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   8556篇
  免费   560篇
  国内免费   48篇
耳鼻咽喉   73篇
儿科学   358篇
妇产科学   216篇
基础医学   1299篇
口腔科学   222篇
临床医学   852篇
内科学   1588篇
皮肤病学   108篇
神经病学   863篇
特种医学   493篇
外科学   1261篇
综合类   159篇
一般理论   2篇
预防医学   597篇
眼科学   115篇
药学   456篇
中国医学   26篇
肿瘤学   476篇
  2021年   131篇
  2020年   77篇
  2019年   131篇
  2018年   138篇
  2017年   105篇
  2016年   121篇
  2015年   137篇
  2014年   201篇
  2013年   275篇
  2012年   381篇
  2011年   374篇
  2010年   230篇
  2009年   214篇
  2008年   344篇
  2007年   332篇
  2006年   370篇
  2005年   363篇
  2004年   351篇
  2003年   347篇
  2002年   291篇
  2001年   273篇
  2000年   286篇
  1999年   259篇
  1998年   140篇
  1997年   128篇
  1996年   107篇
  1995年   70篇
  1994年   87篇
  1993年   90篇
  1992年   192篇
  1991年   183篇
  1990年   166篇
  1989年   172篇
  1988年   148篇
  1987年   174篇
  1986年   132篇
  1985年   164篇
  1984年   113篇
  1983年   96篇
  1982年   66篇
  1981年   63篇
  1979年   69篇
  1978年   94篇
  1976年   58篇
  1975年   59篇
  1974年   64篇
  1973年   63篇
  1972年   71篇
  1971年   62篇
  1970年   57篇
排序方式: 共有9164条查询结果,搜索用时 31 毫秒
101.
Solid-phase chemistry is a category of analytical techniques characterized by three features: dry reagents fixed on or in an inert carrier; they are transformed into a liquid state of reactivity solely by fluid from the sample, movement of fluid in the carrier happens through capillary surface forces. A number of industrial laboratories have adapted these technologies to a majority of parameters of blood or serum respectively. The most frequently used measuring devices are new developed reflectometers; in one system (Ektachem) disposable ion selective electrodes have been newly developed in addition. The most important systems on the market are Ektachem (Kodak), Reflotron (Boehringer, Mannheim) and Seralyzer (Ames). These systems differ with respect to the construction of the reagent carriers and of the reflectometers. Solid-phase chemistry has the following advantages over the conventional analytical techniques: The sample volume is small, and the instrumentation is not complicated. The reagents are ready for use, and one system permits the use of whole blood without centrifugation. In this way it is possible to perform decentralized analyses at the patient's bedside, or in the physician's office. The disadvantages are the complete dependency of the user on the manufacturer with respect to the methodology and the quality of the reagents and instrumentation, the relative high price of the test-elements, and the limited possibility for the processing of long series. Additional problems are associated with quality control and drug interference. Nevertheless it can be expected that in the future increasing numbers of clinical chemical analyses will be performed by solid-phase chemistry, especially in general practice.  相似文献   
102.
