全文获取类型
收费全文 | 12253篇 |
免费 | 1693篇 |
国内免费 | 1400篇 |
专业分类
化学 | 8234篇 |
晶体学 | 149篇 |
力学 | 872篇 |
综合类 | 95篇 |
数学 | 1446篇 |
物理学 | 4550篇 |
出版年
2024年 | 35篇 |
2023年 | 174篇 |
2022年 | 297篇 |
2021年 | 338篇 |
2020年 | 394篇 |
2019年 | 356篇 |
2018年 | 320篇 |
2017年 | 305篇 |
2016年 | 469篇 |
2015年 | 460篇 |
2014年 | 587篇 |
2013年 | 819篇 |
2012年 | 905篇 |
2011年 | 967篇 |
2010年 | 657篇 |
2009年 | 714篇 |
2008年 | 754篇 |
2007年 | 728篇 |
2006年 | 683篇 |
2005年 | 630篇 |
2004年 | 494篇 |
2003年 | 393篇 |
2002年 | 351篇 |
2001年 | 330篇 |
2000年 | 288篇 |
1999年 | 317篇 |
1998年 | 330篇 |
1997年 | 267篇 |
1996年 | 267篇 |
1995年 | 225篇 |
1994年 | 248篇 |
1993年 | 163篇 |
1992年 | 151篇 |
1991年 | 131篇 |
1990年 | 139篇 |
1989年 | 84篇 |
1988年 | 81篇 |
1987年 | 88篇 |
1986年 | 82篇 |
1985年 | 71篇 |
1984年 | 48篇 |
1983年 | 33篇 |
1982年 | 35篇 |
1981年 | 27篇 |
1980年 | 20篇 |
1979年 | 16篇 |
1978年 | 14篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
有机硅耐磨透明涂层的固化分析 总被引:13,自引:0,他引:13
FTIR、TG、TBA等对有机硅耐磨涂料(有机硅溶胶)的热固化过程研究表明有机硅胶体中缔合羟基间的脱水缩合速率很高;羟基脱水程度与固化温度有关,温度越高,达平衡时羟基的浓度越低,在105~130℃间羟基的浓度变化最大,加入适当的固化剂,对羟基的脱水交联有促进作用,在较高的固化温度下,反应体系中出现了环氧环异构化产生的酮羰基的吸收峰 相似文献
72.
Modified modeling of the effect of pH and viscosity on the mass transfer in hydrophobic hollow fiber membrane contactors 总被引:3,自引:0,他引:3
This paper studied the effect of pH and the viscosity of feed solution on the mass transfer in two different specifications of hydrophobic hollow fiber membrane contactors. Experimental results showed that the pH of the feed had a significant effect on the rate of mass transfer, the flux and the removal efficiency of easily ionized volatile compounds (VCs), such as ammonia. In unbuffered feed solutions, both the resistance of membrane and the resistance of feed side were affected by the pH of feed and both of them had contributions to the overall mass transfer. A model, , was proposed to predict the effect of pH and gave good agreement with the experimental data for the two contactors. The relationship between viscosities and the mass transfer coefficient could be described by . Based on our experiments, the change of the viscosities in the concentration range of ammonia from 50 to 10,000 mg l−1 caused about 3–4% variation of the mass transfer coefficients. Moreover, it may be more suitable to use the equilibrium concentrations of volatile species instead of the total concentrations of VCs to estimate mass transfer coefficients, removal efficiency and flux. Experimental results also revealed that the choice of the pH of feed might be one of the most crucial factors for removing easily ionized VCs, such as ammonia, from water and wastewater. 相似文献
73.
Huang F Hou L Wu H Wang X Shen H Cao W Yang W Cao Y 《Journal of the American Chemical Society》2004,126(31):9845-9853
A series of aminoalkyl-substituted polyfluorene copolymers with benzothiadiazole (BTDZ) of different content were synthesized by Suzuki coupling reaction, and their quaternized ammonium polyelectrolyte derivatives were obtained through a postpolymerization treatment on the terminal amino groups. Copolymers are soluble in environmentally friendlier solvents, such as alcohols. It was found that the efficient energy transfer occurs by exciton trapping on the narrow band gap BTDZ site under UV illumination. Only 1% of BTDZ content is needed to completely quench a fluorene emission for both the neutral and the quaternized copolymers in the neat film. Absolute PL efficiencies of copolymer films were greatly enhanced as a result of the suppression of excimer formation. Light-emitting devices fabricated from these copolymers show high external quantum efficiencies over 3% and 1% for the neutral precursor and the quaternized copolymers, respectively, with high work function metals such as Al as a cathode. To the best of our knowledge, this is the first report on an electroluminescent polymer which bears the high EL efficiency, the electron-injection ability from high work function metals, and the solubility in environment-friendly solvents at the same time. These features make them a promising candidate for the next generation of light-emitting copolymers in PLED flat panel display application. 相似文献
74.
