全文获取类型
收费全文 | 1060篇 |
免费 | 89篇 |
国内免费 | 5篇 |
专业分类
化学 | 797篇 |
晶体学 | 1篇 |
力学 | 14篇 |
数学 | 198篇 |
物理学 | 144篇 |
出版年
2024年 | 5篇 |
2023年 | 22篇 |
2022年 | 35篇 |
2021年 | 45篇 |
2020年 | 60篇 |
2019年 | 66篇 |
2018年 | 22篇 |
2017年 | 24篇 |
2016年 | 57篇 |
2015年 | 58篇 |
2014年 | 45篇 |
2013年 | 62篇 |
2012年 | 74篇 |
2011年 | 85篇 |
2010年 | 58篇 |
2009年 | 75篇 |
2008年 | 70篇 |
2007年 | 64篇 |
2006年 | 44篇 |
2005年 | 41篇 |
2004年 | 31篇 |
2003年 | 23篇 |
2002年 | 17篇 |
2001年 | 6篇 |
2000年 | 7篇 |
1999年 | 7篇 |
1998年 | 2篇 |
1997年 | 6篇 |
1996年 | 1篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1969年 | 1篇 |
1967年 | 1篇 |
1966年 | 2篇 |
1965年 | 2篇 |
排序方式: 共有1154条查询结果,搜索用时 31 毫秒
71.
72.
Dominik Schindele Robert Prabel 《Mathematical and Computer Modelling of Dynamical Systems: Methods, Tools and Applications in Engineering and Related Sciences》2013,19(2):105-129
This contribution presents two real-time capable nonlinear model-predictive control (NMPC) approaches for an electro-pneumatic clutch for heavy trucks: a centralized control approach and a cascaded one. A clutch is necessary at start-up or during gear shifts to connect or disconnect the combustion engine and the gear box. This automated actuator disburdens the driver and provides the necessary actuation force according to the large torque typically transmitted through the drive train. The force characteristic of the clutch, however, is subject to hysteresis, which is described by a generalized Bouc–Wen model and used for a feedforward hysteresis compensation in the control algorithm. The proposed NMPC-algorithm involves (i) a minimization of the difference between the desired and predicted state vector at the end of the prediction horizon and (ii) flatness-based techniques to compute desired trajectories for the complete state vector as well as the control input. The optimal control is given by an additional, minimum-norm control input that minimizes the difference between the predicted state vector and the desired one at the end of the prediction horizon. Thereby, the computation effort of the NMPC approaches can be kept relatively small, and a real-time evaluation becomes possible. A reduced-order observer estimates an effective pressure in the clutch that also accounts for an uncertain disturbance force. Thereby, a disturbance compensation and a high tracking accuracy is achievable for the piston position as controlled variable. The efficiency of the two proposed control structures is emphasized by experimental results from a dedicated test rig. 相似文献
73.
Atsushi Nakagawa Dominik Fenn Andreas Koschella Thomas Heinze Hiroshi Kamitakahara 《Journal of polymer science. Part A, Polymer chemistry》2011,49(23):4964-4976
This article describes a new synthesis strategy to prepare diblock copolymers as model compounds for industrially produced cellulose ethers exemplified with methylcellulose (MC). To elucidate a key structure for thermoreversible gelation of MC, five regioselectively methylated celluloses 1 – 5 (236, 23, 26, 3, and 6 MC), five corresponding methyl‐β‐D‐glucopyranosyl‐(1→4)‐cellulosides 6 – 10 , and five equiv methyl‐β‐D‐glucopyranosyl‐(1→4)‐β‐D‐glucopyranosyl‐(1→4)‐cellulosides 11 – 15 were synthesized for the first time via combination of the glycosyl trichloroacetimidate method and the acid‐catalyzed methanolysis method. The structure of compounds 1 – 15 was confirmed by means of NMR spectroscopy and MALDI‐TOF MS. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
74.
This paper investigates the topological properties of the Brazilian term structure of interest rates network. We build the minimum spanning tree (MST), which is based on the concept of ultrametricity, using the correlation matrix for interest rates of different maturities. We show that the short-term interest rate is the most important within the interest rates network, which is in line with the Expectation Hypothesis of interest rates. Furthermore, we find that the Brazilian interest rates network forms clusters by maturity. 相似文献
75.
Dominik Mielczarek 《Monatshefte für Mathematik》2008,84(3):157-171
In this paper we will prove that an averaging projection P
a
: K (H) → Y, given by the formula
Pa(A)=\fracA+AT2P_a(A)=\frac{A+A^T}{2}
, is the only norm-one projection. Here, K (H) is a space of compact operators on a separable real Hilbert space H, and Y is the subspace of K(H) consisting of all symmetric operators. 相似文献
76.
A closure for shocks involving the mixing of the fluids in two-layer stratified flows is proposed. The closure maximizes the rate of mixing, treating the dynamical hydraulic equations and entropy conditions as constraints. This closure may also be viewed as yielding an upper bound on the mixing rate by internal shocks. It is shown that the maximal mixing rate is accomplished by a shock moving at the fastest allowable speed against the upstream flow. Depending on whether the active constraint limiting this speed is the Lax entropy condition or the positive dissipation of energy, we distinguish precisely between internal hydraulic jumps and bores. Maximizing entrainment is shown to be equivalent to maximizing a suitable entropy associated to mixing. By using the latter, one can describe the flow globally by an optimization procedure, without treating the shocks separately. A general mathematical framework is formulated that can be applied whenever an insufficient number of conservation laws is supplemented by a maximization principle. 相似文献
77.
This paper investigates the topological properties of the Brazilian stock market networks. We build the minimum spanning tree, which is based on the concept of ultrametricity, using the correlation matrix for a variety of stocks of different sectors. Our results suggest that stocks tend to cluster by sector. We employ a dynamic approach using complex network measures and find that the relative importance of different sectors within the network varies. The financial, energy and material sectors are the most important within the network. 相似文献
78.
79.
80.