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   9501篇
  免费   1129篇
  国内免费   15篇
耳鼻咽喉   82篇
儿科学   269篇
妇产科学   383篇
基础医学   1239篇
口腔科学   171篇
临床医学   1856篇
内科学   1608篇
皮肤病学   188篇
神经病学   747篇
特种医学   444篇
外科学   1201篇
综合类   278篇
一般理论   7篇
预防医学   1204篇
眼科学   113篇
药学   460篇
  1篇
中国医学   8篇
肿瘤学   386篇
  2023年   65篇
  2021年   115篇
  2020年   92篇
  2019年   133篇
  2018年   165篇
  2017年   199篇
  2016年   160篇
  2015年   208篇
  2014年   224篇
  2013年   346篇
  2012年   363篇
  2011年   413篇
  2010年   305篇
  2009年   288篇
  2008年   386篇
  2007年   345篇
  2006年   363篇
  2005年   335篇
  2004年   311篇
  2003年   276篇
  2002年   301篇
  2001年   305篇
  2000年   281篇
  1999年   282篇
  1998年   191篇
  1997年   196篇
  1996年   166篇
  1995年   152篇
  1994年   113篇
  1993年   117篇
  1992年   212篇
  1991年   205篇
  1990年   200篇
  1989年   205篇
  1988年   198篇
  1987年   176篇
  1986年   188篇
  1985年   193篇
  1984年   134篇
  1983年   121篇
  1982年   102篇
  1981年   93篇
  1980年   87篇
  1979年   80篇
  1978年   101篇
  1977年   73篇
  1976年   75篇
  1975年   64篇
  1974年   74篇
  1971年   68篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Treatment of chronic illnesses such as asthma can often become routine. This is a case report that emphasizes the importance of a thorough history and physical examination for each exacerbation of asthma. An 11-year-old girl with a history of asthma presented to the emergency room with wheezing and dyspnea that was assumed to be an exacerbation of her chronic illness. After careful history taking and physical examination, a chest radiograph was recommended. The x-ray revealed a hemothorax and a new diagnosis was made, thoracic Ewing's sarcoma.  相似文献   
102.
The isolation of a human cDNA encoding the multifunctional protein containing GAR synthetase, AIR synthetase, and GAR transformylase by functional complementation of purine auxotrophy in yeast has been reported. Chinese hamster ovary (CHO) cell mutant purine auxotrophs deficient in GAR synthetase (AdeC) or AIR synthetase plus GAR transformylase (AdeG) activities were transfected with this human GART cDNA subcloned into a mammalian expression vector. This restored 49–140% of the activities of GAR synthetase, AIR synthetase, and GAR transformylase in transfected cells when compared to wild-type CHO K1 parental cells. Study of one stably expressing transfectant, AdeC2, revealed that the human GART cDNA was incorporated into the CHO genome. The enzyme activities appear to be associated with an expressed protein of 110 kDa, very similar to that of purified human GART trifunctional enzyme. The AdeC mutant shows reduced amounts of GART mRNA compared to CHO K1 and a protein of apparently reduced size, results consistent with the purine requirement and enzyme deficiency observed in the mutant. These experiments provide definitive evidence that the human GART cDNA encodes and can direct the production of active human GART trifunctional protein in mammalian cells. They also provide important evidence that the AdeC and AdeG mutants of CHO cells are defective in this gene.  相似文献   
103.
Purine biosynthesis was studied in 8 mutants of Chinese hamster cells which require purines for growth and in wild-type cells which do not show this nutritional requirement. Of these, 6 mutants, ade B, adeD, adeE, adeF, GAT, and AT, were shown to accumulate metabolic intermediates not accumulated by wild-type cells. These intermediates were shown to be compounds unique to the adenylic acid biosynthetic pathway by the following criteria: (a) their radioisotopic labeling properties, (b) their response to agents which specifically inhibit known enzymatic steps in the pathway, (c) their chromatographic properties, and (d) spectrophotometric analysis. Two mutants, adeA and adeC, accumulate no detectable compounds not accumulated by the wild type. These 2 mutants are believed to be defective in steps very early in the purine biosynthetic pathway. The sites of the defects in the other mutants are proposed, and the usefulness of these mutants is discussed.  相似文献   
104.
The nature of the heat precipitation of 3 mononoclonal heat labile immunoglobulins was studied. These included 2 γG pyroglobulins and one γM pyroglobulin. Thermoprecipitable activity of both γG pyroglobulins could be localized to their heavy chains and to the Fab fragments of one of them. Heat precipitability of the γM paraprotein required the presence of the intact γM molecule since 7S subunits did not precipitate. The thermal precipitates appeared to result from intramolecular or intermolecular reactions with the formation of strong covalent bonds rather than weak non-covalent bonds. The importance of disulphide bonding was excluded in the precipitation of both γG but not in the γM pyroglobulins. Heat precipitation of the monoclonal γM resulted in coprecipitation of other proteins, particularly γG globulin, which suggested a specific type of reaction with this immunoglobulin. The interaction of the γM pyroglobulin, normal γG and heat produced an irreversible precipitate.  相似文献   
105.
