全文获取类型
收费全文 | 2952篇 |
免费 | 328篇 |
出版年
2023年 | 7篇 |
2022年 | 7篇 |
2021年 | 47篇 |
2020年 | 40篇 |
2019年 | 47篇 |
2018年 | 90篇 |
2017年 | 76篇 |
2016年 | 89篇 |
2015年 | 151篇 |
2014年 | 140篇 |
2013年 | 190篇 |
2012年 | 206篇 |
2011年 | 185篇 |
2010年 | 137篇 |
2009年 | 106篇 |
2008年 | 159篇 |
2007年 | 135篇 |
2006年 | 138篇 |
2005年 | 129篇 |
2004年 | 111篇 |
2003年 | 114篇 |
2002年 | 114篇 |
2001年 | 95篇 |
2000年 | 73篇 |
1999年 | 65篇 |
1998年 | 39篇 |
1997年 | 30篇 |
1996年 | 27篇 |
1995年 | 29篇 |
1994年 | 29篇 |
1993年 | 17篇 |
1992年 | 42篇 |
1991年 | 43篇 |
1990年 | 35篇 |
1989年 | 32篇 |
1988年 | 32篇 |
1987年 | 28篇 |
1986年 | 49篇 |
1985年 | 28篇 |
1984年 | 22篇 |
1983年 | 17篇 |
1982年 | 12篇 |
1981年 | 11篇 |
1980年 | 9篇 |
1979年 | 12篇 |
1978年 | 16篇 |
1975年 | 7篇 |
1974年 | 12篇 |
1973年 | 18篇 |
1969年 | 6篇 |
排序方式: 共有3280条查询结果,搜索用时 484 毫秒
991.
992.
Orlando Alva Rosa Nair Roa-Roco Ricardo Pérez-Díaz Mónica Yá?ez Jaime Tapia Yerko Moreno Simón Ruiz-Lara Enrique González 《PloS one》2015,10(10)
Parthenocarpic fruit development (PFD) reduces fruit yield and quality in grapevine. Parthenocarpic seedless berries arise from fruit set without effective fertilization due to defective pollen germination. PFD has been associated to micronutrient deficiency but the relation of this phenomenon with pollen polymorphism has not been reported before. In this work, six grapevine cultivars with different tendency for PFD and grown under micronutrient-sufficient conditions were analyzed to determine pollen structure and germination capability as well as PFD rates. Wide variation in non-germinative abnormal pollen was detected either among cultivars as well as for the same cultivar in different growing seasons. A straight correlation with PFD rates was found (R2 = 0.9896), suggesting that natural parthenocarpy is related to defective pollen development. Such relation was not observed when PFD was analyzed in grapevine plants exposed to exogenous gibberellin (GA) or abscissic acid (ABA) applications at pre-anthesis. Increase (GA treatment) or reduction (ABA treatment) in PFD rates without significative changes in abnormal pollen was determined. Although these plants were maintained at sufficient boron (B) condition, a down-regulation of the floral genes VvBOR3 and VvBOR4 together with a reduction of floral B content in GA-treated plants was established. These results suggest that impairment in B mobility to reproductive tissues and restriction of pollen tube growth could be involved in the GA-induced parthenocarpy. 相似文献
993.
Gonzalo Castillo-Campos Gonzalo Halffter Claudia E. Moreno 《Biodiversity and Conservation》2008,17(7):1701-1714
The floristic diversity of Mexican tropical deciduous forests (TDF) is of critical importance given the high species richness
(alpha diversity), species turnover (beta diversity), and the intense deforestation rates. Currently, most TDF landscapes
are mosaics of agricultural land, secondary vegetation, and patches of relatively undisturbed primary vegetation. Here we
illustrate how both primary forest remnants and secondary vegetation patches contribute to the floristic diversity of TDF
in a landscape of volcanic origin in central Veracruz, Mexico. Our objectives were to assess sampling efficiency and inventory
completeness, to compare mean and cumulative species richness between primary forest and secondary vegetation sites, and to
analyze beta diversity between vegetation types. In an area of 12,300 m2 we recorded 105 families, 390 genera, and 682 species.
Species inventories for both vegetation types were about 80% complete. Secondary vegetation is more alpha diverse than primary
forest, both in terms of cumulative and mean species richness. We found a remarkably high beta diversity between vegetation
types (75% of complementarity, 91.60% of mean dissimilarity). We also identified the species that contribute the most to similarity
within vegetation types and to dissimilarity between vegetation types. Our results support the idea that assessing biodiversity
on the landscape scale is an appropriate way to ascertain the impact of human activities. For this land mosaic, conservation
of the flora would not be possible by focusing solely on primary forest remnants. We propose the implementation of a network
of small conservation areas with a flexible structure, following the “archipelago reserve” model. 相似文献
994.
995.
996.
