全文获取类型
收费全文 | 52942篇 |
免费 | 1975篇 |
国内免费 | 2267篇 |
专业分类
系统科学 | 2024篇 |
丛书文集 | 1974篇 |
教育与普及 | 2212篇 |
理论与方法论 | 239篇 |
现状及发展 | 272篇 |
研究方法 | 195篇 |
综合类 | 50258篇 |
自然研究 | 10篇 |
出版年
2024年 | 152篇 |
2023年 | 712篇 |
2022年 | 924篇 |
2021年 | 1025篇 |
2020年 | 678篇 |
2019年 | 253篇 |
2018年 | 446篇 |
2017年 | 601篇 |
2016年 | 536篇 |
2015年 | 1176篇 |
2014年 | 1697篇 |
2013年 | 1528篇 |
2012年 | 1750篇 |
2011年 | 2030篇 |
2010年 | 1922篇 |
2009年 | 2303篇 |
2008年 | 2652篇 |
2007年 | 2499篇 |
2006年 | 1937篇 |
2005年 | 1915篇 |
2004年 | 1354篇 |
2003年 | 1188篇 |
2002年 | 1252篇 |
2001年 | 1430篇 |
2000年 | 1562篇 |
1999年 | 2821篇 |
1998年 | 2649篇 |
1997年 | 2761篇 |
1996年 | 2506篇 |
1995年 | 2213篇 |
1994年 | 2045篇 |
1993年 | 1782篇 |
1992年 | 1511篇 |
1991年 | 1297篇 |
1990年 | 1148篇 |
1989年 | 1027篇 |
1988年 | 856篇 |
1987年 | 544篇 |
1986年 | 302篇 |
1985年 | 108篇 |
1984年 | 30篇 |
1983年 | 8篇 |
1982年 | 7篇 |
1981年 | 3篇 |
1979年 | 5篇 |
1974年 | 6篇 |
1973年 | 4篇 |
1970年 | 4篇 |
1968年 | 3篇 |
1966年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Journal of Systems Science and Complexity - Structural monetary policy and macro-prudential policies are important parts of the policy system of the People’s Bank of China. By constructing a... 相似文献
2.
结合中国城市应对新冠肺炎疫情的成功经验及缺憾,以创造健康、宜居、韧性、生态的城市环境为目标,设计“区域-系统-节点”三类健康城市设计路径;提出“生态健康-生活健康-治愈健康-环境健康-设施健康-救治健康”六位一体应对突发公共事件的城市设计策略,并细化为健康城市在城市空间上的形象化设计表达。 相似文献
3.
For evaluating the influence of the Chinese renminbi(RMB) joining in the special drawing right(SDR) basket on RMB's internationalization, the authors systemically study the risk spillover networks and examine the dynamic relationship of exchange rates among the SDR currencies including the US dollar(USD), European Union euro(EUR), Japanese yen(JPY) and British pound(GBP).The empirical results demonstrate that the USD takes a dominant position and holds the biggest risk spillover to other currencies, and the RMB's inclusion to the SDR basket makes the risk spillover to get average, giving rise to the SDR currency system more stable to a certain degree. The inclusion of the RMB in the SDR not only can reduce the systematic risk of the SDR, but also has a certain impact on the international exchange rate markets. Nowadays, in front of the growing trade friction, more such researches could help to effectively deal with the currency disputes. 相似文献
4.
In this study, we investigate travel mode choice behavior between taxi and subway with an emphasis on the influence of traveling convenience. In the first stage, we examine the Origin-Destination(OD) points of Beijing taxi trips and compare these locations with the respective nearest subway station. Statistics reveal several interesting conclusions. First, for approximately 24.89% of all trips, no convenient subway connections exist between the OD pairs. As such, a taxi becomes the only viable choice. Second, for 80.23% of the remaining 75.11%of trips(equivalent to 60.26% of all trips), access distance from either the origin or the destination to the nearest subway station is greater than 500 meters. This phenomenon indicates that walking distance plays an important role in travel mode choice. In the second stage, we examine groups of taxi trips with similar travel distances and travel times to reveal common features. We establish a preference rule in terms of travel distance and travel time.This determines whether an individual driver will take a taxi or the subway, using a pairwise comparison-based preference regression model. Tests indicate that more than 95% of taxi trips can be correctly predicted by this preference rule. This conclusion reveals that traveling convenience dominates the travel model choice between taxi and subway. All these findings shed light on the factors that influence travel mode choice behavior. 相似文献
5.
以丹寨万达小镇为切入点,分析它的特色之处,引出非物质文化遗产是其内核。阐述非物质文化遗产协同创新保护体系的构成,探索协同创新保护体系运营模式,指出非物质文化遗产协同创新保护之路任重而道远。 相似文献
6.