An evaluation of workers in a plant was conducted because of multiple complaints of ocular, nasal, skin and chest symptoms. Antibody activity against 4 different chemicals was identified: an aliphatic diisocyanate, 4-vinylcyclohexene dioxide, trimellitic anhydride (TMA) and an unknown chemical present in a plasticizing ester known as n-octyl-n-decyl-trimellitate. The source of TMA which resulted in immunization in the plant is unknown. The presence or absence of antibodies did not correlate with the presence or absence of symptoms and it was concluded that no occupational allergic disease was present in these workers. Antibody studies alone do not make a diagnosis of occupational allergic disease and clinical correlation is required. Immunoassays may be useful in identifying exposures to immunizing chemicals in the workplace for potential clinical correlation or for exposure monitoring in the workplace.  相似文献   
106.
A study was undertaken to characterize the antibody response in rats exposed to trimellitic anhydride (TMA) by inhalation. Total antibody levels directed to trimellitic rat serum albumin (TM-RSA) from TMA-exposed rats were assayed by an ammonium sulfate technique. Total antibody levels in bronchoalveolar lavage (BAL) and the matched serum were compared by correction for the albumin content of each. An ELISA was developed to detect IgG, IgA, and IgM directed toward TM-RSA in BAL and serum and to compare class-specific antibody levels in BAL and serum by normalizing for albumin content. The specificity of the rat IgG response was determined by ELISA inhibition with TM-RSA and TM-human serum albumin (TM-HSA) and compared with reciprocal inhibition studies with serum from TMA-exposed workers. The levels of total antibody in BAL were three to 15 times greater than the levels found in the matched serum pair. IgG, IgA, and IgM antibodies were detected in the BAL and the serum of TMA-exposed rats but not in control rats. In each of the four rats tested, all antibody classes were present in equal or greater amounts in the BAL than in the serum. Complete inhibition of the rat IgG binding in ELISA was observed when TM-RSA or TM-HSA were added as inhibitors. Human IgG was inhibited in ELISA only by TM-HSA. In an animal model of human lung disease, the levels of total antibody as well as class-specific antibodies directed against TM-RSA were greater in BAL than in serum.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
107.
Enterococci (Enterococcus faecium and Enterococcus faecalis) and streptococci such as Streptococcus pyogenes (Group A streptococcus), Streptococcus agalactiae (Group B streptococcus), and Streptococcus pneumoniae are increasing in importance as both hospital-acquired and community pathogens. Emerging resistance and increasing incidence of these organisms has necessitated the analysis of their epidemiologic mechanisms of spread. Pulsed-field gel electrophoresis (PFGE) has emerged as the one of the most widely applicable, reproducible, and stable methods to examine strain identity in bacterial organisms. The procedure used in our laboratory for PFGE typing of whole cell DNA digested with SmaI for enterococci, S. pneumoniae, S. pyogenes, and S. agalacatiae is presented. Issues regarding interpretation are also reviewed and discussed.  相似文献   
108.
Immunotherapy with individually polymerized grasses (IPG) and immunotherapy with polymerized ragweed (PRW) have been demonstrated to be immunogenic and safe and to result in lowering of symptom-medication scores compared to placebo. We conducted this study to evaluate the immunogenicity and safety of immunotherapy with concomitantly administered accelerated dosage schedules of IPG and PRW in 12 patients with dual inhalant sensitivities. Patients were treated in nine weekly visits with IPG, comprising 71,950 PNU; they were treated in 11 weekly visits with PRW comprising 2955 allergy units. Eleven additional patients who had been previously treated with IPG received only PRW. There were no systemic reactions and no clinically significant changes in routine laboratory parameters, including hepatic and renal functions, with injections. There were significant rises in IgG titers by ELISA to each grass-pollen allergen administered, orchard, timothy, and Bermuda, and in total antibody binding of antigen E. Changes in IgE against orchard, timothy, Bermuda, and antigen E were minor. Thus, IPG and PRW administered concomitantly in accelerated dosage schedules are safe and immunogenic in patients with dual inhalant sensitivities.  相似文献   
109.
Effect of prostaglandin D2 and I2 on the airways of rhesus monkeys   总被引:2,自引:0,他引:2  
Prostaglandin (PG) D2 and PGI2 were evaluated to determine their effect on pulmonary function parameters when aerosolized in anesthetized rhesus monkeys. PGD2 resulted in an increase in frequency (f) and pulmonary resistance (rl) and a decrease in peak expiratory flow rate (PEFR), tidal volume (VT), and dynamic compliance (Cdyn), with the major effect on RL. PGI2 primarily effected an increase in f and a decrease in PEFR and VT. PGI2 had a variable effect, generally a decrease, on RL. The metabolite of PGI2, 6-keto-PGF 1 alpha, had no effect on the rhesus airway. PGF 2 alpha responses were similar to PGD2 except that the PGF 2 alpha produced a less strikingly consistent increase in RL. When PGI2 and PGD2 were aerosolized simultaneously, they simulated previously described antigen responses. Further, PGI2 plus PGD2 produced an airway response at 1/10 the concentration of either agent alone.  相似文献   
110.
The Staph-Ident system (Analytab Products) for species identification of coagulase-negative staphylococci was compared with the conventional method of Kloos and Schleifer (21). A total of 101 clinical isolates from urine cultures and 95 clinical isolates from blood cultures were studied: overall agreement between the two methods was 86%. We concluded that the Staph-Ident system is a practical test for most clinical microbiology laboratories and that results obtained from this rapid test are comparable to those obtained from the more cumbersome conventional method. Additional investigations are needed to determine the clinical relevance of such species identification.  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