全文获取类型
收费全文 | 946篇 |
免费 | 76篇 |
国内免费 | 11篇 |
专业分类
1033篇 |
出版年
2023年 | 6篇 |
2022年 | 17篇 |
2021年 | 29篇 |
2020年 | 21篇 |
2019年 | 30篇 |
2018年 | 38篇 |
2017年 | 50篇 |
2016年 | 29篇 |
2015年 | 32篇 |
2014年 | 70篇 |
2013年 | 89篇 |
2012年 | 38篇 |
2011年 | 40篇 |
2010年 | 32篇 |
2009年 | 43篇 |
2008年 | 53篇 |
2007年 | 39篇 |
2006年 | 49篇 |
2005年 | 26篇 |
2004年 | 29篇 |
2003年 | 25篇 |
2002年 | 21篇 |
2001年 | 13篇 |
2000年 | 22篇 |
1999年 | 15篇 |
1998年 | 14篇 |
1997年 | 10篇 |
1996年 | 24篇 |
1995年 | 15篇 |
1994年 | 5篇 |
1993年 | 9篇 |
1992年 | 11篇 |
1991年 | 12篇 |
1990年 | 4篇 |
1989年 | 15篇 |
1988年 | 5篇 |
1987年 | 9篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1972年 | 2篇 |
1970年 | 1篇 |
排序方式: 共有1033条查询结果,搜索用时 15 毫秒
61.
J M Suchey D V Wiseley R F Green T T Noguchi 《American journal of physical anthropology》1979,51(4):517-540
Pubic bones from 486 modern American females between the ages of 13 and 99 were studied in an attempt to explore the relationship between the degree of dorsal pitting and the following variables: (1) number of full term pregnancies, (2) inteval since last pregnancy, (3) age of decedent.A statistical association was found between the number of full term pregnancies and the degree of dorsal pitting. However, the correlation is not strong; 17 females reported as being nulliparous have "medium to large" dorsal changes whereas 22 females having from one to five full term pregnancies have an absence of dorsal changes. Females who had their last child 15 or more years prior to death are more apt to have "medium to large" dorsal changes than are females who have more recently given birth. This effect appears to be independent of the number of full term pregnancies, but is probably related to age. When the data are analyzed by multiple regression analaysis, it is found that age and number of pregnancies are most important in predicting the degree of pitting and the effect of the interval on pitting is not significant. Age is found to be an important variable independent of the number of full term pregnancies. In nulliparas, an absence of dorsal pitting is far more frequently found in females younger than 30 than in those over 30. 相似文献
62.
Jasmine V. Abella Christine A. Parachoniak Veena Sangwan Morag Park 《The Journal of biological chemistry》2010,285(32):24956-24967
Dorsal ruffles are apical protrusions induced in response to many growth factors, yet their function is poorly understood. Here we report that downstream from the hepatocyte growth factor (HGF) receptor tyrosine kinase (RTK), Met, dorsal ruffles function as both a localized signaling microdomain as well as a platform from which the Met RTK internalizes and traffics to a degradative compartment. In response to HGF, colonies of epithelial Madin-Darby canine kidney cells form dorsal ruffles for up to 20 min. Met is transcytosed from the basolateral membrane on Rab4 endosomes, to the apical surface where Met, as well as a Met substrate and scaffold protein, Gab1, localize to the dorsal ruffle membrane. This results in activation of downstream signaling proteins, as evidenced by localization of phospho-ERK1/2 to dorsal ruffles. As dorsal ruffles collapse, Met is internalized into EEA1- and Rab5-positive endosomes and is targeted for degradation through delivery to an Hrs-positive sorting compartment. Enhancing HGF-dependent dorsal ruffle formation, through overexpression of Gab1 or activated Pak1 kinase, promotes more efficient degradation of the Met RTK. Conversely, the ablation of dorsal ruffle formation, by pre-treatment with SITS (4-acetamido-4′-isothiocyabatostilbene-2′,2-disulfonic acid) or expression of a Gab1 mutant, impairs Met degradation. Taken together, these data support a function for dorsal ruffles as a biologically relevant signaling microenvironment and a mechanism for Met receptor internalization and degradation. 相似文献
63.
