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   6821篇
  免费   976篇
  国内免费   559篇
化学   4790篇
晶体学   32篇
力学   364篇
综合类   16篇
数学   797篇
物理学   2357篇
  2024年   22篇
  2023年   153篇
  2022年   214篇
  2021年   286篇
  2020年   281篇
  2019年   239篇
  2018年   220篇
  2017年   177篇
  2016年   291篇
  2015年   281篇
  2014年   373篇
  2013年   454篇
  2012年   602篇
  2011年   620篇
  2010年   414篇
  2009年   348篇
  2008年   423篇
  2007年   373篇
  2006年   349篇
  2005年   265篇
  2004年   201篇
  2003年   159篇
  2002年   130篇
  2001年   131篇
  2000年   124篇
  1999年   134篇
  1998年   108篇
  1997年   92篇
  1996年   123篇
  1995年   103篇
  1994年   70篇
  1993年   63篇
  1992年   69篇
  1991年   57篇
  1990年   74篇
  1989年   53篇
  1988年   34篇
  1987年   29篇
  1986年   24篇
  1985年   18篇
  1984年   16篇
  1983年   16篇
  1982年   15篇
  1981年   10篇
  1979年   20篇
  1978年   15篇
  1977年   14篇
  1976年   10篇
  1975年   13篇
  1973年   13篇
排序方式: 共有8356条查询结果,搜索用时 14 毫秒
991.
Zeolitic imidazolate framework-8 (ZIF-8) is synthesized by typical solvothermal method and subsequently calcined under air and nitrogen atmosphere, respectively. The carbon in the calcined ZIF-8 under nitrogen atmosphere was from the carbonization of the guest molecules, without adding any other carbon sources. The samples are characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and electrochemical analyzer system. When the ZIF-8 is used as electrode materials for a supercapacitor in 6 M KOH electrolyte, it displays a pseudocapacitive behavior. The untreated ZIF-8 and calcined ZIF-8 under air and nitrogen atmosphere electrodes exhibit a specific capacitance of 96, 156, and 185 F g?1, respectively, at a scan rate of 5 mV s?1 and good stability over 1,500 cycles. These results indicate that the ZIF-8 is a promising material for supercapacitors.  相似文献   
992.
The activation energy is the minimum amount of energy required to initiate a reaction. It is one of the important indexes for appraising a reaction. The chemical reaction rate is closely related to the value of activation energy, and reducing activation energy is propitious to promoting a chemical reaction. In the present paper, the relationship between the activation energy in Si-KOH reaction system and the ultrasound frequency and power has been discussed for the first time. The range of ultrasound frequency and power is 40-100kHz (interval by 20kHz) and 10-50W (interval by 10W), respectively. The experimental clata indicate that the activation energy decreases with the increasing ultrasound power. Comparing with the activation energy without ultrasound irradiation, the results in our paper indicate that ultrasound irradiation could reduce the activation energy in Si-KOH reaction system and increase the reaction rate.  相似文献   
993.
An efficient and feasible synthetic approach was developed for the synthesis of an array of new flavane derivafives from the substituted benzaldehyde with the reduction of chalcones and subsequent cyclization as the key steps. The purity and structure of the products were confirmed by the elemental analysis and a combination of its IR, ^1H and ^13C NMR, and mass spectra. These synthetic compounds were tested for xanthine oxidase (XO) inhibitions and antifungal actions against Candida albicans, Cryptococcus neoformans, Aspergillus sp. and Trichophyton rubrum. 7-Hydrazinocarbonylmethoxy-4'-methoxyflavane (9) was found to be the most XO inhibitory with IC50=76.4 μmol/L, and the most potent antifungal compound was 4'-hydrazinocarbonylmethoxyflavane (12) with minimal inhibition concentration MIC=8 μg/mL against Trichophyton rubrum.  相似文献   
994.
