全文获取类型
收费全文 | 1125篇 |
免费 | 136篇 |
国内免费 | 57篇 |
专业分类
化学 | 436篇 |
晶体学 | 17篇 |
力学 | 50篇 |
综合类 | 22篇 |
数学 | 116篇 |
物理学 | 677篇 |
出版年
2024年 | 4篇 |
2023年 | 13篇 |
2022年 | 23篇 |
2021年 | 29篇 |
2020年 | 43篇 |
2019年 | 57篇 |
2018年 | 29篇 |
2017年 | 54篇 |
2016年 | 46篇 |
2015年 | 57篇 |
2014年 | 76篇 |
2013年 | 114篇 |
2012年 | 51篇 |
2011年 | 48篇 |
2010年 | 42篇 |
2009年 | 57篇 |
2008年 | 68篇 |
2007年 | 69篇 |
2006年 | 73篇 |
2005年 | 49篇 |
2004年 | 37篇 |
2003年 | 46篇 |
2002年 | 39篇 |
2001年 | 23篇 |
2000年 | 27篇 |
1999年 | 24篇 |
1998年 | 21篇 |
1997年 | 13篇 |
1996年 | 26篇 |
1995年 | 15篇 |
1994年 | 8篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1991年 | 5篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1975年 | 1篇 |
排序方式: 共有1318条查询结果,搜索用时 46 毫秒
181.
182.
设计了一套结合鱼眼摄像头和头戴显示器的新型全景显示系统。采用鱼眼正交投影法建立合适的数学模型,基于该数学模型合理展开虚拟半球的UV,将鱼眼图像映射到虚拟半球上,同时使用双目虚拟摄像头采集已经矫正畸变的图像,并将其显示在头戴显示器中,达到头戴显示器全景显示的效果。通过实际测试验证了该方案的可行性。 相似文献
183.
为实现大型物理实验现场复杂多样的仪器控制,分析了物理实验的特点、过程、环境及仪器控制功能需求,利用虚拟仪器技术、计算机网络技术和数据库技术,建立了一套集成硬件和软件的综合控制管理信息系统,实现记录系统中示波器状态远程批量设置及波形数据自动采集、控制探测系统的高压电源并发加压或退压、保障各测试项目间测试仪器之间时间关联、监控UPS电量和远端现场图片或视频状态。给出了系统的关键的设计思路,列举了某型示波器控制的通用控制代码。结果表明,系统达到了一人总控或多人分权控制实验过程中多种多台仪器的目标,方便快捷地实现不同品牌不同类型示波器的相同功能。 相似文献
184.
We have developed a novel large-scale multicapillary fluorescent differential display (FDD) platform amenable to further automation. The power of the method is demonstrated by the analysis of T helper cell differentiation. Eight RNA samples from wild type, Stat4 knockout and Stat6 knockout mice were analyzed with 16 anchoring primers and 24 arbitrary primers, resulting in 285 294 sample peaks. Visually selected patterns of differential expression suggest two major regulatory mechanisms: activation and Stat4 genotype. A subset of the findings is reproduced in the confirmatory differential display (DD) that included technical and biological replicates. In a small fragment identification pilot study, we identify Ifi27 and Cct8 to be up-regulated by T cell activation. We present a method for the analysis of electropherogram similarity across large datasets, based on correlation of low-resolution representations of electrophoretic data. We show how it can be applied to analyze experimental and technical variables. Using this method, we demonstrate the effect of activation and genotype. In addition, agreement of our real experimental data to the theoretical basis of DD, as well as issues in anchoring primer selectivity, are studied. 相似文献
185.
Ammonium is a toxic waste product that has been reported to negatively inhibit cell growth and recombinant glycosylation in
Chinese hamster ovary (CHO) cells; however, the effect of this toxicity on intracellular gene expression has received only
limited investigation. We used a differential display method to identify genes in CHO cells that were affected by ammonium
stress. Eight genes whose mRNA levels significantly changed in response to elevated ammonium were isolated and identified.