目的:探究天麻素对Ⅱ型糖尿病神经病理性痛的镇痛作用以及天麻素对背根神经节Nav1.6通道的表达调控作用。方法:将60只雄性SD大鼠随机分为空白对照组、糖尿病组和天麻素处理组(10 mg·kg-1·d-1)。通过高脂饮食喂养4周,低剂量腹腔注射STZ(30 mg·kg-1)的方法构建Ⅱ型糖尿病神经病理性痛大鼠模型,利用痛行为学检测观察各组大鼠的机械刺激足缩反应阈值变化,采用免疫荧光组织化学及Western blot方法观察各组大鼠背根神经节上Nav1.6通道的表达变化。结果:与空白对照组相比,糖尿病模型大鼠出现显著的机械刺激疼痛阈值下降(P<0.05),且模型组大鼠背根神经节神经元上的Nav1.6通道表达上调(P<0.05)。与糖尿病组相比,连续腹腔注射天麻素3天、7天、14天后,模型动物的疼痛明显缓解(P<0.05),另外天麻素可以翻转背根神经节上Nav1.6通道的高表达(P<0.05)。结论:天麻素可能通过降低Nav1.6通道的表达来缓解Ⅱ型糖尿病神经病理性疼痛,从而为天麻素缓解糖尿病神经病理性疼痛提供新的理论依据。 相似文献
64.
《Saudi Journal of Biological Sciences》2017,24(4):966-971
We report morphometric data for 133 specimens of Diplometopon zarudnyi (Squamata: Trogonophidae) collected across its range within Riyadh province of Saudi Arabia. One-way analyses of variance revealed that differences exist in most characters. Snout-vent length and vent-tail length showed slight and inconsistent differences among samples. D. zarudnyi is characterized by 164–175 body annuli; 165–178 dorsal annuli; 13–17 caudal annuli with absence of caudal autotomy. In addition, 2–4 lateral annuli; 45–54 mid-body segments; 39–50 posterior segments; 4–5 head’s plates and 4–6 pre-cloacal pores were recorded in both males and females without gender difference. The present study revealed the widespread distribution of this species in the studied region, since land topography in this area is characterized by the absence of any natural barriers which could restrict the spread of this amphisbaenian lizard D. zarudnyi. 相似文献
65.
<正> The use of oscillating flexible fins in propulsion has been the subject of several studies in recent years, but attention israrely paid to the specific role of stiffness profile in thrust production.Stiffness profile is defined as the variation in localchordwise bending stiffness (EI) of a fin, from leading to trailing edge.In this study, flexible fins with a standard NACA0012shape were tested alongside fins with a stiffness profile mimicking that of a Pumpkinseed Sunfish (Lepomis gibbosus).The finswere oscillated with a pitching sinusoidal motion over a range of frequencies and amplitudes, while torque, lateral force andstatic thrust were measured.Over the range of oscillation parameters tested, it was shown that the fin with a biomimetic stiffness profile offered a significantimprovement in static thrust, compared to a fin of similar dimensions with a standard NACA0012 aerofoil profile.Thebiomimetic fin also produced thrust more consistently over each oscillation cycle.A comparison of fin materials of different stiffness showed that the improvement was due to the stiffness profile itself, andwas not simply an effect of altering the overall stiffness of the fin.Fins of the same stiffness profile were observed to follow thesame thrust-power curve, independent of the stiffness of the moulding material.Biomimetic fins were shown to produce up to26% greater thrust per watt of input power, within the experimental range. 相似文献
66.
67.
