首页 | 官方网站   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   25630篇
  免费   1868篇
  国内免费   47篇
医药卫生   27545篇
  2024年   24篇
  2023年   227篇
  2022年   186篇
  2021年   780篇
  2020年   577篇
  2019年   752篇
  2018年   896篇
  2017年   660篇
  2016年   698篇
  2015年   710篇
  2014年   1037篇
  2013年   1500篇
  2012年   2232篇
  2011年   2313篇
  2010年   1221篇
  2009年   1067篇
  2008年   1793篇
  2007年   1891篇
  2006年   1714篇
  2005年   1593篇
  2004年   1447篇
  2003年   1265篇
  2002年   1249篇
  2001年   127篇
  2000年   119篇
  1999年   142篇
  1998年   220篇
  1997年   175篇
  1996年   133篇
  1995年   113篇
  1994年   111篇
  1993年   97篇
  1992年   53篇
  1991年   48篇
  1990年   37篇
  1989年   32篇
  1988年   18篇
  1987年   21篇
  1986年   23篇
  1985年   26篇
  1984年   29篇
  1983年   14篇
  1982年   28篇
  1981年   22篇
  1980年   14篇
  1979年   16篇
  1977年   11篇
  1976年   15篇
  1974年   11篇
  1973年   10篇
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
71.
ABSTRACT: Background: Hands‐and‐knees positioning during labor has been recommended on the theory that gravity and buoyancy may promote fetal head rotation to the anterior position and reduce persistent back pain. A Cochrane review found insufficient evidence to support the effectiveness of this intervention during labor. The purpose of this study was to evaluate the effect of maternal hands‐and‐knees positioning on fetal head rotation from occipitoposterior to occipitoanterior position, persistent back pain, and other perinatal outcomes. Methods: Thirteen labor units in university‐affiliated hospitals participated in this multicenter randomized, controlled trial. Study participants were 147 women laboring with a fetus at ≥37 weeks’ gestation and confirmed by ultrasound to be in occipitoposterior position. Seventy women were randomized to the intervention group (hands‐and‐knees positioning for at least 30 minutes over a 1‐hour period during labor) and 77 to the control group (no hands‐and‐knees positioning). The primary outcome was occipitoanterior position determined by ultrasound following the 1‐hour study period and the secondary outcome was persistent back pain. Other outcomes included operative delivery, fetal head position at delivery, perineal trauma, Apgar scores, length of labor, and women's views with respect to positioning. Results: Women randomized to the intervention group had significant reductions in persistent back pain. Eleven women (16%) allocated to use hands‐and‐knees positioning had fetal heads in occipitoanterior position following the 1‐hour study period compared with 5 (7%) in the control group (relative risk 2.4; 95% CI 0.88–6.62; number needed to treat 11). Trends toward benefit for the intervention group were seen for several other outcomes, including operative delivery, fetal head position at delivery, 1‐minute Apgar scores, and time to delivery. Conclusions: Maternal hands‐and‐knees positioning during labor with a fetus in occipitoposterior position reduces persistent back pain and is acceptable to laboring women. Given this evidence, hands‐and‐knees positioning should be offered to women laboring with a fetus in occipitoposterior position in the first stage of labor to reduce persistent back pain. Although this study demonstrates trends toward improved birth outcomes, further trials are needed to determine if hands‐and‐knees positioning promotes fetal head rotation to occipitoanterior and reduces operative delivery. (BIRTH 32:4 December 2005)  相似文献   
72.
73.
To characterize the lipid and lipoprotein abnormalities in patients with diabetes mellitus and evaluate the risks and benefits of marketed pharmacologic therapies, a MEDLINE search of the National Library of Medicine data base was performed of studies published from January 1966 to March 1994. Clinical trials assessing effects on lipids and lipoproteins, and adverse effects of marketed lipid-lowering agents were extracted. Reviews and other relevant articles were included if they provided information regarding lipid and lipoprotein metabolism or guidelines on the treatment of dyslipidemias in patients with diabetes mellitus. An extensive review of clofibrate was not included. The most common dyslipidemia in patients with poorly controlled insulin-dependent diabetes mellitus (IDDM) is combined elevated triglyceride and cholesterol levels, with reduced high-density lipoprotein (HDL) cholesterol (mixed hyperlipidemia). Hypertriglyceridemia combined with a reduced HDL cholesterol is the most common dyslipidemia in patients with noninsulin-dependent diabetes mellitus, but essentially any pattern of dyslipidemia may be present. Small and dense low-density lipoprotein (LDL), glycosylation of lipoproteins, and increased oxidized lipoproteins may be present in patients with diabetes mellitus; all contribute to accelerated atherosclerotic cardiovascular disease. Insulin therapy generally corrects quantitative lipid abnormalities in patients with IDDM, so drug treatment is seldom indicated. Diet, exercise, and insulin or oral sulfonylureas will improve hypertriglyceridemia and low HDL concentrations, but do not always return them to normal. Drug therapy is indicated when nonpharmacologic measures are inadequate. It is administered based on the effects of each agent on lipids and lipoproteins, patient age, adverse effect profile, patient tolerability, and drug-disease and drug-drug interactions. A fibric acid derivative is the drug of choice for marked hypertriglyceridemia in patients with diabetes mellitus. Niacin can worsen glycemic control, but it may be required in severe hypertriglyceridemia, hypercholesterolemia, or mixed hyperlipidemia. Bile-acid binding resins may accentuate hypertriglyceridemia but may be useful in selected patients with marked hypercholesterolemia and normal triglycerides. Hydroxymethylglutaryl coenzyme A reductase inhibitors are preferred in patients with elevated LDL cholesterol and mild hypertriglyceridemia. Patients with marked lipid abnormalities or mixed hyperlipidemias may require carefully dosed combinations of lipid-lowering drugs.  相似文献   
74.
