全文获取类型
收费全文 | 983篇 |
免费 | 214篇 |
国内免费 | 27篇 |
专业分类
化学 | 164篇 |
晶体学 | 1篇 |
力学 | 23篇 |
综合类 | 59篇 |
数学 | 85篇 |
物理学 | 892篇 |
出版年
2024年 | 1篇 |
2023年 | 23篇 |
2022年 | 65篇 |
2021年 | 42篇 |
2020年 | 21篇 |
2019年 | 35篇 |
2018年 | 28篇 |
2017年 | 65篇 |
2016年 | 55篇 |
2015年 | 66篇 |
2014年 | 86篇 |
2013年 | 105篇 |
2012年 | 76篇 |
2011年 | 67篇 |
2010年 | 49篇 |
2009年 | 52篇 |
2008年 | 70篇 |
2007年 | 52篇 |
2006年 | 38篇 |
2005年 | 44篇 |
2004年 | 33篇 |
2003年 | 26篇 |
2002年 | 34篇 |
2001年 | 9篇 |
2000年 | 16篇 |
1999年 | 10篇 |
1998年 | 9篇 |
1997年 | 12篇 |
1996年 | 6篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1988年 | 5篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 3篇 |
1976年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有1224条查询结果,搜索用时 0 毫秒
991.
针对现有的家用心率监测仪器便携性差、报警功能不完善、成本高等问题,提出一种基于蓝牙4.0 BLE协议栈和GSM移动通信网络的新型无线心率监测仪设计方案。系统可分为主机和从机两部分。从机由光电式脉搏传感器和蓝牙模块组成,负责测量心率和电量,并将得到的数据实时无线发送给主机。主机由蓝牙模块、单片机、液晶屏和GSM模块组成,负责接收从机发送的信息,并对数据进行监视,同时完成人机交互。实验测试表明,系统可稳定实现心率测量、监视、显示及远程设置、查询和报警功能,与市场上同类产品相比,具有使用便携性好、功耗低、测量准确、多重报警方式及成本低等优点,在家用智能监护领域具有广泛的应用前景。 相似文献
992.
The structures of [M-H](-) ions generated from free fatty acids in resonant electron capture at energies of 1.2 and 7.2 eV were investigated using deuterium-labeled isotopomers and collision-induced dissociation. The [M-H](- small middle dot) ions occur in both a carboxylate anion and a carbanion form. While the formation of the carboxylate anion at 1.2 eV involves the loss of a carboxylic hydrogen, that at 7.2 eV involves the loss of a hydrogen from different positions in the aliphatic chain followed by a rearrangement of a carboxylic hydrogen on to the radical site in the chain. The [M-H-H(2)O](-) ion which is a minor ion in the resonant electron capture spectrum at 7.2 eV is shown to be a precursor for the charge-remote fragment ions corresponding to formal losses of a hydrogen and elements of alkanes. The [M-H-H(2)O](-) ion corresponding to the second major ion in the resonant electron capture spectrum at 7.2 eV is demonstrated to be consistent with a cyclopentanone anion structure. On the basis of new insights obtained in the present study and taking into account previous results, an updated proposal is presented for the mechanism of charge-remote fragmentation which operates in resonant electron capture of free fatty acids at 7.2 eV. 相似文献
993.
994.
V. E. Plyuta V. A. Zaitseva L. P. Lovchikova E. K. Naumenko S. V. Nikonenko 《Journal of Applied Spectroscopy》1997,64(5):706-713
We describe investigations carried out by means of a SKIF spectrometer from the orbital stations “Salyut-7” and “Mir”, as
well as from aircraft carriers. We present basic technological characteristics of the device, describe the details of the
construction and the application procedures. The spectral characteristics of underlying surfaces are generalized in the form
of a catalogue and atlas of spectra with geographic, meteorological, time, and subject allocation. We give samples of the
presentation of materials in the catalogue and atlas, as well as summary tables of the data that characterize the place, time,
and other conditions of the experiments. The results of the application of the device for detecting narcotic-containing crops
from aircrafts and space vehicles are described.
Research and development in the field of aerospace instrument manufacture and remote spectrophotometry of the earth surface
were initiated at the Institute of Physics of the Academy of Sciences of Belarus by L. I. Kisilevskii and at first were conducted
under his leadership.
B. I. Stepanov Institite of Physics, Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated
from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 5, pp. 691–697, September–October, 1997. 相似文献
995.
Abstract Fixed access networks widely employ fiber-optical techniques due to the extremely wide bandwidth offered to subscribers. In the last decade, there has also been an enormous increase of user data visible in mobile systems. The importance of fiber-optical techniques within the fixed transmission/transport networks of mobile systems is therefore inevitably increasing. This article summarizes a few reasons and gives examples why and how fiber-optic techniques are employed efficiently in second-generation networks. 相似文献
996.
We present a protocol for probabilistic remote preparation of a four-particle entangled W state.The quantum channel is composed of two partial entangled four-particle cluster states.We calculate the total successful probability and total classical communication cost required for the general case and for all kinds of the special cases,respectively.It is shown that for two maximally entangled four-particle cluster states,such a scheme for the general case has the total successful probability of 25%and only consumes the total classical communication of 1 bit,while this scheme for the special cases under certain conditions can possess successful probability of 50%or 100%,the required classical communication will only be 2 bits or 4 bits.Meantime,we give in detail all unitary transformations for the general case and for all kinds of the special cases,respectively. 相似文献
997.
