全文获取类型
收费全文 | 1249篇 |
免费 | 29篇 |
国内免费 | 69篇 |
专业分类
1347篇 |
出版年
2023年 | 10篇 |
2022年 | 15篇 |
2021年 | 12篇 |
2020年 | 21篇 |
2019年 | 22篇 |
2018年 | 25篇 |
2017年 | 21篇 |
2016年 | 20篇 |
2015年 | 43篇 |
2014年 | 150篇 |
2013年 | 116篇 |
2012年 | 165篇 |
2011年 | 145篇 |
2010年 | 77篇 |
2009年 | 74篇 |
2008年 | 61篇 |
2007年 | 58篇 |
2006年 | 28篇 |
2005年 | 25篇 |
2004年 | 31篇 |
2003年 | 27篇 |
2002年 | 14篇 |
2001年 | 13篇 |
2000年 | 14篇 |
1999年 | 11篇 |
1998年 | 11篇 |
1997年 | 11篇 |
1996年 | 8篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 8篇 |
1992年 | 4篇 |
1991年 | 9篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 7篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1976年 | 3篇 |
1975年 | 7篇 |
1973年 | 5篇 |
1972年 | 2篇 |
1964年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有1347条查询结果,搜索用时 8 毫秒
11.
Barbara C. Banz Jia Wu Michael J. Crowley Marc N. Potenza Linda C. Mayes 《The Yale journal of biology and medicine》2016,89(2):143-151
Adolescence and prenatal cocaine exposure can impact risk-taking. In this study, we evaluated risk-taking and gender-related differences in adolescents with prenatal cocaine exposure in terms of electrophysiological correlates of inhibitory control and sustained attention. No differences related to gender were found within measures of risk-taking, or electrophysiological response relating to risk-taking. Greater responses during inhibition versus attention trials support previous studies, with boys showing the largest responses. Gender-related differences were found when comparing the trials before and after frustration was induced, with greater initial attention indices for girls in both trial types and greater sustained attention for both genders during inhibition trials and for boys during attention trials. These data suggest neural correlates of response inhibition show important gender-related differences in this population. Considering these relationships allows us to further understand underlying processes among adolescents who, as a group, tend to be more inclined toward greater risk behaviors. 相似文献
12.
13.
14.
15.
The intrinsic ability of vascular smooth muscle cells (VSMCs) within arterial resistance vessels to respectively contract and relax in response to elevation and reduction of intravascular pressure is essential for appropriate blood flow autoregulation. This fundamental mechanism, referred to as the myogenic response, is dependent on apposite control of myosin regulatory light chain (LC20) phosphorylation, a prerequisite for force generation, through the coordinated activity of myosin light chain kinase (MLCK) and myosin light chain phosphatase (MLCP). Here, we highlight the molecular basis of the smooth muscle contractile mechanism and review the regulatory pathways demonstrated to participate in the control of LC20 phosphorylation in the myogenic response, with a focus on the Ca2+-dependent and Rho-associated kinase (ROK)-mediated regulation of MLCK and MLCP, respectively. 相似文献
16.
In this work, response surface methodology was used to determine optimum conditions for extraction of polysaccharides from defatted peanut cake. A central composite design including independent variables, such as extraction temperature (x1), extraction time (x2), and ethanol concentration (x3) was used. Selected response which evaluates the extraction process was polysaccharide yield, and the second-order model obtained for polysaccharide yield revealed coefficient of determination of 97.81%. The independent variable with the largest effect on response was ethanol concentration (x3). The optimum extraction conditions were found to be extraction temperature 48.7 °C, extraction time 1.52 h, and ethanol concentration of 61.9% (v/v), respectively. Under these conditions, the extraction efficiency of polysaccharide can increase to 25.89%. The results of structural analysis showed that the main composition of defatted peanut cake polysaccharide was α-galactose. 相似文献
17.
