全文获取类型
收费全文 | 2047篇 |
免费 | 77篇 |
国内免费 | 8篇 |
专业分类
化学 | 1306篇 |
晶体学 | 57篇 |
力学 | 50篇 |
数学 | 197篇 |
物理学 | 522篇 |
出版年
2023年 | 25篇 |
2022年 | 44篇 |
2021年 | 38篇 |
2020年 | 56篇 |
2019年 | 51篇 |
2018年 | 31篇 |
2017年 | 30篇 |
2016年 | 59篇 |
2015年 | 56篇 |
2014年 | 79篇 |
2013年 | 161篇 |
2012年 | 114篇 |
2011年 | 152篇 |
2010年 | 79篇 |
2009年 | 76篇 |
2008年 | 119篇 |
2007年 | 131篇 |
2006年 | 72篇 |
2005年 | 70篇 |
2004年 | 61篇 |
2003年 | 35篇 |
2002年 | 32篇 |
2001年 | 29篇 |
2000年 | 17篇 |
1999年 | 9篇 |
1998年 | 13篇 |
1997年 | 11篇 |
1996年 | 17篇 |
1995年 | 19篇 |
1994年 | 23篇 |
1993年 | 26篇 |
1992年 | 20篇 |
1991年 | 7篇 |
1990年 | 11篇 |
1989年 | 12篇 |
1988年 | 19篇 |
1987年 | 17篇 |
1986年 | 19篇 |
1985年 | 21篇 |
1984年 | 21篇 |
1983年 | 24篇 |
1982年 | 20篇 |
1981年 | 19篇 |
1980年 | 19篇 |
1979年 | 17篇 |
1978年 | 22篇 |
1977年 | 13篇 |
1976年 | 19篇 |
1974年 | 16篇 |
1973年 | 12篇 |
排序方式: 共有2132条查询结果,搜索用时 156 毫秒
171.
This study reports the use of quartz crystal nanobalance (QCN) to study the adsorption of two model molecules namely albumin and doxycycline by hydroxyapatite (HA). The work focuses on the deposition of a stable coating of HA on the quartz crystal, modification of the coating using doxycycline and its subsequent effects on albumin adsorption. The uniformity and thickness of the HA coating has been studied using atomic force microscopy (AFM). The functional groups to ascertain the presence of the selected moieties have been characterized by Raman spectroscopy. The results indicate that the mass of albumin deposited on the surface of the HA coated quartz crystal functionalized with doxycycline shows a substantial increase when compared to the standard HA coated quartz crystal. The adsorbed albumin has also been found to be retained for an enhanced period of time. This surface immobilization of doxycycline and subsequent albumin adsorption seem to be a promising approach to confer biomaterials with antithrombogenic and antibacterial surfaces. 相似文献
172.
Sushant K. Rawal Amit Kumar ChawlaR. Jayaganthan Ramesh Chandra 《Applied Surface Science》2011,257(21):8755-8761
The chromium and titanium oxynitride films on glass substrate were deposited by using reactive RF magnetron sputtering in the present work. The structural and optical properties of the chromium and titanium oxynitride films as a function of power variations are investigated. The chromium oxynitride films are crystalline even at low power of Cr target (≥60 W) but the titanium oxynitride films are amorphous at low target power of Ti target (≤90 W) as observed from glancing incidence X-ray diffraction (GIXRD) patterns. The residual stress and strain of the chromium oxynitride films are calculated by sin2 ψ method, as the average crystallite size decreases with the increase in sputtering power of the Cr target, higher stress and strain values are observed. The chromium oxynitride films changes from hydrophilic to hydrophobic with the increase of contact angle value from 86.4° to 94.1°, but the deposited titanium oxynitride films are hydrophilic as observed from contact angle measurements. The changes in surface energy were calculated using contact angle measurements to substantiate the hydrophobic properties of the films. UV-vis and NIR spectrophotometer were used to obtain the transmission and absorption spectra, and the later was used for determining band gap values of the films, respectively. The refractive index of chromium and titanium oxynitride films increases with film packing density due to formation of crystalline chromium and titanium oxynitride films with the gradual rise in deposition rate as a result of increase in target powers. 相似文献
173.
174.
