全文获取类型
收费全文 | 6941篇 |
免费 | 835篇 |
国内免费 | 466篇 |
专业分类
化学 | 2083篇 |
晶体学 | 25篇 |
力学 | 190篇 |
综合类 | 21篇 |
数学 | 1487篇 |
物理学 | 4436篇 |
出版年
2024年 | 13篇 |
2023年 | 98篇 |
2022年 | 125篇 |
2021年 | 140篇 |
2020年 | 185篇 |
2019年 | 171篇 |
2018年 | 161篇 |
2017年 | 175篇 |
2016年 | 246篇 |
2015年 | 210篇 |
2014年 | 340篇 |
2013年 | 482篇 |
2012年 | 319篇 |
2011年 | 445篇 |
2010年 | 369篇 |
2009年 | 475篇 |
2008年 | 490篇 |
2007年 | 536篇 |
2006年 | 423篇 |
2005年 | 313篇 |
2004年 | 280篇 |
2003年 | 324篇 |
2002年 | 268篇 |
2001年 | 214篇 |
2000年 | 232篇 |
1999年 | 168篇 |
1998年 | 169篇 |
1997年 | 109篇 |
1996年 | 72篇 |
1995年 | 77篇 |
1994年 | 65篇 |
1993年 | 59篇 |
1992年 | 54篇 |
1991年 | 34篇 |
1990年 | 41篇 |
1989年 | 37篇 |
1988年 | 31篇 |
1987年 | 26篇 |
1986年 | 33篇 |
1985年 | 32篇 |
1984年 | 31篇 |
1983年 | 10篇 |
1982年 | 13篇 |
1981年 | 28篇 |
1980年 | 23篇 |
1979年 | 18篇 |
1978年 | 17篇 |
1977年 | 20篇 |
1976年 | 15篇 |
1974年 | 8篇 |
排序方式: 共有8242条查询结果,搜索用时 15 毫秒
1.
《Operations Research Letters》2022,50(2):137-144
In mine planning problems, cutoff grade optimization defines a threshold at every time period such that material above this value is processed, and the rest is considered waste. In orebodies with multiple minerals, which occur in practice, the natural extension is to consider a cutoff surface. We show that in two dimensions the optimal solution is a line, and in n dimensions it is a hyperplane. 相似文献
2.
This paper infers from a generalized Picone identity the uniqueness of the stable positive solution for a class of semilinear equations of superlinear indefinite type, as well as the uniqueness and global attractivity of the coexistence state in two generalized diffusive prototypes of the symbiotic and competing species models of Lotka–Volterra. The optimality of these uniqueness theorems reveals the tremendous strength of the Picone identity. 相似文献
3.
4.
We report optical and nonlinear optical properties of CuS quantum dots and nanoparticles prepared through a nontoxic, green, one-pot synthesis method. The presence of surface states and defects in the quantum dots are evident from the luminescent behavior and enhanced nonlinear optical properties measured using the open aperture Z-scan, employing 5 ns laser pulses at 532 nm. The quantum dots exhibit large effective third order nonlinear optical coefficients with a relatively lower optical limiting threshold of 2.3 J cm−2, and the optical nonlinearity arises largely from absorption saturation and excited state absorption. Results suggest that these materials are potential candidates for designing efficient optical limiters with applications in laser safety devices. 相似文献
5.
Vyacheslav V. Sentyurin Oleg A. Levitskiy Tatiana V. Magdesieva 《Current Opinion in Electrochemistry》2020
This mini-review highlights key structural features that should be taken into account when creating ambipolar redox-active closed-shell metal-free molecules. This type of compound is strongly required for the fabrication of all-organic ‘poleless’ batteries and semiconductors. The suggested strategies aimed at stabilization of both oxidized (cationic) and reduced (anionic) redox-states are based on the comprehensive analysis of the most successful structures taken from the recent publications. 相似文献
6.
Multi-sensor data fusion is an evolving technology whereby data from multiple sensor inputs are processed and combined. The data derived from multiple sensors can, however, be uncertain, imperfect, and conflicting. The present study is undertaken to help contribute to the continuous search for viable approaches to overcome the problems associated with data conflict and imperfection. Sensor readings, represented by belief functions, have to be fused according to their corresponding weights. Previous studies have often estimated the weights of sensor readings based on a single criterion. Mono-criteria approaches for the assessment of sensor reading weights are, however, often unreliable and inadequate for the reflection of reality. Accordingly, this work opts for the use of a multi-criteria decision aid. A modified Analytical Hierarchy Process (AHP) that incorporates several criteria is proposed to determine the weights of a sensor reading set. The approach relies on the automation of pairwise comparisons to eliminate subjectivity and reduce inconsistency. It assesses the weight of each sensor reading, and fuses the weighed readings obtained using a modified average combination rule. The efficiency of this approach is evaluated in a target recognition context. Several tests, sensitivity analysis, and comparisons with other approaches available in the literature are described. 相似文献
7.
Prof. Dr. Yoshio Teki 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(5):980-996
Recently, the potential use of organic π-radicals and related spin systems has been expanded to modern technological applications. The unique excited-state dynamics of organic π-radicals can be useful to improve the stability of photochemically unstable organic compounds, make the polarization transfer applicable to information technology, and achieve effective up-conversion of interest for luminescence bioimaging, among others. Furthermore, highly luminescent stable π-radicals have been recently reported, which are especially interesting for application in organic light-emitting devices owing to their potential to provide an internal quantum efficiency of 100 %. Thus, the excited-state nature of stable π-radicals as well as the control of their excited-state spin dynamics are emerging topics both in terms of fundamental science and related technological applications. In this minireview, we focus on the excited-state dynamics of both photostable non(weakly)-luminescent and luminescent π-radicals, which are opposites of each other. In particular, we cover the following topics: 1) effective generation of high-spin photoexcited states and control of the excited-state dynamics by using non-luminescent π-radicals, 2) unique excited-state dynamics of luminescent π-radicals and radical excimers, and 3) applications utilizing excited-state dynamics of π-radicals. 相似文献
8.
9.
Nonclassical light states are important for both conceptual and practical reasons: they are basic ingredients in testing and exploring quantum foundations, and are crucial resources in quantum technologies. Various useful criteria have been developed to detect nonclassicality in the literature, and several meaningful measures of nonclassicality have been introduced and measured experimentally. In this work, by use of a non-Hermitian generalization of the Wigner-Yanase-Dyson skew information and playing with operator ordering in evaluating average photon number, we develop a novel family of criteria for detecting nonclassicality of light based on Lieb's concavity, which is a deep and powerful result concerning interaction between quantum states and observables. We elucidate the information-theoretic as well as the physical meaning of the criteria, and illustrate their effectiveness in capturing and quantifying nonclassicality of various important light states. 相似文献
10.