首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   22678篇
  免费   1984篇
  国内免费   2339篇
  27001篇
  2024年   79篇
  2023年   412篇
  2022年   820篇
  2021年   1264篇
  2020年   979篇
  2019年   1131篇
  2018年   1054篇
  2017年   802篇
  2016年   1038篇
  2015年   1544篇
  2014年   1863篇
  2013年   1835篇
  2012年   2134篇
  2011年   1881篇
  2010年   1278篇
  2009年   1082篇
  2008年   1136篇
  2007年   998篇
  2006年   930篇
  2005年   784篇
  2004年   659篇
  2003年   690篇
  2002年   536篇
  2001年   326篇
  2000年   257篇
  1999年   246篇
  1998年   197篇
  1997年   142篇
  1996年   146篇
  1995年   123篇
  1994年   101篇
  1993年   70篇
  1992年   88篇
  1991年   77篇
  1990年   67篇
  1989年   53篇
  1988年   29篇
  1987年   25篇
  1986年   36篇
  1985年   27篇
  1984年   14篇
  1983年   11篇
  1982年   11篇
  1981年   7篇
  1980年   3篇
  1979年   3篇
  1976年   2篇
  1970年   1篇
  1962年   2篇
  1950年   3篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.

Background

GPi (Internal globus pallidus) DBS (deep brain stimulation) is recognized as a safe, reliable, reversible and adjustable treatment in patients with medically refractory dystonia.

Objectives

This report describes the long-term clinical outcome of 36 patients implanted with GPi DBS at the Neurosurgery Department of Seoul National University Hospital.

Methods

Nine patients with a known genetic cause, 12 patients with acquired dystonia, and 15 patients with isolated dystonia without a known genetic cause were included. When categorized by phenomenology, 29 patients had generalized, 5 patients had segmental, and 2 patients had multifocal dystonia. Patients were assessed preoperatively and at defined follow-up examinations postoperatively, using the Burke-Fahn-Marsden dystonia rating scale (BFMDRS) for movement and functional disability assessment. The mean follow-up duration was 47 months (range, 12–84)

Results

The mean movement scores significantly decreased from 44.88 points preoperatively to 26.45 points at 60-month follow up (N = 19, P = 0.006). The mean disability score was also decreased over time, from 11.54 points preoperatively to 8.26 points at 60-month follow up, despite no statistical significance (N = 19, P = 0.073). When analyzed the movement and disability improvement rates at 12-month follow up point, no significant difference was noted according to etiology, disease duration, age at surgery, age of onset, and phenomenology. However, the patients with DYT-1 dystonia and isolated dystonia without a known genetic cause showed marked improvement.

