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   9564篇
  免费   820篇
  国内免费   551篇
耳鼻咽喉   40篇
儿科学   57篇
妇产科学   48篇
基础医学   1471篇
口腔科学   265篇
临床医学   538篇
内科学   1168篇
皮肤病学   274篇
神经病学   776篇
特种医学   133篇
外国民族医学   1篇
外科学   515篇
综合类   1279篇
现状与发展   2篇
预防医学   546篇
眼科学   182篇
药学   1898篇
  2篇
中国医学   1250篇
肿瘤学   490篇
  2024年   45篇
  2023年   254篇
  2022年   381篇
  2021年   485篇
  2020年   436篇
  2019年   335篇
  2018年   378篇
  2017年   327篇
  2016年   342篇
  2015年   359篇
  2014年   549篇
  2013年   639篇
  2012年   651篇
  2011年   627篇
  2010年   555篇
  2009年   460篇
  2008年   454篇
  2007年   448篇
  2006年   455篇
  2005年   415篇
  2004年   370篇
  2003年   297篇
  2002年   219篇
  2001年   189篇
  2000年   144篇
  1999年   141篇
  1998年   137篇
  1997年   96篇
  1996年   120篇
  1995年   78篇
  1994年   59篇
  1993年   62篇
  1992年   58篇
  1991年   53篇
  1990年   39篇
  1989年   31篇
  1988年   21篇
  1987年   15篇
  1986年   21篇
  1985年   41篇
  1984年   23篇
  1983年   22篇
  1982年   24篇
  1981年   19篇
  1980年   19篇
  1979年   9篇
  1978年   7篇
  1977年   9篇
  1976年   9篇
  1972年   2篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
The purpose of this study was to investigate the developmental potential of isolated rabbit blastomeres under various culture conditions to gain insight into their ability to form the two cell lineages of a viable blastocyst. Intact embryos at the 4-cell, 8-cell, 16-cell stages and blastomeres isolated from 4-, 8- and 16-cell rabbit embryos (1/4, 1/8 or 1/16 blastomeres respectively) were cultured in drops of one of three different media, each supplemented with either fetal calf serum (FCS), bovine serum albumin (BSA) or polyvinyl alcohol (PVA). The effects of the extracellular matrix fibronectin (FN) on the development of isolated rabbit blastomeres were also investigated. Supplementation of the medium with FCS yielded a higher (P < 0.05) proportion of blastocysts than BSA or PVA, predominantly from 1/4 blastomeres. No major differences were found between the three basic culture media. In 1/4, 1/8 or 1/16 blastomeres, blastocyst formation rates were greater (P < 0.05) in groups cultured in matrix-free (54.5, 59.6 and 54.6% respectively) than in FN-coated groups (35.4, 46.0 and 26.1% respectively). Only in blastocysts derived from 1/4 blastomeres, were the numbers of inner cell mass (ICM) and total cells of blastocysts higher (P < 0.05) in FN-coated groups than in matrix-free groups (12.7 +/- 1.1 versus 8.5 +/- 0.7 ICM, 73.8 +/- 3. 7 versus 57.8 +/- 3.3 total cells). The percentage of blastocysts derived from single blastomeres with ICM cells decreased with increasing cell stage of the parent embryos in FN-coated (93.6, 78.3 and 44.0%, respectively) as well as matrix-free groups (96.2, 69.3 and 55.2%). In FN-coated groups, after 96 h (1/4) or 72 h (1/8 and 1/16) of culture, approximately 20-30% of blastomeres did not develop into normal blastocysts but formed sheets with 30-50 cells attached to the bottom of the dishes. These results indicate that the development of rabbit blastomeres shares important characteristics with those from mouse and domestic species and may thus aid in developing an efficient culture system for blastomeres, derived from human embryos.  相似文献   
22.
