全文获取类型
收费全文 | 1674篇 |
免费 | 106篇 |
国内免费 | 3篇 |
专业分类
1783篇 |
出版年
2023年 | 7篇 |
2022年 | 34篇 |
2021年 | 43篇 |
2020年 | 20篇 |
2019年 | 29篇 |
2018年 | 52篇 |
2017年 | 36篇 |
2016年 | 60篇 |
2015年 | 82篇 |
2014年 | 90篇 |
2013年 | 126篇 |
2012年 | 115篇 |
2011年 | 112篇 |
2010年 | 72篇 |
2009年 | 52篇 |
2008年 | 75篇 |
2007年 | 76篇 |
2006年 | 92篇 |
2005年 | 75篇 |
2004年 | 66篇 |
2003年 | 49篇 |
2002年 | 37篇 |
2001年 | 30篇 |
2000年 | 28篇 |
1999年 | 21篇 |
1998年 | 18篇 |
1997年 | 6篇 |
1996年 | 16篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 12篇 |
1992年 | 29篇 |
1991年 | 23篇 |
1990年 | 20篇 |
1989年 | 17篇 |
1988年 | 22篇 |
1987年 | 16篇 |
1986年 | 13篇 |
1985年 | 12篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1979年 | 10篇 |
1976年 | 7篇 |
1974年 | 6篇 |
1973年 | 6篇 |
1971年 | 4篇 |
1970年 | 6篇 |
1969年 | 5篇 |
排序方式: 共有1783条查询结果,搜索用时 15 毫秒
51.
Supratim Basu Aryadeep Roychoudhury Progya Paromita Saha Dibyendu N. Sengupta 《Acta Physiologiae Plantarum》2010,32(3):551-563
Extensive investigation into plant response and adaptation to diverse osmotic stresses like high salt/dehydration/low temperature,
involving a broad spectrum of cellular physiological and biochemical changes, is essential to unravel intrinsic mechanism
to mitigate against such stresses. In our previous communications, we conducted biochemical analyses of indica rice varieties,
subjected to exogenous salt/abscisic acid-mediated oxidative stress. The aim of this study was to compare differential biochemical
responses of the salt-sensitive (IR-29), salt-tolerant (Pokkali) and aromatic (Pusa Basmati or PB) rice varieties during polyethylene
glycol (PEG)-induced dehydration stress. The greater susceptibility of IR-29 and PB, to water scarcity, was reflected by the
higher toxic Na+ and putrescine accumulation, considerable decrease in (reduced/oxidized) glutathione, maximal increment in protease activity
and greater downregulation of nitrate reductase activity. On the other hand, Pokkali appeared to suffer lesser damages as
evidenced from much lower endogenous Na+ but higher K+, Ca2+ and Mg2+ accumulation, registering the highest levels of osmolytes like glycinebetaine and higher polyamines (spermidine and spermine)
accounting to improved relative water content, higher (reduced/oxidized) glutathione, maximal induction of the enzyme phenylalanine
ammonia-lyase and practically unhindered nitrate reductase activity, following PEG treatment. The highest induction of sugars
and proline in IR-29 and PB probably played the osmoprotective/antioxidative functions, enabling to a certain extent to heighten
their lipoxygenase inhibition or H2O2 scavenging potential, more than Pokkali, to ward off oxidative damages and sustain survival under critical dehydrated situations.
Thus, the salt-tolerant Pokkali also showed prominent dehydration-tolerance properties, whereas the aromatic rice PB, almost
identical in their biochemical responses to IR-29, showed greater sensitivity to PEG-mediated water deficit. 相似文献
52.
Summary Competing risks arise naturally in time‐to‐event studies. In this article, we propose time‐dependent accuracy measures for a marker when we have censored survival times and competing risks. Time‐dependent versions of sensitivity or true positive (TP) fraction naturally correspond to consideration of either cumulative (or prevalent) cases that accrue over a fixed time period, or alternatively to incident cases that are observed among event‐free subjects at any select time. Time‐dependent (dynamic) specificity (1–false positive (FP)) can be based on the marker distribution among event‐free subjects. We extend these definitions to incorporate cause of failure for competing risks outcomes. The proposed estimation for cause‐specific cumulative TP/dynamic FP is based on the nearest neighbor estimation of bivariate distribution function of the marker and the event time. On the other hand, incident TP/dynamic FP can be estimated using a possibly nonproportional hazards Cox model for the cause‐specific hazards and riskset reweighting of the marker distribution. The proposed methods extend the time‐dependent predictive accuracy measures of Heagerty, Lumley, and Pepe (2000, Biometrics 56, 337–344) and Heagerty and Zheng (2005, Biometrics 61, 92–105). 相似文献
53.
54.
