the speed is virtually identical to that of the mean-field theory. 相似文献
95.
Zhuxing Tang Yun Zhou Yikun Zeng Shuliang Zang Pingang He Yuzhi Fang 《Chromatographia》2006,63(11-12):617-622
A method based on capillary electrophoresis with electrochemical detection has been developed for the separation and determination of epicatechin, isovanillic acid, vanillic acid and myricetin in Dioscorea bulbifera L. and its medicinal preparations. The effects of working electrode potential, pH and concentration of running buffer, separation voltage and injection time were investigated. Under optimum conditions, the analytes could be separated in a 40 mmol L?1 borate buffer (pH 8.7) within 15 min. A 300 μm diameter carbon disk electrode has a good response at + 0.95 V (vs. SCE) for all analytes. The response was linear over three orders of magnitude with detection limits (S/N = 3) ranging from 3.0 × 10?8 g mL?1 to 1.0 × 10?7 g mL?1. The method has been successfully applied to the analysis of real samples. 相似文献
96.
Three-dimensional time-dependent quantum wave packet calculation for the O((1)D)+HBr reaction has been carried out using an accurate ab initio global potential energy surface [K. A. Peterson, J. Chem. Phys. 113, 4598 (2000)]. The calculations show that the initial state-selected reaction probabilities are dominated by resonance structures, and the lifetime of the resonance is generally in the subpicosecond time scale. The energy dependence of the reaction cross section is computed, which manifests still resonance structures, and is a decreasing function of the translational energy. The thermal rate constants are also computed, which are nearly independent on the temperature. The calculation results are discussed and compared to similar reaction with deep well. 相似文献
97.
Ning Zhang Qing-Cheng Kong Zhen-Zhen Chen Ke-Hua Xu Bo Tang 《Mikrochimica acta》2007,158(1-2):165-171
A sensitive catalytic kinetic spectrofluorimetric approach for determining ng mL−1 levels of rhodium is presented, and the possible mechanism of the catalytic reaction was investigated. The determination
is based on the catalytic property of rhodium to enhance the reaction of o-vanillin salicylhydrazone (OVSH) with potassium
bromate in a water-ethanol medium at pH 4.80 and 45 °C. The presence of β-cyclodextrin (β-CD) obviously sensitized the assay
due to its high inclusion ability towards OVSH. Under optimized experimental conditions, fluorescence measurements of the
β-CD-rhodium-KBrO3-OVSH catalytic kinetic reaction system were carried out in its fluorescent band centered at λex = 333 nm and λem = 476 nm, respectively. The calibration graph was linear over the concentration range of 0.47–100 ng mL−1 with a detection limit of 0.14 ng mL−1. The effect of interferences was discussed, and the results show that the extraction method can be used to separate rhodium
from interference species such as iridium. The proposed method, applied to several synthetic mixtures containing rhodium mixed
with varying amounts of metal salts, produced satisfactory results. 相似文献
98.
99.
高效液相色谱法测定糙米粉中的维生素 总被引:7,自引:1,他引:7
高效液相色谱法测定糙米粉中的维生素吴红京,唐根源,王勇(中国科学院福建物质结构研究所福州350002)(福建药品检验所福州350001)1前言众所周知,糙米粉有很高的营养价值,含有人体必需的多种维生素。用高效液相色谱法(HPLC)和薄层色谱法(TLC... 相似文献
100.
With the advent of the big data era, information storage and security are becoming increasingly important. However, high capacity information storage and multilevel anti-counterfeiting are typically difficult to achieve simultaneously. To address this challenge, herein, two electrochromic and electrofluorochromic dual-functional polymers with aggregation-induced emission (AIE) characteristics were rationally designed and facilely prepared. Upon applying voltages, the absorption and fluorescence spectra of the AIE polymers can undergo reversible changes, accompanied by variation of their color and emission. By utilizing the controllable characteristics of the polymers, dual-mode display devices were fabricated via a simple spraying technique. More interestingly, a four-dimensional color code device was constructed by adding color change multiplexing to the two-dimensional space, thereby achieving high capacity information storage. Moreover, the color code device can also be applied in the multilevel anti-counterfeiting area. The encrypted information can be dynamically converted under different voltages. Thus, the AIE polymers show great promise for applications in multidimensional information storage and dynamic anti-counterfeiting, and the design strategy may provide a new avenue for advanced information storage and high security technology.By using electrical stimuli-responsive AIE polymers, dual-mode display devices, multidimensional information storage and anti-counterfeiting devices were constructed. 相似文献