全文获取类型
收费全文 | 705篇 |
免费 | 51篇 |
国内免费 | 73篇 |
出版年
2024年 | 2篇 |
2023年 | 7篇 |
2022年 | 9篇 |
2021年 | 23篇 |
2020年 | 26篇 |
2019年 | 33篇 |
2018年 | 22篇 |
2017年 | 23篇 |
2016年 | 26篇 |
2015年 | 25篇 |
2014年 | 38篇 |
2013年 | 39篇 |
2012年 | 34篇 |
2011年 | 34篇 |
2010年 | 36篇 |
2009年 | 28篇 |
2008年 | 43篇 |
2007年 | 40篇 |
2006年 | 27篇 |
2005年 | 41篇 |
2004年 | 22篇 |
2003年 | 22篇 |
2002年 | 24篇 |
2001年 | 23篇 |
2000年 | 19篇 |
1999年 | 10篇 |
1998年 | 12篇 |
1997年 | 8篇 |
1996年 | 9篇 |
1995年 | 5篇 |
1994年 | 12篇 |
1993年 | 11篇 |
1992年 | 8篇 |
1991年 | 12篇 |
1990年 | 3篇 |
1989年 | 7篇 |
1988年 | 2篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 10篇 |
1982年 | 11篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1974年 | 5篇 |
排序方式: 共有829条查询结果,搜索用时 703 毫秒
181.
2013年4月-2015年10月,在四川卧龙国家级自然保护区用录音笔和GPS对2只野化培训的圈养大熊猫Ailuropoda melanoleuca幼体雪雪和华妍进行连续观察,收集声音数据,分析其休息、觅食、嬉戏和活动的行为节律。结果表明:(1)雪雪的日行为节律有3个觅食高峰(08∶00、18∶00和22∶00),2个休息高峰(03∶00-06∶00和11∶00-14∶00),各行为中仅嬉戏表现出有高度统计学意义的差异(F=1.944,df=359,P<0.01);休息时间占比为56.03%±10.58%、觅食为19.43%±18.49%、活动为19.30%±7.81%、嬉戏为5.24%±4.61%。(2)华妍有3个觅食高峰(10∶00、15∶00和20∶00),3个休息高峰(01∶00-06∶00、11∶00-13∶00和16∶00-19∶00);4种行为间的差异无统计学意义;休息时间占比为55.37%±10.38%、觅食为28.09%±17.79%、活动为14.61%±8.52%、嬉戏为1.93%±1.79%。(3)大熊猫幼体的日行为节律存在季节性差异。研究结果为大熊猫野化培训和野外放归提供了基础信息和科学依据。 相似文献
182.
目的:研究肌萎缩侧索硬化(ALS)患者肌电图检查中异常F波与束颤波的特点及其相关性。方法:收集2016年9月至2018年2月就诊于浙江大学医学院附属第二医院神经内科的54例ALS患者,进行常规肌电图检查和F波测定,记录216条正中神经、胫后神经的F波以及324块肌肉的束颤波相关参数,计算F波出现率、巨大F波、束颤波的出现率及其异常率,分析巨大F波、束颤波与病程的关系以及巨大F波和束颤波之间的关联性。结果:F波出现率的异常率88.89%,巨大F波出现率55.56%,束颤波出现率48.15%;有束颤波的病程与没有束颤波病程比较具有明显差异(P<0.01),有巨大F波的病程与未出现巨大F波病程比较无明显差异(P>0.05);上肢正中神经巨大F波出现与束颤波的出现无关联(P>0.05),下肢胫后神经巨大F波出现与束颤波的出现比较具有相关性(P=0.05)。结论:以上肢为主的F波出现率异常、以下肢为主的巨大F波和束颤波的出现可作为ALS电生理诊断阳性指标。有束颤波或巨大F波时可考虑疾病相对较早,且有较好的神经再支配及代偿,进展相对较慢。 相似文献
183.
地形是栖息地的基本要素, 从地形评价动物的空间利用特征能够掌握动物的分布规律并进行预测。为掌握保护区内牲畜的空间利用特征, 并评价它们对主要保护动物的潜在影响, 我们于2018年5-11月调查了王朗国家级自然保护区内牛和马的分布, 并结合红外相机监测结果及历史监测数据进行了分析和评价。结果表明: (1)虽然两种牲畜均偏好低海拔、低坡度、光照良好(半阳坡、阳坡)、距水源近的栖息地, 但它们在地形利用上存在显著差异; (2)牲畜活动最频繁的三条沟分别是竹根岔右一支沟、竹根岔正沟和大窝凼洋洞沟, 且呈现不同的干扰特征; (3)基于监测数据, 羚牛(Budorcas taxicolor tibetana)可能是保护区内最易受牛马活动威胁的保护动物。红外相机监测结果显示, 羚牛沿海拔分布现状可能是回避牲畜密集区域的结果。基于本研究, 我们建议: (1)保护区重点关注竹根岔(右一支沟、正沟、白沙沟)、大窝凼(洋洞沟、外侧坡)两个核心区的牲畜活动情况, 并尽快针对放牧采取措施。例如, 持续监测重点干扰区域牲畜的种群数量和空间分布趋势。(2)严格限制牲畜继续向高海拔栖息地入侵。(3)管控放牧投盐等干扰的发生频率。(4)加强执法力度, 防止牲畜对保护区带来的干扰持续和扩大, 威胁物种安全。 相似文献
184.
