全文获取类型
收费全文 | 102632篇 |
免费 | 20960篇 |
国内免费 | 7490篇 |
出版年
2024年 | 234篇 |
2023年 | 1118篇 |
2022年 | 2528篇 |
2021年 | 4373篇 |
2020年 | 4639篇 |
2019年 | 6737篇 |
2018年 | 6534篇 |
2017年 | 6221篇 |
2016年 | 7197篇 |
2015年 | 8529篇 |
2014年 | 9281篇 |
2013年 | 9863篇 |
2012年 | 8922篇 |
2011年 | 7951篇 |
2010年 | 6961篇 |
2009年 | 5369篇 |
2008年 | 4944篇 |
2007年 | 4133篇 |
2006年 | 3582篇 |
2005年 | 3154篇 |
2004年 | 2677篇 |
2003年 | 2595篇 |
2002年 | 2184篇 |
2001年 | 1637篇 |
2000年 | 1474篇 |
1999年 | 1262篇 |
1998年 | 733篇 |
1997年 | 642篇 |
1996年 | 628篇 |
1995年 | 534篇 |
1994年 | 554篇 |
1993年 | 407篇 |
1992年 | 526篇 |
1991年 | 395篇 |
1990年 | 351篇 |
1989年 | 315篇 |
1988年 | 255篇 |
1987年 | 230篇 |
1986年 | 208篇 |
1985年 | 192篇 |
1984年 | 135篇 |
1983年 | 140篇 |
1982年 | 105篇 |
1981年 | 53篇 |
1980年 | 53篇 |
1979年 | 68篇 |
1976年 | 48篇 |
1974年 | 54篇 |
1973年 | 47篇 |
1972年 | 54篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
Jan Batelka Jakub Prokop Hans Pohl Ming Bai Weiwei Zhang Rolf G. Beutel 《Systematic Entomology》2019,44(2):396-407
Extremely miniaturized longipedes insects (body length c. 0.3 mm) embedded in two pieces of Cretaceous amber from Myanmar are described and interpreted. Using inverted fluorescence and light microscopy for detailed analysis of microstructures, the inclusions were identified as primary larvae of the beetle family Ripiphoridae, subfamily Ripidiinae. While the structure of thoracic and abdominal segments including appendages corresponds well with the groundplan known in recent members of Ripidiinae, a curved prosternal ridge with prominent spines (each c. 5 μm), the reduced condition of stemmata and antennae and the lack of sharp mandibles are unique features within the entire family, apparently apomorphies of the longipedes larvae. A sinuate prosternal edge with a dense row of spines (prosternoctenidium) might be homologous with ‘head ctenidia’ in some previously described miniaturized conicocephalate larvae, but further investigation is needed. The morphological differences between the head of longipedes larvae and extant Ripidiinae are interpreted as adaptations to different groups of hosts and life strategies. Palaeoethology of the longipedes larvae is briefly discussed. In addition, the systematic placement of conicocephalate larvae from Canadian, Myanmar and Russian Cretaceous ambers, already interpreted by various authors as primary instars within Coleopterida (assigned to either Strepsiptera or to the coleopteran Tenebrionoidea: Ripiphoridae), is discussed. 相似文献
93.
94.
T. Phanitchat C. Apiwathnasorn S. Sungvornyothin Y. Samung S. Dujardin J.‐P. Dujardin S. Sumruayphol 《Medical and veterinary entomology》2019,33(4):476-484
Wing geometry helps to identify mosquito species, even cryptic ones. On the other hand, temperature has a well‐known effect on insect metric properties. Can such effects blur the taxonomic signal embedded in the wing? Two strains of Aedes albopictus (laboratory and field strain) were examined under three different rearing temperatures (26, 30 and 33 °C) using landmark‐ and outline‐based morphometric approaches. The wings of each experimental line were compared with Aedes aegypti. Both approaches indicated similar associations between wing size and temperature. For the laboratory strain, the wing size significantly decreased as the temperature increased. For the field strain, the largest wings were observed at the intermediate temperature. The two morphometric approaches describing shape showed different sensibilities to temperature. For both strains and sexes, the landmark‐based approach disclosed significant wing shape changes with temperature changes. The outline‐based approach showed lesser effects, detecting significant changes only in laboratory females and in field males. Despite the size and shape changes induced by temperature, the two strains of Ae. albopictus were always distinguished from Ae. aegypti. The present study confirms the lability of size. However, it also suggests that, despite environmentally‐induced variation, the architecture of the wing still provides a strong taxonomic signal. 相似文献
95.
