全文获取类型
收费全文 | 9458篇 |
免费 | 601篇 |
国内免费 | 1416篇 |
专业分类
化学 | 4878篇 |
晶体学 | 40篇 |
力学 | 1763篇 |
综合类 | 74篇 |
数学 | 2637篇 |
物理学 | 2083篇 |
出版年
2024年 | 18篇 |
2023年 | 153篇 |
2022年 | 139篇 |
2021年 | 210篇 |
2020年 | 284篇 |
2019年 | 262篇 |
2018年 | 225篇 |
2017年 | 307篇 |
2016年 | 391篇 |
2015年 | 279篇 |
2014年 | 478篇 |
2013年 | 883篇 |
2012年 | 483篇 |
2011年 | 563篇 |
2010年 | 494篇 |
2009年 | 649篇 |
2008年 | 632篇 |
2007年 | 647篇 |
2006年 | 523篇 |
2005年 | 537篇 |
2004年 | 523篇 |
2003年 | 400篇 |
2002年 | 381篇 |
2001年 | 298篇 |
2000年 | 257篇 |
1999年 | 219篇 |
1998年 | 178篇 |
1997年 | 149篇 |
1996年 | 128篇 |
1995年 | 139篇 |
1994年 | 106篇 |
1993年 | 90篇 |
1992年 | 87篇 |
1991年 | 59篇 |
1990年 | 37篇 |
1989年 | 35篇 |
1988年 | 37篇 |
1987年 | 30篇 |
1986年 | 23篇 |
1985年 | 25篇 |
1984年 | 25篇 |
1983年 | 13篇 |
1982年 | 20篇 |
1981年 | 9篇 |
1980年 | 10篇 |
1979年 | 15篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1973年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
Polymorphic crystals and complex multiple melting behavior in an aliphatic biodegradable polyester, poly(butylene adipate) (PBA), were thoroughly examined by wide‐angle X‐ray diffraction (WAXD) and differential scanning calorimetry (DSC). Further clarification on mechanisms of multiple melting peaks related to polymorphic crystal forms in PBA was attempted. More stable α‐form crystal is normally favored for crystallization from melt at higher temperatures (31–35 °C), or upon slow cooling from the melt; while the β‐form is the favored species for crystallization at low temperatures (25–28 °C). We further proved that PBA crystallization could also result in all α‐form even at low temperatures (25–28 °C) if it crystallized with the presence of prior α‐form nuclei. PBA packed with both crystal forms could display as many as four melting peaks (P1 ? P4, in ascending temperature order). However, PBA initially containing only the α‐crystal exhibited dual melting peaks of P1 and P3, which are attributed to dual lamellar distributions of the α‐crystal. By contrast, PBA initially containing only the β‐crystal could also exhibit dual melting peaks (P2 and P4) upon scanning. While P2 is clearly associated with melting of the initial β‐crystal, the fourth melting peak (P4), appearing rather broad, was determined to be associated with superimposed thermal events of crystal transformation from β‐ to α‐crystal and final re‐melting of the new re‐organized α‐crystal. Crystal transformation from one to the other or vice versa, lamellae thickening, annealing at molten state, and influence on crystal polymorphism in PBA were analyzed. Relationships and mechanisms of dual peaks for isolate α‐ or β‐crystals in PBA are discussed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1662–1672, 2005 相似文献
982.
Zhen-hua Guo 《应用数学学报(英文版)》2005,21(4):637-654
In this paper, we study the large time asymptotic behavior of solutions to both the Cauchy problem and the exterior problem of the Stokes approximation equations of two dimensional compressible flows. 相似文献
983.
为达到合肥光源二期工程通用模式的设计流强,在储存环上选择垂直方向β函数比较大的位置增加一组八极磁铁。该组八极磁铁对水平方向动力学孔径影响很小,虽然垂直方向动力学孔径明显减小,但仍然大于物理孔径,不会影响束流的注入积累过程。该组八极磁铁产生的垂直方向振荡频率分散可以提供ms量级的Landau阻尼时间,将明显增强抑制垂直方向束流集体不稳定性的能力。该组八极磁铁投入运行后,合肥光源注入积累过程明显改善,注入流强从无八极磁铁时的约100 mA提高到330 mA左右。 相似文献
984.
Static and dynamic hydrophobicities of water droplet on a patterned surface prepared using fluoroalkylsilanes with different molecular chain lengths were investigated. Contact angles on the patterned surfaces well agreed with values predicted using Cassie’s theory. On the same line width ratio, total retention force was governed by the fluoroalkylsilane with slow-sliding acceleration. The total retention force decreased with the decreasing width ratio of silane with slow-sliding acceleration on the surface. These results imply that the sliding acceleration of water droplets on a hydrophobic surface depends both on chemical composition and patterning structure. 相似文献
985.
This paper concerns large time behavior of a regular weak solution for non-Newtonian flow equations. It is shown that the decay of the solution is of exponential type when the force term is equal to zero and the domain is bounded. Moreover, the ratio of the enstrophy over the energy has a limit as time tends to infinity, which is an eigenvalue of the Stokes operator. 相似文献
986.
《Operations Research Letters》2023,51(4):393-400
In this paper, we discuss an application of the Stochastic Dual Dynamic Programming (SDDP) type algorithm to nested risk-averse formulations of Stochastic Optimal Control (SOC) problems. We propose a construction of a statistical upper bound for the optimal value of risk-averse SOC problems. This outlines an approach to a solution of a long standing problem in that area of research. The bound holds for a large class of convex and monotone conditional risk mappings. Finally, we show the validity of the statistical upper bound to solve a real-life stochastic hydro-thermal planning problem. 相似文献
987.
《Operations Research Letters》2023,51(2):133-136
The paper deals with a risk averse dynamic programming problem with infinite horizon. First, the required assumptions are formulated to have the problem well defined. Then the Bellman equation is derived, which may be also seen as a standalone reinforcement learning problem. The fact that the Bellman operator is contraction is proved, guaranteeing convergence of various solution algorithms used for dynamic programming as well as reinforcement learning problems, which we demonstrate on the value iteration and the policy iteration algorithms. 相似文献
988.
Shakhov model is a relaxation approximation of the Boltzmann equation proposed to overcome the deficiency of the original BGK model, namely, the incorrect production of the Prandtl number. In this paper, we address the existence and the asymptotic stability of the Shakhov model when the initial data is a small perturbation of global equilibrium. We derive a dichotomy in the coercive estimate of the linearized relaxation operator between zero and non-zero Prandtl number, and observe that the linearized relaxation operator is more degenerate in the former case. To remove such degeneracy and recover the full coercivity, we consider a micro–macro system that involves an additional non-conservative quantity related to the heat flux. 相似文献
989.
用插层法制备了单层MoS2在水中的悬浊液,采用X射线衍射仪、透射电子显微镜以及扫描电子显微镜表征了单层MoS2的结构,用四球长时摩擦磨损试验机考察了单层MoS2在水中的悬浊液的摩擦学行为.结果表明:MoS2经剥层一重堆过程处理后形成单层MoS2,单层MoS2在水中以单片或者多片重叠形式存在,其间距由0.615nm增大为0.622nm;所合成的单层MoS2悬浊液在一定添加量范围内表现出良好的减摩能力.这是因为其在钢球磨损表面生成含FeS的保护膜,而保护膜的剪切强度较低,因而表现出良好的减摩性能,但活性元素S易导致钢的过度腐蚀而使抗磨性能反而变差. 相似文献
990.