全文获取类型
收费全文 | 5727篇 |
免费 | 128篇 |
国内免费 | 292篇 |
专业分类
系统科学 | 434篇 |
丛书文集 | 182篇 |
教育与普及 | 194篇 |
理论与方法论 | 44篇 |
现状及发展 | 40篇 |
综合类 | 5253篇 |
出版年
2024年 | 27篇 |
2023年 | 81篇 |
2022年 | 85篇 |
2021年 | 103篇 |
2020年 | 82篇 |
2019年 | 82篇 |
2018年 | 67篇 |
2017年 | 68篇 |
2016年 | 64篇 |
2015年 | 133篇 |
2014年 | 252篇 |
2013年 | 238篇 |
2012年 | 278篇 |
2011年 | 302篇 |
2010年 | 299篇 |
2009年 | 380篇 |
2008年 | 433篇 |
2007年 | 397篇 |
2006年 | 323篇 |
2005年 | 306篇 |
2004年 | 286篇 |
2003年 | 276篇 |
2002年 | 216篇 |
2001年 | 227篇 |
2000年 | 177篇 |
1999年 | 160篇 |
1998年 | 146篇 |
1997年 | 110篇 |
1996年 | 100篇 |
1995年 | 83篇 |
1994年 | 68篇 |
1993年 | 66篇 |
1992年 | 54篇 |
1991年 | 44篇 |
1990年 | 53篇 |
1989年 | 32篇 |
1988年 | 20篇 |
1987年 | 14篇 |
1986年 | 8篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1980年 | 1篇 |
排序方式: 共有6147条查询结果,搜索用时 156 毫秒
921.
构建自动生产线图形信息系统 总被引:1,自引:0,他引:1
杜宝江 《上海理工大学学报》2002,24(4):328-332
从AutoCAD矢量方式的静态网络图形出发,对自动生产线网络图形中的物流源、物流线路以及物流控制设备等进行识别、处理和转换,自动生成生产线图形信息系统的图形拓扑关系数据库,再与生产线实时信息进行合成,构建自动生产线图形信息系统,实践证明,这种自动生成方法,突破了人工描述拓扑关系的复杂困难的瓶颈,效率更高、速度更快,为自动化生产线信息系统的广泛实用化奠定了基础。 相似文献
922.
在飞行试验中,机载PCM数据流实时监控一般采用以工控机和PCM解调卡为构架的方案,所研制设备体积大,重量大,不适合小型飞行器使用。采用嵌入式FPGA/DSP技术设计了一种机载PCM数据流实时监控显示系统,详细阐述了解调电路、控制程序和数据显示的设计方法。该系统实现了PCM数据流的机载实时解调、数据显示功能,满足小型飞行器机载PCM数据流实时监控的需求。 相似文献
923.
简要回顾了基于粒子滤波的同频混合信号盲分离算法.着重研究了混合信号的定时问题,提出了基于Gardner算法的定时方法并从理论上分析了其有效性.在此基础上提出了一种Gardner定时+粒生子滤波+Viterbi序列检测的同频混合信号实时盲解调方案,其中Viterbi算法可以根据粒子滤波估计出的信号参数,对信号符号作进一步估计以达到更好的解调效果.仿真结果验证了该方案的可行性. 相似文献
924.
L-selectin plays a crucial role in inflammation cascade by initiating the tethering and rolling of leukocytes on endothelium wall. While many L-selectin molecules are rapidly shed from the cell surface upon activation, the remaining membrane-anchored L-selectin may still play an important role in regulating leukocyte rolling and adhesion with different binding kinetics. Here we developed an in vitro model to activate Jurkat cells via interlukin-8 (IL-8) and quantified the two-dimensional (2D) binding kinetics, using a micropipette aspiration assay, of membrane-anchored L-selectin to P-selectin glycoprotein ligand 1 (PSGL-1) ligand coupled onto human red blood cells (RBCs). The data indicated that L-selectin shedding reduced the amount of membrane-anchored L-selectin and lowered both its reverse and forward rates. These results suggested that the rolling dynamics of activated leukocytes was determined by two opposite impacts: reducing the surface presentation would enhance the rolling but lowering the kinetic rates would decrease the rolling. This finding provides a new insight into understanding how L-selectin shedding regulates leukocyte rolling and adhesion. 相似文献
925.
