全文获取类型
收费全文 | 3269篇 |
免费 | 187篇 |
国内免费 | 230篇 |
专业分类
化学 | 1725篇 |
晶体学 | 5篇 |
力学 | 92篇 |
综合类 | 35篇 |
数学 | 83篇 |
物理学 | 350篇 |
综合类 | 1396篇 |
出版年
2024年 | 5篇 |
2023年 | 33篇 |
2022年 | 101篇 |
2021年 | 132篇 |
2020年 | 93篇 |
2019年 | 81篇 |
2018年 | 72篇 |
2017年 | 82篇 |
2016年 | 113篇 |
2015年 | 126篇 |
2014年 | 145篇 |
2013年 | 177篇 |
2012年 | 234篇 |
2011年 | 141篇 |
2010年 | 125篇 |
2009年 | 151篇 |
2008年 | 153篇 |
2007年 | 160篇 |
2006年 | 144篇 |
2005年 | 157篇 |
2004年 | 135篇 |
2003年 | 136篇 |
2002年 | 119篇 |
2001年 | 105篇 |
2000年 | 112篇 |
1999年 | 82篇 |
1998年 | 85篇 |
1997年 | 65篇 |
1996年 | 69篇 |
1995年 | 56篇 |
1994年 | 54篇 |
1993年 | 38篇 |
1992年 | 26篇 |
1991年 | 31篇 |
1990年 | 33篇 |
1989年 | 25篇 |
1988年 | 21篇 |
1987年 | 13篇 |
1986年 | 8篇 |
1985年 | 13篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1982年 | 11篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1976年 | 3篇 |
排序方式: 共有3686条查询结果,搜索用时 78 毫秒
31.
The thermodynamics of the conversion of aqueous glucose to fructose has been investigated using both heat conduction microcalorimetry
and high pressure liquid chromatography (HPLC). The reaction was carried out in both aqueous Tris/HCl buffer and in aqueous
phosphate buffer in the pH range 7–8 using the enzyme glucose isomerase and the cofactors CoCl2 and MgSO4. The temperature range over which this reaction was investigated was 298.15–358.15 K. We have found that the enthalpy of
reaction is independent of pH over the range investigated. A combined analysis of both the HPLC and microcalorimetric data
leads to the following results at 298 15 K:ΔG° = 349 ± 53 J mol-1, ΔH° = 2.78 ± 0.20 kJ mol-1, and ΔC
p
°
= 76 ± 30 J mol-1 K-1. The stated uncertainties are based upon an analysis of both the random and systematic errors inherent in the measurements.
Comparisons are made with literature data. The percent conversion of glucose to fructose has been calculated for the temperature
range 300–373.15 K. 相似文献
32.
Two guanidino acid oxovanadium(Ⅳ) complexes have been synthesized. Preliminary tests in vivo have shown that the two title complexes all display lowering glucose activity in vivo to STZ-rats. The effect of glucose-lowering of guanidino acetic acid oxovanadium(Ⅳ) complex in vivo is higher than that of guanidino propanoic acid oxovanadium(Ⅳ) complex. 相似文献
33.
34.
Cellulase retention and sugar removal by membrane ultrafiltration during lignocellulosic biomass hydrolysis 总被引:1,自引:0,他引:1
Technologies suitable for the separation and reuse of cellulase enzymes during the enzymatic saccharification of pretreated
corn stover are investigated to examine the economic and technical viability of processes that promote cellulase reuse while
removing inhibitory reaction products such as glucose and cellobiose. The simplest and most suitable separation is a filter
with relatively large pores on the order of 20–25 mm that retains residual corn stover solids while passing reaction products
such as glucose and cellobiose to form a sugar stream for a variety of end uses. Such a simple separation is effective because
cellulase remains bound to the residual solids. Ultrafiltration using 50-kDa polyethersulfone membranes to recover cellulase
enzymes in solution was shown not to enhance further the saccharification rate or overall conversion. Instead, it appears
that the necessary cellulase enzymes, including β-glucosidase, are tightly bound to the substrate; when fresh corn stover
is contacted with highly washed residual solids, without the addition of fresh enzymes, glucose is generated at a high rate.
When filtration was applied multiple times, the concentration of inhibitory reaction products such as glucose and cellobiose
was reduced from 70 to 10 g/L. However, an enhanced saccharification performance was not observed, most likely because the
concentration of the inhibitory products remained too high. Further reduction in the product concentration was not investigated,
because it would make the reaction unnecessarily complex and result in a product stream that is much too dilute to be useful.
Finally, an economic analysis shows that reuse of cellulase can reduce glucose production costs, especially when the enzyme
price is high. The most economic performance is shown to occur when the cellulase enzyme is reused and a small amount of fresh
enzyme is added after each separation step to replace lost or deactivated enzyme. 相似文献
35.
