全文获取类型
收费全文 | 8115篇 |
免费 | 1515篇 |
国内免费 | 2032篇 |
专业分类
化学 | 6027篇 |
晶体学 | 207篇 |
力学 | 520篇 |
综合类 | 347篇 |
数学 | 994篇 |
物理学 | 3567篇 |
出版年
2024年 | 22篇 |
2023年 | 89篇 |
2022年 | 278篇 |
2021年 | 289篇 |
2020年 | 315篇 |
2019年 | 338篇 |
2018年 | 267篇 |
2017年 | 334篇 |
2016年 | 328篇 |
2015年 | 396篇 |
2014年 | 509篇 |
2013年 | 625篇 |
2012年 | 659篇 |
2011年 | 689篇 |
2010年 | 587篇 |
2009年 | 628篇 |
2008年 | 684篇 |
2007年 | 624篇 |
2006年 | 578篇 |
2005年 | 526篇 |
2004年 | 430篇 |
2003年 | 304篇 |
2002年 | 368篇 |
2001年 | 338篇 |
2000年 | 278篇 |
1999年 | 255篇 |
1998年 | 141篇 |
1997年 | 126篇 |
1996年 | 113篇 |
1995年 | 79篇 |
1994年 | 80篇 |
1993年 | 74篇 |
1992年 | 51篇 |
1991年 | 43篇 |
1990年 | 36篇 |
1989年 | 28篇 |
1988年 | 25篇 |
1987年 | 28篇 |
1986年 | 12篇 |
1985年 | 18篇 |
1984年 | 14篇 |
1983年 | 12篇 |
1982年 | 10篇 |
1981年 | 5篇 |
1980年 | 13篇 |
1979年 | 10篇 |
1975年 | 1篇 |
1964年 | 1篇 |
1959年 | 2篇 |
1909年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
Fourier transform infrared-attenuated total reflection (FTIR-ATR) spectra have been recorded of 11-layer Langmuir-Blodgett (LB) films of stearic acid deposited at various surface pressures (0.1, 15, and 35 mN/m), and the molecular orientation angles were evaluated quantitatively, which supplied insight into the molecular order with the alkyl chains tightly packed like crystal in the LB films deposited at the zero and higher surface pressures. These experimental results indicate that, in the Langmuir film as the precursor of LB films, stearic acid molecules self-aggregate to form two-dimensional crystalline domains already even at the zero surface pressure, which results in the inhomogeneity of monolayer. The analysis of dependence of nu(C=O) intensity on the surface pressure, surface density, and subphase temperature leads to the conclusion that the defects in LB films originate from the Langmuir film and be conserved upon deposition. Annealing below 50 degrees C and cooling could improve the monolayer homogeneity, and thus a defect-free or low-defect LB films can be deposited. Furthermore, ion exchange conducted in the LB films, on the other hand, confirms the existence of structure defects in LB films of stearic acid. The polar plane microstructure, lateral transport along the polar planes and the coordination types of stearic acid/cation system may be the rate-limiting process. The results have implication on the possible uses of stearic acid LB films as ion-exchange materials or sensors. Copyright 2001 Academic Press. 相似文献
32.
Determination of Gossypol in Trace Level by Flow Injection Analysis with Chemiluminescence Detection
Bing Chun XUE Er Bao LIU College of Chemistry Life Sciences Tianjin Normal University Tianjin 《中国化学快报》2006,17(1):57-60
Gossypol, [1, 1′, 6, 6′, 7,7′-hexahydroxyl-5,5′-diisopropyl-3,3′-dimethyl-(2,2′-binaphtha- lene)-8,8′-dicarboxaldehyde] is a polyphenolic yellow compound naturally occurring in various parts of cotton plants1. The compound has been associated with 相似文献
33.
34.
