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   529篇
  免费   31篇
化学   368篇
晶体学   5篇
力学   22篇
数学   40篇
物理学   97篇
无线电   28篇
  2024年   2篇
  2023年   12篇
  2022年   12篇
  2021年   20篇
  2020年   18篇
  2019年   21篇
  2018年   14篇
  2017年   13篇
  2016年   24篇
  2015年   16篇
  2014年   19篇
  2013年   18篇
  2012年   31篇
  2011年   47篇
  2010年   33篇
  2009年   20篇
  2008年   39篇
  2007年   31篇
  2006年   26篇
  2005年   35篇
  2004年   24篇
  2003年   8篇
  2002年   7篇
  2000年   9篇
  1998年   5篇
  1997年   4篇
  1996年   2篇
  1995年   3篇
  1994年   7篇
  1992年   3篇
  1991年   2篇
  1990年   2篇
  1989年   4篇
  1988年   2篇
  1985年   2篇
  1982年   1篇
  1980年   4篇
  1979年   1篇
  1978年   1篇
  1977年   1篇
  1975年   1篇
  1974年   2篇
  1973年   1篇
  1971年   1篇
  1970年   1篇
  1968年   1篇
  1966年   1篇
  1963年   1篇
  1960年   1篇
  1912年   1篇
排序方式: 共有560条查询结果,搜索用时 31 毫秒
101.
A bridged high-spin complex,bis-[Ni(II)(rac-5,5,7,l2,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane)]-2,5-pyridinedicarboxylate diperchlorate monohydrate has been obtained by reaction of [Ni(II)(rac-5,5,7, 12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane)](ClO4)2 and 2,5-pyridinedicarboxylic acid in aqueousalkaline (NH4OH) medium. C39H77Cl2N9Ni2O13, chemical formula weight 1068.42, orthorhombic, P212121, a = 11 .423(3) Å,b = 14.770(6) Å, c = 31.608(7) Å, = = =90.00°, V = 5333(3) Å3, Z = 4, Dcalc = 1.331 g cm-3, calc = 0.869 mm-1, F(000) = 2272, T = 293(2), R = 0.0870 for 2686 observed reflections [I > 2(I)]. The complexincludes two folded [Ni(rac- Me6[14]aneN4)]2+ units havingopposite diastereomeric configuration. They are bridged through a dianion of2,5-pyridinedicarboxylic acid, with one Ni-atom coordinated to the O-atom ofthe 2-carboxylic group and the pyridine N-atom (forming a 5-membered chelatering), and with the second Ni-atom coordinated to both O-atoms of the 5-carboxylic group (forming a 4-membered chelate ring). Hydrogen bonding involving macrocyclic NH groups, both 2- and 5-carboxylic groups, perchlorate anions and water molecules gives rise to the formation of an infinite supramolecular network in the title compound's crystals.  相似文献   
102.
Locally oxidized patterns on flat poly(dimethylsiloxane) stamps for microcontact printing were used as a platform for the transfer of a hydrophilic fluorescent ink to a glass substrate. The contrast was found to be limited. These locally oxidized patterns were conversely used as barriers for the transfer of hydrophobic n-octadecanethiol. In this case a good contrast was obtained, but the pattern was found to be susceptible to defects (cracks) in the barrier layer. Local stamp surface oxidation and subsequent modification with 1H,1H,2H,2H-perfluorodecyltrichlorosilane, for use as a barrier in the transfer of n-octadecanethiol, 16-mercaptohexadecanoic acid, and octanethiol, resulted in remarkably good contrast and stable patterns. The improved ink transfer control is ascribed to the reduction of undesired surface spreading and a superior mechanical stability of the stamp pattern. This new approach substantially expands the applicability of microcontact printing and provides a tool for the faithful reproduction of even extremely low filling ratio patterns.  相似文献   
103.
The natural products vinaxanthone and xanthofulvin promote regeneration in animal models of spinal cord injury and corneal transplant. However, inhibition of the initially described biological target of these compounds, semaphorin 3A, does not fully account for the recovery demonstrated in vivo following administration of the natural products. Through chemical synthesis substantial quantities of both natural products have been accessed with early reaction development paving the way for synthesizing both compounds. The success of a model system, first disclosed herein, translated to the syntheses of both natural products. Following from this we also report for the first time the discovery of a new target of the natural products, the succinate receptor 1 (SUCNR1). Both natural products function as positive allosteric modulators of SUCNR1. As the first known allosteric modulators of SUCNR1, the compounds represent powerful new tools to understand the pharmacology of SUCNR1 and its control of growth and cellular defense.  相似文献   
104.
