全文获取类型
收费全文 | 11591篇 |
免费 | 807篇 |
国内免费 | 738篇 |
专业分类
化学 | 1636篇 |
晶体学 | 56篇 |
力学 | 206篇 |
综合类 | 133篇 |
数学 | 2174篇 |
物理学 | 2553篇 |
综合类 | 6378篇 |
出版年
2024年 | 38篇 |
2023年 | 105篇 |
2022年 | 191篇 |
2021年 | 213篇 |
2020年 | 222篇 |
2019年 | 253篇 |
2018年 | 246篇 |
2017年 | 305篇 |
2016年 | 306篇 |
2015年 | 341篇 |
2014年 | 676篇 |
2013年 | 705篇 |
2012年 | 718篇 |
2011年 | 719篇 |
2010年 | 536篇 |
2009年 | 646篇 |
2008年 | 700篇 |
2007年 | 824篇 |
2006年 | 721篇 |
2005年 | 609篇 |
2004年 | 546篇 |
2003年 | 533篇 |
2002年 | 419篇 |
2001年 | 340篇 |
2000年 | 325篇 |
1999年 | 278篇 |
1998年 | 223篇 |
1997年 | 214篇 |
1996年 | 213篇 |
1995年 | 161篇 |
1994年 | 138篇 |
1993年 | 116篇 |
1992年 | 106篇 |
1991年 | 95篇 |
1990年 | 79篇 |
1989年 | 57篇 |
1988年 | 63篇 |
1987年 | 37篇 |
1986年 | 25篇 |
1985年 | 16篇 |
1984年 | 16篇 |
1983年 | 6篇 |
1982年 | 21篇 |
1981年 | 9篇 |
1980年 | 3篇 |
1979年 | 10篇 |
1978年 | 8篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
921.
922.
Iddo Eliazar 《Physica A》2011,390(4):699-706
This paper explores an elemental connection between call options-the most commonly tradable financial derivatives, implied volatility term structures-critical “market information” emanating from call-option prices, and the Pietra index-a quantitative economic measure of societal egalitarianism. Our study: (i) unveils an intrinsic “Pietra structure” of call-option prices; (ii) introduces the notion of the “Pietra term structures” of financial assets; (iii) describes the probabilistic meaning of the Pietra term structures; (iv) establishes an explicit nonlinear one-to-one mapping between the Pietra term structures and the implied volatility term structures of financial assets. The results presented in this paper provide a deep insight into the econophysics of call options and implied volatility term structures. 相似文献
923.
高光谱技术分析茶树叶片中叶绿素含量及分布 总被引:4,自引:0,他引:4
植物叶片叶绿素含量及分布是植物营养信息表达的一个重要指标.以茶树为研究对象,利用高光谱技术分析茶树叶片中叶绿素含量及其分布.通过采集茶树鲜叶的高光谱图像,利用7种不同的算法从高光谱数据中提取相应的特征参数,并根据特征参数和叶绿素含量的参考测量值分别拟合出相应的预测模型.结果显示,二次土壤调节植被指数算法提取的特征参数最... 相似文献
924.
基于环境星CCD数据的环境植被指数及叶面积指数反演研究 总被引:4,自引:0,他引:4
利用PROSAIL前向模型模拟的植被冠层光谱,在植被指数构造时,引入修正大气、土壤背景影响的蓝、绿波段,构建了避免过早饱和的环境植被指数(environmental vegetation index,EVI)。基于多个典型冬小麦生育期的地面观测数据,建立基于EVI-LAI长时间序列反演模型,并对模型进行不同品种间的交叉检验。研究表明,EVI建立的叶面积指数(leaf area index,LAI)反演模型精度优于同类植被指数模型,并具有较好的普适性,能应用于冬小麦遥感多时相长势监测及LAI反演。 相似文献
925.
Computational aspects of simplex and MBU-simplex algorithms using different anti-cycling pivot rules
Tibor Illés 《Optimization》2014,63(1):49-66
AbstractSeveral variations of index selection rules for simplex-type algorithms for linear programming, like the Last-In-First-Out or the Most-Often-Selected-Variable are rules not only theoretically finite, but also provide significant flexibility in choosing a pivot element. Based on an implementation of the primal simplex and the monotonic build-up (MBU) simplex method, the practical benefit of the flexibility of these anti-cycling pivot rules is evaluated using public benchmark LP test sets. Our results also provide numerical evidence that the MBU-simplex algorithm is a viable alternative to the traditional simplex algorithm. 相似文献
926.
O.I. Kostyukova 《Optimization》2014,63(1):67-91
In the paper, we consider a problem of convex Semi-Infinite Programming with an infinite index set in the form of a convex polyhedron. In study of this problem, we apply the approach suggested in our recent paper [Kostyukova OI, Tchemisova TV. Sufficient optimality conditions for convex Semi Infinite Programming. Optim. Methods Softw. 2010;25:279–297], and based on the notions of immobile indices and their immobility orders. The main result of the paper consists in explicit optimality conditions that do not use constraint qualifications and have the form of criterion. The comparison of the new optimality conditions with other known results is provided. 相似文献
927.
《Applied Mathematical Modelling》2014,38(9-10):2303-2310
Acceptance sampling has been widely used tool for determining whether the submitted lot should be accepted or rejected. However, it cannot avoid two kinds of risks, accepting undesired poor product lots and rejecting good product lots. Such risks are even more significant as the rapid advancement of the manufacturing technology and stringent customers demand is enforced. A yield index Spk has been developed to provide an exact measure on process yield or fraction nonconforming for normally distributed processes with two-sided specification limits. Therefore, the aim of this paper is to develop a variables sampling plan for evaluating the lot or process fraction nonconforming based on the yield index. The probability of lot acceptance is derived based on the sampling distribution and two-point condition on OC curve is used to determine the plan parameters. Tables of the plan parameters and step-by-step procedure are provided for the practitioner to make decision on lot sentencing especially for situations of products with very low fraction of nonconformities. 相似文献
928.
The circular chromatic index of a graph G, written , is the minimum r permitting a function such that whenever e and are adjacent. It is known that for any , there is a 3‐regular simple graph G with . This article proves the following results: Assume is an odd integer. For any , there is an n‐regular simple graph G with . For any , there is an n‐regular multigraph G with . 相似文献
929.
We study the numerical radius of Lipschitz operators on Banach spaces via the Lipschitz numerical index, which is an analogue of the numerical index in Banach space theory. We give a characterization of the numerical radius and obtain a necessary and sufficient condition for Banach spaces to have Lipschitz numerical index 1. As an application, we show that real lush spaces and C -rich subspaces have Lipschitz numerical index 1. Moreover, using the Gâteaux differentiability of Lipschitz operators, we characterize the Lipschitz numerical index of separable Banach spaces with the RNP. Finally, we prove that the Lipschitz numerical index has the stability properties for the c0-, l1-, and l∞-sums of spaces and vector-valued function spaces. From this, we show that the C(K) spaces, L1(μ)-spaces and L∞(ν)-spaces have Lipschitz numerical index 1. 相似文献
930.