全文获取类型
收费全文 | 6407篇 |
免费 | 892篇 |
国内免费 | 336篇 |
专业分类
化学 | 2378篇 |
晶体学 | 86篇 |
力学 | 1333篇 |
综合类 | 43篇 |
数学 | 317篇 |
物理学 | 2454篇 |
无线电 | 1024篇 |
出版年
2025年 | 25篇 |
2024年 | 108篇 |
2023年 | 117篇 |
2022年 | 117篇 |
2021年 | 184篇 |
2020年 | 264篇 |
2019年 | 188篇 |
2018年 | 177篇 |
2017年 | 215篇 |
2016年 | 275篇 |
2015年 | 234篇 |
2014年 | 357篇 |
2013年 | 383篇 |
2012年 | 318篇 |
2011年 | 430篇 |
2010年 | 331篇 |
2009年 | 402篇 |
2008年 | 380篇 |
2007年 | 431篇 |
2006年 | 369篇 |
2005年 | 314篇 |
2004年 | 326篇 |
2003年 | 288篇 |
2002年 | 234篇 |
2001年 | 193篇 |
2000年 | 170篇 |
1999年 | 174篇 |
1998年 | 108篇 |
1997年 | 95篇 |
1996年 | 84篇 |
1995年 | 58篇 |
1994年 | 44篇 |
1993年 | 30篇 |
1992年 | 21篇 |
1991年 | 37篇 |
1990年 | 21篇 |
1989年 | 11篇 |
1988年 | 17篇 |
1987年 | 14篇 |
1986年 | 10篇 |
1985年 | 7篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 13篇 |
1981年 | 4篇 |
1980年 | 9篇 |
1979年 | 12篇 |
1973年 | 5篇 |
1971年 | 3篇 |
1957年 | 4篇 |
排序方式: 共有7635条查询结果,搜索用时 0 毫秒
111.
A matrix-free, high sensitivity, nanostructured silicon surface assisted laser desorption/ionization mass spectrometry (LDI-MS) method fabricated by metal-assisted etching was investigated. Effects of key process parameters, such as etching time, substrate resistance and etchant composition, on the nanostructured silicon formation and its LDI-MS efficiency were studied. The results show that the nanostructured silicon pore depth and size increase with etching time, while MS ion intensity increases with etching time to 300 s then decreases until 600 s for both low resistance (0.001–0.02 Ω cm) and high resistance (1–100 Ω cm) silicon substrates. The nanostructured silicon surface morphologies were found to directly affect the LDI-MS signal ion intensity. By characterizing the nanostructured silicon surface roughness using atomic force microscopy (AFM) and sample absorption efficiency using fluorescence microscopy, it was further demonstrated that the nanostructured silicon surface roughness was highly correlated to the LDI-MS performance. 相似文献
112.
为了探索趋磁微生物体对水溶液中Ni2+的吸附机理,考察微观作用力对吸附过程的影响,本文通过酸碱滴定实验确定了趋磁微生物体具有吸附作用的表面功能基团,建立了由体内磁小体Fe3O4和表面功能基团-PO3H,-OH,-COOH构成的趋磁生物体模型,并通过分子动力学模拟方法从静电作用、分子间作用、热运动等方面研究了磁小体和功能基团对Ni2+的吸附过程的影响规律。模拟结果证明对Ni2+的吸附过程是基团的静电吸引力和范德华力相互作用的综合结果,不同基团的静电引力强弱是有区别的。模拟结果还表明,Ni2+对-PO3H的趋聚倾向最大,对-OH的趋聚倾向次之,而对-COOH和Fe3O4的趋聚作用较弱。采用化学修饰法分别掩蔽菌体表面基团,并做了吸附实验,吸附效果与模拟结果完全吻合。这些结论将对生物磁选的开发应用提供新的理论依据。 相似文献
113.
QIN GuoTing & CAI ChengZhi 《中国科学:化学》2010,(1)
Functionalization of silicon substrate surfaces with a stable monolayer for resisting non-specific adsorption of proteins has attracted great interest,since it is directly relevant to the development of miniature,silicon-based biosensors and implantable microdevices,such as silicon-neuron interfaces.This brief review summarizes our contribution to the development of robust monolayers grown by surface hydrosilylation on atomically flat,hydrogen-terminated silicon surfaces.The review also outlines our strateg... 相似文献
114.
The interaction between the cell adhesion molecule CD11b and its ligand ICAM-1 plays an important role in inflammatory responses in the disease of atherosclerosis. Atorvastatin is a commonly prescribed statin drug which has been considered as one of the most potent therapeutic agents for atherosclerosis due to its lipid-lowering effect. Recently, there is a growing body of evidence that atorvastatin has anti-inflammatory effect. We have applied the advanced method of live-cell single-molecule force spectros... 相似文献
115.
A hydrophilic interaction liquid chromatography (HILIC) method was developed to measure the composition of humic substances from river, reservoir, and treated wastewater based on their physicochemical properties. The current method fractionates the humic substances into four well-defined groups based on parallel analyses with a neutral and a cationic HILIC column, using mobile phases of varied compositions and pH. The results indicate that: (i) the proportion of carboxylic acids in the humic substances from terrestrial origins is less than half of that from treated wastewater (Jeddah, KSA), (ii) a higher content of basic compounds was observed in the humic substances from treated wastewater and Ribou Reservoir (Cholet, France) than in the sample from Loire River (France), (iii) a higher percentage of hydrophobic macromolecules were found in the humic substances from Loire River than in the other samples, and (iv) humic substances of treated wastewater contained less ionic neutral compounds (i.e., pKa 5–9) than the waters from terrestrial origins. The physicochemical property disparity amongst the compounds in each humic substances sample was also evaluated. The humic substances from the lightly humic Loire river displayed the highest disparity, whereas the highly humic Suwannee river (Georgia, USA) showed the most homogeneous humic substances. 相似文献
116.
