全文获取类型
收费全文 | 3478篇 |
免费 | 41篇 |
国内免费 | 9篇 |
专业分类
教育 | 2430篇 |
科学研究 | 346篇 |
各国文化 | 58篇 |
体育 | 233篇 |
综合类 | 2篇 |
文化理论 | 29篇 |
信息传播 | 430篇 |
出版年
2023年 | 15篇 |
2022年 | 37篇 |
2021年 | 57篇 |
2020年 | 114篇 |
2019年 | 141篇 |
2018年 | 156篇 |
2017年 | 161篇 |
2016年 | 146篇 |
2015年 | 103篇 |
2014年 | 151篇 |
2013年 | 853篇 |
2012年 | 111篇 |
2011年 | 104篇 |
2010年 | 106篇 |
2009年 | 102篇 |
2008年 | 97篇 |
2007年 | 81篇 |
2006年 | 78篇 |
2005年 | 43篇 |
2004年 | 45篇 |
2003年 | 54篇 |
2002年 | 42篇 |
2001年 | 48篇 |
2000年 | 45篇 |
1999年 | 31篇 |
1998年 | 24篇 |
1997年 | 25篇 |
1996年 | 22篇 |
1995年 | 21篇 |
1994年 | 16篇 |
1993年 | 25篇 |
1992年 | 21篇 |
1991年 | 30篇 |
1990年 | 23篇 |
1989年 | 24篇 |
1988年 | 21篇 |
1987年 | 23篇 |
1986年 | 18篇 |
1985年 | 26篇 |
1984年 | 16篇 |
1983年 | 17篇 |
1982年 | 24篇 |
1981年 | 13篇 |
1980年 | 17篇 |
1979年 | 16篇 |
1978年 | 18篇 |
1975年 | 9篇 |
1973年 | 7篇 |
1971年 | 11篇 |
1885年 | 9篇 |
排序方式: 共有3528条查询结果,搜索用时 15 毫秒
41.
42.
43.
This study explores the impact of teachers’ perception of trust in colleagues on their sense of empowerment in Mainland China, with a particular focus on the mediating role of teacher efficacy. The results of a survey of 1646 teachers indicate that although teachers scored positively on trust in colleagues, efficacy and empowerment, they had relatively lower scores on general teaching efficacy (GTE) and participation in decision-making. Trust in colleagues was a significant predictor of teacher empowerment. In addition, personal teaching efficacy had a significant mediation effect on the relationship between trust in colleagues and teacher empowerment, while GTE had not. These findings lead to some implications for understanding the nature of GTE and the relationship between trust and teacher empowerment. 相似文献
44.
This study experimentally verifies that the mixing process in a droplet can be enhanced by driving the droplet at resonant frequencies and at alternating driving frequencies using a parallel-plate electrowetting on dielectric device. The mixing time, which is defined as the time required for reaching the well-mixed state, in a resonant droplet is found to be significantly shorter than that in a non-resonant droplet. Besides, it is also found that a higher driving potential leads to a better mixing effect, especially at resonant frequencies. Furthermore, when a droplet is driven by alternating two driving frequencies, especially two resonant frequencies, the mixing efficiency is found to be significantly enhanced for a specific alternating duration of these two frequencies. 相似文献
45.
Tunable pores (TPs) have been used for resistive pulse sensing of 1 μm superparamagnetic beads, both dispersed and within a magnetic field. Upon application of this field, magnetic supraparticle structures (SPSs) were observed. Onset of aggregation was most effectively indicated by an increase in the mean event magnitude, with data collected using an automated thresholding method. Simulations enabled discrimination between resistive pulses caused by dimers and individual particles. Distinct but time-correlated peaks were often observed, suggesting that SPSs became separated in pressure-driven flow focused at the pore constriction. The distinct properties of magnetophoretic and pressure-driven transport mechanisms can explain variations in the event rate when particles move through an asymmetric pore in either direction, with or without a magnetic field applied. Use of TPs for resistive pulse sensing holds potential for efficient, versatile analysis and measurement of nano- and microparticles, while magnetic beads and particle aggregation play important roles in many prospective biosensing applications. 相似文献
46.
Lee K Kim C Young Yang J Lee H Ahn B Xu L Yoon Kang J Oh KW 《Biomicrofluidics》2012,6(1):14114-141147
We propose a simple method for forming massive and uniform three-dimensional (3-D) cell spheroids in a multi-level structured microfluidic device by gravitational force. The concept of orienting the device vertically has allowed spheroid formation, long-term perfusion, and retrieval of the cultured spheroids by user-friendly standard pipetting. We have successfully formed, perfused, and retrieved uniform, size-controllable, well-conditioned spheroids of human embryonic kidney 293 cells (HEK 293) in the gravity-oriented microfluidic device. We expect the proposed method will be a useful tool to study in-vitro 3-D cell models for the proliferation, differentiation, and metabolism of embryoid bodies or tumours. 相似文献
47.
This study reports a droplet-based microfluidic device for on-demand electrostatic droplet charging and sorting. This device combines two independent modules: one is a hydrodynamic flow focusing structure to generate water-in-oil droplets, and the other is the two paired-electrodes for charging and sorting of the droplets. Depending on the polarity on charging electrodes, water-in-oil droplets can be electrostatically charged positively or negatively, followed by automatic real-time electric sorting. This approach will be useful when preformed droplets, with a positive, a negative, or with no charge, need to be manipulated for further on-chip droplet manipulation. 相似文献
48.
Recent advances in droplet microfluidics have led to the fabrication of versatile vesicles with a structure that mimics the cellular membrane. These artificial cell-like vesicles including polymersomes and liposomes effectively enclose an aqueous core with well-defined size and composition from the surrounding environment to implement various biological reactions, serving as a diverse functional reactor. The advantage of realizing various biological phenomena within a compartment separated by a membrane that resembles a natural cell membrane is actively explored in the fields of synthetic biology as well as biomedical applications including drug delivery, biosensors, and bioreactors, to name a few. In this Perspective, we first summarize various methods utilized in producing these polymersomes and liposomes. Moreover, we will highlight some of the recent advances in the design of these artificial cell-like vesicles for functional bioreactors and discuss the current issues and future perspectives. 相似文献
49.
50.
This paper presents a droplet-based microfluidic device for concurrent droplet charging and sorting by electrostatic actuation. Water-in-oil droplets can be charged on generation by synchronized electrostatic actuation. Then, simultaneously, the precharged droplets can be electrostatically steered into any designated laminar streamline, thus they can be sorted into one of multiple sorting channels one by one in a controlled fashion. In this paper, we studied the size dependence of the water droplets under various relative flow rates of water and oil. We demonstrated the concurrent charging and sorting of up to 600 droplets∕s by synchronized electrostatic actuation. Finally, we investigated optimized voltages for stable droplet charging and sorting. This is an essential enabling technology for fast, robust, and multiplexed sorting of microdroplets, and for the droplet-based microfluidic systems. 相似文献