全文获取类型
收费全文 | 18671篇 |
免费 | 1154篇 |
国内免费 | 792篇 |
专业分类
系统科学 | 1818篇 |
丛书文集 | 410篇 |
教育与普及 | 339篇 |
理论与方法论 | 322篇 |
现状及发展 | 930篇 |
研究方法 | 42篇 |
综合类 | 16754篇 |
自然研究 | 2篇 |
出版年
2024年 | 40篇 |
2023年 | 161篇 |
2022年 | 252篇 |
2021年 | 298篇 |
2020年 | 250篇 |
2019年 | 141篇 |
2018年 | 912篇 |
2017年 | 944篇 |
2016年 | 676篇 |
2015年 | 526篇 |
2014年 | 614篇 |
2013年 | 620篇 |
2012年 | 914篇 |
2011年 | 1609篇 |
2010年 | 1407篇 |
2009年 | 1126篇 |
2008年 | 1248篇 |
2007年 | 1401篇 |
2006年 | 565篇 |
2005年 | 478篇 |
2004年 | 521篇 |
2003年 | 591篇 |
2002年 | 670篇 |
2001年 | 602篇 |
2000年 | 446篇 |
1999年 | 524篇 |
1998年 | 376篇 |
1997年 | 390篇 |
1996年 | 346篇 |
1995年 | 305篇 |
1994年 | 301篇 |
1993年 | 263篇 |
1992年 | 218篇 |
1991年 | 220篇 |
1990年 | 189篇 |
1989年 | 152篇 |
1988年 | 148篇 |
1987年 | 83篇 |
1986年 | 42篇 |
1985年 | 20篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1967年 | 1篇 |
1960年 | 1篇 |
1955年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
971.
Radon-Nikodym theorem in signed Loeb space 总被引:1,自引:0,他引:1
MA Chunhui LI Shenggang SHI Yanwei . College of Mathematics Information Science Shaanxi Normal University Xi’an Shaanxi China . School of Science Xi’an Architecture Technology University Xi’an . Department of Basic Courses Xi’an Peihua University Xi’an 《武汉大学学报:自然科学英文版》2010,15(1):21-24
This paper gives the Radon-Nikodym theorem in signed Loeb space under 1-saturated nonstandard model. First,the nonstandard characterization of absolute continuity is discussed,on which Radon-Nikodym theorem in signed Loeb space is obtained. Then,some facts about a finite signed Loeb measure and its variation are shown. 相似文献
972.
Birds of a Feather Protest Together: Theorizing Self-Organizing Political Protests with Flock Theory 总被引:1,自引:0,他引:1
The current research theorizes decentralized and self-organized political protests via flock theory (Rosen 2002), a theory of emergent self-organization in communicative human interaction. Flock theory draws from a theoretical basis
of emergence and self-organizing systems, and is presented as a theory of decentralized communication structures. Focusing
on the optimization of decentralized networks and roadmap based coordination of organizationally homopholous foci; the current
theory poses a model of human interaction that captures the potentially egalitarian effects of cooperative evolution and collective
action. Case studies of two separate decentralized political protests against Korean government and FARC are offered as evidences
of such phenomena. 相似文献
973.
In order to improve removal for nitrogen in a pilot-scale submerged membrane bioreactor (SMBR), intermittent aeration was
conducted, and the effect on the treatment performance under four kinds of operation condition (run 1, continuous aeration;
run 2, 60/60 min aeration on/off time; run 3, 60/90 min aeration on/off time; run 4, 60/75 min aeration on/off time) was evaluated.
The results showed that depending on the specific on/off of the aeration time ratio, removal efficiency of nitrogen could
be improved significantly, and the removal rates of total nitrogen (TN) under different operation conditions were 28.0%, 59.5%,
66.8% and 70.7%, respectively. There were no obvious differences for removal rates for CODCr and ammonia among different operation conditions. In general, intermittent aeration could be used as a feasible way to improve
treatment performance for nitrogen in the SMBR. 相似文献
974.