Two unrelated adult sibling cases (36- and 32-year-old females) of Juvenile hyaline fibromatosis are presented. The parents of one of these patients were non-consanguineous but natives of a small Island, and one elder sister among four siblings was affected with the same disease. The parents of the other patient were consanguineous, and one other sibling suffered from the identical disease. Both patients presented with multiple subcutaneous nodules, which they had had since infancy, and had undergone numerous surgical excisions. Light microscopy examination of skin lesions from both patients showed identical histology; an abundance of a homogenous, amorphous, eosinophlllc extracellular matrix in which spindle-shaped cells were embedded. Electron microscopically, the spindle-shaped cells had hypertrophic Golgi apparatus and dilated, rough endoplasmlc reticulum. Fine flbrillar and granular material-filled structures, the contents of which were occasionally released into the extracellular matrix, were also seen, immunohistochemically, the spindle-shaped cells were vlmentin-positive but negative for α-smooth muscle actln and S-100 protein, and the hyaline ground substance was positive for type I and type III collagen but negative for type II and type IV collagen and tenascin. Matrix metalloprotelnase-1, -2, and -9, and tissue inhibitor of matrix metalloproteinase (TlMP)-2 was positive but TIMP-1 was negative. A review of 39 cases of juvenile hyaline fibromatosis In the literature is also presented. In summary, skin lesions may be the most outstanding symptoms of juvenile hyaline fibromatosis, but joint contracture and gingival hypertrophy precede the skin manifestation.  相似文献   
23.
Patients with chronic mucocutaneous candidiasis (CMC) succumb to persistent infections with the opportunistic yeast Candida. Impaired cell-mediated responses to Candida have been repeatedly reported while antibody responses were mostly found to be normal. The underlying defect remains poorly understood. It has recently been shown that CMC patients are also susceptible to infections with encapsulated bacteria, and may have associated IgG2 and IgG4 deficiency. Our previous studies demonstrated altered cytokine production in CMC patients. As cytokines can influence production and isotype of specific antibody, in 10 patients with CMC we measured the levels and isotype distributions of serum antibodies to Candida antigens (CAg), pneumococcal polysaccharide (PPS) and tetanus toxoid (TT) antigens. Peripheral blood lymphocytes were also stimulated in culture and the antibodies made in vitro were measured. Our data demonstrated that in vivo, CMC patients had very high levels of IgG and IgA CAg-specific antibodies. CAg-specific and PPS-specific IgG1 was markedly higher than in controls. Children but not adults with CMC had significantly lower levels of IgG2-specific antibody to CAg and PPS compared with age-matched controls. Patients had significantly higher levels of IgG3-specific antibody to all three antigens tested. These findings were in accordance with increased total IgG and IgG3 levels seen in CMC patients. In vitro, CMC patients, particularly children, did not respond as frequently to antigen stimulation as did their healthy controls. The level of specific antibody produced was also lower to all antigens tested, as was the amount of total immunoglobulins following antigenic and particularly mitogenic stimulation. Addition of interferon-alpha (IFN-α) or IFN-γ to cultures had variable, sometimes marked, effects. Our results demonstrate that CMC patients manifest subtle alterations in specific antibody responses to CAg, PPS and TT, which are most pronounced in children. This may relate to altered cytokine production also seen in these patients.  相似文献   
24.
Extracellular levels of striatal gamma-aminobutyric acid (GABA) and taurine were monitored during insulin-induced hypoglycemia using microdialysis. At the onset of isoelectricity in the electroencephalogram (EEG), a transient 5-fold increase in the levels of GABA occurred. Taurine levels increased 5 min following the onset of isoelectricity and continued to increase during the entire isoelectric period. The results demonstrate that events associated with the onset of isoelectricity during hypoglycemia trigger an increase in extracellular concentrations of GABA and taurine. The discrepancy in time-course of these changes may reflect differences in compartmentation, function and metabolism of the two amino acids.  相似文献   
25.
高山红景天多糖对小鼠抗柯萨奇B5病毒感染能力的研究   总被引:11,自引:0,他引:11  
对感染柯萨奇B5病毒(CVB)小鼠模型研究结果表明,高山红景天多糖对发病小鼠心肌功能改善和免疫功能提高均具有明显的促进作用。增强了小鼠抗CVB5感染的能力,并对由CBV感染性疾病也有一定的防治作用。  相似文献   
26.
