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   3280篇
  免费   309篇
  国内免费   49篇
耳鼻咽喉   71篇
儿科学   185篇
妇产科学   59篇
基础医学   498篇
口腔科学   63篇
临床医学   466篇
内科学   710篇
皮肤病学   42篇
神经病学   265篇
特种医学   275篇
外国民族医学   1篇
外科学   323篇
综合类   61篇
预防医学   234篇
眼科学   35篇
药学   203篇
  1篇
中国医学   9篇
肿瘤学   137篇
  2023年   15篇
  2022年   19篇
  2021年   51篇
  2020年   30篇
  2019年   54篇
  2018年   79篇
  2017年   57篇
  2016年   55篇
  2015年   70篇
  2014年   108篇
  2013年   140篇
  2012年   133篇
  2011年   146篇
  2010年   113篇
  2009年   139篇
  2008年   144篇
  2007年   177篇
  2006年   164篇
  2005年   149篇
  2004年   103篇
  2003年   98篇
  2002年   94篇
  2001年   98篇
  2000年   72篇
  1999年   73篇
  1998年   97篇
  1997年   103篇
  1996年   81篇
  1995年   78篇
  1994年   61篇
  1993年   63篇
  1992年   58篇
  1991年   39篇
  1990年   35篇
  1989年   66篇
  1988年   59篇
  1987年   74篇
  1986年   45篇
  1985年   53篇
  1984年   48篇
  1983年   35篇
  1982年   24篇
  1981年   25篇
  1980年   27篇
  1979年   22篇
  1978年   18篇
  1977年   26篇
  1974年   15篇
  1973年   11篇
  1969年   11篇
排序方式: 共有3638条查询结果,搜索用时 0 毫秒
21.
This paper presents the results of a qualitative study conducted by midwife researchers into women's experience of new motherhood. Data were collected using focus groups involving 55 first-time mothers and analysed using grounded theory method. The analysis produced six categories: 'realizing', 'unready', 'drained', 'aloneness', 'loss' and 'working it out'. The core category, 'becoming a mother', integrates all other categories and encapsulates the process of change experienced by women. Also explained are factors mediating the often distressing experience of becoming a mother. The analysis provides a conceptualization of early motherhood enabling the development of strategies for midwives, nurses and others helping women negotiate this challenge.  相似文献   
22.
Summary— Experiments were designed to determine whether or not indapamide, an antihypertensive agent with vasodilator properties, inhibits endothelium-dependent contractions. Rings of aortae with and without endothelium from spontaneously hypertensive rats (SHR) were suspended in conventional organ chambers for the measurement of isometric force. Acetylcholine and adenosine diphosphate-β-S in the presence of a nitric oxide synthase inhibitor, caused endothelium-dependent contractions, which were inhibited by indapamide. The compound (10−4M) also slightly reduced the contractions of rings without endothelium evoked by U-46,619, which activates thromboxane-endoperoxide receptors. These results demonstrate that indapamide inhibits endothelium-dependent contractions in the SHR aorta, and suggest that the inhibition is due, at least in part, to the action of the drug on the hypertensive vascular smooth muscle.  相似文献   
23.
We evaluated the sonographic findings in 133 consecutive children referred for suspected appendicitis. Fifty-eight of these patients (44%) ultimately underwent surgery, with 54 of these proved to have acute appendicitis. Thirty-one (58%) of the 54 had nonperforated appendicitis, and 23 (43%) had evidence of perforation. Previously described sonographic findings that have been employed in the diagnosis of appendicitis were evaluated, with the presence or absence of these findings being compared in patients with non-perforated and perforated appendicitis. In those patients who did not undergo surgery, the following findings were documented and compared to the findings in patients with proved appendicitis: (1) an identifiable appendix and its sonographic characteristics, (2) fluid localized to the right peritoneal reflection or periappendiceal region, or both, (3) free pelvic fluid, and (4) right lower quadrant adenopathy. Our results suggest that high-resolution, real-time sonography, using graded compression, is very sensitive in the identification of acute nonperforated appendicitis. Perforated appendicitis, however, can be a more difficult diagnosis because the appendix frequently decompresses with perforation and yet may not "wall off" or form a well-defined abscess. As a result, the appendix can be very difficult to identify.  相似文献   
24.