Lorena Ortega Moreno Olga Lamacchia Massimiliano Copetti Lucia Salvemini Concetta De Bonis Salvatore De Cosmo Mauro Cignarelli Vincenzo Trischitta Claudia Menzaghi 《PloS one》2015,10(10)
High serum adiponectin has been increased in several conditions of kidney disease. Only sparse and conflicting results have been reported in patients with type 2 diabetes (T2D), a subgroup of individuals who are at high risk for renal dysfunction. The aim of this study was to fill up this gap of knowledge by investigating such association in a large sample of Italian diabetic patients. The association between serum adiponectin levels and estimated glomerular filtration rate (eGFR by Chronic Kidney Disease-Epidemiology Collaboration CKD-EPI equation) was investigated in 1,243 patients with T2D from two cross-sectional Italian studies: 878 from San Giovanni Rotondo (SGR) and 365 from Foggia (FG). Serum adiponectin was inversely associated with eGFR in SGR [β (standard error, SE) for 1 standard deviation (SD) of adiponectin = -3.26 (0.64)] and in FG [β(SE)=-5.70(1.28)] sample, as well as in the two studies combined [β(SE)=-3.99(0.59)];(p<0.0001 for all). In this combined analysis, the association was still significant after adjusting for sex, smoking habits, body mass index (BMI), waist circumference, diabetes duration, glycated hemoglobin (HbA1c), albumin creatinine ratio (ACR) and anti-hyperglycemic, anti-hypertensive and anti-dyslipidemic treatments [β (SE)= -2.19 (0.59), p = 0.0001]. A stronger association between each SD adiponectin increment and low eGFR was observed among patients with micro-/macro-albuminuria, as compared to those with normo-albuminuria [adjusted β(SE)=-4.42(1.16) ml/min/1.73m2 vs. -1.50 (0.67) ml/min/1.73m2, respectively; p for adiponectin-by-albuminuric status = 0.022]. For each adiponectin SD increment, the odds of having eGFR < 60 ml/min/1.73m2 increased by 41% (odds ratio, OR = 1.41; 95% confidence interval, CI 1.21–1.64) in SGR sample, 53% (OR = 1.53; 95% CI 1.21–1.94) in FG sample, and 44% (OR = 1.44; 95%CI 1.27–1.64) in the two studies considered together (p<0.0001 for all). In the combined sample, further adjustment for the above mentioned covariates did not change the observed association (OR = 1.36; 95%CI 1.16–1.60; p<0.0001). Our study, so far the largest addressing the relationship between serum adiponectin and GFR in T2D, strongly suggests that the paradoxical inverse association, previously reported in different clinical sets, is also observed in diabetic patients. Further studies are needed to unravel the biology underlying this counterintuitive relationship. 相似文献
997.
Elaine Cristina Marqueze Suleima Vasconcelos Johanna Garefelt Debra J. Skene Claudia Roberta Moreno Arne Lowden 《PloS one》2015,10(4)
Objectives
This study aimed to investigate the relationship between individual natural light exposure, sleep need, and depression at two latitudes, one extreme with a few hours of light per day during winter, and the other with equal hours of light and darkness throughout the year.Methods
This cross-sectional study included a sample of Brazilian workers (Equatorial, n = 488 workers) and a Swedish sample (Arctic, n = 1,273).Results
The reported mean total natural light exposure per 4-week cycle differed significantly between the Equatorial and Arctic regions. However, shiftworkers from both sites reported similar hours of natural light exposure. Short light exposure was a predictor for insufficient sleep.Conclusion
Reduced exposure to natural light appears to increase the perception of obtaining insufficient sleep. Arctic workers were more prone to develop depression than Equatorial workers. 相似文献998.
Cristina Bocanegra Sara Gallego Jacobo Mendioroz Milagros Moreno Elena Sulleiro Fernando Salvador Nicolau Sikaleta Arlette Nindia Daniel Tchipita Morais Joromba Sebastiao Kavaya Adrián Sánchez Montalvá Teresa López Israel Molina 《PLoS neglected tropical diseases》2015,9(10)
Introduction
Schistosomiasis remains a public health major problem and little is known in many areas, mainly in Sub-Saharan AfricaObjectives
To assess the burden and risk factors of schistosomiasis and intestinal parasitic helminthes in the children of Cubal, Angola, and to compare different diagnostic approaches for urinary schistosomiasis under field conditions.Methods
A cross-sectional study was conducted. Urine and faeces samples of school children were microscopically studied. A random sample of children was obtained from an alphabetically arranged list of children, taking one of two children. Urine dipstick, colorimetric test and macrohaematuria were considered as indirect diagnostic methods and compared to direct urine examination. Possible risk factors for the infection were sex, age, distance to the river and previous treatment with praziquantel; the assessment was performed using Chi-square test.Results
A total of 785 (61.18%) children showed S. haematobium eggs in urine; children living within 500 meters from the river had a higher odds for infection: Odds ratio 1.97 (1.45–2.7 CI 95%); urine dipstick showed sensitivity of 96% and specificity of 61.3%, with a positive predictive value; colorimetric test showed sensitivity of 52.5%, specificity of 74.6% and a positive predictive value of 77%. Proteinuria was present in 653 (51.1%) children, being more frequent in children with S. haematobium in urine (75.2%); 32 of 191 stool samples (16%) showed the presence of other intestinal parasites and 8 (4%) for S. haematobium.Conclusions
Prevalence of urinary schistosomiasis in our study area is much higher than the national average, considering it as a high-risk community. Proximity to a source of water was a risk factor for the infection. Indirect tests, as urine dipstick and colorimetric test, were useful tools for diagnosis, due to ease of use and low cost. Proteinuria was a common finding, probably showing an early structural damage due to schistosomiasis in this group of children. 相似文献999.
1000.
Irisin levels before and after physical activity among school‐age children with different BMI: A direct relation with leptin 下载免费PDF全文