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   4569篇
  免费   324篇
  国内免费   27篇
耳鼻咽喉   105篇
儿科学   145篇
妇产科学   94篇
基础医学   575篇
口腔科学   185篇
临床医学   460篇
内科学   996篇
皮肤病学   65篇
神经病学   474篇
特种医学   155篇
外科学   680篇
综合类   52篇
一般理论   1篇
预防医学   271篇
眼科学   42篇
药学   200篇
中国医学   8篇
肿瘤学   412篇
  2023年   46篇
  2022年   105篇
  2021年   164篇
  2020年   103篇
  2019年   129篇
  2018年   143篇
  2017年   87篇
  2016年   148篇
  2015年   125篇
  2014年   170篇
  2013年   204篇
  2012年   336篇
  2011年   337篇
  2010年   183篇
  2009年   171篇
  2008年   267篇
  2007年   251篇
  2006年   253篇
  2005年   218篇
  2004年   221篇
  2003年   204篇
  2002年   179篇
  2001年   51篇
  2000年   61篇
  1999年   48篇
  1998年   34篇
  1997年   31篇
  1996年   40篇
  1995年   29篇
  1994年   33篇
  1993年   31篇
  1992年   42篇
  1991年   40篇
  1990年   32篇
  1989年   27篇
  1988年   22篇
  1987年   26篇
  1986年   32篇
  1985年   21篇
  1984年   21篇
  1983年   25篇
  1982年   18篇
  1981年   23篇
  1980年   19篇
  1979年   13篇
  1978年   15篇
  1977年   15篇
  1975年   15篇
  1974年   12篇
  1972年   17篇
排序方式: 共有4920条查询结果,搜索用时 15 毫秒
41.
42.
43.
ObjectiveTo estimate the impact of reduced consumption of free sugars in line with World Health Organization recommendations, on sugar farmers globally.MethodsUsing multiregion input–output analysis, we estimated the proportional impact on production volumes of a 1% reduction in free sugars consumption by the public. We extracted data on sugar production from the Food and Agriculture Organization of the United Nations database for the top 15 sugar-cane- and beet-producing countries globally, and created a custom multiregion input–output database to assess the proportions of production going to human consumption, drawing on household expenditure surveys and national input–output databases (data valid for years 2000–2015). We also considered the impact on production volumes in relation to countries’ gross domestic product.FindingsA high proportion of current sugar production from these countries goes to human consumption, and would thus be impacted by reduced consumption of sugars. The largest impacts on cane sugar production, and thus on farmers, would likely occur in Brazil, China, India and Thailand and on beet production in Belarus, Germany, Russian Federation and United States of America.ConclusionA global opportunity exists for public health leadership to bring together the health, economic, environmental and agriculture sectors to collaborate and build capacity for promotion of alternative livelihoods for sugar farmers. Lessons regarding strategy and the importance of political economy factors can be learnt from tobacco control measures. Further research to quantify the impact of reductions in sugars consumption would provide useful insights for designing policies to complement and strengthen efforts to improve diets and health.  相似文献   
44.
  1. The sigma-drug binding site of guinea-pig liver is carried by a protein which shares significant amino acid sequence similarities with the yeast sterol C8–C7 isomerase (ERG2 protein). Pharmacologically - but not structurally - the sigma1-site is also related to the emopamil binding protein, the mammalian sterol C8–C7 isomerase. We therefore investigated if sterol C8–C7 isomerase inhibitors are high affinity ligands for the (+)-[3H]-pentazocine labelled sigma1-binding site.
  2. Among the compounds which bound with high affinity to native hepatic and cerebral as well as to yeast expressed sigma1-binding sites were the agricultural fungicide fenpropimorph (Ki 0.005 nM), the antihypocholesterinaemic drugs triparanol (Ki 7.0 nM), AY-9944 (Ki 0.46 nM) and MDL28,815 (Ki 0.16 nM), the enantiomers of the ovulation inducer clomiphene (Ki 5.5 and 12 nM, respectively) and the antioestrogene tamoxifen (Ki 26 nM).
  3. Except for tamoxifen these affinities are essentially identical with those for the [3H]-ifenprodil labelled sterol C8–C7 isomerase of S. cerevisiae. This demonstrates that sigma1-binding protein and yeast isomerase are not only structurally but also pharmacologically related. Because of its affiliations with yeast and mammalian sterol isomerases we propose that the sigma1-binding site is localized on a sterol isomerase related protein, involved in postsqualene sterol biosynthesis.
  相似文献   
45.
Papillary carcinomas (PCs) of thyroid are among the most common but least aggressive human malignancies. The factors explaining the indolence of these tumors are unknown but host-tumor immune interactions may play a role. This study was designed to determine if there is morphologic evidence of these. Frozen tissues collected from 21 PCs, 4 follicular adenomas (FAs), 4 follicular carcinomas (FCs), and 11 nodular hyperplasias (NHs) were stained immunohistochemically for HLA-D antigens, lymphocyte and macrophage markers; results were graded numerically. Paraffin-embedded tumors (35 PCs, 10 FAs, and 10 FCs) were stained for S-100 protein to detect Langerhans' cells (LCs). Diffuse staining for HLA-D antigens and heavy mononuclear infiltrates were found more commonly in PCs compared to follicular neoplasms (FNs) or NHs. No consistent relationship was found between lymphocyte/macrophage infiltrates and expression of HLA-D antigens. The largest number of LCs was in PCs (median 11.8 cells/standard microscopic field [c/smf]), fewer cells were found in FA (3.7 c/smf), and the least in FC (0.05 c/smf). Features of host-tumor interaction including HLA-D expression and infiltrates with lymphocyte macrophages and LC are more strongly expressed in PC than other tumors. This may play a role in explaining their biological behavior.  相似文献   
46.