Irena F. Creed Adam T. Spargo Julia A. Jones Jim M. Buttle Mary B. Adams Fred D. Beall Eric G. Booth John L. Campbell Dave Clow Kelly Elder Mark B. Green Nancy B. Grimm Chelcy Miniat Patricia Ramlal Amartya Saha Stephen Sebestyen Dave Spittlehouse Shannon Sterling Mark W. Williams Rita Winkler Huaxia Yao 《Global Change Biology》2014,20(10):3191-3208
Climate warming is projected to affect forest water yields but the effects are expected to vary. We investigated how forest type and age affect water yield resilience to climate warming. To answer this question, we examined the variability in historical water yields at long‐term experimental catchments across Canada and the United States over 5‐year cool and warm periods. Using the theoretical framework of the Budyko curve, we calculated the effects of climate warming on the annual partitioning of precipitation (P) into evapotranspiration (ET) and water yield. Deviation (d) was defined as a catchment's change in actual ET divided by P [AET/P; evaporative index (EI)] coincident with a shift from a cool to a warm period – a positive d indicates an upward shift in EI and smaller than expected water yields, and a negative d indicates a downward shift in EI and larger than expected water yields. Elasticity was defined as the ratio of interannual variation in potential ET divided by P (PET/P; dryness index) to interannual variation in the EI – high elasticity indicates low d despite large range in drying index (i.e., resilient water yields), low elasticity indicates high d despite small range in drying index (i.e., nonresilient water yields). Although the data needed to fully evaluate ecosystems based on these metrics are limited, we were able to identify some characteristics of response among forest types. Alpine sites showed the greatest sensitivity to climate warming with any warming leading to increased water yields. Conifer forests included catchments with lowest elasticity and stable to larger water yields. Deciduous forests included catchments with intermediate elasticity and stable to smaller water yields. Mixed coniferous/deciduous forests included catchments with highest elasticity and stable water yields. Forest type appeared to influence the resilience of catchment water yields to climate warming, with conifer and deciduous catchments more susceptible to climate warming than the more diverse mixed forest catchments. 相似文献
55.
Data from a nationally representative study in Bangladesh (BDHS 1996-97) were analysed to identify significant predictors of use of periodic abstinence, in comparison with other modern contraceptive methods. The study found that women in Bangladesh mostly use modern methods during their peak reproductive years, after which some of them switch to periodic abstinence. These women tend to be more from educated and from higher socioeconomic backgrounds and with at least one living son. Another set of data from the Matlab DSS was analysed and the results were in the same direction. Focus group discussions found that women were using the periodic abstinence method incorrectly, abstaining for more days than is necessary. For Bangladeshi contraceptive users to reach a higher degree of use-effectiveness for period abstinence, more IEC materials need to be developed. 相似文献
56.
M Saha A Carriere M Cheerathodi X Zhang G Lavoie J Rush PP Roux BA Ballif 《The Biochemical journal》2012,447(1):159-166
The extent and duration of MAPK (mitogen-activated protein kinase) signalling govern a diversity of normal and aberrant cellular outcomes. Genetic and pharmacological disruption of the MAPK-activated kinase RSK (ribosomal S6 kinase) leads to elevated MAPK activity indicative of a RSK-dependent negative feedback loop. Using biochemical, pharmacological and quantitative MS approaches we show that RSK phosphorylates the Ras activator SOS1 (Son of Sevenless homologue 1) in cultured cells on two C-terminal residues, Ser1134 and Ser1161. Furthermore, we find that RSK-dependent SOS1 phosphorylation creates 14-3-3-binding sites. We show that mutating Ser1134 and Ser1161 disrupts 14-3-3 binding and modestly increases and extends MAPK activation. Together these data suggest that one mechanism whereby RSK negatively regulates MAPK activation is via site-specific SOS1 phosphorylation. 相似文献
57.
Chatterjee Mahasweta Saha Sharmistha Shom Sayanti Sinha Swagata Mukhopadhyay Kanchan 《Molecular biology reports》2021,48(4):3213-3222
Molecular Biology Reports - Primary symptoms of Attention Deficit Hyperactivity Disorder (ADHD) are age inappropriate inattention, hyperactivity and impulsivity. Caucasoid individuals showed... 相似文献
58.
Hemanta Chowdhury Asit Kumar Bera Subhashree Subhasmita Raut Ramesh Chandra Malick Himanshu Sekhar Swain Ajoy Saha Basanta Kumar Das 《化学与生物多样性》2023,20(3):e202200668
In aquaculture, diseases caused by the Aeromonads with high antibiotic resistance are among the most common and troublesome diseases. Application of herbs is emerging as a tool in controlling these diseases. Plant extracts besides disease control, favor various physiological activities in fish. In this study, essential oil of Cymbopogon flexuosus (Poaceae family) was studied in vitro for its antibacterial efficacy against two oxytetracycline (OTC) resistant and one sensitive strains of Aeromonas hydrophila. The oil was found rich (86.93 %) in oxygenated terpenoids containing 74.15 % of citral. The oil exhibited dose dependent growth inhibition of the bacteria. Mean MIC value of the oil against the sensitive strain was recorded as 2.0 mg mL−1 whereas MBC value was recorded as 4.0 mg mL−1. The oil was found effective against the OTC resistant isolates with the MIC and MBC values ranging from 2.67–3.33 and 4.0–6.67 mg mL−1, respectively. In silico molecular docking of the essential oil components against DNA gyrase-B, a vital macromolecule in bacterial cell, was carried out to computationally asses the efficacy of the oil against the bacteria. Some of the components of the essential oil strongly bonded with the enzyme to inhibit its efficacy. Binding energy of some components of the oil was comparable to that of the conventional antibiotic, OTC. The identified phytochemicals exhibited favorable physicochemical and pharmacokinetic properties and satisfied the rule of five (Ro5). 相似文献
59.
Rats, acclimatized on a control diet, were fed for 60 days with diets, supplemented with 10% fat of either marine Hilsa fish (Hilsa ilisa) or fresh-water Chital fish (Notopterus chitala). The percentage of eicosapentaenoic acid in chital oil diet was 0.57 times that of the hilsa oil diet, but the eicosapentaenoic to arachidonic acid ratio in the latter (4.08) was 3.2 times that of the former (1.27). Otherwise these two diets were comparable in respect to total saturated, monounsaturated and n-3 polyunsaturated fatty acid contents. Results showed that of the two only hilsa oil diet could significantly lower platelet aggregability and in vitro thromboxane production, through replacement of arachidonic acid in platelet phospholipid by eicosapentaenoic acid. The antithrombic criteria of the oil seems to be a combination of low arachidonic acid content and high eicosapentaenoic to arachidonic acid ratio. 相似文献
60.