全文获取类型
收费全文 | 12709篇 |
免费 | 245篇 |
国内免费 | 604篇 |
专业分类
系统科学 | 1487篇 |
丛书文集 | 628篇 |
教育与普及 | 1970篇 |
理论与方法论 | 154篇 |
现状及发展 | 475篇 |
研究方法 | 665篇 |
综合类 | 8137篇 |
自然研究 | 42篇 |
出版年
2021年 | 53篇 |
2019年 | 37篇 |
2018年 | 67篇 |
2017年 | 76篇 |
2016年 | 72篇 |
2015年 | 104篇 |
2014年 | 188篇 |
2013年 | 125篇 |
2012年 | 440篇 |
2011年 | 555篇 |
2010年 | 269篇 |
2009年 | 153篇 |
2008年 | 516篇 |
2007年 | 665篇 |
2006年 | 815篇 |
2005年 | 979篇 |
2004年 | 687篇 |
2003年 | 737篇 |
2002年 | 534篇 |
2001年 | 536篇 |
2000年 | 613篇 |
1999年 | 336篇 |
1998年 | 194篇 |
1997年 | 142篇 |
1996年 | 132篇 |
1995年 | 111篇 |
1994年 | 126篇 |
1993年 | 183篇 |
1992年 | 145篇 |
1991年 | 153篇 |
1990年 | 130篇 |
1989年 | 139篇 |
1988年 | 193篇 |
1987年 | 201篇 |
1986年 | 234篇 |
1985年 | 226篇 |
1984年 | 242篇 |
1983年 | 226篇 |
1982年 | 216篇 |
1981年 | 183篇 |
1980年 | 160篇 |
1979年 | 75篇 |
1964年 | 37篇 |
1959年 | 166篇 |
1958年 | 255篇 |
1957年 | 182篇 |
1956年 | 166篇 |
1955年 | 159篇 |
1954年 | 151篇 |
1948年 | 47篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
本文研究了乙烷和丙烷的混合裂解,并与乙烷、丙烷单独裂解进行了比较。解决了微分方程组的刚性问题,提出了混合裂解反应动力学模型。明确了三种选择性的概念,即;真实选择性、迭加选择性和总选择性,从而澄清了国际上对于选择性有正偏差和负偏差的不同观点。为乙烯生产提供了有效利用乙烷和丙烷的分析评价方法。 相似文献
52.
我们眼球的后部整齐地排列着10亿个特殊的光敏感神经细胞,阏读这些文字需要其中四分之一以上的细胞协同参与.反映在组构精密被称为视网膜的神经组织上,由这些字母组成明暗不同的各种文字被转 相似文献
53.
Song Liuping Sun ZhongkangDept. of Electronic Eng. National Univ. of Defense Technology Changsha China 《系统工程与电子技术(英文版)》1991,(2)
The purpose of this paper is to develop a high speed detection scheme for moving and / or stationary point targets in a multitarget environment as registered in an IR image sequence. An iterative approximate 3-D line searching algorithm based upon the geometric representation of lines (for non-maneuvering targets in space) in a 3-D space is derived. The convergency of the algorithm is proved. An analysis is performed of the theoretical detection performance of the algorithm. The statistical experiment results show high effectiveness and computational efficiency of the algorithm in the case of low SNR. The idea may be employed to satisfy the real-time processing requirement of an IR system. 相似文献
54.
Zhongsheng WANG Zhigang ZENG Xiaoxin LIAODepartment of Control Science Engineering Huazhong University of Science Technology Wuhan Hubei P. R. China 《系统科学与系统工程学报(英文版)》2003,12(2):204-209
Some stability criteria are obtained for a class of uncertain systems with time-delay usingLyapunov functional and analytic techniques. It is easy to check the criteria by making use of theboundedness of the uncertainties. 相似文献
55.
OrCAD9.2是国际通用电子设计自动化(EDA)软件包,文中介绍了用该软件对电路进行噪声计算的方法,并给出用模拟分析计算的典型电路噪声,证明这种方法在分析复杂电路的噪声时方便、简单、准确。 相似文献
56.
Ju-liang ZHANG Jian CHENDepartment of Management Science EngineeringSchool of Economics Management Tsinghua University Beijing China. 《系统科学与系统工程学报(英文版)》2003,12(3):360-371
This paper investigates the impact of a secondary market, where retailers can buy and sell excessinventories, on the supply chain. We develop a two-period model with a single manufacturer and tworetailers. At the beginning of the first period the retailers order and receive products from themanufacturer, but at the beginning of the second period, they can trade surplus products betweenthemselves in the secondary market. We investigate the impact of the correlated dependence ofretailers' demand on both the quantity effect and the allocation effect under the secondary market.Lastly,we study potential strategies for the manufacturer to increase sales with the existence of thesecondary market. 相似文献
57.
CHEN Yaojun 《系统科学与复杂性》2003,(2)
A subset of S of the vertex set of a graph G is called acyclic if the subgraph it induces in G contains no cycles. S is called an acyclic dominating set of G if it. is both acyclic and dominating. The minimum cardinality of an acyclic dominating set, denoted by 7a(G), is called the acyclic domination number of G. S. M. Hedetniemi et al. on 2000 introduced the concept of acyclic domination and posed the following open problem: Is -ya(G) < <5(G) for any graph whose diameter is two? In this paper, we give a counterexample which disproves the problem. 相似文献
58.
FROM MANUFACTURING SCHEDULING TO SUPPLY CHAIN COORDINATION:THE CONTROL OF COMPLEXITY AND UNCERTAINTY
Peter B.LUH 《系统科学与系统工程学报(英文版)》2003,12(3):279-297
With time-based competition and rapid technology advancements, effective manufacturingscheduling and supply chain coordination are critical to quickly respond to changing marketconditions. These problems, however, are difficult in view of inherent complexity and variousuncertainties involved. Based on a series of results by the authors, decomposition and coordination byusing Lagrangian relaxation is identified in this paper as an effective way to control complexity anduncertainty.A manufacturing scheduling problem is first formulated within the job shop context withuncertain order arrivals, processing times, due dates, and part priorities as a separable optimizationproblem. A solution methodology that combines Lagrangian relaxation, stochastic dynamicprogramming, and heuristics is developed. Method improvements to effectively solve large problemsare also highlighted. To extend manufacturing scheduling within a factory to coordinate autonomicmembers across chains of suppliers, a decentralized supply chai 相似文献
59.
Qiangfu Zhao Zhong Wang Youan KeDept. of Electronic Eng. Beijing Institute of Technology P.O.Box Beijing China 《系统工程与电子技术(英文版)》1991,(2)
It has long been realized that the problem of radar imaging is a special case of image reconstruction in which the data are incomplete and noisy. In other fields, iterative reconstruction algorithms have been used successfully to improve the image quality. This paper studies the application of iterative algorithms in radar imaging. A discrete model is first derived, and the iterative algorithms are then adapted to radar imaging. Although such algorithms are usually time consuming, this paper shows that, if the algorithms are appropriately simplified, it is possible to realize them even in real time. The efficiency of iterative algorithms is shown through computer simulations. 相似文献
60.
XI Zengzhe LI Zhenrong XU Zhuo ZHANG Liangying & YAO Xi . Functional Materials Research Laboratory Tongji University Shanghai China . Key Laboratory of the Ministry of Education Xi抋n Jiaotong University Xi抋n China 《科学通报(英文版)》2003,48(19):2038-2040
It has been reported that the single crystal of relaxor ferroelectrics (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT) with the compositions near the morphotropic phase boundary (MPB, 0.28相似文献