全文获取类型
收费全文 | 21930篇 |
免费 | 1829篇 |
国内免费 | 3034篇 |
出版年
2024年 | 72篇 |
2023年 | 338篇 |
2022年 | 738篇 |
2021年 | 1227篇 |
2020年 | 873篇 |
2019年 | 1101篇 |
2018年 | 925篇 |
2017年 | 750篇 |
2016年 | 1012篇 |
2015年 | 1435篇 |
2014年 | 1686篇 |
2013年 | 1704篇 |
2012年 | 2021篇 |
2011年 | 1845篇 |
2010年 | 1167篇 |
2009年 | 1074篇 |
2008年 | 1223篇 |
2007年 | 1030篇 |
2006年 | 939篇 |
2005年 | 747篇 |
2004年 | 657篇 |
2003年 | 599篇 |
2002年 | 519篇 |
2001年 | 496篇 |
2000年 | 446篇 |
1999年 | 376篇 |
1998年 | 234篇 |
1997年 | 215篇 |
1996年 | 194篇 |
1995年 | 174篇 |
1994年 | 129篇 |
1993年 | 118篇 |
1992年 | 142篇 |
1991年 | 114篇 |
1990年 | 99篇 |
1989年 | 62篇 |
1988年 | 51篇 |
1987年 | 53篇 |
1986年 | 26篇 |
1985年 | 32篇 |
1984年 | 18篇 |
1983年 | 25篇 |
1982年 | 10篇 |
1958年 | 8篇 |
1957年 | 6篇 |
1955年 | 8篇 |
1953年 | 12篇 |
1950年 | 5篇 |
1949年 | 6篇 |
1948年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
991.
目的:探讨不同的诊断标准的妊娠期糖尿病的妊娠结局。方法:回顾性分析我院2001-2004年产前检查并分娩,无显性糖尿病及其他内分泌疾病的单胎孕妇共337例,按糖尿痛不同的诊断标准分成三组进行比较:干预组78例(OGTT(oral glucose toler- ante test)血糖值达到妊娠期糖尿病诊断标准,予饮食调整、运动指导,和或胰岛素治疗);未干预组91例(OGTT值小于妊娠期糖尿病诊断标准,但第2小时血糖≥7.8mmol/L,一般产科检查,无相应血糖的检测与治疗);对照组168例(OGTT正常,且第2小时血糖<7.8mmol/L一般产科检查)。结果:未干预组在巨大胎与干预组及对照组间有显著差异。干预组在妊娠周数与对照组及未干预组之间有差异。三组在年龄、分娩前体重指数、分娩方式等方面无显著差异。结论:未干预糖尿病组与巨大胎有关。建议诊断妊娠期糖尿病标准采用空腹血糖≥5.8mmol/L和或75克糖耐量试验2小时血糖≥7.8mmol/L。 相似文献
992.
太空诱变玉米核不育材料花粉败育的细胞学观察(简报) 总被引:1,自引:0,他引:1
玉米是最早利用雄性不育系生产杂交种的作物之一。在玉米T型细胞质雄性不育杂交种遭受毁灭性病害侵袭之后,科学家认识到利用细胞质雄性不育制种存在潜在的遗传脆弱性,从此试图通过多种途径来创造新的雄性不育.并对雄性不育材料的遗传多样性进行研究。空间诱变育种是80年代于我国发展起来的新技术,在农作物品种改良和种质创新上已初见成效。[第一段] 相似文献
993.
