全文获取类型
收费全文 | 1427篇 |
免费 | 123篇 |
国内免费 | 1篇 |
专业分类
1551篇 |
出版年
2022年 | 8篇 |
2021年 | 16篇 |
2020年 | 9篇 |
2019年 | 11篇 |
2018年 | 11篇 |
2017年 | 12篇 |
2016年 | 9篇 |
2015年 | 44篇 |
2014年 | 46篇 |
2013年 | 56篇 |
2012年 | 81篇 |
2011年 | 135篇 |
2010年 | 92篇 |
2009年 | 63篇 |
2008年 | 47篇 |
2007年 | 54篇 |
2006年 | 62篇 |
2005年 | 50篇 |
2004年 | 38篇 |
2003年 | 44篇 |
2002年 | 51篇 |
2001年 | 24篇 |
2000年 | 52篇 |
1999年 | 33篇 |
1998年 | 24篇 |
1997年 | 18篇 |
1996年 | 15篇 |
1995年 | 18篇 |
1994年 | 18篇 |
1993年 | 26篇 |
1992年 | 26篇 |
1991年 | 25篇 |
1990年 | 17篇 |
1989年 | 18篇 |
1988年 | 24篇 |
1987年 | 17篇 |
1986年 | 29篇 |
1985年 | 20篇 |
1984年 | 18篇 |
1983年 | 20篇 |
1982年 | 11篇 |
1981年 | 11篇 |
1979年 | 14篇 |
1977年 | 7篇 |
1976年 | 12篇 |
1975年 | 14篇 |
1974年 | 11篇 |
1973年 | 14篇 |
1972年 | 10篇 |
1969年 | 7篇 |
排序方式: 共有1551条查询结果,搜索用时 15 毫秒
1.
Hauser JE Kadekaro AL Kavanagh RJ Wakamatsu K Terzieva S Schwemberger S Babcock G Rao MB Ito S Abdel-Malek ZA 《Pigment cell research / sponsored by the European Society for Pigment Cell Research and the International Pigment Cell Society》2006,19(4):303-314
Malignant transformation of melanocytes leads to melanoma, the most fatal form of skin cancer. Ultraviolet radiation (UVR)-induced DNA photoproducts play an important role in melanomagenesis. Cutaneous melanin content represents a major photoprotective mechanism against UVR-induced DNA damage, and generally correlates inversely with the risk of skin cancer, including melanoma. Melanoma risk is also determined by susceptibility genes, one of which is the melanocortin 1 receptor (MC1R) gene. Certain MC1R alleles are strongly associated with melanoma. We hereby present experimental evidence for the role of two melanoma risk factors, constitutive pigmentation, as assessed by total melanin, eumelanin and pheomelanin contents, and MC1R genotype and function, in determining the induction and repair of DNA photoproducts in cultured human melanocytes after irradiation with increasing doses of UVR. We found that total melanin and eumelanin contents (MC and EC) correlated inversely with the extent of UVR-induced growth arrest, apoptosis and induction of cyclobutane pyrimidine dimers (CPD), but not with hydrogen peroxide release in melanocytes expressing functional MC1R. In comparison, melanocytes with loss-of-function MC1R, regardless of their MC or EC, sustained more UVR-induced apoptosis and CPD, and exhibited reduced CPD repair. Therefore, MC, mainly EC, and MC1R function are independent determinants of UVR-induced DNA damage in melanocytes. 相似文献
2.
The plantae of 83 male and 95 female healthy, full-term Caucasian newborns from Austria (gestational age 235–301 days) were photographed and the flexion creases in the distal part were examined. Analysis of the creases was done under four different aspects, the main evaluation based on a scheme of nine creases introduced by Schenk and Patzer (1959). Two transversal (No. 1 and No. 9) and three longitudinal (Nos. 3, 6, and 7) creases are always or predominantly present, a finding corresponding with the data of Schenk on 52 male and 48 female newborns from Germany. In addition, the nine plantar creases were evaluated according to six degrees of expression, and some typical crease combinations are shown. Bilateral and bisexual similarity prevails. The results of this study might serve investigations of different populations and of medical disorders. 相似文献
3.
4.
Pentzos Daponte A. Vienna A. Brant L. Hauser G. 《International Journal of Anthropology》2004,19(4):289-295
In 14141 male and 14141 female Greek children and adolescents ranging in age between seven and fifteen years the presence
of cheek dimples was investigated. Neither sex (12.6% in both female and males) nor side differences when expressed unilaterally
were observed. There was however a significant increase of dimples with age as well as significantly higher numbers of asymmetric
than symmetric expressions in all age groups.