To clarify the water erosion mechanism of the mild carbon steels, the water erosion experiments were performed by using deionized water as steam source. The results showed that under the damage threshold velocity of liquid impact, the material surface would not be destroyed. However, when the micro-particles were added into the steam, the pits appeared on the surface soon. By comparison, it is found that the pits are quite different from those induced by micro-particles impact without steam, but similar to those induced by cavitation erosion. The results indicated that the water erosion mechanism was similar to that of cavitation erosion under the damage threshold velocity. The micro-particles carry the micro-bubbles to approach the surface of the material, and the micro-bubbles collapse and generate micro-jet to impinge vertically on the surface, which lead to the produce of pits. 相似文献
926.
Pteris vittata can hyperaccumulate arsenic (As) to 〉1% of its dry weight without showing any signs of toxicity, indicating the existence of effective plant-internal detoxificaUon mechanisms. Although vacuolar compartmentalization is known to play an important role in heavy metal detoxification and tolerance, direct evidence of arsenic compartmentalization in this hyperaccumulator was lacking. Here we report the subcellular localization of As in the callus of P. vittata. The callus induced from gametophytes of P. vittata exposed to 0.2 mmol/L arsenate for 20 days were examined by directly isolating cell walls, protoplasts and vacuoles, and determining arsenic concentrations. Of the total As in the callus, about 94% was in the protoplast, and of that, 91% was present in the vacuoles, indicating that vacuoles are a major storage site for As in P. vittata. In addition, the changes in the chemical components of vacuoles were analyzed by Fourier transform infrared spectroscopy (FTIR). 相似文献
927.
Yeon-Suk Oh Hee-Young Kwon Soo-Jin Jeong Ki-Young Park Sun-Young Kim Hyo-Jung Lee Hyo-Jeong Lee Eun-Ok Lee Kwang Seok Ahn Sung-Hoon Kim 《科学通报(英文版)》2009,54(23):4387-4392
Sojucktang (SJT) has long been used for the treatment of endometrial diseases in Korea. However, the mechanisms responsible for the SJT-induced apoptosis in endometrial cancer cells remain unclear. In the present study, SJT was demonstrated to show cytotoxic effect and induce apoptotic cell death via mitochondrial regulation in KLE endometrial cancer cells. Linderae Radix, Glycyrrhizae Radix, Zedoariae Rhizoma, Trogopterorum Faeces and Agelicae Gigantis Radix were found to be the potent constituent herbs of SJT to significantly decrease the viability of KLE cells by a tetra zolium salt (XTT) assay. Apoptotic bodies were observed in SJT-treated KLE cells by 4′-6-diamidino-2-phenylindole (DAPI) and TdT-mediated-dUTP nick-end labeling (TUNEL) assay. SJT also increased sub-G1 DNA contents of the cell cycle undergoing apoptosis in a dose-dependent manner. Furthermore, it was observed that SJT activated caspase-3 and cleaved poly (ADP-ribose) polymerase (PARP), and decreased mitochondrial membrane potential in a dose-dependent manner. Taken together, this study shows that SJT exerts anti-tumor activity against KLE endometrial cancer cells via mitochondrial dependent apoptosis induction. 相似文献
928.
在考虑先进的出行者信息对出行路径选择行为影响的基础上,建立了信息影响下的路径选择模型,基于驾驶员群体的划分和路网混合均衡建模理论,构建了一随机网络混合随机用户均衡模型,提出了同时求解诱导比例和诱导系统服从率的数学模型,设计了模型求解算法,并利用算例进行了计算分析. 相似文献
929.
930.
目的:观察缺氧后不同时段小鼠脑匀浆提取液对儿童骨髓间充质干细胞(MSCs)分化为神经元样细胞的影响,为筛选MSCs的最佳移植时间提供依据.方法:制作缺氧小鼠模型;并制取缺氧不同时间段脑匀浆提取液;诱导儿童MSCs;比较MSCs分化为神经元样细胞的阳性率.结果:缺氧后1、4,7、10、13 d小鼠脑匀浆提取液均可将MSCs诱导成神经元样细胞,经免疫学鉴定NES染色强阳性;但各组阳性率不同,以缺氧10 d后阳性率(21.02±3.38)%最高,与其他各组比较有统计学差异(P<0.05).结论:缺氧后小鼠脑匀浆提取液可诱导儿童MSCs分化为神经元样细胞,缺氧后10 d的分化率最高. 相似文献