首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   13957篇
  免费   688篇
  国内免费   1286篇
系统科学   1294篇
丛书文集   402篇
教育与普及   39篇
理论与方法论   25篇
现状及发展   129篇
综合类   14033篇
自然研究   9篇
  2024年   38篇
  2023年   92篇
  2022年   234篇
  2021年   272篇
  2020年   245篇
  2019年   230篇
  2018年   203篇
  2017年   278篇
  2016年   337篇
  2015年   473篇
  2014年   446篇
  2013年   404篇
  2012年   904篇
  2011年   653篇
  2010年   610篇
  2009年   629篇
  2008年   686篇
  2007年   1141篇
  2006年   1117篇
  2005年   956篇
  2004年   919篇
  2003年   644篇
  2002年   514篇
  2001年   474篇
  2000年   457篇
  1999年   462篇
  1998年   302篇
  1997年   323篇
  1996年   286篇
  1995年   241篇
  1994年   241篇
  1993年   207篇
  1992年   179篇
  1991年   192篇
  1990年   134篇
  1989年   164篇
  1988年   111篇
  1987年   62篇
  1986年   39篇
  1985年   21篇
  1984年   6篇
  1981年   3篇
  1980年   1篇
  1955年   1篇
排序方式: 共有10000条查询结果,搜索用时 26 毫秒
991.
基于遗传算法与模糊选择的多播路由优化   总被引:2,自引:0,他引:2  
遗传算法在优化计算特别是在多播路由问题中得到了广泛应用,但在进行大规模优化时,遗传算法存在着爬山能力差以及不成熟收敛等缺点。为此,提出基于启发式遗传算法和模糊选择机制的新型多播树计算方法,本算法采用树型结构编码和高效的遗传操作,同时优化时延、丢包率和带宽利用率等多个参数。仿真实验表明,这种算法用于多播路由多目标优化问题时,可以克服采用遗传算法进行多目标优化的缺陷。  相似文献   
992.
对Ag纳米线的熔化和过热作了研究,提出了一种经典热力学模型对Ag纳米线的过热机制作了阐述;当考虑到低能Ag/Ni界面的作用时,推导了过热的定量表达式,说明了过热与纳米线的半径和界面能有密切关系.  相似文献   
993.
市售8B铅笔芯经镀铂处理后,将葡萄糖氧化酶共沉积到新型多巴胺电氧化聚合膜中,最外层再修饰聚邻氨基酚薄膜,研制出新型葡萄糖氧化酶修饰电极用于葡萄糖检测.  相似文献   
994.
Some new criteria for the global asymptotic stability of the equilibrium point for the bi-directional associative memory neural networks with time varying delays are presented. The obtained results present the structure of linear matrix inequality which can be solved efficiently. The comparison with some previously reported results in the literature demonstrates that the results in this paper provide one more set of criteria for determining the stability of the bi-directional associative memory neural networks with delays.  相似文献   
995.
利用电导法分别测定了咪唑类离子液体C12mimBr、C14mimBr、C16mimBr和季铵盐类表面活性剂C16H33N (CH3)3Br-在不同的溶剂水、乙醇、乙酸中的临界胶束浓度(CMC).发现离子液体的CMC值具有一定的规律性:其CMC值随疏水基团中碳氢链的增长而减小,离子液体在不同溶剂中的电导率的变化规律,其顺序为:k(水作溶剂)>k(乙醇作溶剂)>k(乙酸作溶剂).在相同温度下,离子液体的电导率随浓度的增大而增大.在相同的测定条件下,离子液体的电导率随着其侧链基团中碳氢链的增长而减小.C12mimBr、C14mimBr、C16mimBr在不同溶剂中的CMC值顺序为:CMC(水作溶剂)>CMC(乙醇、乙酸作溶剂)  相似文献   
996.
