全文获取类型
收费全文 | 527篇 |
免费 | 27篇 |
国内免费 | 21篇 |
出版年
2023年 | 16篇 |
2022年 | 11篇 |
2021年 | 14篇 |
2020年 | 16篇 |
2019年 | 51篇 |
2018年 | 32篇 |
2017年 | 18篇 |
2016年 | 14篇 |
2015年 | 14篇 |
2014年 | 21篇 |
2013年 | 65篇 |
2012年 | 22篇 |
2011年 | 23篇 |
2010年 | 15篇 |
2009年 | 23篇 |
2008年 | 24篇 |
2007年 | 17篇 |
2006年 | 18篇 |
2005年 | 20篇 |
2004年 | 13篇 |
2003年 | 14篇 |
2002年 | 5篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1999年 | 8篇 |
1998年 | 10篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 7篇 |
1994年 | 3篇 |
1993年 | 7篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1987年 | 2篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1978年 | 1篇 |
1977年 | 4篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有575条查询结果,搜索用时 640 毫秒
121.
This article examines whether media portrayals of Islam and Muslims are overwhelmingly negative, whether they have evolved over time, and what factors most consistently affect their tone. We analyse every fourth New York Times headline about Islam or Muslims between 1985 and 2013. We find that headlines have not been predominantly negative. In addition, New York Times headlines about Islam and Muslims have become more positive over the long term, even after the 9/11 attacks. Most counter-intuitively, we find that terrorist attacks have had a systematic positive effect on headline tone. During the first four weeks after each Islamist terrorist attack on an American target, the tone of New York Times headlines became significantly more positive compared to the four weeks prior to the attack. However, over the subsequent few months, coverage reverted back toward the tone that prevailed during the weeks before the event. 相似文献
122.
Data are presented on the isolation, biosynthesis, and identification of a small peptide (H) from parathyroid gland. Under our experimental conditions this peptide (H) represents, in addition to secretory protein-I and proparathyroid hormone, the other major protein which is rapidly synthesized during shorterm incubations of tissue slices. N-terminal sequence analysis was performed on samples of peptide H and the resulting data used to conduct a search of the sequence data bank. The search established the identity of peptide H as ubiquitin. These findings establish parathyroid gland as another system which rapidly produces ubiquitin , in addition to the systems employing hypothalamus and pituitary where ubiquitin biosynthesis was initially observed by Seidah and Scherrer . 相似文献
123.
A survey of dermatophytes isolated from patients seeking medical advice was made from 1985 to 1987 in the United States. The survey included 54 locations with data from 45 cities and one state. Listing of the isolated dermatophytes and the frequency given by percentage of the total follows: Trichophyton rubrum 54.8%, T. tonsurans 31.3%, T. mentagrophytes 6.0%, Microsporum canis 4.0%, Epidermophyton floccosum 2.0%, M. gypseum 0.6%, and T. verrucosum 0.2%. Out of a total of 14,696 isolates M. audouinii was cultured 13 times, T. violaceum 12 times, M. nanum 6 times, T. terrestre 4 times, and T. soudanense twice. Single isolations were made of M.fulvum, M. ferrugineum and T. schoenleinii.Collection of dermatophyte data in Tucson, Arizona, began in 1966. In 1987, the first case of tinea capitis caused by T. tonsurans was observed. Other isolates of this organism as the cause of tinea capitis were made in this city during that year. These infections were in black children. With the recent growth of Tucson, the percentage of blacks in the population increased and this pathogen was introduced into the general population. 相似文献
124.