Ning Li Chunhui Deng Ning Yao Xizhong Shen Xiangmin Zhang 《Analytica chimica acta》2005,540(2):317-323
In the study, we developed a simple, rapid, sensitive, and inexpensive method for determination of the disease biomarkers of acetone, hexanal and heptanal in human blood. For the first time, derivatization of carbonyls with O-2,3,4,5,6-(pentafluorobenzyl)hydroxylamine (PFBHA) was combined with headspace single-drop microextractin (HS-SDME) and gas chromatography-mass spectrometry (GC–MS) and applied to the analysis of acetone, hexanal, and heptanal in human blood. At first, acetone, hexanal and heptanal in blood were derivatized with PFBHA and formed oximes in several seconds. Sequentially, the oximes were headspace extracted and concentrated by a microdrop solvent. Finally, the extracted oximes were analyzed by GC–MS. HS-SDME conditions and method validations were studied. Due to needing of only 2 μl organic solvent, short extraction time of 8 min, and simple operation, derivatization-HS-SDME was shown to be a rapid, simple, and inexpensive technique for analysis of acetone, hexanal, and heptanal in human blood. Moreover, it had low detection limit values from 0.24 to 0.62 nM, and good reproducibility (R.S.D. less than 12%). 相似文献
75.
76.
Carbon monoxide adsorbed species on Ru/silicalite and their reactivity towards oxygen have been studied using in situ diffuse reflectance infrared spectroscopy (DRIFT). Four species were detected: a bridge bonded CO on metallic Ru (1980 cm -1), a linearly adsorbed CO on metallic Ru (2040 cm-1), a linearly adsorbed CO on partially oxidized Ru (2081 cm-1), and a multicarbonyl on oxidized Ru (2081 and 2133 cm-1). Among the four CO species the most strongly held species was the bridge bonded CO on metallic Ru while the multicarbonyl was the most weakly held species. These four species have different reactivities towards oxygen. Only the linearly adsorbed CO on metallic Ru can be oxidized at room temperature. 相似文献
77.
78.
Developing low-cost but efficient hydrogen evolution reaction(HER)electrocatalysts over whole pH values is a significant but daunting task for the large-scale application of electrochemical hydrogen production.Herein,we develop,for the first time,a scalable MOF-assisted strategy for the fabrication and microstructural optimization of multi-shelled hollow N-doped carbon nanosheet arrays with confined Co/CoP heterostructures on carbon cloth(Co/CoP@NC/CC)for boosting HER performances.The key to this strategy is the step-by-step epitaxial growth of unprecedented multilayer ZIF-L arrays on carbon cloth,which are subsequently pyrolyzed and controllably phosphorized to achieve the precise control over the shell number and nanoarchitectures of the Co/CoP@NC/CC.Impressively,the HER performances can be significantly enhanced by increasing hollow shell number,and the optimal triple-shelled hollow Co/CoP@NC/CC exhibits low overpotentials of 86,78 and 145 mV in acidic,alkaline and neutral media to deliver a current density of 10 mA cm-2,respectively,ranking as one of the best Co-based HER electrocatalysts over whole pH values.Further DFT calculations suggest that the Co/CoP heterostructures can effectively boost the cleavage of H–OH to generate protons and optimize the adsorption energy of hydrogen(ΔGH*),which,together with the large electrode/electrolyte interface and accelerated charge/mass transfer of multi-shelled hollow array structure as well as the good conductivity and dispersity,are responsible for the remarkably improved HER performances.This study not only provides a new toolbox for enriching the family of multi-shelled nanoarchitecture materials,but also points out a general and effective route to develop highly efficient self-supported electrode materials for energy-related applications and beyond. 相似文献
79.
80.
Determination of Organophosphorus Pesticides in Soil by MMSPD-GC-NPD and Confirmation by GC-MS 总被引:1,自引:0,他引:1
A novel method, modified matrix solid-phase dispersion (MMSPD), has been developed for quantitative analysis of organophosphorus
pesticide residues in soil. It was based on matrix solid-phase dispersion (MSPD) and continuous liquid-solid extraction (continuous
LSE), using Florisil as sorbent and dichloromethane as the recycling solvent. Two soils with different texture and physicochemical
properties were studied to validate the method. The effect of residence time of pesticides in soil was also studied. MMSPD
was compared with MSPD and continuous LSE respectively. Determination was carried out by gas chromatography with nitrogen-phosphorus
detection (GC-NPD). The method gave recoveries ranging from 72–105% with relative standard deviations (RSDs) lower than 15%
for the pesticides studied. The limits of detection (LODs) ranged from 0.1 to 0.6 ng g−1. Two pesticide residues have been detected in real soil samples from Fujian, China, using MMSPD. The pesticides were confirmed
by gas chromatography-mass spectrometry (GC-MS) in a selected-ion monitoring (SIM) mode.
Revised: 4 and 9 April 2006 相似文献