全文获取类型
收费全文 | 5524篇 |
免费 | 599篇 |
专业分类
系统科学 | 1074篇 |
理论与方法论 | 275篇 |
现状及发展 | 895篇 |
研究方法 | 17篇 |
综合类 | 3860篇 |
自然研究 | 2篇 |
出版年
2024年 | 1篇 |
2022年 | 1篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2018年 | 727篇 |
2017年 | 733篇 |
2016年 | 432篇 |
2015年 | 33篇 |
2014年 | 5篇 |
2013年 | 2篇 |
2012年 | 267篇 |
2011年 | 954篇 |
2010年 | 818篇 |
2009年 | 454篇 |
2008年 | 513篇 |
2007年 | 767篇 |
2006年 | 10篇 |
2005年 | 42篇 |
2004年 | 123篇 |
2003年 | 154篇 |
2002年 | 62篇 |
2000年 | 2篇 |
1994年 | 2篇 |
1991年 | 3篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1974年 | 1篇 |
1973年 | 3篇 |
1969年 | 1篇 |
1967年 | 1篇 |
1966年 | 1篇 |
1960年 | 1篇 |
1956年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有6123条查询结果,搜索用时 15 毫秒
1.
Static extracting method of software intended behavior based on API functions invoking 总被引:1,自引:0,他引:1
The method of extracting and describing the intended behavior of software precisely has become one of the key points in the fields of software behavior's dynamic and trusted authentication. In this paper, the author proposes a specified measure of extracting SIBDS (software intended behaviors describing sets) statically from the binary executable using the software's API functions invoking, and also introduces the definition of the structure used to store the SIBDS in detail. Experimental results demonstrate that the extracting method and the storage structure definition offers three strong properties: (i) it can describe the software's intended behavior accurately; (ii) it demands a small storage expense; (iii) it provides strong capability to defend against mimicry attack. 相似文献
2.
A theoretical model for mid-and low-latitude ionospheric electric fields in realistic geomagnetic fields 总被引:1,自引:1,他引:0
The geomagnetic fields, which play important roles in the ionospheric dynamo, can greatly affect the global distribution of ionospheric electric fields, currents and other ionospheric electrodynamics phenomena. In the study of ionospheric electrodynamics phenomena, such as the longitudinal variations of ionospheric electric fields, the non-dipolar component of the geomagnetic fields must be taken into account. In this paper, we deduce a theoretical electric field model for ionospheric dynamo at mid- and low-latitude which adopt a modified magnetic apex coordinates system. In the new electric field model, the geomagnetic fields can be calculated from either the IGRF model or the dipole field model, and the neutral winds and conductivities are calculated based on empirical models. Then the dynamo equation for the electric potential is finally solved in terms of the line-by-line iteration method, and the ionospheric electric fields and currents are derived from the calculated potential. Our model can reproduce the main features of the ionospheric electrodynamics processes, so it will be a useful tool for the investigation of the upper atmosphere and ionosphere. 相似文献
3.
C. Baroni Urbani G. S. Boyan A. Blarer J. Billen T. M. Musthak Ali 《Cellular and molecular life sciences : CMLS》1994,50(1):63-71
The Indian antHarpegnathos saltator may be unique among insects in using its jumping capacity not only as an escape mechanism but also as a normal means of locomotion, and for catching its prey in flight. High-speed cinematography used to analyse the various phases of the jump suggests thatHarpegnathos employs a novel jumping mechanism to mediate these behaviours: namely the synchronous activation of its middle and hindlegs. Electrophysiological recordings from muscles or nerves in pairs of middle and hindlegs show remarkably synchronous activity during fictive jumping, supporting the synchronous activation hypothesis.Harpegnathos is not the only ant to jump, and a cladistic analysis suggests that jumping behaviour evolved independently three times during ant evolutionary history. 相似文献
4.
An Fe-based amorphous alloy was found to significantly enhance the reductive degradation of an azo dye in aqueous solution. The surface-area normalized rate constant was up to 2.0 L m-2 min-1 at room temperature,an order of magnitude larger than any previously reported value. The activation energy of the degradation process was calculated according to the Arrhenius equation,and a much lower value than those previously reported was obtained. Valence band measurement indicated that a depressed valence band maximum and a widened empty band were established in the amorphous ribbon. The unique structure of the amorphous alloy is important-it may reduce the activation energy of the degradation process and enhance the activity of the electrons,thus accelerating the degradation process. 相似文献
5.
