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   30579篇
  免费   1724篇
  国内免费   1303篇
耳鼻咽喉   116篇
儿科学   458篇
妇产科学   128篇
基础医学   3365篇
口腔科学   584篇
临床医学   1969篇
内科学   3279篇
皮肤病学   542篇
神经病学   1600篇
特种医学   772篇
外国民族医学   1篇
外科学   1677篇
综合类   3595篇
现状与发展   2篇
预防医学   1574篇
眼科学   422篇
药学   10255篇
  25篇
中国医学   2492篇
肿瘤学   750篇
  2023年   260篇
  2022年   591篇
  2021年   823篇
  2020年   700篇
  2019年   607篇
  2018年   611篇
  2017年   657篇
  2016年   725篇
  2015年   724篇
  2014年   1514篇
  2013年   1816篇
  2012年   1581篇
  2011年   1634篇
  2010年   1359篇
  2009年   1143篇
  2008年   1168篇
  2007年   1217篇
  2006年   1129篇
  2005年   1531篇
  2004年   1540篇
  2003年   1151篇
  2002年   711篇
  2001年   643篇
  2000年   519篇
  1999年   505篇
  1998年   449篇
  1997年   452篇
  1996年   513篇
  1995年   575篇
  1994年   540篇
  1993年   525篇
  1992年   459篇
  1991年   442篇
  1990年   357篇
  1989年   377篇
  1988年   357篇
  1987年   297篇
  1986年   291篇
  1985年   448篇
  1984年   355篇
  1983年   221篇
  1982年   318篇
  1981年   295篇
  1980年   239篇
  1979年   196篇
  1978年   169篇
  1977年   140篇
  1976年   153篇
  1975年   97篇
  1973年   102篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
We have studied the mortality between 1950 and 1980 of a cohort of 1,143 workers in an electrochemical plant producing cobalt and sodium. The mortality of the whole cohort is significantly lower than in the French population for all causes of death (SMR = 0.77), and especially for deaths from circulatory system diseases (SMR = 0.59). However, among cobalt production workers, there is a relative over-mortality, especially from lung cancers (SMR = 4.66, 4 cases). The relationship between cobalt production and lung cancer mortality was supported by a case-control study nested in the cohort study. The authenticity of the occupational origin of this risk could not be established due to the low number of cases and because the role of tobacco consumption could not be taken into account. Other studies should be carried out in plants producing or using cobalt.  相似文献   
62.
目的:观察力竭运动前后大鼠脑中海马谷氨酸受体NR2A蛋白含量和基因表达的变化,探讨其与运动性疲劳的可能联系。方法:50只SD雄性大鼠,随机分为安静对照组(S,n=10),力竭运动后即刻组(AE1,n=10),力竭运动后恢复0.5小时组(AE2,n=10),力竭运动后恢复3小时组(AE3,n=10)和力竭运动后恢复24小时组(AE4,n=10)。分别采用免疫印迹法和RT-PCR法测定一次性力竭运动后大鼠脑中海马谷氨酸受体NR2A蛋白含量和基因表达。结果:与安静对照组相比,力竭运动后即刻,大鼠NR2A蛋白含量明显升高,而mRNA表达显著减少;恢复0.5小时后,蛋白含量略有下降,mRNA表达显著增加;恢复3小时后蛋白含量显著下降,mRNA表达继续增加;恢复24小时后蛋白含量恢复到安静时水平,mRNA表达则减少至恢复0.5小时后水平。结论:力竭运动后即刻及恢复过程中,大鼠脑中海马谷氨酸受体NR2A蛋白含量及mRNA表达变化趋势不同,提示基因表达对蛋白含量的调控可能具有延迟性。  相似文献   
63.
根据蓝四氮唑与泼尼松生成蓝色产物,并于525nm 波长处测定吸光度。测定条件为:反应管长度为3.8m(0.5mm id);流速为1.6ml/min;反应温度为55±0.5℃;注射样品溶液为100μl;本测定系统的测定速度可达100次/h;线性范围可达0.09mg/ml;检测限量为1.54μg/ml;测定结果的变异系数小于1%。  相似文献   
64.
65.
2%HPMC对兔眼内压及角膜内皮影响的实验研究   总被引:5,自引:0,他引:5  
杨惠英  窦宏亮 《眼科研究》1992,10(3):164-166
报导了2%羟丙基甲基纤维素(HPMC)、1%透明质酸钠(Na-HA)及平衡盐液(BSS)分别注入兔眼前房后,其眼内压、角膜内皮细胞数及内皮细胞形态的变化。证实自制2%HPMC 与进口1%Na-HA 性能基本相同,仅有一过性眼压升高,不损害角膜内皮,能在眼前节手术及人工晶体植入时有效地保护角膜内皮细胞。  相似文献   
66.
