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   6310篇
  免费   295篇
  国内免费   29篇
耳鼻咽喉   86篇
儿科学   110篇
妇产科学   68篇
基础医学   704篇
口腔科学   218篇
临床医学   354篇
内科学   1262篇
皮肤病学   154篇
神经病学   478篇
特种医学   217篇
外科学   1277篇
综合类   22篇
一般理论   1篇
预防医学   151篇
眼科学   125篇
药学   421篇
中国医学   6篇
肿瘤学   980篇
  2023年   30篇
  2022年   64篇
  2021年   104篇
  2020年   63篇
  2019年   97篇
  2018年   106篇
  2017年   83篇
  2016年   125篇
  2015年   124篇
  2014年   168篇
  2013年   182篇
  2012年   276篇
  2011年   285篇
  2010年   216篇
  2009年   169篇
  2008年   259篇
  2007年   253篇
  2006年   253篇
  2005年   256篇
  2004年   250篇
  2003年   218篇
  2002年   217篇
  2001年   204篇
  2000年   240篇
  1999年   206篇
  1998年   79篇
  1997年   74篇
  1996年   61篇
  1995年   54篇
  1994年   58篇
  1993年   51篇
  1992年   175篇
  1991年   144篇
  1990年   152篇
  1989年   184篇
  1988年   151篇
  1987年   146篇
  1986年   127篇
  1985年   100篇
  1984年   69篇
  1983年   65篇
  1980年   25篇
  1979年   59篇
  1978年   43篇
  1977年   41篇
  1974年   27篇
  1973年   28篇
  1972年   39篇
  1971年   33篇
  1969年   29篇
排序方式: 共有6634条查询结果,搜索用时 15 毫秒
91.
In this report, we provide evidence using a serial bone marrow transplantation (BMT) protocol that intra-bone marrow (IBM)-BMT (IBM-BMT) can efficiently reconstitute the hemopoietic system with cells of donor origin, in contrast to conventional intravenous (IV)-BMT (IV-BMT). Furthermore, the hematolymphoid system of secondary recipients that had received bone marrow cells (BMCs) from primary recipients treated with IBM-BMT recovered earlier than that of the secondary recipients of BMCs from primary recipients treated with IV-BMT. This was the case when the Lin-/c-kit+ progenitor cells of the secondary and tertiary recipients were examined. These findings indicate that IBM-BMT can facilitate the development of not only cells of various lineages but also the effective generation and, more importantly, the maintenance of the progenitor cells. Furthermore, we show that IBM-BMT can reconstitute the dendritic cell (DC) subsets (myeloid and lymphoid DCs), which are critical for the initiation of both adaptive and innate immune responses. The frequency of both myeloid and lymphoid DC subsets was approximately equal to that of normal age-matched untreated controls and, after second and third BMT, this ratio was close to that observed in the normal controls. However, the lymphoid DCs were clearly reduced in the secondary and tertiary recipients of BMCs from mice that had received IV-BMT. Therefore, the development of DC subsets is also normally maintained in the IBM-BMT group.  相似文献   
92.
The egg dormancy and embryogenesis of the univoltine black fly, Prosimulium kiotoense Shiraki, in southwestern Japan were examined under natural and laboratory conditions. Eggs laid in April remained dormant until August (approximately 14 wk after oviposition). Hatching commenced in early October (after 23 wk), when air and water temperatures decreased to 20 and 15 degrees C, respectively, and continued until mid-December (32 wk) in the field. Laboratory experiments showed that lower temperatures (10 and 14 degrees C) supported embryogenesis similar to that observed in the field. In contrast, higher temperatures (18 and 22 degrees C) retarded or completely suppressed embryogenesis after the termination of dormancy. However, completion of dormancy was accelerated when eggs were exposed experimentally to these higher temperatures for 3-12 wk, then returned to a constant low temperature (14 degrees C). Daylength did not affect the maintenance and termination of dormancy. Therefore, temperature played an important role differentially affecting completion of dormancy and postdormancy development. Variable lengths of developmental periods among egg batches under the same conditions indicated possible genetic control of dormancy intensity.  相似文献   
93.
