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   4253篇
  免费   371篇
  国内免费   5篇
耳鼻咽喉   56篇
儿科学   144篇
妇产科学   49篇
基础医学   699篇
口腔科学   149篇
临床医学   471篇
内科学   738篇
皮肤病学   44篇
神经病学   359篇
特种医学   387篇
外科学   480篇
综合类   41篇
预防医学   195篇
眼科学   28篇
药学   527篇
肿瘤学   262篇
  2023年   19篇
  2022年   29篇
  2021年   48篇
  2020年   45篇
  2019年   55篇
  2018年   66篇
  2017年   61篇
  2016年   89篇
  2015年   100篇
  2014年   128篇
  2013年   184篇
  2012年   204篇
  2011年   222篇
  2010年   158篇
  2009年   116篇
  2008年   228篇
  2007年   203篇
  2006年   196篇
  2005年   188篇
  2004年   167篇
  2003年   148篇
  2002年   170篇
  2001年   152篇
  2000年   155篇
  1999年   130篇
  1998年   79篇
  1997年   84篇
  1996年   92篇
  1995年   87篇
  1994年   69篇
  1993年   56篇
  1992年   87篇
  1991年   71篇
  1990年   72篇
  1989年   70篇
  1988年   67篇
  1987年   66篇
  1986年   55篇
  1985年   50篇
  1984年   39篇
  1983年   22篇
  1982年   35篇
  1981年   21篇
  1980年   20篇
  1979年   28篇
  1978年   24篇
  1977年   29篇
  1976年   29篇
  1975年   30篇
  1974年   21篇
排序方式: 共有4629条查询结果,搜索用时 15 毫秒
71.
A pilot study was designed to examine whether the outcome of embryo transfer in women with a hydrosalpinx might be improved by surgical drainage of the hydrosalpinx at the time of oocyte collection for in- vitro fertilization treatment. A comparative, controlled but retrospective analysis of the results was performed of all women with infective tubal damage aged <40 years old, who had ovulatory cycles, a normal uterus and a partner with normal spermatozoa. A standardized treatment regimen was used. A maximum of three embryos were transferred. Hydrosalpinx was defined by prior hysterosalpingography and/or laparoscopy with transcervical dye injection. A total of 237 embryo transfer cycles in women with hydrosalpinges (tubal distension not visible in 151, visible but not drained in 30 and drained in 56) were compared with 705 embryo transfer cycles in women with tubal disease but no hydrosalpinx. Results were analysed in the first three cycles but also separately in the first cycle to check for bias. Success rates were higher in the first cycle, but did not significantly influence overall differences. Implantation rates were significantly reduced overall in the hydrosalpinx group (8.0 versus 13.2% for controls; P < 0.001), being 8.3% (P < 0.01) in the subgroup without evident tubal distension and 7.5% (not significant) in the drained hydrosalpinx group. This study shows that tubal damage with distal occlusion is associated with a marked reduction in embryo implantation, even in the absence of obvious fluid distension. Surgical drainage of distended hydrosalpinges appears to offer no benefit.   相似文献   
72.
The performance of the Etest for fluconazole susceptibility testing of 402 yeast isolates was assessed against the National Committee for Clinical Laboratory Standards (NCCLS) microdilution broth method. The NCCLS method employed RPMI 1640 broth medium, and MICs were read after incubation for 48 h at 35°C. Etest MICs were determined with RPMI agar containing 2% glucose (RPG), Casitone agar (CAS), and Mueller-Hinton agar (MHA) and were read after incubation for 48 h at 35°C. The yeast isolates included Candida albicans (n = 161), Candida glabrata (n = 41), Candida tropicalis (n = 35), Candida parapsilosis (n = 29), Candida krusei (n = 32), Candida lusitaniae (n = 31), Candida species (n = 19), Cryptococcus neoformans (n = 40), and miscellaneous yeast species (n = 14). The Etest results correlated well with reference MICs. Overall agreement was 94% with RPG, 97% with CAS, and 53% with MHA. When RPG was used, agreement ranged from 89% for Candida spp. to 100% for C. krusei. When CAS was utilized, agreement ranged from 93% for Cryptococcus neoformans to 100% for C. tropicalis, C. parapsilosis, C. lusitaniae, Candida spp., and miscellaneous yeast species. With MHA, agreement ranged from 17% for C. parapsilosis to 90% for C. krusei. Both RPG and CAS supported growth of all yeast species, whereas growth on MHA was comparatively weaker. Etest results were somewhat easier to read on CAS. The Etest method using either RPG or CAS, but not MHA, appears to be a viable alternative to the NCCLS reference method for determining fluconazole susceptibilities of yeasts.  相似文献   
73.
