全文获取类型
收费全文 | 8975篇 |
免费 | 433篇 |
国内免费 | 583篇 |
专业分类
化学 | 1850篇 |
晶体学 | 57篇 |
力学 | 154篇 |
综合类 | 180篇 |
数学 | 6619篇 |
物理学 | 1131篇 |
出版年
2024年 | 7篇 |
2023年 | 47篇 |
2022年 | 151篇 |
2021年 | 186篇 |
2020年 | 188篇 |
2019年 | 241篇 |
2018年 | 244篇 |
2017年 | 185篇 |
2016年 | 211篇 |
2015年 | 193篇 |
2014年 | 357篇 |
2013年 | 613篇 |
2012年 | 369篇 |
2011年 | 445篇 |
2010年 | 446篇 |
2009年 | 578篇 |
2008年 | 613篇 |
2007年 | 628篇 |
2006年 | 539篇 |
2005年 | 417篇 |
2004年 | 378篇 |
2003年 | 362篇 |
2002年 | 305篇 |
2001年 | 274篇 |
2000年 | 273篇 |
1999年 | 252篇 |
1998年 | 220篇 |
1997年 | 189篇 |
1996年 | 137篇 |
1995年 | 105篇 |
1994年 | 92篇 |
1993年 | 101篇 |
1992年 | 79篇 |
1991年 | 60篇 |
1990年 | 56篇 |
1989年 | 49篇 |
1988年 | 50篇 |
1987年 | 42篇 |
1986年 | 36篇 |
1985年 | 38篇 |
1984年 | 32篇 |
1983年 | 24篇 |
1982年 | 34篇 |
1981年 | 23篇 |
1980年 | 26篇 |
1979年 | 27篇 |
1978年 | 27篇 |
1977年 | 8篇 |
1976年 | 11篇 |
1975年 | 9篇 |
排序方式: 共有9991条查询结果,搜索用时 15 毫秒
101.
The spectral structure of two parameter unbounded operator pencils of waveguide type is studied. Theorems on discreteness
of the spectrum for a fixed parameter are proved. Variational principles for real eigenvalues in some parts of the root zones
are established. In the case of n = 1 (quadratic pencils) domains containing the spectrum are described (see Fig. 1–3). Conditions in the definition of the
pencils of waveguide type arise naturally from physical problems and each of them has a physical meaning. In particular a
connection between the energetic stability condition and a perturbation problem for the coefficients is given. 相似文献
102.
Banach空间二阶非线性脉冲微分-积分方程的极值解 总被引:1,自引:0,他引:1
通过建立一个新的比较定理研究了B anach空间二阶非线性混合型脉冲微分-积分方程初值问题的极值解,所得结果推广和改进了现有文献的主要结果. 相似文献
103.
考虑一类具时滞的 Liénard型方程x+f[x(t) ]x(t) +g[t,x(t-τ(t) ) ]=p(t) =p(t+T) ,利用重合度理论 ,获得了此方程至少存在一个 T周期解的充分条件 相似文献
104.
Vsevolod K. Malinovskii 《Acta Appl Math》1994,34(1-2):261-281
Edgeworth expansions for the distribution of a sequential least squares estimator in the random coefficient autoregressive (RCA) model are derived. The regenerative approach to second-order asymptotic analysis of Markov-type statistical models is developed. 相似文献
105.