The molecular species composition of alpha-mycolic acids ranging from C68 to C86 in 13 rapidly growing and 12 slowly growing mycobacterial species was determined by gas chromatography, gas chromatography-mass spectrometry, and mass chromatography. In gas chromatographic analysis, the molecular species of alpha-mycolic acids were well separated as trimethylsilyl ether derivatives of the methyl esters, according to their total carbon numbers. The total carbon and double-bond numbers of mycolic acids at each peak on gas chromatograms were determined from the [M]+, [M - 15]+, and [M - 90]+ ions on the mass spectrum, and straight and branched chain structures were identified by the mass fragment ions [A]+, due to C2--C3 cleavage [R-CH-O-Si(CH3)3]+, and [B]+, due to C3--C4 cleavage [(CH3)3-Si-O-CH-CH(R')-COOCH3]+. The concentration of odd- and even-carbon-numbered mycolic acids, which often overlap each other on gas chromatograms, and the composition of three homologous mycolic acids with different alpha units (C22:0, C24:0, and C26:0) were clearly determined by mass chromatography monitoring [M - 15]+ ions and [B - 29]+ ions, respectively. The molecular species composition of alpha-mycolic acids and their average carbon numbers (av. cn.) as a simple expression of the composition were calculated from the mass chromatograms. Each mycobacterial species examined was demonstrated to possess a characteristic profile of alpha-mycolic acid composition, and based on this the species were classified approximately into eight groups: C68 to C76 (av. cn. 72), dienoic, possessing a C20 alkyl branch at the 2 position (C22 alpha-unit) for Mycobacterium diernhoferi and Mycobacterium sp. strain 3707, a chromogenic rapid grower; C72 to C78 (av. cn. 75), dienoic with both C22 and C24 alpha units, containing a small or a large amount of odd-carbon-numbered molecules, for M. vaccae, M. rhodesiae, and M. phlei (chromogenic rapid growers); C72 to C80 (av. cn. 75 to 77), dienoic with C24 alpha-unit, containing a moderate or a large amount of odd-carbon-numbered molecules, for M. smegmatis, M. chitae, M. chelonae (M. chelonei), and M. fortuitum (nonchromogenic rapid growers); C78 to C82 (av. cn. 80), even-carbon-numbered dienoic with C24 alpha unit for M. agri and M. thermoresistible (rapid growers); C75 to C81 (av. cn. 77 to 79), odd-carbon-numbered dienoic with C24 alpha unit for M. nonchromogenicum complex (M. nonchromogenicum, M. terrae, and "M. novum") (slow growers); (vi) C76 to C84 (av. cn. 79 to 81), even-carbon-numbered dienoic with C24 alpha unit for MAIS complex including M. scrofulaceum, M. avium, and M. intracellulare (slow growers); (vii) C72 to C80 (av. cn. 77 to 79), even-carbon-numbered dienoic with C24 alpha unit for M. szulgai, M. gordonae, and M. kansasii (chromogenic slow growers); and (viii) C76 to C86 (av. cn. 79 to 81), even-carbon-numbered dienoic with C26 alpha unit M. bovis Ravenol and BCG and M. tuberculosis H37Rv. This study demonstrated that gas chromatography-mass spectrometric analysis of the molecular species composition of alpha-mycolic acid can give rapid, important, and very precise information for the identification of pathogenic and nonpathogenic mycobacterial species.  相似文献   
94.
Five cases of primary sclerosing scrotal lipogranuloma were examined histologically and immunohistochemically. Every case lacked a history of injection or trauma, and revealed Common histologicat features; a typical granuloma composed of epithelioid cells and multinucleated giant cells, and inflammatory infiltrates of eosinophils, lymphocytes and macrophageimonocytes in the interstitium. lmmunahistochemistry disclosed the epithelioid cells and multinuclaated giant cells of the granuloma to be monocytetr in nature, as bath types of cells were positive for lyso-yme, α-1-antltrypin, α-1-antichymotrypsin, and KP-1. In the interstitium, KP-1 positive monocytes, L-26 positive B lymphocytes, UCHL-1 positive T lymphocytes and 5–100 protein positive Langerhans-like cells were frequently found. 5100 protein positive cells could not be detected in the granuloma. Primary sclerosing lipogranuloma of the scrotum, therefore, is a peculiar inflammation characterized by granulomas consisting of monocytes and marked tissue eosinophilia of unknown etiology.  相似文献   
95.
Obstructive jaundice was produced in rats by ligation and transection of bile duct outside the liver; the control group underwent laparotomy alone. Pancreatic wet weight, amylase, lipase, protein, DNA, RNA, RNA/DNA ratio, and weight/100 g DNA were significantly increased in jaundiced rats when compared to control rats. Histologic evaluation of pancreatic tissue obtained from jaundiced rats revealed the appearance of large or multiple nuclei in pancreatic acinar cells. Basal plasma levels of immunoreactive CCK were significantly increased in haundiced rats at two weeks and four weeks but, when compared to the levels obtained in laparotomized controls at those time intervals, CCK levels were not significantly different. In jaundiced rats, plasma immunoreactive gastrin was found to be significantly decreased at two and four weeks. Plasma gastrin levels were also found significantly decreased when the jaundiced group was compared with laparotomized control group. The results suggest that obstructive jaundice induced enlargement of the pancreas, probably due to hyperplasia and hypertrophy of pancreatic cells. Whether or not this phenomenon is related to changes in gastrin and CCK is not known.This work was presented in part at the 36th Kinki Section Meeting of Japanese Gastroenterological Association (January 1982) in Osaka, Japan; at the Annual Meeting of the Japanese Pancreatic Association (March 1982) in Hiroshima, Japan; and at the American Gastroenterological Association (May 1983) in Washington, D.C.; and appeared in abstract form inGastroenterology 84: 1095, 1983.  相似文献   
96.
