全文获取类型
收费全文 | 41958篇 |
免费 | 4493篇 |
国内免费 | 14篇 |
出版年
2022年 | 195篇 |
2021年 | 565篇 |
2020年 | 367篇 |
2019年 | 449篇 |
2018年 | 569篇 |
2017年 | 545篇 |
2016年 | 946篇 |
2015年 | 1701篇 |
2014年 | 1662篇 |
2013年 | 2201篇 |
2012年 | 2496篇 |
2011年 | 2210篇 |
2010年 | 1522篇 |
2009年 | 1388篇 |
2008年 | 1918篇 |
2007年 | 1897篇 |
2006年 | 1682篇 |
2005年 | 1653篇 |
2004年 | 1569篇 |
2003年 | 1359篇 |
2002年 | 1340篇 |
2001年 | 1246篇 |
2000年 | 1242篇 |
1999年 | 1121篇 |
1998年 | 624篇 |
1997年 | 585篇 |
1996年 | 567篇 |
1995年 | 545篇 |
1994年 | 496篇 |
1993年 | 527篇 |
1992年 | 1017篇 |
1991年 | 761篇 |
1990年 | 790篇 |
1989年 | 762篇 |
1988年 | 662篇 |
1987年 | 607篇 |
1986年 | 615篇 |
1985年 | 713篇 |
1984年 | 541篇 |
1983年 | 419篇 |
1982年 | 351篇 |
1981年 | 322篇 |
1980年 | 260篇 |
1979年 | 391篇 |
1978年 | 351篇 |
1977年 | 248篇 |
1976年 | 229篇 |
1975年 | 207篇 |
1974年 | 295篇 |
1973年 | 253篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Chantal N. van Dijk Merel van Witteloostuijn Nada Vasi? Sergey Avrutin Elma Blom 《PloS one》2016,11(3)
When sending text messages on their mobile phone to friends, children often use a special type of register, which is called textese. This register allows the omission of words and the use of textisms: instances of non-standard written language such as 4ever (forever). Previous studies have shown that textese has a positive effect on children’s literacy abilities. In addition, it is possible that children’s grammar system is affected by textese as well, as grammar rules are often transgressed in this register. Therefore, the main aim of this study was to investigate whether the use of textese influences children’s grammar performance, and whether this effect is specific to grammar or language in general. Additionally, studies have not yet investigated the influence of textese on children’s cognitive abilities. Consequently, the secondary aim of this study was to find out whether textese affects children’s executive functions. To investigate this, 55 children between 10 and 13 years old were tested on a receptive vocabulary and grammar performance (sentence repetition) task and various tasks measuring executive functioning. In addition, text messages were elicited and the number of omissions and textisms in children’s messages were calculated. Regression analyses showed that omissions were a significant predictor of children’s grammar performance after various other variables were controlled for: the more words children omitted in their text messages, the better their performance on the grammar task. Although textisms correlated (marginally) significantly with vocabulary, grammar and selective attention scores and omissions marginally significantly with vocabulary scores, no other significant effects were obtained for measures of textese in the regression analyses: neither for the language outcomes, nor for the executive function tasks. Hence, our results show that textese is positively related to children’s grammar performance. On the other hand, use of textese does not affect—positively nor negatively—children’s executive functions. 相似文献
103.
104.
105.
106.
107.
M J Bussemakers A van Bokhoven J J van Groningen F M Debruyne J A Schalken 《Biochemical and biophysical research communications》1992,182(1):318-324
Differential hybridization analysis revealed two cDNA clones, pBUS19 and pBUS30, to be overexpressed in progressionally advanced rat prostatic tumors. Northern blot analysis suggested the clones to be related although no homology in nucleotide sequence could be shown. Isolation and characterization of a pBUS19-related clone, pJG116, and computer-assisted database comparison showed that all three clones could be mapped within a rat-specific endogenous retrovirus. The importance of overexpression of retroviral sequences in advanced prostatic cancer remains unclear. 相似文献
108.
Often we must balance being prepared to act quickly with being prepared to suddenly stop. The stop signal task (SST) is widely used to study inhibitory control, and provides a measure of the speed of the stop process that is robust to changes in subjects’ response strategy. Previous studies have shown that preparation affects inhibition. We used fMRI to separate activity that occurs after a brief (500 ms) warning stimulus (warning-phase) from activity that occurs during responses that follow (response-phase). Both of these phases could contribute to the preparedness to stop because they both precede stop signals. Warning stimuli activated posterior networks that signal the need for top-down control, whereas response phases engaged prefrontal and subcortical networks that implement top-down control. Regression analyses revealed that both of these phases affect inhibitory control in different ways. Warning-phase activity in the cerebellum and posterior cingulate predicted stop latency and accuracy, respectively. By contrast, response-phase activity in fronto-temporal areas and left striatum predicted go speed and stop accuracy, in pre-supplementary motor area affected stop accuracy, and in right striatum predicted stop latency and accuracy. The ability to separate hidden contributions to inhibitory control during warning-phases from those during response-phases can aid in the study of models of preparation and inhibitory control, and of disorders marked by poor top-down control. 相似文献
109.
J. P. van der Walt 《Antonie van Leeuwenhoek》1992,62(4):247-250
The Lipomycetaceae (Endomycetales) are known from the generaDipodascopsis, Lipomyces andZygozyma with budding anamorphic states inMyxozyma. The family is easily recognized culturally and physiologically but is phenotypically and ecologically extremely diverse. This natural taxon is phylogenetically distinct from the Saccharomycetaceae, but probably related to the Dipodascaceae. The possible evolution of the lipomycetaceous anamorphs is discussed. 相似文献
110.
Cytokine production in a model of wound healing: the appearance of MIP-1, MIP-2, cachectin/TNF and IL-1 总被引:9,自引:1,他引:8
T J Fahey B Sherry K J Tracey S van Deventer W G Jones J P Minei S Morgello G T Shires A Cerami 《Cytokine》1990,2(2):92-99
Macrophages are essential for normal wound repair and many of their effects on healing wounds are likely to be mediated by the secretion of cytokines. This study examines the appearance of messenger RNA (mRNA) for cachectin/tumor necrosis factor (TNF), IL 1, and macrophage inflammatory proteins 1 and 2 (MIP-1 and MIP-2), as well as the mature peptides, in a model of wound healing using wound chambers. RNA for all four cytokines can be detected in wound inflammatory cells by polymerase chain reaction amplification throughout the first 7 days. Cachectin/TNF and IL 1 protein levels peaked on the first day after wound chamber implantation, and MIP-1 and MIP-2 were detected only on day 3. The data suggest that these cytokines participate in the early inflammatory response to wounding. 相似文献