全文获取类型
收费全文 | 10672篇 |
免费 | 917篇 |
国内免费 | 886篇 |
专业分类
12475篇 |
出版年
2024年 | 43篇 |
2023年 | 178篇 |
2022年 | 374篇 |
2021年 | 602篇 |
2020年 | 427篇 |
2019年 | 492篇 |
2018年 | 474篇 |
2017年 | 374篇 |
2016年 | 453篇 |
2015年 | 681篇 |
2014年 | 793篇 |
2013年 | 776篇 |
2012年 | 985篇 |
2011年 | 859篇 |
2010年 | 555篇 |
2009年 | 442篇 |
2008年 | 503篇 |
2007年 | 470篇 |
2006年 | 412篇 |
2005年 | 357篇 |
2004年 | 321篇 |
2003年 | 264篇 |
2002年 | 287篇 |
2001年 | 122篇 |
2000年 | 84篇 |
1999年 | 101篇 |
1998年 | 102篇 |
1997年 | 70篇 |
1996年 | 77篇 |
1995年 | 66篇 |
1994年 | 67篇 |
1993年 | 41篇 |
1992年 | 42篇 |
1991年 | 37篇 |
1990年 | 38篇 |
1989年 | 40篇 |
1988年 | 31篇 |
1987年 | 35篇 |
1986年 | 27篇 |
1985年 | 28篇 |
1984年 | 23篇 |
1983年 | 18篇 |
1982年 | 31篇 |
1981年 | 29篇 |
1980年 | 20篇 |
1979年 | 27篇 |
1978年 | 26篇 |
1977年 | 26篇 |
1976年 | 18篇 |
1974年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Plant Molecular Biology - 相似文献
2.
Caitlin M. Cossaboom Laura Córdoba Dianjun Cao Yan-Yan Ni Xiang-Jin Meng 《Journal of virology》2012,86(23):13124-13125
Hepatitis E virus (HEV) is a single-strand positive-sense RNA virus in the family Hepeviridae. The disease caused by HEV, hepatitis E, is an important public health problem in developing countries of Asia and Africa and is also endemic in many industrialized countries, including the United States. HEV has been identified from several other animal species in addition to humans, including the pig, chicken, mongoose, deer, rabbit, ferret, bat, and fish. Here we report the complete genome sequence of the first strain of HEV from rabbits in the United States. Sequence and phylogenetic analyses revealed that the U.S. rabbit HEV is a distant member of the zoonotic genotype 3 HEV, thus raising a concern for potential zoonotic human infection. A unique 90-nucleotide insertion within the X domain of the ORF1 was identified in the rabbit HEV, and this insertion may play a role in the species tropism of HEV. 相似文献
3.
4.
Halasz Norbert; Nowycky Martha C.; Shepherd Gordon M.; Hofelt Tomas 《Chemical senses》1985,10(2):203-218
aftographic exeperiments on the localization of radiolabelednoradrenaline, dopamine and dopa, as well as immunohistochemicalstudies on hydroxylase-like activity, are summarized and comparedin both rat and turtle olfactory bulbs. Evoked field potentialstudies on effects of dopamine are also discussed. The histochemicalstudies suggest that dopaminergic periglomerular neurons arethe most significant cellular component of the catecholaminergicsystem in the olfactory bulb of both species. Scattered fluorescentcell group was also present in the internal plexiform layerand superficial granule cell layer of the turtle olfactory bulb.Other fibres, not related to intrinsic bulbar neuronal cellbodies, were also labeled, mostly in the granule cell layerbut also in the external plexiform layer. These might belongto a centrifugal catecholaminergic system from brain stem neurons.In the in vitro turtle olfactory bulb, dopamine and apomorphinedepressed the amplitude of field potentials evoked by a singlevolley in the olfactory nerve or lateral olfactory tract, andreduced the depression and latency of reponses when paired volleywere delivered. It is suggested that catecholaminergic systemsplay a key role in modulating mitral cell activity through actionsin both superficial (glomerular) and deep (granule) layers.This may involve direct actions, or other, non-catecholaminergicinterneurons. 相似文献
5.
