全文获取类型
收费全文 | 679篇 |
免费 | 26篇 |
国内免费 | 3篇 |
专业分类
化学 | 399篇 |
晶体学 | 1篇 |
力学 | 31篇 |
数学 | 171篇 |
物理学 | 106篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 17篇 |
2021年 | 28篇 |
2020年 | 7篇 |
2019年 | 13篇 |
2018年 | 8篇 |
2017年 | 15篇 |
2016年 | 24篇 |
2015年 | 23篇 |
2014年 | 28篇 |
2013年 | 29篇 |
2012年 | 52篇 |
2011年 | 49篇 |
2010年 | 51篇 |
2009年 | 38篇 |
2008年 | 37篇 |
2007年 | 48篇 |
2006年 | 36篇 |
2005年 | 20篇 |
2004年 | 32篇 |
2003年 | 15篇 |
2002年 | 12篇 |
2001年 | 7篇 |
2000年 | 5篇 |
1999年 | 13篇 |
1998年 | 7篇 |
1997年 | 8篇 |
1996年 | 8篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1992年 | 7篇 |
1991年 | 2篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1979年 | 5篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有708条查询结果,搜索用时 78 毫秒
81.
Poineau F Malliakas CD Weck PF Scott BL Johnstone EV Forster PM Kim E Kanatzidis MG Czerwinski KR Sattelberger AP 《Journal of the American Chemical Society》2011,133(23):8814-8817
Technetium dichloride has been discovered. It was synthesized from the elements and characterized by several physical techniques, including single crystal X-ray diffraction. In the solid state, technetium dichloride exhibits a new structure type consisting of infinite chains of face sharing [Tc(2)Cl(8)] rectangular prisms that are packed in a commensurate supercell. The metal-metal separation in the prisms is 2.127(2) ?, a distance consistent with the presence of a Tc≡Tc triple bond that is also supported by electronic structure calculations. 相似文献
82.
Karaiskos CS Matiadis D Markopoulos J Igglessi-Markopoulou O 《Molecules (Basel, Switzerland)》2011,16(7):6116-6128
Catalytic hydrogenation of 3,5-bis-arylidenetetramic acids, known for their biological activity, has been developed. The chemoselective ruthenium-catalyzed reduction of the exocyclic carbon-carbon double bonds on pyrrolidine-2,4-dione ring system, containing other reducible functions, has been investigated. Depending on the substrate the yield of the hydrogenation process can reach up to 95%. The structural elucidation has been established using NMR and HRMS spectral data. 相似文献
83.
Bhurruth-Alcor Y Røst T Jorgensen MR Kontogiorgis C Skorve J Cooper RG Sheridan JM Hamilton WD Heal JR Berge RK Miller AD 《Organic & biomolecular chemistry》2011,9(4):1169-1188
Peroxisome proliferator activated receptors (PPARs) have been shown to have critical roles in fatty acid oxidation, triglyceride synthesis, and lipid metabolism - making them an important target in drug discovery. Here we describe the in silico design, synthesis and in vitro characterisation of a novel series of 2,5-disubstituted indoles as PPARα/γ dual agonists. PPAR activation assays are performed with known agonists diazabenzene (WY14.643), aminopyridine (BRL49653) and bisaryl (L165.041), as positive controls. All the indole compounds synthesized are found to be active PPARα and PPARγ agonists, with particular efficacy from those with 2-naphthylmethyl substitution. This is a useful demonstration of a new de novo design methodology implemented by the protobuild program and its ability to rapidly produce novel modulators for a well characterized drug target. 相似文献
84.
Palladium catalyzed Suzuki-Miyaura, Stille, and Sonogashira coupling reactions are reported for the electron-deficient heterocyclic scaffold 3,5-dichloro-4H-1,2,6-thiadiazin-4-one (1). Furthermore, 3,5-di(thien-2-yl)-4H-1,2,6-thiadiazin-4-one (7m) is further elaborated to afford the tetrathienyl 3,5-bis[(2,2'-bithien)-5-yl]-4H-1,2,6-thiadiazin-4-one (9). All compounds are fully characterized. 相似文献
85.