A Rapid and Simple PCR-based Method for Analysis of Transgenic Fish using a Restricted Amount of Fin Tissue 总被引:3,自引:0,他引:3
The protocol described in this paper offers a simple and rapid method for PCR analysis of transgenes using a restricted amount of fin tissue from small-sized transgenic fish. A simple preparation of fin lysate using a buffer containing a low concentration of an ionic detergent, SDS (0.01%), followed by neutralization with a second buffer containing higher concentrations of non-ionic detergents NP40 (2%) and Tween 20 (2%) consistently provides a reliable quantity of high-quality DNA template for PCR amplification of transgenes. Based on this protocol, transgenic fish can be clearly distinguished from non-transgenic fish using PCR in a rapid and reproducible manner. Tedious DNA purifications are avoided while fidelity of amplification and efficient identification of transgenic fish are maintained. 相似文献
68.
WNTs are secreted signaling molecules which control cell differentiation and proliferation. They are known to play essential roles in various developmental processes. Wnt genes have been identified in a variety of animals, and it has been shown that their amino acid sequences are highly conserved throughout evolution. To investigate the role of wnt genes during fish development from the evolutionary viewpoint, six medaka wnt genes (wnt4, wnt5a, wnt6, wnt7b, wnt8b and wnt8-like) were isolated and their embryonic expression was examined. These wnt genes were expressed in various tissues during embryonic development, and most of their expression patterns were conserved or comparable to those of other vertebrates. Thus, these wnt genes may be useful as molecular markers to investigate development and organogenesis using the medaka. Focus was on wnt5a, which was expressed in the pectoral fin buds, because its expression pattern was particularly comparable to that in tetrapod limbs. Its detailed expression pattern was further examined during pectoral fin bud development. The conservation and diversification of Wnt5a expression through the evolutionary transition from fish fins to tetrapod limbs is discussed. 相似文献
69.
条螽属和桑螽属雌性发声刺的比较观察 总被引:1,自引:0,他引:1
报道了对尖翅条螽Ducetia attenuata Xia et Liu、日本条 螽D. japonica(Thunberg)、施氏条螽D. strelkovi Gorochov et Storozhenk o和中华桑螽K uwayamaea chinensis(Brunner)、长翅桑螽K. longipennis Shi et Zheng、札 幌桑螽K.sap porensis Mats.et Shir.的雌性发声刺的观察结果。这6个种的雌性发声刺在数量与 形态上具较明显的差异。 相似文献
70.
Sango K Horie H Saito H Ajiki K Tokashiki A Takeshita K Ishigatsubo Y Kawano H Ishikawa Y 《Life sciences》2002,71(20):2351-2368
We examined the effects of diabetes on the morphological features and regenerative capabilities of adult mouse nodose ganglia (NG) and dorsal root ganglia (DRG). By light and electron microscopy, no apoptotic cell death was detected in the ganglia obtained from either streptozotocin (STZ)-induced diabetic or normal C57BL/6J mice in vivo. Neurite regeneration from transected nerve terminals of NG and DRG explants in culture at normal (10 mM) and high (30 mM) glucose concentrations was significantly enhanced in the diabetic mice. Chromatolytic changes (i.e. swelling and migration of the nucleus to an eccentric position in the neurons, and a loss of Nissl substance in the neuronal perikarya) and apoptotic cell death (less than one-fifth of the neurons) in the cultured ganglia were present, but neither hyperglycemia in vivo nor high glucose conditions in vitro altered the morphological features of the ganglia or the ratios of apoptotic cells at 3 days in culture. By semiquantitative RT-PCR analysis, the mRNA expressions of ciliary neurotrophic factor (CNTF) in DRG from both mice were down-regulated at 1 day in culture. The expression in diabetic DRG, but not in control DRG, was significantly up-regulated at later stages (3 and 7 days) in culture. In summary, hyperglycemia is unlikely to induce cell death in the sensory ganglia, but enhances the regenerative capability of vagal and spinal sensory nerves in vitro. The up-regulation of CNTF mRNA expression during the culture of diabetic DRG may play a role in the enhanced neurite regeneration. 相似文献