全文获取类型
收费全文 | 3054篇 |
免费 | 117篇 |
国内免费 | 190篇 |
专业分类
化学 | 1137篇 |
晶体学 | 16篇 |
力学 | 82篇 |
综合类 | 2篇 |
数学 | 1238篇 |
物理学 | 487篇 |
无线电 | 399篇 |
出版年
2024年 | 3篇 |
2023年 | 37篇 |
2022年 | 51篇 |
2021年 | 43篇 |
2020年 | 54篇 |
2019年 | 56篇 |
2018年 | 55篇 |
2017年 | 64篇 |
2016年 | 80篇 |
2015年 | 84篇 |
2014年 | 151篇 |
2013年 | 250篇 |
2012年 | 179篇 |
2011年 | 196篇 |
2010年 | 150篇 |
2009年 | 232篇 |
2008年 | 203篇 |
2007年 | 214篇 |
2006年 | 188篇 |
2005年 | 133篇 |
2004年 | 118篇 |
2003年 | 107篇 |
2002年 | 80篇 |
2001年 | 53篇 |
2000年 | 55篇 |
1999年 | 68篇 |
1998年 | 56篇 |
1997年 | 67篇 |
1996年 | 35篇 |
1995年 | 40篇 |
1994年 | 39篇 |
1993年 | 34篇 |
1992年 | 24篇 |
1991年 | 24篇 |
1990年 | 20篇 |
1989年 | 13篇 |
1988年 | 4篇 |
1987年 | 10篇 |
1986年 | 5篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 12篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 12篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1974年 | 3篇 |
排序方式: 共有3361条查询结果,搜索用时 15 毫秒
161.
162.
两亲嵌段共聚物溶液内胶束形成的温度效应 总被引:2,自引:0,他引:2
合成了一系列具有两亲嵌段结构的聚(乙二醇)(PEO)一聚(丙二醇)(PPO)共聚物.利用荧光探针及示差量热法测定了共聚物水溶液的临界胶束形成温度(CMT)值.发现二嵌段共聚物(PEO-PPO)和三嵌段共聚物(PEO-PPO-PEO)有着类似的变化规律,即随共聚物分子中疏水链(PPO)长度的增大,其CMT值降低.但三嵌段共聚(PPO-PEO-PPO)则因疏水链段处于共聚物分子的两端,因而在溶液中有可能形成立体网状交联结构.此外,利用探针分子在不同极性溶剂中荧光峰值波长发生位移的现象可以对形成胶束内核的组织程度、极性大小进行估测. 相似文献
163.
基于直立碳纳米管上的大面积金粒子构建了新型的电化学DNA生物传感器,用于急性早幼粒细胞白血病PML/RARα融合基因的检测。首先在直立碳纳米管电极表面溅射金粒子,采用自组装方法将巯基修饰的单链DNA固定到电极上,将氨基修饰的单链DNA和羧基化的CdTe量子点通过酰胺缩合反应生成CdTe修饰的DNA探针,通过与目标DNA的双杂交反应形成三明治结构,利用差分脉冲阳极溶出伏安法检测电极表面捕获的CdTe量子点,从而对DNA进行定量分析。结果表明,电极上Cd2+峰电流与目标DNA浓度(1.0×10-12~1.0×10-8 mol/L)的对数值呈线性关系,线性方程为ipa(μA)=1.626+0.132lgC(mol/L)(R=0.996),检出限为4.0×10-13 mol/L(3σ)。传感器表现出良好的重现性和稳定性。 相似文献
164.
采用差分脉冲伏安(DPV)法,结合密度泛函理论(Density Functional Theory,DFT)计算,研究了抗氧化剂2,6-二叔丁基对甲酚(T501)的电化学行为,考察了工作电极的材料和大小,及电解质溶液的组成和浓度等实验条件。最佳实验条件为直径6mm石墨电极为工作电极,KOH-乙醇溶液(KOH浓度0.15mol/L)为电解质溶液。在优化条件下,基于变压器油T501使用浓度范围内(质量分数0.05%~0.50%),T501的浓度(c)与峰电流(Ip,μA)之间呈现良好的线性关系,建立了一种快速、准确测定变压器油中T501含量的新方法。该方法检测结果与国家标准方法的测定结果没有显著性差异,在保证准确性的前提下,大大提高了变压器油中T501含量测定的效率。检出限为0.032%,加标回收率为99.61%~101.43%。 相似文献
165.
