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   4876篇
  免费   278篇
  国内免费   30篇
耳鼻咽喉   41篇
儿科学   86篇
妇产科学   153篇
基础医学   897篇
口腔科学   122篇
临床医学   357篇
内科学   788篇
皮肤病学   99篇
神经病学   475篇
特种医学   204篇
外国民族医学   1篇
外科学   553篇
综合类   20篇
预防医学   639篇
眼科学   104篇
药学   339篇
中国医学   7篇
肿瘤学   299篇
  2022年   38篇
  2021年   83篇
  2020年   48篇
  2019年   60篇
  2018年   74篇
  2017年   65篇
  2016年   63篇
  2015年   76篇
  2014年   119篇
  2013年   152篇
  2012年   227篇
  2011年   252篇
  2010年   141篇
  2009年   114篇
  2008年   216篇
  2007年   228篇
  2006年   180篇
  2005年   243篇
  2004年   245篇
  2003年   197篇
  2002年   229篇
  2001年   194篇
  2000年   201篇
  1999年   158篇
  1998年   59篇
  1997年   55篇
  1996年   47篇
  1995年   52篇
  1994年   31篇
  1992年   77篇
  1991年   73篇
  1990年   99篇
  1989年   86篇
  1988年   67篇
  1987年   64篇
  1986年   69篇
  1985年   74篇
  1984年   48篇
  1983年   55篇
  1979年   66篇
  1978年   33篇
  1977年   31篇
  1975年   28篇
  1974年   36篇
  1973年   31篇
  1972年   33篇
  1971年   33篇
  1970年   28篇
  1969年   38篇
  1968年   29篇
排序方式: 共有5184条查询结果,搜索用时 281 毫秒
31.
The genetical types were classified according to the clinical findings and biochemical results in cases of 13 newborn/children suffering from various aminoacidopathies. The genetical types were: 3 neonatal and 4 infantile types were found out of 7 non-ketotic disease (MSUD) patient was infantile type with 9.1 per cent keto acid decarboxylase activity in leukocyte homogenate. Among the 3 histidinemic patients 1 was severe neonatal type and 2 cases were chronic types. The 2 treated tyrosinemic children proved to be type III. (chronic with rickets).  相似文献   
32.
We have shown previously that connexin43 in the adult rat central nervous system (CNS) is predominantly localized at astrocytic gap junctions. Here we document immunohistochemically the emergence of connexin43-immunoreactive (connexin43-IR) structures and the regional patterns of connexin43 expression during postnatal maturation of the rat brain. On Western blots, connexin43 was detected in brain samples at postnatal day (P) 5, the earliest age studied. Immunohistochemically, most brain regions displayed a characteristic sequence of transient immunoreactive profiles that ultimately gave rise to the uneven distribution of the protein seen in adults. Generally, brains at P1-P5 exhibited long, fibrous connexin43-IR elements which were identified as radial glial cells. This fibrous immunostaining was considerably diminished at P5 and was replaced by short immunoreactive processes which predominated up to P10. These processes had a stellate appearance, emanated from partially stained astrocytic cell bodies and were heterogeneously distributed throughout the developing brain. By P15, there occurred only punctate immunolabelling similar to that seen in adult brain. Some brain regions including the amygdaloid complex, septohypothalamic nucleus, preoptic hypothalamus, zona incerta, ependyma and subfornical organ were exceptional in that they displayed adult immunostaining patterns at early postnatal ages suggesting a precocious maturation of gap junctions in these areas. We conclude that the highly heterogeneous distribution of connexin43-immunoreactivity among defined nuclear structures in adult brain does not reflect an antecedent requirement for connexin43 in early brain morphogenesis, but rather is related to the development of neuronal activity, the establishment of functional circuitry and the contribution of astrocytic gap junctions to glial metabolic coupling and potassium spatial buffering in the mature CNS.  相似文献   
33.
