首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   17285篇
  免费   2604篇
  国内免费   2151篇
化学   13245篇
晶体学   277篇
力学   936篇
综合类   187篇
数学   1715篇
物理学   5680篇
  2024年   24篇
  2023年   251篇
  2022年   390篇
  2021年   510篇
  2020年   605篇
  2019年   616篇
  2018年   470篇
  2017年   483篇
  2016年   781篇
  2015年   753篇
  2014年   912篇
  2013年   1258篇
  2012年   1521篇
  2011年   1601篇
  2010年   1146篇
  2009年   993篇
  2008年   1146篇
  2007年   969篇
  2006年   969篇
  2005年   922篇
  2004年   732篇
  2003年   646篇
  2002年   719篇
  2001年   480篇
  2000年   434篇
  1999年   384篇
  1998年   285篇
  1997年   263篇
  1996年   254篇
  1995年   236篇
  1994年   191篇
  1993年   173篇
  1992年   160篇
  1991年   138篇
  1990年   123篇
  1989年   99篇
  1988年   86篇
  1987年   58篇
  1986年   61篇
  1985年   63篇
  1984年   33篇
  1983年   29篇
  1982年   21篇
  1981年   20篇
  1980年   9篇
  1979年   7篇
  1974年   2篇
  1971年   2篇
  1957年   6篇
  1936年   1篇
排序方式: 共有10000条查询结果,搜索用时 979 毫秒
191.
In this study a relationship between the surface and textural properties of carbon blacks and the gasification process induced thermally in air is noted. A temperature jump method was used to follow the gasification in air and to establish the relevant Arrhenius parameters. This can be associated with the activity of ‘basal’ plane carbon atoms as well as ‘edge’ carbon atoms at the surface. This is based on a model of carbon black structure consisting of the irregular packing of small graphite carbon structures. The carbon black surface was measured using a single measurement of adsorption based essentially on the BET volumetric method. The carbon black surface had a rate of oxidation per unit are which clearly indicated that the lower area carbon blacks had a predominately active area of ‘edge’ atoms at the surface while the surface of the higher area carbon blacks had a predominate amount of ‘basal’ plane graphite carbon atoms.  相似文献   
192.
193.
赵勇  张宝文 《应用化学》1993,10(3):51-53
本文将3-三氰基乙烯基-N-十六烷基吲哚与花生酸混合制成单分子膜。不同摩尔比混合膜的π-A曲线均出现平台,表明膜压缩过程中分子排列相态发生变化。混合LB膜的紫外吸收光谱证明吲哚分子形成聚集体,X-射线衍射结果说明这种聚集体被夹带在花生酸的框架结构中。  相似文献   
194.
本文研究了B15C5冠醚萃取锂盐时,不同阴离子对体系的同位素分离效应的影响。结果表明,阴离子在冠醚萃取过程中不仅对萃取络合物的稳定性有显著影响,而且阴离子半径及软度越大时,萃取体系的锂同位素分离系数(α_(LI))也越大。  相似文献   
195.
Molybdenum trioxide (MoO3) xerogel films modified with poly(vinyl alcohol)+poly(vinyl pyrrolidone) (PVP+PVA) polyblends were obtained by ion-exchange method with sol-gel technique. Investigations were conducted using X-ray “diffractometry”, Fourier transform infrared spectroscopy, and cyclic voltammetry. The results show that the H atoms in polyblend are H-bonded with the O atoms in the Mo=O bonds of MoO3 xerogel, which effectively shield the electrostatic interaction between MoO3 interlayer and Li+ ions when MoO3 xerogel is modified by the intercalation of (PVP+PVA). The reversibility of the insertion/extraction of Li+ ions is greatly improved by the modification with polyblend of MoO3 nanocomposite films. MoO3 and (PVP+PVA) x MoO3 (x = 0, 0.5) nanobelts were obtained by a simple hydrothermal process from MoO3 sol. The electrochemical cells with configuration Li/(LiPF6+EC+DMC)/MoO3 modified by (PVP+PVA) were fabricated and their discharge profiles studied.  相似文献   
196.
Cellulose/cellulose acetate membranes were prepared and functionalized by introducingamino group on it, and then immobilized the glucose oxidase (Gox) on the functionalizd membrane.SECM was applied for the detection of enzyme activity immobilized on the membrane.Immobilized biomolecules on such membranes was combined with analysis apparatus and can beused in bioassays.  相似文献   
197.
本文将超声雾化技术与MIP-AAS联用,以“L”型吸收管代替“T”型吸收管作为AAS测量的吸收池,采用水冷凝和浓H_2SO_4吸收相结合去溶,研究TUSN-MIP-AAS方法测银时的某些影响因素,讨论了微波前向功率,载气流速、去溶系统、溶液酸度、共存离子及易也离元素等对吸收信号的影响,本法所得的测银的特征浓度为0.01μg/ml(328.1nm)和0.03μg/ml(338.3nm),相对标准偏差为7.5%.  相似文献   
198.
Self-assembly of lanthanide mixed-carboxylates coordination polymers   总被引:1,自引:0,他引:1  
Two new mixed-ligands lanthanide coordination polymers, [Ln(Ac)(ip)(H2O)2]·0.5H2O (Ln=La (1); Ln=Eu (2); Ac=acetate; ip=isophthalate) have been synthesized under hydrothermal condition. Single-crystal X-ray analyses show that complexes 1 and 2 are three-dimensional structure in which lanthanide ions are bridged by monocarboxylate ligand, acetate or dicarboxylate ligand, isophthalate. And the central lanthanide ions, La3+ and Eu3+, are both nine-coordinate with oxygen atoms. The thermogravimetric analysis was carried out to examine the thermal stability of the title complexes. And the photoluminescence property of complex 2 was also investigated.  相似文献   
199.
The development of highly active and stable reversible oxygen electrocatalysts is crucial for improving the efficiency of metal-air battery devices. Herein, an efficient liquid exfoliation strategy was designed for producing silk-like FeS2/NiS2 hybrid nanocrystals with enhanced reversible oxygen catalytic performance that displayed excellent properties for Zn-air batteries. Because of the unique silk-like morphology and interface nanocrystal structure, they can catalyze the oxygen evolution reaction (OER) efficiently with a low overpotential of 233 mV at j = 10 mA cm?2. This is an improvement from the recently reported catalysts in 1.0 M KOH. Meanwhile, the oxygen reduction reaction (ORR) activity of the silk-like FeS2/NiS2 hybrid nanocrystals showed an onset potential of 911 mV and a half-wave potential of 640 mV. In addition, the reversible oxygen electrode activity of the silk-like FeS2/NiS2 hybrid nanocrystals was calculated to be 0.823 V, based on the potential of the OER and ORR. Further, the homemade rechargeable Zn-air batteries using FeS2/NiS2 hybrid nanocrystals as the air-cathode displayed a high open-circuit voltage of 1.25 V for more than 17 h and an excellent rechargeable performance for 25 h. The solid Zn-air batteries exhibited an excellent rechargeable performance for 15 h. This study provided a new method for designing interface nanocrystals with a unique morphology for efficient multifunctional electrocatalysts in electrochemical reactions and renewable energy devices.  相似文献   
200.
超临界二氧化碳介质中钯催化炔烃羰基化反应   总被引:2,自引:0,他引:2  
研究了以超临界二氧化碳为反应介质实现改善钯催化炔烃羰基化反应绿色性的方法 .研究结果表明 :醇的用量、二氧化碳压力和反应温度等因素均对钯催化炔烃羰基化反应的化学选择性均有影响 ,即存在炔烃的羰基化反应与氧化偶合反应的竞争  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号