The existence of three distinct strains of E. granulosus in Australia has been previously demonstrated on the basis of several criteria. In the present study, numerous isolates of E. granulosus from domestic and wild animal populations in different geographical areas of Australia were subjected to detailed biochemical analysis using isoelectric focusing of soluble proteins. Three different populations were recognised which corresponded to the three strains described previously, thus confirming their genetic distinction. One strain is common to all domestic intermediate hosts on the Australian mainland. Evidence is presented that humans and macropod marsupials are also susceptible to infection with this strain and that it is similar to E. granulosus occurring in sheep in New Zealand and the United Kingdom. The other two strains are confined to macropod marsupials on the Australian mainland and sheep in Tasmania respectively. 相似文献
125.
Peter F. Zika 《Brittonia》2003,55(2):150-156
Juncus effusus s. str. has two native representatives on the coast of western North America. A new combination is provided forJuncus effusus subsp.pacificus, ranging from California to British Columbia.Juncus effusus subsp.austrocalifornicus is newly described from southernmost California, Arizona, and Baja California, México. It differs from subsp.pacificus by its pale sheaths, with less thickened and less overlapping margins, and its disjunct distribution. A key is provided for
the subspecies ofJ. effusus in North America. 相似文献
126.
This article reviews efforts made by the United Nations Environment Programme to assess the progress in life cycle assessment
(LCA) implementation worldwide. The effort was approached in two stages. First, research was carried out which included a
document search and a survey of LCA practitioners. Secondly, an expert workshop of LCA practitioners was held to review the
survey results and to develop recommendations for action. Results highlight that there is significant and growing interest
in LCA and that its use is increasing. To foster better LCA adoption, industry, government and other societal groups will
have to address barriers due to a lack of: a perceived need for LCA, of expertise or know how, of funding and a lack of data
and methodology. 相似文献
127.
In the enclosed fresh-water environmsnt of Hanningfield Reservoir, Essex, England, Anisakis sp. larvae (parasites of marine fish) were found in 55 per cent of 40 brown trout and in 26·2 per cent of 61 rainbow trout. Experimental infection by intubating larvae into the stomach was more successful in brown trout (50·6 per cent recovery rate) than in rainbow trout (27 per cent recovery rate). Some larvae reached the body-cavity as early as 2 h after infection. They penetrated the region between the oesophagus and intestine immediately posterior to the caecal openings. Fewer larvae successfully penetrated the gut wall of brown trout within 24 h at 8°C than at 15 ± 1°C. It appears that the reservoir trout acquired Anisakis by being fed as juveniles on untreated marine fish offal containing live larvae. 相似文献
128.
P B Eveleth 《American journal of physical anthropology》1972,37(2):223-232
Nearly 200 males from a distinct Brazilian population referred to as “Nordestinos” were examined for 11 bodily measurements, two derived measurements, four indices, and nine anthroposcopic observations. The population, formed principally from a mixture of Portuguese whites, Bantu Negroes, and Brazilian Indians inhabits a marginal area characterized by extreme poverty. They are small to medium in stature with leg length slightly shorter than sitting height. They are broad-headed, and more than half have broad faces and medium nose shapes. The majority have brown eyes and black hair. A total of 36.9% show normal occlusion. The hybrid population is more variable in many metrical traits than Xingú Indians of Brazil. In stature and cephalic index and in a number of other characters the averages do not lie in an intermediate position between those of the parental populations even when these traits are distinct in the latter. 相似文献
129.
