全文获取类型
收费全文 | 2098篇 |
免费 | 65篇 |
国内免费 | 3篇 |
专业分类
化学 | 1487篇 |
晶体学 | 44篇 |
力学 | 63篇 |
数学 | 172篇 |
物理学 | 400篇 |
出版年
2023年 | 22篇 |
2022年 | 40篇 |
2021年 | 48篇 |
2020年 | 43篇 |
2019年 | 73篇 |
2018年 | 52篇 |
2017年 | 46篇 |
2016年 | 72篇 |
2015年 | 45篇 |
2014年 | 70篇 |
2013年 | 161篇 |
2012年 | 129篇 |
2011年 | 156篇 |
2010年 | 81篇 |
2009年 | 68篇 |
2008年 | 103篇 |
2007年 | 101篇 |
2006年 | 91篇 |
2005年 | 84篇 |
2004年 | 100篇 |
2003年 | 49篇 |
2002年 | 35篇 |
2001年 | 21篇 |
2000年 | 17篇 |
1999年 | 24篇 |
1998年 | 10篇 |
1997年 | 10篇 |
1996年 | 12篇 |
1995年 | 16篇 |
1994年 | 9篇 |
1993年 | 14篇 |
1992年 | 14篇 |
1990年 | 12篇 |
1989年 | 20篇 |
1988年 | 12篇 |
1987年 | 14篇 |
1986年 | 11篇 |
1985年 | 11篇 |
1984年 | 14篇 |
1983年 | 15篇 |
1982年 | 13篇 |
1981年 | 10篇 |
1980年 | 27篇 |
1979年 | 15篇 |
1978年 | 14篇 |
1977年 | 23篇 |
1976年 | 13篇 |
1975年 | 12篇 |
1974年 | 9篇 |
1973年 | 9篇 |
排序方式: 共有2166条查询结果,搜索用时 46 毫秒
11.
V. Sree Krishna Chaitanya 《Nonlinear Analysis: Real World Applications》2005,6(5):845-857
In this paper, a structurally unstable man–machine system is considered and a rigorous mathematical analysis is performed to study the influence of time delays in the control force on stability of the equilibrium solution of this system. Results on stability, instability and conditions for the preservation of stability (instability), besides the existence of bifurcation are presented. 相似文献
12.
An age-dependent branching process where disasters occur as a renewal process leading to annihilation or survival ofall the cells, is considered. For such a process, the total mean sojourn time of all the cells in the system is analysed using the regeneration point technique. The mean number of cells which die in timet and its asymptotic behaviour are discussed. When the disasters arrival as a Poisson process and the lifetime of the cells follows exponential distribution, elegant inter-relationships are found among the means of (i) the total number of cells which die in timet (ii) the total sojourn time of all cells in the system upto timet and (iii) the number of living cells at timet. Some of the existing results are deduced as special cases for related processes. 相似文献
13.
U.D. Rapol A. Krishna V. Natarajan 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(2):185-188
We demonstrate a technique to measure hyperfine structure using a frequency-stabilized diode laser and an acousto-optic modulator
locked to the frequency difference between two hyperfine peaks. We use this technique to measure hyperfine intervals in the
5
P
3/2
state of 85Rb and obtain a precision of 20 kHz. We extract values for the magnetic-dipole coupling constant A
= 25.038(5) MHz and the electric-quadrupole coupling constant B
= 26.011(22) MHz. These values are a significant improvement over previous results.
Received 6 March 2003 Published online 15 April 2003 相似文献
14.
Krishna Kumar 《Hyperfine Interactions》1992,75(1-4):43-50
Calculations of the Dynamic Deformation Model for the E2/M1 mixing ratios for ψ-band to ground-band transitions in166Er have been extended to higher spins (up to I=20). Previous comparisons with the experimental values and with the IBA-1 predictions,
available at present up to spins 8 only, are also included for the sake of completeness. Additional comparison with the Frankfurt
Model is also given. While all three models give reasonable magnitudes of the mixing ratios, only the DDM gives the sign changes
at the correct spin values. Predictions are presented for additional sign changes of the mixing ratios, as well as those of
the E2 and the M1 transition moments. 相似文献
15.