Ming Ming Fumiaki Obata Erina Kuranaga Masayuki Miura 《The Journal of biological chemistry》2014,289(11):7558-7568
Apoptosis is an evolutionarily conserved mechanism that removes damaged or unwanted cells, effectively maintaining cellular homeostasis. It has long been suggested that a deficiency in this type of naturally occurring cell death could potentially lead to necrosis, resulting in the release of endogenous immunogenic molecules such as damage-associated molecular patterns (DAMPs) and a noninfectious inflammatory response. However, the details about how danger signals from apoptosis-deficient cells are detected and translated to an immune response are largely unknown. In this study, we found that Drosophila mutants deficient for Dronc, the key initiator caspase required for apoptosis, produced the active form of the endogenous Toll ligand Spätzle (Spz). We speculated that, as a system for sensing potential DAMPs in the hemolymph, the dronc mutants constitutively activate a proteolytic cascade that leads to Spz proteolytic processing. We demonstrated that Toll signaling activation required the action of Persephone, a CLIP domain serine protease that usually reacts to microbial proteolytic activities. Our findings show that the Persephone proteolytic cascade plays a crucial role in mediating DAMP-induced systemic responses in apoptosis-deficient Drosophila mutants. 相似文献
18.
一类具有非单调增长率和功能反应的捕食者-食饵系统的定性分析 总被引:4,自引:1,他引:4
考虑一类食饵密度具有非单调增长率,捕食者具有功能性反应的捕食者一食饵系统。得到系统在第一象限内正平衡点的区域稳定的条件和极限环存在唯一的条件,完整地讨论了系统(1)的拓扑结构。 相似文献
19.
以飞龙掌血(Toddalia asiatica(L.)Lam.)的根为实验材料,以总生物碱的含量为检测指标,应用响应面法对飞龙掌血中总生物碱的提取工艺进行了优化。结果显示,当提取条件为乙醇体积分数74.76%、料液比20∶1和提取时间32.87 min时,飞龙掌血提取物中总生物碱的理论含量值可达11.09 mg/g,总生物碱含量达到最高值。按照最佳提取工艺条件进行验证,3次平行实验的均值为(10.74 ±0.18)mg/g,与理论值差异较小,表明利用响应面法来优化飞龙掌血中总生物碱的最佳提取工艺模型拟合良好,具有一定实用价值。 相似文献
20.
黄萎病菌胁迫下野生茄子托鲁巴姆防卫反应的生理生化分析 总被引:1,自引:0,他引:1
以野生茄子托鲁巴姆(Solanum torvum Swartz)和苏崎茄(Solanum melongena L.)为主要材料,通过比较两种茄子在大丽轮枝菌(Verticillium dahliae Kleb)侵染过程中体内的生理生化指标变化,分析托鲁巴姆对黄萎病的抗性响应机制。结果表明:(1)与苏崎茄植株相比,托鲁巴姆植株表现出很强的自我防御和自我修复能力。(2)托鲁巴姆体内存在的活性氧清除系统(如SOD、POD、CAT等酶的活性)高于苏崎茄;在侵染后,托鲁巴姆体内各种酶的活性快速增加,其幅度高于苏崎茄;MDA的变化则恰恰相反。这个结果提示,黄萎病菌胁迫可能激活了托鲁巴姆体内活性氧清除系统,从而加快了某些防御物质(如木质素和抗菌物质绿原酸等)的形成,同时减缓或降低MDA等有害物质在植株体内的积累。(3)黄萎病菌侵染后各生理指标的响应时间表现出差异。托鲁巴姆中POD、PAL的活性和可溶性蛋白含量在侵染后的12h内就迅速作出响应(POD增加、PAL和可溶性蛋白减少);而SOD、PPO、CAT的活性和MDA的含量则在处理后初始阶段(至少12h)进行了一些调整,随后才进入持续性的增加或减少阶段。由此可见,托鲁巴姆对黄萎病病菌侵染的响应具有时序性,其体内POD酶、PAL酶和可溶性蛋白首先参与植物的防卫反应以应对黄萎病的胁迫,其它酶随后参与响应,它们的共同作用形成对黄萎病菌的有效防卫。 相似文献