全文获取类型
收费全文 | 19087篇 |
免费 | 1209篇 |
国内免费 | 912篇 |
专业分类
系统科学 | 1841篇 |
丛书文集 | 442篇 |
教育与普及 | 283篇 |
理论与方法论 | 324篇 |
现状及发展 | 945篇 |
研究方法 | 31篇 |
综合类 | 17340篇 |
自然研究 | 2篇 |
出版年
2024年 | 69篇 |
2023年 | 168篇 |
2022年 | 324篇 |
2021年 | 330篇 |
2020年 | 270篇 |
2019年 | 161篇 |
2018年 | 955篇 |
2017年 | 987篇 |
2016年 | 712篇 |
2015年 | 567篇 |
2014年 | 697篇 |
2013年 | 762篇 |
2012年 | 1072篇 |
2011年 | 1716篇 |
2010年 | 1630篇 |
2009年 | 1274篇 |
2008年 | 1368篇 |
2007年 | 1558篇 |
2006年 | 685篇 |
2005年 | 583篇 |
2004年 | 576篇 |
2003年 | 546篇 |
2002年 | 631篇 |
2001年 | 592篇 |
2000年 | 413篇 |
1999年 | 372篇 |
1998年 | 256篇 |
1997年 | 279篇 |
1996年 | 247篇 |
1995年 | 245篇 |
1994年 | 204篇 |
1993年 | 205篇 |
1992年 | 153篇 |
1991年 | 147篇 |
1990年 | 140篇 |
1989年 | 117篇 |
1988年 | 96篇 |
1987年 | 47篇 |
1986年 | 22篇 |
1985年 | 9篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1967年 | 1篇 |
1960年 | 1篇 |
1955年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
The World Wide Web has become a global information service center with a vast amount of news, advertisements, product and
service information, and disparate information from diversified sources. However, only a small portion of information is truly
relevant and useful to the users who are seeking information on specific topics. In this paper, common relations among nodes
are taken into consideration when constructing site style tree, and a new node type is introduced. Experimental results show
that the proposed algorithm has higher precision and recall.
相似文献
993.
994.
基AT89C51多路信号检测和语音报警器的设计 总被引:3,自引:0,他引:3
以AT89C51为核心,采用单片语音录放芯片ISD1420和A/D转换器ADC0809,设计了多路信号检测和语音报警器,包括信号放大、处理电路,A/D转换电路,语音报警模块、显示模块、键盘输入模块等. 相似文献
995.
The abundant entities and entity-attribute relations in medical websites are important data resources for medical research. However, the medical websites are usually characterized of storing entity and attribute values in different pages. To extract those data records efficiently, we propose an automatic extraction system which is related to entity and attribute relations (attributes and values) of separate storage. Our system includes following modules: (1) rich-information interactive annotation page rendering; (2) separate storage attribute relations annotating; (3) annotated relations for pattern generating and data records extracting. This paper presents the relations about the attributes which are stored in many pages by effective annotation, then generates rules for data records extraction. The experiments show that the system can not only complete attribute relations of separate storage extraction, but also be compatible with regular relation extraction, while maintaining high accuracy. 相似文献
996.
Hydrothermal reactions of oxalic acid(H2ox) and 2-sulfobenzoic acid(H2L) with lanthanide oxide or hydroxide yielded five lanthanide oxalatosulfocarboxylates.They have a general formula [Ln2L2(ox)(H2O)6]n[Ln = La(1),Nd(2),Eu(3),Gd(4),Tb(5)].Their structures were characterized by single crystal X-ray diffraction,powder X-ray diffraction(PXRD),infrared(IR) spectroscopy,elemental analysis(EA),and thermogravimetric analysis(TGA).1-5 are isostructural coordination polymers and feature one-dimensional(1D) chains,which are extended into 3D supramolecular frameworks through inter-chain hydrogen bonds between coordinated H2O donors and oxygen acceptors from carboxylate,sulfonate and oxalate groups.In addition,the solid-state photoluminescence properties of the Nd(2),Eu(3) and Tb(5) derivatives have been measured at room temperature.The Eu and Tb-containing coordination polymers(CPs) exhibit intense red and green luminescence emissions,respectively,with lifetimes in the order of millisecond. 相似文献
997.
998.
999.
在Belle实验B±→K±ω道的物理分析中,对神经元网络法和Fisher判别法在压制连续过程本底应用中的性能进行了比较研究.应用神经元网络法可以获得对BB信号事例42.3%的选择效率和99.2%的连续过程本底排除水平;应用Fisher判别法可以获得57.9%的信号事例选择效率和98.6%的连续过程本底排除水平. 相似文献
1000.
Bi2Se3 thin films were electrochemically deposited on Ti and indium tin oxide-coated glass substrates, respectively, at room temperature,
using Bi(NO3)3·5H2O and SeO2 as starting materials in diluted HNO3 solution. A conventional three-electrode cell was used with a platinum sheet as a counter electrode, and a saturated calomel
electrode was used as a reference electrode. The films were annealed in argon atmosphere. The influence of cold isostatic
pressing before annealing on the microstructure and thermoelectric properties of the films was investigated. X-ray diffraction
analysis indicates that the film grown on the indium tin oxide-coated glass substrate is pure rhombohedral Bi2Se3, and the film grown on the Ti substrate consists of both rhombohedral and orthorhombic Bi2Se3. 相似文献