全文获取类型
收费全文 | 5233篇 |
免费 | 91篇 |
国内免费 | 335篇 |
专业分类
化学 | 1185篇 |
晶体学 | 8篇 |
力学 | 165篇 |
综合类 | 28篇 |
数学 | 3030篇 |
物理学 | 1243篇 |
出版年
2024年 | 4篇 |
2023年 | 59篇 |
2022年 | 32篇 |
2021年 | 29篇 |
2020年 | 67篇 |
2019年 | 42篇 |
2018年 | 45篇 |
2017年 | 70篇 |
2016年 | 87篇 |
2015年 | 85篇 |
2014年 | 232篇 |
2013年 | 379篇 |
2012年 | 363篇 |
2011年 | 359篇 |
2010年 | 272篇 |
2009年 | 403篇 |
2008年 | 343篇 |
2007年 | 450篇 |
2006年 | 258篇 |
2005年 | 200篇 |
2004年 | 175篇 |
2003年 | 158篇 |
2002年 | 142篇 |
2001年 | 159篇 |
2000年 | 137篇 |
1999年 | 118篇 |
1998年 | 124篇 |
1997年 | 98篇 |
1996年 | 111篇 |
1995年 | 83篇 |
1994年 | 46篇 |
1993年 | 64篇 |
1992年 | 37篇 |
1991年 | 39篇 |
1990年 | 29篇 |
1989年 | 43篇 |
1988年 | 31篇 |
1987年 | 10篇 |
1986年 | 12篇 |
1985年 | 58篇 |
1984年 | 50篇 |
1983年 | 20篇 |
1982年 | 43篇 |
1981年 | 33篇 |
1980年 | 28篇 |
1979年 | 18篇 |
1978年 | 6篇 |
1976年 | 4篇 |
1973年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有5659条查询结果,搜索用时 359 毫秒
31.
32.
J. M. Kumpula J. Saramäki K. Kaski J. Kertész 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,56(1):41-45
According to Fortunato and Barthélemy, modularity-based community detection
algorithms have a resolution threshold such that small communities in a large
network are invisible. Here we generalize their work and show that the q-state
Potts community detection method introduced by Reichardt and Bornholdt
also has a resolution threshold. The model contains a parameter by which this threshold can be tuned, but no a priori principle
is known to select the proper value.
Single global optimization criteria do not seem capable for detecting all
communities if their size distribution is broad. 相似文献
33.
In apparel industry, manufacturers developed standard allowed minutes (SAMs) databases on various manufacturing operations in order to facilitate better scheduling, while effective production schedules ensure smoothness of downstream operations. As apparel manufacturing environment is fuzzy and dynamic, rigid production schedules based on SAMs become futile in the presence of any uncertainty. In this paper, a fuzzification scheme is proposed to fuzzify the static standard time so as to incorporate some uncertainties, in terms of both job-specific and human related factors, into the fabric-cutting scheduling problem. A genetic optimisation procedure is also proposed to search for fault-tolerant schedules using genetic algorithms, such that makespan and scheduling uncertainties are minimised. Two sets of real production data were collected to validate the proposed method. Experimental results indicate that the genetically optimised fault-tolerant schedules not only improve the operation performance but also minimise the scheduling risks. 相似文献
34.
Marco Merkli 《Journal of Mathematical Analysis and Applications》2007,327(1):376-399
Level shift operators describe the second-order displacement of eigenvalues under perturbation. They play a central role in resonance theory and ergodic theory of open quantum systems at positive temperatures. We exhibit intrinsic properties of level shift operators, properties which stem from the structure of open quantum systems at positive temperatures and which are common to all such systems. They determine the geometry of resonances bifurcating from eigenvalues of positive temperature Hamiltonians and they relate the Gibbs state, the kernel of level shift operators, and zero energy resonances. We show that degeneracy of energy levels of the small part of the open quantum system causes the Fermi Golden Rule Condition to be violated and we analyze ergodic properties of such systems. 相似文献
35.
After more than 20 years of impressive development since the economic reforms in 1978, today western China is facing an increasing
development gap between its regions, particularly between urban and rural areas. Using the fuzzy comprehensive evaluation
model, this paper aims to demonstrate the evolution of the economic competitiveness levels base on two categories of geographical
unity in the province of Gansu located in Northwest China between 2000 and 2004. The results of fuzzy modeling are integrated
into GIS spatiotemporal analyses in order to identify the spatial variation of each significant change in terms of the regional
economic development. Our research effectively illustrates that there is a particular spatial dynamic of the economic development
from region to region. Although the cities have improved very well in their economic competitiveness, the rural areas and
minority regions still have a lot of progress to be achieved. 相似文献
36.
Fuzzy random vector is a measurable map from a probability space to a collection of fuzzy vectors. Our aim in this paper is
to discuss the measurability criteria for fuzzy random vectors, and show that under mild assumption, the measurability criteria
for upper semicontinuous fuzzy random vectors can be expressed in several different but equivalent formulations. Finally,
applying the obtained results, we resolve an open problem about the relationship between fuzzy random vectors and fuzzy random
variables. 相似文献
37.
一类死区非线性输入系统的自适应模糊控制 总被引:1,自引:0,他引:1
针对一类具有死区非线性输入的非线性系统,基于滑模控制的基本原理,利用II型模糊逻辑系统对未知函数进行在线逼近,提出了一种具有监督器的自适应模糊滑模控制方法。该方法通过监督控制器保证闭环系统所有信号有界,并通过引入最优逼近误差的自适应补偿项来消除建模误差的影响。通过理论分析,证明了跟踪误差收敛到零。 相似文献
38.
基于伽罗瓦连接,分别在交换伴随对与对合剩余格条件下,讨论了模糊概念格的四种定义形式。并证明了在对合剩余格上,对偶性成立,四种模糊算子将具有与经典意义下一致的相互关系。最后我们提出了一种基于模糊概念格的模糊推理规则,并证明了其还原性。 相似文献
39.
The feature selection consists of obtaining a subset of these features to optimally realize the task without the irrelevant
ones. Since it can provide faster and cost-effective learning machines and also improve the prediction performance of the
predictors, it is a crucial step in machine learning. The feature selection methods using support machines have obtained satisfactory
results, but the noises and outliers often reduce the performance. In this paper, we propose a feature selection approach
using fuzzy support vector machines and compare it with the previous work, the results of experiments on the UCI data sets
show that feature selection using fuzzy SVM obtains better results than using SVM. 相似文献
40.
讨论了Fuzzy矩阵A的同解简化矩阵A^(2),指出陈贻源论文《解Fuzzy关系方程》中定量3的错误。研究Fuzzy矩阵方程的摄动问题,解决了汤服成(2000)提出的未解决问题。 相似文献