Lauren Petrullo Matthew J. Jorgensen Noah Snyder‐Mackler Amy Lu 《American journal of primatology》2019,81(10-11)
The human milk microbiome is vertically transmitted to offspring during the postnatal period and has emerged as a critical driver of infant immune and metabolic development. Despite this importance in humans, the milk microbiome of nonhuman primates remains largely unexplored. This dearth of comparative work precludes our ability to understand how species‐specific differences in the milk microbiome may differentially drive maternal effects and limits how translational models can be used to understand the role of vertically transmitted milk microbes in human development. Here, we present the first culture‐independent data on the milk microbiome of a nonhuman primate. We collected milk and matched fecal microbiome samples at early and late lactation from a cohort of captive lactating vervet monkeys (N = 15). We found that, similar to humans, the vervet monkey milk microbiome comprises a shared community of taxa that are universally present across individuals. However, unlike in humans, this shared community is dominated by the genera Lactobacillus, Bacteroides, and Prevotella. We also found that, in contrast to previous culture‐dependent studies in humans, the vervet milk microbiome exhibits greater alpha‐diversity than the gut microbiome across lactation. Finally, we did not find support for the translocation of microbes from the gut to the mammary gland within females (i.e., “entero‐mammary pathway”). Taken together, our results show that the vervet monkey milk microbiome is taxonomically diverse, distinct from the gut microbiome, and largely stable. These findings demonstrate that the milk microbiome is a unique substrate that may selectively favor the establishment and persistence of particular microbes across lactation and highlights the need for future experimental studies on the origin of microbes in milk. 相似文献
96.
97.
Fragile X syndrome is a developmental disorder that affects sensory systems. A null mutation of the Fragile X Mental Retardation protein 1 (Fmr1) gene in mice has varied effects on developmental plasticity in different sensory systems, including normal barrel cortical plasticity, altered ocular dominance plasticity and grossly impaired auditory frequency map plasticity. The mutation also has different effects on long-term synaptic plasticity in somatosensory and visual cortical neurons, providing insights on how it may differentially affect the sensory systems. Here we present evidence that long-term potentiation (LTP) is impaired in the developing auditory cortex of the Fmr1 knockout (KO) mice. This impairment of synaptic plasticity is consistent with impaired frequency map plasticity in the Fmr1 KO mouse. Together, these results suggest a potential role of LTP in sensory map plasticity during early sensory development. 相似文献
98.
99.
Philippe Fernandez‐Fournier Samantha Straus Ruth Sharpe Leticia Avils 《Ecological Entomology》2019,44(2):157-162
1. Manipulation of host behaviour by parasitoids has long captured the imagination of ecologists. Parasitoid wasps in the Polysphincta group of genera develop as external parasitoids of spiders. 2. In the present study, the previously undescribed interaction between a Zatypota sp. wasp (Ichneumonidae) and a social spider Anelosimus eximius (Theridiidae) is described. The larva of this Zatypota wasp is found to induce its host to disperse from their communal web and build an entirely enclosed web consisting of densely spun silk. 3. The wasp is observed to target primarily immature A. eximius individuals, with 37.5–44% of nests in a given area being parasitised. Of those nests, approximately 1.3–2.0% of individuals are hosts to the parasitoid larvae. Larger spider colonies had a significantly higher probability of harbouring parasitoids. 4. This interaction results in unusual behaviours for A. eximius induced by the parasitoid: (i) leaving the protection of the social nest and (ii) building a unique, altered web that it would not otherwise build. It is suggested that the wasp may be tapping into ancestral dispersal behaviours in its host and that a social species provides this wasp an evolutionary advantage by allowing a stable host source. 相似文献