全文获取类型
收费全文 | 662篇 |
免费 | 62篇 |
专业分类
724篇 |
出版年
2023年 | 6篇 |
2022年 | 7篇 |
2021年 | 18篇 |
2020年 | 7篇 |
2019年 | 9篇 |
2018年 | 8篇 |
2017年 | 12篇 |
2016年 | 12篇 |
2015年 | 31篇 |
2014年 | 17篇 |
2013年 | 26篇 |
2012年 | 32篇 |
2011年 | 39篇 |
2010年 | 10篇 |
2009年 | 22篇 |
2008年 | 30篇 |
2007年 | 22篇 |
2006年 | 25篇 |
2005年 | 27篇 |
2004年 | 15篇 |
2003年 | 18篇 |
2002年 | 18篇 |
2001年 | 19篇 |
2000年 | 14篇 |
1999年 | 14篇 |
1998年 | 10篇 |
1997年 | 10篇 |
1996年 | 8篇 |
1995年 | 7篇 |
1993年 | 9篇 |
1992年 | 18篇 |
1991年 | 13篇 |
1990年 | 8篇 |
1989年 | 8篇 |
1988年 | 8篇 |
1987年 | 8篇 |
1986年 | 9篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 9篇 |
1979年 | 7篇 |
1977年 | 7篇 |
1974年 | 6篇 |
1973年 | 6篇 |
1971年 | 5篇 |
1970年 | 8篇 |
1967年 | 6篇 |
1966年 | 5篇 |
排序方式: 共有724条查询结果,搜索用时 0 毫秒
31.
D. Philip Whitfield Alan H. Fielding David Anderson Stuart Benn Robin Reid Ruth Tingay Ewan Weston 《Ibis》2024,166(1):146-155
Natal dispersal distance (NDD) is critical in understanding and defining populations and their conservation. It is defined as the linear distance between the natal location and first reproductive (‘effective NDD’) or potential reproductive (‘gross NDD’) location. It is a measure of gene flow and the functional connectivity across generations between individuals breeding in the same or different geographies. NDD is difficult to record in large raptors. GPS-satellite telemetry has facilitated its recording. Previous Scottish studies showed that gross and effective NDD were apparently equivalent, and an algorithm based on telemetric data could identify the territory settlement timing and location of birds originally tagged as nestlings. We analysed natal dispersal data from 39 Golden Eagles GPS-tagged in Scotland to estimate NDD. Raw median estimates were 29.8 km for males (n = 22) and 58.6 km for females (n = 17), 38.1 km averaged across sexes. Males had significantly shorter NDD, as theoretically predicted. Our NDD estimates were shorter but not grossly dissimilar to those from the USA, where sex differences in NDD had not been confirmed. Respective sample sizes may underly the latter contrast in confirmation. We also showed that in the absence of data from sexed birds, NDD estimates can be different. Natal dispersal duration was not related to NDD, suggesting that time to prospect a territory opportunity was not associated with the selected territory's distance from the natal site. The previous status of the subsequent settled territory (occupied or vacant) was also not related to NDD. We conclude that sex differences in NDD are important in application to population demography and conservation. Although we found no support for two other potential drivers of NDD (natal dispersal duration and previous territory status), identifying additional influences on NDD is in its infancy in large raptors and deserves more study. 相似文献
32.
Hayes CA Karlsson NG Struwe WB Lisacek F Rudd PM Packer NH Campbell MP 《Bioinformatics (Oxford, England)》2011,27(9):1343-1344
Glycosylation is one of the most important post-translational modifications of proteins, known to be involved in pathogen recognition, innate immune response and protection of epithelial membranes. However, when compared to the tools and databases available for the processing of high-throughput proteomic data, the glycomic domain is severely lacking. While tools to assist the analysis of mass spectrometry (MS) and HPLC are continuously improving, there are few resources available to support liquid chromatography (LC)-MS/MS techniques for glycan structure profiling. Here, we present a platform for presenting oligosaccharide structures and fragment data characterized by LC-MS/MS strategies. The database is annotated with high-quality datasets and is designed to extend and reinforce those standards and ontologies developed by existing glycomics databases. AVAILABILITY: http://www.unicarb-db.org 相似文献
33.
