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   124601篇
  免费   8247篇
  国内免费   454篇
耳鼻咽喉   1630篇
儿科学   3298篇
妇产科学   2070篇
基础医学   15964篇
口腔科学   2370篇
临床医学   12556篇
内科学   26349篇
皮肤病学   1917篇
神经病学   11972篇
特种医学   4272篇
外国民族医学   4篇
外科学   18009篇
综合类   1888篇
现状与发展   1篇
一般理论   167篇
预防医学   11111篇
眼科学   2913篇
药学   8713篇
  2篇
中国医学   172篇
肿瘤学   7924篇
  2023年   511篇
  2022年   831篇
  2021年   2071篇
  2020年   1227篇
  2019年   2013篇
  2018年   2321篇
  2017年   1788篇
  2016年   1957篇
  2015年   2413篇
  2014年   3438篇
  2013年   5331篇
  2012年   7760篇
  2011年   8280篇
  2010年   4694篇
  2009年   4514篇
  2008年   7969篇
  2007年   8515篇
  2006年   8350篇
  2005年   8637篇
  2004年   8170篇
  2003年   7999篇
  2002年   7570篇
  2001年   1180篇
  2000年   930篇
  1999年   1230篇
  1998年   1704篇
  1997年   1424篇
  1996年   1162篇
  1995年   1147篇
  1994年   943篇
  1993年   960篇
  1992年   754篇
  1991年   707篇
  1990年   672篇
  1989年   625篇
  1988年   576篇
  1987年   543篇
  1986年   545篇
  1985年   664篇
  1984年   831篇
  1983年   832篇
  1982年   1162篇
  1981年   1052篇
  1980年   950篇
  1979年   464篇
  1978年   575篇
  1977年   547篇
  1976年   449篇
  1975年   408篇
  1974年   365篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A study was carried out to determine factors affecting place of death (home, hospital, nursing home or other places) among all 426,115 resident deaths in Washington State during 1968–1981, using death certificate information. Sixteen percent of deaths occurred at home, 74% in institutions (51% in hospitals, 23% in nursing homes) and 9% at other places. Age, marital status and cause of death all strongly affect place of death. Further, the effect of each factor was strongly dependent on the others. Sex had no effect on place of death after controlling for other factors. Elderly people died relatively more frequently in nursing homes, infants and middle aged people in hospitals and young adults in other places. The frequency of deaths at home was quite constant by age. Hospitals were the most common place of death following both vascular disease (including heart attack) and neoplasms, and nursing homes were the most common place of death following cerebrovascular disease (including stroke). Race, socioeconomic status and urban or rural residents affected the place of death only slightly or not at all. The place of death pattern changed little during the time period 1968–1981, except for a slight increase in frequency of home deaths and a corresponding decrease in the frequency of deaths in other places.Among cancer patients, the likelihood of death at home was positively associated with longer periods of survival after diagnosis. Cancer patients of hospitals serving targeted populations, such as veterans, were relatively more likely to die in a hospital and less likely to die in a nursing home compared to other cancer patients, suggesting that the targeted hospitals are sometimes serving a nursing home function. There was a marked difference in the terminal cancer caseload by hospital. The number of cancer deaths per cancer diagnosis varied widely across hospitals (0.1 to 1.6) and was unrelated to size of the hospital or level of services offered.Intervention aimed at affecting place of death, such as increasing the number of deaths at home, will need to take account of the joint effect of age, marital status and disease.Lincoln Polissar, Ph.D., is Associate Member, Fred Hutchinson Cancer Research Center, Division of Public Health Sciences, Seattle, WA and Associate Professor, Department of Biostatistics, University of Washington in Seattle. Richard K. Severson, M.S., is the Project Coordinator, Fred Hutchinson Cancer Research Center. Norman K. Brown, M.D., is Clinical Professor of Medicine, School of Medicine, University of Washington.This research was supported by NCI Grant Nos. NCI-SR18, CA 29770–03 Requests for reprints should be sent to Lincoln Polissar, Ph.D., Fred Hutchinson Cancer Research Center, 1124 Columbia Street, Seattle, WA 98104  相似文献   
992.