With respect to these observations hypotheses of origin of cheek dimples and related effects of age are discussed. 相似文献
5.
6.
JINDŘIŠKA BOJKOVÁ KLÁRA KOMPRDOVÁ TOMÁŠ SOLDÁN SVĚTLANA ZAHRÁDKOVÁ 《Freshwater Biology》2012,57(12):2550-2567
1. Rapid expansion and intensification of anthropogenic activities in the 20th century has caused profound changes in freshwater assemblages. Unfortunately, knowledge of the extent and causes of species loss (SL) is limited due to the lack of reliable historical data. An unusual data set allows us to compare changes in the most sensitive of aquatic insect orders, the Plecoptera, at some 170 locations in the Czech Republic between two time periods, 1955–1960 and 2006–2010. Historical data (1890–1911) on assemblages of six lowland rivers allow us to infer even earlier changes. 2. Regional stonefly diversity decreased in the first half of the 20th century. Streams at lower altitudes lost a substantial number of species, which were never recovered. In the second half of the century, large‐scale anthropogenic pressure caused SL in all habitats, leading to a dissimilarity of contemporary and previous assemblages. The greatest changes were found at sites affected by organic pollution and a mixture of organic pollution and channelisation or impoundment. Colonisation of new habitats was observed in only three of the 80 species evaluated. 3. Species of moderate habitat specialisation and tolerance to organic pollution were most likely to be lost. Those with narrow specialisations in protected habitats were present in both historical and contemporary collections. 4. Contemporary assemblages are the consequence of more than a 100 years of anthropogenic impacts. In particular, streams at lower altitude and draining intensively exploited landscapes host a mere fragment of the original species complement. Most stonefly species are less frequently present than before, although their assemblages remain almost intact in near‐natural mountain streams. Our analyses demonstrate dramatic restriction of species ranges and, in some cases, apparent changes in altitudinal preference throughout the area. 相似文献
7.
Kirchengast S Knogler W Hauser G 《Anthropologischer Anzeiger; Bericht über die biologisch-anthropologische Literatur》2002,60(2):187-197
The effect of weight, classified by body mass index (BMI), on bone mass (BMC) of the whole body and on bone mineral density BMD of the hip joint was analysed in a sample of 120 Austrians of Vienna and surroundings. The 68 females and 52 males of this cross sectional study ranged in age between 60 and 92 years (x = 71.7 +/- 7.7). Age distribution was not significantly different between sexes. The WHO (1997) classification of body mass index (BMI) was used for weight classification, i.e. normal weight (BMI 18.5-24.99) and moderate overweight (BMI 25.0-29.99). Obese subjects (BMI 30+) were not included in this study. Bone mass of the whole body as well as bone density of the hip joint were determined by Dual-energy-X-ray absorptiometry (DEXA) using a hologic 2000 scanner. As expected BMC and BMD values were significantly higher in males than in females. While in both females and males moderately overweight BMD of the hip was significantly higher than in those with normal BMI, statistically significant differences of BMC were restricted to females only. Such positive association between body weight and BMC and BMD is in agreement with previous studies on mature subjects, and menopausal and postmenopausal women in particular. In addition, this study demonstrates corresponding positive associations between moderate overweight and bone mass and -density in the elderly and old aged. 相似文献
8.
Marília Hauser Fabrice Duponchelle Theodore W. Hermann Karin E. Limburg Leandro Castello Donald J. Stewart Gislene Torrente-Vilara Aurea García-Vásquez Carmen García-Davila Marc Pouilly Christophe Pecheyran Emmanuel Ponzevera Jean-François Renno Arthur S. Moret Carolina R. C. Doria 《Freshwater Biology》2020,65(2):325-336
- Amazonian goliath catfishes are widespread in the Amazon Basin. Recently, otolith 87Sr:86Sr analyses using laser ablation–multi-collector–inductively coupled plasma mass spectrometry (LA-MC-ICPMS) revealed a >8,000 km trans-Amazonian natal homing in Brachyplatystoma rousseauxii among fish caught and hatched in the largest Amazon River tributary, the upper Madeira basin. Although also suspected for fish in the upper Amazon, homing could not be demonstrated owing to less distinct environmental 87Sr:86Sr gradients along the Amazon mainstem. Using scanning X-ray fluorescence microscopy (SXFM), a separate study provided evidence that Se:Ca and Sr:Ca are useful markers for identifying migration into Andean headwaters and the estuarine environment.
- We analysed otoliths of known 87Sr:86Sr profiles using SXFM mapping to test if Sr:Ca and Se:Ca patterns could demonstrate natal homing for three fish caught in the upper Amazon, using as reference two individuals that were natal homers and two forced residents (hatched after the construction of hydroelectric dams on the Madeira River) from the upper Madeira River.