A 50 per cent dextrose in water solution, containing 1 mg. of hydrocortisone per 100 ml., was used successfully in 70 patients for intravenous nutritional maintenance and repletion. There were no adverse systemic effects during or following 216 infusions. The only undesirable local reaction was the rare occurrence of pain in the arm when the concentrated solutions were given too rapidly. Glycosuria was minimal if the infusion rate did not exceed 0.85 gm. of glucose per kilogram of body weight per hour, particularly if 50 units of insulin were added to each 550 ml. bottle of 50 per cent dextrose. In patients without significantly elevated serum potassium content, 30 mEq. of potassium chloride, acetate or phosphate was added to each bottle to prevent hypokalemia.Preliminary observations suggest that this new solution may be given safely intravenously, without need for cutdowns or plastic catheters, if the needle is carefully inserted and well immobilized in the arm vein and the duration of the infusion is not too prolonged. Further studies on the effect of such high caloric supplementation plus protein hydrolysates in parenteral nutritional repletion and maintenance are indicated. 相似文献
34.
35.
Latif Sajid Gurusinghe Saliya Weston Paul A. Quinn Jane C. Piltz John W Weston Leslie A 《Plant and Soil》2020,447(1-2):199-218
Plant and Soil - Weed suppressive potential of annual pasture legumes has been previously described, the mechanism of interference with weeds has not been clearly elucidated. We, therefore, aimed... 相似文献
36.
Previous studies have identified unique cell surface antigens which are associated with the specific binding of lymphocytes to high endothelial venules (HEV). Evidence is presented in this paper which demonstrates that uptake of the fluorescent dye calcein by lymphocytes represents an additional marker for the lymph node homing subpopulation of lymphocytes. Calcein exhibits a characteristic ability to label lymphocytes differentially into two distinct populations, based on fluorescence intensity, that does not occur with three other structurally related, fluorescein-based dyes. In vivo lymphocyte migration studies revealed that cells displaying the "dull" fluorescence phenotype, although entering all lymphoid organs examined, preferentially homed to the lymph nodes, particularly the popliteal lymph node (PLN). By contrast, lymphocytes displaying the "bright" phenotype were essentially excluded from entering lymphoid organs, where entry is HEV dependent, but were observed entering spleen, where entry is HEV independent. Furthermore, a high proportion (76.5%) of lymphocytes displaying the dull fluorescence phenotype expressed the PLN homing receptor MEL-14. Based on these observations it is suggested that calcein uptake may be a marker for general membrane properties, such as fluidity and plasticity, essential for the passage of lymphocytes through HEV. 相似文献
37.
Laura X. L. Tan Katherine L. Buchanan Grainne S. Maguire Michael A. Weston 《Journal of avian biology》2015,46(5):482-488
Predator exclosures (‘nest cages’) around nests are increasingly used to enhance hatching success of declining ground‐nesting birds. However, such exclosures are contentious and have been suggested to have detrimental effects on the species which they aim to protect. This study examines whether exclosures increase physiological stress of incubating birds, a hitherto unrecognised and untested potential drawback of exclosures. Red‐capped plover Charadrius ruficapillus hatching success was radically altered and significantly higher for nests with exclosures (96.2%) compared with those without (6.8%). Chronic physiological stress in parents (as measured by the heterophil/lymphocyte [H/L] ratio in blood) did not vary between nests with and without exclosures, or between the sexes. However the absence of vegetative cover at the nest site was associated with a 62.7% elevation in H/L ratio, indicating that incubating birds which place their nests in the open are subject to increased levels of chronic stress. The results from this study demonstrate the fundamental importance of predation for the nesting success of this species and confirm that chronic stress levels are not a detrimental side effect of exclosure use. 相似文献
38.