Numerical methods for ordinary initial value problems that do not depend on special properties of the system are usually found in the class of linear multistage multivalue methods, first formulated by J.C. Butcher. Among these the explicit methods are easiest to implement. For these reasons there has been considerable research activity devoted to generating methods of this class which utilize independent function evaluations that can be performed in parallel. Each such group of concurrent function evaluations can be regarded as a stage of the method. However, it turns out that parallelism affords only limited opportunity for reducing the computing time with such methods. This is most evident for the simple linear homogeneous constant-coefficient test problem, whose solution is essentially a matter of approximating the exponential by an algebraic function. For a given number of stages and a given number of saved values, parallelism offers a somewhat enlarged set of algebraic functions from which to choose. However, there is absolutely no benefit in having the degree of parallelism (number of processors) exceed the number of saved values of the method. Thus, in particular, parallel one-step methods offer no speedup over serial one-step methods for the standard linear test problem. Although the implication of this result for general nonlinear problems is unclear, there are indications that dramatic speedups are not possible in general. Also given are some results relevant to the construction of methods.Work supported in part by National Science Foundation grants DMS 89 11410 and DMS 90 15533 and by US Department of Energy grant DOE DEFG02-87ER25026. Work of the second author was completed while at the University of Illinois. 相似文献
106.
Alexander O. Smirnov 《Letters in Mathematical Physics》2006,76(2-3):297-316
We find a new class of Fuchsian equations, with algebro-geometric solutions associated to a hyperelliptic curve. A method for calculating its arithmetic genus and branching points is suggested. Numerous examples are given. 相似文献
107.
Kim Dang Phung 《Journal of Differential Equations》2007,240(1):92-124
Using Fourier integral operators with special amplitude functions, we analyze the stabilization of the wave equation in a three-dimensional bounded domain on which exists a trapped ray bouncing up and down infinitely between two parallel parts of the boundary. 相似文献
108.
We introduce an interesting hierarchy of rational order chaotic maps that possess an invariant measure. In contrast to the
previously introduced hierarchy of chaotic maps [1–5], with merely entropy production, the rational order chaotic maps can
simultaneously produce and consume entropy. We compute the Kolmogorov-Sinai entropy of these maps analytically and also their
Lyapunov exponent numerically, where the obtained numerical results support the analytical calculations. 相似文献
109.
Trace pollutants analysis in soil by a time-resolved laser-induced breakdown spectroscopy technique 总被引:5,自引:0,他引:5
A. Ciucci V. Palleschi S. Rastelli R. Barbini F. Colao R. Fantoni A. Palucci S. Ribezzo H. J. L. van der Steen 《Applied physics. B, Lasers and optics》1996,63(2):185-190
The results of a joint experiment of IFAM-Pisa and ENEA-Frascati for the detection of traces of pollutants in soil by a time-resolved laser-induced spectroscopy technique are reported. Using samples of soil with known pollutants' concentration [Geochemical Exploration Reference (GXR) silicate from US Geological Survey], we were able to estimate the sensitivity of this Laser-Induced Breakdown Spectroscopy (LIBS) technique to be of the order of some parts per million for a vast class of metallic pollutants, including extremely dangerous soil pollutants such as copper, lead and chromium.ENEA guest with HC&M fellowship 相似文献
110.
Xiao Huang Bishwa Ranjan Nayak Tao Lu Lowe 《Journal of polymer science. Part A, Polymer chemistry》2004,42(20):5054-5066
A series of novel multifunctional hydrogels that combined the merits of both thermoresponsive and biodegradable polymeric materials were designed, synthesized, and characterized. The hydrogels were copolymeric networks composed of N‐isopropylacrylamide (NIPAAM) as a thermoresponsive component, poly(L‐lactic acid) (PLLA) as a hydrolytically degradable and hydrophobic component, and dextran as an enzymatically degradable and hydrophilic component. The chemical structures of the hydrogels were characterized by an attenuated total reflection–Fourier transform infrared spectroscopy (ATR–FTIR) technique. The hydrogels were thermoresponsive, showing a lower critical solution temperature (LCST) at approximately 32 °C, and their swelling properties strongly depended on temperature changes, the balance of the hydrophilic/hydrophobic components, and the degradation of the PLLA component. The degradation of the hydrogels caused by hydrolytic cleavage of ester bonds in the PLLA component was faster at 25 °C below the LCST than at 37 °C above the LCST, determined by the ATR–FTIR technique. Due to their multifunctional properties, the designed hydrogels show great potential for biomedical applications, including drug delivery and tissue engineering. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5054–5066, 2004 相似文献