全文获取类型
收费全文 | 323186篇 |
免费 | 4058篇 |
国内免费 | 1167篇 |
专业分类
化学 | 176797篇 |
晶体学 | 4509篇 |
力学 | 13150篇 |
综合类 | 7篇 |
数学 | 37712篇 |
物理学 | 96236篇 |
出版年
2020年 | 2177篇 |
2019年 | 2104篇 |
2018年 | 2052篇 |
2017年 | 1958篇 |
2016年 | 4096篇 |
2015年 | 3426篇 |
2014年 | 4647篇 |
2013年 | 14406篇 |
2012年 | 11191篇 |
2011年 | 13889篇 |
2010年 | 8587篇 |
2009年 | 8544篇 |
2008年 | 12808篇 |
2007年 | 13027篇 |
2006年 | 12672篇 |
2005年 | 11589篇 |
2004年 | 10382篇 |
2003年 | 9111篇 |
2002年 | 9016篇 |
2001年 | 10265篇 |
2000年 | 7869篇 |
1999年 | 6253篇 |
1998年 | 5037篇 |
1997年 | 4868篇 |
1996年 | 4916篇 |
1995年 | 4478篇 |
1994年 | 4254篇 |
1993年 | 4054篇 |
1992年 | 4534篇 |
1991年 | 4387篇 |
1990年 | 4091篇 |
1989年 | 3886篇 |
1988年 | 4168篇 |
1987年 | 3845篇 |
1986年 | 3723篇 |
1985年 | 5414篇 |
1984年 | 5481篇 |
1983年 | 4438篇 |
1982年 | 4846篇 |
1981年 | 4871篇 |
1980年 | 4622篇 |
1979年 | 4739篇 |
1978年 | 4737篇 |
1977年 | 4708篇 |
1976年 | 4679篇 |
1975年 | 4561篇 |
1974年 | 4402篇 |
1973年 | 4578篇 |
1972年 | 2606篇 |
1971年 | 1912篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
321.
322.
Frank W. Schmidt 《Linear and Multilinear Algebra》1991,30(3):229-230
This section appears from time to time. Contributions are invited, and should be submitted to R. C. Thompson, Mathematics Department, University of California, Santa Barbara, CA 93106. 相似文献
323.
J. Jena 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2007,22(2):416-430
A Lie group of transformations method is used to establish self-similar solutions to the problem of shock wave propagation
through a relaxing gas and its interaction with the weak discontinuity wave. The forms of the equilibrium value of the vibrational
energy and the relaxation time, varying with the density and pressure are determined for which the system admits self-similar
solutions. A particular solution to the problem has been found out and used to study the effects of specific heat ratio and
ambient density exponent on the flow parameters. The coefficients of amplitudes of reflected and transmitted waves after the
interaction are determined. 相似文献
324.
325.
Ph. Komninou Th. Kehagias A. Delimitis G.P. Dimitrakopulos J. Kioseoglou E. Dimakis A. Georgakilas Th. Karakostas 《Superlattices and Microstructures》2004,36(4-6):509
The structural properties of InN thin films, grown by rf plasma-assisted molecular beam epitaxy on Ga-face GaN/Al2O3(0001) substrates, were investigated by means of conventional and high resolution electron microscopy. Our observations showed that a uniform InN film of total thickness up to 1 μm could be readily grown on GaN without any indication of columnar growth. A clear epitaxial orientation relationship of , was determined. The quality of the InN film was rather good, having threading dislocations as the dominant structural defect with a density in the range of 109–1010 cm−2. The crystal lattice parameters of wurtzite InN were estimated by electron diffraction analysis to be a=0.354 nm and c=0.569 nm, using Al2O3 as the reference crystal. Heteroepitaxial growth of InN on GaN was accomplished by the introduction of a network of three regularly spaced misfit dislocation arrays at the atomically flat interface plane. The experimentally measured distance of misfit dislocations was 2.72 nm. This is in good agreement with the theoretical value derived from the in-plane lattice mismatch of InN and GaN, which indicated that nearly full relaxation of the interfacial strain between the two crystal lattices was achieved. 相似文献
326.
