全文获取类型
收费全文 | 3024篇 |
免费 | 118篇 |
国内免费 | 31篇 |
专业分类
化学 | 1712篇 |
晶体学 | 10篇 |
力学 | 79篇 |
数学 | 388篇 |
物理学 | 482篇 |
无线电 | 502篇 |
出版年
2023年 | 26篇 |
2022年 | 35篇 |
2021年 | 41篇 |
2020年 | 51篇 |
2019年 | 53篇 |
2018年 | 45篇 |
2017年 | 24篇 |
2016年 | 89篇 |
2015年 | 52篇 |
2014年 | 81篇 |
2013年 | 126篇 |
2012年 | 165篇 |
2011年 | 190篇 |
2010年 | 107篇 |
2009年 | 99篇 |
2008年 | 211篇 |
2007年 | 148篇 |
2006年 | 186篇 |
2005年 | 167篇 |
2004年 | 131篇 |
2003年 | 120篇 |
2002年 | 107篇 |
2001年 | 60篇 |
2000年 | 66篇 |
1999年 | 40篇 |
1998年 | 33篇 |
1997年 | 40篇 |
1996年 | 53篇 |
1995年 | 28篇 |
1994年 | 43篇 |
1993年 | 45篇 |
1992年 | 33篇 |
1991年 | 36篇 |
1990年 | 32篇 |
1989年 | 24篇 |
1988年 | 23篇 |
1987年 | 20篇 |
1986年 | 32篇 |
1985年 | 22篇 |
1984年 | 34篇 |
1983年 | 21篇 |
1982年 | 23篇 |
1981年 | 25篇 |
1980年 | 27篇 |
1979年 | 22篇 |
1978年 | 20篇 |
1977年 | 29篇 |
1976年 | 23篇 |
1974年 | 17篇 |
1973年 | 14篇 |
排序方式: 共有3173条查询结果,搜索用时 765 毫秒
1.
A Savitzky–Golay filtering for smoothing and peak search written in Python is presented in this paper alongside its applications in the list-mode digital data acquisition dual gamma–gamma coincidence bismuth germanate (BGO) detector. The study has demonstrated that the software provides a reliable and effective way to quantify trace amounts of 22Na and 7Be in aerosol samples collected at Resolute Bay, Canada with a critical limit of 3 mBq and 5 Bq respectively for a 20 h counting interval, which are believed to be the inherent limitations of the dual-BGO system.
相似文献2.
The extended quadratic residue code is the only (48,24,12) self-dual doubly-even code 总被引:3,自引:0,他引:3
Houghten S.K. Lam C.W.H. Thiel L.H. Parker J.A. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2003,49(1):53-59
An extremal self-dual doubly-even binary (n,k,d) code has a minimum weight d=4/spl lfloor/n/24/spl rfloor/+4. Of such codes with length divisible by 24, the Golay code is the only (24,12,8) code, the extended quadratic residue code is the only known (48,24,12) code, and there is no known (72,36,16) code. One may partition the search for a (48,24,12) self-dual doubly-even code into three cases. A previous search assuming one of the cases found only the extended quadratic residue code. We examine the remaining two cases. Separate searches assuming each of the remaining cases found no codes and thus the extended quadratic residue code is the only doubly-even self-dual (48,24,12) code. 相似文献
3.
An optimal control model of exhaustible resources is used to clarify the long run relationship between mineral rent and depletion cost at the industry level. A standard first order condition of the time rate of change of rents is reformulated to reveal that rent data may be used to help forecast the rise in extraction costs resulting from resource depletion. This application of the theory of exhaustible resources is illustrated using historical mineral industry rent and extraction cost data. A forecast of U.S. coal extraction costs, following the method proposed in this paper, suggests that future rates of extraction cost increases will be similar to rates experienced in the past. 相似文献
4.
This letter presents some further results on the local stability in equilibrium for Internet congestion control algorithm proposed by Low et al., (IEEE/ACM Transactions on Networking, 1999). The propagation delay d(t) is assumed to be time-varying and have maximum and minimum delay bounds (i.e., d/sub m//spl les/d(t)/spl les/d/sub M/), which is more general than the assumption (0相似文献
5.
6.
Ching Sum Hui Lillian Sze Man Lam Chun Yin Wai Kin Chan Aleksandra B. Djurii 《Journal of polymer science. Part A, Polymer chemistry》2003,41(11):1708-1715
Polyurethanes incorporated with rhenium diimine complexes were synthesized. The polymers exhibited interesting morphologies and solution properties. Results from gel permeation chromatography suggested the formation of polymer aggregates in solutions. The polymers could act as probes for metal ions. The addition of metal ions to polymer solutions led to significant changes in the electronic absorption properties of the polymer solutions. This was attributed to the interactions between the polyether moieties and metal ions. The metal complexes could also act as efficient photosensitizers. After doping with charge‐transport viologens, the photoconductivity of the polymers was greatly enhanced. The experimental quantum efficiency was simulated with Onsager's theory. The thermalization distances and the primary yields were typically 12–14 Å and 10?3, respectively. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1708–1715, 2003 相似文献
7.
8.
According to a multiphase mixture theory, we have mathematically developed a multiphysical model with chemoelectromechanical coupling considerations, termed the multieffect‐coupling electric‐stimulus (MECe) model, to simulate the responsive behavior of electric‐sensitive hydrogels immersed in a bath solution under an externally applied electric field. For solutions of the MECe model consisting of coupled nonlinear partial differential governing equations, a meshless Hermite–Cloud method with a hierarchical iteration technique has been used for a one‐dimensional steady‐state analysis of a hydrogel strip. The computed results are compared with the experimental data, and there is very good agreement. Simulations within the domains of both hydrogels and surrounding solutions also present distributions of the ionic concentrations and electric potential as well as the hydrogel displacement. The effects of various physical parameters on the response behavior of electric‐stimulus responsive hydrogels are discussed in detail. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1514–1531, 2004 相似文献
9.
A technique for the characterization of an interior crack perpendicular to the surface of the plates is presented. A time-harmonic line load is applied on the upper surface of the plate. The scattered displacement field is calculated by using the strip element method. It is found that there are additional superimposed oscillations in the curve of the absolute values of the displacement in the region between the load and the crack. The mean value of the peaks of the additional oscillations increases with the crack length, and is less dependent on the distance from the load to the crack. The crack position is determined from the displacement distribution curve and the crack length is determined from the mean value of the peaks of the additional oscillations. Approximate polynomial formula of degree four for predicting the length of interior vertical cracks in isotropic homogeneous plates is also proposed. Numerical examples are given to demonstrate the present technique. 相似文献
10.
The application of reflex optoelectronic switching matrices (ROSM) to signal processing in the gigahertz region is analyzed. Various signal processing functions such as delay generation, loop filtering, word generation/detection, integration, and digital to analog conversion are identified and their respective realizations in a ROSM are presented. It is found that for dedicated signal processing functions, simpler submatrices instead of full matrices can be employed with significant reduction in complexity and cost. The performance of ROSM's using currently commercially available components confirms the feasibility of gigahertz signal processing with ROSM's. 相似文献