Mast AR Milton EF Jones EH Barker RM Barker WR Weston PH 《American journal of botany》2012,99(3):472-487
? Premise of the study: A past study based on morphological data alone showed that the means by which plants of the Australian genus Hakea reduce florivory is related to the evolution of bird pollination. For example, bird pollination was shown to have arisen only in insect-pollinated lineages that already produced greater amounts of floral cyanide, a feature that reduces florivory. We examine a central conclusion of that study, and a common assumption in the literature, that bird pollination arose in insect-pollinated lineages, rather than the reverse. ? Methods: We combined morphological and DNA data to infer the phylogeny and age of the Australian genus Hakea, using 9.2 kilobases of plastid and nuclear DNA and 46 morphological characters from a taxonomically even sampling of 55 of the 149 species. ? Key results: Hakea is rooted confidently in a position that has not been suggested before. The phylogeny implies that bird pollination is primitive in Hakea and that multiple shifts to insect pollination have occurred. The unexpectedly young age of Hakea (a crown age of ca. 10 Ma) makes it coincident with its primary bird pollinators (honeyeaters) throughout its history. ? Conclusions: Our study demonstrates that Hakea is an exception to the more commonly described shift from insect to bird pollination. However, we note that only one previous phylogenetic study involved Australian plants and their honeyeater pollinators and that our finding might prove to be more common on that continent. 相似文献
39.
Effects of fire and harvesting on nitrogen transformations and ionic mobility in soils of Eucalyptus regnans forests of south-eastern Australia 总被引:1,自引:0,他引:1
Summary Effects of fire and forest harvesting on inorganic-N in the soil, on net N-mineralization, and on the leaching of NO
inf3
sup-
-N and metallic cations were measured in forests of Eucalyptus regnans following a severe wildfire in 1983. E. regnans regenerates profusely by seed after fire, and this study compared unburnt forest with forests burnt at varying intensities (surface fire and crown fire), and with logged and burnt forest (slash fire). Total inorganic-N in soil (0–5 cm) increased with increasing fire intensity to a maximum of 158 g g-1 in the slash fire plot (compared with 51 g g-1 in the unburnt forest) over the first 205 days after fire. Total inorganic-N returned to a concentration equal to that in the unburnt forest after 485 days at the slash fire plot, and after only 205 days at the surface fire plot. Studies of net mineralization in situ and of NO
inf3
sup-
-N in soil solution support the hypothesis that inorganic-N was immobilized in all of the burnt forests; microbial immobilization after fire is identified as a key process in N-conservation, limiting the substrate available for nitrification and thereby limiting the loss of N from the system by leaching. The concentrations of NO
inf3
sup-
-N and metallic cations in soil solution increased with increasing fire intensity. For the first 318 days after the fire, [NO
inf3
sup-
-N] in soil solution at 10 cm averaged 0.6 g ml-1 in the unburnt forest, 9.7 mg l-1 in the surface fire plot, 26 mg l-1 in the crown fire plot, and 70 mg l-1 in the slash fire plot. The concentration of metallic cations in soil solution was significantly correlated with [NO
inf3
sup-
-N], the observed order of mobility being Ca2+>Mg2+>K+>Na+. Processes which limit the production and persistence of NO
inf3
sup-
-N in soil solution following disturbance will significantly reduce nutrient losses or redistribution. 相似文献
40.
van Eeden FJ Palacios IM Petronczki M Weston MJ St Johnston D 《The Journal of cell biology》2001,154(3):511-523
The localization of Oskar at the posterior pole of the Drosophila oocyte induces the assembly of the pole plasm and therefore defines where the abdomen and germ cells form in the embryo. This localization is achieved by the targeting of oskar mRNA to the posterior and the localized activation of its translation. oskar mRNA seems likely to be actively transported along microtubules, since its localization requires both an intact microtubule cytoskeleton and the plus end-directed motor kinesin I, but nothing is known about how the RNA is coupled to the motor. Here, we describe barentsz, a novel gene required for the localization of oskar mRNA. In contrast to all other mutations that disrupt this process, barentsz-null mutants completely block the posterior localization of oskar mRNA without affecting bicoid and gurken mRNA localization, the organization of the microtubules, or subsequent steps in pole plasm assembly. Surprisingly, most mutant embryos still form an abdomen, indicating that oskar mRNA localization is partially redundant with the translational control. Barentsz protein colocalizes to the posterior with oskar mRNA, and this localization is oskar mRNA dependent. Thus, Barentsz is essential for the posterior localization of oskar mRNA and behaves as a specific component of the oskar RNA transport complex. 相似文献