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   700篇
  免费   17篇
  国内免费   5篇
化学   378篇
晶体学   7篇
力学   42篇
数学   137篇
物理学   158篇
  2023年   5篇
  2022年   21篇
  2021年   16篇
  2020年   25篇
  2019年   20篇
  2018年   27篇
  2017年   18篇
  2016年   30篇
  2015年   17篇
  2014年   20篇
  2013年   62篇
  2012年   44篇
  2011年   46篇
  2010年   31篇
  2009年   31篇
  2008年   30篇
  2007年   23篇
  2006年   24篇
  2005年   18篇
  2004年   22篇
  2003年   17篇
  2002年   9篇
  2001年   12篇
  2000年   6篇
  1999年   12篇
  1998年   5篇
  1997年   7篇
  1996年   2篇
  1995年   5篇
  1994年   12篇
  1993年   9篇
  1992年   8篇
  1991年   8篇
  1990年   8篇
  1989年   9篇
  1988年   9篇
  1987年   9篇
  1986年   2篇
  1985年   5篇
  1984年   2篇
  1983年   6篇
  1982年   5篇
  1981年   2篇
  1980年   3篇
  1976年   2篇
  1975年   3篇
  1974年   3篇
  1967年   2篇
  1956年   2篇
  1955年   2篇
排序方式: 共有722条查询结果,搜索用时 15 毫秒
1.
We consider the rate of convergence for a class of perturbed hemivariational inequalities in reflexive Banach Spaces. Our results can be viewed as an extension and refinement of some previous known results in this area.  相似文献   
2.
3.
Dendritic cellls (DCs) comprise an essential component of the immune system. These cells, as antigen presenting cells (APCs) to na?ve T cells, are crucial in the initiation of antigen specific immune responses. In the past years, several DC subsets have been identified in different organs which exert different effects in order to elicit adaptive immune responses. Thus, identification of such DC subsets has led to a better understanding of their distribution and function in the body. In this review, several key properties of the immunobiology, immunopathogenesis and vaccine strategies using DCs will be discussed.  相似文献   
4.
Polystyrenes with different concentrations of side groups with cyano groups were prepared and complex dielectric constants were measured in the range of the glass transition temperature and the frequency range of 10–2–107 Hz.The GPC and DSC measurements showed that the molecular weight of these polystyrenes was about 10500 g/mole and the glass transition temperatures were 89.5°C for all samples.The dielectric relaxation spectra obtained for the side group polystyrene labels and also the chain-end polystyrene labels prepared before [9] were analyzed to find out the degree of coupling of the chain-end and side-group labels with the cooperative reorientation of the polymeric matrix. The analysis of the spectra was carried out using the analysis method developed by Mansour and Stoll [6].The results obtained showed that both end- and side-group labels are strongly coupled with the segmental reorientation and relax with relaxation times longer than that of the segments.The value of logf m = (logf m(label)) – logf m(matrix)) was obtained from the recently designed comparison diagram suggested by Mansour and Stoll [6, 14]. The value of logf m depends on the label length in the case of chain-end labels.It was surprising to find that the side groups relax slower than the segments by only 0.9 decades. These results obtained implied that the label relaxes through a multistep relaxation mechanism of the side and end groups and not through a diffusion mechanism of the whole chain. In addition, the effective lengths of the relaxing units were determined using the empirical equation obtained before in the case of rodlike molecules in polyisoprene [7].  相似文献   
5.
6.
Summary The electrochemical behaviour of pure indium in KOH solutions (1–4M) was studied at different temperatures (25–70°C) by potentiostatic techniques. Two anodic peaks corresponding to the formation of In(OH)3 and In2O3 were observed. The heights of the two peaks increased with the increase of alkali concentration. An increase of temperature increased the peak currents and shifted their corresponding potentials to more negative values. The variation of the peak currents and peak potentials with scan rate suggested that the anodic dissolution of indium was a diffusion controlled process. In cyclic voltammetry, the reverse scan consistently showed one peak which was attributed to the reduction of anodic oxidation products into indium. X-ray diffraction analysis confirmed the presence of In(OH)3 at the first anodic peak, In(OH)3 and In2O3 at the second anodic peak and In2O3 in the permanent passive region.
Zum elektrochemischen Verhalten einer Indium-Elektrode in konzentrierter Kalilauge bei verschiedenen Temperaturen
Zusammenfassung Es wurde das Verhalten von reinem Indium in 1 – 4M KOH-Lösungen bei Temperaturen zwischen 25 und 70°C mittels potentiostatischer Methoden untersucht. Zwei anodische Peaks, entsprechend der Bildung von In(OH)3 und In2O3, traten auf. Die Höhe der beiden Peaks wurde mit zunehmender Alkalikonzentration gesteigert. Eine Temperaturerhöhung verstärkte die Peakströme und verschob die entsprechenden Potentiale zu negativeren Werten. Die Abhängigkeit der Peakströme und Peakpotentiale von der Scangeschwindigkeit legte den Schluß nahe, daß die anodische Lösung von Indium in einem diffusionskontrollierten Prozeß stattfindet. Bei der cyclischen Voltammetrie zeigte der reverse Scan einheitlich einen Peak, der der Reduktion der anodischen Oxidationsprodukte zu Indium zugeschrieben wurde. Röntgendiffraktionsanalyse bestätigte die Präsenz von In(OH)3 beim ersten anodischen Peak, In(OH)3 beim zweiten Peak und In2O3 im permanent passiven Bereich.