Martha Macintyre 《The Australian journal of anthropology》2012,23(1):121-122
6.
The garlic stalk is a byproduct of garlic production and normally abandoned or burned, both of which cause environmental pollution. It is therefore appropriate to determine the conditions of efficient decomposition, and equally appropriate to determine the impact of this decomposition on soil properties. In this study, the soil properties, enzyme activities and nutrient dynamics associated with the decomposition of garlic stalk at different temperatures, concentrations and durations were investigated. Stalk decomposition significantly increased the values of soil pH and electrical conductivity. In addition, total nitrogen and organic carbon concentration were significantly increased by decomposing stalks at 40°C, with a 5∶100 ratio and for 10 or 60 days. The highest activities of sucrase, urease and alkaline phosphatase in soil were detected when stalk decomposition was performed at the lowest temperature (10°C), highest concentration (5∶100), and shortest duration (10 or 20 days). The evidence presented here suggests that garlic stalk decomposition improves the quality of soil by altering the value of soil pH and electrical conductivity and by changing nutrient dynamics and soil enzyme activity, compared to the soil decomposition without garlic stalks. 相似文献
7.
8.
9.
Martha L. Bohórquez Alonso Jorge Martínez Cotrina David Aguilar Pardo Enrique Font Miguel Molina-Borja 《Journal of Ethology》2010,28(2):305-311
Many vertebrate species show display behaviors when predators are in their vicinity. Some of these displays may inform the
predator of the improbability of capturing the prey (i.e., pursuit-deterrent displays) and are potentially advantageous to
both predator and prey. Here we present data on a tail display performed by Gonatodes albogularis, a diurnal tropical gecko. We performed transect surveys in three habitats near Bogotá in Colombia. Geckos detected during
transects were approached by the observer in a standardized way, and details of their tail-waving displays were recorded.
In control recordings animals were watched from a distant site without approaching them. Results showed sexual differences
in tail-waving display: when approached by the observer, males performed this behavior more frequently than females. We found
no significant differences between males and females in flight-initiation distances and height above the substratum when they
were initially located. Results also showed that males displayed more frequently when approached than when the simulated predator
remained stationary. We interpret these results as evidence that the display functions as a pursuit-deterrent signal to potential
predators. However, as some tail displays were performed in the presence of conspecifics, the display may also have a social
function. 相似文献
10.
Twenty-four-hour variations in activity,core temperature,metabolic rate,and respiratory quotient in captive chinese pangolins 总被引:1,自引:0,他引:1
Martha E. Heath 《Zoo biology》1987,6(1):1-10
The circadian rhythms in activity, core temperature (Tc), O2 consumption, CO2 production, and respiratory quotient (RQ) were monitored in four captive Chinese pangolins (Manis pentadactyla). The pangolins were strictly nocturnal, never emerging from their nest before 1600 h, and their intermittent activity continued no later than 0230. As is usual in nocturnal mammals, the highest values observed in Tc, O2 consumption, and CO2 production occurred during the night; the lowest values occurred during the day. The magnitude of the variation in Tc, O2 consumption, CO2 production, and RQ averaged 1.2°C, 1.3 ml O2 kg?1 min?1, 1.2 ml CO2 kg?1 min?1, and 0.24, respectively. The circadian pattern in RQ was independent of activity, Tc, and the metabolic parameters and was of a different character than the patterns exhibited in the other variables. RQ remained constant at either a high or low level for long periods (8–10 h) and then increased or decreased relatively rapidly (1–2h) to the other level as in a square wave, whereas the rhythms in the other variables are similar to sine waves. The sharp increase in RQ was followed by a slow decline in Tc, and the sharp decline in RQ was followed by a slow increase in Tc. 相似文献