延长油田东部裸眼井区早期测井资料普遍只有自然电位(SP)、自然伽马(GR)及梯度电阻率(R2.5)三条曲线,因缺失声波(AC)、地层电阻率(RT)等测井曲线,难以满足精细油藏地质研究需求。东部裸眼井区开发时间长、单井产量低,重新测井缺乏可行性及经济性。采用长短期记忆循环神经网络(Long Short-Term Memory,LSTM)进行缺失测井曲线重构是一种经济有效方法,适用于地层测井序列数据。然而延长油田东部浅层油藏上覆黄土层段测井数据信号干扰大,直接应用模型精度较差。针对此问题,本文采用考虑地质分层约束的LSTM模型进行缺失测井曲线的重构,通过分层数据截取每口井长6层段测井数据作为样本数据,既保留了LSTM模型处理序列数据的优势,同时又避免了上覆黄土层测井数据对模型的干扰。利用裸眼井区完整测井数据进行模型训练优化和验证,讨论了考虑地质分层约束的LSTM测井曲线重构精度,结果表明通过引入地质分层约束,模型重构测井曲线精度更高。应用优化后模型实现裸眼井区50口仅有GR、SP、R2.5三条曲线数据井的AC、RT曲线重构,对50口井的142个射孔段进行二次解释,对比试油解释结论符合率达到89.4%,验证了该方法对测井曲线重构的实用性和有效性。 相似文献
6.
Automatically allocation of more attention to negative stimuli is called emotional negativity bias. An event-related potentials (ERPs) experiment investigated whether or not this bias was altered by positive mood arousal. The results suggested that the attention bias towards negative stimuli was attenuated when positive information was accessible. 相似文献
7.
This paper further investigates cluster synchronization in a complex dynamical network with two-cluster. Each cluster contains a number of identical dynamical systems, however, the subsystems composing the two clusters can be different, i.e., the individual dynamical system in one cluster can differ from that in the other cluster. Complete synchronization within each cluster is possible only if each node from one cluster receives the same input from nodes in other cluster. In this case, the stability condition of one-cluster synchronization is known to contain two terms: the first accounts for the contribution of the inner-cluster coupling structure while the second is simply an extra linear term, which can be deduced by the "same-input" condition. Applying the connection graph stability method, the authors obtain an upper bound of input strength for one cluster if the first account is known, by which the synchronizability of cluster can be scaled. For different clusters, there are different upper bound of input strength by virtue of different dynamics and the corresponding cluster structure. Moreover, two illustrative examples are presented and the numerical simulations coincide with the theoretical analysis. 相似文献
8.
This paper considers a problem of optimal preventive maintenance and replacement schedule of equipment devoted to extracting resources from known deposits. Typical examples are oil drills, mine shovels, etc. At most one replacement of the existing machinery by a new one is allowed. The problem is formulated as an optimal control problem subject to the state constraint that the remaining deposit at any given time is nonnegative. We show that the optimal preventive maintenance, production rates, and the replacement and salvage times of the existing machinery and the new one, if required, can be obtained by solving sequentially a series of free-end-point optimal control problems. Moreover, an algorithm based on this result is developed and used to solve two illustrative examples. 相似文献
9.
An improved branch-and-bound algorithm to minimize the weighted flowtime on identical parallel machines with family setup times 总被引:1,自引:0,他引:1
Belgacem BETTAYEB Imed KACEM Kondo H.ADJALLAH LOSI-ICD CNRS FRE Universitéde technologie de Troyes France 《系统科学与系统工程学报(英文版)》2008,17(4):446-459
This article investigates identical parallel machines scheduling with family setup times. The objective function being the weighted sum of completion times, the problem is known to be strongly NP-hard. We propose a constructive heuristic algorithm and three complementary lower bounds. Two of these bounds proceed by elimination of setup times or by distributing each of them to jobs of the corresponding family, while the third one is based on a lagrangian relaxation. The bounds and the heuristic are incorporated into a branch-and-bound algorithm. Experimental results obtained outperform those of the methods presented in previous works, in term of size of solved problems. 相似文献
10.
Interval Time Series Analysis with an Application to the Sterling-Dollar Exchange Rate 总被引:2,自引:0,他引:2
Traditional econometrics has long employed "points" to measure time series data. In real life situations, however, it suffers the loss of volatility information, since many variables are bounded by intervals in a given period. To address this issue, this paper provides a new methodology for interval time series analysis. The concept of "interval stochastic process" is formally defined as a counterpart of "stochastic process" in point-based econometrics. The authors introduce the concepts of interval stationarity, interval statistics (including interval mean, interval variance, etc.) and propose an interval linear model to investigate the dynamic relationships between interval processes. A new interval-based optimization approach for estimation is proposed, and corresponding evaluation criteria are derived. To demonstrate that the new interval method provides valid results, an empirical example on the sterling-dollar exchange rate is presented. 相似文献