环孢素A对人早孕期滋养细胞MMP-9与MMP-2表达的调控作用 总被引:1,自引:0,他引:1
本研究的目的是探讨环孢素A对人早孕期滋养细胞侵袭能力及基质金属蛋白酶9与2 (matrix metalloproteinase 9 and 2,简称MMP-9与MMP-2)表达的调节作用,为治疗反复自然流产等妊娠疾患提供新的线索。侵袭试验观察CsA对人早孕期滋养细胞侵袭能力的调节作用;RT-PCR与明胶酶谱分析CsA对滋养细胞MMP-9与MMP-2 mRNA及蛋白水平表达的影响;In-cell West- ern检测CsA作用后滋养细胞ERK1/2磷酸化水平。结果发现,1.0μmol/L CsA明显增强滋养细胞侵袭能力,MEK激酶抑制剂U0126可抑制CsA对滋养细胞的促侵袭作用;1.0μmol/L CsA可诱导MMP- 9与MMP-2基因的转录与蛋白分泌;该诱导效应同样可被U0126所阻滞;1.0μmol/L CsA以时间依赖方式促进ERK1/2的磷酸化。结果表明,CsA可激活ERK1/2,通过MAPK/ERK1/2途径促进滋养细胞MMP-9与MMP-2基因的转录与蛋白分泌,从而增强滋养细胞的侵袭能力,对滋养细胞生物学功能具有良性调节作用。 相似文献
994.
995.
In the attempt to discover new genes involved in the floral development in monoeotyledonousin species,we have cloned and characterized the homologous PISTALLATA-like (PI-like) gone from Phalaenopsis hybrid cultivar named PhPI9 (Phalaenopsis PI STILLATA # 9).The eDNA of PhPI9 has a fragment of 834 bp and has 60% identity with the PISTILATA from Arabidopsis.The deduced amino acid sequence of PhPI9 had the typical PI-motif.It also formed a subelade with other monoeot PI-type genes in phylogenetie analysis.Southern analysis showed that PhPI9 was present in the Phalaenopsis orchid genome as a single copy.Furthermore,it was expressed only in the lip of the Phalaenopsis flower and no expression was detected in vegetative organs.Thus,as a B-function MADS-box gone,PhP19 specifies floral organ identity in orchids. 相似文献
996.
This study identified mutations of the idumate-2-suffatase (IDS) gene in a patient with Hunter syndrome,and established a basis for the diagnosis of the prenatal gene of Hunter syndrome.Urine glyeosaminoglycan (GAG) assay was used to make the preliminary diagnosis of mucopolysaccharidosis type H.Polymerase chain reaction (PCR) from dried blood spots and DNA sequencing were applied to analyze hotspot mutations in exons 9,3 and 8 of the IDS gene in the proband and his parents.A new missense mutation (T1140C) in exon 8 of the IDS gene was found by using DNA sequencing.This mutation caused a substitution of codon 339 from CTA (leucine) to CCA (praline).The patient is a hemizygote,and his mother is a heterozygote.The new missense mutation results in a change in the primary and tertiary structure of the IDS protein.It is possible that this mutation severely impairs enzymatic activity and is the underlying basis for the pathology seen in this patient with Hunter syndrome. 相似文献
997.
Lai X Zhao Y Liang H Bai Y Wang B Guo D 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2007,852(1-2):108-114
A SPE-HPLC method was developed and validated for the simultaneous determination of flavonols, isoquercitrin (1), hibifolin (2), myricetin (3), quercetin-3'-O-d-glucoside (4) and quercetin (5) in rat plasma and urine after oral administration of the total flavonoids from Abelmoschus manihot (TFA). The astragalin (6) and kaempferol (7) were used as internal standards (IS). Plasma and urine samples were pretreated by solid-phase extraction using Winchem C(18) reversed-phase cartridges. Analysis of the plasma and urinary extract was performed on YMC-Pack ODS-A C(18) and Thermo ODS-2HYEPRSIL C(18) reversed-phase column, respectively and a mobile phase of acetonitrile-0.1% phosphoric acid was employed. HPLC analysis was conducted with different elution gradients. The flow rate was 1.0 mL/min and the detection wavelength was set at 370 nm. Calibration ranges in plasma for flavonols 2-5 were at 0.011-2.220, 0.014-2.856, 0.022-4.320, and 0.028-5.600 microg/mL, respectively. In urine calibration ranges for flavonols 1, 2, 4 and 5 were at 2.00-16.00, 8.56-102.72, 2.70-21.60, and 3.00-24.00 microg/mL, respectively. The RSD of intra- and inter-day was less than 5.40% and 4.89% in plasma, and less than 3.96% and 6.85% in urine for all the analyses. A preliminary experiment to investigate the plasma concentration and urinary excretion of the flavonols after oral administration of TFA to rats demonstrated that the present method was suitable for determining the flavonols in rat plasma and urine. 相似文献
998.
