全文获取类型
收费全文 | 4801篇 |
免费 | 338篇 |
国内免费 | 370篇 |
专业分类
化学 | 2311篇 |
晶体学 | 22篇 |
力学 | 141篇 |
综合类 | 26篇 |
数学 | 1589篇 |
物理学 | 1420篇 |
出版年
2024年 | 12篇 |
2023年 | 55篇 |
2022年 | 147篇 |
2021年 | 173篇 |
2020年 | 191篇 |
2019年 | 181篇 |
2018年 | 150篇 |
2017年 | 134篇 |
2016年 | 155篇 |
2015年 | 155篇 |
2014年 | 266篇 |
2013年 | 416篇 |
2012年 | 227篇 |
2011年 | 260篇 |
2010年 | 231篇 |
2009年 | 286篇 |
2008年 | 322篇 |
2007年 | 307篇 |
2006年 | 224篇 |
2005年 | 187篇 |
2004年 | 186篇 |
2003年 | 175篇 |
2002年 | 127篇 |
2001年 | 86篇 |
2000年 | 91篇 |
1999年 | 77篇 |
1998年 | 82篇 |
1997年 | 68篇 |
1996年 | 85篇 |
1995年 | 59篇 |
1994年 | 45篇 |
1993年 | 37篇 |
1992年 | 37篇 |
1991年 | 29篇 |
1990年 | 21篇 |
1989年 | 35篇 |
1988年 | 30篇 |
1987年 | 16篇 |
1986年 | 17篇 |
1985年 | 15篇 |
1984年 | 20篇 |
1983年 | 10篇 |
1982年 | 15篇 |
1981年 | 12篇 |
1980年 | 9篇 |
1979年 | 11篇 |
1978年 | 9篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1974年 | 4篇 |
排序方式: 共有5509条查询结果,搜索用时 15 毫秒
131.
132.
133.
The human leukocyte antigen class II (HLA II) molecules are implicated in the immunopathogenesis of allergic rhinitis (AR). The HLA II contains three allelic isotypes HLA-DR, -DQ, and -QP that exhibit considerably different susceptibility to AR. Here, we investigated the structural basis and energetic landscape of the susceptibility difference between the three HLA II isotypes to AR by combining computational analysis and experimental assay. Multiple sequence alignment revealed a low conservation among the three subtypes with sequence identity of ∼10% between them, suggesting that the peptide repertoires presented by HLA-DR, -DP and -DQ are not overlapped to each other, and they may be involved in different immune functions and dysfunctions. Structural analysis imparted that the antigenic peptides are rooted on the peptide-binding groove of HLA molecules and hold in a PPII-like helical conformation. Subsequently, the interaction behavior of 17 AR allergen-derived peptides with HLA-DR, −DP and −DQ was investigated using a statistics-based quantitative structure-activity relationship (QSAR) predictor. It was found a significant difference between the binding capabilities of these antigenic peptides to HLA-DR and to HLA-DP/-DQ; the former showed a generally higher affinity than the latter with p-value of 0.02 obtained from 2-tailed Student’s t-test. The computational findings were then confirmed by HLA II–peptide stability assay, which demonstrated that the AR allergen-derived peptides have a high in vitro selectivity for HLA-DR over HLA-DP/-DQ. Thus, the HLA-DR isotype, rather than HLA-DP and −DQ, is expected to associate with the pathological process of AR. 相似文献
134.
设计了一个针对高年级本科生的毛细管电泳分离实验,用以研究pH对生物小分子多肽分离的影响。5种多肽包括Bradykinin、[Hyp3]-bradykinin、Angiotensin I、Leucine Enkephalin和[Met5]-Enkaphalin,被用于毛细管电泳的分离实验。研究了毛细管电泳生物分析实验中最重要的2个因素即电渗流和样品吸附随pH的变化以及对于分离的影响。在pH=10的条件下,酸性多肽几乎没有吸附,少量的碱性多肽有吸附。在pH=6的条件下,碱性多肽具有非常强的吸附从而导致非常差的分离效果,在pH=2.3的条件下,5种多肽都能被很好地分离,由于多肽此时都带有正电荷因此几乎没有吸附。而在此pH,电渗流消失。对具有一定分析化学基础理论知识的学生而言,这是一个非常好的生物分析实验,有助于学生充分理解相关环境因素对仪器分析的重要影响。 相似文献
135.