75.
76.
Integrated surveillance of infectious multi-source diseases using a combination of epidemiology, ecology, genetics and evolution can provide a valuable risk-based approach for the control of important human pathogens. This includes a better understanding of transmission routes and the impact of human activities on the emergence of zoonoses. Until recently New Zealand had extraordinarily high and increasing rates of notified human campylobacteriosis, and our limited understanding of the source of these infections was hindering efforts to control this disease. Genetic and epidemiological modeling of a 3-year dataset comprising multilocus sequence typed isolates from human clinical cases, coupled with concurrent data on food and environmental sources, enabled us to estimate the relative importance of different sources of human disease. Our studies provided evidence that poultry was the leading cause of human campylobacteriosis in New Zealand, causing an estimated 58–76% of cases with widely varying contributions by individual poultry suppliers. These findings influenced national policy and, after the implementation of poultry industry-specific interventions, a dramatic decline in human notified cases was observed in 2008. The comparative-modeling and molecular sentinel surveillance approach proposed in this study provides new opportunities for the management of zoonotic diseases.  相似文献   
77.
Despite their large size, antibodies (Abs) are suitable carriers to deliver systemic radiotherapy, often molecular image-based, for lymphoma and leukemia. Lym-1 Ab has proven to be an effective radioisotope carrier, even in small amounts, for targeting human leukocyte antigen DR (HLA-DR), a surface membrane protein overexpressed on B-cell lymphoma. Pairs of molecules (referred to as ligands), shown by computational and experimental methods to bind to each of 2 sites within the Lym-1 epitopic region, have been linked to generate small (<2 kDa) molecules (referred to as selective high-affinity ligands [SHALs]) to mimic the targeting properties of Lym-1 Ab. METHODS: A lysine-polyethylene glycol (PEG) backbone was used to synthetically link 2 of the following ligands: deoxycholate, 5-leuenkephalin, triiodothyronine, thyronine, dabsyl-L-valine, and N-benzoyl-L-arginyl-4-amino-benzoic acid to generate a series of 13 bidentate SHALs with a biotin or 1,4,7,10-tetraazacyclododecane-N,N',N',N'-tetraacetic acid (DOTA) chelate attached to the linker. These SHALs have been assessed for their selectivity in binding to HLA-DR10-expressing cells and for their pharmacokinetics and tissue biodistribution in mice. Biotinylated versions of these SHALs discriminated cell lines positive for HLA-DR10 expression with near-nanomolar affinity. The DOTA versions of 4 SHALs were labeled with (111)In for pharmacokinetic studies in mice with HLA-DR10-expressing malignant Raji xenografts. RESULTS: The bidentate, biotinylated, and DOTA-SHALs were synthesized in high-purity, multimilligram amounts. Mean radiochemical and product yields and purities were 90%, 75%, and 90% at mean specific activities of 3.9 MBq/microg (105 microCi/microg) for the (111)In-labeled SHALs. As expected, rapid blood clearance and tumor targeting were observed. The pharmacokinetics of the SHALs was influenced by the component ligands. Biliary clearance, kidney localization, and serum receptor binding contributed to less favorable tumor targeting. CONCLUSION: A series of SHALs was readily synthesized in multimilligram amounts and showed the expected selective binding in vitro. Better selection of the SHAL components should provide second-generation SHALs with improved properties to fulfill the substantial potential of these novel molecular carriers for targeting.  相似文献   
78.
79.
Chronically elevated levels of cortisol have been associated with changes in cognitive functioning and brain morphology. Using Cushing's disease as a model to assess the effects of high levels of cortisol on cognitive functioning, 27 patients with Cushing's disease were examined at baseline and three successive follow-up periods up to 18 months after successful surgical treatment. At all follow-up periods, patients were administered cognitive tests as well as measures of plasma and urinary free cortisol. Structural MRIs and a depression measure were taken at baseline and one-year follow-up. Results showed that there is a specific pattern of significant cognitive and morphological improvement following successful treatment. Verbal fluency and recall showed recovery, although brief attention did not. Age of participants was a significant factor as to when recovery of function occurred; younger patients regained and sustained their improvement in cognitive functioning more quickly than older participants. Improvement in verbal recall also was associated with a decrease in cortisol levels as well as an increase in hippocampal formation volume one year after treatment. Overall, these findings suggest that at least some of the deleterious effects of prolonged hypercortisolemia on cognitive functioning are potentially reversible, up to at least 18 months post treatment.  相似文献   
80.
The production of phonological features of African American English (AAE) was examined for 64 typically developing African American children in the 2nd through the 5th grade. Students read aloud passages written in Standard American English. Sixty of the students read the passages using AAE, and 8 different phonological features were represented in their readings. Phonological features were more frequent than morphosyntactic features. The findings as a whole support use of the taxonomy developed for this investigation in characterizing the phonological features of child AAE.  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-23

京公网安备 11010802026262号