Conclusions

GPi DBS is a safe and efficient therapeutic method for treatment of dystonia patients to improve both movement and disability. However, this study has some limitations caused by the retrospective design with small sample size in a single-center.  相似文献   
142.
为了研究家蚕 Bombyx mori 溶茧酶基因 (cocoonae)真核表达及其产物的生物活性,将溶茧酶基因(GenBank 登录号 EF428980)克隆至杆状病毒转移载体 pFastBacTM 1 中获得 pFast-cocoonase,将其转化 DH10Bac 感受态细胞后,PCR 方法检测证实所分离的重组病毒 DNA 中含有目的片段溶茧酶基因。用脂质体法 转染家蚕 BmN 细胞,获得重组病毒。SDS-PAGE 分析显示,感染重组杆状病毒 Bac-cocoonase 的细胞表达产物在约为 27.6 kD 处出现特异性条带,这与预测的蛋白大小相符。用该表达产物与茧丝反应后,电镜下观察茧丝的形态,结果表明表达产物对茧丝的丝胶层有一定的水解作用。  相似文献   
143.
吴欣仪  王蒙  郑希龙  张锐  何松  严岳鸿 《广西植物》2023,43(8):1414-1427
物种的遗传多样性是决定物种适应性和生存能力的关键因素。生境片段化是造成生物多样性丧失的重要因素之一,对植物种群的遗传多样性有着重要影响。水角(Hydrocera triflora)作为一种濒危植物,其遗传多样性状况和濒危机制尚未有报道。该文收集了水角7个种群共计34个样本,利用简化基因组测序技术(RAD-seq)获得了单核苷酸变异位点(SNP)。通过种群遗传多样性和遗传结构的分析,并结合种群历史动态分析和不同气候情景下物种潜在分布区预测,探讨了水角的濒危机制。结果表明:(1)水角遗传多样性较低(Ho=0.156 9、He=0.165 4、π=0.186 5),遗传分化系数较高; AMOVA分析表明,遗传变异主要发生在种群内。(2)Mantel检测表明环境距离与遗传距离、地理距离均呈显著正相关,分别为P=0.041 2和P=0.008 2。(3)水角的有效种群大小从全新世中期开始持续下降,与琼北火山群的喷发时间一致。(4)与当代气候相比,虽然在未来气候变化下水角的潜在分布区总面积变动不大,但在高CO2排放的情景下,大量的高适生区将会丧失并转化为低适生区,特别是位于马来群岛的适生区几乎完全消失。该研究结果表明,生境片段化导致了水角较低的遗传多样性和有效种群大小的持续下降。因此,自身更新能力低以及人为活动干扰、城市化等不利的环境条件是导致其濒危的主要原因。建议加强对水角的就地保护,采用人工授粉等方法提高其基因流以增加其种群的遗传多样性,同时,要着重保护湿地免遭破坏。  相似文献   
144.
Inflammation is a crucial step for the wound healing process. The effect of linoleic and oleic acids on the inflammatory response of the skin during the healing process and on the release of pro-inflammatory cytokines by rat neutrophils in vitro was investigated. A wound in the dorsal surface of adult rats was performed and fatty acids were then topically administered. Both oleic and linoleic acids increased the wound healing tissue mass. The total protein and DNA contents of the wounds were increased by the treatment with linoleic acid. The treatments with oleic and linoleic acids did not affect vascular permeability. However, the number of neutrophils in the wounded area and air pouches was increased and the thickness of the necrotic cell layer edge around the wound was decreased. A dose-dependent increase in vascular endothelial growth factor-alpha (VEGF-alpha) and interleukin-1beta (IL-1beta) by neutrophils incubated in the presence of oleic and linoleic acid was observed. Oleic acid was able to stimulate also the production of cytokine-induced neutrophil chemoattractant in inflammation 2 alpha/beta (CINC-2alpha/beta). This pro-inflammatory effect of oleic and linoleic acids may speed up the wound healing process.  相似文献   
145.
Yao J  Xu Y  Ji F  Wang C  Zhang Y  Ni J  Wang R 《Peptides》2011,32(5):1047-1054
The monocyte locomotion inhibitory factor (MLIF) is an anti-inflammatory oligopeptide produced by Entamoeba histolytica. Among its different effects, it inhibits locomotion of human monocytes, hence its original name. The carboxyl-terminal end group Cys-Asn-Ser is the pharmacophore of anti-inflammatory peptide Met-Gln-Cys-Asn-Ser. In this study, the N-terminal of Cys-Asn-Ser was modified. With the aim to enhance the antioxidant ability and penetrability of Cys-Asn-Ser, we designed and synthesized two tetrapeptides Tyr-Cys-Asn-Ser and His-Cys-Asn-Ser. The neuroprotective effects of Tyr-Cys-Asn-Ser and His-Cys-Asn-Ser on focal ischemia reperfusion were investigated, and their pharmacological activities compared with Cys-Asn-Ser were studied. In order to study the mechanism of neuroprotective effect of these peptides, the level of oxidative stress markers malondialdehyde (MDA) and superoxide dismutase (SOD) and pro-inflammatory factors interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), and myeloperoxidase (MPO) were detected in brain tissue homogenate.  相似文献   
146.
Archaea have evolved various strategies in chromosomal organization. While histone homologues exist in most archaeal phyla, Cren7 is a chromatin protein conserved in the Crenarchaeota. Here, we show that Cren7 preferentially binds DNA with AT‐rich sequences over that with GC‐rich sequences with a binding size of 6~7 bp. Structural studies of Cren7 in complex with either an 18‐bp or a 20‐bp double‐stranded DNA fragment reveal that Cren7 binds to the minor groove of DNA as monomers in a head‐to‐tail manner. The neighboring Cren7 monomers are located on the opposite sides of the DNA duplex, with each introducing a single‐step sharp kink by intercalation of the hydrophobic side chain of Leu28, bending the DNA into an S‐shape conformation. A structural model for the chromatin fiber folded by Cren7 was established and verified by the analysis of cross‐linked Cren7‐DNA complexes by atomic force microscopy. Our results suggest that Cren7 differs significantly from Sul7, another chromatin protein conserved among Sulfolobus species, in both DNA binding and deformation. These data shed significant light on the strategy of chromosomal DNA organization in crenarchaea.  相似文献   
147.
