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   126318篇
  免费   10731篇
  国内免费   8173篇
耳鼻咽喉   1019篇
儿科学   1567篇
妇产科学   2325篇
基础医学   14819篇
口腔科学   2062篇
临床医学   16433篇
内科学   20695篇
皮肤病学   1450篇
神经病学   6882篇
特种医学   4306篇
外国民族医学   70篇
外科学   13118篇
综合类   18968篇
现状与发展   24篇
一般理论   5篇
预防医学   7813篇
眼科学   3653篇
药学   12803篇
  115篇
中国医学   6047篇
肿瘤学   11048篇
  2024年   348篇
  2023年   1837篇
  2022年   4681篇
  2021年   5890篇
  2020年   4235篇
  2019年   4069篇
  2018年   4132篇
  2017年   3695篇
  2016年   3467篇
  2015年   5219篇
  2014年   6543篇
  2013年   6104篇
  2012年   8915篇
  2011年   9771篇
  2010年   5950篇
  2009年   4747篇
  2008年   6517篇
  2007年   6497篇
  2006年   6546篇
  2005年   6481篇
  2004年   4462篇
  2003年   4216篇
  2002年   3563篇
  2001年   3223篇
  2000年   3313篇
  1999年   3452篇
  1998年   2245篇
  1997年   2171篇
  1996年   1566篇
  1995年   1457篇
  1994年   1269篇
  1993年   824篇
  1992年   1229篇
  1991年   1077篇
  1990年   932篇
  1989年   823篇
  1988年   712篇
  1987年   668篇
  1986年   509篇
  1985年   463篇
  1984年   249篇
  1983年   178篇
  1982年   118篇
  1981年   116篇
  1980年   76篇
  1979年   120篇
  1978年   59篇
  1976年   52篇
  1975年   55篇
  1974年   65篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
本文采用SDS—PAGE法,测定7例健康育龄男子在肌肉注射十一酸睾酮(TU)前,用药后l、2、3个月及停药后精子计数恢复正常时的精浆蛋白浓度和组份变化,并结合血清测定激素水平及常规精液分析,以探讨TU对上述指标的影响及其相互关系。结果显示:用药早期精浆总蛋白浓度开始逐步降低,在停药后精子计数恢复正常时仍未达到正常水平。精浆总蛋白浓度的变化与精子活动率、前向运动率及LH呈正相关(r值分别为0.8975、0.7776、0.6406,P<0.01或0.05)。精浆蛋白组份也发生变化,其中51KD、37KD的蛋白条带变化最为明显,其变化除与精子活动率相关外(r=0.9094,P<0.01),其中51KD蛋白条带的变化还与精子前向运动率相关(r=0.7660,P<0.05)。上述结果提示TU可能在抑制生精之前即通过改变精浆蛋白而影响精子的功能,说明单用睾酮(T)的避孕机理是多因素的。  相似文献   
952.
Kremer试验与伊红Y水试验在精子功能检查中的意义   总被引:1,自引:0,他引:1  
本文比较作为精子功能检查的Kremer试验与伊红Y水试验的临床意义。以Kremer试验精子穿透CM高度分组,I组精子穿透高度<2.0cm/30min,Ⅱ组精子穿透高度2.0~3.9cm/30min,Ⅲ组精子穿透高度≥4.0cm/30min。伊红Y水试验Ⅰ组精子头部未着色同时尾部膨胀率为16.2±12.6%,Ⅱ组43.1±11.1%,Ⅲ组56.9±8.5%,Kremer试验与精液常规检查,Ⅰ组与Ⅱ、Ⅲ组比较均有非常显著差异,Ⅱ组与Ⅲ组比较只伊红Y水试验有非常显著差异,显示Kremer试验与伊红Y水试验临床意义的区别。两种方法各自在不同角度反映精子的功能状态。作为精子功能检查都具有方法简便、经济、结果有临床意义的优点,均可作为临床检查的常规手段。  相似文献   
953.