Summary Resistance to teniposide (VM-26) by VM-26 selected resistant L1210 cells in culture was attributed to alterations in the flux of VM-26 across the plasma membrane and to functions of homogeneously staining regions that appeared on one or more chromosomes. In the present study, electrophoresis of membrane-cytosol fractions of these resistant sublines demonstrated a protein band, Mr 22 kd, that was not evident in similar fractions of drugsensitive L1210 cells or three revertant sublines. The distribution of this protein among various cellular fractions could be altered by manipulation of the concentration of calcium ions. A representative subline, LIa5 M, was observed to have vesicles that reacted with Sudan black B stain, an indication of altered lipid metabolism. The LIa5 M subline was cross-resistant to etoposide, vincristine, doxorubicin, amsacrine, and actinomycin D. Concentrations of VM-26 that inhibited cell division to the same extent caused an accumulation of fewer cells in the G2 stage of cell division in LIa5 M cultures than in L1210 cultures. These observations indicate that the LIa5 M subline expressed multiple drug resistance, as well as changes in the expression of cytotoxicity to VM-26.This investigation was supported by Research Project Grant CA 35319, by Cancer Center Support (CORE) Grant CA 21765 from the National Cancer Institute, and by the American Lebanese Syrian Associated Charities.Recipient of research support from a training grant, American Cancer Society Grant IN-85-06, to the University of Tennessee Center for the Health Sciences  相似文献   
993.
This article explains divergent reports on the relative efficacy of unilateral and bilateral electroconvulsive therapy (ECT) by hypothesizing a therapeutic effect of both seizure and electrical stimulus, with the seizure's effect based on its intensity and generalization. The effect of the stimulus is normally obscured by the seizure but emerges with reduced electrical dosage or elevated threshold. These circumstances favor a therapeutic advantage for bilateral ECT, which introduces more electrical charge into a larger and differently distributed volume of brain and induces greater seizure generalization, more diencephalic stimulation, and a relative decrease in left relative to right hemisphere electroencephalographic (EEG) frequencies.  相似文献   
994.
Conflicting results continue to be reported for studies contrasting the therapeutic efficacy of bilateral and unilateral nondominant electroconvulsive therapy (ECT). At least in part, the therapeutic advantage for bilateral ECT observed by some investigators may be related to the use of nonoptimum unilateral ECT technique. Consideration of technique-related factors, such as stimulus electrode location, contact at the electrode-scalp interface, stimulus dosing, and seizure monitoring, will allow unilateral ECT to be carried out with maximal therapeutic potency.  相似文献   
995.
996.
Summary A total of 14 patients, 7 male and 7 female, received in all 21 evaluable courses of cyclophosphamide administered by 5-day continuous infusion. Cyclophosphamide doses were escalated from 300 to 400 mg/m2 per day for 5 days and repeated every 21–28 days. The patient population had a median age of 55 years (range 38–76) and a median Karnofsky performance status of 80 (range 60–100). Only 1 patient had not received prior therapy; 5 patients had received only prior chemotherapy, 1 had received only prior radiotherapy, and 7 had received both. Tumor types were gastric (1), lung (2), colon (4), urethral adenocarcinoma (1), cervical (2), chondrosarcoma (1), melanoma (1), uterine leiomyosarcoma (1), and pancreatic (1). The dose-limiting toxicity was granulocytopenia, with median WBC nadir of 1700/l (range 100–4800) in 8 heavily pretreated patients treated at 350 mg/m2 per day for 5 days. One patient without heavy prior treatment received two courses at 400 mg/m2 and had WBC nadirs of 800/l and 600l. WBC nadirs occurred between days 9 and 21 (median 14). Drug-induced thrombocytopenia occurred in only one patient (350 mg/m2 per day, nadir 85000/l). Neither hyponatremia nor symptomatic hypoosmolality was observed. Radiation-induced hemorrhagic cystitis may have been worsened in one patient. Nausea and vomiting were mild. Objective remissions were not observed. The maximum tolerated dose for previously treated patients is 350 mg/m2 per day for 5 days. This dose approximates the doses of cyclophosphamide commonly used with bolus administration. Plasma steady-state concentrations (Css) of cyclophosphamide, measured by gas liquid chromatography, were 2.09–6.79 g/ml. Steady state was achieved in 14.5±5.9 h (mean ±SD). After the infusion, cyclophosphamide disappeared from plasma monoexponentially, with a t1/2 of 5.3±3.6 h. The area under the curve of plasma cyclophosphamide concentrations versus time (AUC) was 543±150 g/ml h and reflected a cyclophosphamide total-body clearance (CLTB) of 103±31.6 ml/min. Plasma alkylating activity, assessed by p-nitrobenzyl-pyridine, remained steady at 1.6–4.3 g/ml nor-nitrogen mustard equivalents. Urinary excretion of cyclophosphamide and alkylating activity accounted for 9.3%±7.6% and 15.1%±2.0% of the administered daily dose, respectively. The t1/2 and AUC of cyclophosphamide associated with the 5-day continuous infusion schedule are similar to those reported after administration of cyclophosphamide 1500 mg/m2 as an i.v. bolus. The AUC of alkylating activity associated with the 5-day continuous infusion of cyclophosphamide is about three times greater than the AUC of alkylating activity calculated after a 1500-mg/m2 bolus dose of cyclophosphamide. Daily urinary excretions of cyclophosphamide and alkylating activity associated with the 5-day continuous infusion schedule are similar to those reported after bolus doses of cyclophosphamide.  相似文献   
997.