V. Chandra Z. Huang W. Qiu R. Kumar 《Mathematical and Computer Modelling of Dynamical Systems: Methods, Tools and Applications in Engineering and Related Sciences》2013,19(3):255-280
Interaction of multiple discrete event systems (DESs) represented as automata are carried out using composition operations. These operations on automata enforce concurrency, wherein an event exists in the composed automaton if it exists in the participating states of the interacting automata possessing the event in their event set. Heymann generalized this by introducing event priorities, wherein an event exists in the composed automaton if it exists in the participating state of the interacting automata having priority over the event. For two interacting automata P and Q, while prioritized composition can model the P, Q, AND, and OR boolean interactions, it cannot model boolean interactions which require exclusivity of participation, namely, “exclusive P”, “exclusive Q”, “exclusive P or exclusive Q”, “exclusive P and exclusive Q”. In order to also model these additional interactions we propose a generalization of prioritized composition by introducing an exclusivity set besides the existing priority sets. The resulting composition is called prioritized composition with exclusion. We also introduce prioritized composition with exclusion and generation that allows for all sixteen boolean modes of interaction possible when two automata interact. This is done by the further introduction of a nor-generative set. This event set together with the two priority sets and an exclusivity set makes it possible to model eight additional boolean interactions which do not require either of the interacting automata to participate for the event to be enabled in the composed automaton. The applicability of these interactions to decentralized supervisory decision fusion and in composing the rules based model of systems has been illustrated. 相似文献
175.
J.C. Misra G.C. ShitS. Chandra P.K. Kundu 《Applied mathematics and computation》2011,217(20):7932-7939
The paper presents a comprehensive theoretical study on the electro-osmotic flow of a viscoelastic fluid past a channel having stretching walls. An attempt has been made to investigate the effect of rheological and electro-osmotic parameters on the kinematics of the fluid. Results presented here pertain to the case where the channel height is much greater than the thickness of electrical double layer comprising the Stern and diffuse layers. The study reveals that an increase in electro-osmotic parameter leads to an increase in the axial velocity throughout the channel for a fluid having viscoelastic coefficient equal to that of blood. This aspect provides a source of novel insight into the process of designing bio-sensing and micro-fluidic devices. 相似文献
176.
ESR and optical absorption studies have been carried out on Cu2+-doped lithium hydrazinium sulphate single crystals at 303 K. The spin-Hamiltonian parameters evaluated indicate a N2O2 square planar environment for Cu2+ ion in this lattice. The correlation ofESR and crystal structure data leads us to conclude that Cu2+ ion enters the lattice interstitially. Charge compensation is achieved by the release of protons. Using the optical absorption
andESR data, bonding parameters and orbital reduction factors are also evaluated. 相似文献
177.
Nimai Kumar Chandra 《Statistics & probability letters》1990,10(5):431-437
Though the sample mean
is a natural estimator for the mean μ of an Inverse Gaussian (IG) distribution having another parameter λ, when a guess μ0 for μ seems plausible, an alternative adaptive estimator which shrinks towards μ0 when a preliminary test for H0:μ = μ0 is tenable or else towards
, is considered a suitable competitor. Certain numerical illustrations are presented showing higher efficiency of such a testimator over
in several situations when the sample size is small and λ is either known or unknown. 相似文献
178.
The total synthesis of the recently isolated marine natural products of mixed biosynthetic origin, yanuthones A, B, C and 22-deacylyanuthone A, has been accomplished following a short regio- and stereocontrolled approach involving the key intermediacy of 2-farnesyl-p-benzoquinone. 相似文献
179.
The purpose of this research was to understand how one teacher reflected on different classroom situations and to understand whether the teacher's approach to these reflections changed over time. For the purposes of this study, we considered reflection as the teacher's act of interpreting her own practices and students' thinking to make sense of student understanding and how teaching might relate to that understanding. We investigated a middle school mathematics teacher's reflection on her students while watching videotapes of her classroom and categorized the reflection as Assess, Interpret, Describe, Justify, and Extend. The results show a higher percentage of Extend instances in later interviews than in earlier ones indicating the teacher's increasing attention to her own teaching in how her students developed their understanding. In addition, her reflection became clearer and better integrated as defined by the Cohen and Ball's triangle of interactions. 相似文献
180.
K. D. Krori T. Chaudhury Chandra Rekha Mahanta 《General Relativity and Gravitation》1994,26(3):265-274
Some Bianchi type cosmological models-two in four and one in higher dimensions-are here studied in the context of cosmic strings. The physical implications of the models are briefly discussed. It is interesting to note that cosmic strings do not occur in Bianchi type V cosmology. 相似文献