C. von Borczyskowski F. Cichos J. Martin J. Schuster A. Issac J. Brabandt 《The European physical journal. Special topics》2007,144(1):13-25
Optical spectroscopy in combination with wide field or confocal optical
microscopy enables the investigation of single quantum objects such as
organic molecules, II/VI semiconductor quantum dots and silicon nanocrystals.
They all have fluctuations of luminescence intensities on time scales longer
than μs in common. A comparison reveals that despite the large differences
of the nature of the respective quantum objects, the intensity fluctuations
are related to a slow ionisation process followed
by a trapping of the photoejected charge in the non-conducing environment.
Detailed aspects of the dynamics are controlled by the dielectric properties
of the matrix. 相似文献
327.
Numerical studies were conducted to investigate the natural convection heat transfer around a uniformly heated thin plate
with arbitrary inclination in an infinite space. The numerical approach was based on the finite volume technique with a nonstaggered
grid arrangement. For handling the pressure–velocity coupling the SIMPLE-algorithm was used. QUICK scheme and first order
upwind scheme were employed for discretization of the momentum and energy convective terms respectively. Plate width and heating
rate were used to vary the modified Rayleigh number over the range of 4.8×106 to 1.87×108. Local and average heat transfer characteristics were compared with regarding to the inclination angle. The empirical expressions
for local and average Nusselt number were correlated. It has been found that for inclination angle less than 10∘, the flow and heat transfer characteristics are complicated and the average Nusselt number can not be correlated by one equation
while for inclination angle larger than 10∘, the average Nusselt number can be correlated into an elegant correlation.
Received on 18 April 2001 / Published online: 29 November 2001 相似文献
328.
Thomas M. F. Case G. S. Bland J. Herring A. D. F. Stirling W. G. Tixier S. Boni P. Ward R. C. C. Wells M. R. Langridge S. 《Hyperfine Interactions》2002,141(1-4):471-476
Hyperfine Interactions - Multilayers of Ce/Fe and U/Fe were fabricated by sputtering and studied by X-ray diffraction and reflectivity, Mössbauer spectroscopy and polarised neutron... 相似文献
329.
Experimental research on the improvement of the sensitivity and time resolution of pulsed magnetic resonance spectrometers
is discussed. It is shown that application of a time-variable feedback of a signal to the input of the receiver amplifier
can decouple, the “fixed” relationship between the quality factorQ and the ringdown time of the resonance system. Experiments were performed with low-frequency, radio-frequency and microwave
pulse-type magnetic resonance receivers. Modifications of an S/C-band electron spin echo modulation spectrometer carried out
to check the “time-variable feedback” performance are described. It is demonstrated that the application of a time-variable
feedback can significantly reduce the ringdown time and improve the recovery properties of the magnetic resonance receiver
system. It is also demonstrated that the time-variable feedback can improve the overall receiver sensitivity due to the fact
that the working bandwidth of the resonance system can be optimized separately for the transmitting and the receiving mode.
Signal values could be increased at least three times and the signal-to-noise ratio about 1.5–2 times. The largest improvement
is achieved with the initially overcoupled resonator. Experimental spectra of test samples for different settings of the time-variable
feedback are shown. 相似文献
330.
Dashan Huang Yoshitaka Kai Frank J. Fabozzi Masao Fukushima 《European Journal of Operational Research》2007
This paper presents a model for optimally designing a collateralized mortgage obligation (CMO) with a planned amortization class (PAC)-companion structure using dynamic cash reserve. In this structure, the mortgage pool’s cash flow is allocated by rule to the two bond classes such that PAC bondholders receive substantial prepayment protection, that protection being provided by the companion bondholders. The structure we propose provides greater protection to the PAC bondholders than current structures during periods of rising interest rates when this class of bondholders faces greater extension risk. We do so by allowing a portion of the cash flow from the collateral to be reserved to meet the PAC’s scheduled cash flow in subsequent periods. The greater protection is provided by the companion bondholders exposure to interest loss. To tackle this problem, we transform the problem of designing the optimal PAC-companion structure into a standard stochastic linear programming problem which can be solved efficiently. Moreover, we present an extended model by considering the quality of the companion bond and by relaxing the PAC bondholder shortfall constraint. Based on numerical experiments through Monte Carlo simulation, we show the utility of the proposed model. 相似文献