全文获取类型
收费全文 | 293篇 |
免费 | 22篇 |
出版年
2022年 | 1篇 |
2021年 | 1篇 |
2020年 | 5篇 |
2019年 | 4篇 |
2018年 | 9篇 |
2017年 | 7篇 |
2016年 | 10篇 |
2015年 | 4篇 |
2014年 | 14篇 |
2013年 | 33篇 |
2012年 | 12篇 |
2011年 | 13篇 |
2010年 | 9篇 |
2009年 | 9篇 |
2008年 | 8篇 |
2007年 | 11篇 |
2006年 | 5篇 |
2005年 | 7篇 |
2004年 | 13篇 |
2003年 | 8篇 |
2002年 | 18篇 |
2001年 | 5篇 |
2000年 | 7篇 |
1999年 | 10篇 |
1998年 | 7篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 5篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 7篇 |
1991年 | 7篇 |
1990年 | 8篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1981年 | 2篇 |
1979年 | 2篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 2篇 |
1969年 | 2篇 |
1968年 | 3篇 |
1966年 | 2篇 |
1963年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有315条查询结果,搜索用时 31 毫秒
31.
Psychodid sand flies are blood-sucking fly vectors of several parasitic diseases. The oldest definitive record of this group is from the Lower Cretaceous amber of Lebanon (circa-135 to -125 My), but the high diversity within this group supports the idea that the psychodoids originated much earlier in history. The palaeontology demonstrates that the Lower Creataceous representatives of the different subfamilies of Psychodidae had similar morphology and were blood-feeders, which supports Hennig's hypothesis on the ground plan structure of this family. Historical relationship between sand flies and diseases is unclear up to the present time, but this relationship could be as old as the origin of psychodoids because of the blood-feeding life mode. 相似文献
32.
Khoshnan A Tindell C Laux I Bae D Bennett B Nel AE 《Journal of immunology (Baltimore, Md. : 1950)》2000,165(4):1743-1754
We explored the role of the NF-kappa B pathway in the survival of primary human CD4+ T lymphocytes during CD28 costimulation. Transduction of proliferating CD4+ T cells with a tetracycline-regulated retrovirus encoding for a dominant-interfering, degradation-resistant I-kappaBalpha (inhibitor of kappa B alpha factor) mutant induced apoptosis. Using DNA arrays, we show that Bcl-xL features as a prominent anti-apoptotic member among a number of early CD28-inducible genes. A 1.2-kb segment of the proximal Bcl-xL promoter, linked to a luciferase reporter, responded to CD3/CD28 stimulation in Jurkat cells. Mutation of an NF-kappa B site around -840 decreased, while ectopic expression of I-kappa B kinase-beta (IKK beta) enhanced reporter gene activity. Na+-salicylate and cyclopentenone PGs, direct inhibitors of IKK beta, interfered in the activation of the Bcl-xL promoter and induced apoptosis in CD28-costimulated CD4+ T cells. Moreover, salicylate blocked nuclear localization of NF-kappa B factors that bind to the NF-kappa B binding site in the Bcl-xL promoter, as well as the expression of Bcl-xL protein. HuT-78, a lymphoblastoid T cell line with constitutive NF-kappa B activity, contained elevated levels of Bcl-xL protein and, similar to proliferating CD4+ T cells, was resistant to apoptotic stimuli such as anti-Fas and TNF-alpha. In contrast, the same stimuli readily induced apoptosis in a Jurkat T cell clone with no detectable Bcl-xL expression. Jurkat BMS2 cells also differed from HuT-78 in collapse of mitochondrial membrane potential and superoxide generation in the mitochondrium. Taken together, these data demonstrate that CD3/CD28-induced activation of IKK beta and expression of Bcl-xL promote the survival of primary human CD4+ T lymphocytes. 相似文献
33.
Mongoliaeshna sinica gen. et sp. n., third record of the Mesozoic aeshnopteran family Progobiaeshnidae is described from the Lower Cretaceous of Yixian Formation in Liutiaogou (Ningcheng County, Inner Mongolia, China). 相似文献
34.