Data are presented on the family distribution of nearsightedness, including the frequency of the disorder in the children of two myopes. The previous literature is reviewed, embracing several quantitative family or population studies in addition to extensive pedigree material. It is concluded that there is substantial evidence that recessive inheritance is the principal mechanism of transmission, and that most instances of myopia probably fall into that category.  相似文献   
74.
The susceptibilities of 105 clinical isolates of anaerobic bacteria were determined by a new method, the E test (AB Biodisk, Solna, Sweden), and were compared with the MICs for these organisms obtained by the reference agar dilution method by using supplemented brucella and Wilkins-Chalgren agars. The E test is a plastic strip with a predefined antibiotic gradient immobilized on one side and a MIC interpretive scale printed on the other side. Strips with cefoxitin, cefotaxime, imipenem, penicillin, metronidazole, and clindamycin were used in this study. A suspension of the test strain equal to the visual turbidity of a no. 0.5 McFarland standard was prepared and swabbed onto a 150-mm-diameter plate. The strips were applied in a radial fashion, and the plates were incubated under anaerobic conditions. After growth had occurred, an ellipse of inhibition was seen around each strip. At the point of intersection of the ellipse with the strip, the MIC was read from the interpretive scale. For most antibiotic-organism combinations, the ellipse was clear and the endpoint was sharp. The E-test MICs were interpreted after overnight and 48-h incubation for 58 of the strains. After overnight incubation, 87% of the E-test MICs were within 1 dilution of the agar dilution MICs, and 98% were within 2 dilutions. After 48 h of incubation, agreement was 86 and 97% respectively. E-test MICs obtained for the Bacteroides fragilis group after overnight incubation were more comparable than those obtained after 48 h of incubation to agar dilution MICs determined at 48 h for all drugs except clindamycin. On brucella agar, there was a 2% categorical discrepancy rate between the E-test MICs and agar dilution MICs, which occurred mostly with cefoxitin. The E test is easy to perform and read, is suitable for all anaerobes, can be used to test single patient isolates as needed, and offers the laboratory a reliable method for susceptibility testing of anaerobic bacteria.  相似文献   
75.
76.
The in situ degradation of rapidly transported proteins in nerve terminals of retinal ganglion cells was studied in pieces of the superior colliculus of the rabbit. Proteolytic degradation was found to be dependent upon extracellular calcium and intact calcium channels. Degradation was inhibited by leupeptin and SH-group blocking agents.  相似文献   
77.
This double-blind immunotherapy trial in children, using a purified and standardized Cladosporium herbarum allergen preparation, has shown that children with mould asthma and/or rhinoconjunctivitis, responded to immunotherapy with a decrease in specific IgE and a significant increase in specific IgG. There was a marked increase in the ratio specific IgG/specific IgE as a result of active treatment. IgE-CRIE radiostaining patterns showed no pronounced changes after 10 months' active treatment and no "new sensitivities" could be detected in the studied patients. IgG-CRIE radiostaining, primarily directed towards the important allergens, was significantly increased in the active group and particularly towards Ag-12 (partially identical to a previously described major allergen in Cladosporium herbarum, Ag-54). Children treated with histamine placebo showed no change in antibody patterns during 10 months of treatment.  相似文献   
78.
The enzyme-linked immunosorbent assay (ELISA) was applied for immunological diagnosis of human tularemia, using lipopolysaccharide from Francisella tularensis as antigen. Sera collected from patients, healthy individuals, and vaccinated volunteers were investigated for antibodies against F. tularensis by ELISA and tube agglutination. In ELISA all sera were titrated with a polyspecific anti-immunoglobulin enzyme conjugate. A limited number of consecutive sera from individual patients were also investigated for immunoglobulin G (IgG) and IgM antibodies by means of immunoglobulin class-specific conjugates. On an average ELISA was more than 10-fold as sensitive as tube agglutination. Two weeks after onset of disease, sera from patients had significantly higher titers in ELISA than sera from healthy controls. High titers persisted after more than 2 years. Significant amounts of both IgG and IgM antibodies were present within 1 to 2 weeks after infection. The antibody activity increased during the first month, without any significant change of the relation between IgG and IgM titers. After 2.5 years the IgG/IgM titer ratio of sera from patients was significantly increased. Within 6 weeks after vaccination sera from about half of the vaccinees had significantly elevated titers in ELISA. Titers observed after vaccination were generally lower than those found after infection. An elevated ELISA titer can be of diagnostic importance by the end of the first week of illness. A significant increase of titer in consecutive serum samples indicates a diagnosis of tularemia. Determination of IgG and IgM antibodies may be of value in determing whether a positive titer of a single serum sample is of longstanding or recent origin.  相似文献   
79.
