全文获取类型
收费全文 | 14640篇 |
免费 | 199篇 |
国内免费 | 12篇 |
专业分类
教育 | 9988篇 |
科学研究 | 1310篇 |
各国文化 | 152篇 |
体育 | 1511篇 |
综合类 | 22篇 |
文化理论 | 105篇 |
信息传播 | 1763篇 |
出版年
2021年 | 109篇 |
2020年 | 210篇 |
2019年 | 302篇 |
2018年 | 344篇 |
2017年 | 417篇 |
2016年 | 371篇 |
2015年 | 239篇 |
2014年 | 321篇 |
2013年 | 2627篇 |
2012年 | 280篇 |
2011年 | 321篇 |
2010年 | 253篇 |
2009年 | 284篇 |
2008年 | 271篇 |
2007年 | 262篇 |
2006年 | 248篇 |
2005年 | 229篇 |
2004年 | 474篇 |
2003年 | 362篇 |
2002年 | 386篇 |
2001年 | 247篇 |
2000年 | 260篇 |
1999年 | 205篇 |
1998年 | 100篇 |
1997年 | 124篇 |
1996年 | 153篇 |
1995年 | 140篇 |
1994年 | 131篇 |
1993年 | 126篇 |
1992年 | 180篇 |
1991年 | 180篇 |
1990年 | 163篇 |
1989年 | 219篇 |
1988年 | 177篇 |
1987年 | 207篇 |
1986年 | 183篇 |
1985年 | 238篇 |
1984年 | 199篇 |
1983年 | 175篇 |
1982年 | 156篇 |
1981年 | 132篇 |
1980年 | 112篇 |
1979年 | 175篇 |
1978年 | 137篇 |
1977年 | 121篇 |
1976年 | 141篇 |
1975年 | 103篇 |
1974年 | 119篇 |
1973年 | 96篇 |
1971年 | 107篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
To increase participation of students of color in science graduate programs, research has focused on illuminating student experiences to inform ways to improve them. In biology, Black students are vastly underrepresented, and while religion has been shown to be a particularly important form of cultural wealth for Black students, Christianity is stigmatized in biology. Very few studies have explored the intersection of race/ethnicity and Christianity for Black students in biology where there is high documented tension between religion and science. Since graduate school is important for socialization and Black students are likely to experience stigmatization of their racial and religious identity, it is important to understand their experiences and how we might be able to improve them. Thus, we interviewed 13 Black Christian students enrolled in biology graduate programs and explored their experiences using the theoretical lens of stigmatized identities. Through thematic content analysis, we revealed that students negotiated experiences of cultural isolation, devaluation of intelligence, and acts of bias like other racially minoritized students in science. However, by examining these experiences at the intersection of race/ethnicity and religion, we shed light on interactions students have had with faculty and peers within the biology community that cultivated perceptions of mistrust, conflict, and stigma. Our study also revealed ways in which students' religious/spiritual capital has positively supported their navigation through biology graduate school. These results contribute to a deeper understanding of why Black Christian graduate students are more likely to leave or not pursue advanced degrees in biology with implications for research and practice that help facilitate their success. 相似文献
992.
N. García-Chan L.J. Alvarez-Vázquez A. Martínez M.E. Vázquez-Méndez 《Journal of The Franklin Institute》2014
Within the framework of numerical modelling and multi-objective control of partial differential equations, in this work we deal with the problem of determining the optimal location of a new industrial plant. We take into account both economic and ecological objectives, and we look not only for the optimal location of the plant but also for the optimal management of its emissions rate. In order to do this, we introduce a mathematical model (a system of nonlinear parabolic partial differential equations) for the numerical simulation of air pollution. Based on this model, we formulate the problem in the field of multi-objective optimal control from a cooperative viewpoint, recalling the standard concept of Pareto-optimal solution, and pointing out the usefulness of Pareto-optimal frontier in the decision making process. Finally, a numerical algorithm – based on a characteristics/Galerkin discretization of the adjoint model – is proposed, and some numerical results for a hypothetical situation in the region of Galicia (NW Spain) are presented. 相似文献
993.
Ali E. Akgün Gary S. Lynn Halit Keskin Derya Dogan 《International Journal of Information Management》2014
This study investigates the antecedents and consequences of team learning, which is composed of information acquisition, dissemination, and implementation, in information technology (IT) implementation projects. By investigating 129 IT implementation project teams, we found that (1) information acquisition and information dissemination have a positive impact on project outcomes, such as speed-to-users, lower implementation cost, and operational effectiveness, and (2) team behavior and enabler variables, such as teamwork, team communication, interpersonal trust between team members, team commitment, and senior manager support, positively influence team learning. We also found that team anxiety moderates the relationship between team learning and project outcomes. 相似文献
994.