Han J Ye M Xu M Sun J Wang B Guo D 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2007,848(2):355-362
The root of Scutellaria baicalensis, called Huangqin in Chinese, is one of the most commonly used traditional Chinese medicines for the treatment of hepatitis, tumors, diarrhea, and inflammatory diseases. The major chemical constituents of Huangqin are flavonoids. In the present paper, HPLC-DAD-ESI-MS(n) was used to analyze flavonoids in the roots of S. baicalensis. A total of 26 flavonoids were identified or tentatively characterized, including 5 C-glycosides, 12 O-glycosides, and 9 free aglycones. Two C-glycosides, apigenin-6-C-glucyl-8-C-arabinoside and chrysin-6,8-di-C-glucoside, together with some O-glycosides, are reported from S. baicalensis for the first time. This method is simple, reliable and sensitive, and could be used for the quality control of Huangqin and its related preparations. 相似文献
999.
Many diseases of the mammalian CNS, including Parkinson's (PD) and Lesch Nyhan disease (LND), are associated with programmatic neurodegeneration or dysfunction of dopaminergic neurons in the mesencephalon, the nigrostriatal pathway, and its projections in the striatum [1-4]. Proteomic studies on brain tissue of both animal models and human PD patients have provided evidence for dysfunction and damage of many pathways, including oxidative stress-related damage, ubiquitin-proteasome dysfunction, mitochondrial energy metabolism deficiencies, and synaptic function [5-11]. To date no such proteomic studies have been reported in the related and rare basal ganglia disorder LND, a developmental rather than a neurodegenerative neurological disorder caused by deficiency of the enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT) that regulates a major step in the purine salvage pathway [12]. Many studies have demonstrated that the both human LND patients and a mouse knockout model of HPRT deficiency have significantly reduced levels and uptake of dopamine in the striatum [4, 13-16] that is likely to be the principal cause of the CNS disorder. The precise molecular and cellular mechanisms that underlie this neurotransmitter defect are unknown. 相似文献
1000.
小麦胚芽鞘扩展蛋白特性及对水分胁迫的响应 总被引:3,自引:0,他引:3
扩展蛋白是植物细胞壁延伸过程中的关键调节因子,在植物的生长发育以及对逆境的响应过程中起着重要作用。本文选用小麦(HF 9703)胚芽鞘为材料,采用Hepes法和SDS法分别提取小麦胚芽鞘扩展蛋白,通过改良的植物组织伸长测定仪测定其活性,并利用扩展蛋白抗体进行免疫印迹以检测其丰度,主要研究了小麦胚芽鞘扩展蛋白的特性及对水分胁迫的响应。结果表明:Hepes法提取的扩展蛋白活性较高,而SDS法的提取效率高;离体小麦胚芽鞘扩展蛋白的活性具有pH依赖性,且随缓冲液的交替更换(pH 4.5:pH 6.8)而反复逆转;扩展蛋白主要定位于细胞壁中;小麦胚芽鞘扩展蛋白和黄瓜下胚轴扩展蛋白具有交叉重组活性,但这种活性具有种属特异性。水分胁迫诱导小麦胚芽鞘扩展蛋白的活性和丰度提高,扩展蛋白活性的提高在小麦对水分胁迫的抗性方面可能具有重要作用。 相似文献