The appearance and activity of various porcine pancreatic hydrolases were studied during fetal and postnatal development. Quantitatively, the enzyme activities in activated pancreas homogenates were low but increased during the second half of the fetal period, using the substrates Bz-Arg-pNA for measuring anodal and cathodal trypsin, Suc-Phe-pNA (chymotrypsin A and C, and elastase II) and Suc-(Ala)3-pNA (elastase I and protease E). Postnatally, after an initial decrease during the first week, the enzyme activities increased markedly, especially from 10-14 weeks to 6 months. The individual hydrolases were identified after electrophoretic separation in agarose gel and staining with various substrates either directly in the gel or after transfer to nitrocellulose membranes (enzymoblotting). During the fetal period, chymotrypsin A and B, elastase II, carboxypeptidase A, and amylase appeared at approximately 65 days and anodal trypsin, at approximately 76 days. After birth, new proteinases appeared after the first week including chymotrypsin C, cathodal trypsin, and protease E, whereas elastase I was found from 5 weeks after birth. Concomitantly, unidentified "fetal proteinase(s)" with caseinolytic, Ac-Phe-beta NE and CBZ-Ala-beta NE activities began to diminish and disappeared 10-14 weeks after birth. This study showed a marked increase in the overall pancreatic enzyme activities, as well as an age-dependent expression of the variety of pancreatic hydrolases during porcine ontogeny.  相似文献   
80.
Dual-energy X-ray absorptiometry (DXA)-derived appendicular lean mass/height2 (ALM/ht2) is the most commonly used estimate of muscle mass in the assessment of sarcopenia, but its predictive value for fracture is substantially attenuated by femoral neck (fn) bone mineral density (BMD). We investigated predictive value of 11 sarcopenia definitions for incident fracture, independent of fnBMD, fracture risk assessment tool (FRAX®) probability, and prior falls, using an extension of Poisson regression in US, Sweden, and Hong Kong Osteoporois Fractures in Men Study (MrOS) cohorts. Definitions tested were those of Baumgartner and Delmonico (ALM/ht2 only), Morley, the International Working Group on Sarcopenia, European Working Group on Sarcopenia in Older People (EWGSOP1 and 2), Asian Working Group on Sarcopenia, Foundation for the National Institutes of Health (FNIH) 1 and 2 (using ALM/body mass index [BMI], incorporating muscle strength and/or physical performance measures plus ALM/ht2), and Sarcopenia Definitions and Outcomes Consortium (gait speed and grip strength). Associations were adjusted for age and time since baseline and reported as hazard ratio (HR) for first incident fracture, here major osteoporotic fracture (MOF; clinical vertebral, hip, distal forearm, proximal humerus). Further analyses adjusted additionally for FRAX-MOF probability (n = 7531; calculated ± fnBMD), prior falls (y/n), or fnBMD T-score. Results were synthesized by meta-analysis. In 5660 men in USA, 2764 Sweden and 1987 Hong Kong (mean ages 73.5, 75.4, and 72.4 years, respectively), sarcopenia prevalence ranged from 0.5% to 35%. Sarcopenia status, by all definitions except those of FNIH, was associated with incident MOF (HR = 1.39 to 2.07). Associations were robust to adjustment for prior falls or FRAX probability (without fnBMD); adjustment for fnBMD T-score attenuated associations. EWGSOP2 severe sarcopenia (incorporating chair stand time, gait speed, and grip strength plus ALM) was most predictive, albeit at low prevalence, and appeared only modestly influenced by inclusion of fnBMD. In conclusion, the predictive value for fracture of sarcopenia definitions based on ALM is reduced by adjustment for fnBMD but strengthened by additional inclusion of physical performance measures. © 2021 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).  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