全文获取类型
收费全文 | 6894篇 |
免费 | 517篇 |
国内免费 | 1354篇 |
专业分类
化学 | 7363篇 |
晶体学 | 36篇 |
力学 | 32篇 |
综合类 | 42篇 |
数学 | 23篇 |
物理学 | 578篇 |
无线电 | 691篇 |
出版年
2024年 | 11篇 |
2023年 | 91篇 |
2022年 | 106篇 |
2021年 | 219篇 |
2020年 | 190篇 |
2019年 | 216篇 |
2018年 | 136篇 |
2017年 | 210篇 |
2016年 | 243篇 |
2015年 | 255篇 |
2014年 | 280篇 |
2013年 | 317篇 |
2012年 | 705篇 |
2011年 | 359篇 |
2010年 | 322篇 |
2009年 | 405篇 |
2008年 | 471篇 |
2007年 | 533篇 |
2006年 | 500篇 |
2005年 | 442篇 |
2004年 | 449篇 |
2003年 | 335篇 |
2002年 | 243篇 |
2001年 | 192篇 |
2000年 | 189篇 |
1999年 | 168篇 |
1998年 | 153篇 |
1997年 | 155篇 |
1996年 | 107篇 |
1995年 | 123篇 |
1994年 | 119篇 |
1993年 | 110篇 |
1992年 | 94篇 |
1991年 | 87篇 |
1990年 | 86篇 |
1989年 | 51篇 |
1988年 | 30篇 |
1987年 | 13篇 |
1986年 | 13篇 |
1985年 | 7篇 |
1984年 | 10篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有8765条查询结果,搜索用时 0 毫秒
941.
高性能PTCR电极浆料生产工艺的改进 总被引:1,自引:1,他引:0
通过增加分散剂松香的用量,提高了欧姆银浆的关键中间体材料银泥的质量稳定性。将压滤法应用于银泥洗涤工艺,既节省了设备投资,又避免了设备腐蚀。在欧姆银浆中掺入10%的活性铝粉,降低了浆料成本,而且增强了浆料的工艺适应性。表层银浆的配制采用辊轧工艺替代球磨工艺,并对有机载体进行了调整,提高了生产效率,改善了膜层光洁度。 相似文献
942.
943.
The behavior of (ferrocene)amylose (FA), in the presence of amylolytic depolymerases (α-amylase from Aspergillus oryzae and human saliva), has been investigated by cyclic voltammetry at a rotating disk electrode (CVA/RDE). Growth of the limiting current with time in the presence of the enzymes is proportional to the amount of enzyme introduced. The quantitative data treatment to assay the endoamylolytic activity of enzymes at CVA/RDE involves plotting (idt/id0)4.5 against time; the slope of the linear plot being equal to (rate) Mn0C−1, where idt and id0 are the limiting currents at time t and 0, respectively, (rate) is the enzymatic activity, Mn0 is the number averaged molecular weight of FA at t = 0, and c is its concentration. The comparison of CVA/RDE with the 3,5-dinitrosalicylic acid and the Somogyi–Nelson reducing saccharides procedures shows advantages of the former, especially in assaying small quantities of enzymes. Also the CVA/RDE approach is simpler and takes place under much milder conditions. The main disadvantage of CVA/RDE is the inhibiting effect of Triton X-100 in the reaction between FA and the amylases which is not observed in the case of native, ferrocene-free amylose. In general, CVA/RDE appears to be an attractive analytical method for monitoring diverse enzymatic depolymerization reactions. 相似文献
944.