Five of the genes were identified as having lower expression under the ammonium stress, whereas three genes were identified
as having higher expression. Sequence homology with other mammalian organisms was used to attribute function to these newly
identified genes. The identified ammonium-sensitive genes were grouped into three broad functional groups: cellular processes,
energy metabolism, and genetic-information processing. The three cellular process-related genes had lower expression (anaphase-promoting
complex subunit 5, eukaryotic initiation factor 5A II, KIAA1091 protein). The two energy-related genes had higher expression
under ammonium stress (adenosine triphosphate synthase subunit C and mitofusin 1). Both of the genetic information-processing
genes (endoplasmic reticulum [ER]-resident protein ERdj5 and structure-specific recognition protein 1) had lower expression
under the ammonium stress, whereas the 26S proteasome subunit adenosine triphosphatase 3 gene had higher expression. These
preliminary results indicate that ammonium stress lowers expression of genes controlling cell cycle, protein folding, and
quality and raises genes that control energy metabolism and degradation. Our findings demonstrate the usefulness of mRNA differential-display
techniques for the detection of CHO cell genes affected by ammonium stress. 相似文献
186.
CdII complexes with glycine (gly) and sarcosine (sar) were studied by glass electrode potentiometry, direct current polarography, virtual potentiometry, and molecular modelling. The electrochemically reversible CdII–glycine–OH labile system was best described by a model consisting of M(HL), ML, ML2, ML3, ML(OH) and ML2(OH) (M = CdII, L = gly) with the overall stability constants, as log β, determined to be 10.30 ± 0.05, 4.21 ± 0.03, 7.30 ± 0.05, 9.84 ± 0.04, 8.9 ± 0.1, and 10.75 ± 0.10, respectively. In case of the electrochemically quasi-reversible CdII–sarcosine–OH labile system, only ML, ML2 and ML3 (M = CdII, L = sar) were found and their stability constants, as log β, were determined to be 3.80 ± 0.03, 6.91 ± 0.07, and 8.9 ± 0.4, respectively. Stability constants for the ML complexes, the prime focus of this work, were thus established with an uncertainty smaller than 0.05 log units. The observed departure from electrochemical reversibility for the Cd–sarcosine–OH system was attributed mainly to the decrease in the transfer coefficient . The MM2 force field, supplemented by additional parameters, reproduced the reported crystal structures of diaqua-bis(glycinato-O,N)nickel(II) and fac-tri(glycinato)-nickelate(II) very well. These parameters were used to predict structures of all possible isomers of (i) [Ni(H2O)4(gly)]+ and [Ni(H2O)4(sar)]+; and (ii) [Ni(H2O)3(IDA)] and [Ni(H2O)3(MIDA)] (IDA = iminodiacetic acid, MIDA = N-methyl iminodiacetic acid) by molecular mechanics/simulated annealing methods. The change in strain energy, ΔUstr, that accompanies the substitution of one ligand by another (ML + L′ → ML′ + L), was computed and a strain energy ΔUstr = +0.28 kcal mol−1 for the reaction [Ni(H2O)4(gly)]+ + sar → [Ni(H2O)4(sar)]+ + gly was found. This predicts the monoglycine complex to be marginally more stable. By contrast, for the reaction [Ni(H2O)3IDA] + MIDA → [Ni(H2O)3MIDA] + IDA, ΔUstr = −0.64 kcal mol−1, and the monoMIDA complex is predicted to be more stable. This correlates well with (i) stability constants for Cd–gly and Cd–sar reported here; and (ii) known stability constants of ML complex for glycine, sarcosine, IDA, and MIDA. 相似文献
187.
188.
本文通过对外电极气体放电物理过程的计算机模拟,研究了一些主要电学参量(包括电源电压、外电路阻抗、介质层电容和介质层上的壁电荷等)对放电过程的影响.文中给出了关于放电电流、辐射亮度和电功损耗等项放电特性随外电路阻抗变化的一维数值分析实例. 相似文献
189.
190.
Radosaw W. Piast Rafa M. Wieczorek Nicola Marzec Maciej Garstka Aleksandra Misicka 《Molecules (Basel, Switzerland)》2021,26(19)
Chondrocalcinosis is a metabolic disease caused by the presence of calcium pyrophosphate dihydrate crystals in the synovial fluid. The goal of our endeavor was to find out whether short peptides could be used as a dissolving factor for such crystals. In order to identify peptides able to dissolve crystals of calcium pyrophosphate, we screened through a random library of peptides using a phage display. The first screening was designed to select phages able to bind the acidic part of alendronic acid (pyrophosphate analog). The second was a catalytic assay in the presence of crystals. The best-performing peptides were subsequently chemically synthesized and rechecked for catalytic properties. One peptide, named R25, turned out to possess some hydrolytic activity toward crystals. Its catalysis is Mg2+-dependent and also works against soluble species of pyrophosphate. 相似文献