Alberola A Carter E Constantinides CP Eisler DJ Murphy DM Rawson JM 《Chemical communications (Cambridge, England)》2011,47(9):2532-2534
The β-sheet structure associated with chlorinated aromatics (d(Cl···Cl)≈ 4.0 ?) has been implemented to drive formation of π-stacked structures of dithiadiazolyl radicals. Both title compounds exhibit an increase in paramagnetism above 150 K but solid-state EPR studies indicate that the origin of the paramagnetism in these two systems is different. 相似文献
86.
The stability of equilibrium and the possibility of generation of business cycles in a discrete interregional Kaldorian macrodynamic model with fixed exchange rates are explored using numerical methods. One of the aims is to illustrate the feasibility and effectiveness of the numerical approach for dynamical systems of moderately high dimensionality and several parameters. The model considered is five-dimensional with four parameters, the speeds of adjustment of the goods markets and the degrees of economic interactions between the regions through trade and capital movement. Using a grid search method for the determination of the region of stability of equilibrium in two-dimensional parameter subspaces, and coefficient criteria for the flip bifurcation - and Hopf bifurcation - curve, we determine the stability region in several parameter ranges and identify Hopf bifurcation curves when they exist. It is found that interregional cycles emerge only for sufficient interregional trade. The relevant threshold is predicted by the model at 14 - 16 % of trade transactions. By contrast, no minimum level of capital mobility exists in a global sense as a requirement for the emergence of interregional cycles; the main conclusion being, therefore, that cycles may occur for very low levels of capital mobility if trade is sufficient. Examples of bifurcation and Lyapunov exponent diagrams illustrating the occurrence of cycles or period doubling, and examples of the development of the occurring cycles, are given. Both supercritical and subcritical bifurcations are found to occur, the latter type indicating coexistence of a point and a cyclical attractor. 相似文献
87.
We detail a new method of generating kinematic simulation fields in a channel. We employ a new decomposition for kinematic
simulation which ensures that the boundary conditions are automatically satisfied while preserving incompressibility. We impose
statistics up to second order, including the Reynolds shear-stress and one-dimensional spectral densities. We observe streak-like
structures kinematically similar to those observed in the laboratory, with a similar scaling with the wall-normal distance.
We explain the appearance and scaling of the streak-like structures in terms of the two-dimensional spectra imposed on the
fields. 相似文献
88.
Christos Ordoudis Pierre Pinson Juan M. Morales 《European Journal of Operational Research》2019,272(2):642-654
In energy systems with high shares of weather-driven renewable power sources, gas-fired power plants can serve as a back-up technology to ensure security of supply and provide short-term flexibility. Therefore, a tighter coordination between electricity and natural gas networks is foreseen. In this work, we examine different levels of coordination in terms of system integration and time coupling of trading floors. We propose an integrated operational model for electricity and natural gas systems under uncertain power supply by applying two-stage stochastic programming. This formulation co-optimizes day-ahead and real-time dispatch of both energy systems and aims at minimizing the total expected cost. Additionally, two deterministic models, one of an integrated energy system and one that treats the two systems independently, are presented. We utilize a formulation that considers the linepack of the natural gas system, while it results in a tractable mixed-integer linear programming (MILP) model. Our analysis demonstrates the effectiveness of the proposed model in accommodating high shares of renewables and the importance of proper natural gas system modeling in short-term operations to reveal valuable flexibility of the natural gas system. Moreover, we identify the coordination parameters between the two markets and show their impact on the system’s operation and dispatch. 相似文献
89.
Tutueva Aleksandra V. Karimov Timur I. Moysis Lazaros Nepomuceno Erivelton G. Volos Christos Butusov Denis N. 《Nonlinear dynamics》2021,104(1):727-737
Nonlinear Dynamics - One of the widely-used ways in chaos-based cryptography to generate pseudo-random sequences is to use the least significant bits or digits of finite-precision numbers defined... 相似文献
90.