《Electroanalysis》2002,14(23):1644-1647
The activity of urease varies by its redox reaction. Active urease has an SH group that is essential to exhibit its activity, however, oxidation agents such as quinone compounds can oxidize the SH group in urease and a S–S bond is produced, resulting in the loss of enzyme activity. The reduction potential of cystine was almost the same as that of the recovery of urease activity. In this work, it has been found that the SH group of urease can be oxidized by not only chemical reaction but also by the direct electrode oxidation of urease and the produced S–S bond can be reduced to SH group by chemical and electrode reactions, and the original enzyme activity is recovered. This research shows that the regulation of urease activity is easily possible by changing the electrode potential of the porous carbon felt immobilized urease. The variation of urease activity was monitored by ammonia or carbon dioxide electrode equipped with the urease immobilized carbon felt, and the ammonia or carbon oxide generated from urea can transfer through the carbon felt to reach the each gas permeable membrane. The combination of gas electrode with porous conducting material such as carbon can supply the novel device for the electrochemical investigation of enzyme activity. 相似文献
945.
946.
Oleg G. Voronin Daan J. van Haaster Elena E. Karyakina Wilfred R. Hagen Arkady A. Karyakin 《Electroanalysis》2007,19(21):2264-2266
The direct bioelectrocatalysis by an NAD(P)‐reducing hydrogenase is reported for the first time. In contrast to previous attempts to involve similar enzymes in bioelectrocatalysis [1–4], which were in fact unsuccessful, in our report an effective electrocatalysis by Pyrococcus furiosus hydrogenase is convincingly shown by (i) achievement of the hydrogen equilibrium potential and (ii) a high current of hydrogen oxidation (0.3 mA cm?2 at 100 mV overpotential and at 75 °C). The latter is just a few times lower compared to enzyme electrodes based on NAD(P)‐independent hydrogenases. 相似文献
947.
微分电位溶出分析法应用于金膜电极的研究 总被引:1,自引:0,他引:1
本文介绍将微分电位溶出分析法应用于金膜电极,建立了相应的理论体系和应用条件。可使用的金膜厚度在1.8×10~(-7)~4.3×10~(-7)cm范围。检测限较原法降低近两个数量极。用本法测定花生乳中的铜,回收率在94~102%间。 相似文献
948.
本文提出一种氟电极测铝的新方法,即二次回归校正曲线法及分段抛物插值法。由于汇集了1.该法依据的数学模型与实验数据相符;2.AppleⅡ-ISE智能离子计具有较强的数据处理功能;3.氟电极性能良好等三个特点,故本法准确可靠,快速方便,具有一定理论意义和较大实用价值。 相似文献
949.
The electroless nickel plating on an aluminum input/output (I/O) pad was investigated. The aluminum pad was pretreated in
a zincate solution prior to electroless nickel plating. Zinc particles on the aluminum pad gave a good adherent nickel layer.
The adhesion and uniformity of zinc on the aluminum is the key factor in under-bump metallurgy (UBM). The electrode potential
changes with and without zinc ions in the bath were measured to analyze the sequence of two competing reactions: zinc deposit
and hydrogen evolution. The relationship between aluminum dissolution and the ratio of zinc and NaOH was investigated. The
electroless nickel deposition rate was dependent on bath composition. The effects of complexing ligand and additive on the
nickel deposit were analyzed. Electrode potential changes were measured with time to confirm nucleation and grain growth.
Adhesion of the UBM was related to zinc-particle dissolution and nickel nucleation. The uniform nickel UBM was fabricated
on a real Al I/O pad. 相似文献
950.
Dilek ÇökelilerMehmet Mutlu 《Analytica chimica acta》2002,469(2):217-223
A single-layer alcohol electrode was prepared by plasma polymerization technique. Ethylenediamine was used to incorporate amino groups on tract-etched polycarbonate membranes in glow discharge reactor. In order to determine the plasma polymerization parameters (discharged power, monomer flow rate, exposure time) on membrane permeability, hydrogen peroxide was used as tracer. The single-layer alcohol electrode that was produced by 0.6% (w/v) of alcohol oxidase (AOx) solution on the polycarbonate membrane, which was modified at 30 W, 20 ml/min monomer flow rate and 15 min exposure time, was selected for optimum performance. Sensitivity, linearity and response time of that particular layer were 5.6 nA/mM, 2 mM and 50 s, respectively. The performance of the amperometric alcohol electrode was tested on commercial alcoholic beverages. 相似文献