Viability criteria for differential inclusions 总被引:2,自引:0,他引:2
Yan Gao 《系统科学与复杂性》2011,24(5):825-834
A method of verifying the viability criterion at a given point for a region with nonsmooth boundary, which is expressed by
a quasidifferentiabl function, under a differential inclusion which is a convex hull of finitely many functions, is proposed.
By this method, determining the viability is transformed into solving a number of systems of linear inequalities, or equivalently
solving a number of linear programming problems. For the other differential inclusion, called the generalized convex process,
it is shown that viability condition holds for a polytope if and only if it holds at all of its vertices. This result is an
extension of corresponding one for a linear control system. 相似文献
975.
976.
The state transfer under control fields is analyzed based on the Bloch sphere representation of a single qubit. In order to
achieve the target from an arbitrary initial state to a target state, the conditions that parameters should satisfy are deduced
separately in two different requirements: One is in the case of the rotation angle around the x-axis being fixed and another is in the situation with a given evolution time. Several typical states trajectories are demonstrated
by numerical simulations on the Bloch sphere. The relations between parameters and the trajectories are analyzed. 相似文献
977.
A rapid process of hybridisation of man and technology, organisation and technology and society and technology is currently
sweeping the world. This process requires a way of (scientific) thinking that takes hybrid systems as the starting point.
Such an approach makes it increasingly important for hybrid systems to be interlinked, enabling them to exchange and share
information through these links. This linking of (hybrid) systems to enable them to exchange and share information can also
be denoted as the realisation of interoperability between (hybrid) systems. Five principles from Luhmann’s systems theory
can help us understand interoperability. Interoperability enables (hybrid) systems to join random coalitions and networks.
The network centric warfare concept is currently the basis for international efforts aimed at the development and application
of interoperability that would enable armed forces to act effectively and efficiently. This paper demonstrates what we can
learn from Luhmann’s system’s theory. 相似文献
978.
文章结合目前西藏自治区大学生就业困难的严峻形势,分析了培养大学生创业意识的重要性和紧迫性,从社会层面、高校层面和大学生自身层面对西藏大学生创业意识的培养方法提出了相应对策,认为只有外因和内因结合、大环境和小环境相互映照,才能全面培养大学生的创业意识。 相似文献
979.
Vegetation effects on mean daily maximum and minimum surface air temperatures over China 总被引:5,自引:0,他引:5
Changes in the daily maximum (Tmax) and minimum (Tmin) surface air temperatures and the associated temperature extremes have severe consequences on human society and the natural environment. In this study, we assess vegetation effects on mean Tmax and Tmin over China by computing a vegetation feedback parameter using the satellite-sensed Normalized Difference Vegetation Index (NDVI) and observed temperatures for the period 1982–2002. In all seasons, vegetation exerts a much stronger forcing on Tmax than on Tmin, and thus has a substantial effect on the diurnal temperature range (DTR) over China. Significant positive feedbacks on Tmax and the DTR occupy many areas of China with the feedback parameters exceeding 1°C (0.1 NDVI)–1, while significant negative effects only appear over the summertime climatic and ecological transition zone of northern China and some other isolated areas. Also, the vegetation feedbacks are found to vary with season. In areas where significant feedbacks occur, vegetation contributes to typically 10%–30% of the total variances in Tmax, Tmin, and the DTR. These findings suggest that vegetation memory offers the potential for improving monthly-to-seasonal forecasting of Tmax and Tmin, and the associated temperature extremes over China. Meanwhile, the limitations and uncertainties of the study should be recognized. 相似文献
980.
<正> Carvalho,Lucchesi and Murty proved that any 1-extendable graph G different from K_2and C_(2n)has at least Δ(G)edge-disjoint removable ears,and any brick G distinct from K_4 and■hasat least Δ(G)-2 removable edges,where Δ(G)denotes the maximum degree of G.In this paper,weimprove the lower bounds for numbers of removable ears and removable edges of 1-extendable graphs.It is proved that any 1-extendable graph G different from K_2 and C_(2n)has at least χ′(G)edge-disjointremovable ears,and any brick G distinct from K_4 and■has at least χ′(G)-2 removable edges,whereχ′(G)denotes the edge-chromatic number of G. 相似文献