185.
Information on the olfactory system in antennae of Geometridae moths is very limited, and odorant-binding proteins (OBPs)
working as transporters of lipophilic odors have not been identified. In the first investigation on this family of insects,
we examined antennal OBPs of the Japanese giant looper, Ascotis selenaria cretacea. RT-PCR experiments using several pairs of degenerate primers designed from known cDNA sequences encoding lepidopteran OBPs
successfully amplified partial sequences of two pheromone-binding proteins (PBPs), named AscrPBP1 and AscrPBP2 in reference
to their corresponding nucleotide sequence homologies with other PBPs. Using 5′- and 3′-rapid amplification of cDNA end strategies,
a cDNA clone for AscrPBP1 encoding a protein of 141 amino acids was isolated. Western blotting with the antiserum against
recombinant AscrPBP1 overexpressed in Escherichia coli showed that the AscrPBP1 gene was more strongly expressed in male antennae than in female antennae. Furthermore, natural
AscrPBP1was isolated by immunoprecipitation with the antiserum, and its binding ability was evaluated by using synthetic sex
pheromonal compounds with a C19 chain. The result indicated that AscrPBP1 bound not only the pheromone components, 3,6,9-nonadecatriene and its 3,4-epoxy
derivative, but also unnatural 6,7- and 9,10-epoxy derivatives. While no general odorant-binding proteins (GOBPs) were amplified
in the RT-PCR experiments, two antisera prepared from GOBP1 and GOBP2 of Bombyx mori suggested the occurrence of at least two GOBPs in the A. s. cretacea antennae. 相似文献
186.
187.
B Lontay B Pál Z Serfőző A Kőszeghy G Szücs Z Rusznák F Erdődi 《Journal of neurochemistry》2012,123(1):84-99
Protein phosphatase-1M (PP1M, myosin phosphatase) consists of a PP1 catalytic subunit (PP1c) and the myosin phosphatase target subunit-1 (MYPT1). RhoA-activated kinase (ROK) regulates PP1M via inhibitory phosphorylation of MYPT1. Using multidisciplinary approaches, we have studied the roles of PP1M and ROK in neurotransmission. Electron microscopy demonstrated the presence of MYPT1 and ROK in both pre- and post-synaptic terminals. Tautomycetin (TMC), a PP1-specific inhibitor, decreased the depolarization-induced exocytosis from cortical synaptosomes. trans-4-[(1R)-1-aminoethyl]-N-4-pyridinylcyclohexanecarboxamide dihydrochloride, a ROK-specific inhibitor, had the opposite effect. Mass spectrometry analysis identified several MYPT1-bound synaptosomal proteins, of which interactions of synapsin-I, syntaxin-1, calcineurin-A subunit, and Ca(2+) /calmodulin-dependent kinase II with MYPT1 were confirmed. In intact synaptosomes, TMC increased, whereas Y27632 decreased the phosphorylation levels of MYPT1(Thr696) , myosin-II light chain(Ser19) , synapsin-I(Ser9) , and syntaxin-1(Ser14) , indicating that PP1M and ROK influence their phosphorylation status. Confocal microscopy indicated that MYPT1 and ROK are present in the rat ventral cochlear nucleus both pre- and post-synaptically. Analysis of the neurotransmission in an auditory glutamatergic giant synapse demonstrated that PP1M and ROK affect neurotransmission via both pre- and post-synaptic mechanisms. Our data suggest that both PP1M and ROK influence synaptic transmission, but further studies are needed to give a full account of their mechanism of action. 相似文献
188.
189.
Stomeo F Bianchini C Ciorba A Padovani D Pedriali M Pelucchi S Pastore A 《Gerodontology》2012,29(2):e1152-e1156
Although liposarcoma is a reasonably common soft tissue sarcoma in adults, its occurrence within the head and neck region is very rare. The following report presents the case of a giant dedifferentiated liposarcoma initially located in the temporal region and then extending to the entire right maxillofacial region. Clinical as well as histopathological features and therapeutic approaches of dedifferentiated liposarcoma are discussed, and a literature review is presented. 相似文献
190.
Artificial insemination (AI) is an important component of captive breeding programs for endangered species, such as the giant panda. The panda has been the subject of increasingly successful captive breeding programs involving a compilation of assisted breeding techniques, including AI using cryopreserved spermatozoa. AI implementation is currently hampered by a lack of understanding of the factors that may cause failure. We investigated factors influencing the probability of success of AI for 14 giant panda females housed at the China Center for Research and Conservation of the Giant Panda (CCRCGP) inseminated in a total of 20 instances using cryopreserved spermatozoa from 11 males currently residing in 6 different captive breeding institutions. One of the pandas was the oldest giant panda female to ever successfully conceive from AI (20.5 years old). The success of AI was significantly affected by the timing of AI in relationship to both timing of peak urinary estrogen of the female and percent decline in urinary estrogen between the peak level and the first AI attempt. Our results suggest that the window for successful AI in giant pandas may be narrower than previously suspected, although individual differences in rates of decline in urinary estrogen may reflect some degree of variation in this crucial window across females. Our results are consistent with recent research on pandas and other species that demonstrates the efficacy of cryopreserved spermatozoa for AI and highlights the need for more in‐depth analysis of factors related to female physiology that may influence its success. Zoo Biol 31:561‐573, 2012. © 2011 Wiley Periodicals, Inc. 相似文献