全文获取类型
收费全文 | 2705篇 |
免费 | 130篇 |
国内免费 | 187篇 |
专业分类
系统科学 | 148篇 |
丛书文集 | 68篇 |
教育与普及 | 32篇 |
理论与方法论 | 8篇 |
现状及发展 | 24篇 |
研究方法 | 11篇 |
综合类 | 2731篇 |
出版年
2024年 | 13篇 |
2023年 | 38篇 |
2022年 | 78篇 |
2021年 | 86篇 |
2020年 | 76篇 |
2019年 | 53篇 |
2018年 | 47篇 |
2017年 | 63篇 |
2016年 | 84篇 |
2015年 | 116篇 |
2014年 | 207篇 |
2013年 | 189篇 |
2012年 | 185篇 |
2011年 | 171篇 |
2010年 | 161篇 |
2009年 | 189篇 |
2008年 | 223篇 |
2007年 | 201篇 |
2006年 | 137篇 |
2005年 | 119篇 |
2004年 | 82篇 |
2003年 | 55篇 |
2002年 | 46篇 |
2001年 | 44篇 |
2000年 | 54篇 |
1999年 | 52篇 |
1998年 | 31篇 |
1997年 | 39篇 |
1996年 | 28篇 |
1995年 | 23篇 |
1994年 | 22篇 |
1993年 | 20篇 |
1992年 | 19篇 |
1991年 | 19篇 |
1990年 | 20篇 |
1989年 | 12篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 1篇 |
排序方式: 共有3022条查询结果,搜索用时 15 毫秒
101.
ShuangXi Chen TieGang Li Zheng Tang XiaoHua Qiu ZhiFang Xiong QingYun Nan ZhaoKai Xu FengMing Chang 《科学通报(英文版)》2011,56(24):2628-2634
The deglacial δ~13C minimum events that originated from the ventilation of the deep Southern Ocean around Antarctica, have been recorded in a range of marine sediments from the southern to tropical oceans in late Pleistocene. However, the broad δ~13C minimum event was also reported as far as to the northern middle latitudes, in northwestern Pacific marginal sea areas, during the last deglaciation. In the northwestern Pacific, forcing from the northern high latitudes is strongly expressed, while the records of in- fluence from the southern high latitudes are few. The Kuroshio Source Region (KSR) forms a boundary between the northwestern Pacific and the southern, tropical Pacific. So, high-resolution planktonic foraminiferal records in core MD06-3054 from the KSR are well positioned to identify signals from the southern hemisphere in the northwestern Pacific. Planktonic foraminiferal tests from the upper 1030 cm of the core were subject to AMS14C, carbon and oxygen isotopic measurements. A negative excursion was found to occur from about 20.0-6.0 ka BP in δ~13C records of both surface (Globigerinoides ruber) and subsurface (Pulleni- atina obliquiloculata) dwellers, but the overall trends of the two curves have reversed since 26.5 ka BP. Moreover, the δ~13C rec- ord of G. ruber (the surface dweller) shows a robust link to the record of atmospheric CO2, and its changes precede the records of P. obliquiloculata (the subsurface dweller). According to the hydrologic conditions, the broad δ~13C minimum event recorded in the KSR is also a response to the increasing ventilation of the deep Southern Ocean around Antarctica during the last deglaciation. The inconsistency between the records of the surface and subsurface dwellers was possibly caused by the ways that the low δ~13C signal was transmitted. Subsurface water primarily received the low δ~13C signal from the Antarctic Intermediate Water (AAIW), whereas the surface water was probably mainly impacted by atmospheric CO2 in the KSR. The records from the KSR confirm the deduction that the broad δ~13C minimum event in the Okinawa Trough was due to the impact of tropical Pacific surface water dur- ing the last deglaciation, and suggest that signals from the southern high latitudes also can be delivered to the northern middle latitudes. 相似文献
102.
针对不完整决策系统属性约简算法时间复杂度较高问题,基于正域不变条件下,决策系统分类能力保持不变原则,提出不完整决策系统前向顺序特征选择算法.该算法从约简集为空集开始,根据在约简集合中加入各属性后对正域影响程度大小将属性降序排列,采用顺序前向搜索,选择当前最佳特征加入特征约简集合,确定最佳特征子集.将该算法扩展到基于邻域... 相似文献
103.
宽带认知无线电网络分布式协作压缩频谱感知算法 总被引:5,自引:3,他引:2
针对宽带认知无线电网络中压缩频谱感知算法在低信噪比环境下频谱检测性能下降的问题,提出了一种基于高斯过程的分布式压缩频谱感知(PBCS)算法.首先应用层次化的正态分布概率模型来表示压缩频谱的重构,然后各个认知无线电用户交换模型参数并结合本地的压缩采样数据进行压缩频谱感知.有别于其他直接融合频谱感知结果或检测数据的协作式算法,PBCS算法通过模型参数融合来进行协作,能有效减小信噪比低的协作用户的影响,从而提高算法的抗噪性.仿真结果表明,PBCS算法可以在-5dB的信噪比条件下达到检测概率大于0.9、误检概率为0.1的频谱检测性能. 相似文献
104.
105.
106.
2008—2014年,科技部先后分5批认定了共371家国家技术转移示范中心,有力地推进了政府、大学、科研机构、中介组织和企业等创新主体在技术转移工作中的作用,完善了国家技术转移体系和机制。以网上调研为主,结合情报学的方法,对这5批示范中心的现状进行了调研和整理。 相似文献
107.
Fractal characteristics of particle size distribution in dynamic flocculation process 总被引:1,自引:0,他引:1
This study selected polyaluminum chloride(PAC) coagulant to remove suspended particles in Kaolin suspension solution and used
a turbidimeter and particle counter to monitor the flocculation process online and collected the experiment data. The experiments
were conducted to study the dynamic distribution characteristics of suspended particles under different hydrodynamic conditions.
The results show the self-similarity and scale invariance of particle size distribution. The study further proposed the concept
of fractal dimension of particle size distribution and found out that fractal dimension changed in a similar way as residual
turbidity did and could excellently indicate the variation of coagulation effect. Therefore, fractal dimension could be adopted
to optimize the addition of coagulants and the quality of outflow could be further improved to reduce production costs. 相似文献
108.
109.
110.