Alkyl carboxylic acid-based nanostructured solvents, synthesized in mixtures of tetrahydrofuran (THF) and water through self-assembly and coacervation, were proved to behave as restricted access liquids. Both physical and chemical mechanisms were found responsible for exclusion of macromolecules such as proteins and polysaccharides. The potential of these solvents for extracting small molecules from complex solid samples, without interference from large biomolecules, was here evaluated. For this purpose, they were applied to the extraction of 14 priority polycyclic aromatic hydrocarbons (PAHs) from mosses prior to their separation by liquid chromatography and fluorescence detection (LC-FLD). Sample treatment involved the vortex shaking of 200 mg of moss with 200 μL of decanoic acid-based solvent for 5 min, subsequent centrifugation for 8 min and analysis of the extract by LC-FLD using external calibration. Proteins precipitated during extraction because of both the decrease of the dielectric constant of the solution caused by THF and the formation of macromolecular complexes with decanoic acid. Polysaccharides were not solubilized in the aqueous cavities of the solvent because of their size exclusion. In-house method validation was performed according to the recommendations of the European Commission Decision 202/657/EC. Method detection and quantification limits for the different PAHs were in the ranges 0.04–0.24 and 0.14–0.80 μg kg−1, respectively. The method was applied to the determination of different moss species collected in both polluted and unpolluted sites in the South of Spain. Recoveries were within the range 71–110%. The results obtained show that solvents with restricted access properties have the potential to expand the scope of application of restricted access materials to areas other than biological fluids because of their suitability to combine analyte isolation and sample cleanup of solid samples in a single step. 相似文献
998.
Kenneth B. Gagnon Sally Caine Nazanin Samadi Mercedes Martinson Melanie van der Loop Jane Alcorn L. Dean Chapman George Belev Helen Nichol 《Journal of synchrotron radiation》2015,22(5):1297-1300
High‐resolution computed tomography (CT) imaging of a live animal within a lead‐lined synchrotron light hutch presents several unique challenges. In order to confirm that the animal is under a stable plane of anaesthesia, several physiological parameters (e.g. heart rate, arterial oxygen saturation, core body temperature and respiratory rate) must be remotely monitored from outside the imaging hutch. In addition, to properly scan the thoracic region using CT, the animal needs to be held in a vertical position perpendicular to the fixed angle of the X‐ray beam and free to rotate 180°–360°. A new X‐ray transparent mouse restraint designed and fabricated using computer‐aided design software and three‐dimensional rapid prototype printing has been successfully tested at the Biomedical Imaging and Therapy bending‐magnet (BMIT‐BM) beamline at the Canadian Light Source. 相似文献
999.
Forming‐free resistive switching characteristics and improved reliability in sub‐stoichiometric NbNx films 下载免费PDF全文
In this study, we demonstrate forming‐free and reliable resistive switching (RS) characteristics by controlling the stoichiometry of niobium nitride (NbNx) films. Compared to a perfect stoichiometric NbNx film, a decrease of 6% nitrogen content and an increase of 5% O2 content are found in the sub‐stoichiometric NbNx sample (s‐NbNx), and a structural change for the s‐NbNx film is observed from X‐ray diffraction results, which results in the possibility of abundant defect generation in the s‐NbNx film at virgin state. In the RS test, the s‐NbNx film normally carries out well without initial forming because of the already‐formed conducting filaments; in particular, in the reliability study, the s‐NbNx film shows more stable dc cycling characteristics for 1000 cycles without any degradation and smaller variations in the operating current and voltage characteristics. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
1000.
以磁性二氧化硅(Fe2O3@SiO2)为基质,利用表面原子转移自由基聚合技术(SI-ATRP),在改性后的Fe2O3@SiO2内表面接枝甲基丙烯酸十八烷基酯(SMA)、外表面接枝甲基丙烯酸缩甘油酯(GMA),酸解后得到磁性反相限进材料Fe2O3@SiO2-SMA-GMMA,并通过扫描电镜(SEM)、X射线衍射(XRD)、透射电镜(TEM)、振动样品磁强计(VSM)和元素分析对其进行表征。研究表明,Fe2O3@SiO2-SMA-GMMA对牛血清白蛋白(BSA)的排阻能力为90.4%;对磺胺异恶唑(SIZ)、磺胺二甲氧基嘧啶(SDM)、甲氧苄啶(TMP)和磺胺甲基嘧啶(SMR)的最大吸附量分别为2.76、2.24、1.51和1.34 mg/g。Fe2O3@SiO2-SMA-GMMA应用于牛奶和牛血清样品中SIZ、SMR和SDM的分离富集,SIZ、SMR和SDM的加标回收率为88.7%~90.8%,相对标准偏差为3.3%~5.3%。磁性反相限进材料可简化生物基质样品的前处理过程,对血液样品或食品样品等领域的分析检测具有重要价值。 相似文献