全文获取类型
收费全文 | 3182篇 |
免费 | 342篇 |
专业分类
3524篇 |
出版年
2022年 | 23篇 |
2021年 | 42篇 |
2018年 | 26篇 |
2016年 | 42篇 |
2015年 | 82篇 |
2014年 | 87篇 |
2013年 | 103篇 |
2012年 | 168篇 |
2011年 | 148篇 |
2010年 | 70篇 |
2009年 | 77篇 |
2008年 | 118篇 |
2007年 | 113篇 |
2006年 | 113篇 |
2005年 | 115篇 |
2004年 | 109篇 |
2003年 | 100篇 |
2002年 | 96篇 |
2001年 | 91篇 |
2000年 | 105篇 |
1999年 | 82篇 |
1998年 | 38篇 |
1996年 | 30篇 |
1995年 | 24篇 |
1994年 | 26篇 |
1993年 | 36篇 |
1992年 | 77篇 |
1991年 | 72篇 |
1990年 | 70篇 |
1989年 | 48篇 |
1988年 | 62篇 |
1987年 | 64篇 |
1986年 | 59篇 |
1985年 | 53篇 |
1984年 | 49篇 |
1983年 | 42篇 |
1982年 | 36篇 |
1981年 | 40篇 |
1980年 | 26篇 |
1979年 | 66篇 |
1978年 | 63篇 |
1977年 | 45篇 |
1976年 | 53篇 |
1975年 | 37篇 |
1974年 | 38篇 |
1973年 | 30篇 |
1972年 | 37篇 |
1971年 | 27篇 |
1968年 | 26篇 |
1966年 | 22篇 |
排序方式: 共有3524条查询结果,搜索用时 15 毫秒
61.
Helen Y. Weng Andrew S. Fox Heather C. Hessenthaler Diane E. Stodola Richard J. Davidson 《PloS one》2015,10(12)
Compassion, the emotional response of caring for another who is suffering and that results in motivation to relieve suffering, is thought to be an emotional antecedent to altruistic behavior. However, it remains unclear whether compassion enhances altruistic behavior in a uniform way or is specific to sub-types of behavior such as altruistic helping of a victim or altruistic punishment of a transgressor. We investigated the relationship between compassion and subtypes of altruistic behavior using third-party paradigms where participants 1) witnessed an unfair economic exchange between a transgressor and a victim, and 2) had the opportunity to either spend personal funds to either economically a) help the victim or b) punish the transgressor. In Study 1, we examined whether individual differences in self-reported empathic concern (the emotional component of compassion) was associated with greater altruistic helping or punishment behavior in two independent samples. For participants who witnessed an unfair transaction, trait empathic concern was associated with greater helping of a victim and had no relationship to punishment. However, in those who decided to punish the transgressor, participants who reported greater empathic concern decided to punish less. In Study 2, we directly enhanced compassion using short-term online compassion meditation training to examine whether altruistic helping and punishment were increased after two weeks of training. Compared to an active reappraisal training control group, the compassion training group gave more to help the victim and did not differ in punishment of the transgressor. Together, these two studies suggest that compassion is related to greater altruistic helping of victims and is not associated with or may mitigate altruistic punishment of transgressors. 相似文献
62.
Fragile X syndrome (FX), the most common heritable cause of mental retardation and autism, is a developmental disorder characterized by physical, cognitive, and behavioral deficits. FX results from a trinucleotide expansion mutation in the fmr1 gene that reduces levels of fragile X mental retardation protein (FMRP). Although research efforts have focused on FMRP's impact on mGluR signaling, how the loss of FMRP leads to the individual symptoms of FX is not known. Previous studies on human FX blood cells revealed alterations in the cyclic adenosine 3', 5'-monophosphate (cAMP) cascade. We tested the hypothesis that cAMP signaling is altered in the FX nervous system using three different model systems. Induced levels of cAMP in platelets and in brains of fmr1 knockout mice are substantially reduced. Cyclic AMP induction is also significantly reduced in human FX neural cells. Furthermore, cAMP production is decreased in the heads of FX Drosophila and this defect can be rescued by reintroduction of the dfmr gene. Our results indicate that a robust defect in cAMP production in FX is conserved across species and suggest that cAMP metabolism may serve as a useful biomarker in the human disease population. Reduced cAMP induction has implications for the underlying causes of FX and autism spectrum disorders. Pharmacological agents known to modulate the cAMP cascade may be therapeutic in FX patients and can be tested in these models, thus supplementing current efforts centered on mGluR signaling. 相似文献
63.
