全文获取类型
收费全文 | 1114篇 |
免费 | 83篇 |
专业分类
1197篇 |
出版年
2023年 | 6篇 |
2022年 | 6篇 |
2021年 | 11篇 |
2019年 | 18篇 |
2018年 | 22篇 |
2017年 | 29篇 |
2016年 | 27篇 |
2015年 | 42篇 |
2014年 | 31篇 |
2013年 | 85篇 |
2012年 | 74篇 |
2011年 | 81篇 |
2010年 | 61篇 |
2009年 | 48篇 |
2008年 | 48篇 |
2007年 | 44篇 |
2006年 | 51篇 |
2005年 | 37篇 |
2004年 | 57篇 |
2003年 | 46篇 |
2002年 | 44篇 |
2001年 | 15篇 |
2000年 | 15篇 |
1999年 | 15篇 |
1998年 | 10篇 |
1997年 | 15篇 |
1996年 | 9篇 |
1995年 | 11篇 |
1994年 | 11篇 |
1993年 | 10篇 |
1992年 | 7篇 |
1990年 | 10篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 6篇 |
1983年 | 13篇 |
1982年 | 11篇 |
1981年 | 9篇 |
1980年 | 10篇 |
1975年 | 4篇 |
1971年 | 6篇 |
1955年 | 8篇 |
1954年 | 27篇 |
1953年 | 8篇 |
1952年 | 9篇 |
1951年 | 9篇 |
1950年 | 7篇 |
1949年 | 7篇 |
排序方式: 共有1197条查询结果,搜索用时 0 毫秒
41.
Personality and fitness consequences of flight initiation distance and mating behavior in subdominant male reindeer (Rangifer tarandus) 下载免费PDF全文
Justin S. Strong Robert B. Weladji Øystein Holand Knut H. Røed Mauri Nieminen 《Ethology : formerly Zeitschrift fur Tierpsychologie》2017,123(6-7):484-492
Animal personality has been studied extensively in recent years, yet multidimensionality in tendencies of risk‐related behavior, and the role of such consistency from a mating tactics perspective, is yet to be investigated. We used a semi‐domesticated herd of reindeer (Rangifer tarandus) to examine individual subdominant male propensity to risk mating attempts on guarded females, as well as flight initiation distance (FID), within the personality paradigm to elucidate potential fitness consequences of consistency from an adaptive perspective. Data were collected at the Kutuharju Reindeer Research Station in Kaamanen, Finland, where measures of personality were generated using field observation data based on the relative frequency of dominant male–subdominant male agonistic interactions over 4 years and subdominant males' FID measured over 1 year. Individual propensity for transient mating attempts was not significantly repeatable and did not significantly predict reproductive success or somatic cost during the mating season. Individuals varied consistently in FID, and although repeatable, FID was not related to reproductive success or somatic cost. Proximate state‐dependent or social mechanisms may be driving decision‐making with respect to mating effort, whereas consistent between‐individual differences in FID may be maintained by mechanisms unrelated to life‐history trade‐offs involving productivity. 相似文献
42.
Two strains of viral hemorrhagic septicemia virus (VHSV) with known different virulence characteristics in vivo were studied (by a time course approach) for their abilities to infect and translocate across a primary culture of gill epithelial cells (GEC) of rainbow trout (RBT; Oncorhynchus mykiss). The strains included one low-virulence marine VHSV (ma-VHSV) strain, ma-1p8, and a highly pathogenic freshwater VHSV (fw-VHSV) strain, fw-DK-3592B. Infectivities toward trout head kidney macrophages were also studied (by a time course method), and differences in in vivo virulence were reconfirmed, the aim being to determine any correlation between in vivo virulence and in vitro infectivity. The in vitro studies showed that the fw-VHSV isolate infected and caused a cytotoxic effect in monolayers of GEC (demonstrating virulence) at an early time point (2 h postinoculation) and that the same virus strain had translocated over a confluent, polarized GEC layer by 2 h postinoculation. The marine isolate did not infect monolayers of GEC, and delayed translocation across polarized GEC was seen by 48 h postinoculation. Primary cultures of head kidney macrophages were also infected with fw-VHSV, with a maximum of 9.5% virus-positive cells by 3 days postinfection, while for the ma-VHSV strain, only 0.5% of the macrophages were positive after 3 days of culture. In vivo studies showed that the fw-VHSV strain was highly virulent for RBT fry and caused high mortality, with classical features of viral hemorrhagic septicemia. The ma-VHSV showed a very low level of virulence (only one pool of samples from the dead fish was VHSV positive). This study has shown that the differences in virulence between marine and freshwater strains of VHSV following the in vivo infection of RBT correlate with in vitro abilities to infect primary cultures of GEC and head kidney macrophages of the same species. 相似文献
43.
