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   1728篇
  免费   95篇
  国内免费   22篇
耳鼻咽喉   1篇
儿科学   151篇
妇产科学   34篇
基础医学   188篇
口腔科学   47篇
临床医学   163篇
内科学   372篇
皮肤病学   23篇
神经病学   34篇
特种医学   470篇
外科学   101篇
综合类   30篇
预防医学   63篇
眼科学   14篇
药学   84篇
中国医学   3篇
肿瘤学   67篇
  2022年   5篇
  2021年   9篇
  2020年   9篇
  2019年   7篇
  2018年   18篇
  2017年   11篇
  2016年   22篇
  2015年   27篇
  2014年   32篇
  2013年   58篇
  2012年   33篇
  2011年   26篇
  2010年   78篇
  2009年   62篇
  2008年   34篇
  2007年   33篇
  2006年   40篇
  2005年   31篇
  2004年   19篇
  2003年   22篇
  2002年   24篇
  2001年   19篇
  2000年   27篇
  1999年   27篇
  1998年   136篇
  1997年   118篇
  1996年   124篇
  1995年   91篇
  1994年   75篇
  1993年   81篇
  1992年   23篇
  1991年   21篇
  1990年   15篇
  1989年   59篇
  1988年   44篇
  1987年   49篇
  1986年   45篇
  1985年   47篇
  1984年   24篇
  1983年   31篇
  1982年   34篇
  1981年   20篇
  1980年   36篇
  1979年   14篇
  1978年   15篇
  1977年   17篇
  1976年   23篇
  1975年   24篇
  1971年   2篇
  1966年   2篇
排序方式: 共有1845条查询结果,搜索用时 15 毫秒
51.
52.
The relationship between fecundability and month of birth was investigated in a cohort of 1526 women who married between 1802 and 1929, using only women whose first marriage occurred before the age of 35 years. On the basis of their time to pregnancy (TTP, calculated as time between wedding and first birth minus gestational length), women were categorized into two groups: fecunds (TTP up to 12 months or prenuptial conceptions, n = 1348) and subfecunds (TTP >18 months, n = 118). By use of logistic regression, cosinor functions with a period of 1 year or 6 months and variable shift and amplitude were fitted through the monthly odds of subfecunds versus fecunds. The best fitting curve was unimodal, with a zenith in September (P = 0.13 for H0: no differences). Exclusion of childless women (n = 36, minimum follow-up 5 years) from the subfecunds led to a similar curve (P < 0.01), while childless women, as compared with fecunds, showed a birth distribution that was best represented with a bimodal curve with zeniths in January and July (P = 0.06). This study provides evidence for the existence of differences in fecundability by month of birth. The cause of this relationship is unclear, but may lie in a melatonin-dependent circannual variability of the quality of the oocyte.   相似文献   
53.
Koo JS, Shin E, Hong SW. Immunohistochemical characteristics of diffuse sclerosing variant of papillary carcinoma: comparison with conventional papillary carcinoma. APMIS 2010; 118: 744–52. Diffuse sclerosing variant of papillary carcinoma (DSVPC) is a rare variant of papillary thyroid carcinoma (PTC). It shows different clinicopathologic features to the conventional PTC, but the immunohistochemical characteristics of DSVPC are yet to be more clearly defined. The purpose of this study was to investigate the immunohistochemical features of DSVPC, which are different from those of PTC. Tissue microarray was constructed from the paraffin‐embedded tissue of 49 DSVPC and 50 conventional PTC samples. Immunohistochemical stains for p63, p53, galectin‐3, cytokeratin 19, β‐catenin, Bcl‐2, EMA, E‐cadherin, CD15, and CD56 were performed on each tissue microarray. Immunohistochemical stain for p63 was negative in all conventional PTCs, but 14 (28.6%) cases of DSVPC showed p63 expression (p = 0.000). p53 was expressed in 38 (76.0%) cases of conventional PTC and 21 (42.9%) cases of DSVPC (p = 0.001). Galectin‐3 was expressed in all 50 cases of conventional PTC, but eight (16.3%) cases of DSVPC did not express galectin‐3 (p = 0.003). EMA was expressed more in DSVPC (40.8%) than in conventional PTC (20.0%, p = 0.024). In univariate analyses, Bcl‐2 positivity (p = 0.016) and EMA negativity (p = 0.036) in DSVPC were associated with shorter time interval to tumor recurrence, but there was no significance for the two in multivariate analyses. DSVPC, a rare variant of PTC, has different immunohistochemical features from the conventional PTC, showing higher expression rate of p63 and lower expression rate of p53. It also shows galectin‐3 negativity and EMA positivity.  相似文献   
54.
55.