This paper addresses synchronization problem for discrete-time complex dynamical networks with interval time-varying delays. In order to achieve the synchronization, a feedback controller subjected to randomly occurring perturbations will be considered. The randomly occurring perturbations are assumed to belong to the Binomial sequence. By constructing a suitable Lyapunov–Krasovskii functional, and utilizing reciprocally convex approach and Finsler?s lemma, the synchronization criteria for the networks are established in terms of linear matrix inequalities (LMIs) which can be easily solved by various effective optimization algorithms. The networks are represented by the use of Kronecker product technique. The effectiveness of the proposed methods will be verified via numerical examples. 相似文献
995.
We present in this paper a method for obtaining a low cost and high replication precision 2D (two dimensional) nanofluidic chip with a PET (polyethylene terephthalate) sheet, which uses hot embossing and a thermal bonding technique. The hot embossing process parameters were optimized by both experiments and the finite element method to improve the replication precision of the 2D nanochannels. With the optimized process parameters, 174.67 ± 4.51 nm wide and 179.00 ± 4.00 nm deep nanochannels were successfully replicated into the PET sheet with high replication precision of 98.4%. O2 plasma treatment was carried out before the bonding process to decrease the dimension loss and improve the bonding strength of the 2D nanofluidic chip. The bonding parameters were optimized by bonding rate of the nanofluidic chip. The experiment results show that the bonding strength of the 2D PET nanofluidic chip is 0.664 MPa, and the total dimension loss of 2D nanochannels is 4.34 ± 7.03 nm and 18.33 ± 9.52 nm, in width and depth, respectively. The fluorescence images demonstrate that there is no blocking or leakage over the entire micro- and nanochannels. With this fabrication technology, low cost polymer nanochannels can be fabricated, which allows for commercial manufacturing of nano-components. 相似文献
996.
Stephen E. Erfle 《Measurement in physical education and exercise science》2014,18(3):168-183
This article examines the proclivity and performance attributes of focal students across time and activities using data from 9,345 students. Three systematic focal behavior partitions are examined: Across activities, across time, and across activities and time. A student’s performance is focal if it ends in 0 or 5 for push-ups and 0 for curl-ups. Chi-square tests confirm that individual focal outcomes and systematic focal outcomes occur more frequently than random processes would suggest. In each instance, the only cell that is less populated than random processes would suggest is the one that exhibits no systematic focal behavior and the cell that exhibits the greatest deviation from expected is the full focal cell. Focal students outperform their peers on three activities at two assessments. Students with two-systematically focal outcomes have superior performance to students with no systematic focal outcomes but inferior performance to those with three or four focal outcomes. 相似文献
997.
Marc F. Moreira Jorge E. Morais Daniel A. Marinho António J. Silva Tiago M. Barbosa 《Sports biomechanics / International Society of Biomechanics in Sports》2014,13(1):62-74
This study aimed to analyse the effect of growth during a summer break on biomechanical profile of talented swimmers. Twenty-five young swimmers (12 boys and 13 girls) undertook several anthropometric and biomechanical tests at the end of the 2011–2012 season (pre-test) and 10 weeks later at the beginning of the 2012–2013 season (post-test). Height, arm span, hand surface area, and foot surface area were collected as anthropometric parameters, while stroke frequency, stroke length, stroke index, propelling efficiency, active drag, and active drag coefficient were considered as biomechanical variables. The mean swimming velocity during an all-out 25 m front crawl effort was used as the performance outcome. After the 10-week break, the swimmers were taller with an increased arm span, hand, and foot areas. Increases in stroke length, stroke index, propelling efficiency, and performance were also observed. Conversely, the stroke frequency, active drag, and drag coefficient remained unchanged. When controlling the effect of growth, no significant variation was determined on the biomechanical variables. The performance presented high associations with biomechanical and anthropometric parameters at pre-test and post-test, respectively. The results show that young talented swimmers still present biomechanical improvements after a 10-week break, which are mainly explained by their normal growth. 相似文献
998.
999.
Frederick W. Derrick Nancy A. Williams Charles E. Scott 《Journal of Cultural Economics》2014,38(2):173-189
This paper advances the ongoing discussion of methods for predicting movie box office revenues with two contributions to the methodology and an out-of-sample test of the model. The first innovation is the development of a two-stage model using publicly available pre-release indicators to predict (1) initial week and (2) subsequent run box office revenues. To incorporate the experience-good nature of movies, the second stage is estimated by incorporating a proxy variable for box office success during the first week relative to predicted first week success. The second contribution is an empirical test of De Vany and Walls’ (J Econ Dyn Control 28:1035–1057, 2004) finding that the distribution of movie revenues has “heavy tails” and follows a non-Gaussian stable distribution with infinite variance. We estimate the two-stage model of a movie’s box office success on all general release movies in 1 year with both the Gaussian and stable distribution with heavy tails and infinite variance and find no evidence for the stable distribution in either stage of the estimation. This two-stage model is validated by comparing all general release movies in 3 future years (out-of-sample data) to the model’s predictions. 相似文献
1000.