Graphene field-effect transistors (GFET) have emerged as powerful detection platforms enabled by the advent of chemical vapor deposition (CVD) production of the unique atomically thin 2D material on a large scale. DNA aptamers, short target-specific oligonucleotides, are excellent sensor moieties for GFETs due to their strong affinity to graphene, relatively short chain-length, selectivity, and a high degree of analyte variability. However, the interaction between DNA and graphene is not fully understood, leading to questions about the structure of surface-bound DNA, including the morphology of DNA nanostructures and the nature of the electronic response seen from analyte binding. This review critically evaluates recent insights into the nature of the DNA graphene interaction and its affect on sensor viability for DNA, small molecules, and proteins with respect to previously established sensing methods. We first discuss the sorption of DNA to graphene to introduce the interactions and forces acting in DNA based GFET devices and how these forces can potentially affect the performance of increasingly popular DNA aptamers and even future DNA nanostructures as sensor substrates. Next, we discuss the novel use of GFETs to detect DNA and the underlying electronic phenomena that are typically used as benchmarks for characterizing the analyte response of these devices. Finally, we address the use of DNA aptamers to increase the selectivity of GFET sensors for small molecules and proteins and compare them with other, state of the art, detection methods. 相似文献
117.
微波辐射下秸秆纤维微观结构的变化 总被引:3,自引:0,他引:3
利用原子力显微镜(AFM)对微波处理前后秸秆纤维表面的变化进行了研究,并结合XRD和FTIR研究了处理前后其化学结构及结晶形态的变化情况。结果表明,未经微波处理的秸秆纤维表面比较光滑,平均粗糙度(Ra)为(86.7±6.335)nm,均方根粗糙度(Rq)为(141.1±9.055)nm;经微波处理的秸秆纤维表面比较粗糙,并出现许多细小孔洞,其Ra为(445.0±28.14)nm,Rq为(558.9±33.458)nm,微波辐射处理前后秸秆纤维的表面形态差异较大。经微波辐射处理后,秸秆纤维在2θ=22.3°处的衍射峰移至21.8°,且峰宽稍有增加,在38.1°、44.3°、64.6°、78.9°处出现的4个衍射峰,除强度稍有增强,其峰形和位置与未经处理秸秆纤维的衍射峰基本一致,表明微波处理没有改变纤维的结晶形态。FTIR光谱表明,微波处理样中未产生新的官能团,但分子间氢键及分子内氢键发生变化。微波作用未引起秸秆纤维化学结构的变化。 相似文献
118.
The aim of this work was to demonstrate the potential of a localized impedance measurement technique to identify and spatially localize the onset spots of polymeric coating degradation. The technique, which has not yet been applied in the field of organic coatings, utilizes atomic force microscopy (AFM) in contact mode. During the scan a single-frequency voltage perturbation signal is applied between the AFM tip and the coated metal substrate. A current response signal is registered. As a result an impedance map of the scanned region is created. The method was applied to investigation of acrylic coating degradation during exposure to UV radiation. Localized topography and impedance images revealed formation of micro-cracks in the coating layer, which gradually converted into through-the-coating defects with an increase in the irradiation time. Thus the method allowed early identification and localization of the sites of degradation onset, which was not possible using classical impedance measurement. 相似文献
119.
A need for rapid toxicity techniques has seen recent research into developing new microbiological assays and characterising their toxicity responses using a range of substances. A microbiological bioassay that determines changes in ferricyanide-mediated respiration for toxicity measurement (FM-TOX) shows particular promise. The development and optimisation of an improved FM-TOX method, incorporating novel features, is described using Escherichia coli as the biocatalyst. Omission of an exogenous carbon source, used in previously described FM-TOX assays, substantially improves the assay sensitivity. In addition, the development of a two-step procedure (toxicant exposure followed by determination of microbial respiratory activity) was found to enhance the inhibition of E. coli by 3,5-dichlorophenol and four other toxicants, compared to single-step procedures. Other assay parameters, such as the ferricyanide concentration, exposure times and optical density of the biocatalyst were also optimised, sometimes based on practical aspects. Toxicity tests were carried out using the adopted technique on both organic and inorganic toxicants, with classic sigmoid-shaped dose-response curves observed, as well as some non-standard responses. IC50 data is presented for a number of common toxicants. The optimised assay provides a good foundation for further toxicity testing using E. coli, as well as the potential for expanding the technique to utilise other bacteria with complementary toxicity responses, thereby allowing use of the assay in a range of applications. 相似文献
120.
P. Hazot J. P. Chapel C. Pichot A. Elaissari T. Delair 《Journal of polymer science. Part A, Polymer chemistry》2002,40(11):1808-1817
Monodisperse, thermosensitive poly(N‐ethyl methacrylamide) microgel particles were prepared by the batch precipitation/emulsion polymerization of water‐soluble N‐ethyl methacrylamide and the hydrophobic crosslinker ethylene glycol dimethacrylate initiated by potassium persulfate. Particular attention was paid to the effect of the crosslinker agent on the polymerization process (kinetics, conversion, and water‐soluble oligomer content). Particles were characterized in terms of their size distribution and swelling capacity. A polymerization mechanism for the water‐soluble monomer and non‐water‐soluble crosslinker is proposed and discussed on the basis of a combination of both emulsion and precipitation polymerization processes. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1808–1817, 2002 相似文献