Purpose

This case report describes a radiologically proven subdural catheter placed in a term parturient, which consistently performed as an epidural catheter for both labour analgesia as well as surgical anaesthesia.

Clinical features

The patient was a 26-yr-old, 52.7 kg, 140 cm healthy woman with a 39 wk intrauterine pregnancy. At initiation of epidural blockade, and for many hours throughout labour, an appropriate volume and concentration of local anaesthetic achieved an appropriate analgesic sensory level (10 ml bupivacaine 0.25%, bilateral T10 sensory level). However, for Caesarean section, while an appropriate volume and concentration of local anaesthetic achieved an appropriate surgical anaesthetic sensory level (15 ml bupivacaine 0.5%, bilateral T4 sensory level), there was no demonstrable motor blockade (0 on the Bromage scale). The Caesarean section was performed without incident, and without the need for supplemental intravenous opioids or anxiolytics.

Conclusion

We report the case to question the commonly held beliefs of subdural catheter presentation. We questioned the catheter position, and proved its subdural placement, only after larger volumes of higher concentration local anaesthetic did not achieve expected goals. It is possible that a high percentage of epidural catheters may be subdural, unbeknownst to the practitioner.  相似文献   
47.
The high rates of abdominal disorders in a growing population of geriatric patients and the greater willingness of the surgeon to cope with major problems in the elderly are factors contributing to a steady increase in abdominal procedures in this group. Four hundred consecutive major abdominal surgical procedures in patients over 70 years of age were submitted for computer analysis, the purpose of which was to determine the principal factors affecting mortality and morbidity. The etiological profile of abdominal surgery in the elderly was characterized by a high percentage of procedures related to the biliary tract, with the second largest group being those for intestinal obstruction due to benign and malignant conditions. The decision-making process in geriatric surgery is of great importance, requiring consideration of ethical, medico-legal and economic factors in addition to the purely medical ones. Analysis of data presented in this series leads to the following conclusions:
  1. There is a declining mortality rate in all elective operations in the elderly, in the absence of widespread malignancy.
  2. Timing is all important in abdominal emergencies in the elderly, and early operations are usually more successful than either immediate or delayed operations.
  3. Definitive procedures are sometimes both safer and more cost effective than minimal procedures performed under such circumstances.
  4. The principal factors leading to high mortality rates are the presence of malignancy, generalized peritonitis, and moderate-to-severe involvement of life-support systems.
  相似文献   
48.
49.
Microsomal monooxygenases catalyze the biosynthesis of epoxides from olefinic and aromatic compounds whilst microsomal epoxide hydratase and cytoplasmic glutathione S-transferases are responsible for their further biotransformation. Although catalytically very efficient the cytoplasmic glutathione S-transferases play, due to their subcellular localization, a minor role in the inactivation of epoxides derived from large lipophilic compounds and were, therefore, not included in this study. It was shown with such a lipophilic compound, benzo(a)pyrene, as a model substance and with liver enzyme mediated bacterial mutagenesis as biological endpoint that species and strain differences in epoxide hydratase and monooxygenases are reflected in very dramatic differences in mutagenicity of benzo(a)pyrene which varied from extremely potent to a degree which could easily be overlooked. In order to investigate whether the differences in enzyme activities were causally linked to the observed differences in mutagenicity, the enzyme activities were modulated by inhibition and induction. These manipulations were always accompanied by the corresponding changes in mutagenicity.It is concluded that species such as mice which possess high monooxygenase activity but very low epoxide hydratase activity are much more susceptible than man to those toxic effects which are mediated by metabolically formed epoxides which are substrates of epoxide hydratase. In this regard, it is especially noteworthy that mice possess a much lower hepatic epoxide hydratase activity than man.Presented at the Symposium Influence of Metabolic Activations and Inactivations on Toxic Effects held at the 18th Spring Meeting of the Deutsche Pharmakologische Gesellschaft, Section Toxicology, D-6500 Mainz, March 15, 1977  相似文献   
50.
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