全文获取类型
收费全文 | 17752篇 |
免费 | 210篇 |
国内免费 | 11篇 |
专业分类
教育 | 12987篇 |
科学研究 | 1456篇 |
各国文化 | 147篇 |
体育 | 1439篇 |
综合类 | 8篇 |
文化理论 | 124篇 |
信息传播 | 1812篇 |
出版年
2021年 | 144篇 |
2020年 | 217篇 |
2019年 | 361篇 |
2018年 | 480篇 |
2017年 | 502篇 |
2016年 | 453篇 |
2015年 | 289篇 |
2014年 | 401篇 |
2013年 | 3450篇 |
2012年 | 407篇 |
2011年 | 459篇 |
2010年 | 308篇 |
2009年 | 311篇 |
2008年 | 433篇 |
2007年 | 338篇 |
2006年 | 399篇 |
2005年 | 293篇 |
2004年 | 270篇 |
2003年 | 248篇 |
2002年 | 289篇 |
2001年 | 370篇 |
2000年 | 348篇 |
1999年 | 318篇 |
1998年 | 172篇 |
1997年 | 199篇 |
1996年 | 227篇 |
1995年 | 222篇 |
1994年 | 185篇 |
1993年 | 194篇 |
1992年 | 279篇 |
1991年 | 245篇 |
1990年 | 250篇 |
1989年 | 274篇 |
1988年 | 272篇 |
1987年 | 228篇 |
1986年 | 229篇 |
1985年 | 238篇 |
1984年 | 210篇 |
1983年 | 246篇 |
1982年 | 191篇 |
1981年 | 186篇 |
1980年 | 182篇 |
1979年 | 247篇 |
1978年 | 199篇 |
1977年 | 176篇 |
1976年 | 168篇 |
1975年 | 141篇 |
1974年 | 138篇 |
1973年 | 140篇 |
1971年 | 116篇 |
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
991.
992.
John R. Anderson is an international leader in the computational representation and simulation of human cognition. He is credited as having developed the first “cognitive architecture”—a computational framework for specifying both the abilities and limitations of human behavior. Anderson has also made fundamental contributions in applying cognitive architectures to practical problems, most notably in the development of intelligent tutoring systems: computer-based tutors that continually infer the cognitive state of the student, striving to determine what the student knows and does not know, and targeting further instruction accordingly. For these achievements, Anderson was awarded the 2011 Benjamin Franklin Medal in Computer and Cognitive Science. 相似文献
993.
In the present article Parameterized Perturbation Method (PPM) is used to obtain the solutions of momentum and heat transfer equations of non-Newtonian fluid flow in an axisymmetric channel with porous wall for turbine cooling applications. The validity of the results of PPM solution were verified by comparison with numerical results obtained using a fourth order Runge–Kutta method. These comparisons reveal that Parameterized Perturbation Method is a powerful approach for solving this problem. The analytical investigation is carried out for different governing parameters namely, Reynolds number, injection Reynolds number, Prandtl number and power law index. The results show that skin friction coefficient increases with increase of Reynolds number, especially at high Reynolds numbers. Also it can be found that Nusselt number has direct relationship with Reynolds number, Prandtl number and power law index. 相似文献
994.
Arnold Chen Royal Wang Candace R. S. Bever Siyuan Xing Bruce D. Hammock Tingrui Pan 《Biomicrofluidics》2014,8(6)
The emerging technologies on mobile-based diagnosis and bioanalytical detection have enabled powerful laboratory assays such as enzyme-linked immunosorbent assay (ELISA) to be conducted in field-use lab-on-a-chip devices. In this paper, we present a low-cost universal serial bus (USB)-interfaced mobile platform to perform microfluidic ELISA operations in detecting the presence and concentrations of BDE-47 (2,2′,4,4′-tetrabromodiphenyl ether), an environmental contaminant found in our food supply with adverse health impact. Our point-of-care diagnostic device utilizes flexible interdigitated carbon black electrodes to convert electric current into a microfluidic pump via gas bubble expansion during electrolytic reaction. The micropump receives power from a mobile phone and transports BDE-47 analytes through the microfluidic device conducting competitive ELISA. Using variable domain of heavy chain antibodies (commonly referred to as single domain antibodies or Nanobodies), the proposed device is sensitive for a BDE-47 concentration range of 10−3–104 μg/l, with a comparable performance to that uses a standard competitive ELISA protocol. It is anticipated that the potential impact in mobile detection of health and environmental contaminants will prove beneficial to our community and low-resource environments. 相似文献
995.
Recent simulations by Chen and Dorfman [Electrophoresis 35, 405–411 (2014)]
suggested that “tilting” the electric field with respect to the lattice vectors of a hexagonal post
array would lead to a substantial improvement in electrophoretic DNA separations therein. We
constructed such an array where the electric field is applied at an angle equidistant between the
two lattice vectors. This tilted array leads to (i) baseline resolution of 20 kbp DNA and λ DNA
(48.5 kbp) in a 4 mm channel and (ii) measurable separation resolutions for electric fields up to
50 V/cm, both of which are improvements over untilted post arrays of the same post density. The
predicted time required to reach a resolution of unity is approximately 5 min, independent of
electric field. The separations are more reproducible at higher fields. 相似文献
996.
997.
998.
999.
1000.
D Queen 《Library technology reports》1980,16(6):563-612