Creatinine sensor based on a molecularly imprinted polymer-modified hanging mercury drop electrode 总被引:1,自引:0,他引:1
Molecularly imprinted polymers (MIP) have been elucidated to work as artificial receptors. In our present study, a MIP was applied as a molecular recognition element to a chemical sensor. We have constructed a creatinine sensor based on a MIP layer selective for creatinine and its differential pulse, cathodic stripping voltammetric detection (DPCSV) on a hanging mercury drop electrode (HMDE). The creatinine sensor was fabricated by the drop coating of dimethylformamide (DMF) solution of a creatinine-imprinted polymer onto the surface of HMDE. The modified-HMDE, preanodised in neutral medium at +0.4 V versus Ag/AgCl for 120 s, exhibited a marked enhancement in DPCSV current in comparison to the less anodised (≤+0.3 V) HMDE. The creatinine was preconcentrated and instantaneously oxidised in MIP layer giving DPCSV response in the concentration range of 0.0025-84.0 μg mL−1 [detection limit (3σ) 1.49 ng mL−1]. The sensor was found to be highly selective for creatinine without any response of interferents viz., NaCl, urea, creatine, glucose, phenylalanine, tyrosine, histidine and cytosine. The non-imprinted polymer-modified electrode did not show linear response to creatinine. The imprinting factor as high as 9.4 implies that the imprinted polymer exclusively acts as a recognition element of creatinine sensor. The proposed procedure can be used to determine creatinine in human blood serum without any preliminary treatment of the sample in an accurate, rapid and simple way. 相似文献
166.
制备了氧化锆修饰的玻碳电极,采用示差脉冲伏安法和循环伏安法探究了槲皮素在该电极上的电化学行为。结果表明,制备的修饰电极在pH=7.00的磷酸盐缓冲溶液(PBS)中对槲皮素的氧化还原具有明显的电催化作用。采用槲皮素的氧化峰电流作为分析信号。在浓度为2.5×10-8~5×10-5 mol/L的范围内,氧化峰电流和浓度成良好的线性关系,线性方程为ip(μA)=0.0825c-9.861 84,检出限为5.35×10-9 mol/L。 相似文献
167.
甲磺酸帕珠沙星的热分解机理及动力学 总被引:2,自引:0,他引:2
采用热重(TG)和差示扫描量热(DSC)法测定了甲磺酸帕珠沙星(PZFX)在氮气氛和空气氛中的热分解过程,测定了PZFX及其在热分解过程中不同阶段残余物的红外光谱,运用量子化学GAMESS软件计算了PZFX分子的键级,推断了PZFX的热分解机理.结果表明PZFX的热分解过程的起始步骤是甲磺酸的分解.采用Ozawa方法计... 相似文献
168.
A technique for production of nanocrystalline cellulose with a narrow size distribution 总被引:3,自引:0,他引:3
Nanocrystalline cellulose (NCC) was prepared by sulfuric acid hydrolysis of microcrystalline cellulose. A differential centrifugation
technique was studied to obtain NCC whiskers with a narrow size distribution. It was shown that the volume of NCC in different
fractions had an inverse relationship with relative centrifugal force (RCF). The length of NCC whiskers was also fractionized
by differential RCF. The aspect ratio of NCC in different fractions had a relatively narrow range. This technique provides
an easy way of producing NCC whiskers with a narrow size distribution. 相似文献
169.
Amanda L. Santos Gilberto O. Chierice Kenneth S. Alexander Alan Riga Ellen Matthews 《Journal of Thermal Analysis and Calorimetry》2009,96(3):821-825
Eugenol is the main volatile compound extracted oil from clove bud, Syzygium aromaticum L., and used in traditional medicine, as a bactericide, fungicide, anesthetic, and others. Its extraction was performed using
hydrodistillation which is the most common extraction technique. Its components and thermal behavior were evaluated using
gas chromatography (GC) and differential scanning calorimetry (DSC), which provide a better characterization of these natural
compounds. This extracted product was compared to the standard eugenol results. The GC results suggested ~90% eugenol was
found in the total extracted oil, and some of its boiling characteristics were 270.1 °C for peak temperature and 244.1 J g−1 for the enthalpy variation.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
170.
This study demonstrates an on-chip resistive pulse-sensing scheme with a design of symmetric mirror channels, which significantly reduces the noise and achieves better signal-to-noise ratio. Polystyrene particles of different sizes have been detected with the developed sensing scheme and a record low volume ratio of the particle to the sensing channel, or 0.0004%, has been detected with particles of 520 nm in diameter in a sensing aperture of 50x16x20 microm3. This volume ratio is about ten times lower than the lowest volume ratio reported in the literature including that specified for commercial Coulter counters. 相似文献