Jongbloet PH Groenewoud HM Huber S Fieder M Roeleveld N 《Human biology; an international record of research》2007,79(5):479-490
To determine the associations of fecundity and childlessness with month of conception and to find a causal mechanism for these associations, we reanalyzed some of our previous data according to the predictions of the seasonal optimal ripening oocyte (SOptRO) and seasonal preovulatory over-ripeness ovopathy (SPrOO) hypotheses. Prime and minor SOptRO months as well as high-risk, no-risk, and very high risk SPrOO months were defined on the basis of a priori knowledge of the existence of ovulatory and anovulatory seasons in mammals and of the general birth distribution in Europe. The month of birth was assessed among 899 mothers with three or more children and 388 childless women extracted from a 1% sample of the Austrian population. The women with three or more children were born in excess during the prime and less often during the minor SOptRO months (chi2 = 2.81; p = 0.045; relative risk = 1.16; 95% CI = 1.01-1.33). This is in line with the SOptRO predictions. The childless women were more frequently born during the high-risk SPrOO months compared to the no-risk months but less often during the very high risk months. The linear trend (chi2 = 8.43; p = 0.009) is in line with the SPrOO predictions. We suggest that fecundity and childlessness are dependent on the gradient of oocyte maturation reflected by mother's month of birth, which may modulate future constitution. 相似文献
35.
H. J. T. Hoving M. R. Lipinski M. A. C. Roeleveld M. D. Durholtz 《Reviews in Fish Biology and Fisheries》2007,17(2-3):259-270
Lycoteuthis lorigera is an oceanic squid that is abundant in the Benguela system. Little is known about the biology of this squid except that
it is eaten in large numbers by numerous oceanic predators and that males grow to larger size than females, which is unique
for oegopsid squid. The aim of this study was to better understand the biology of this species by investigating its age and
growth, as well as its mating system. Toward this end, the age of 110 individuals, ranging from 35 to 110 mm, was estimated
by counting statolith growth increments. Estimates of age ranged from 131 to 315 days and varied with mantle length. No significant
differences were found in the size of males and females of equivalent ages. The relationship between ML and age for both sexes
was best described by an exponential growth curve, probably because no early life stages were aged in this study. Only one
mature male (ML 160 mm) was aged, and preliminary estimates suggest it was 386 days old. Instantaneous growth rates were low
(0.54% ML/day and 1.4% BM/day) but consistent with enoploteuthid growth rates. When the growth rate of L. lorigera was corrected for temperature encountered during the animal’s life, the growth rate was fast (0.47% BM/degree-days) and consistent
with the hypothesis that small cephalopods grow fast and that large cephalopods grow older, rather than fast. Mature females
were often mated and had spermatangia in a seminal receptacle on the dorsal pouch behind the nuchal cartilage. Males probably
transfer spermatangia to the females using their long second and/or third arm pair since the paired terminal organs open far
from the mantle opening.
M. A. C. Roeleveld deceased. 相似文献
36.
Jeanne L. Nel Dirk J. Roux Gillian Maree Cornelius J. Kleynhans Juanita Moolman Belinda Reyers Mathieu Rouget Richard M. Cowling 《Diversity & distributions》2007,13(3):341-352
This paper establishes a framework within which a rapid and pragmatic assessment of river ecosystems can be undertaken at a broad, subcontinental scale, highlighting some implications for achieving conservation of river biodiversity in water‐limited countries. The status of river ecosystems associated with main rivers in South Africa was assessed based on the extent to which each ecosystem had been altered from its natural condition. This requires consistent data on river integrity for the entire country, which was only available for main rivers; tributaries were thus excluded from the analyses. The state of main river ecosystems in South Africa is dire: 84% of the ecosystems are threatened, with a disturbing 54% critically endangered, 18% endangered, and 12% vulnerable. Protection levels were measured as the proportion of conservation target achieved within protected areas, where the conservation target was set as 20% of the total length of each river ecosystem. Sixteen of the 112 main river ecosystems are moderately to well represented within protected areas; the majority of the ecosystems have very low levels of representation, or are not represented at all within protected areas. Only 50% of rivers within protected areas are intact, but this is a higher proportion compared to rivers outside (28%), providing some of the first quantitative data on the positive role protected areas can play in conserving river ecosystems. This is also the first assessment of river ecosystems in South Africa to apply a similar approach to parallel assessments of terrestrial, marine, and estuarine ecosystems, and it revealed that main river ecosystems are in a critical state, far worse than terrestrial ecosystems. Ecosystem status is likely to differ with the inclusion of tributaries, since options may well exist for conserving critically endangered ecosystems in intact tributaries, which are generally less regulated than main rivers. This study highlights the importance of healthy tributaries for achieving river conservation targets, and the need for managing main rivers as conduits across the landscape to support ecological processes that depend on connectivity. We also highlight the need for a paradigm shift in the way protected areas are designated, as well as the need for integrated river basin management plans to include explicit conservation visions, targets, and strategies to ensure the conservation of freshwater ecosystems and the services they provide. 相似文献
37.