Transforming growth factor-beta 1 was localized by means of immunohistochemical reaction in liver biopsy specimens taken from patients having different chronic liver diseases with extending fibrosis. Two polyclonal antibodies that were produced in rabbits were directed against the amino terminal of transforming growth factor-beta 1. Staining by anti-CC(1-30) was primarily extracellular and located in the portal and periportal fibrotic areas of all seven cases with chronic active hepatitis. No staining was noted in the four chronic persistent cases studied. A strong reaction was seen with the antibody in nine of the ten cirrhotic samples, whereas it was negative in one inactive cirrhosis case and in all five cases with normal liver histological findings. No positive staining could be detected by the anti-LC(1-30) in any of the liver tissues. Detection of transforming growth factor-beta 1 in active liver diseases at the site of fibrosis suggests that transforming growth factor-beta 1 might have a role in the process and progression of fibrosis during the development of the disease.  相似文献   
34.
This study was undertaken to determine if dietary eicosapentaenoic acid (EPA) could affect the production of PGE (PGE2 and/or PGE3) by splenic macrophages and the mitogen-induced proliferation of splenic lymphocytes.Guinea pigs received a 30% total body surface area burn following installation of gastrostomy feeding tubes. All animals received identical diets except for the lipid component which equalled 10% of total energy. The control diet contained only linoleic acid (LA) as the lipid component. The experimental diets contained increasing amounts of EPA. Fourteen days postburn, the animals were sacrificed and splenic lymphocytes and macrophages were obtained and cultured for lymphocyte proliferation with and without mitogen stimulation and for PGE2 synthesis in response to bacterial lipopolysaccharide (LPS), respectively.Increasing amounts of EPA in the diets had no statistically significant effect on the total production of PGE (PGE2 and/or PGE3) by macrophages stimulated with LPS, however, when 100% EPA was used as the lipid component, the production of PGE2 was increased. Also, increasing amounts of EPA in the diet did not affect lymphocyte proliferation following stimulation of the cells with various mitogens, although at an EPA:LA ratio of 75:25%, a significant increase in proliferation of unstimulated but not stimulated lymphocytes was observed. However, at a 100:0 ratio of EPA:LA, lymphocyte proliferation was back down to the control level. This study shows that dietary EPA in high concentrations may have some complex interaction with the immune system at least in the animal under the stress of a burn.  相似文献   
35.
This case illustrates the possibility of obtaining oocytes that fertilize and cleave normally after the administration of a second ovulatory dose of human chorionic gonadotrophin (HCG) in a case of 'empty follicle syndrome'. The present patient underwent ovarian stimulation with gonadotrophin-releasing hormone analogue (GnRHa)/menotropin for intracytoplasmic sperm injection (ICSI). After the failure of the first oocyte retrieval, a second dose of HCG was administered to trigger ovulation. A total of 13 oocytes was retrieved during the second procedure and 11 good quality embryos were obtained (fertilization and cleavage rates of 92 and 91% respectively). No pregnancy was achieved after the replacement of three embryos. In a subsequent cycle stimulated with clomiphene citrate, three frozen- thawed embryos were replaced and a twin pregnancy was achieved. The patient delivered two healthy babies at term.   相似文献   
36.
We report on a 19-year-old girl with hepatosplenomegaly and possible hematological disease. We suspected Gaucher's disease on account of histological and biochemical evidence found in specimens from the liver, spleen, and bone marrow. 18 months later, pebbled skin developed on her neck and upper back. Histological examination revealed large amounts of mucous material between the collagen bundles deep in the dermis, which proved to be dermatan sulfate. The clinical and histological symptoms are characteristic for Hunter's disease.  相似文献   
37.
38.
Human herpesvirus 6 (HHV-6) and human immunodeficiency virus type 1 (HIV-1) may interact during transplacental transmission of HIV-1. The placental syncytiotrophoblast layer serves as the first line of defense of the fetus against viruses. Patterns of replication of HHV-6 variant A (HHV-6A) and HIV-1 were analyzed in singly and dually infected human term syncytiotrophoblast cells cultured in vitro. For this purpose, the GS strain of HHV-6A and the Ba-L and IIIB strains of HIV-1 were used. HHV-6A replication was restricted at the level of early gene products in singly infected syncytiotrophoblasts, whereas no viral protein expression was found in cells infected with HIV-1 alone. Coinfection of syncytiotrophoblast cells with HHV-6A and HIV-1 resulted in production of infectious HIV-1. In contrast, no enhancement of HHV-6A expression was observed in cell cultures infected with both viruses. Uninfected syncytiotrophoblast cells were found to express CXCR4 and CCR3 but not CD4 or CCR5 receptors. Infection of syncytiotrophoblasts with HHV-6A did not induce CD4 expression and had no influence on chemokine receptor expression. Activation of HIV-1 from latency in coinfected cells was mediated by the immediate-early (IE)-A and IE-B gene products of HHV-6A. Open reading frames U86 and U89 of the IE-A region were able to activate HIV-1 replication in a synergistic manner. The data suggest that in vivo double infection of syncytiotrophoblast cells with HHV-6A and HIV-1 could contribute to the transplacental transmission of HIV-1 but not HHV-6A.  相似文献   
39.