Although capsaicin has been studied extensively as an activator of the transient receptor potential vanilloid cation channel subtype 1 (TRPV1) channels in sensory neurons, little is known about its TRPV1-independent actions in gastrointestinal health and disease. Here, we aimed to investigate the pharmacological actions of capsaicin as a food additive and medication on intestinal ion transporters in mouse models of ulcerative colitis (UC). The short-circuit current (Isc) of the intestine from WT, TRPV1-, and TRPV4-KO mice were measured in Ussing chambers, and Ca2+ imaging was performed on small intestinal epithelial cells. We also performed Western blots, immunohistochemistry, and immunofluorescence on intestinal epithelial cells and on intestinal tissues following UC induction with dextran sodium sulfate. We found that capsaicin did not affect basal intestinal Isc but significantly inhibited carbachol- and caffeine-induced intestinal Isc in WT mice. Capsaicin similarly inhibited the intestinal Isc in TRPV1 KO mice, but this inhibition was absent in TRPV4 KO mice. We also determined that Ca2+ influx via TRPV4 was required for cholinergic signaling–mediated intestinal anion secretion, which was inhibited by capsaicin. Moreover, the glucose-induced jejunal Iscvia Na+/glucose cotransporter was suppressed by TRPV4 activation, which could be relieved by capsaicin. Capsaicin also stimulated ouabain- and amiloride-sensitive colonic Isc. Finally, we found that dietary capsaicin ameliorated the UC phenotype, suppressed hyperaction of TRPV4 channels, and rescued the reduced ouabain- and amiloride-sensitive Isc. We therefore conclude that capsaicin inhibits intestinal Cl- secretion and promotes Na+ absorption predominantly by blocking TRPV4 channels to exert its beneficial anti-colitic action.  相似文献   
148.
目的了解临床分离耐甲氧西林溶血性葡萄球菌(MRSH)的SCCmec基因型别及相同SCCmec型别菌株的同源性。方法多重PCR进行SCCmec分型,ERIC-PCR法对相同SCCmec型别菌株进行同源性分析。结果83株临床分离MRSH菌株中,SCCmecI型有23株(27.7%),SCCmecⅡ型有10株(12.1%),SCCmecm型有24株(28.9%),SCCmecIV型有1株(1.2%),I、Ⅱ混合型有8株(9.6%),I、Ⅲ混合型有6株(7.2%),Ⅱ、11混合型有5株(6.0%),I、Ⅱ、Ⅲ混合型有3株(3.6%),未分型3株(3.6%)。ERIC—PCR结果显示,23株SCCmecI型分为11型,其中A型5株,B型5株,C型3株,其余8株各为1型,2株未分型;10株SCCmecⅡ型分为6型,其中D型4株,E型2株,3株各为1型,1株未分型;24株SCCmecm型分为9型,其中F型11株,G型2株,H型2株,I型2株,5株各为1型,2株未分型。结论临床分离MRSH中,SCCmecI、Ⅲ型为多,部分菌株呈混合型别;相同SCCmec型别的部分菌株之间可能存在克隆传播。  相似文献   
149.
Adequate fluid secretion from airway mucosa is essential for maintaining mucociliary clearance, and fluid hypersecretion is a prominent feature of inflammatory airway diseases such as allergic rhinitis. House dust mite extract (HDM) has been reported to activate protease‐activated receptors (PARs), which play various roles in airway epithelia. However, the role of HDM in regulating ion transporters and fluid secretion has not been investigated. We examined the effect of HDM on ion transport in human primary nasal epithelial cells. The Ca2+‐sensitive dye Fura2‐AM was used to determine intracellular Ca2+ concentration ([Ca2+]i) by means of spectrofluorometry in human normal nasal epithelial cells (NHNE). Short‐circuit current (Isc) was measured using Ussing chambers. Fluid secretion from porcine airway mucosa was observed by optical measurement. HDM extract (10 µg/Ml) effectively cleaved the PAR‐2 peptide and induced an increase of [Ca2+]i that was abolished by desensitization with trypsin, but not with thrombin. Apical application of HDM‐induced Isc sensitive to both a cystic fibrosis transmembrane conductance regulator (CFTR) inhibitor and a Ca2+‐activated Cl? channel (CaCC) inhibitor. HDM extract also stimulated fluid secretion from porcine airway mucosa. HDM extract activated PAR‐2 and apical Cl? secretion via CaCC and CFTR, and HDM‐induced fluid secretion in porcine airway mucosa. Our results suggest a role for PAR‐2 in mucociliary clearance and fluid hypersecretion of airway mucosa in response to air‐borne allergens such as HDM. J. Cell. Biochem. 109: 1254–1263, 2010. © 2010 Wiley‐Liss, Inc.  相似文献   
150.
This study sought to determine whether invariant NKT (iNKT) cells play an essential role in inflammation-induced preterm delivery. Preterm delivery and fetal death rates were determined in wild-type (WT) C57BL/6 mice and iNKT cell-deficient Jα18(-/-) mice injected i.p. with LPS. The percentages of decidual immune cells, including activated subsets, and costimulatory molecule expression were analyzed by flow cytometry. Th1 and Th2 cytokine production in the culture supernatants of decidual mononuclear cells was measured by ELISA. To some extent, Jα18(-/-) mice were resistant to LPS-induced preterm delivery. The proportions of decidual CD3(+) and CD49b(+) cells were slightly lower in Jα18(-/-) mice than in WT Jα18(+/+) mice, whereas almost no CD3(+)CD49b(+) cells could be found in Jα18-null mice. The percentages of activated decidual DCs, T cells, and NK cells were significantly lower in LPS-treated Jα18(-/-) mice than in WT mice. The CD40, CD80, and CD86 expression levels on decidual CD11c(+) cells from Jα18(-/-) mice were also significantly lower than in WT mice. Mean concentrations of Th1 cytokines IFN-γ and IL-12p70 in the culture supernatants of decidual mononuclear cells from LPS-treated Jα18(-/-) mice were apparently lower than those of LPS-induced WT mice. Additionally, the proportions of activated CD11c(+) cells, CD3(+) cells, and CD49b(+) cells in LPS-induced preterm delivery mice were strikingly higher in both WT and null mice when compared with the control PBS group and LPS-injected but normally delivered mice. Our results suggest that iNKT cells may play an essential role in inflammation-induced preterm birth.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号