The adsorptive and electrochemical behaviors of medecamycin were investigated on a glassy carbon electrode (GCE) pretreated by anodic oxidation at +1.8 V for 5 min in 0.025 mol l–1 NH3-NH4Cl (pH 8.6) solution. An adsorptive stripping voltammetric method for the determination of medecamycin at the pretreated glassy carbon electrode has been developed. Medecamycin was accumulated in NH3-NH4Cl buffer (pH 9.0) at a potential of –0.7 V (vs. saturated calomel electrode (SCE)) for a certain time, and then determined by second-order differential anodic stripping voltammetry. The second-order differential anodic stripping peak current at +0.72 V was proportional to the concentration of medecamycin in the range 2.0 g ml–1 to 50.0 g ml–1. The detection limit (three times the signal-to-noise) was 1.0 g ml–1 and the relative standard deviation of the results was 3.28% for eight successive determinations of 10.0 g ml–1 medecamycin. This method has been applied to the direct determination of medecamycin in commercial tablets and spiked urine samples with satisfactory results. 相似文献
35.
36.
摘要运用多参考微扰理论(Multireference MΦller-Plesset theory)计算了SSCH3垂直激发能及其S-C与S-S两种断键方式的绝热(Adiabatic)与非绝热(Diabatic)的基态和激发态势能曲线, 研究了在193nm激光作用下SSCH3的光解离过程, 理论计算值与实验值相符. 相似文献
37.
Most magnetorheological materials, composed of magnetic microparticles in a liquid, require significant amounts of magnetic particles and a large magnetic field to achieve the desired effects. Here, we report on a new type of magnetorheological materials consisting of small amounts of magnetic nanoparticles (0.8 wt %) but exhibiting large rheological change (i.e., a gel-sol transition) upon the application of a small magnetic field. We use self-assembly to create hybrid nanofibers, which consist of supramolecular hydrogelators and magnetic nanoparticles, as the matrices of the hydrogel. Localized in the nanofibers at a distance of 1-2 nm, the magnetic nanoparticles occupy a small volume fraction of the hydrogel, significantly enhancing the magnetic dipole interactions between them, which results in the large magnetoresponse. This strategy generates a hierarchical nanostructure and eliminates several drawbacks of the simple mixture of polymers with nanoparticles, and thus provides a new methodology that uses magnetic force to control the nanostructures and properties of soft materials. 相似文献
38.
The kinetics of complexation reaction of Cu(II) with 9-ethyl-3-carbazolecarboxaldehyde-thiosemicarbazone (ECCAT) has been
examined spectrophotometrically. The ligand was synthesized for the first time. The complexation reaction was carried out
in a DMF-water medium at 35°C. The complex has maximum absorbance at 393 nm. Kinetic and activation parameters of the complexation
reaction were calculated by the Arrhenius and Eyring equations using the data obtained from investigating the effect of temperature
on reaction rates under the specified conditions. We also proposed reaction rate equations. Based on the studied complexation
reaction, a simple kinetic method for the spectrophotometric determination of copper(II) has been developed. The calibration
graphs are linear in the concentration range 0.2–1.9 μg/mL. The species that caused interference were investigated.
The text was submitted by the authors in English. 相似文献
39.
Summary Three novel heterotrinuclear complexes have been prepared, [Cu2(oxdn)2Zn](ClO4)2 (1) and [Cu2(oxdn)2-M(H2O)2](ClO4)2 with M=Mn (2) and Co (3) [oxdn-oxamidobis (propionato)], and characterized by spectral data. The temperature dependence of the magnetic susceptibilities of (2) and (3) has been studied in the 4–300K range, and the exchange integrals J=–20.90cm–1 for (2) and J=–62.36cm–1 for (3) calculated. These results are commensurate with antiferromagnetic interactions between the adjacent metal ions. 相似文献
40.
BODIPY dyes are privileged fluorophores that are now widely used in highly diverse research fields. An overview of BODIPY dyes and a summarization of the different synthetic methodologies reported for direct C-H functionalization of the BODIPY framework have been provided. 相似文献