OBJECTIVE: Studies suggest that African American women may have a greater risk of hot flashes compared to Caucasian women, but the reasons for this are unknown. This study tested the hypothesis that African American women have an increased risk of hot flashes due to racial differences in risk factors for hot flashes, including high body mass index (BMI) and lower estrogen levels. METHODS: A population-based study was conducted among women aged 45-54 years. Participants were divided into women who reported ever experiencing hot flashes (n=356) and women who reported never experiencing hot flashes (n=257). Participants provided a blood sample for hormone assays, were weighed and measured, and completed a questionnaire. RESULTS: Among peri-menopausal women, African American women were more likely than Caucasian women to report any hot flashes (RR=2.08), severe hot flashes (RR=2.19), and hot flashes for more than 5 years (RR=1.61). The risk ratios for the associations between race and the hot flash outcomes were attenuated after controlling for other important hot flash risk factors (i.e. obesity and low estrogen levels). CONCLUSIONS: African American women have an increased risk of hot flashes compared to Caucasian women due to racial differences in a number of risk factors for hot flashes, including advanced age, obesity, current smoking, less than 12 drinks in the past year, and lower estrogen levels.  相似文献   
56.
Securinega virosa is used traditionally as sedative in children and in mental illnesses. In this study, the behavioral effects of methanolic root bark extract of S. virosa were investigated in mice. The results revealed that the extract significantly (P<0.05) and dose-dependently reduced the onset and prolonged the duration of sleep. The extract significantly (P<0.05) decreased exploratory activity and reduced the rate of apomorphine-induced stereotyped climbing at the doses tested (6.25–25mg/kg). It also produced a significant and dose-dependent motor coordination deficit in mice at the doses tested (P<0.01). The intraperitoneal median lethal dose in mice was 774.6mg/kg while the preliminary phytochemical screening revealed the presence of alkaloids, tannins, saponins and flavonoids. These results suggest that methanolic root bark extract of S. virosa contains biologically active principles that are sedative in nature and lend pharmacological credence to the ethnomedical use of the plant.  相似文献   
57.
Glycogen storage disease due to phosphorylase kinase deficiency occurs in several variants that differ in mode of inheritance and tissue- specificity. This heterogeneity is suspected to be largely due to mutations affecting different subunits and isoforms of phosphorylase kinase. The gene of the ubiquitously expressed beta subunit, PHKB, was a candidate for involvement in autosomally transmitted phosphorylase kinase deficiency of liver and muscle. To identify such mutations, the complete PHKB coding sequence was amplified by RT-PCR of RNA isolated from blood samples of patients and analyzed by direct sequencing of PCR products. The characterization of mutations was complemented by PCR of genomic DNA. In one female and four male patients, we identified five independent nonsense mutations (Y418ter; R428ter; Y974H+E975ter; Q656ter in two cases), one single-base insertion in codon N421, one splice-site mutation affecting exon 31, and a large deletion involving the loss of exon 8. Although these severe translation-disrupting mutations occur in constitutively expressed sequences of the only known beta subunit gene of phosphorylase kinase, PHKB, they are associated with a surprisingly mild clinical phenotype, affecting virtually only the liver, and relatively high residual enzyme activity of approximately 10%.   相似文献   
58.
The objective was to test the hypothesis that the optimal cryoprotective agent for cryopreservation of human spermatozoa would be a solute for which cells have the highest plasma membrane permeability, resulting in the least amount of volume excursion during its addition and removal. To test this hypothesis, theoretical simulations were performed using membrane permeability coefficients to predict optimal procedures for the addition and removal of a cryoprotectant. Simulations were performed using data from four different cryoprotectants: (i) glycerol, (ii) dimethyl sulphoxide, (iii) propylene glycol and (iv) ethylene glycol. Thermodynamic formulations were applied to determine approaches for the addition and removal of 1 M and 2 M final concentrations of cryoprotectant, allowing the spermatozoa to maintain a cell volume within their osmotic tolerance limits. Based on these data, ethylene glycol was predicted to be optimal for minimizing volume excursions among the solutes evaluated. These predictions were then experimentally tested using glycerol as the control cryoprotectant and ethylene glycol as the experimental cryoprotectant. The results indicate that there was a higher (P < 0.05) recovery of motile spermatozoa after cryopreservation when using 1 M ethylene glycol than with 1 M glycerol, supporting the hypothesis that use of the cryoprotectant for which the cell has the highest permeability will result in higher cell survival.   相似文献   
59.
The aim of this study was to compare 70 couples who had conceived by in- vitro fertilization (IVF) with 63 matched controls for the prevalence of anxiety and quality of attachment to the baby during pregnancy. Results for mothers showed no group differences using a global measure of anxiety, the Spielberger State-Trait Anxiety Inventory. However, pregnancy-specific measures revealed significantly higher levels of anxiety in IVF mothers about the survival and normality of their unborn babies, about damage to their babies during childbirth and about separating from their babies after birth. When IVF mothers were differentiated according to the number of treatment cycles, more differences in anxiety level were revealed, with most increases occurring in mothers who had experienced two or more treatment cycles. IVF fathers did not differ from controls on the global anxiety measure. No data on pregnancy-specific anxiety were available for fathers. Neither IVF mothers nor IVF fathers differed from controls on measures of attachment to the baby during pregnancy. Results are discussed in the context of the need for researchers to employ differentiated and issue-specific measures to identify concerns that may be unique to IVF couples. Clinical implications regarding the need for psychological support during pregnancy are also discussed.   相似文献   
60.
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   
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