目的了解集体儿童蛲虫感染的情况,以利采取相应的防治措施,加强幼托机构的卫生保健管理。方法对8所幼托机构503例儿童进行蛲虫感染抽样调查,采用玻片粘胶纸粘取肛周物在显微镜下找蛲虫卵的方法。结果集体儿童蛲虫感染率为8.35%,男女儿童感染率无差异(P>0.05)。儿童蛲虫感染率4~6岁组明显高于0~3岁组(P<0.005),私立所明显高于其他幼托园所(P<0.005),全托制所明显高于日托制所。42例蛲虫感染儿童中,20人有不良卫生习惯,18人有明显的症状。结论根治蛲虫感染重在预防,要广泛开展卫生宣教,使家庭和幼托机构都要重视培养儿童良好的卫生习惯,同时要加强对幼托机构的卫生保健管理,定期对儿童和保育人员进行普查普治,切实降低集体儿童蛲虫感染率。  相似文献   
954.
目的观察放射线对心脏的影响及复方丹参对心脏的保护作用.方法 30例肺癌病人随机分为单纯放疗组和配合应用复方丹参组各15例,动态观察放疗前后及疗后3月、1年的心电图和心肌酶学变化.结果单放组治疗后心电图异常率明显高于治疗前(P<0.05),且以缺血型ST-T改变为主,心肌酶学变化不明显.复方丹参组治疗后心电图异常发生率明显低于单放组(P<0.05).结论放射线对心脏的损伤以微循环改变为主,复方丹参对心脏有保护作用.  相似文献   
955.
目的 研究 L盐酸赖氨酸对脑损伤后大鼠的胰高血糖素、胰岛素及血糖含量的影响。方法 采用落体法致大鼠脑损伤;伤后立刻一次腹腔注射 L盐酸赖氨酸,24h 后断头处死,用免疫组织化学 A B C 法结合图像分析技术,观察 L盐酸赖氨酸(621 .5mg·kg - 1 及310 .8mg·kg - 1) 对脑损伤后大鼠胰岛 A 细胞内胰高血糖素( Glu) 及 B 细胞内胰岛素( Ins) 免疫反应强度和光密度值的影响;用生化分析仪测定血糖含量。结果  L盐酸赖氨酸能显著增强 A 细胞内 Glu 免疫反应强度,提高平均光密度值,增加 Glu 的含量,并降低血糖水平,但对 B 细胞内 Ins 的免疫反应强度及光密度值无明显影响。结论  L盐酸赖氨酸可抑制 Glu 的释放并产生显著的降血糖作用。  相似文献   
956.
P选择素和ICAM—1在肾缺血再灌注损伤中的作用   总被引:5,自引:0,他引:5  
目的 探讨P选择素和细胞间粘附分子-1(ICAM-1)在肾缺血再灌注损伤中的作用。方法 建立缺血再灌注损伤大鼠模型,观察缺血再灌注后肾组织P选择素和ICAM-1的表达,并用P选择单克隆抗体进行了治疗。结果 发现缺血再灌注后肾小管人泡变性玫片状坏死,血尿素氮(BUN)和肌酐(SCr)水平升高;但再灌注前5min经P选择互单抗处理的动物肾组织与正常相近,肾小管上皮细胞未见变性及坏死,血BUN和SCr水  相似文献   
957.
BACKGROUND: We have shown that the age-associated increase in prostaglandin E(2) production contributes to the decline in T cell-mediated function with age. Black currant seed oil (BCSO), rich in both gamma-linolenic (18:3n-6) and alpha-linolenic (18:3n-3) acids, has been shown to modulate membrane lipid composition and eicosanoid production. OBJECTIVE: Our objectives were to 1) test whether dietary supplementation with BCSO can improve the immune response of healthy elderly subjects, and 2) determine whether the altered immune response is mediated by a change in the factors closely associated with T cell activation. DESIGN: A randomized, double-blind, placebo-controlled (soybean oil) study was conducted to examine the effect of 2 mo of BCSO supplementation on the immune response of 40 healthy subjects aged >/=65 y. In vivo immune function was determined by delayed-type hypersensitivity skin response. Peripheral blood mononuclear cells (PBMCs) were tested for in vitro immune response. RESULTS: In subjects supplemented with BCSO, the total diameter of induration at 24 h and individual responses to tetanus toxoid and Trichophyton mentagrophytes were significantly higher than their baseline values. The change in response to tetanus toxoid was significantly different from that of the placebo group. The BCSO group showed a significant increase in proliferative response of PBMCs to the T cell mitogen phytohemagglutinin that was not significantly different from that observed in the placebo group. BCSO had no effect on concanavalin A-induced mitogenic response, interleukin 2 and -1beta production, and PBMC membrane fluidity. Prostaglandin E(2) production was significantly reduced in the BCSO-supplemented group, and this change was significantly different from that of the placebo group. CONCLUSION: BCSO has a moderate immune-enhancing effect attributable to its ability to reduce prostaglandin E(2) production.  相似文献   
958.