With increasing demand diversification and short product lifecycles, industries now encounter challenges of demand uncertainty. The Japanese seru production system has received increased attention owing to its high efficiency and flexibility. In this paper, the problem of seru production system formation under uncertain demand is researched. A multi-objective optimization model for a seru production system formation problem is developed to minimize the cost and maximize the service level of the system. The purpose of this paper is to formulate a robust production system that can respond efficiently to the stochastic demand. Sample average approximation (SAA) is used to approximate the expected objective of the stochastic programming. The non-dominated sorting genetic algorithm II (NSGA-II) is improved to solve the multi-objective optimization model. Numerical experiments are conducted to test the tradeoff between cost and service level, and how the performance of the seru production system varies with the number of product types, mean and deviation of product volume, and skill-level-based cost. 相似文献
7.
This paper presents and discusses a simulation method for analyzing and evaluating system performance on a rail line from the perspective of speed profile. Dynamic analysis for train motions is introduced, and a discrete time-operation graph is proposed to represent the relation between speed profile and energy consumption. Based on them, an analytical model is formulated to provide a quick insight into the system performance. The discrete-time simulation (DTS) method is then implemented to study the system in detail. Compared to the existing simulations, two innovations are included in the DTS: (1) the analytical lookup tables that can simplify the dynamic computation and, (2) the speed profile adjustment process that forecasts and avoids future conflicts based on practical constraints. The numerical results show that the DTS speed profile has advantages over existing methods. Finally, the DTS method is used to analyze and evaluate the system performance of the current timetable on Beijing Yizhuang Metro Line. The results suggest that the current timetable is not robust enough, and thus possible improvements are discussed at both scheduling and operating stages. The proposed method is verified to be effective and reliable for practical uses. 相似文献
8.
Yi-min Zhang Li-na Wang De-sheng Chen Wei-jing Wang Ya-hui Liu Hong-xin Zhao Tao Qi 《北京科技大学学报》2018,(2)
An innovative method for recovering valuable elements from vanadium-bearing titanomagnetite is proposed. This method involves two procedures: low-temperature roasting of vanadium-bearing titanomagnetite and water leaching of roasting slag. During the roasting process, the reduction of iron oxides to metallic iron, the sodium oxidation of vanadium oxides to water-soluble sodium vanadate, and the smelting separation of metallic iron and slag were accomplished simultaneously. Optimal roasting conditions for iron/slag separation were achieved with a mixture thickness of 42.5 mm, a roasting temperature of 1200°C, a residence time of 2 h, a molar ratio of C/O of 1.7, and a sodium carbonate addition of 70 wt%, as well as with the use of anthracite as a reductant. Under the optimal conditions, 93.67% iron from the raw ore was recovered in the form of iron nugget with 95.44% iron grade. After a water leaching process, 85.61% of the vanadium from the roasting slag was leached, confirming the sodium oxidation of most of the vanadium oxides to water-soluble sodium vanadate during the roasting process. The total recoveries of iron, vanadium, and titanium were 93.67%, 72.68%, and 99.72%, respectively. 相似文献
9.
Jieting Zhang Yan Wang Xiaohua Jiang Hsiao Chang Chan 《Cellular and molecular life sciences : CMLS》2018,75(10):1737-1756
Mutations of cystic fibrosis transmembrane conductance regulator (CFTR) cause cystic fibrosis, the most common life-limiting recessive genetic disease among Caucasians. CFTR mutations have also been linked to increased risk of various cancers but remained controversial for a long time. Recent studies have begun to reveal that CFTR is not merely an ion channel but also an important regulator of cancer development and progression with multiple signaling pathways identified. In this review, we will first present clinical findings showing the correlation of genetic mutations or aberrant expression of CFTR with cancer incidence in multiple cancers. We will then focus on the roles of CFTR in fundamental cellular processes including transformation, survival, proliferation, migration, invasion and epithelial–mesenchymal transition in cancer cells, highlighting the signaling pathways involved. Finally, the association of CFTR expression levels with patient prognosis, and the potential of CFTR as a cancer prognosis indicator in human malignancies will be discussed. 相似文献
10.
Li-ying Huang Kuai-she Wang Wen Wang Kai Zhao Jie Yuan Ke Qiao Bing Zhang Jun Cai 《北京科技大学学报》2019,(2)
Low-carbon steel plates were successfully subjected to normal friction stir processing(NFSP) in air and submerged friction stir processing(SFSP) under water, and the microstructure, mechanical properties, and corrosion behavior of the NFSP and SFSP samples were investigated. Phase transformation and dynamic recrystallization resulted in fine-grained ferrite and martensite in the processed zone. The SFSP samples had smaller ferrites(5.1 μm), finer martensite laths(557 nm), and more uniform distribution of martensite compared to the NFSP samples. Compared to the base material(BM), the microhardness of the NFSP and SFSP samples increased by 19.8% and 27.1%, respectively because of the combined strengthening effects of grain refinement, phase transformation, and dislocation. The ultimate tensile strengths(UTSs) of the NFSP and SFSP samples increased by 27.1% and 38.7%, respectively. Grain refinement and martensite transformation also improved the electrochemical corrosion properties of the low-carbon steel. Overall, the SFSP samples had better mechanical properties and electrochemical corrosion resistance than the NFSP samples. 相似文献