Summary Cirripedes are fascinating models for studying both functional constraints and diversity in larval development. Adult cirripedes display an amazing variation in morphology from sessile suspension feeders that still retain many crustacean characters to parasites that have lost virtually all arthropod traits. In contrast, cirripede larval development follows a common scheme with pelagic larvae comprising a series of nauplii followed by a cyprid. Variations are mostly concerned with whether or not the nauplii are feeding and the degree of abbreviation of development, culminating in species where the larvae hatch as cyprids. The cypris larvae are very similar among the ingroups of the Cirripedia, but interesting variations occur in structures used for substrate location and attachment. The cyprid is specialized to both swim through the water and actively explore the substratum by walking on the antennules and using an array of sensory organs in search for a suitable site to attach. This unique morphology and behavior of the cyprid have enabled the Cirripedia to colonize widely different habitats ranging from hard rock to soft animal tissue. Yet, the cyprid can metamorphose into juveniles as different as a setose feeding barnacle and the vermiform stages of the parasitic forms. This emphasizes the importance of the cyprid as one of the key features for the evolutionary success of the Cirripedia. 相似文献
44.
Using museum data of adult specimens whose sex, age, and locality are known, we studied temporal and geographical body size trends among the otter, Lutra lutra, in Norway. We found that body size of the otters increased during the last quarter of the twentieth century, and suggest that this trend is related to increased food availability from fish farming and possibly also to energy saving due to elevated sea temperatures. Birth year and death year explained 38.8 and 43.5%, respectively, of the variation in body size. Body size of otters was positively related to latitude, thus conforming to Bergmann’s rule. 相似文献
45.
Vidar Selås Geir A. Sonerud Olav Hjeljord Lars Erik Gangsei Helge B. Pedersen Erik Framstad Tor Kristian Spidsø Øystein Wiig 《European Journal of Wildlife Research》2011,57(3):523-535
The plant stress hypothesis states that plant stress factors other than herbivory improve herbivore performance due to changes
in the content of nutritive or defensive compounds in the plants. In Norway, the bilberry (Vaccinium myrtillus) is important forage for the bank vole (Myodes glareolus) in winter and for the moose (Alces alces) in summer and autumn. The observed peaks in bank vole numbers after years with high production of bilberries are suggested
to be caused by increased winter survival of bank voles due to improved forage quality. High production of bilberries should
also lead to higher recruitment rates in moose in the following year. We predict, however, that there is an increasing tendency
for a 1-year delay of moose indices relative to vole indices with decreasing summer temperatures, because low temperatures
prolong the period needed by plants to recover in the vole peak year, and thus positively affect moose reproduction also in
the succeeding year. In eight out of nine counties in south-eastern Norway, there was a positive relationship between the
number of calves observed per female moose during hunting and a bilberry seed production index or an autumn bank vole population
index. When dividing the study area into regions, there was a negative relationship between a moose-vole time-lag index and
the mean summer temperature of the region. These patterns suggest that annual fluctuations in the production of bilberries
affect forage quality, but that the effect on moose reproduction also depends on summer temperatures. 相似文献
46.
Øivind Løvstad 《Hydrobiologia》1983,107(3):221-230
Laboratory batch experiments with dilute phytoplankton communities were carried out to determine growth-limiting nutrients and the degree of growth limitation for Asterionella formosa, Hass., Tabellaria fenestrata (Lyngb.) Kütz. and red species of Oscillatoria under specific temperature and light conditions. Water samples from five Norwegian lakes with average epilimnetic total phosphorus concentrations ranging from 5 to 30 µg P per 1 were investigated. Both enrichment and transplant experiments were carried out. In samples from the most oligotrophic lakes (Lake Randsfjorden and Lake Tyrifjorden) phosphorus was found to be the growth-limiting nutrient. In samples from Lake Mjøsa silicate was also growth-limiting for the diatoms, while nitrogen could be limiting for both asterionella and Oscillatoria from Lake Steinsfjorden. Phosphorus was often the only limiting nutrient determined for Oscillatoria in Lake Gjersjøen (the most eutrophic of the lakes). In samples from this lake, however, Asterionella was also growth-limited directly or indirectly as a result of high (pH > 9). This was also found for Asterionella and Tabellaria from lake Mjøsa by means of transplant experiments. Oscillatoria from Lake Gjersjøen could not grow in filtered water from Lake Mjøsa but obtained maximum growth rate after addition of phosphate and chelated iron in combination. 相似文献
47.
48.
49.
David Ryberg Toril Tefre Steinar Øvrebø Vidar Skaug Lodve Stangeland Anne Naalsund Rita Bæra Anne-Lise Børresen Aage Haugen 《Human genetics》1990,86(1):40-44
Summary We have examined DNA restriction fragment length polymorphisms (RFLP) of the Ha-ras-1 gene in DNA from 118 lung cancer patients and 123 unaffected controls. When DNA samples were digested with MspI/ HpaII restriction endonucleases. Southern blot analysis demonstrated 4 common, 4 intermediate and 7 different rare alleles in the combined population after hybridization to the pGDa1 probe. Six of the rare alleles were unique for the lung cancer group and 1 rare allele for the control group. The frequency of rare alleles in lung cancer patients (10/236) was significantly different (P<0.01) from the control group (1/246). The lung cancer group also had a significantly lower frequency of the common 2.57 kb fragment than the controls (P<0.02). The results thus indicate that Ha-ras genotyping may be of value in lung cancer risk assessment. 相似文献
50.
Mouse Models for Assessing the Protective Efficacy of Lactobacillus gasseri SBT2055 against Helicobacter suis Infection Associated with the Development of Gastric Mucosa‐Associated Lymphoid Tissue Lymphoma 下载免费PDF全文