Matcha, a type of green tea, has a higher amino acid content than other types of tea. We previously examined the ability of matcha to improve cognitive function in older adults and determined that continuous matcha intake improves attention and executive function. This study aimed to compare the effects of matcha and caffeine and clarify the differences between these effects. The study was registered at the University Hospital Medical Information Network (UMIN000036578). The effect of single and continuous intake was compared, and the usefulness of continuous intake was evaluated under the stress condition. The Uchida–Kraepelin test (UKT) was used to induce mild acute stress, and the Cognitrax was used to evaluate cognitive function. A single dose of caffeine improved attentional function during or after stress loading. The reduced reaction time in the Cognitrax, observed following a single dose of matcha, was likely due to caffeine. The matcha group showed an increase in the amount of work after continuous intake, whereas the caffeine group only showed an increase in the amount of work for the UKT after a single dose. Ingesting matcha with caffeine improves both attention and work performance when suffering from psychological stress compared with caffeine alone.  相似文献   
97.
BACKGROUND: Many studies have suggested a possible aetiological role for obstetric complications in the development of schizophrenia. We focused on prenatal physical growth in schizophrenia, a contentious issue in the literature. METHODS: We compared gestational age at birth, birth weight (BW) and birth head circumference (BHC) between 312 schizophrenics and 517 controls, and between 187 schizophrenics and their matched healthy siblings. Information on obstetric histories was obtained from the Maternal and Child Health Handbooks (i.e. contemporaneous records). RESULTS: Gestational age at birth was significantly earlier in the schizophrenics than in the controls (P = 0.017). Pre-term birth (gestational age of 36 weeks or less) was more common in schizophrenics than in controls (8.0% v. 3.4%, P = 0.005, odds ratio 2.5). Low BW (2500 g or less) was more frequent in schizophrenics than in controls (9.6% v. 4.6%, P = 0.005, odds ratio 2.2). The schizophrenics had significantly lighter BW (P = 0.0003) and tended to have smaller BHC (P = 0.081) compared with controls. However, multiple regression analysis showed that there was no significant difference in BW or BHC between the schizophrenics and controls when gestational age and maternal weight were controlled. There was no significant difference in BW or BHC between schizophrenics and their siblings, although the schizophrenics tended to be born at earlier gestational age than their siblings. CONCLUSIONS: Our results suggest that prematurity at birth is associated with a risk of developing schizophrenia in adulthood. When gestational age and maternal body weight were allowed for, there was no evidence that schizophrenics tend to have lower mean BW or smaller BHC.  相似文献   
98.
We have previously reported that concanavalin A-immobilized polystyrene nanospheres (Con A-NS) could efficiently capture HIV-1 particles and that intranasal immunization with inactivated HIV-1-capturing nanospheres (HIV-NS) induced vaginal anti-HIV-1 IgA antibody response in mice. In this study, to evaluate the protective effect of immunization, each three macaques was intranasally immunized with Con A-NS or inactivated simian/human immunodeficiency virus KU-2-capturing nanospheres (SHIV-NS) and then intravaginally challenged with a pathogenic virus, SHIV KU-2. After a series of six immunizations, vaginal anti-HIV-1 gp120 IgA and IgG antibodies were detected in all SHIV-NS-immunized macaques. After intravaginal challenge, one of the three macaques in each of the Con A-NS- and SHIV-NS-immunized groups was infected. Plasma viral RNA load of infected macaque in SHIV-NS-immunized macaques was substantially less than that in unimmunized control macaque and reached below the detectable level. However, it could not be determined whether intranasal immunization with SHIV-NS is effective in giving complete protection against intravaginal challenge. To explore the effect of the SHIV-NS vaccine, the remaining non-infected macaques were rechallenged intravenously with SHIV KU-2. After intravenous challenge, all macaques became infected. However, SHIV-NS-immunized macaques had lower viral RNA loads and higher CD4(+) T cell counts than unimmunized control macaques. Plasma anti-HIV-1 gp120 IgA and IgG antibodies were induced more rapidly in the SHIV-NS-immunized macaques than in the controls. The rapid antibody responses having neutralizing activity might contribute to the clearance of the challenge virus. Thus, SHIV-NS-immunized macaques exhibited partial protection to vaginal and systemic challenges with SHIV KU-2.  相似文献   
99.
Total removal of an arteriovenous malformation embedded in the brain stem   总被引:1,自引:0,他引:1  
The removal of brain stem arteriovenous malformations is one of the most challenging problems in neurosurgery. The authors report a successful total removal of an arteriovenous malformation situated in the middle cerebellar peduncle, which was embedded in the floor of the fourth ventricle. The importance of dissection "flush" with coils of an arteriovenous malformation is stressed.  相似文献   
100.
We report on a case of multiple bone metastasis and disseminated intravascular coagulation (DIG) in a 49-year-old Japanese man. He underwent total gastrectomy for advanced gastric cancer in July 1992, He was diagnosed as a case of multiple bone metastasis in August 1993. Severe anemia, thrombocytopenia, and elevated fibrinogen degradative products were indicative of DIG. He was treated with sequential i.v. administration of methotrexate (MTX) and 5-fluorouracil (5-FU) and continuous i.v. infusion of heparin and gabexate mesilate. After two weeks of treatment with MTX combined with 5-FU, the findings of DIC disappeared and his general condition improved dramatically.  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