Brenda J. Hanley André A. Dhondt María J. Forzán Elizabeth M. Bunting Mark A. Pokras Kevin P. Hynes Ernesto Dominguez-Villegas Krysten L. Schuler 《The Journal of wildlife management》2022,86(2):e22177
Bald eagles (Haliaeetus leucocephalus) are considered a recovery success in the United States after rebounding from near extirpation due to widespread use of the insecticide dichlorodiphenyltrichloroethane (DDT) in the twentieth century. Although abundances of bald eagles have increased since DDT was banned, other contaminants have remained in the environment with unknown influence on eagle population trends. Ingestion of spent lead (Pb) ammunition, the source of Pb most available to eagles and other scavengers in the United States, is known to kill individual eagles, but the influence of the contaminant on overall population dynamics remains unclear, resulting in longstanding controversy over the continued legality of the use of Pb in terrestrial hunting ammunition. We hypothesized that mortalities from the ingestion of Pb reduced the long-term growth rate and resiliency of bald eagles in the northeast United States over the last 3 decades. We used Holling's definition of resilience (the ability of a system to absorb changes of state variables, driving variables, and parameters and still persist) to quantify how reduction in survival from Pb-associated mortalities reduced the likelihood of population persistence. We used a population matrix model and necropsy records gathered between 1990 and 2018 from a 7-state area to compare population dynamics under current versus hypothetical Pb-reduced and Pb-free scenarios. Despite a robust increase in eagle abundances in the northeast United States over that period, we estimated that deaths arising from ingestion of Pb was associated with a 4.2% (females) and 6.3% (males) reduction in the asymptotic long-term growth rate (lambda). Comparison between real (current) and counterfactual (Pb-reduced and Pb-free) population dynamics indicated that the deaths from acute Pb poisoning were additive because the mortality events were associated with marked reduction in annual survival performance of hatchlings and reproductive females. These shifts in survival performance were further associated with a reduction in resilience for hatchling (95.4%) and breeding (81.6%) female eagles. Counterintuitively, the current conditions produced an increase in resilience (68.9%) for immature and non-breeding female eagles over hypothetical Pb-free conditions, suggesting that the population of eagles in the northeast United States reorganized (in a population dynamics sense) to ensure population expansion despite additive mortalities associated with Pb. This study can be used by state and federal wildlife managers or non-governmental organizations to inform policy surrounding the use of lead ammunition or to educate hunters on the population-scale effects of their ammunition choices. 相似文献
130.
Lixian Chen Tianhao Zhou Nan Wu April OBrien Julie Venter Ludovica Ceci Konstantina Kyritsi Paolo Onori Eugenio Gaudio Amelia Sybenga Linglin Xie Chaodong Wu Luca Fabris Pietro Invernizzi David Zawieja Suthat Liangpunsakul Fanyin Meng Heather Francis Shannon Glaser 《生物化学与生物物理学报:疾病的分子基础》2019,1865(6):1525-1539
Melatonin, a neuroendocrine hormone synthesized by the pineal gland and cholangiocytes, decreases biliary hyperplasia and liver fibrosis during cholestasis-induced biliary injury via melatonin-dependent autocrine signaling through increased biliary arylalkylamine N-acetyltransferase (AANAT) expression and melatonin secretion, downregulation of miR-200b and specific circadian clock genes. Melatonin synthesis is decreased by pinealectomy (PINX) or chronic exposure to light. We evaluated the effect of PINX or prolonged light exposure on melatonin-dependent modulation of biliary damage/ductular reaction/liver fibrosis. Studies were performed in male rats with/without BDL for 1 week with 12:12 h dark/light cycles, continuous light or after 1 week of PINX. The expression of AANAT and melatonin levels in serum and cholangiocyte supernatant were increased in BDL rats, while decreased in BDL rats following PINX or continuous light exposure. BDL-induced increase in serum chemistry, ductular reaction, liver fibrosis, inflammation, angiogenesis and ROS generation were significantly enhanced by PINX or light exposure. Concomitant with enhanced liver fibrosis, we observed increased biliary senescence and enhanced clock genes and miR-200b expression in total liver and cholangiocytes. In vitro, the expression of AANAT, clock genes and miR-200b was increased in PSC human cholangiocyte cell lines (hPSCL). The proliferation and activation of HHStecs (human hepatic stellate cell lines) were increased after stimulating with BDL cholangiocyte supernatant and further enhanced when stimulated with BDL rats following PINX or continuous light exposure cholangiocyte supernatant via intracellular ROS generation. Conclusion: Melatonin plays an important role in the protection of liver against cholestasis-induced damage and ductular reaction. 相似文献