全文获取类型

收费全文 |
51541篇 |

免费 |
3446篇 |

国内免费 |
3601篇 |

专业分类

化学 |
19629篇 |

晶体学 |
391篇 |

力学 |
4134篇 |

综合类 |
577篇 |

数学 |
14227篇 |

物理学 |
19630篇 |

出版年

2024年 |
59篇 |

2023年 |
430篇 |

2022年 |
825篇 |

2021年 |
1043篇 |

2020年 |
1126篇 |

2019年 |
1159篇 |

2018年 |
1033篇 |

2017年 |
1193篇 |

2016年 |
1339篇 |

2015年 |
995篇 |

2014年 |
1675篇 |

2013年 |
3247篇 |

2012年 |
1971篇 |

2011年 |
2212篇 |

2010年 |
1813篇 |

2009年 |
2934篇 |

2008年 |
3223篇 |

2007年 |
3612篇 |

2006年 |
3066篇 |

2005年 |
2419篇 |

2004年 |
2045篇 |

2003年 |
2330篇 |

2002年 |
2768篇 |

2001年 |
2087篇 |

2000年 |
1969篇 |

1999年 |
1701篇 |

1998年 |
1632篇 |

1997年 |
977篇 |

1996年 |
915篇 |

1995年 |
775篇 |

1994年 |
836篇 |

1993年 |
601篇 |

1992年 |
680篇 |

1991年 |
481篇 |

1990年 |
445篇 |

1989年 |
335篇 |

1988年 |
299篇 |

1987年 |
301篇 |

1986年 |
261篇 |

1985年 |
252篇 |

1984年 |
250篇 |

1983年 |
158篇 |

1982年 |
208篇 |

1981年 |
199篇 |

1980年 |
132篇 |

1979年 |
163篇 |

1978年 |
111篇 |

1977年 |
101篇 |

1976年 |
45篇 |

1973年 |
42篇 |

**排序方式：**共有10000条查询结果，搜索用时 203 毫秒

1.

Tomoyuki Nakatsuka 《Mathematische Nachrichten》2021,294(1):98-117

We study the existence of a time‐periodic solution with pointwise decay properties to the Navier–Stokes equation in the whole space. We show that if the time‐periodic external force is sufficiently small in an appropriate sense, then there exists a time‐periodic solution $\{u,p\}$ of the Navier–Stokes equation such that $|{?}^{j}{u(t,x)|=O(|x|}^{1?n?j})$ and $|{?}^{j}{p(t,x)|=O(|x|}^{?n?j})\phantom{\rule{0.28em}{0ex}}(j=0,1,\dots )$ uniformly in $t\in \mathbb{R}$ as $|x|\to \infty $. Our solution decays faster than the time‐periodic Stokes fundamental solution and the faster decay of its spatial derivatives of higher order is also described. 相似文献

2.

M. Amar D. Andreucci R. Gianni C. Timofte 《Journal of Mathematical Analysis and Applications》2021,493(2):124533

We prove a well-posedness result for two pseudo-parabolic problems, which can be seen as two models for the same electrical conduction phenomenon in heterogeneous media, neglecting the magnetic field. One of the problems is the concentration limit of the other one, when the thickness of the dielectric inclusions goes to zero. The concentrated problem involves a transmission condition through interfaces, which is mediated by a suitable Laplace-Beltrami type equation. 相似文献

3.

Bifurcation analysis of visual angle model with anticipated time and stabilizing driving behavior

*下载免费PDF全文* Xueyi Guan 《中国物理 B》2022,31(7):70507-070507

In the light of the visual angle model (VAM), an improved car-following model considering driver's visual angle, anticipated time and stabilizing driving behavior is proposed so as to investigate how the driver's behavior factors affect the stability of the traffic flow. Based on the model, linear stability analysis is performed together with bifurcation analysis, whose corresponding stability condition is highly fit to the results of the linear analysis. Furthermore, the time-dependent Ginzburg-Landau (TDGL) equation and the modified Korteweg-de Vries (mKdV) equation are derived by nonlinear analysis, and we obtain the relationship of the two equations through the comparison. Finally, parameter calibration and numerical simulation are conducted to verify the validity of the theoretical analysis, whose results are highly consistent with the theoretical analysis. 相似文献

4.

Chemical bonding in representative astrophysically relevant neutral,cation, and anion HCnH chains

*下载免费PDF全文* Ioan Baldea 《中国物理 B》2022,31(12):123101-123101

Most existing studies assign a polyynic and cumulenic character of chemical bonding in carbon-based chains relying on values of the bond lengths. Building on our recent work, in this paper we add further evidence on the limitations of such an analysis and demonstrate the significant insight gained via natural bond analysis. Presently reported results include atomic charges, natural bond order and valence indices obtained from

*ab initio*computations for representative members of the astrophysically relevant neutral and charged HC_{2k/2k+1}H chain family. They unravel a series of counter-intuitive aspects and/or help naive intuition in properly understanding microscopic processes,*e.g*., electron removal from or electron attachment to a neutral chain. Demonstrating that the Wiberg indices adequately quantify the chemical bonding structure of the HC_{2k/2k+1}H chains—while the often heavily advertised Mayer indices do not—represents an important message conveyed by the present study. 相似文献5.