Targeted gene disruption of murine CD7   总被引:2,自引:0,他引:2  
CD7 is a 40 kDa type I transmembrane glycoprotein member of the Ig superfamily. CD7 is a marker of mature human T cells and NK cells, and is expressed early in their development. Cross-linking CD7 positively modulates T cell and NK cell activity as measured by calcium fluxes, expression of adhesion molecules, cytokine secretion and proliferation. CD7 associates directly with phosphoinositol 3'-kinase, and CD7 ligation induces production of D-3 phosphoinositides and tyrosine phosphorylation. Severe combined immunodeficiency has been associated with a lack of lymphocyte surface CD7. The CD7 ligand is unknown. The murine CD7 homolog is encoded by a single gene on chromosome 11. In order to characterize the role of CD7 in lymphocyte development and function we have eliminated the CD7 gene by targeted disruption. CD7- deficient mice display normal histology of thymus and spleen, normal lymphocyte populations in primary and secondary lymphoid tissues, and normal serum Ig levels. Specific antibody responses after immunization with T-dependent and T-independent antigens are equivalent in wild-type and CD7 knockout mice. CD7-deficient lymphocytes respond normally to T cell mitogenic and allogeneic stimuli, and display normal NK cell cytotoxicity.   相似文献   
25.
Familial lipoprotein lipase deficiency (FLD) is of particular interest to the French Canadian population of Québec since the largest concentration of homozygotes and carriers of this genetic disease in the world resides in this area. We have previously described a missense mutation (M-188) in the lipoprotein lipase (LPL) gene which was present in FLD patients belonging to different ancestries, including a number of French Canadians (Monsalve MV et al. J Clin Invest 1990: 86: 728-734). In the present report, we show that this mutation, although found in largest absolute numbers among French Canadians as compared to other groups in the world, accounts for only a small proportion (24%) of all the LPL mutant alleles in this population. The M-188 occurs either in the homozygote state or as a compound heterozygote with another LPL mutation. Analysis of geographic distribution indicates that the M-188 is more prevalent in western Québec, with the highest carrier rate in the Mauricie region. Genealogical reconstruction leads to the recognition of four founders for M-188, all emigrants from France to Québec in the 17th century.  相似文献   
26.
Preclinical testing in Huntington disease   总被引:1,自引:0,他引:1  
  相似文献   
27.
We developed a rapid thermocycling, real-time detection (also known as real-time PCR) method for the detection of Legionella species directly from clinical specimens. This method uses the LightCycler (Roche Molecular Biochemicals, Indianapolis, Ind.) and requires approximately 1 to 2 h to perform. Both a Legionella genus PCR assay and Legionella pneumophila species-specific PCR assay were designed. A total of 43 archived specimens from 35 patients were evaluated, including 19 bronchoalveolar lavage (BAL) specimens and 24 formalin-fixed, paraffin-embedded open lung biopsy specimens. Twenty-five of the specimens were culture-positive for Legionella (9 BAL specimens and 16 tissue specimens). BAL specimens were tested by LightCycler PCR (LC-PCR) methods and by a direct fluorescent antibody (DFA) assay, which detects L. pneumophila serogroups 1 to 6 and several other Legionella species. Tissue sections were tested by the two LC-PCR methods, by DFA, by an in situ hybridization (ISH) assay, specifically designed to detect L. pneumophila, and by Warthin-Starry (WS) staining. The results were compared to the "gold standard" method of bacterial culture. With BAL specimens the following assays yielded the indicated sensitivities and specificities, respectively: Legionella genus detection by Legionella genus LC-PCR, 100 and 100%; Legionella genus detection by DFA assay, 33 and 100%; and L. pneumophila detection by L. pneumophila species-specific LC-PCR, 100 and 100%. With open lung biopsy specimens the following assays yielded the indicated sensitivities and specificities, respectively: Legionella genus detection by LC-PCR 68.8 and 100%; Legionella genus detection by DFA assay, 44 and 100%; Legionella genus detection by WS staining, 63 and 100%; L. pneumophila species-specific detection by LC-PCR, 17 and 100%; and L. pneumophila species-specific detection by ISH, 100 and 100%. The analytical sensitivity of both LC-PCR assays was <10 CFU/reaction. LC-PCR is a reliable method for the direct detection of Legionella species from BAL specimens. The Legionella genus LC-PCR assay could be performed initially; if positive, L. pneumophila species-specific LC-PCR could then be performed (if species differentiation is desired). The speed with which the LC-PCR procedure can be performed offers significant advantages over both culture-based methods and conventional PCR techniques. In contrast, for the methods evaluated, culture was the best for detecting multiple Legionella species in lung tissue. WS staining, Legionella genus LC-PCR, and L. pneumophila species-specific ISH were useful as rapid tests with lung tissue.  相似文献   
28.
