全文获取类型
收费全文 | 1224篇 |
免费 | 23篇 |
国内免费 | 3篇 |
专业分类
化学 | 598篇 |
晶体学 | 18篇 |
力学 | 62篇 |
数学 | 112篇 |
物理学 | 460篇 |
出版年
2023年 | 7篇 |
2022年 | 16篇 |
2021年 | 12篇 |
2020年 | 22篇 |
2019年 | 27篇 |
2018年 | 16篇 |
2017年 | 25篇 |
2016年 | 41篇 |
2015年 | 19篇 |
2014年 | 34篇 |
2013年 | 57篇 |
2012年 | 70篇 |
2011年 | 77篇 |
2010年 | 61篇 |
2009年 | 41篇 |
2008年 | 72篇 |
2007年 | 73篇 |
2006年 | 58篇 |
2005年 | 46篇 |
2004年 | 36篇 |
2003年 | 37篇 |
2002年 | 32篇 |
2001年 | 20篇 |
2000年 | 23篇 |
1999年 | 11篇 |
1998年 | 17篇 |
1997年 | 15篇 |
1996年 | 17篇 |
1995年 | 14篇 |
1994年 | 13篇 |
1993年 | 19篇 |
1992年 | 11篇 |
1991年 | 5篇 |
1990年 | 11篇 |
1989年 | 18篇 |
1988年 | 6篇 |
1987年 | 19篇 |
1986年 | 7篇 |
1985年 | 14篇 |
1984年 | 12篇 |
1983年 | 13篇 |
1982年 | 13篇 |
1981年 | 10篇 |
1980年 | 11篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1972年 | 4篇 |
1960年 | 4篇 |
1954年 | 5篇 |
排序方式: 共有1250条查询结果,搜索用时 375 毫秒
181.
Optimization in microbial pest control: An integrated approach 总被引:1,自引:0,他引:1
The paper deals with optimal management of agricultural pest population under integrated control arising out of viral infection and spraying of pesticide. The costs of the control measures and the profits or projected profits of the biomass of species give rise to a control theoretic optimization problem. We take a four dimensional mathematical model of pest control under viral infection and pesticide, and apply Pontryagin’s maximum principle (PMP) to find out the necessary conditions on economic as well as on ecological parameters to make the control process maximum profitable. 相似文献
182.
A formalism has been developed to calculate the steady-state temperature profiles induced by a cw laser in a composite system comprising a thick medium covered with a film of another medium. The analysis is carried out assuming that thermal and optical properties of the media are temperature-independent. A concept of the effective thermal conductivity for the system is introduced in terms of the maximum temperature rise. Temperature-distributions are numerically computed in typical cases for a circular Gaussian beam to illustrate dependence on film thickness, thermal conductivities and absorption coefficients of the media and size of the laser beam. 相似文献
183.
Rahul Singh Jaya Baghel S. Shukla B. Bhattacharya Pramod K. Singh 《Phase Transitions》2013,86(12):1237-1245
The biopolymer solid electrolyte has been synthesized and characterized. Potassium iodide (KI) has been added in polymer matrix to develop solid polymer electrolyte. Relationships between electrical, ionic transport parameter and mechanism have been studied in detail. Impedance spectroscopy reveals the detailed electrical studies and ion transport mechanism. The ion dissociation factor is compared with a measured dielectric constant at a fixed frequency. The dielectric data are calculated which support the ionic conductivity data. 相似文献
184.
Abstract In this article, we have designed a microstructure fiber, which consists of elliptical air holes at the core region. We have investigated its optical properties using finite difference time domain method. The fundamental mode of the proposed microstructure fiber can induce very high birefringence. It has been realized that the value of birefringence is mainly decided by the shape of the air holes present in the first and second rings. The zero dispersion wavelengths of both fast and slow axes have been shifted to 0.64 micrometer. The proposed birefringent microstructure fiber may be useful in optical communication and sensors. 相似文献
185.
Garratt-Braverman cyclization has been employed to synthesize a series of dihydroisofuran fused phenanthridine derivatives. The established protocol proposes a simpler synthetic alternative to have access to these therapeutically relevant cytotoxic scaffolds. Single crystal X-ray data unambiguously confirmed the structures of the synthesized phenanthridine derivatives. UV–Vis absorption titration with calf-thymus DNA followed by fluorescence-based competitive ethidium bromide displacement assay established the synthesized target compounds as potent DNA-intercalating agents with intrinsic binding constant of the range 103-105. Results obtained from the molecular docking further justified the spectroscopically obtained results. 相似文献
186.