With one billion people overweight worldwide, the need to identify risk factors and treatments for obesity is urgent. The present study determined whether rats genetically prone to diet-induced obesity (DIO) show preexisting differences in meal microstructure and are sensitive to central anorectic effects of corticotropin-releasing factor type 2 (CRF2) receptor stimulation. Male, selectively bred DIO rats and their diet resistant (DR) counterparts ( n = 9/genotype) were weaned onto low-fat chow and compared as young adults for spontaneous or intracerebroventricular urocortin 2 administration-induced (0, 0.3, 1, 3 μg) differences in ingestion. DIO rats were hyperphagic selectively at the dark cycle onset, showing shorter latencies to initiate feeding, faster returns to eating following meal completion, and a lower satiety ratio than DR rats. At other times, DIO rats had briefer postmeal intervals, but ate smaller and briefer meals, resulting in normal intake. DIO rats also ate faster than DR rats. Urocortin 2 was less potent in DIO rats, ineffective at the 0.3 μg dose, but produced CRF2 antagonist-reversible anorexia at higher doses. Though heavier, chow-maintained DIO rats were proportionately as or more lean than DR rats. Thus, DIO rats showed signs of a preexisting, heritable deficit in the maintenance of postmeal satiety and a reduced sensitivity to anorectic CRF2 agonist stimulation. The meal patterns of DIO rats temporally resemble human 'snacking' behaviour, which predicts adult obesity. Because central CRF2 stimulation retains full anorectic efficacy at higher doses in the DIO model, manipulating this neuropeptidergic system might yield new therapeutic approaches for diet-induced obesity.  相似文献   
40.
The intense immunohistochemical reaction for the enzyme adenosine deaminase displayed by neurons in the tuberomammillary nucleus in the rat was used to study the distribution and morphology of cells comprising this nucleus, their fiber fields within the posterior hypothalamus and their projection pathways from the hypothalamus. Neurons immunoreactive for adenosine deaminase were found along ventricular and basal aspects of the hypothalamus from the level of the dorsomedial nucleus to the caudal pole of the mammillary body. Approximately 4500 neurons were seen on each side of the brain. Positive neurons showed a complex distribution, largely avoiding nuclear boundaries within the posterior basal hypothalamus and mammillary body. This distribution is mapped in detail and a nomenclature based on topography is introduced so that different regions of the cell distribution may be discussed more easily. Reactive neurons showed a Golgi-like staining which allowed careful study of their morphology. In general, neurons were large, with major axes of from 22 to 30 micron, and bipolar in shape. A second, smaller cell type, 14-16 micron in diameter was also seen and, although often less intensely stained, it was considered a constituent of tuberomammillary nucleus of the hypothalamus as well. Stained dendritic arbours extended considerable distances from the parent cell bodies and branched regularly. Dendrites showed very sparse spines and had an apparently scalloped surface. Features suggestive of varicose segments of dendrites were also noted. The long, smooth dendrites of positive neurons were often seen to aggregate into bundles which avoided nuclear boundaries and tended to collect adjacent to basal and ventricular surfaces of the posterior hypothalamus. Varicose fibers immunoreactive for adenosine deaminase formed a dense network within the hypothalamus. These fibers were considered to derive from the positive neurons in the tuberomammillary nucleus and were similar to adenosine deaminase-immunoreactive fibers seen throughout much of the rest of the brain. The density of this type of positive fiber was, however, much greater within the hypothalamus. The region of the posterior basal hypothalamus also contained relatively sparse populations of adenosine deaminase-positive fibers, apparently distinct from this network. These consisted of a field of fine fibers in the median division of the medial mammillary nucleus and a few large varicosities in the dorsolateral part of the median eminence.(ABSTRACT TRUNCATED AT 400 WORDS)  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