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   1343826篇
  免费   112878篇
  国内免费   6394篇
耳鼻咽喉   16771篇
儿科学   43167篇
妇产科学   36714篇
基础医学   184301篇
口腔科学   36666篇
临床医学   121090篇
内科学   279641篇
皮肤病学   32023篇
神经病学   111039篇
特种医学   55632篇
外国民族医学   274篇
外科学   210989篇
综合类   31562篇
现状与发展   2篇
一般理论   416篇
预防医学   107220篇
眼科学   28141篇
药学   94103篇
  5篇
中国医学   2244篇
肿瘤学   71098篇
  2018年   13595篇
  2017年   10771篇
  2016年   12950篇
  2015年   14459篇
  2014年   20150篇
  2013年   30022篇
  2012年   36668篇
  2011年   39304篇
  2010年   24587篇
  2009年   24069篇
  2008年   36654篇
  2007年   39088篇
  2006年   40172篇
  2005年   38771篇
  2004年   36931篇
  2003年   36014篇
  2002年   34029篇
  2001年   66159篇
  2000年   68010篇
  1999年   56663篇
  1998年   16753篇
  1997年   15048篇
  1996年   16041篇
  1995年   16258篇
  1994年   15116篇
  1993年   14162篇
  1992年   47148篇
  1991年   45802篇
  1990年   44016篇
  1989年   41848篇
  1988年   38791篇
  1987年   38104篇
  1986年   35881篇
  1985年   34662篇
  1984年   26373篇
  1983年   22130篇
  1982年   13858篇
  1981年   12459篇
  1980年   11727篇
  1979年   23553篇
  1978年   17083篇
  1977年   14393篇
  1976年   13192篇
  1975年   13726篇
  1974年   16102篇
  1973年   15405篇
  1972年   14183篇
  1971年   13042篇
  1970年   11893篇
  1969年   11104篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The urinalysis practices of 324 methadone maintenance clinics were surveyed using a brief self-report questionnaire. Results indicate that there is wide variability in collection practices and clinic responses to positive findings. Virtually all clinics provide counseling and revocation of take-home methadone doses as a response to positive urinalysis results. However, increase in urine screening frequency, methadone dose adjustments, contingency contracting, group therapy, and eventual discharge are interventions also used. The implementation of different interventions varied as a function of clinic size, city size, region of the country, and program funding source.  相似文献   
992.
Transvaginal ultrasonography with color flow mapping has been used to study changes in intrafollicular blood flow and morphology during follicular rupture and presumed ovulation in one human volunteer. Detailed monitoring started on day 11 of the menstrual cycle and the follicle began to rupture at 14.30 on day 13. This event was preceded by a defined rise and peak in the level of immunoreactive serum luteinizing hormone (LH) by 42 h and 17 h 20 min, respectively. Blood vessels were clearly visible in the inner ring of the follicle (the granulosa layer) at the time of the LH peak and part of the granulosa (probably containing the oocyte) started to detach before the follicle ruptured. The maximum value for the peak blood velocity in the inner vessels was observed 10 s after the start of follicular rupture and there was a concurrent increase in the impedance to blood flow, as reflected by the resistance index and the pulsatility index. The follicle took 14 min 29 s to empty and the corpus haemorrhagicum started to form about 1 min later. These preliminary data suggest that intrafollicular angiogenesis and changes in blood flow can be monitored by a relatively non-invasive technique. Changes in vascularity might be used to predict imminent ovulation and could possibly be identified or modified biochemically to help achieve or avoid a pregnancy.  相似文献   
993.
The anterior hypothalamus-preoptic area and ventromedial hypothalamus are sexually dimorphic in the reproductively active whiptail lizard Cnemidophorus inornatus. The anterior hypothalamus-preoptic area, which is involved in the control of male-typical copulatory behaviors, is larger in males, whereas the ventromedial hypothalamus, which is involved in the control of female-typical receptivity, is larger in females. In the parthenogenetic whiptail lizard C. uniparens, which is a direct descendant of C. inornatus and exhibits both male-like and female-like pseudosexual behaviors, both brain areas are comparable in size to those of female C. inornatus. This study was conducted to determine whether these brain areas change in size in either species or sex during a time of year when these animals are reproductively inactive, or after removal of the gonads. In male C. inornatus both brain areas changed during reproductive inactivity (either seasonally or surgically induced) and became equivalent to the size characteristic of reproductively active female C. inornatus. When corrected for brain size, the anterior hypothalamus-preoptic area was significantly smaller in intact hibernating and castrated males than in intact males from the summer breeding season. Conversely, the ventromedial hypothalamus was significantly larger in intact hibernating and castrated males than in intact males from the summer breeding season. The two brain areas were not significantly different among the groups of female C. inornatus or parthenogenetic C. uniparens. These results suggest that 1) the brain of whiptail lizards may differentiate seasonally and 2) the female state may be a neutral one to which the male brain reverts during reproductive inactivity.  相似文献   
994.
An experiment is described in which deluded subjects with a diagnosis of schizophrenia or of delusional disorder (paranoia) were compared with a nondeluded psychiatric control group and a normal control group on a probabilistic inference task. Factors relevant to belief formation and maintenance were investigated. Deluded subjects requested less information before reaching a decision and were more ready to change their estimates of the likelihood of an event when confronted with potentially disconfirmatory information. No differences were found between the two diagnostic groups of deluded subjects. The results are discussed in light of prevailing theories of the importance of abnormal experience rather than reasoning biases in the formation and maintenance of delusional beliefs. It is suggested that a reasoning abnormality is involved, which may coexist with perceptual abnormalities.  相似文献   
995.
Carnitine, valproate, and toxicity   总被引:1,自引:0,他引:1  
Carnitine is an important nutrient that is present in the diet (particularly in meat and dairy products) and is synthesized from dietary amino acids. It functions to assist long-chain fatty acid metabolism and to regulate the ratio of free coenzyme A to acylcoenzyme A in the mitochondrion. Carnitine deficiency occurs in primary inborn errors of metabolism, in nutritional deficiency, and in various other disorders including antiepileptic drug therapy. Valproate therapy is often associated with decreased carnitine levels and occasionally with true carnitine deficiency. Some experimental and clinical evidence links valproate-induced carnitine deficiency with hepatotoxicity, but this evidence is limited and inconclusive. Carnitine supplementation has been useful in some studies, but these data are also limited. Young children with neurologic disabilities taking multiple antiepileptic drugs may have the greatest risk for carnitine deficiency. Measurement of carnitine levels appears warranted in these patients and in patients with symptoms and signs of possible carnitine deficiency.  相似文献   
996.
997.
998.
999.
The isolated azygos continuation of the inferior vena cave is a very rare variation of this organ. It is accompanied by the absence of the retrohepatic segment of the vena cava with two new observations, the literature is revised and the origin discussed.  相似文献   
1000.
Congenital herpes simplex retinitis   总被引:2,自引:0,他引:2  
An 1,810-g girl born at 37 weeks of gestation had true congenital herpes simplex virus type 2 infection. The neonate was born with hypo-pigmented skin lesions, brain lesions, and old heavily pigmented retinal scars in the posterior pole. There was no active ocular disease. Viral cultures, immunoperoxidase stains, and antibody determination by enzyme-linked immunosorbent assay were all positive for herpes simplex virus. Treatment with acyclovir healed the lesions within ten days. The clinical and laboratory findings indicated that the herpetic infection probably occurred in the second trimester.  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