羧基功能化的聚[(9,9-二辛基芴基-2,7-二基)-co-(1,4-苯并-{2,1′,3}-噻二唑)]聚合物点(PFBT-COOH)在无外加共反应试剂的条件下具有高的电致化学发光(ECL)信号,且过氧化氢(H_2O_2)对其ECL具有高效猝灭作用。采用PFBT-COOH修饰玻碳电极,进一步交联葡萄糖氧化酶(GOD)以构建酶传感器(GOD/PFBT-COOH/GCE)。随着检测底液中葡萄糖浓度的增加,葡萄糖在GOD催化下原位产生的H_2O_2量增加,导致传感器的ECL信号逐渐减弱,从而实现葡萄糖的准确、快速、灵敏检测。此方法测得葡萄糖的线性范围为1.0×10~(-7)~3.0×10~(-3) mol/L,检出限为3.0×10~(-8) mol/L。血清样品中葡萄糖的加标回收率为98.5%~106%。该策略为酶传感器的构建提供了新思路,为葡萄糖的检测提供了新方法。 相似文献
36.
慢性支气管炎急性发作期病人血中微量元素的变化分析 总被引:2,自引:1,他引:2
韦民 《广东微量元素科学》1997,4(2):35-38
为观察慢性支气管炎急性女作期血液中微量元素的变化,对101例慢性支气管炎急性发作期病人和30例正常人全血中锌、铁、铜及钙进行检测。结果显示:慢性支气管炎急性发作期病人锌、铁、铜和钙4种元素均明显于正常人。提示患者血中微量元素总量减少,可能是慢性支气官炎易反复感染、加剧病变发展的原因之一。认为合理补充缺乏的微量元素,有助于疾病的防治。 相似文献
37.
The present short review deals with electroanalytical aspects of electrochemical response of ascorbic acid (Vitamin C) at conducting and electrogenerated polymer modified electrodes. Two main topics are considered: (i) electrocatalytic oxidation of ascorbate at conducting polymer modified electrodes, leading to electroanalytical techniques for ascorbate assay, and (ii) retardation of ascorbate penetration through a layer of electrogenerated polymers, leading to permselective coatings and their diverse uses, especially for biosensing devices. 相似文献
38.
《Electroanalysis》2004,16(3):224-230
The 3′‐azido‐3′‐deoxythymidine (AZT, Zidovudine) is an antiproliferative and virostatic drug widely used in human immunodeficiency virus type 1 (HIV‐1) infection treatment. With respect to side effects of high doses and a short half‐life of AZT, a fast and simple detection method for this agent could be helpful. The aim of our study was to determine AZT levels in natural samples (urine, serum, whole blood, and cell cultures, such as the HaCaT line of keratinocytes) without their mineralization and/or purification, by means of electrochemical methods using hanging mercury drop electrode (HMDE). On this electrode, AZT undergoes irreversible reduction at the peak potential near Ep?1.1 V (vs. Ag/AgCl/3 M KCl). Reduction AZT signals were measured by cyclic voltammetry (CV), differential pulse voltammetry (DPV), square‐wave voltammetry (SWV), and constant current chronopotentiometric stripping analysis (CPSA). In phosphate buffer (pH 8) the SWV yielded the best AZT signal with the detection limit of 1 nM. The determination of AZT concentration in biological materials is affected by electroactive components, such as proteins and DNA. For monitoring the influence of these compounds, AZT reduction was performed in the presence of 10 μg/mL calf thymus ssDNA and/or 100 μg/mL bovine serum albumin. In these cases, the detection limit increased to 0.25 μM. Also studied was the AZT concentration in keratinocyte cells (HaCaT line) during cell cultivation. It has been shown that the SWV may be considered as a useful tool for the determination of AZT concentration in cell cultures, and for monitoring AZT pharmacokinetics. 相似文献
39.
葛淼 《四川师范大学学报(自然科学版)》1998,21(4):457-461
为制定中国健康中青年女性全血比粘度参考值的统一标准提供科学依据,收集了中国各地用毛细管法测定的健康中青年女性全血比粘度参考值最主要的因素,随着海拔高度的逐渐增大,健康中青年女性全血比粘度参考值也在逐渐的增大,相关性很显著,用多元回归分析的方法推导出了一个回归方程.如果知道了中国某地的地理因素,就可以用回归方程估算这个地区的健康中青年女性全血比粘度参考值.依据健康中青年女性全血比粘度参考值与地理因素的依赖关系把中国分为青藏区、西南区、西北区、东南区、华北区、东北区等6个区. 相似文献
40.
山羊血液蛋白多态性的研究动态 总被引:2,自引:0,他引:2
潘爱銮 《西南民族学院学报(自然科学版)》1998,24(4):414-419
综述了山羊血液蛋白多态性的研究动态,较详细地介绍了山羊血液生化遗传标记的研究现状及其在山羊育种中的应用,并对其应用前景作了展望 相似文献