Adamson P Andreopoulos C Arms KE Armstrong R Auty DJ Ayres DS Baller B Barr G Barrett WL Becker BR Belias A Bernstein RH Bhattacharya D Bishai M Blake A Bock GJ Boehm J Boehnlein DJ Bogert D Bower C Buckley-Geer E Cavanaugh S Chapman JD Cherdack D Childress S Choudhary BC Coleman SJ Culling AJ de Jong JK Diwan MV Dorman M Dytman SA Escobar CO Evans JJ Falk Harris E Feldman GJ Frohne MV Gallagher HR Goodman MC Gouffon P Gran R Grashorn EW Grossman N Grzelak K Habig A Harris D Harris PG 《Physical review letters》2008,101(15):151601
A search for a sidereal modulation in the MINOS near detector neutrino data was performed. If present, this signature could be a consequence of Lorentz and CPT violation as predicted by the effective field theory called the standard-model extension. No evidence for a sidereal signal in the data set was found, implying that there is no significant change in neutrino propagation that depends on the direction of the neutrino beam in a sun-centered inertial frame. Upper limits on the magnitudes of the Lorentz and CPT violating terms in the standard-model extension lie between 10(-4) and 10(-2) of the maximum expected, assuming a suppression of these signatures by a factor of 10(-17). 相似文献
187.
Given a graph sequence denote by T3(Gn) the number of monochromatic triangles in a uniformly random coloring of the vertices of Gn with colors. In this paper we prove a central limit theorem (CLT) for T3(Gn) with explicit error rates, using a quantitative version of the martingale CLT. We then relate this error term to the well-known fourth-moment phenomenon, which, interestingly, holds only when the number of colors satisfies . We also show that the convergence of the fourth moment is necessary to obtain a Gaussian limit for any , which, together with the above result, implies that the fourth-moment condition characterizes the limiting normal distribution of T3(Gn), whenever . Finally, to illustrate the promise of our approach, we include an alternative proof of the CLT for the number of monochromatic edges, which provides quantitative rates for the results obtained in [7]. 相似文献
188.
189.
Liquid crystalline elastomers (LCEs) can undergo extremely large reversible shape changes when exposed to external stimuli, such as mechanical deformations, heating or illumination. The deformation of LCEs result from a combination of directional reorientation of the nematic director and entropic elasticity. In this paper, we study the energetics of initially flat, thin LCE membranes by stress driven reorientation of the nematic director. The energy functional used in the variational formulation includes contributions depending on the deformation gradient and the second gradient of the deformation. The deformation gradient models the in-plane stretching of the membrane. The second gradient regularises the non-convex membrane energy functional so that infinitely fine in-plane microstructures and infinitely fine out-of-plane membrane wrinkling are penalised. For a specific example, our computational results show that a non-developable surface can be generated from an initially flat sheet at cost of only energy terms resulting from the second gradients. That is, Gaussian curvature can be generated in LCE membranes without the cost of stretch energy in contrast to conventional materials. 相似文献
190.
Megha Sen Chowdhury Dr. Selcuk Gumus Dr. Sanchari Dasgupta Dr. Ishani Majumder Dr. Abir Bhattacharya Dr. Debasis Das Dr. Jayanta Mukhopadhyay Dr. Debosreeta Bose Dr. Saumya Dasgupta Dr. Yuksel Akinay Dr. Madhumita Mukhopadhyay 《ChemistryOpen》2022,11(6):e202200033
We report, for the first time, a detailed crystallographic study of the supramolecular arrangement for a set of zinc(II) Schiff base complexes containing the ligand 2,6-bis((E)-((2-(dimethylamino)ethyl)imino)methyl)-4-R-phenol], where R=methyl/tert-butyl/chloro. The supramolecular study acts as a pre-screening tool for selecting the compartmental ligand R of the Schiff base for effective binding with a targeted protein, bovine serum albumin (BSA). The most stable hexagonal arrangement of the complex [Zn − Me] (R=Me) stabilises the ligand with the highest FMO energy gap (ΔE=4.22 eV) and lowest number of conformations during binding with BSA. In contrast, formation of unstable 3D columnar vertebra for [Zn − Cl] (R=Cl) tend to activate the system with lowest FMO gap (3.75 eV) with highest spontaneity factor in molecular docking. Molecular docking analyses reported in terms of 2D LigPlot+ identified site A, a cleft of domains IB, IIIA and IIIB, as the most probable protein binding site of BSA. Arg144, Glu424, Ser428, Ile455 and Lys114 form the most probable interactions irrespective of the type of compartmental ligands R of the Schiff base whereas Arg185, Glu519, His145, Ile522 act as the differentiating residues with ΔG=−7.3 kcal mol−1. 相似文献