A metal-organic complex, which has the potential property of absorbing gases, [LaCu6(μ-OH)3(Gly)6im6](ClO4)6 was synthesized through the self-assembly of La3+, Cu2+, glycine (Gly) and imidazole (Im) in aqueous solution and characterized by IR, element analysis and powder XRD. The molar heat capacity, Cp,m, was measured from T = 80 to 390 K with an automated adiabatic calorimeter. The thermodynamic functions [HT − H298.15] and [ST − S298.15] were derived from the heat capacity data with temperature interval of 5 K. The thermal stability of the complex was investigated by differential scanning calorimetry (DSC).  相似文献   
995.
在260~380 K范围内, 用DSC法研究液晶HpBAB的相变。实验查明HpBAB在室温还以玻璃性晶体状态存在。它的玻璃转变、熔化和清亮过程的热力学参数准确地被测到。提出对-正烷氧基亚苄基-对-氨基苯腈同系列中熔化熵和烷基碳原子数的线性关系; 改进Aranow统计模型并估算直线斜率为Rln(3/g)(1相似文献   
996.
甘新民  唐宁 《应用化学》1989,6(2):73-76
1,8-萘啶氮氧化物(简写napyo)是一种配位能力较强的中性配体,关于它与金属离子形成的配合物已有报道.但工作主要集中在配合物的合成及性质的研究,它与金属离子形成的配合物的晶体结构至今未见报道.本工作旨在探讨1,8-萘啶氮氧化物与铜(Ⅱ)的配合物中配体与金属离子的配位情况以及铜(Ⅱ)的配位构型.  相似文献   
997.
The computation of the interaction energy between an adsorbed dye molecule and the silver halide surface has been accomplished through the use of a new code which is based upon CHEMLAB. The surface interaction energies have been computed for 1,1′-ethylene-2,2′-cyanine, a dye molecule, in both monomeric and aggregated configurations on the (100) surfaces of AgBr and AgCl. The model predicts reasonable configurations for the adsorbed dye monomer and its H- and B-aggregates. At high dye levels, the adsorption of aggregated forms is found to be favored over an adsorbed monolayer of monomeric dye molecules. Using the current interaction potentials, however, it was found that the adsorption of the dye on the AgCl (100) surface was slightly favored over that on the AgBr (100) surface. This finding, although at variance with experimental data, may be attributed to the use of an unrelaxed silver halide surface in these computations.  相似文献   
998.
用普通材料自制和组装一套能梯度淋洗和柱后反应光度法连续检测萃取色层柱的流出曲线的设备。详细叙述了淋洗液切换阀、六通样样阀、四通混合器、盘管反应器的制作和将国产原子吸分光光度计改装流动光度计。  相似文献   
999.
用非水滴定法和Hammett系列指示剂测定了COS水解碱改性γ-Al_2O_3催化剂的表面碱强度分布.发现表面碱强度分布不均匀与表面能量分布不均匀相呼应.采用零点酸碱强度(H_(0,max))及碱中心区域分析法,Bronsted催化定律,进一步证实COS水解反应具有明显碱催化特征,较高活性催化剂的H_(0,max)一般为10左右,对COS水解反应起主要作用的碱性中心的碱强度(H_0)为4.8≤H_0≤9.8.对碱金属氧化物改性后的γ-Al_2O_3催化剂,Bronsted规律在每个碱强度分区域内是适用的.  相似文献   
1000.
A microcalorimetric technique was used to evaluate the influence of both Levofloxacin lactate in sodium chloride injection (drug A) and Levofloxacin hydrochloride in sodium chloride injection (drug B) on the metabolism of Escherichia coli. By means of an isothermal calorimeter and ampoule method at 37 °C, the power-time curves of E. coli growth were obtained under different conditions. The parameters such as the growth rate constant k, maximum power output P m, time t m corresponding to the maximum power output and inhibitory ratio I of these two drugs were obtained. The results reveal that the inhibitory abilities enhance with increasing concentrations of the two drugs. The critical growth concentration and the half-inhibitory concentration IC50 were 0.15 and 0.079 μg mL?1 (for drug A), 0.13 and 0.061 μg mL?1 (for drug B), respectively. These results show the drug A has slightly better inhibitory effect on E. coli than that of drug B.  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