Summary: The present studies assessed the effects of manipulating extracellular sodium (Na) concentration and Na transport on cellular hypertrophy and hyperplasia in primary culture of rat proximal tubular cells. A concentration-dependent effect on thymidine incorporation and protein content was observed with cell culture media Na concentration of 130, 140 and 150 mmol/L. This effect was independent of osmolality (matched with mannitol) and no stimulatory effect occurred if choline was substituted for Na. Cells derived from sham-operated (Sx) animals exposed to a higher media concentration of Na (150 vs 140 mmol/L) had both stimulated thymidine incorporation to 186.8 ± 35.41% (P<0.05) and enhanced cell protein content to 134.7 ± 135% (P<0.05). This effect was more pronounced in cell cultures derived from unilaterally nephrectomized (Nx) animals, being 212.8 ± 31.5% (P<0.01) for thymidine incorporation (P<0.05 vs cells from sham-operated animals grown in high Na media) and 114.4 ± 3.2% (P<0.001) for protein content (P=0.11 vs sham-operated cells grown in similar conditions). the addition of 10?4 mmol/L ethylisopropyl amiloride hydrochloride (EIPA) to Nx cells in a normal or high Na concentration media resulted in a decrease in cellular protein content to 82.6 ± 6.8% (P<0.05) and 85.5 ± 0.2% (P<0.0001) compared to respective controls. 10?4 mol/L EIPA in media supplemented with insulin-like growth factor (IGF-1) blocked the proliferative response normally seen in response to this growth factor from 156.6 ± 13.7 to 27.5 ± 3.1% (P<0.0001) compared to control. However, the presence of EIPA did not abrogate the hypertrophic response elicited by IGF-1 (cell protein content 128.1 ± 13.1% of control with IGF-1 vs 124.9 ± 12.5 with IGF-1 and EIPA; P= n.s.). Addition of 10?4 mol/L EIPA to 10% serum derived from either Sx or Nx animals blocked the growth response to the sera, limiting the cellular protein content to 76.6 ± 5.5% (P<0.0001) and 89.7 ± 4.4% (P<0.0001) and thymidine incorporation to quiescent levels of 0.2 ± 0.1% (P<0.0001) and 0.4 ± 0.1% (P<0.0001) compared to respective controls. In summary, rat renal proximal tubular cell growth is influenced by Na concentrations in the cell culture environment and inhibited in the presence of EIPA. This supports a role for altered epithelial transport in the cellular growth response to a number of stimuli.  相似文献   
67.
68.
目的 用高效液相色谱法(HPLC法)测定去氧氟尿苷的含量及其有关物质。方法 采用Diamonsil C—粒(250mm×4.6mm,5μm),流动相为乙腈-水(1:1),检测波长为269nm,流速为0.8mL/min。结果 去氧氟尿苷质量浓度在10.0~200.4μg/mL范围内与峰面积线性关系良好,r:0.9999(n:5),平均回收率为100.2%,RSD=0.14%。结论 HPLC法简便、准确,专属性好,灵敏度高,可用于去氧氟尿苷含量及有关物质的测定。  相似文献   
69.
Current clinical staging, which includes the use of serum tumor markers and imaging techniques, fails to identify the 30–40% of clinical stage I (CS I) nonseminomatous germ cell testicular tumor (NSGCT) patients who have occult metastatic disease. Therefore, there is a real clinical need to evaluate new biological parameters of the primary tumor that might be useful as predictors of occult metastatic disease. This study was undertaken to compare quantitative DNA measurements by flow cytometry and image analysis in CS I NSGCT, and to analyze the relevance of these parameters for predicting occult lymph node involvement. Different blocks of formalin-fixed, paraffin-embedded NSGCTs of 62 CS I patients who underwent retroperitoneal lymph node dissection between 1985 and 1989 were prepared according to the Hedley technique, and analyzed by quantitative cytometry. Thirty-six (58.1%) patients had histologically proven lymph node involvement (pathological stage II), whereas 26 (41.9%) patients (pathological stage I) had neither lymph node metastases according to retroperitoneal lymph node dissection (RPLND) specimens nor tumor recurrence during follow-up. Concordant results were found in 76.5% of the samples by both cytometric techniques. For flow cytometry, the percentages of aneuploid cells in the S- and the G2M+S-phase were the most robust predictive parameters for lymph node involvement, whereas for image analysis the 5c exceeding rate (5cER) had the most predictive significance. Based on the experience obtained in this study, both cytometric techniques provide additional information on tumor aggressiveness that might be useful in therapeutic selection of early stage NSGCT patients for either RPLND or surveillance only.  相似文献   
70.
乳腺囊性增生病癌变过程中部分因素变化的意义   总被引:3,自引:0,他引:3  
检测乳腺囊性增生病(FCD)经不典型增生到癌变部分因素的变化。结果提示:从因明显FCD症状活检至癌变为2~10年;从Ⅱ级以上不典型增生到临床癌变需2~7年;癌变率为3.1%。FCD患者存在性激素分泌调控失常,血浆雌激素和催乳素含量增加,导致上皮细胞增生。乳腺一般性增生细胞的DNA含量和超微结构与正常乳腺上皮细胞相似;无肿瘤相关抗原及异常基因产物表达。而发生在一般性增生基础上的不典型增生则呈现细胞基因物质DNA含量增加,部分为超4C的多倍体细胞;同时出现细胞膜和细胞核超微结构异常;雌激素受体含量增加,对性激素的依赖性和敏感性增强;部分不典型增生细胞出现胚胎性肿瘤相关抗原和异常基因产物表达。随不典型增生程度加重至乳腺癌,上述诸因素的变化趋势具有明显规律性。提示FCD上皮细胞从一般性增生经不典型增生至乳腺癌为细胞生物学连续逐渐变化的过程。部分不典型增生细胞中具有癌倾向的细胞生物学行为异常和表型变化与乳腺癌发生密切相关。细胞核DNA含量等异常变化及程度可作为乳腺癌前病变发展程度的客观标志  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