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   956篇
  免费   66篇
  国内免费   7篇
耳鼻咽喉   14篇
儿科学   19篇
妇产科学   8篇
基础医学   126篇
口腔科学   94篇
临床医学   74篇
内科学   201篇
皮肤病学   34篇
神经病学   101篇
特种医学   15篇
外科学   109篇
综合类   4篇
预防医学   90篇
眼科学   14篇
药学   59篇
中国医学   16篇
肿瘤学   51篇
  2024年   1篇
  2023年   15篇
  2022年   34篇
  2021年   47篇
  2020年   29篇
  2019年   42篇
  2018年   37篇
  2017年   30篇
  2016年   33篇
  2015年   42篇
  2014年   48篇
  2013年   56篇
  2012年   75篇
  2011年   91篇
  2010年   50篇
  2009年   28篇
  2008年   40篇
  2007年   33篇
  2006年   42篇
  2005年   54篇
  2004年   39篇
  2003年   24篇
  2002年   28篇
  2001年   19篇
  2000年   11篇
  1999年   10篇
  1998年   6篇
  1997年   1篇
  1996年   8篇
  1995年   1篇
  1993年   2篇
  1992年   8篇
  1991年   9篇
  1990年   5篇
  1989年   4篇
  1988年   5篇
  1987年   1篇
  1986年   4篇
  1985年   3篇
  1983年   2篇
  1978年   2篇
  1976年   1篇
  1975年   1篇
  1974年   2篇
  1973年   1篇
  1972年   1篇
  1971年   1篇
  1969年   1篇
  1968年   2篇
排序方式: 共有1029条查询结果,搜索用时 31 毫秒
1.
Melatonin, the main hormone produced by the pineal gland, is secreted in a circadian manner (24‐hr period), and its oscillation influences several circadian biological rhythms, such as the regulation of clock genes expression (chronobiotic effect) and the modulation of several endocrine functions in peripheral tissues. Assuming that the circadian synchronization of clock genes can play a role in the regulation of energy metabolism and it is influenced by melatonin, our study was designed to assess possible alterations as a consequence of melatonin absence on the circadian expression of clock genes in the epididymal adipose tissue of male Wistar rats and the possible metabolic repercussions to this tissue. Our data show that pinealectomy indeed has impacts on molecular events: it abolishes the daily pattern of the expression of Clock, Per2, and Cry1 clock genes and Pparγ expression, significantly increases the amplitude of daily expression of Rev‐erbα, and affects the pattern of and impairs adipokine production, leading to a decrease in leptin levels. However, regarding some metabolic aspects of adipocyte functions, such as its ability to synthesize triacylglycerols from glucose along 24 hr, was not compromised by pinealectomy, although the daily profile of the lipogenic enzymes expression (ATP‐citrate lyase, malic enzyme, fatty acid synthase, and glucose‐6‐phosphate dehydrogenase) was abolished in pinealectomized animals.  相似文献   
2.
To evaluate the impact of pregnancy on bone, we studied bone turnover at the first (T1) and third (T3) trimester of gestation in 58 adolescents and 28 healthy adolescents who had never been pregnant. Total body (TB) and lumbar spine (LS) bone mineral density (BMD) and body composition were evaluated by dual-energy X-ray absorptiometry in all control patients (C) and after parturition in 28 pregnant patients (G). Paired and unpaired t tests, Mann-Whitney and Pearson correlation tests were used. Bone turnover markers were above the reference range for adult women in more than 80% of the adolescents, with no difference between C and G patients at T1. Increase in urinary N-telopeptide crosslinks of type I collagen and serum bone-specific alkaline phosphatase, markers of bone turnover, was seen during pregnancy ( p < 0.0001). Body composition did not differ between groups, but LS BMD, percentage of expected LS BMD, LS Z-score, percentage of expected TB BMD and TB Z-score were lower in G than C patients ( p < 0.05). TB BMD was positively correlated with LS BMD (r2 = 0.52). The inverse correlations between bone markers and LS BMD suggest that the increased bone turnover during pregnancy probably explains the low bone density after parturition. The impact on future peak bone mass must be studied.  相似文献   
3.
Impaired ability to conduct daily activities is a diagnostic criterion for dementia and a determinant of healthcare services utilization and caregiver burden. What predicts decline in instrumental activities of daily living (IADLs) is not well understood. This study examined measures of episodic memory, executive function, and MRI brain volumes in relation to baseline IADLs and as predictors of rate of IADL change. Participants were 124 elderly persons with cognitive function between normal and moderate dementia both with and without significant small vessel cerebrovascular disease. Random effects modeling showed that baseline memory and executive function (EXEC) were associated with baseline IADL scores, but only EXEC was independently associated with rate of change in IADLs. Whereas hippocampal and cortical gray matter volumes were significantly associated with baseline IADL scores, only hippocampal volume was associated with IADL change. In a model including cognitive and neuroimaging predictors, only EXEC independently predicted rate of decline in IADL scores. These findings indicate that greater executive dysfunction at initial assessment is associated with more rapid decline in IADLs. Perhaps executive function is particularly important with respect to maintaining IADLs. Alternatively, executive dysfunction may be a sentinel event indicating widespread cortical involvement and poor prognosis.  相似文献   
4.