Gong KW Zhao W Li N Barajas B Kleinman M Sioutas C Horvath S Lusis AJ Nel A Araujo JA 《Genome biology》2007,8(7):R149
Background
Ambient air pollution is associated with increased cardiovascular morbidity and mortality. We have found that exposure to ambient ultrafine particulate matter, highly enriched in redox cycling organic chemicals, promotes atherosclerosis in mice. We hypothesize that these pro-oxidative chemicals could synergize with oxidized lipid components generated in low-density lipoprotein particles to enhance vascular inflammation and atherosclerosis. 相似文献38.
39.
Background
Since use of non-steroidal anti-inflammatory drugs (NSAIDs) during pregnancy is common, small increases in the risk of birth defects may have significant implications for public health. Results of human studies on the teratogenic risks of NSAIDs are inconsistent. Therefore, we evaluated the risk of selected birth defects after prenatal exposure to prescribed and over-the-counter NSAIDs.Methods and Findings
We used data on 69,929 women enrolled in the Norwegian Mother and Child Cohort Study between 1999 and 2006. Data on NSAID exposure were available from a self-administered questionnaire completed around gestational week 17. Information on pregnancy outcome was obtained from the Medical Birth Registry of Norway. Only birth defects suspected to be associated with NSAID exposure based upon proposed teratogenic mechanisms and previous studies were included in the multivariable logistic regression analyses. A total of 3,023 women used NSAIDs in gestational weeks 0–12 and 64,074 women did not report NSAID use in early pregnancy. No associations were observed between overall exposure to NSAIDs during pregnancy and the selected birth defects separately or as a group (adjusted odds ratio 0.7, 95% confidence interval 0.4–1.1). Associations between maternal use of specific types of NSAIDs and the selected birth defects were not found either, although an increased risk was seen for septal defects and exposure to multiple NSAIDs based on small numbers (2 exposed cases; crude odds ratio 3.9, 95% confidence interval 0.9–15.7).Conclusions
Exposure to NSAIDs during the first 12 weeks of gestation does not seem to be associated with an increased risk of the selected birth defects. However, due to the small numbers of NSAID-exposed infants for the individual birth defect categories, increases in the risks of specific birth defects could not be excluded. 相似文献40.
Global conservation priorities for marine turtles 总被引:2,自引:0,他引:2
Wallace BP DiMatteo AD Bolten AB Chaloupka MY Hutchinson BJ Abreu-Grobois FA Mortimer JA Seminoff JA Amorocho D Bjorndal KA Bourjea J Bowen BW Briseño Dueñas R Casale P Choudhury BC Costa A Dutton PH Fallabrino A Finkbeiner EM Girard A Girondot M Hamann M Hurley BJ López-Mendilaharsu M Marcovaldi MA Musick JA Nel R Pilcher NJ Troëng S Witherington B Mast RB 《PloS one》2011,6(9):e24510
Where conservation resources are limited and conservation targets are diverse, robust yet flexible priority-setting frameworks are vital. Priority-setting is especially important for geographically widespread species with distinct populations subject to multiple threats that operate on different spatial and temporal scales. Marine turtles are widely distributed and exhibit intra-specific variations in population sizes and trends, as well as reproduction and morphology. However, current global extinction risk assessment frameworks do not assess conservation status of spatially and biologically distinct marine turtle Regional Management Units (RMUs), and thus do not capture variations in population trends, impacts of threats, or necessary conservation actions across individual populations. To address this issue, we developed a new assessment framework that allowed us to evaluate, compare and organize marine turtle RMUs according to status and threats criteria. Because conservation priorities can vary widely (i.e. from avoiding imminent extinction to maintaining long-term monitoring efforts) we developed a “conservation priorities portfolio” system using categories of paired risk and threats scores for all RMUs (n = 58). We performed these assessments and rankings globally, by species, by ocean basin, and by recognized geopolitical bodies to identify patterns in risk, threats, and data gaps at different scales. This process resulted in characterization of risk and threats to all marine turtle RMUs, including identification of the world''s 11 most endangered marine turtle RMUs based on highest risk and threats scores. This system also highlighted important gaps in available information that is crucial for accurate conservation assessments. Overall, this priority-setting framework can provide guidance for research and conservation priorities at multiple relevant scales, and should serve as a model for conservation status assessments and priority-setting for widespread, long-lived taxa. 相似文献