Objective: Previous work has shown that manic-depressive illness and alcohol abuse are linked. This study further explores the relationship of alcohol and drug abuse in bipolar I patients and unipolar depressives and a comparison group obtained through the acquaintance method. Method: Diagnosis was accomplished according to Research Diagnostic Criteria (RDC): controls=469; bipolars=277; unipolar depressives=678. Systematic data were gathered using the SADS on lifetime and current drug abuse and alcoholism. Both patients and comparison subjects were then followed prospectively for 10 years. First degree family members were interviewed using the RDC family history method. Results: The group of bipolar patients and the group of unipolar patients had higher rates of drug and alcohol abuse than the comparison group when primary and secondary affective disorder patients were combined. However, primary unipolar patients did not have higher rates of alcohol or drug abuse than the comparison group. In contrast, primary bipolar patients had higher rates of alcoholism, stimulant abuse, and ever having abused a drug than the primary unipolar group and the control group. In an evaluation of the bipolar patients, drug abusers were significantly younger at intake and had a significantly younger age of onset of bipolar disorder. There was a significant increase in family history of mania or schizoaffective mania in the drug-abusing bipolar patients as compared to the non-abusing bipolar patients. Limitation: As in all adult samples of patients with affective illness, the chronology of alcohol and substance problems vis-à-vis the onset of illness was determined retrospectively. Conclusions: (1) Alcoholism and drug abuse are more frequent in bipolar than unipolar patients. (2) The drug abuse of bipolar patients tends toward the abuse of stimulant drugs. (3) In a bipolar patient, familial diathesis for mania is significantly associated with the abuse of alcohol and drugs. (4) More provocatively, these findings suggest the hypothesis of a common familial-genetic diathesis for a subtype of bipolar I, alcohol and stimulant abuse. Clinical implications: The present analyses, coupled with two previous ones from the CDS, suggest that drug abuse may precipitate an earlier onset of bipolar I disorder in those who already have a familial predisposition for mania. Furthermore, in dually diagnosed patients with manic-depressive and alcohol/stimulant abuse history, mood stabilization of the bipolar disorder represents a rational approach to control concurrent alcohol and drug problems, and should be studied in systematic controlled trials.  相似文献   
103.
We report on a 34-year-old developmentally disabled man referred to our clinic for evaluation of possible Prader-Willi syndrome on the basis of obesity and voracious appetite. Cytogenetic and molecular analysis revealed a 47, XYY karyotype and the presence of a trinucleotide repeat expansion resulting in fragile X syndrome. To our knowledge, this is the first report of concurrence of XYY and fragile X syndrome in the medical literature. Review of sex chromosome abnormalities associated with fragile X syndrome and phenotypic considerations are presented.  相似文献   
104.
Resistance to paracoccidioidomycosis, the most important endemic mycosis in Latin America, is thought to be primarily mediated by cellular immunity and the production of gamma interferon. To assess the role of interleukin-4 (IL-4), a Th2 cytokine, pulmonary paracoccidioidomycosis in IL-4-depleted susceptible (B10.A) and intermediate (C57BL/6) mice was studied. Two different protocols were used to neutralize endogenous IL-4 in B10.A mice: 1 mg of anti-IL-4 monoclonal antibody (MAb)/week and 8 mg 1 day before intratracheal infection with 10(6) Paracoccidioides brasiliensis yeast cells. Unexpectedly, both protocols enhanced pulmonary infection but did not alter the levels of pulmonary cytokines and specific antibodies. Since in a previous work it was verified that C57BL/6 mice genetically deficient in IL-4 were more resistant to P. brasiliensis infection, we also investigated the effect of IL-4 depletion in this mouse strain. Treatment with the MAb at 1 mg/week led to less severe pulmonary disease associated with impaired synthesis of Th2 cytokines in the lungs and liver of control C57BL/6 mice. Conversely, in IL-4-depleted C57BL/6 mice, increased levels of tumor necrosis factor alpha and IL-12 were found in the lungs and liver, respectively. In addition, higher levels of immunoglobulin G2a (IgG2a) and lower levels of IgG1 antibodies were produced by IL-4-depleted mice than by control mice. Lung pathologic findings were equivalent in IL-4-depleted and untreated B10.A mice. In IL-4-depleted C57BL/6 mice, however, smaller and well-organized granulomas replaced the more extensive lesions that developed in untreated mice. These results clearly showed that IL-4 can have a protective or a disease-promoting effect in pulmonary paracoccidioidomycosis depending on the genetic background of the host.  相似文献   
105.