- As hypothesised, although the Sr isotope profiles of the upper Amazon individuals were uninformative, two of them presented similar alternating mirror patterns of Sr:Ca and Se:Ca to those of the upper Madeira natal homers, indicating migrations out of the Andean region and into the estuary area. Both were therefore natal homers from the upper Amazon.
- The third individual from the upper Amazon presented similar Sr:Ca and Se:Ca patterns to those of the upper Madeira residents, suggesting it was a natural resident from the upper Amazon.
- By combining the results of 87Sr:86Sr analyses (LA-MC-ICPMS) and Sr:Ca and Se:Ca mappings (SXFM) that are completely independent of one another, we demonstrated that B. rousseauxii also performs natal homing in the upper Amazon. Our results indicate that the life cycle of B. rousseauxii is more complex than previous literature hypothesised, with the existence of partial migration, even in absence of physical barriers. Quantifying the relative importance of these different life-history strategies will have important implications for fisheries management. Our results also lay the groundwork for conservation efforts in the context of hydropower development in the Amazon Basin and set testable hypotheses of the potential impacts of the Madeira River dams.
9.
Hauser S Bickel L Weinspach D Gerg M Schäfer MK Pfeifer M Hazin J Schelter F Weidle UH Ramser J Volkmann J Meindl A Schmitt M Schrötzlmair F Altevogt P Krüger A 《PloS one》2011,6(4):e18989
Tumour-specific splicing is known to contribute to cancer progression. In the case of the L1 cell adhesion molecule (L1CAM), which is expressed in many human tumours and often linked to bad prognosis, alternative splicing results in a full-length form (FL-L1CAM) and a splice variant lacking exons 2 and 27 (SV-L1CAM). It has not been elucidated so far whether SV-L1CAM, classically considered as tumour-associated, or whether FL-L1CAM is the metastasis-promoting isoform. Here, we show that both variants were expressed in human ovarian carcinoma and that exposure of tumour cells to pro-metastatic factors led to an exclusive increase of FL-L1CAM expression. Selective overexpression of one isoform in different tumour cells revealed that only FL-L1CAM promoted experimental lung and/or liver metastasis in mice. In addition, metastasis formation upon up-regulation of FL-L1CAM correlated with increased invasive potential and elevated Matrix metalloproteinase (MMP)-2 and -9 expression and activity in vitro as well as enhanced gelatinolytic activity in vivo. In conclusion, we identified FL-L1CAM as the metastasis-promoting isoform, thereby exemplifying that high expression of a so-called tumour-associated variant, here SV-L1CAM, is not per se equivalent to a decisive role of this isoform in tumour progression. 相似文献
10.
Sawhney RS Cookson MM Sharma B Hauser J Brattain MG 《The Journal of biological chemistry》2004,279(45):47379-47390
Recently, we showed that autocrine transforming growth factor alpha (TGFalpha) controls the epidermal growth factor receptor (EGFR)-mediated basal expression of integrin alpha2, cell adhesion and motility in highly progressed HCT116 colon cancer cells. We also reported that the expression of basal integrin alpha2 and its biological effects are critically controlled by the constitutive activation of the ERK/MAPK pathway (Sawhney, R. S., Sharma, B., Humphrey, L. E., and Brattain, M. G. (2003) J. Biol. Chem. 278, 19861-19869). In the present report, we further examine the downstream signaling mechanisms underlying EGFR/ERK signaling and integrin alpha2 function in HCT116 cells. Selective MEK inhibitors attenuated TGFalpha-mediated basal activation of p70S6K (S6K) specifically at Thr-389, indicating that this S6K site is downstream of ERK/MAPK signaling. Cells were treated with the selective protein kinase C (PKC) inhibitor bisindolylmaleimide to determine the role of PKC in S6K activation. The Thr-421 and Ser-424 phosphorylation sites of S6K were specifically inhibited by bisindolylmaleimide, which also blocked integrin alpha2 expression, cell adhesion, and motility. These data establish a novel cell motility function of S6K via PKC activation in a cancer cell. In addition, we examined whether mammalian target of rapamycin signaling controls S6K activation. Rapamycin inhibited constitutive S6K phosphorylation specifically at Thr-389, Thr-421, and Ser-424 sites. The assignment of these phosphorylation sites on S6K to biological functions was unequivocally confirmed by transfection of cells with specific single phosphorylation site dominant negative mutants. These experiments show for the first time that autocrine TGFalpha regulates cell adhesion function by multiple signaling pathways via specific phosphorylation sites of S6K in cancer cells. 相似文献