The health monitoring has been studied to ensure integrity of design of engine structure by detection, quantification, and prediction of damages. Early detection of faults may allow the downtime of maintenance to be rescheduled, thus preventing sudden shutdown of machines. In cylinder pressure developed, vibrations and noise emissions data provide a rich source of information about condition of engines. Monitoring of vibrations and noise emissions are novel non-intrusive methodologies for which positioning of various transducers are important issue. The presented work shows applicability of these diagnosis methodologies adopted in case of diesel engines. The effects of changing various fuel injection parameters was analyzed. Scope of using non-intrusive technique has been analyzed by changing locations of microphone. Novelty of this worklies in exploring signal processing methods for various locations around the engine test set up. Various frequency ranges of contributing noise and vibration sources were identified. Time-Frequency analysis showed the onset of various cyclic. Based on the identification of various frequency bands, it is possible to device suitable filters in order to extract more information. 相似文献

6.

7.

Pattern transition and regulation in a subthalamopallidal network under electromagnetic effect

*下载免费PDF全文*Although the significant roles of magnetic induction and electromagnetic radiation in the neural system have been widely studied, their influence on Parkinson's disease (PD) has yet to be well explored. By virtue of the magnetic flux variable, this paper studies the transition of firing patterns induced by magnetic induction and the regulation effect of external magnetic radiation on the firing activities of the subthalamopallidal network in basal ganglia. We find: (i) The network reproduces five typical waveforms corresponding to the severity of symptoms: weak cluster, episodic, continuous cluster, episodic, and continuous wave. (ii) Magnetic induction is a double-edged sword for the treatment of PD. Although the increase of magnetic coefficient may lead the physiological firing activity to transfer to pathological firing activity, it also can regulate the pathological intensity firing activity with excessive

*β*-band power transferring to the physiological firing pattern with weak*β*-band power. (iii) External magnetic radiation could inhibit continuous tremulous firing and*β*-band power of subthalamic nucleus (STN), which means the severity of symptoms weakened. Especially, the bi-parameter plane of the regulation region shows that a short pulse period of magnetic radiation and a medium level of pulse percentage can well regulate pathological oscillation. This work helps to understand the firing activity of the subthalamopallidal network under electromagnetic effect. It may also provide insights into the mechanisms behind the electromagnetic therapy of PD-related firing activity. 相似文献8.

9.

《Studies in Applied Mathematics》2018,141(3):399-417

We extend our previous results characterizing the loading properties of a diffusing passive scalar advected by a laminar shear flow in ducts and channels to more general cross‐sectional shapes, including regular polygons and smoothed corner ducts originating from deformations of ellipses. For the case of the triangle and localized, cross‐wise uniform initial distributions, short‐time skewness is calculated exactly to be positive, while long‐time asymptotics shows it to be negative. Monte Carlo simulations confirm these predictions, and document the timescale for sign change. The equilateral triangle appears to be the only regular polygon with this property—all others possess positive skewness at all times. Alternatively, closed‐form flow solutions can be constructed for smooth deformations of ellipses, and illustrate how both nonzero short‐time skewness and the possibility of multiple sign switching in time is unrelated to domain corners. Exact conditions relating the median and the skewness to the mean are developed which guarantee when the sign for the skewness implies front (more mass to the right of the mean) or back (more mass to the left of the mean) “loading” properties of the evolving tracer distribution along the pipe. Short‐ and long‐time asymptotics confirm this condition, and Monte Carlo simulations verify this at all times. The simulations are also used to examine the role of corners and boundaries on the distribution for short‐time evolution of

*point source*, as opposed to cross‐wise uniform, initial data. 相似文献10.

Martin Kellert Jan-Simon Jeshua Friedrichs Nadine Anke Ullrich Alexander Feinhals Jonas Tepper Peter Lnnecke Evamarie Hey-Hawkins 《Molecules (Basel, Switzerland)》2021,26(7)

The development of novel, tumor-selective and boron-rich compounds as potential agents for use in boron neutron capture therapy (BNCT) represents a very important field in cancer treatment by radiation therapy. Here, we report the design and synthesis of two promising compounds that combine

*meta*-carborane, a water-soluble monosaccharide and a linking unit, namely glycine or ethylenediamine, for facile coupling with various tumor-selective biomolecules bearing a free amino or carboxylic acid group. In this work, coupling experiments with two selected biomolecules, a coumarin derivative and folic acid, were included. The task of every component in this approach was carefully chosen: the carborane moiety supplies ten boron atoms, which is a tenfold increase in boron content compared to the l-boronophenylalanine (l-BPA) presently used in BNCT; the sugar moiety compensates for the hydrophobic character of the carborane; the linking unit, depending on the chosen biomolecule, acts as the connection between the tumor-selective component and the boron-rich moiety; and the respective tumor-selective biomolecule provides the necessary selectivity. This approach makes it possible to develop a modular and feasible strategy for the synthesis of readily obtainable boron-rich agents with optimized properties for potential applications in BNCT. 相似文献