136.
137.
Investigation on the stress behavior of cellulose acetate and the development of highly moisture‐resistant optical films for display devices
下载免费PDF全文
![点击此处可从《Journal of Polymer Science.Polymer Physics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Min Sang Park Seokwon Jung So Jeong Heo Seung Geol Lee 《Journal of Polymer Science.Polymer Physics》2017,55(19):1470-1479
An optical film with high optical anisotropy was prepared by the stretching of a cellulose acetate film and the consequential orienting of a retardation‐enhancing additive. The change in retardation in response to moisture absorption was explored and it was found that the degree of the retardation variation is strongly related to the stretching temperature. Stress generated by the stretching and its relaxation was systematically investigated to elucidate the effect of stretching temperature on the irreversible change in retardation upon moisture absorption. The results show that the magnitude of releasable stress plays an important role in controlling changes in optical properties. In addition, the difference in the deformation behavior between glassy and rubbery states should be taken into account in the development of a moisture‐resistant optical film. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1470–1478 相似文献
138.
Jürg Nussberger Dorette B. Brunner Bernard Waeber Hans R. Brunner 《International journal of environmental analytical chemistry》2013,93(1-3):257-268
Abstract Angiotensin-(1–8)octapeptide (angiotensin II) is the active principle of the reninangiotensin system. Crossreaction of angiotensin II-antisera with inactive precursors and metabolic fragments prevented the specific quantitation of this hormone in biological fluids. Peptide-extraction on bonded-phase silica followed by peptide-separation using isocratic reverse-phase high performance liquid chromatography and subsequent radioimmunoassay rendered possible the octapeptide-specific measurement of angiotensin II in 2 ml plasma with a detection limit of 0.4fmol/ml. The coefficient of variation for intra-assay precision was 0.06 and for inter-assay precision 0.13. 125Iangiotensin II was recovered from plasma by solid-phase extraction to 99±2% (mean ± S.D.). The overall recovery of 5, 10 and 20 fmol unlabeled angiotensin II added to plasma was 80±10%. Plasma concentrations in supine normal humans averaged 4.1 ± 1.6 fmol/ml and were suppressed below the detection limit by angiotensin I converting enzyme inhibition. 相似文献
139.
An in situ self-assembled molecular layer of 1-pyrenesulfonic acid sodium salt as an alignment agent was formed on indium tin oxide substrates for vertically aligning liquid crystals (LCs). The thus-aligned LCs exhibited uniform vertical alignment under crossed polarisers. The electro-optical characteristic of the LC cell fabricated using this method exhibited better performance than those of conventional LC cells with a polyimide alignment layer. Because the proposed alignment method is a simple one and involves low concentrations of the alignment agent (0.05 wt%), it is highly cost-effective. Further, the pyrene derivative, when mixed with LCs, exhibited photoluminescence (PL) under ultraviolet light. Given that the proposed method resulted in highly vertically aligned LCs and the alignment agent exhibited PL, the method should find wide use in the fabrication of colour-filter-free LC displays. 相似文献
140.
A new asymmetric integral imaging (AII) system for real-time pickup and three-dimensional (3-D) display of far outdoor scenes based on dynamic-pixel-mapping (DPM) is proposed. DPM is a digital process to transform the elemental images captured with a lens array into the perspective-variant object images (POIs) whose structures are matched with those of display lenses, where the orders of pixels in each POI are reversely mapped, and then capture a set of virtual elemental images (EIs) at the specific depth planes from the back-propagated POIs. This DPM enables an asymmetrical use of pickup and display lens arrays, allowing the long-ranged pickup of far outdoor scenes and their resolution-enhanced 3-D reconstruction. Experiments with a pair of pickup and display lens arrays whose pitches and focal lengths are given by 7.5 mm, 30 mm and 1.2 mm, 8 mm, respectively, show that the effective pickup-range and resolution of the proposed system have been increased up to 6 m and 1600×1600 pixels, respectively, from 0.064 m and 480×480 pixels of the conventional systems employing the same pickup and display lens arrays. In addition, experiments with an implemented test bed confirms that the proposed system can provide real-time 3-D images in 25 frames per second. 相似文献