全文获取类型
收费全文 | 5824篇 |
免费 | 127篇 |
国内免费 | 22篇 |
专业分类
化学 | 2466篇 |
晶体学 | 131篇 |
力学 | 225篇 |
数学 | 667篇 |
物理学 | 1507篇 |
无线电 | 977篇 |
出版年
2022年 | 91篇 |
2021年 | 101篇 |
2020年 | 117篇 |
2019年 | 115篇 |
2018年 | 96篇 |
2017年 | 103篇 |
2016年 | 151篇 |
2015年 | 111篇 |
2014年 | 165篇 |
2013年 | 395篇 |
2012年 | 257篇 |
2011年 | 282篇 |
2010年 | 184篇 |
2009年 | 189篇 |
2008年 | 227篇 |
2007年 | 240篇 |
2006年 | 196篇 |
2005年 | 196篇 |
2004年 | 154篇 |
2003年 | 107篇 |
2002年 | 113篇 |
2001年 | 76篇 |
2000年 | 72篇 |
1999年 | 64篇 |
1998年 | 61篇 |
1997年 | 48篇 |
1996年 | 62篇 |
1995年 | 58篇 |
1994年 | 73篇 |
1993年 | 87篇 |
1992年 | 81篇 |
1991年 | 60篇 |
1990年 | 72篇 |
1989年 | 64篇 |
1988年 | 73篇 |
1987年 | 64篇 |
1986年 | 46篇 |
1985年 | 112篇 |
1984年 | 122篇 |
1983年 | 83篇 |
1982年 | 71篇 |
1981年 | 77篇 |
1980年 | 75篇 |
1979年 | 76篇 |
1978年 | 75篇 |
1977年 | 65篇 |
1976年 | 64篇 |
1975年 | 50篇 |
1974年 | 53篇 |
1973年 | 68篇 |
排序方式: 共有5973条查询结果,搜索用时 15 毫秒
11.
In the present paper we derive three interesting expressions for the composition of two most general fractional integral oprators whose kernels involve the product of a general class of polynomials and a multivariableH-function. By suitably specializing the coefficients and the parameters in these functions we can get a large number of (new and known) interesting expressions for the composition of fractional integral operators involving classical orthogonal polynomials and simpler special functions (involving one or more variables) which occur rather frequently in problems of mathematical physics. We have mentioned here two special cases of the first composition formula. The first involves product of a general class of polynomials and the Fox’sH-functions and is of interest in itself. The findings of Buschman [1] and Erdélyi [4] follow as simple special cases of this composition formula. The second special case involves product of the Jacobi polynomials, the Hermite polynomials and the product of two multivariableH-functions. The present study unifies and extends a large number of results lying scattered in the lierature. Its findings are general and deep. 相似文献
12.
In the present article the characterstics of a finite range failure time distribution, that includes the rectangular distribution as a particular case, are studied. When shape parameter surpass unity then the distribution is IFR otherwise it always remains IFRA. A graphic shape of the distribution is also formed for certain admissible values of the constants. 相似文献
13.
The coupling of visible nanosecond laser pulses to metallic targets irradiated in vacuum is studied. The expressions of the vapour and plasma ignition times are obtained. Two cases for vapour breakdown in the plasma ignition process are considered. The first case is that 40 generations of new electrons are born in vapour generation time before plasma formation as assumed in the literature. The second case is that 10 generations of new electrons are born in vapour generation time. Molybdenum (Mo), niobium (Nb) and aluminium (Al) targets are considered for illustrations of our results. The expression of the plasma ignition time for the Al target is substantially different from that reported in the literature. The vapour and plasma ignition threshold laser intensities are calculated and compared with those reported in the literature. Reasons for disagreement are discussed. The plasma ignition threshold estimated in the second case is noted to be in good agreement with the reported experimental result. 相似文献
14.
In the present paper, we study the rate of convergence in simultaneous approximation for the Bézier variant of the Baskakov-Beta operators by using the decomposition technique of functions of bounded variation. 相似文献
15.
JPC – Journal of Planar Chromatography – Modern TLC - A high-performance thin-layer chromatographic (HPTLC) method has been established for simple and rapid quantification of two... 相似文献
16.
We present exact numerical results for a symmetric layered medium (prism/Ag film/nonlinear dielectric/Ag film/prism) where
the middle dielectric slab is assumed to have a saturation-type nonlinearity. We show bistable behaviour in the power dependence
of the reflectivity ofp-polarized light under the condition when coupled surface modes are excited in the structure. Moreover, we study the effect
of saturation on the bistable behaviour to show that multivalued character is inhibited by saturation effects. The field distributions
corresponding to the minimum reflectivity states of the nonlinear structure are also presented. 相似文献
17.
In this paper, electromagnetically coupled (EMC) patch-antenna configurations on two-layered dielectric substrates are investigated. The radiating patch is located on the top of the upper substrate and is excited by feed circuitry underneath it on the lower substrate. The electromagnetic field problem is transformed into a network problem and a multiport network model (MNM) is developed to characterize the three-dimensional (3-D) fields associated with the radiating structure. Antenna characteristics such as input impedance and radiation pattern are computed using the MNM model and the approach is validated by comparison with experimental results 相似文献
18.
Gamma ray bursts (GRBs) have been proposed as one possible class of sources of the ultrahigh energy cosmic ray (UHECR) events
observed up to energies ≳ 1020 eV. The synchrotron radiation of the highest energy protons accelerated within the GRB source should produce gamma rays up
to TeV energies. Here we briefly discuss the implications on the energetics of the GRB from the point of view of the detectability
of the prompt TeV γ-rays of proton-synchrotron origin in GRBs in the up-coming ICECUBE muon detector in the south pole. 相似文献
19.
Sen Gupta A. Hanjura A.K. Mathur B.S. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1991,79(7):973-982
The authors discuss the advantages of broadcasting time from a satellite over the more traditional ground based methods such as short wave and low frequency standard time and frequency broadcasts. The authors describe several one way satellite time services currently operational and discuss, in particular, a broadcast service using the Indian domestic satellite INSAT. The signal format, transmitting and receiving setups, and the methods for satellite position prediction are described in detail for the INSAT broadcast. Some typical results of time and frequency calibration are also discussed 相似文献
20.
Distributed fair scheduling in a wireless LAN 总被引:1,自引:0,他引:1
Fairness is an important issue when accessing a shared wireless channel. With fair scheduling, it is possible to allocate bandwidth in proportion to weights of the packet flows sharing the channel. This paper presents a fully distributed algorithm for fair scheduling in a wireless LAN. The algorithm can be implemented without using a centralized coordinator to arbitrate medium access. The proposed protocol is derived from the Distributed Coordination Function in the IEEE 802.11 standard. Simulation results show that the proposed algorithm is able to schedule transmissions such that the bandwidth allocated to different flows is proportional to their weights. An attractive feature of the proposed approach is that it can be implemented with simple modifications to the IEEE 802.11 standard. 相似文献