全文获取类型
收费全文 | 296篇 |
免费 | 2篇 |
国内免费 | 1篇 |
专业分类
化学 | 156篇 |
晶体学 | 9篇 |
力学 | 15篇 |
数学 | 50篇 |
物理学 | 69篇 |
出版年
2021年 | 3篇 |
2015年 | 5篇 |
2014年 | 3篇 |
2013年 | 3篇 |
2012年 | 5篇 |
2011年 | 5篇 |
2008年 | 8篇 |
2007年 | 8篇 |
2006年 | 8篇 |
2005年 | 3篇 |
2004年 | 4篇 |
2003年 | 3篇 |
2002年 | 6篇 |
2001年 | 4篇 |
2000年 | 10篇 |
1999年 | 6篇 |
1998年 | 3篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 5篇 |
1993年 | 12篇 |
1992年 | 6篇 |
1991年 | 8篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 9篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 10篇 |
1981年 | 3篇 |
1980年 | 7篇 |
1979年 | 8篇 |
1978年 | 10篇 |
1976年 | 7篇 |
1975年 | 5篇 |
1973年 | 3篇 |
1972年 | 5篇 |
1971年 | 5篇 |
1944年 | 2篇 |
1939年 | 2篇 |
1936年 | 2篇 |
1933年 | 3篇 |
1931年 | 2篇 |
1930年 | 2篇 |
1928年 | 4篇 |
1924年 | 4篇 |
1911年 | 3篇 |
1910年 | 3篇 |
排序方式: 共有299条查询结果,搜索用时 312 毫秒
91.
H. Brauer 《Heat and Mass Transfer》1992,27(5):321-329
Zusammenfassung In diesem Teil 2 des Berichtes werden die Ergebnisse der theoretischen Untersuchung über die Umströmung verzögerter Partikeln diskutiert. Die berechneten Stromlinienfelder vermitteln einen umfassenden Einblick in die Umströmung und in die damit verbundene Entwicklung der zunächst auf der Kugelrückseite entstehenden Wirbel. Es zeigt sich, daß nach einer vorausgehenden stationären Bewegung der Partikeln mit Wirbelbildung auf der Partikelrückseite eine Verzögerung sowohl ein Verschwinden der Wirbel als auch ein starkes Anwachsen der Wirbel auslösen kann. Setzt ein Wachstum der Wirbel ein, so hüllen die Wirbel schließlich die Partikeln vollkommen ein.Sowohl die Länge der Wirbel als auch der Ablösepunkt der Strömung von der Partikeloberfläche werden in Abhängigkeit von der Zeit dargestellt.In einem besonderen Abschnitt werden die Widerstandsbeiwerte bestimmt. Sie zeigen bei verzögerter Bewegung eine sehr bemerkenswerte Abhängigkeit von der momentanen Reynolds-ZahlRe
t
, die physikalisch erklärt wird.
Fluid flow around accelerated and decelerated particles. Part 2
This report on theoretical-numerical investigation on fluid flow around accelerated and decelerated particles is presented in two parts. The preceding first part includes the physical fundamentals of unsteady state motion of particles, the numerical methods applied for the solution of the differential equations, and a discussion of results for the case of accelerated particles.The second part of this report is devoted to the discussion of results for fluid flow around decelerated particles. Special attention is given to formation and development of the vortex and detachment of the streamlines from the particle surface.相似文献
92.
O. Brauer E. Kirchuk L. Raviola M. Socolovsky 《International Journal of Theoretical Physics》2014,53(1):333-338
We compute the entropy of a Rindler particle-detector (observer) in the presence of a quantum field in the Minkowski vacuum state; due to the Unruh effect, the observer is immersed in a thermal bath at a temperature proportional to its proper acceleration. 相似文献
93.