  相似文献   
7.
8.
In recent decades, the use of herbs and plants has been of great interest, as they have been the sources of natural products, commonly named as bioactive compounds. In specific, the natural compounds from the Capparaceae family which has been proved to have antioxidant, anti-inflammatory, antimicrobial and anti-carcinogenic activities, by several studies. Cleome arabica L. (CA) specie is the most used medicinal plants in Tunisia and elsewhere in North African countries for treatment of various diseases including diabetes, rheumatism, inflammation, cancer, and digestive disorders. The current work was undertaken to estimate the total phenolic, flavonoid and condensed tannin contents, to identify and quantify the polyphenolic compounds, and to evaluate the antioxidant and the anti-inflammatory proprieties of CA fruits extract against formalin induced chronic inflammation in Female Wistar rats. In fact, the antioxidant activity was tested by Diphenyl-1-Picrylhydrazyl free radical scavenging (DPPH), Ferric reducing antioxidant power (FRAP) and Nitric Oxide radical (NO·). Anti-inflammatory effect of fruits extract was examined using formalin (2%) induced paw edema in rats. Molecular docking tools were used to investigate the interaction of some compounds from CA fruits extract with the cyclooxygenase-2 (COX-2) target protein. Our results showed that, the total phenolic, flavonoid and tannins contents, which were assessed by the Folin-Ciocalteu, Quercetin, and Catechin methods, respectively, were 230.22 mg gallic acid equivalent/g dry weight (mg GAE/g DW), 55.08 mg quercetin equivalent/g dry weight (QE/g DW) and 15.17 mg catechin equivalents/g dry weight (CatE/g DW), respectively. HPLC analysis revealed the presence of five polyphenolic compounds whose catechin was found to be the most abundant compounds. The antioxidant activity of extract was quantified by DPPH, FRAP and NO· tests and IC50 reached the values of 3.346 mg/mL, 2.306 and 0.023 mg/mL, respectively. Cleome fruits ameliorated the histological integrity of the skin and alleviated the disruptions in hematological parameters (WBC, LYM, RBC, and HGB), inflammatory cytokines (IL-1β, IL-6, TNF-α), C-reactive protein, and some oxidative stress markers (TBARS (−49%) and AOPP (−42%) levels, SOD (+33%) and GPx (+75%) activities, and GSH (+49%) content) induced by formalin injection. Moreover, the in-silico investigation had shown that CA fruits extract compounds have a stronger interaction with COX-2 active site, more than the reference drug “indomethacin” (two H-bonds). Our research gives pharmacological backing to the healthcare utilization of Cleome plant in the treatment of inflammatory diseases and oxidative harm.  相似文献   
9.
Herein, we describe an isothermal proximity CRISPR Cas12a assay that harnesses the target-induced indiscrimitive single-stranded DNase activity of Cas12a for the quantitative profiling of gene expression at the mRNA level and detection of proteins with high sensitivity and specificity. The target recognition is achieved through proximity binding rather than recognition by CRISPR RNA (crRNA), which allows for flexible assay design. A binding-induced primer extension reaction is used to generate a predesigned CRISPR-targetable sequence as a barcode for further signal amplification. Through this dual amplification protocol, we were able to detect as low as 1 fM target nucleic acid and 100 fM target protein isothermally. The practical applicability of this assay was successfully demonstrated for the temporal profiling of interleukin-6 gene expression during allergen-mediated mast cell activation.

Herein, we develop an isothermal proximity CRISPR Cas12a assay that harnesses the target-induced collateral cleavage activity of Cas12a for the quantitative profiling of gene expression and detection of proteins with high sensitivity and specificity.  相似文献   
10.
Some physical properties (such as lattice parameter, density and porosity) and magnetic properties of the system Mg1‐xZnxFe2O4; where x=0,0.1,0.2,0.3,0.4,0.5and 0.6 have been studied. It was found that the lattice parameter increases with increasing the zinc concentration. The composition dependence of the physical properties is divided into two regions. The first one is for x ≤ 0.3 and the second one is for x > 0.3. From the magnetization measurements, the basic composition (MgFe2O4) shows the lowest magnetization, while the composition of x=0.4 shows the highest one. The behaviour of magnetization M versus composition shows also two regions for x <>0.3. The behaviour of M versus x was discussed in the bases of cation distribution. From the B‐H loops, the remanence induction Br, saturation induction Bs and the coercive force Hc were determined and studied with x. The Curie temperature TC was determined from the measurements of the initial permeability μi versus temperature. It was found TC decreases with increasing Zn‐content. Also paramagnetic temperature TP was determined from the behaviour of MS vs. T. In general it was found TP > TC by about 7‐10 K.  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