Journal of Sol-Gel Science and Technology - A silsesquioxane based on a silica matrix and 4-(aminomethyl)pyridine group was successfully synthesized using the sol–gel process with the...  相似文献   
105.

Fog computing improves efficiency and reduces the amount of bandwidth to the cloud. In many use cases, the internet of things (IoT) devices do not know the fog nodes in advance. Moreover, as the fog nodes are often placed in open publicly available places, they can be easily captured. Therefore, it should be ensured that even if the key material is leaked from the fog devices, the previously generated session keys and the identity of the devices can be kept secret, i.e. satisfying anonymity, unlinkability, perfect forward secrecy and resistance against stolen devices attack. Such demands require a multi-factor authentication scheme, which is typically done by providing input of the user with password or biometric data. However, in real use case scenarios, IoT devices should be able to automatically start the process without requiring such manual interaction and also fog devices need to autonomously operate. Therefore, this paper proposes a physical unclonable function (PUF) based mutual authentication scheme, being the first security scheme for a fog architecture, capable of providing simultaneously all these suggested security features. In addition, we also show the resistance against other types of attacks like synchronization and known session specific temporary information attack. Moreover, the scheme only relies on symmetric key based operations and thus results in very good performance, compared to the other fog based security systems proposed in literature.

  相似文献   
106.
Probing nanoscale electrical properties of organic semiconducting materials at the interface with an electrolyte solution under externally applied voltages is key in the field of organic bioelectronics. It is demonstrated that the conductivity and interfacial capacitance of the active channel of an electrolyte-gated organic field-effect transistor (EGOFET) under operation can be probed at the nanoscale using scanning dielectric microscopy in force detection mode in liquid environment. Local electrostatic force versus gate voltage transfer characteristics are obtained on the device and correlated with the global current–voltage transfer characteristics of the EGOFET. Nanoscale maps of the conductivity of the semiconducting channel show the dependence of the channel conductivity on the gate voltage and its variation along the channel due to the space charge limited conduction. The maps reveal very small electrical heterogeneities, which correspond to local interfacial capacitance variations due to an ultrathin non-uniform insulating layer resulting from a phase separation in the organic semiconducting blend. Present results offer insights into the transduction mechanism at the organic semiconductor/electrolyte interfaces at scales down to ≈100 nm, which can bring substantial optimization of organic electronic devices for bioelectronic applications such as electrical recording on excitable cells or label-free biosensing.  相似文献   
107.
108.
Reactions of arene‐ and pyridinecarbaldehydes with ferrocenyl‐4,5‐dihydropyrazoles afforded 1‐arylmethyl‐ and 1‐pyridylmethyl‐3,5‐aryl(ferrocenyl)pyrazoles. Their structures were established based on spectroscopic methods and, for 4‐[(3,5‐diferrocenylpyrazol‐1‐yl)methyl]pyridine, based on X‐ray diffraction analysis.  相似文献   
109.
Inspired by the current representation of the ligand-receptor binding process, a normal-mode-based methodology is presented to incorporate receptor flexibility in ligand docking and virtual screening. However, the systematic representation of the deformation space grows geometrically with the number of modes, and furthermore, midscale loop rearrangements like those found in protein kinase binding pockets cannot be accounted for with the first lowest-frequency modes. We thus introduced a measure of relevance of normal modes on a given region of interest and showed that only very few modes in the low-frequency range are necessary and sufficient to describe loop flexibility in cAMP-dependent protein kinase. We used this approach to generate an ensemble of representative receptor backbone conformations by perturbing the structure along a combination of relevant modes. Each ensemble conformation is complexed with known non-native binders to optimize the position of the binding-pocket side chains through a full flexible docking procedure. The multiple receptor conformations thus obtained are used in a small-scale virtual screening using receptor ensemble docking. We evaluated this algorithm on holo and apo structures of cAMP-dependent protein kinase that exhibit backbone rearrangements on two independent loop regions close to the binding pocket. Docking accuracy is improved, since the ligands considered in the virtual screening docked within 1.5 A to at least one of the structures. The discrimination between binders and nonbinders is also enhanced, as shown by the improvement of the enrichment factor. This constitutes a new step toward the systematic integration of flexible ligand-flexible receptor docking tools in structure-based drug discovery.  相似文献   
110.
Tetrahedral naphthalenediimide compound 1 has been synthesized as an example of a new class of amorphous n-type materials, in which the nondirectionality obtained by its shape is decoupled from its optoelectronic properties. 1 forms bicontinuous films with p-type polymers and effectively quenches the excited state, yielding long-lived mobile charge carriers on pulsed illumination.  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