全文获取类型
收费全文 | 23368篇 |
免费 | 3429篇 |
国内免费 | 2860篇 |
专业分类
化学 | 7767篇 |
晶体学 | 139篇 |
力学 | 1142篇 |
综合类 | 176篇 |
数学 | 2218篇 |
物理学 | 8514篇 |
综合类 | 9701篇 |
出版年
2024年 | 74篇 |
2023年 | 241篇 |
2022年 | 511篇 |
2021年 | 560篇 |
2020年 | 666篇 |
2019年 | 527篇 |
2018年 | 521篇 |
2017年 | 644篇 |
2016年 | 775篇 |
2015年 | 827篇 |
2014年 | 1156篇 |
2013年 | 1448篇 |
2012年 | 1374篇 |
2011年 | 1517篇 |
2010年 | 1292篇 |
2009年 | 1465篇 |
2008年 | 1527篇 |
2007年 | 1761篇 |
2006年 | 1561篇 |
2005年 | 1422篇 |
2004年 | 1139篇 |
2003年 | 1186篇 |
2002年 | 1060篇 |
2001年 | 896篇 |
2000年 | 810篇 |
1999年 | 721篇 |
1998年 | 541篇 |
1997年 | 514篇 |
1996年 | 460篇 |
1995年 | 391篇 |
1994年 | 356篇 |
1993年 | 280篇 |
1992年 | 241篇 |
1991年 | 225篇 |
1990年 | 193篇 |
1989年 | 187篇 |
1988年 | 152篇 |
1987年 | 99篇 |
1986年 | 50篇 |
1985年 | 61篇 |
1984年 | 39篇 |
1983年 | 24篇 |
1982年 | 39篇 |
1981年 | 21篇 |
1980年 | 16篇 |
1979年 | 20篇 |
1978年 | 6篇 |
1977年 | 12篇 |
1976年 | 13篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
In this paper, we study the existence, uniqueness, and the global exponential stability of the periodic solution and equilibrium of hybrid bidirectional associative memory neural networks with discrete delays. By ingeniously importing real parameters di > 0 (i = 1,2, …, n) which can be adjusted, making use of the Lyapunov functional method and some analysis techniques, some new sufficient conditions are established. Our results generalize and improve the related results in [9]. These conditions can be used both to design globally exponentially stable and periodical oscillatory hybrid bidirectional associative neural networks with discrete delays, and to enlarge the area of designing neural networks. Our work has important significance in related theory and its application. 相似文献
92.
《科学通报(英文版)》1991,36(20):1697-1697
93.
反馈网络的反馈系数与负载效应的函数性 总被引:7,自引:1,他引:6
给出了四种负反馈电路反馈系数F的精确计算公式和近似计算公式。证明了电压负反馈电路的反馈系数和反馈网络的负载效应,都是负载RL的函数。 相似文献
94.
95.
96.
朱兆军 《上饶师范学院学报》2007,27(4):10-15
二元政治权力结构的形成与党在国家政权创建过程中的历史作用密切相关.党的历史使命首先是为了获得国家统一和民族解放,然后才能建立民主政体.这种历史条件决定了党在建国后国家权力体系中的核心领导地位,从而形成党的权力机构与国家权力机构并行运行的二元结构.而中国现代化转型的社会环境又给该权力结构的运行提供了社会基础.集中强大的国家权力是我国目前实现经济和社会转型的决定力量. 相似文献
97.
Nadya Dencheva Teresa G. Nunes M. Jovita Oliveira Zlatan Denchev 《Journal of Polymer Science.Polymer Physics》2005,43(24):3720-3733
The crystalline structure of polyamide‐12 (PA12) was studied by solid‐state 13C nuclear magnetic resonance (NMR) as well as by synchrotron wide‐ and small‐angle X‐ray scattering (WAXS and SAXS). Isotropic and oriented PA12 showed different NMR spectra ascribed to γ‐ and γ′‐crystalline modifications, respectively. On the basis of the position of the first diffraction peak, the isotropic γ‐form and the oriented γ′‐form were shown to be with hexagonal crystalline lattice at room temperature. When heated, the two PA12 polymorphs demonstrated different behaviors. Above 140 °C, the isotropic γ‐PA12 partially transformed into α‐modification. No such transition was observed with the oriented γ′‐PA12 phase even after annealing at temperatures close to melting. A γ′–γ transition was observed here only after isotropization by melting point. Various structural parameters were extracted from the WAXS and SAXS patterns and analyzed as a function of temperature and orientation: the degree of crystallinity, the d‐spacings, the Bragg's long spacings, the average thicknesses of the crystalline (lc) and amorphous (la) phases, and the linear crystallinity xcl within the lamellar stacks. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3720–3733, 2005 相似文献
98.
We have studied the temperature dependence of the radiative deactivation of the Pd-porphine triplet states in Shpol’skii matrices
in the temperature range 1.2–210 K. A substantial transformation of the phosphorescence spectra is observed as the temperature
increases and is due to the inclusion of thermally activated Pd-porphine states in the radiative deactivation processes. The
activation energy Ea of these Pd-porphine states is measured in matrices of n-octane and n-nonane. The splitting of the lowest quasidegenerate
triplet state ΔE(T2−T1) is determined for planar and distorted conformations of the Pd-porphine macrocycle in the n-octane matrix as 40 and 57 cm−1, respectively. The ability to use the temperature dependence of the phosphorescence properties of Pd-porphine to fabricate
molecular thermometers for the low-temperature range is analyzed.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 4, pp. 460–464, July–August, 2007. 相似文献
99.
LIANG Liang 《原子与分子物理学报》2003,20(4):575-578
By using the multichannel quantum defect theory(MQDT),we have evaluated the energy levels and lifetimes of 2sns ^3 S1,2snd ^3D(n=3-25)of BeI and 1 sns ^3s1,1snd ^3D(n=3-25)of BeⅢ,These energies and lifetimes that we have calculated not only agree with the recent measurements and theoretical calculation of Ref.4 and Ref.3, but also predict the lifetimes of 66 other highly excited states. 相似文献
100.
We develop two implementable algorithms, the first for the solution of finite and the second for the solution of semi-infinite min-max-min problems. A smoothing technique (together with discretization for the semi-infinite case) is used to construct a sequence of approximating finite min-max problems, which are solved with increasing precision. The smoothing and discretization approximations are initially coarse, but are made progressively finer as the number of iterations is increased. This reduces the potential ill-conditioning due to high smoothing precision parameter values and computational cost due to high levels of discretization. The behavior of the algorithms is illustrated with three semi-infinite numerical examples. 相似文献