In guinea-pigs infected with schistosomes, delayed cutaneous reactions rich in basophils (CBH) were found to characterize skin test responses to schistosome egg antigens. In addition, strong contact hypersensitivity-like skin eruptions with large basophil infiltrates resulted from skin penetration challenge by live cercariae (larvae) in these animals. Oedema and diminished basophil granule staining were noted around schistosomula which had penetrated the skin of sensitized animals. CBH responses to egg antigens and to live cercarial challenges were also noted after immunization with a single injection of dead cercariae.

Using peritoneal exudates from guinea-pigs immunized with dead cercariae or infected with schistosomes, direct macrophage migration inhibition with schistosome antigens was found only in animals with infections. Thus, CBH correlated with intradermal exposure to schistosome cercarial antigens, while MMI correlated with live infections. It is suggested that cutaneous basophil responses may play a role in protection from re-infection with schistosomes, and that dead cercarial vaccines might stimulate this beneficial response, without immunizing for potentially harmful granulomatous hypersensitivity.

  相似文献   
29.
In order to assess whether multiple-locus-variable number tandem repeat analysis (MLVA) could replace pulsed-field gel electrophoresis (PFGE) for genotyping vancomycin-resistant isolates of Enterococcus faecium (VREF), this study compared the typeability, discriminatory power, concordance and costs of these methods for VREF isolates obtained from patients, environmental samples and the hands of healthcare workers (HCWs) in a medical intensive care unit (ICU) where VREF was endemic. Over a 58-day period, 393 VREF isolates (373 vanA, one vanA/B, 19 vanB) were cultured from patient rectal swabs (n = 76), the environment (n = 270) and the hands of HCWs (n = 47). PFGE was able to divide 358 (91.1%) isolates into 19 PFGE types (>six bands different) and 24 subtypes (one to three bands different). MLVA was able to type 391 (99.5%) isolates into 11 genotypes. The discriminatory power of PFGE subtypes was 83%, as compared to 68% for MLVA. Concordance between the two methods, based on matched or mismatched MLVA types and PFGE types or subtypes, was 67.5% and 82.8%, respectively. Using PFGE, 13 isolates could be genotyped in 3 days; MLVA genotyped 94 isolates in 2 days. For both methods, the estimated costs were Euro 7 ($10)/isolate. PFGE and MLVA produced highly concordant results when assigning genotypes to nosocomial VREF isolates. MLVA was faster, but PFGE subtyping was more discriminatory.  相似文献   
30.
A controlled trial of acyclovir for chickenpox in normal children   总被引:4,自引:0,他引:4  
BACKGROUND. Chickenpox, the primary infection caused by the varicella-zoster virus, affects more than 3 million children a year in the United States. Although usually self-limited, chickenpox can cause prolonged discomfort and is associated with infrequent but serious complications. METHODS. To evaluate the effectiveness of acyclovir for the treatment of chickenpox, we conducted a multicenter, double-blind, placebo-controlled study involving 815 healthy children 2 to 12 years old who contracted chickenpox. Treatment with acyclovir was begun within the first 24 hours of rash and was administered by the oral route in a dose of 20 mg per kilogram of body weight four times daily for five days. RESULTS. The children treated with acyclovir had fewer varicella lesions than those given placebo (mean number, 294 vs 347; P less than 0.001), and a smaller proportion of them had more than 500 lesions (21 percent, as compared with 38 percent with placebo; P less than 0.001). In over 95 percent of the recipients of acyclovir no new lesions formed after day 3, whereas new lesions were forming in 20 percent of the placebo recipients on day 6 or later. The recipients of acyclovir also had accelerated progression to the crusted and healed stages, less itching, and fewer residual lesions after 28 days. In the children treated with acyclovir the duration of fever and constitutional symptoms was limited to three to four days, whereas in 20 percent of the children given placebo illness lasted more than four days. There was no significant difference between groups in the distribution of 11 disease complications (10 bacterial skin infections and 1 case of transient cerebellar ataxia). Acyclovir was well tolerated, and there was no significant difference between groups in the titers of antibodies against varicella-zoster virus. CONCLUSIONS. Acyclovir is a safe treatment that reduces the duration and severity of chickenpox in normal children when therapy is initiated during the first 24 hours of rash. Whether treatment with acyclovir can reduce the rare, serious complications of chickenpox remains uncertain.  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