With technology scaling into nanometer regime, rampant process variations impact visible influences on leakage power estimation of very large scale integrations (VLSIs). In order to deal with the case of large inter- and intra-die variations, we induce a novel theory prototype of the statistical leakage power analysis (SLPA) for function blocks. Because inter-die variations can be pinned down into a small range but the number of gates in function blocks is large(>1000), we continue to simplify the prototype. At last, we induce the efficient methodology of SLPA. The method can save much running time for SLPA in the low power design since it is of the local-updating advantage. A large number of experimental data show that the method only takes feasible running time (0.32 s) to obtain accurate results (3 σ-error <0.5% on maximum) as function block circuits simultaneous suffer from 7.5%(3 σ/mean) inter-die and 7.5% intra-die length variations, which demonstrates that our method is suitable for statistical leakage power analysis of VLSIs under rampant process variations.  相似文献   
997.
A novel hierarchical neural networks (HNNs) method for fault diagnosis of large-scale circuits is proposed. The presented techniques using neural networks(NNs) approaches require a large amount of computation for simulating various faulty component possibilities. For large scale circuits, the number of possible faults, and hence the simulations, grow rapidly and become tedious and sometimes even impractical. Some NNs are distributed to the torn sub-blocks according to the proposed torn principles of large scale circuits. And the NNs are trained in batches by different patterns in the light of the presented rules of various patterns when the DC, AC and transient responses of the circuit are available. The method is characterized by decreasing the over-lapped feasible domains of responses of circuits with tolerance and leads to better performance and higher correct classification. The methodology is illustrated by means of diagnosis examples.  相似文献   
998.
考虑多厂商多仓库的分布式库存系统,根据总成本最小原则,建立基于战略联盟的系统数学优化模型.模型允许不同厂商的多个仓库联合订货,以享受价格折扣,所有仓库之间库存完全共享,可进行调拨.利用遗传算法确定各仓库的订货点和期望补货水平等决策变量,并将其作为仿真模型的输入数据,在eM-plant软件上进行仿真,对调拨量和调拨点进行决策.通过对不同的控制策略仿真的数据统计分析可知,基于战略联盟的联合订货和允许调拨的库存共享策略,可以获得较高的客户服务水平和较低的总费用.  相似文献   
999.
There are abundant natural gas resources in Chinese marine sedimentary basin. The exploration hot shots of natural gas are the Palaeozoic marine strata here in recent years, and several large scale gas fields have been discovered. Chinese Palaeozoic high-post matured and coal measure hydrocarbon source rocks are mainly prone to gas generation in the present. This research considered that gas source rocks and TSR are the key cause of gas enrichment of marine strata. High-quality argillaceous and coal measure hydrocarbon rocks are distributed widely in the Palaeozoic marine strata, which have been in highly matured phase in the present. The argillaceous source rock generally contains various sulfates that could accelerate crude oil cracking to gas for TSR occurrence, and coal measure source rock mainly generates gas, so Chinese marine basin gives priority to accumulating gas. Marine strata have not founded oil reservoirs in the Sichuan Basin and Ordos Basin, and they consist mainly of dry gas. Marine natural gases are the mixed gases of oil cracking gas and coal-formed gas in a general way, oil cracking gases contain usually some H2S and CO2. Hydrocarbon carbon isotopes are very complicated, and methane and ethane isotopic values bear apparent reversal caused by thermal evolution and mixing among different genetic types of natural gas. Coal-formed gases are the main component of Chinese marine natural gas. The Upper Permian of the Sichuan Basin and the Carboniferous-Permian of the Ordos Basin coal measure hydrocarbon source rock present large hydrocarbon generation potential, which are the prospecting highlight of marine natural gas hereafter. Oil cracking gas exploration will be paid much attention to in the Tarim Basin because of the lack of coal measure hydrocarbon source rock.  相似文献   
1000.
体素模型与Monte Carlo模拟计算方法相结合已开始应用于辐射防护的研究中.然而,通常的模拟计算需要很长的时间,这限制了体素模型的广泛应用.该文对模拟计算中体素模型的描述进行研究,实现了把三维体素合并算法用在MCNP(Monte Carlo N-particle)程序描述体素模型的方法.结果表明,使用该方法描述体素模型,粒子输运过程要比传统的方法快32%,但是对粒子在组织器官中沉积能量的纪录需要更多时间.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号