BACKGROUND: The present analyses were designed to compare the clinical characteristics and long-term episode course of Bipolar-I and Bipolar-II patients in order to help clarify the relationship between these disorders and to test the bipolar spectrum hypothesis. METHODS: The patient sample consisted of 135 definite RDC Bipolar-I (BP-I) and 71 definite RDC Bipolar-II patients who entered the NIMH Collaborative Depression Study (CDS) between 1978 and 1981; and were followed systematically for up to 20 years. Groups were compared on demographic and clinical characteristics at intake, and lifetime comorbidity of anxiety and substance use disorders. Subsets of patients were compared on the number and type of affective episodes and the duration of inter-episode well intervals observed during a 10-year period following their resolution of the intake affective episode. RESULTS: BP-I and BP-II had similar demographic characteristics and ages of onset of their first affective episode. Both disorders had more lifetime comorbid substance abuse disorders than the general population. BP-II had a significantly higher lifetime prevalence of anxiety disorders in general, and social and simple phobias in particular, compared to BP-I. Intake episodes of BP-I were significantly more acutely severe. BP-II patietns had a substantially more chronic course, with significantly more major and minor depressive episodes and shorter inter-episode well intervals. BP-II patients were prescribed somatic treatment a substantially lower percentage of time during and between affective episodes. LIMITATIONS: BP-I patients with severe manic course are less likely to be retained in long-term follow-up, whereas the reverse might be true for BP-II patients who are significantly more prone to depression (i.e., patients with less inclination to depression and with good prognosis may have dropped out in greater proportions); this could increase the gap in long term course characteristics between the two samples. The greater chronicity of BP-II may be due, in part, to the fact that the patients were prescribed somatic treatments substantially less often both during and between affective episodes. CONCLUSIONS: The variety in severity of the affective episodes shows that bipolar disorders, similar to unipolar disorders, are expressed longitudinally during their course as a dimensional illness. The similarities of the clinical phenotypes of BP-I and BP-II, suggest that BP-I and BP-II are likely to exist in a disease spectrum. They are, however, sufficiently distinct in terms of long-term course (i.e., BP-I with more severe episodes, and BP-II more chronic with a predominantly depressive course), that they are best classified as two separate subtypes in the official classification systems.  相似文献   
106.
107.
Phenomenology and family history in DSM-III psychotic depression   总被引:1,自引:0,他引:1  
Depressed inpatients with psychotic features were compared to those without them in terms of demographic features, depressive symptoms at intake and family history. These variables were then used to compare patients with mood-congruent psychotic features to those with mood-incongruent psychotic features. Patterns of familial psychopathology were similar for psychotic and non-psychotic patients. In accord with other studies, the families of mood-incongruent patients had slightly more schizophrenia and significantly less depression than did the families of mood-congruent patients. Depressive symptoms, particularly those used to define major depression and melancholia, were more severe in psychotic patients. Moreover, these particular depressive symptoms were more likely to distinguish mood-congruent from mood-incongruent patients than were other depressive symptoms. Thus mood-congruent psychotic features accompanied a more typical depressive syndrome than did mood-incongruent psychotic features.  相似文献   
108.
109.
110.
Summary.  Peptide and cationic lipid-based gene transfer vectors have shown promise for gene therapy but are still less efficient than viral gene transfer vectors. We have examined the mechanism of gene transfer of different adenovirus-mimetic peptides in the presence and absence of a cationic lipid, lipofectamine and/or adenovirus with the aim of improving the design of nonviral vectors for efficient gene transfer. Three polylysine-adenovirus-mimetic peptides were synthesised and examined for their efficacy for gene transfer. Transfection levels in four cell lines: adenovirus permissive human tracheal epithelial (56FHTE8o), human lung carcinoma (A549), human colon carcinoma (Caco-2) cells, and adenovirus low-permissive Chinese hamster ovary (CHO) cells, were examined. The polylysine-adenovirus-mimetic peptides increased the level of transfection of a reporter transgene in all cell lines. Transfection was substantially increased when an adenovirus was added to cells after pre-incubation with the vector complexes. Formulation of the peptide vector complexes with lipofectamine increased their transfection efficacy and the subsequent addition of an adenovirus increased transfection levels even further but only in permissive cells. Pre-incubation of cells with lipofectamine-peptide vector complexes increased cell binding of the adenovirus but uptake was only increased in intermediate- or non-permissive cells. The addition of lipofectamine increased transgene expression of a recombinant adenovirus in non-permissive cells but not in permissive cells. Enhancement with an adenovirus of peptide vector gene transfer is probably due to more efficient endosome escape while enhancement of gene transfer by peptide vectors complexed to lipofectamine is due to an increase in cellular binding and/or internalisation of the adenovirus. Received February 8, 2002; accepted August 23, 2002  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