Hyperparathyroidism contributes significantly to decreased bone mineral density (BMD) in end-stage renal disease patients, but this negative influence is not homogeneous throughout the skeleton. We studied the BMD by dual-energy X-ray absorptiometry on total body and on different regions of the skeleton in 42 patients with severe hyperparathyroidism on hemodialysis. We also evaluated the relationship between different risk factors and BMD found on the regions examined in these patients. The legs and other sites where cortical bone predominate were mostly affected, whereas trabecular bone was relatively preserved. This is probably the result of the different effects of hyperparathyroidism on cortical and trabecular bone, but we cannot rule out the interference of ectopic calcifications and sclerotic lesions of vertebral end-plates falsely increasing lumbar spine BMD. The main determinants of low total-body BMD were, in order of importance, immobility, high intact parathyroid hormone levels, low body mass index, and low albumin. Eleven patients presented with pathologic fractures, mainly in the legs, and BMD was lower in this group than in patients without fractures. In conclusion, our study makes clear that hyperparathyroidism is a great threat to bone density in hemodialysis patients, mainly in the legs, the site mostly affected by fragility fractures in our patients. Physicians must worry not only with high parathyroid hormone levels, but also with the nutritional state of these patients.  相似文献   
5.
Transplantation of any organ has some inherent risk of disease transmission, such as infection and malignancy. The present study aims to describe 2 cases of choriocarcinoma transmission after kidney and liver transplantation originating from the same patient. The donor was a 17-year-old woman who died of cerebral hemorrhage. Both organ recipients died of metastatic choriocarcinoma few months after the transplantation, within days after starting chemotherapy. Retrospective hCG (human chorionic gonadotropin hormone) analysis in donor's blood stored at the time of donation had a result of 9324 mIU/mL. Despite its rarity, clinicians should be aware of the risk of transplant-related choriocarcinoma from female donors in childbearing age. In some cases, hCG dosage should be performed before donation.  相似文献   
6.
The methanolic extract from the roots of WILBRANDIA EBRACTEATA afforded, in addition to the known dihydrocucurbitacins B and E, dihydroisocucurbitacin B, Cucurbitacins B, D, E, G, H, P, and 22-deoxycucurbi-tacin D, four new compounds whose structures were elucidated as (20 R,24xi)-3)3beta,16alpha,20)24,25-pentahydroxy-10alpha-cucurbit-5-ene-2,11,22-trione (3- EPI-isocucurbitacin G) ( 8), (20 R,22xi)-2beta16a,20,22,25-pentahydroxy-10alpha-cucurbita-5,23 T-diene-3,11-dione ( 13), (20 R)-25-acetoxy-3,16alpha,20-trihydroxy-30- NOR-2-(beta- D-glucopyranosyloxy)-1,2,3,4,5,10-dehydrocucurbit-6-ene-11,22-dione ( 14), and dihydroisocucurbitacin B-3-glucoside ( 16).  相似文献   
7.
8.
The mutation in the hypoxanthine-guanine phosphoribosyltransferase (HPRT) gene has been determined in two brothers affected with Lesch-Nyhan syndrome. Female members of the family who are at risk for being heterozygous carriers of the HPRT mutation were also studied to determine whether they carry the mutation. DNA sequencing revealed that the boys' mother is heterozygous for the mutation in her somatic cells, but that three maternal aunts are not heterozygous. Such carrier information is important for the future pregnancy plans of at-risk females. The mutation, an A-->T transversion at cDNA base 590 (590A-->T), results in an amino acid change of glutamic acid to valine at codon 197, and has not been reported previously in a Lesch-Nyhan syndrome male. This mutation is designated HPRTBrasil.  相似文献   
9.
We have investigated the role of coagulation and fibrinolysis during the metastatic lung colonization of F3II mouse mammary carcinoma cells. The selective synthetic urokinase inhibitor B623 significantly enhanced lung colonization and blocked the antimetastatic effect of heparin when administered i.p. during the first stages of metastasis formation. In B623-treated mice the overall activity of the fibrinolytic system was reduced and circulating urokinase was specifically inhibited by this agent. In vitro studies demonstrated that B623 induces the aggregation of F3II cells in the presence of mouse plasma and facilitates the entrapment of tumor cells in a fibrin gel matrix. Our data suggest that imbalances of fibrin deposition and removal may dramatically influence metastatic lung colonization.  相似文献   
10.
175 patients using oral contraceptives (OCs) for periods from 2 months-6 years were studied. A survey was made of the secondary effects of the treatment. Among the total group, 101 of them had not presented headache before the use of contraceptives, and the remaining 75 patients had previously complained of chronic headaches which were considered due to different etiologies. 50 patients from the group without previous headache claimed that OC treatment marked the initiation of the headaches. 25 had vascular headaches and 25 had tension headaches. Among the 75 patients included in the other group as complainers of chronic headache prior to treatment, 30 had a worsening of the symptoms after use of the OCs. The authors compare their results with those referred to in the literature. (author's)  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