全文获取类型
收费全文 | 7432篇 |
免费 | 77篇 |
国内免费 | 2篇 |
专业分类
教育 | 5031篇 |
科学研究 | 736篇 |
各国文化 | 91篇 |
体育 | 769篇 |
综合类 | 3篇 |
文化理论 | 90篇 |
信息传播 | 791篇 |
出版年
2021年 | 76篇 |
2020年 | 132篇 |
2019年 | 240篇 |
2018年 | 310篇 |
2017年 | 259篇 |
2016年 | 243篇 |
2015年 | 156篇 |
2014年 | 216篇 |
2013年 | 1626篇 |
2012年 | 159篇 |
2011年 | 184篇 |
2010年 | 159篇 |
2009年 | 139篇 |
2008年 | 167篇 |
2007年 | 170篇 |
2006年 | 151篇 |
2005年 | 127篇 |
2004年 | 117篇 |
2003年 | 112篇 |
2002年 | 97篇 |
2001年 | 84篇 |
2000年 | 101篇 |
1999年 | 95篇 |
1998年 | 92篇 |
1997年 | 65篇 |
1996年 | 69篇 |
1995年 | 56篇 |
1994年 | 64篇 |
1993年 | 73篇 |
1992年 | 70篇 |
1991年 | 76篇 |
1990年 | 79篇 |
1989年 | 82篇 |
1988年 | 81篇 |
1987年 | 68篇 |
1986年 | 76篇 |
1985年 | 70篇 |
1984年 | 76篇 |
1983年 | 76篇 |
1982年 | 72篇 |
1981年 | 50篇 |
1980年 | 50篇 |
1979年 | 70篇 |
1978年 | 59篇 |
1977年 | 54篇 |
1976年 | 53篇 |
1974年 | 40篇 |
1973年 | 44篇 |
1937年 | 42篇 |
1936年 | 40篇 |
排序方式: 共有7511条查询结果,搜索用时 46 毫秒
941.
M. I. Akpanabiatu I. B. Umoh E. O. Udosen A. E. Udoh E. E. Edet 《Indian journal of clinical biochemistry : IJCB》2005,20(2):29-34
Aqueous extract of the leaf and root ofNauclea latifolia Sm. (Rubiaceae) is used in Nigerian folk medicine for the treatment of hypertension. This work is carried out to investigate
the effect ofNauclea latifolia leaf extract on lipid profile and cardiovascular activity of rats. Normal and 10% coconut oil fed rats were treated with
the water-soluble fraction of the ethanol extract ofNauclea latifolia leaf for 2 weeks. Forty-eight mature male albino rats of the Wistar strain were divided into two experiments of four groups,
each group having 6 animals. Experiment I animals were treated with the water-soluble fraction of the ethanol extract whilst
experiment II animals were fed 10% coconut oil meal before treatment with the water-soluble fraction of the ethanol extract.
A single oral dose ofNauclea latifolia was 170, 340 and 510 mg/kg body wt/day of the extracts respectively for 2 wks. There was no significant change in the lipid
profile of the experimental animals as compared with the controls. There was about 40% relaxation on contracted thoracic aorta
that was pre-contracted with 2 μM phenylephrine. The viability of the tissue was tested against 10 μM of acetylcholine. There
was no significant (P>0.05) change in Na+ concentration in the serum. However, the K+ concentration in the serum of the experimental animals showed a significant increase. The study shows that ethanol extract
ofNauclea latifolia has vasodilator action on the aorta and that lipid profiles of experimental rats were not affected. Furthermore, the increase
in the K+ may be contributing to the vasodilator effect ofNauclea latifolia. 相似文献
942.
943.
Thomas J. Cooney 《Educational Studies in Mathematics》1999,38(1-3):163-187
This article addresses issues related to the ways teachers learn mathematics and the teaching of mathematics and the relevance of those ways to their professional development. Preservice teachers' understanding of school mathematics lacks sophistication, a situation that needs to be addressed in mathematics teacher education programs. What is critical is the means by which they encounter and explore the mathematics they will be teaching. Fundamentally, their mathematical experiences need to be congruous with the kind of teaching we would expect of a reflective, adaptive teacher. The article contains both practical and theoretical considerations of how these experiences might be structured. Theoretical orientations for conceptualizing teachers' belief structures are offered as a foundation for conceptualizing teachers' ways of knowing. The moral dimension of teacher education is considered as a backdrop for understanding how teachers come to know.This revised version was published online in September 2005 with corrections to the Cover Date. 相似文献
944.
Aitken (1999) argues that, in a simultaneous discrimination, reports of the transfer of value from the positive to the negative stimulus can be more readily explained in terms of an artifact produced by the procedure in which differential inhibition accrues to the negative test stimuli during training, together with stimulus generalization (similarity between the positive and negative stimuli). We argue that (1) there is little evidence for differential inhibition, and it often occurs in the wrong direction; (2) value transfer can be demonstrated when differential value is established to the positive stimuli afterdiscrimination training, when differential inhibition is not likely to be a factor; and (3) on both logical and empirical grounds, stimulus similarity does not provide an adequate account of the transfer of value from the positive to the negative stimulus (i.e., the strongest evidence for value transfer occurs when there is least stimulus similarity). We propose that value transfer occurs whenever there is relatively little experience with the negative stimuli. However, when there is extended experience with the negative stimuli, contrast will be found. 相似文献
945.
Following simultaneous discrimination training with pigeons, in which responding to the S−was reinforced on half of the trials and responding to the S− was never reinforced, we examined the effect on the S− of presenting the S− by itself and the effect on the S+ of presenting the S− by itself (relative to an S− or an S− for which there had been no single-stimulus presentations). For Group A−, responding to the S− presented by itself was always reinforced, whereas for Group A−, such responding was extinguished. For Group B−, responding to the S− presented by itself was always reinforced, whereas for Group B+, responding was extinguished. Although both Group A+ and Group A−tended to avoid their associated S− (relative to a control S−), Group A+ avoided its associated S− less than did Group A−. In contrast, although for Group B−, presentation of the S− alone increased the pigeons’ preference for its associated S−(relative to a control S+), for Group B−, presentation of the S−alone had little effect on its preference for its associated S+. These results suggest that presentation of one stimulus from a simultaneous discrimination has two independent and sometimes opposite effects on the other discriminative stimulus. First, it reduces the strength of within-event conditioning between the S+ and the S−, and second, if the value of the singly presented stimulus has increased, some of its newly acquired value will transfer retroactively to the stimulus with which it was originally paired. 相似文献
946.
In four conditioned suppression experiments with rats (Rattus norvegicus), backward pairings of a shock unconditioned stimulus (US) and a tone conditioned stimulus (CS) eliminated an already established conditioned response (CR), but there was recovery of the CR if the shock was later withheld. In Experiment 1, there was recovery after backward pairings, regardless of whether the period after the US was normally shock free or not. In Experiment 2, the occurrence of recovery depended on the CS’s being presented closely after the US in response elimination. Levels of recovery were positively correlated with the resistance of the response to elimination during backward pairings (Experiments 3 and 4). Taken together, these data support the notion that recovery after backward pairings is a form of renewal (see, e.g., Bouton, 1991) and is not due toprotection from extinction. 相似文献
947.
Means-ends epistemology 总被引:1,自引:0,他引:1
948.
949.
950.