全文获取类型
收费全文 | 8409篇 |
免费 | 324篇 |
国内免费 | 503篇 |
专业分类
系统科学 | 377篇 |
丛书文集 | 268篇 |
教育与普及 | 196篇 |
理论与方法论 | 38篇 |
现状及发展 | 61篇 |
研究方法 | 23篇 |
综合类 | 8272篇 |
自然研究 | 1篇 |
出版年
2024年 | 47篇 |
2023年 | 89篇 |
2022年 | 179篇 |
2021年 | 158篇 |
2020年 | 128篇 |
2019年 | 58篇 |
2018年 | 108篇 |
2017年 | 127篇 |
2016年 | 142篇 |
2015年 | 244篇 |
2014年 | 329篇 |
2013年 | 362篇 |
2012年 | 392篇 |
2011年 | 374篇 |
2010年 | 456篇 |
2009年 | 450篇 |
2008年 | 476篇 |
2007年 | 497篇 |
2006年 | 404篇 |
2005年 | 349篇 |
2004年 | 290篇 |
2003年 | 278篇 |
2002年 | 418篇 |
2001年 | 443篇 |
2000年 | 294篇 |
1999年 | 306篇 |
1998年 | 225篇 |
1997年 | 232篇 |
1996年 | 224篇 |
1995年 | 208篇 |
1994年 | 162篇 |
1993年 | 180篇 |
1992年 | 125篇 |
1991年 | 110篇 |
1990年 | 111篇 |
1989年 | 107篇 |
1988年 | 82篇 |
1987年 | 42篇 |
1986年 | 16篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1976年 | 1篇 |
1955年 | 3篇 |
排序方式: 共有9236条查询结果,搜索用时 15 毫秒
251.
Wearable devices usually work together with smart phones. To ensure only legitimate smart phones can read the data, they must conduct pairing to establish a shared key. Traditional pairing methods require that the pairing devices have a keyboard or screen for user interaction. However, due to the size limitation, keyboards or screens are hard to be installed in the wearable devices. To solve this problem, we propose a novel pairing method by using ambient sound and light. In this new scheme, any pairing request from smart phone will trigger wearable device vibration. Only after users press the confirm key on the device can the pairing process continues. Then pairing devices collect ambient sound and light at the predetermined time and establish a shared key by using the Diffie-Hellman protocol. To protect against potential man-in-the-middle attacks in the key establishment process, an improved interlock protocol with sound and light comparison is conducted to authenticate the key. If both the sound and light collected by the pairing devices are similar enough, the key is accepted. Otherwise, it is rejected. Compared with current context based pairing methods, our scheme does not impose strict synchronization on devices to collect ambient context data. Moreover, our scheme need not collect and exchange contextual information for multiple times to resist offline brute force attacks. The experimental results and security analysis prove the effectiveness of our scheme. 相似文献
252.
Evolutionary game analysis of low-carbon behavior credit supervision of logistics enterprises 下载免费PDF全文
Based on the low-carbon obligation fulfillment of Chinese logistics enterprises, this study constructs a tripartite evolutionary game model to analyze the evolutionary process of the interaction between the local government, logistics enterprises and the public in the process of low-carbon behavior credit supervision. Then using Netlogo software, a parameter simulation experiment is conducted to determine the optimal policy for improving the effect of supervision. The results are as follows: ① The combined influence of the local government and the public can effectively change the strategic choice of enterprises and promote the low-carbon behavior of enterprises. ② In terms of improving the effect of supervision, reducing the cost of government supervision would have a highly significant effect, and reducing the cost of the public would be counterproductive. ③ Increasing the government subsidies to enterprises and the government’s fines to enterprises both have a significant effect, and the effect of improving the former is better. However, increasing the severity of higher-level governments punishing local governments will reduce the stability of the system. ④ Supervision can be more effective by increasing the public’s impact on enterprises’ earnings rather than by increasing government subsidies to the public. 相似文献
253.
正As an extension of our earlier study on the structural properties of the clusters,a recently developed method to calculate the low-temperature vibrational heat capacities of clusters shall be presented.Subsequently,it shall be applied to Aun,Nan,Sin,Gen,and SinGen clusters.Our approach does not attempt to identify phase transitions but focuses on the low temperature behaviour,we find that the vibrational heat capacity of the clusters is strongly 相似文献
254.
介绍增强现实( AR)技术的概念和产生背景,分析增强现实系统的主要技术特点和其在国内外的部分应用现状,并对增强现实技术的发展进行展望。 相似文献
255.
256.
Over the past ten years,the enthusiasm to harness small RNA molecules,mainly small interfering RNAs(siRNAs) and microRNA mimics,into therapeutic weapons has never been quenched.However,a major obstacle hindering the clinical application of these small molecules is how to efficiently and precisely deliver siRNAs in vivo into target cells to silence target genes.An international collaborative study led by Song Erwei from the Memorial Hospital of Sun-YatSen University and Wang Jun from Hefei National Laboratory for Physical Sciences at Microscale and School of Life Sciences of University of Science and Tech- 相似文献
257.
旅游业作为第三产业的支柱产业之一,低污染、低能耗的特点使其备受各级政府的重视。曲靖市旅游业拥有宜人的气候、丰富的资源、发达的经济等优势,但是也存在着观光旅游的景点知名度相对较低、基础性公共服务部门的服务意识薄弱、旅游配套设施不足等问题。为此,应通过科学规划,大力发展休闲游、自驾游等方式,以促进整个旅游业的产业升级。 相似文献
258.
文章通过文献资料法、问卷调查法、数理统计法和逻辑分析法,对太原市参与滑雪的游客运动感知分析,其结论是:太原市滑雪游客参与滑雪的主要动机是缓解过度疲劳、工作压力、调节精神;加强交通和滑雪旅游基础设施的建设,同时引进高水平的专业人才进入滑雪旅游业,培训现有的从业人员,提高从业人员的业务水平;管理者应注意滑雪旅游的开发和保护,和体育部门相互协作,加强联合,充分利用体育资源,做好保持太原市滑雪旅游持续发展的规划. 相似文献
259.
带自动荧光显微镜的HCS(high content screening)系统是一种新兴的显微摄影、筛选和处理系统.HCS系统在摄影过程中会产生大量数据,人工筛选和识别费时费力.本文为了进行Monastrol抑制剂的筛选,基于前馈式神经网络技术研究了一种对HCS系统摄影的大量细胞同时进行特征提取和细胞显型识别的自动算法.在得到各个通道分离的图像后,对不同通道图像进行并行预处理,并采用神经网络和逻辑运算相结合的算法进行处理.我们将该方法运用于Monastrol抑制剂的筛选中,并将结果与人工识别结果进行分析比较.相比较前人提出的multi-phenotypic mitotic analysis(MMA)算法自动识别的正确率得以提高,可更好评估抗癌药剂效用. 相似文献
260.
穿江管道的最小埋深受到多方面因素的影响,如何确定最小埋深是穿江管道埋深设计中必须重视的关键问题.针对最小埋深传统算法的不足,提出了基于有限元的优化算法.该优化算法可综合考虑上覆土层厚度、河道行洪冲刷、地震荷载等因素的影响,得到的管道最小埋深更加符合工程实际情况.结合某实际的穿江管道工程,进行了2种计算方法的对比,分析了有限元优化算法的优越性. 相似文献