全文获取类型
收费全文 | 14197篇 |
免费 | 2419篇 |
国内免费 | 1859篇 |
专业分类
化学 | 5354篇 |
晶体学 | 379篇 |
力学 | 899篇 |
综合类 | 137篇 |
数学 | 181篇 |
物理学 | 5554篇 |
无线电 | 5971篇 |
出版年
2024年 | 36篇 |
2023年 | 144篇 |
2022年 | 287篇 |
2021年 | 421篇 |
2020年 | 398篇 |
2019年 | 368篇 |
2018年 | 385篇 |
2017年 | 544篇 |
2016年 | 639篇 |
2015年 | 630篇 |
2014年 | 846篇 |
2013年 | 1143篇 |
2012年 | 1102篇 |
2011年 | 1048篇 |
2010年 | 853篇 |
2009年 | 920篇 |
2008年 | 946篇 |
2007年 | 972篇 |
2006年 | 834篇 |
2005年 | 759篇 |
2004年 | 703篇 |
2003年 | 587篇 |
2002年 | 479篇 |
2001年 | 428篇 |
2000年 | 411篇 |
1999年 | 376篇 |
1998年 | 309篇 |
1997年 | 282篇 |
1996年 | 249篇 |
1995年 | 210篇 |
1994年 | 184篇 |
1993年 | 186篇 |
1992年 | 154篇 |
1991年 | 90篇 |
1990年 | 92篇 |
1989年 | 79篇 |
1988年 | 87篇 |
1987年 | 48篇 |
1986年 | 41篇 |
1985年 | 24篇 |
1984年 | 19篇 |
1983年 | 13篇 |
1982年 | 30篇 |
1981年 | 25篇 |
1980年 | 15篇 |
1979年 | 25篇 |
1978年 | 15篇 |
1977年 | 12篇 |
1976年 | 7篇 |
1974年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
181.
温控非水液/液两相催化,是指一类由两种或多种液态有机物组成的催化反应体系,其特点是体系的相态变化可通过温度来调控,即体系在高温时相互混溶呈均相,低温不溶分成两相,催化剂和产物分别处于两相,从而为解决均相催化剂分离难的问题开拓了一个新方向,是液/液两相催化研究领域最引人注目的进展之一.首次以"温控"为主线将氟两相催化作为温控液/液两相催化的一个特定类型纳入"温控非水液/液两相催化"范畴,并与其它通过温度来调控的有机液/液两相和作者提出的温控相分离催化串在一起作一较为详细的评述. 相似文献
182.
Vapor pressure,speciation, and chemical activities in highly concentrated sodium borate solutions at 277 and 317°C 总被引:2,自引:0,他引:2
Oleh Weres 《Journal of solution chemistry》1995,24(5):409-438
The system H2O-B2O3-Na2O has been studied experimentally at 277 and 317°C. The activities of water and boric acid have been determined at mole ratios Na/B from 0 to 1.5, and total dissolved solids 3 to 80 weight percent. The activity of boric acid has been fitted to within experimental error using a speciation model with eight complex species. This model is consistent with the model previously published by Mesmer et al. The electrolyte properties of the liquid are modeled using the Pitzer-Simonson model of very concentrated electrolyte solutions. The calculated values of water activity agree with experiment, and the activity of NaOH and pOH have also been calculated. The potassium borate system also was briefly studied at 317°C, and is adequately described by a model with five complex species. The potassium borate liquid is more alkaline at K/B= 1 than a sodium borate liquid at the same mole ratio, but pOH in the two systems is the same at lower mole ratios. 相似文献
183.
184.
单分散纳米InVO4(正交相)的低温合成 总被引:1,自引:0,他引:1
InVO4 is a new developed visible light responding photocatalyst for water decomposition, which is obtained by a solid-state reaction at high temperature traditionally. In this paper, pure InVO4 nano-crystalline powder has been prepared by a hydrothermal process at low temperature and was characterized by TEM, IR, and X-ray diffraction. Many factors such as pH value, reaction time and temperature have been investigated. It is found that the optimal conditions for the preparation is: nInCl3∶nNaVO3=1∶2; temperature : 150 ℃; Reaction time: 4~8 h; pH=7.9~8.0. And the experimental result shows that it is a convenient way to get single dispersing InVO4 nano-crystalline powder by flux in alkyl alcohol. 相似文献
185.
Muhammad Ilyas Sarwar Sonia Zulfiqar Zahoor Ahmad 《Colloid and polymer science》2007,285(15):1733-1739
Fluoro-aramid-based sol/gel-derived nanocomposites were synthesized by condensing a mixture of 4,4′-(hexafluoro-isopropylidene)dianiline
and 1,3-phenylenediamine with terephthaloylchloride (TPC) in dimethylacetamide. TPC was added in slight excess to produce
amide chains with carbonyl chloride end groups and then replaced with alkoxy groups using aminophenyltrimethoxysilane to develop
bonding with the silica network. Mechanical, dynamic mechanical thermal, water absorption and morphological measurements were
carried out on the thin hybrid films. Increase in the tensile strength and modulus was observed as compared to pristine polyamide.
The thermal decomposition temperature was found in the range of 400–500 °C. The water absorption was found to be reduced with
higher silica content. The glass transition temperature and the storage moduli increased with increasing silica concentration.
The maximum increase in the T
g value (345 °C) was observed with 20 wt% silica. Scanning electron microscopy revealed the uniform distribution of silica
in the matrix with an average particle size ranging from 8 to 50 nm. 相似文献
186.
187.
188.
189.
The present work is an attempt to assess racemization in stepwise solid-phase peptide synthesis at elevated temperatures (SPPS-ET), a high-speed approach in which peptide elongation occurs at 55-75 °C. This attempt was based on the notion that a high propensity for this side reaction would hamper employment of this alternative approach and would dampen interest in its further development. Simple peptide models were synthesized using customized protocols for classical SPPS or SPPS-ET. Systematic analyses of the resulting crude peptides by reversed-phase HPLC, ion-exchange HPLC, capillary electrophoresis and electrospray ionization mass spectrometry revealed low diastereomeric byproduct contents. These results indicate that, from the standpoint of racemization, classical SPPS and SPPS-ET protocols were equivalent. Therefore, further studies employing SPPS-ET protocols are justified. 相似文献
190.
《Surface and interface analysis : SIA》2003,35(12):1015-1017
Material surface properties of polymers, plastics, ceramics and textiles can be modified by atmospheric or low‐pressure glow discharge plasma. The aim of the present work is to study the surface modification of biaxially oriented polypropylene (BOPP) film in order to improve its hydrophilic and wetting properties. In this article we used low‐pressure, low‐temperature oxygen plasma for the surface treatment of BOPP. Scanning electron microscopy indicates that plasma treatment causes mainly physical changes by creating microcraters and roughness on the surface and increasing surface friction. Attenuated total reflectance infrared spectra show oxygen‐containing groups such as ? OH at 3513 cm?1 and C?O at 1695 cm?1. Microscopic investigations of water droplets on BOPP (treated, untreated) show that the interfacial adhesion of treated surfaces is increased. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献