Cyclic AMP stimulates luteinizing-hormone (lutropin) exocytosis in permeabilized sheep anterior-pituitary cells. Synergism with protein kinase C and calcium. 下载免费PDF全文
Sheep anterior-pituitary cells permeabilized with Staphylococcus aureus alpha-toxin were used to investigate the role of cyclic AMP (cAMP) in exocytosis of luteinizing hormone (lutropin, LH) under conditions where the intracellular free Ca2+ concentration ([Ca2+]free) is clamped by Ca2+ buffers. At resting [Ca2+]free (pCa 7), cAMP rapidly stimulated LH exocytosis (within 5 min) and continued to stimulate exocytosis for at least 30 min. When cAMP breakdown was inhibited by 3-isobutyl-1-methylxanthine (IBMX), the concentration giving half-maximal response (EC50) for cAMP-stimulated exocytosis was 10 microM. cAMP-stimulated exocytosis required millimolar concentrations of MgATP, as has been found with Ca2(+)- and phorbol-ester-stimulated LH exocytosis. cAMP caused a modest enhancement of Ca2(+)-stimulated LH exocytosis by decreasing in the EC50 for Ca2+ from pCa 5.6 to pCa 5.9, but had little effect on the maximal LH response to Ca2+. Activation of protein kinase C (PKC) with phorbol 12-myristate 13-acetate (PMA) dramatically enhanced cAMP-stimulated LH exocytosis by both increasing the maximal effect 5-7-fold and decreasing the EC50 for cAMP to 3 microM. This synergism between cAMP and PMA was further augmented by increasing the [Ca2+]free. Gonadotropin-releasing hormone (gonadoliberin, GnRH) stimulated cAMP production in intact pituitary cells. Since GnRH stimulation is reported to activate PKC and increase the intracellular [Ca2+]free, our results suggest that a synergistic interaction of the cAMP, PKC and Ca2+ second-messenger systems is of importance in the mechanism of GnRH-stimulated LH exocytosis. 相似文献
64.
The mammalian pacemaker in the suprachiasmatic nucleus (SCN) contains a population of neural oscillators capable of sustaining cell-autonomous rhythms in gene expression and electrical firing. A critical question for understanding pacemaker function is how SCN oscillators are organized into a coherent tissue capable of coordinating circadian rhythms in behavior and physiology. Here we undertake a comprehensive analysis of oscillatory function across the SCN of the adult PER2::LUC mouse by developing a novel approach involving multi-position bioluminescence imaging and unbiased computational analyses. We demonstrate that there is phase heterogeneity across all three dimensions of the SCN that is intrinsically regulated and extrinsically modulated by light in a region-specific manner. By investigating the mechanistic bases of SCN phase heterogeneity, we show for the first time that phase differences are not systematically related to regional differences in period, waveform, amplitude, or brightness. Furthermore, phase differences are not related to regional differences in the expression of arginine vasopressin and vasoactive intestinal polypeptide, two key neuropeptides characterizing functionally distinct subdivisions of the SCN. The consistency of SCN spatiotemporal organization across individuals and across planes of section suggests that the precise phasing of oscillators is a robust feature of the pacemaker important for its function. 相似文献
65.
A Puri R Sethi B Singh SK Dwivedi VS Narain RK Saran VK Puri 《Indian pacing and electrophysiology journal》2009,9(3):186-189
A 25-year-old previously asymptomatic pregnant woman at 36 weeks'' gestation was noticed to have repetitive monomorphic ventricular tachycardia. A dilated left ventricle with moderately reduced systolic function was found on echocardiographic examination. This is a very rare presentation of peripartum cardiomyopathy (PPCMP) presenting with repetitive monomorphic ventricular tachycardia. 相似文献
66.
Selective method for identification and quantification of Bifidobacterium animalis subspecies lactis BB‐12 (BB‐12) from the gastrointestinal tract of healthy volunteers ingesting a combination probiotic of BB‐12 and Lactobacillus rhamnosus GG 下载免费PDF全文
67.
Simon J. Watson Pinky Langat Scott M. Reid Tommy Tsan-Yuk Lam Matthew Cotten Michael Kelly Kristien Van Reeth Yu Qiu Ga?lle Simon Emilie Bonin Emanuela Foni Chiara Chiapponi Lars Larsen Charlotte Hjulsager Iwona Markowska-Daniel Kinga Urbaniak Ralf Dürrwald Michael Schlegel Anita Huovilainen Irit Davidson ádám Dán Willie Loeffen Stephanie Edwards Michel Bublot Thais Vila Jaime Maldonado Laura Valls ESNIP Consortium Ian H. Brown Oliver G. Pybus Paul Kellam 《Journal of virology》2015,89(19):9920-9931
68.
69.
Sequence complexity of heterogeneous nuclear RNA in sea urchin embryos. 总被引:12,自引:0,他引:12
The sequence complexity of heterogeneous nuclear RNA is sea urchin gastrulas was measured by RNA-driven hybridization reactions with nonrepetitive sea urchin DNA. 28.5% of the sequence complexity of the genome is represented in the nuclear RNA. This amounts to 1.74 X 10(8) nucleotides of diverse sequence, more than 10 times the nucleotide complexity of the polysomal messenger RNA extracted from sea urchin embryos at the same stage. The complex set of nuclear RNA sequences driving this hybridization reaction was shown to be the same as the rapidly labeled hnRNA, using pulse-labeled nuclear RNA as driver. 相似文献
70.
Miriam E. Koome Joanne O. Davidson Paul P. Drury Sam Mathai Lindsea C. Booth Alistair Jan Gunn Laura Bennet 《PloS one》2013,8(10)