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   6498篇
  免费   531篇
  国内免费   26篇
耳鼻咽喉   85篇
儿科学   363篇
妇产科学   83篇
基础医学   780篇
口腔科学   185篇
临床医学   546篇
内科学   1520篇
皮肤病学   121篇
神经病学   467篇
特种医学   216篇
外科学   791篇
综合类   213篇
现状与发展   20篇
一般理论   1篇
预防医学   426篇
眼科学   136篇
药学   434篇
中国医学   54篇
肿瘤学   614篇
  2023年   64篇
  2022年   75篇
  2021年   220篇
  2020年   118篇
  2019年   134篇
  2018年   185篇
  2017年   135篇
  2016年   148篇
  2015年   170篇
  2014年   232篇
  2013年   319篇
  2012年   429篇
  2011年   403篇
  2010年   268篇
  2009年   236篇
  2008年   284篇
  2007年   288篇
  2006年   260篇
  2005年   253篇
  2004年   230篇
  2003年   227篇
  2002年   204篇
  2001年   180篇
  2000年   180篇
  1999年   178篇
  1998年   96篇
  1997年   90篇
  1996年   83篇
  1995年   77篇
  1994年   51篇
  1993年   51篇
  1992年   111篇
  1991年   88篇
  1990年   94篇
  1989年   98篇
  1988年   85篇
  1987年   76篇
  1986年   65篇
  1985年   65篇
  1984年   53篇
  1983年   49篇
  1982年   31篇
  1981年   23篇
  1979年   40篇
  1978年   37篇
  1977年   22篇
  1976年   23篇
  1974年   22篇
  1973年   22篇
  1970年   22篇
排序方式: 共有7055条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
BACKGROUND: Endothelin, a peptide with strong vasoconstrictive and mitogenic properties, has been found to increase after cardiac transplantation. We therefore assessed the association between its precursor peptide, big endothelin-1, and intimal hyperplasia and coronary flow reserve after heart transplantation. METHODS: Thirty-five patients without hemodynamically significant coronary artery disease after heart transplantation were investigated: Average peak flow velocity in the left anterior descending artery (LAD) was assessed by intracoronary Doppler at baseline as well as after injection of adenosine; coronary flow reserve was calculated as a ratio of both and was corrected for patient age and baseline average peak flow velocity. Lumen, intima + media and total vessel area were measured by intracoronary ultrasound. The plasma concentration of big endothelin-1 in venous blood was determined by radioimmunoassay. RESULTS: Patients with elevated big endothelin-1 levels (>2 fmol/ml) tended to have a decreased corrected coronary flow reserve (2.60 +/- 0.9 vs 3.21 +/- 1.0, p = 0.078). They also had a significantly larger intima + media area (5.82 +/- 2.9 vs 2.37 +/- 2.9 mm(2), p = 0.004) and total vessel area (18.36 +/- 5.8 vs 12.81 +/- 4.8 mm(2), p = 0.012) than those with normal plasma concentrations. CONCLUSIONS: Our study suggests an association between elevated big endothelin-1 plasma levels and the development of intimal hyperplasia and reduction of coronary flow reserve after cardiac transplantation.  相似文献   
5.
6.
Representative examples of folate and antifolate poly-gamma-glutamyl metabolites were synthesized via the [(9-fluorenylmethoxy)oxy]carbonyl (Fmoc) chemistry using the KH polyamide resin. Polyglutamate yields were consistently better in all cases compared to the previous Merrifield method, and the crude products were obtained in greater than 85% purity. The symmetrical anhydride (7) derived from alpha-tert-butyl N-Fmoc-L-glutamate (6) was used for the initial coupling of the first glutamate residue to the KH resin and also for subsequent chain elongation. The alpha-tert-butyl protective groups were not labile under the conditions used for the cleavage of the finished peptide from the resin. A series of poly-gamma-glutamyl metabolites of methotrexate (MTX) with a chain length ranging from two to five glutamyl residues were synthesized and coupled with poly(L-lysine) having an average molecular weight of 27,000 and 52,000. Each conjugate was tested for its ability to inhibit the growth of wild type (H35) and MTX transport resistant (H35R) strains of hepatoma cells in culture, the latter having a 100-fold reduced sensitivity to MTX. 4-Amino-4-deoxy-N10-methylpteroylglutamyl-gamma-glutamylpoly (L-lysine) conjugate [MTX(G2)-poly-L-Lys-52000] and MTX(G4)-poly-L-Lys-52000 were among the most active (I50 = 8.0 and 10 nM against H35 cells) MTX-polylysines synthesized to date, and they were somewhat more inhibitory to the transport resistant cells. MTX(G5)-poly-L-Lys-52000 was approximately 1000 times more effective than MTX(G5)-poly-D-Lys-52000 in inhibiting the growth of H35R hepatoma cells in culture, indicating that internal cleavage of the gamma-glutamate chain of the conjugate with subsequent release of MTX or shorter chain polyglutamates of MTX is unlikely to be an important determinant of MTX-polyglutamate polylysine cytotoxicity. The results indicate that MTX-polyglutamate poly(L-lysine) conjugates are taken up by the cells independently of MTX and probably via endocytosis.  相似文献   
7.
Norethisterone enanthate (NET-En), an established intramuscular long-acting contraceptive agent, has previously been shown to be effective in inhibiting fertility in two rodent species even 4 days after oral ingestion. Pharmacokinetics of NET and NET-En were studied after oral and intramuscular doses in two animal species and a few women. The results suggest that the NET-En was absorbed within a day in all the species after oral dose. The estimates of relative bioavailability ranged from 13 to 51% in rabbits, monkeys, and women. The elimination half-life was 5–10 days. The presence of the active component, NET, in the circulation over the experimental period of 15 days suggests that NET-En could be useful as a long-acting oral pill. The suppression of progesterone levels during the luteal phase of menstrual cycle in women also supports this finding.  相似文献   
8.
L. G. Nair  C. P. Kurtz 《Thorax》1996,51(7):765-766
Lymphangiomatosis is a rare disorder of the lymphatic system that is known to cause chylothorax. Chyloptysis may occur but chylous bronchial cast formation is rare. A case is reported of lymphangiomatosis in a 34 year old woman whose initial manifestation was cough productive of bronchial casts. Two years later the patient developed a chylothorax. Ligation of the thoracic duct through a low thoracotomy was curative.  相似文献   
9.
Sublethal stress of toxicants on organisms is generally measured through metabolic changes. The effects of three pesticides (endosulfan, malathion, and methyl parathion) on tissue lipid levels in the estuarine bivalve, Villorita cyprenoids var. cochinensis, have been measured. The reduction in lipid content was expressed as a function of the pesticide concentrations and the duration of the exposure periods (24, 48, 72, and 96 h). The results point to the existence of a direct relationship between the applied stress and the fall in the lipid content. The order of toxicity was endosulfan > malathion > methyl parathion. The depletion in lipid content observed may reflect an adaptive response of the organism to pesticide stress. Thus lipids in bivalves have been shown to be an important reserve material that may be utilized under stressed conditions as an energy source. © by John Wiley & Sons, Inc.  相似文献   
10.
H T Nair  G Little 《Journal of postgraduate medicine》1991,37(4):232B, 233-232B, 234
A case of bladder tumour arising as a metastasis of renal carcinoma and presenting as obstruction to urinary outflow is described. The possible mechanism of spread to bladder is also suggested.  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