全文获取类型
收费全文 | 10438篇 |
免费 | 1303篇 |
国内免费 | 3305篇 |
专业分类
化学 | 6218篇 |
晶体学 | 391篇 |
力学 | 489篇 |
综合类 | 142篇 |
数学 | 5164篇 |
物理学 | 2642篇 |
出版年
2024年 | 32篇 |
2023年 | 92篇 |
2022年 | 259篇 |
2021年 | 306篇 |
2020年 | 332篇 |
2019年 | 327篇 |
2018年 | 317篇 |
2017年 | 468篇 |
2016年 | 623篇 |
2015年 | 410篇 |
2014年 | 628篇 |
2013年 | 1233篇 |
2012年 | 928篇 |
2011年 | 893篇 |
2010年 | 744篇 |
2009年 | 790篇 |
2008年 | 787篇 |
2007年 | 802篇 |
2006年 | 634篇 |
2005年 | 553篇 |
2004年 | 449篇 |
2003年 | 411篇 |
2002年 | 411篇 |
2001年 | 369篇 |
2000年 | 297篇 |
1999年 | 295篇 |
1998年 | 238篇 |
1997年 | 201篇 |
1996年 | 190篇 |
1995年 | 178篇 |
1994年 | 160篇 |
1993年 | 100篇 |
1992年 | 85篇 |
1991年 | 76篇 |
1990年 | 63篇 |
1989年 | 46篇 |
1988年 | 46篇 |
1987年 | 32篇 |
1986年 | 21篇 |
1985年 | 40篇 |
1984年 | 25篇 |
1983年 | 26篇 |
1982年 | 26篇 |
1981年 | 10篇 |
1980年 | 16篇 |
1979年 | 23篇 |
1978年 | 10篇 |
1977年 | 14篇 |
1976年 | 10篇 |
1975年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
本文提出的MMD算法用于提高模型区别错误信息和正确信息的能力.利用该算法在对模型的参数进行重估计时.涉及到复杂的目标函数的梯度运算.击运用矩阵运算使得梯度运算变得简单明了,因此本文给出了MMD算法下的HMM参数重估计的矩阵表示形式并给出了证明. 相似文献
12.
13.
Chin‐Ping Yang Sheng‐Huei Hsiao Che‐Yu Tsai Guey‐Sheng Liou 《Journal of polymer science. Part A, Polymer chemistry》2004,42(10):2416-2431
Two series of fluorinated polyimides were prepared from 2,2′‐bis(4‐amino‐2‐trifluoromethylphenoxy)biphenyl ( 2 ) and 2,2′‐bis(4‐amino‐2‐trifluoromethylphenoxy)‐1,1′‐binaphthyl ( 4 ) with various aromatic dianhydrides via a conventional, two‐step procedure that included a ring‐opening polyaddition to give poly(amic acid)s, followed by chemical or thermal cyclodehydration. The inherent viscosities of the polyimides ranged from 0.54 to 0.73 and 0.19 to 0.36 dL/g, respectively. All the fluorinated polyimides were soluble in many polar organic solvents, such as N,N‐dimethylacetamide and N‐methylpyrrolidone, and afforded transparent and light‐colored films via solution‐casting. These polyimides showed glass‐transition temperatures in the ranges of 222–280 and 257–351 °C by DSC, softening temperatures in the range of 264–301 °C by thermomechanical analysis, and a decomposition temperature for 10% weight loss above 520 °C both in nitrogen and air atmospheres. The polyimides had low moisture absorptions of 0.23–0.58%, low dielectric constants of 2.84–3.61 at 10 kHz, and an ultraviolet–visible absorption cutoff wavelength at 351–434 nm. Copolyimides derived from the same dianhydrides with an equimolar mixture of 4,4′‐oxydianiline and diamine 2 or 4 were also prepared and characterized. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2416–2431, 2004 相似文献
14.
We deal with MAXH0-FREE PARTIAL SUBGRAPH. We mainly prove that 3-locally optimum solutions achieve approximation ratio (δ0+1)/(B+2+ν0), where B=maxv∈VdG(v), δ0=minv∈V(H0)dH0(v) and ν0=(|V(H0)|+1)/δ0. Next, we show that this ratio rises up to 3/(B+1) when H0=K3. Finally, we provide hardness results for MAXK3-FREE PARTIAL SUBGRAPH. 相似文献
15.
The control of piecewise-deterministic processes is studied where only local boundedness of the data is assumed. Moreover the discount rate may be zero. The value function is shown to be solution to the Bellman equation in a weak sense; however the solution concept is strong enough to generate optimal policies. Continuity and compactness conditions are given for the existence of nonrelaxed optimal feedback controls. 相似文献
16.
In this paper, we study the stability conditions of the MMAP[K]/G[K]/1/LCFS preemptive repeat queue. We introduce an embedded Markov chain of matrix M/G/1 type with a tree structure and identify conditions for the Markov chain to be ergodic. First, we present three conventional methods for the stability problem of the queueing system of interest. These methods are either computationally demanding or do not provide accurate information for system stability. Then we introduce a novel approach that develops two linear programs whose solutions provide sufficient conditions for stability or instability of the queueing system. The new approach is numerically efficient. The advantages and disadvantages of the methods introduced in this paper are analyzed both theoretically and numerically. 相似文献
17.
The main purpose of this paper is to use a mean value theorem of Dirichlet L-functions to study the asymptotic property of a hybrid mean value of a generalized Cochrane sum, and give an interesting mean value formula.2000 Mathematics Subject Classification: Primary—11F20; Secondary—11F99 相似文献
18.
胡迪鹤 《数学物理学报(B辑英文版)》2005,25(1):23-29
This paper is a continuation of [8]. In Section 1, three kinds of communication are introdnced for two states and the relations among them are investigated. In Section 2, two kinds of period of a state are introdnced and it is obtained that the period is a “class property” ,i.e. two states x and y belong to same class implies the period of x is equal to the period of y. 相似文献
19.
In this paper we show that the Boltzmann weights of the three-dimensional Baxter-Bazhanov model give representations of the braid group if some suitable spectral limits are taken. In the trigonometric case we classify all possible spectral limits which produce braid group representations. Furthermore, we prove that for some of them we get cyclotomic invariants of links and for others we obtain tangle invariants generalizing the cyclotomic ones. 相似文献
20.