Breast cancer incidence has historically been 4-7 times higher in the United States than in Asia. A previous study by the authors in Asian-American women demonstrated a substantial increase in breast cancer risk in women who migrated from Asia to the United States, with the risk almost doubling during the first decade after migration. Increased use of oral contraceptives soon after migration to the United States could possibly explain this rapid rise in risk. In a population-based case-control study of Chinese, Filipino, and Japanese-American women, aged 20-55 years, who lived in San Francisco-Oakland, California; Los Angeles, California; and Oahu, Hawaii during 1983-1987, 597 cases (70% of those eligible) and 966 controls (75%) were interviewed. Controls were matched to cases on age, ethnicity, and area of residence. Oral contraceptive (OC) use increased with time since migration; 15.0% of Asian-born women who had been in the West <8 years, 33.4% of Asian-born women who had been in the West > or =8 years, and 49.6% of Asian women born in the West had ever used OCs. However, duration of OC use (adjusted for age, ethnicity, study area, years since migration, education, family history of breast cancer and age at first full-term birth) was not associated with increased risk of breast cancer. Moreover, neither OC use before age 25 years nor before first full-term birth was associated with increased risk. Results were unchanged when restricted to women under age 45 years or under age 40 years. After adjustment for duration of OC use, women who had been in the United States > or =8 years were still at almost twice the risk of breast cancer compared with women who had been in the United States 2-7 years. This study suggests that OC use cannot explain the elevated risk observed in Asian women who migrated to the United States > or =7 years ago.  相似文献   
959.
Tobacco smoking and depressed mood in late childhood and early adolescence   总被引:11,自引:0,他引:11  
OBJECTIVES: This study builds on previous observations about a suspected causal association linking tobacco smoking with depression. With prospective data, the study sheds new light on the temporal sequencing of tobacco smoking and depressed mood in late childhood and early adolescence. METHODS: The epidemiologic sample that was studied consisted of 1731 youths (aged 8-9 to 13-14 years) attending public schools in a mid-Atlantic metropolitan area, who were assessed at least twice from 1989 to 1994. A survival analysis was used to examine the temporal relationship from antecedent tobacco smoking to subsequent onset of depressed mood, as well as from antecedent depressed mood to subsequent initiation of tobacco use. RESULTS: Tobacco smoking signaled a modestly increased risk for the subsequent onset of depressed mood, but antecedent depressed mood was not associated with a later risk of starting to smoke tobacco cigarettes. CONCLUSIONS: This evidence is consistent with a possible causal link from tobacco smoking to later depressed mood in late childhood and early adolescence, but not vice versa.  相似文献   
960.
A number of hematological, immunological, and biochemical parameters were measured in Peromyscus leucopus pups born from dams exposed to a single dose (300 mg/kg body weight) of Aroclor 1254. To increase the chances of uncovering even modest consequences of the exposure, in one protocol the pups were weaned at 3 weeks and examined at 6 weeks of age, while in a second protocol the pups were kept with their mother for 4 weeks, at which time they were examined. The older pups showed significant decreases in body weight, ratio of spleen weight to body weight, numbers of peripheral white blood cells and lymphocytes, and number and percentage of monocytes. They also showed significant increases in the stimulation index in response to the mitogen phytohemagglutinin (PHA), percentage of peripheral blood neutrophils and liver EROD induction. Pups sacrificed at 4 weeks of age showed even more significant differences. Their body and liver weights, percentage and number of peripheral blood lymphocytes, and serum antibody titers were significantly lower than those of their controls, while spleen to body weight ratios, percent of neutrophils in their peripheral blood, and liver EROD, PROD, and BROD levels were significantly higher than those of the controls. The primary implication of this work is that white-footed mouse pups could be used as biomonitors of contaminated sites. Females could be captured at the sites and bred in captivity with normal males. The vulnerable parameters identified in this study could then be measured in the resulting offspring and compared with a database collected from normal pups. Received: 8 July 1998/Accepted: 13 December 1998  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