全文获取类型
收费全文 | 1784篇 |
免费 | 155篇 |
国内免费 | 1篇 |
出版年
2023年 | 5篇 |
2022年 | 13篇 |
2021年 | 23篇 |
2020年 | 16篇 |
2019年 | 28篇 |
2018年 | 25篇 |
2017年 | 28篇 |
2016年 | 55篇 |
2015年 | 80篇 |
2014年 | 96篇 |
2013年 | 116篇 |
2012年 | 147篇 |
2011年 | 154篇 |
2010年 | 83篇 |
2009年 | 72篇 |
2008年 | 101篇 |
2007年 | 96篇 |
2006年 | 88篇 |
2005年 | 120篇 |
2004年 | 74篇 |
2003年 | 115篇 |
2002年 | 92篇 |
2001年 | 25篇 |
2000年 | 16篇 |
1999年 | 21篇 |
1998年 | 18篇 |
1997年 | 21篇 |
1996年 | 19篇 |
1995年 | 17篇 |
1994年 | 10篇 |
1993年 | 14篇 |
1992年 | 12篇 |
1991年 | 8篇 |
1990年 | 4篇 |
1989年 | 11篇 |
1988年 | 11篇 |
1986年 | 8篇 |
1985年 | 6篇 |
1982年 | 6篇 |
1980年 | 4篇 |
1977年 | 3篇 |
1975年 | 7篇 |
1974年 | 3篇 |
1973年 | 12篇 |
1972年 | 7篇 |
1971年 | 5篇 |
1970年 | 5篇 |
1967年 | 5篇 |
1966年 | 4篇 |
1958年 | 3篇 |
排序方式: 共有1940条查询结果,搜索用时 15 毫秒
971.
972.
Bettina Karsten Eneko Larumbe-Zabala Gokhan Kandemir Tahir Hazir Andreas Klose Fernando Naclerio 《PloS one》2016,11(3)
The objectives of this study were to examine the effects of a moderate intensity strength training on changes in critical velocity (CV), anaerobic running distance (D''), sprint performance and Yo-Yo intermittent running test (Yo-Yo IR1) performances. Methods: two recreational soccer teams were divided in a soccer training only group (SO; n = 13) and a strength and soccer training group (ST; n = 13). Both groups were tested for values of CV, D'', Yo-Yo IR1 distance and 30-m sprint time on two separate occasions (pre and post intervention). The ST group performed a concurrent 6-week upper and lower body strength and soccer training, whilst the SO group performed a soccer only training. Results: after the re-test of all variables, the ST demonstrated significant improvements for both, YoYo IR1 distance (p = 0.002) and CV values (p<0.001) with no significant changes in the SO group. 30-m sprint performance were slightly improved in the ST group with significantly decreased performance times identified in the SO group (p<0.001). Values for D'' were slightly reduced in both groups (ST -44.5 m, 95% CI = -90.6 to 1.6; SO -42.6 m, 95% CI = -88.7 to 3.5). Conclusions: combining a 6-week moderate strength training with soccer training significantly improves CV, Yo-Yo IR1 whilst moderately improving 30-m sprint performances in non-previously resistance trained male soccer players. Critical Velocity can be recommended to coaches as an additional valid testing tool in soccer. 相似文献
973.
UV-absorbing mycosporine-like amino acid compounds (MAA) were identified and quantified in 13 macroalgal Chlorophyceae, six Phaeophyceae and 28 Rhodophy-ceae collected in the intertidal zone from the tropical island Hainan, People's Republic of China, as well as from tropical mangrove locations in America, Africa, Australia and Japan. All of these habitats receive naturally high solar ultraviolet (UV) irradiances. The study revealed that all Rhodophyceae contained several MAA, which are assumed to function as natural UV sunscreens. Within all species investigated eight distinct compounds were found, seven of which were identified as mycosporine-glycine, shinorine, porphyra-334, pal-ythine, asterina-330, palythinol and palythene. The unknown substance had an absorption spectrum with a maximum at 357 nm. This compound was restricted to two red algal species from Hainan. In contrast, the Chlorophyceae and Phaeophyceae did not contain MAA or exhibited only trace concentrations. Compared with data from the literature, the amount of all MAA in the tropical Rhodophyceae seemed to be higher than in temperate organisms, probably reflecting acclimation to the stronger solar radiation which is typical for lower latitudes. The data suggest that accumulation of MAA may represent a natural defence system against exposure to biologically harmful UV radiation. 相似文献
974.
975.
This longitudinal study tracked the neuro-cognitive changes associated with second language (L2) grammar learning in adults in order to investigate how L2 processing is shaped by a learner’s first language (L1) background and L2 proficiency. Previous studies using event-related potentials (ERPs) have argued that late L2 learners cannot elicit a P600 in response to L2 grammatical structures that do not exist in the L1 or that are different in the L1 and L2. We tested whether the neuro-cognitive processes underlying this component become available after intensive L2 instruction. Korean- and Chinese late-L2-learners of English were tested at the beginning and end of a 9-week intensive English-L2 course. ERPs were recorded while participants read English sentences containing violations of regular past tense (a grammatical structure that operates differently in Korean and does not exist in Chinese). Whereas no P600 effects were present at the start of instruction, by the end of instruction, significant P600s were observed for both L1 groups. Latency differences in the P600 exhibited by Chinese and Korean speakers may be attributed to differences in L1–L2 reading strategies. Across all participants, larger P600 effects at session 2 were associated with: 1) higher levels of behavioural performance on an online grammaticality judgment task; and 2) with correct, rather than incorrect, behavioural responses. These findings suggest that the neuro-cognitive processes underlying the P600 (e.g., “grammaticalization”) are modulated by individual levels of L2 behavioural performance and learning. 相似文献
976.
Karsten R.O. Hazlett Kerry A. Cirillo 《Microbes and infection / Institut Pasteur》2009,11(10-11):828-834
Concerns over weaponizable bacteria have recently prompted considerable interest in Francisella tularensis (Ft). In addition to its potential illicit use, Ft occurs naturally in diverse ecological niches including mammals, arthropods, and fresh water protozoans. Here we review the current knowledge of Ft adaptation which has ramifications for both basic and applied research. 相似文献
977.
978.
979.
980.
Griffin Lentsch Mihaela Balu Joshua Williams Sanghoon Lee Ronald M. Harris Karsten Knig Anand Ganesan Bruce J. Tromberg Nirmala Nair Uma Santhanam Manoj Misra 《Pigment cell & melanoma research》2019,32(3):403-411
Melasma is a skin disorder characterized by hyperpigmented patches due to increased melanin production and deposition. In this pilot study, we evaluate the potential of multiphoton microscopy (MPM) to characterize non‐invasively the melanin content, location, and distribution in melasma and assess the elastosis severity. We employed a clinical MPM tomograph to image in vivo morphological features in melasma lesions and adjacent normal skin in 12 patients. We imaged dermal melanophages in most dermal melasma lesions and occasionally in epidermal melasma. The melanin volume fraction values measured in epidermal melasma (14% ± 4%) were significantly higher (p < 0.05) than the values measured in perilesional skin (11% ± 3%). The basal keratinocytes of melasma and perilesions showed different melanin distribution. Elastosis was predominantly more severe in lesions than in perilesions and was associated with changes in melanin distribution of the basal keratinocytes. These results demonstrate that MPM may be a non‐invasive imaging tool for characterizing melasma. 相似文献