目的比较不同细胞外基质(ECM)及其共同基质受体在大鼠胚胎心脏中的表达规律,探讨ECM在胚胎期心脏发生、发育过程中的作用。方法将胎龄天数(ED)为11~19d的胚鼠用酶免疫组织化学染色检测ECM中的FN、LMN、Vn、CoⅣ及其受体β1在胚胎心脏中的表达。结果①ECM及其受体在胚胎各期心脏的空间性分布各不相同,FN及LMN有明显的空间分布互补关系,β1的空间分布主要与FN相似,但在空间隔及心外膜中又与LMN相似;②FN、LMN及β1在不同心脏部位的表达高峰及持续时间各不相同,β1的表达高峰要早于FN及LMN。结论ECM(主要是FN与LMN)及其受体β1在胚胎心脏的发生发育中起着一定的介导作用,其作用的时期、部位及作用机制各不相同。  相似文献   
27.
茯苓多糖颗粒剂的研制及质量检测   总被引:1,自引:0,他引:1  
以提取的茯苓多糖为主要原料,制成颗粒剂保健品,并拟定质检项目其进行定性、定量检测。工艺简单易行,具有较好的治疗、保健功效。  相似文献   
28.
Seprase is a serine protease that is integral to the plasma membrane and is overexpressed by invasive tumor cells (Piñeiro-Sánchez et al., J Biol Chem 1997; 272: 7595–601; Monsky et al., Cancer Res 1994; 54: 5702–10). Seprase activity is most often assessed by zymography, which is not a quantitative assay. This study establishes a relatively simple and quantitative method for determining seprase activity. The degradation of a 3H-gelatin substrate is measured in the presence of 5 mM EDTA which inhibits matrix metalloproteinases but not seprase. The quantitative character of the assay was demonstrated using partially purified seprase from chicken embryos, a preparation that lacks detectable matrix metalloproteinase activity. In this assay, release of 3H-gelatin fragments is linear over time for 1.5 g/assay seprase concentration as well as for preparations concentrated or diluted by five fold (7.5 g/assay and 0.3 g/assay respectively). Additional experiments were performed to validate the quantification of seprase activity using the radiographic assay by comparing the results to zymography. Exposure to 22 or 37°C results in maximal seprase activity while exposure to 80 or 100°C completely abolishes seprase activity in both zymography and the radiographic assay. Exposure to 60°C abolished seprase activity as judged by zymography, but about 50% gelatinase activity was observed using the 3H-gelatin substrate. Immunopreciptiation with seprase-specific antibody specifically removed seprase and lowered the seprase activity remaining in the extracts as judged by both assays. Investigation of the seprase that was partially purified from human breast cancer tissue revealed that its specific activity (cpm gelatin fragments released/ {mg protein×h}) is five times greater than that of seprase purified from chicken embryos. This assay will be useful for determining the seprase activity in extracts of tumor tissues and cells as well as for identifying inhibitors of seprase.  相似文献   
29.
目的:探索枸杞多糖(LBP)是否有抗脂质过氧化作用。方法:建立密闭缺氧的急性缺氧模式,采用NBT测定SOD活性、TBA测定MDA含量。结果:实验组与对照组织MDA含量有显著性差别,其余组织SOD、MDA虽无显著性差异,但实验组均有SOD活性升高,MDA含是下降的趋势。结论:LBP具有抗脂质过氧化作用的倾向。  相似文献   
30.
从我国沿海红灌中撮的粗多糖,经DEAE-纤维素柱层析得到红藻多糖RP1实验证实有明显抗病毒作用。通过气相色谱、红外光谱、Yaphe测定方法,证明红藻多糖RP1含硫酸基是一种硫酸酯化多糖,其单糖组成为半乳糖和3,6-内醚半乳糖,定量分析含量分别为半乳糖70.04%、3,6-内醚半乳糖9.56%1硫酸基17.30%。  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