全文获取类型
收费全文 | 577篇 |
免费 | 23篇 |
国内免费 | 6篇 |
专业分类
化学 | 326篇 |
晶体学 | 8篇 |
力学 | 18篇 |
数学 | 146篇 |
物理学 | 108篇 |
出版年
2023年 | 3篇 |
2022年 | 15篇 |
2021年 | 25篇 |
2020年 | 22篇 |
2019年 | 27篇 |
2018年 | 20篇 |
2017年 | 19篇 |
2016年 | 46篇 |
2015年 | 15篇 |
2014年 | 31篇 |
2013年 | 42篇 |
2012年 | 37篇 |
2011年 | 36篇 |
2010年 | 18篇 |
2009年 | 12篇 |
2008年 | 23篇 |
2007年 | 9篇 |
2006年 | 12篇 |
2005年 | 13篇 |
2004年 | 17篇 |
2003年 | 10篇 |
2002年 | 12篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 5篇 |
1997年 | 2篇 |
1996年 | 11篇 |
1995年 | 9篇 |
1994年 | 14篇 |
1993年 | 9篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 9篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1981年 | 8篇 |
1980年 | 3篇 |
1978年 | 6篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有606条查询结果,搜索用时 20 毫秒
71.
For a left pure semisimple ring R, it is shown that the local duality establishes a bijection between the preinjective left R-modules and the preprojective right R-modules, and any preinjective left R-module is the source of a left almost split morphism. Moreover, if there are no nonzero homomorphisms from preinjective modules to non-preinjective indecomposable modules in R-mod, the direct sum of all non-preinjective indecomposable direct summands of products of preinjective left R-modules is a finitely generated product-complete module. This generalizes a recent theorem of Angeleri Hügel [L. Angeleri Hügel, A key module over pure-semisimple hereditary rings, J. Algebra 307 (2007) 361-376] for hereditary rings. 相似文献
72.
M. Ebihara Y. S. Chung H. M. Dung J. H. Moon B. -F. Ni T. Otoshi Y. Oura F. L. Santos F. Sasajima Sutisna B. S. Wee W. Wimolwattanapun A. K. B. H. Wood 《Journal of Radioanalytical and Nuclear Chemistry》2008,278(2):463-467
Air particulate matter (APM) samples (PM2.5 and PM10–2.5) were collected at 13 sampling points in 8 Asian countries and their chemical compositions were determined by using neutron
activation analysis (NAA) with the k
0-standardization method in addition to conventional comparative method of NAA. Analytical data showed that mass concentration
and elemental composition of the APM collected are variable in terms of time and space, and are related to the characteristics
of the sampling sites concerned. NAA was proved to be highly effective for the regional characterization of APM in chemical
composition. 相似文献
73.
74.
To study the effect of a local, spatial inhomogeneity on the progress of a chemical reaction which may exhibit a nonequilibrium phase transition, we have studied a (slightly) generalized version of a model proposed originally by Schlögl. Focusing on that regime of parameter space where the reaction sequence A + 2X[lrarr2]3X and B + X[lrarr2]C allows a first-order transition, we consider the consequences of introducing a spatially-varying diffusion coefficient characterized by a correlation length which calibrates the region over which the spatial inhomogeneity persists. We find that if the inhomogeneity is localized, only small quantitative differences are found between the exact solution reported earlier by Schlögl and the solutions generated here. However, as the correlation length becomes larger, abruptly at a certain critical value, a qualitative change in the nature of the solutions is found, with apparent oscillations produced in the concentration variable of the problem. We interpret this behavior as indicating the onset of pattern formation, and suggest that this behavior may be of importance in those radiation-induced phenomena where high-energy intermediates are produced. 相似文献
75.
G. Barreau A. Sicre F. Caïtucoli M. Asghar T.P. Doan B. Leroux G. Martinez T. Benfoughal 《Nuclear Physics A》1985,432(2):411-420
Fragment-mass and kinetic-energy distribution measurements for 252Cf(sf) have been extended to the far-out asymmetric low-yield fission region of MH = 190 compared with the existing data that go up to MH ≈ 168. The mass yield Y(m) shows a shoulder for MH ≈ 163 and an important enhancement for MH ? 176. The 〈EK〉(m), σEK(m) and, to a lesser extent, Y(m) distributions show strong and correlated amplitude fluctuations for MH ? 170. These data indicate strong and rapid changes in deformation of the nascent fragments and the coexistence of more than one deformed-shell stabilized scission configuration for the same mass splits. These structures and those present in the relatively high-yield regions are discussed in terms of the static macro-microscopic potential-energy calculations. 相似文献
76.
77.
We propose both robust and data-driven approaches to a fluid model of call centers that incorporates random arrival rates with abandonment to determine staff levels and dynamic routing policies. We test the resulting models with real data obtained from the call center of a US bank. Computational results show that the robust fluid model is significantly more tractable as compared to the data-driven one and produces overall better solutions to call centers in most experiments. 相似文献
78.
In this paper, we study smooth metric measure space (M, g, e ?f dv) satisfying a weighted Poincaré inequality and establish a rigidity theorem for such a space under a suitable Bakry–Émery curvature lower bound. We also consider the space of f-harmonic functions with finite energy and prove a structure theorem. 相似文献
79.
This paper presents a new design for an insensitive-polarization all-optical switch using 2 × 2 multimode interference (MMI) couplers. The switching structure can operate at central operating wavelength 1550 nm for both polarizations. A nonlinear directional coupler is used to realize the phase shifter and therefore switching mechanism is obtained. The transfer matrix method and beam propagation method are used to design and optimize the whole device structure. 相似文献
80.
We show that a-priori weak Lp dissipativity implies strong L ∞ dissipativity for a class of weakly coupled quasilinear parabolic systems satisfies general structure conditions. The existence of global attractors of general nonlinear reaction diffusion systems will be proven. 相似文献