Spherically symmetric static cosmological models filled with black-body radiation are considered. The models are isotropic
about a central observer but inhomogeneous. It is suggested that the energy density of the free gravitational field, which
is coupled to the isotropic radiation energy density, might play an important role in generating sufficient field (vacuum)
energy (when converted into thermal energy) and initiate processes like inflation. On the central world line the energy density
of the free gravitational field vanishes whereas the proper pressure and density of the isotropic black-body radiation are
constants. Further, it is shown that the cosmological constant is no more arbitrary but given in terms of the central pressure
and density. Also, at its maximum value the energy density of the free gravitational field is proved to be equal to one third
of the combined value of radiation pressure and density. 相似文献
16.
Mixed thin films of (CdO)1−x(PbO)x and (CdS)1−x(PbS)x (x=0.25) were prepared on glass substrates by spray pyrolysis technique for various substrate temperatures 300, 320 and 340 °C. Structural and optical properties were studied. XRD studies reveal the formation of mixed films. The substrate temperature of 340 °C seems to be critical for the formation of CdO-PbO mixed films. It is observed that (CdS)1−x(PbS)x mixed films were formed at all the three substrate temperatures. The direct band gap value of (CdO)1−x(PbO)x and (CdS)1−x(PbS)x mixed films is about 2.6 and 2.37 eV, respectively. 相似文献
17.
A Jayanth Kumar N M Gowri R Venkateswara Raju G Nirmala B S Bellubbi T Radha Krishna 《Pramana》2006,67(2):383-387
Over the last two decades, the fiber optic technology has passed through many analytical stages. Some commercially available
fiber optic sensors, though in a small way, are being used for automation in mechanical and industrial environments. They
are also used for instrumentation and controls.
In the present work, an intensity-modulated intrinsic fiber optic sugar sensor is presented. This type of sensor, with slight
modification, can be used for on-line determination of the concentration of sugar content in sugarcane juice in sugar industry.
In the present set-up, a plastic fiber made of polymethylmethacrylate is used. A portion of the cladding (1 cm, 2 cm, 3 cm)
at the mid-point along the length of the fiber is removed. This portion is immersed in sugar solution of known concentration
and refractive index. At one end of the fiber an 850 nm source is used and at the other end a power meter is connected. By
varying the concentration of sugar solution, the output power is noted. These studies are made due to the change in refractive
index of the fluid. The device was found to be very sensitive which is free from EMI and shock hazards, stable and repeatable
and they can be remotely interfaced with a computer to give on-line measurements and thus become useful for application in
sugar industries. 相似文献
18.
19.
Anupama Chaurasia Krishna K. Verma 《Fresenius' Journal of Analytical Chemistry》1995,351(2-3):335-337
2,4-Dinitrophenylhydrazine has been suggested as a new reagent for the flow-injection spectrophotometric determination of residual chlorine based on its oxidation to 2,4-dinitrophenyldiazonium ion. The measurement of the decrease in colour intensity under reversed flow-injection (reagent injection) conditions has been used for the determination of 0.1–10 mg/l Cl present as free or combined chlorine, and for its speciation. The limit of detection was 0.05 mg/l Cl. Copper (II), iron (III) and many other ions have been found not to vitiate the results. 相似文献
20.
M Krishna 《Proceedings Mathematical Sciences》1993,103(3):333-339
In this paper we show that bounded perturbation of the discrete laplacian with a potential that is sparsely supported (a notion made precise in the paper) produces absolutely continuous spectrum in the interval [?2ν, 2ν] for large dimension ν. We note that the potential need not give rise to a compact operator, let alone have decay at infinity. 相似文献