The temperature dependence of the decay time (τ) of the luminescence pulses from the 440 nm emission band as well as the rise time (τR) of luminescence pulses from the 575 nm emission band has been investigated for KI : In by pulsed light excitation in the A absorption band. From the agreement of τ and τR independent of the temperature it can be concluded that the X minimum on the 3T14 adiabatic potential energy surface (APES) is mainly populated by a radiationless transition from the tetragonal T minimum of the same APES.Furthermore, a comparison of parameters for the impurity centre luminescence corresponding to the tetragonal emission band in KI : In and KI : Tl has been drawn. 相似文献
94.
Trace elements in soil are quantified by direct X-ray fluorescence method. Gallium is used an internal standard to compensate for variations in sample matrix, instrumental operating characteristics, and sample preparation. At the 50-mg kg?1 level, V, Cr, Ni, Cu, Zn and As can be determined within a precision and accuracy of ± 20% or less. Sample prepartion is less elaborate than for some other methods. 相似文献
95.
96.
97.
Th. Blumenstock K. Jesse F. J. Comes R. Schmidt H. -D. Brauer 《Chemical physics》1989,130(1-3):289-298
Studies on various aromatic endoperoxides (POs) reveal a different photodynamic behavior despite similar excitation conditions and despite similar chromophore structures. Using picosecond laser pump-probe technique it was found that heterocoerdianthrone (HECD), dissolved in dichloromethane, is produced from photocycloreversion of its endoperoxide with a time constant of τ=40±10 ps. Since the lifetime of the photoreactive S3 state is less than 3 ps, a two-step mechanism is expected. Photocleavage of the endoperoxide of anthradichromene (ADCPO) happens in 55±15 ps, whereas the endoperoxides of dimethylhomöocoerdianthrone (HOCDPO) and dimethoxyhomöocoerdianthrone (DMHDPO) photodissociate much faster. For their photodissociation we can state an upper time limit of 5 ps. The results of polarization and solvent dependent experiments demonstrate that the observed rise of signal is directly correlated with the formation of the parent compound in the ground state. The dynamics of the photodissociation of HECPO does not depend on polarity or viscosity of solvent. Therefore, an oxciplex configuration or an intermediate zwitterion cannot be involved in the photocycloreversion of aromatic endoperoxides. The model of a biradical mechanism must be claimed instead. 相似文献
98.
The flow behind a vibrating flexible cable at low Reynolds numbers can exhibit complex wake structures such as lace-like patterns,
vortex dislocations and frequency cells. These structures have been observed in experiments and numerical simulations, and
are predicted by a previously developed low-order coupled map lattice (CML). The discrete (in time and space) CML models consist
of a series of diffusively coupled circle map oscillators along the cable span. Motivated by a desire to modify the complex
wake patterns behind flexible vibrating cables we have studied the addition of control terms into the highly efficient CML
models and explored the resulting dynamics. Proportional, adaptive proportional and discontinuous non-linear (DNL) control
methods were used to derive the control laws. The first method employed occasional proportional feedback. The adaptive method
used spatio-temporal feedback control. The DNL method used a discontinuous feedback linearization procedure, and the controller
was designed for the resulting linearized system using eigenvalue assignment. These techniques were applied to a modeled vortex
dislocation structure in the wake of a vibrating cable in uniform freestream flow. Parallel shedding patterns were achieved
for a range of forcing frequency-forcing amplitude combinations studied to validate the control theory. The adaptive proportional
and DNL methods were found to be more effective than the proportional control method due to the incorporation of a spatially
varying feedback gain across the cylinder span. The DNL method was found to be the most efficient controller of the low-order
CML model. The required control level across the cable span was correlated to the 1/1 lock-on behavior of the temporal circle
map. 相似文献
99.
The highly reversible thermally stable photochromic system consisting of heterocoerdianthrone-endoperoxide (HCDPO) and its parent compounds HCD and 02 is proposed as a new reusable liquid chemical actinometer in the UV region 248 ≤λ≤ 334 nm. The foremost advantageous features of this new system are: (1) high reproducibility and accuracy, (2) high sensitivity, (3) almost wavelength independent quantum yields, (4) no loss in accuracy even after 100 repeated actinometric cycles and (5) very easy handling and straightforward calculability of the radiation quantum flux. 相似文献
100.