Summary Although it has been the subject of considerable interest for 15 years, originally as a cytotoxic agent and more recently as a radiosensitizer, there is very little pharmacokinetic information on CB 1954 (2,4-dinitro-5-aziridinylbenzamide). We have developed a rapid high-performance liquid chromatography assay for the drug and its metabolites and applied it to detailed examination of the pharmacokinetics of CB 1954 in mice and dogs. With IV administration a dose of 50 mg/kg gave peak blood concentrations of 100 g/ml in mice, while 25 mg/kg gave peak palsma concentrations of 27 g/ml in dogs. Peak concentrations were 3 to 5-fold lower for the IP route in mice and the oral route in dogs, and the bioavailabilities were 85% and 40%, respectively. Elimination t1/2 values were 1.4–2 h in mice and 2.5–4 h in dogs and were independent of route of administration. Plasma protein binding was 57% but tissue penetration in mice was generally good. Tumour: plasma ratios were 50%–90%, while brain: plasma ratios were lower, at 37%–50%. The parent drug and several metabolites were identified and quantified in mouse urine, the total recovery being 24%–29%, of which 16%–25% was parent drug. The metabolites were also found in the circulation and in tissues. No changes in pharmacokinetics were seen with repeated dosing in mice or with administration of the protective agent phenyl AIC. Phenobarbitone pretreatment produced a small reduction in elimination t1/2, mainly by accelerating aziridine ring removal. Allopurinol increased the blood levels of the 5-amino nitroreduction product. These studies provide a pharmacokinetic basis for interpreting the antitumour activity and toxicity of CB 1954, as well as for the development of new mixed-function sensitizers.  相似文献   
998.
The effect of ellagic acid and some of its more lipophilk derivativeson the mutagenicity of (? )-7ß, 8-di-hydroxy-9 10-epoxy-7,8, 910-etrahydrobenz[a]pyrene was examined in Salmonella typhimuriumTA100. Ellagic acid, 3, 3' -di-O-methylellagic add, 4, 4' -di-O-methylellagicacid and 3-O-decyiellagic acid were found to have approximatelyequal antimutagenic activity. The tissue distribution and eliminationof ellagic add, 3, 3' -di-O-methyleCagic add and 3-O-decylellagicacid were examined in CD-I mice. Little or no ellagic acid (<1 nmol/g) was found in blood, lung or liver after the oral administrationby gavage of 300 µunol of ellagic acid per kg body weightor after feeding 1% of ellagic acid in the diet for 1 week.Following the i.p. administration of 120 µmol/kg of ellagicacid, the blood and lung levels of ellagic acid were 15–20nmol/g at 30 min after the dose, and the concentrations of ellagicacid decreased to 1–3 nmol/g at 6–8 h after thedose. A portion of the administered i.p. dose precipitated inthe abdominal cavity. After i.v. administration, ellagic acidwas eliminated very rapidly from blood, lung and liver, and 70% of the administered dose was recovered in the urine andfeces as free ellagic acid and its conjugates. At 2 h afteran i.v. injection of 60 µ/kg of ellagic add, 46% of thedose was recovered in the urine as ellagic acid and its conjugates.Of this amount, about half was excreted as free ellagic acidand half was excreted as conjugates. An additional 25% of thedose was recovered in the feces (mostly as free ellagic acid)after 7 h. The disposition of 3, 3' -di-O-methylelIagic acidor 3–O-decyIellagic acid after i.v. administration (32µmol;sol;kg) was examined and compared to the dispositionof the same i.v. dose of ellagic acid. The concentrations ofellagic acid, 3,3' -di-O-methylellagic acid and 3-O-decytellagicadd decreased rapidly in the blood, liver and lung, but theconcentrations of 3-O-decylellagic add in the lung throughoutthe experimental period (2–360 min) was on average 20-to 40-fold higher than the corresponding average concentrationsof ellagic acid or 3, 3' -di-O-methylellagic acid.  相似文献   
999.
Summary The interaction between rauwolscine and angiotensin II was investigated in the isolated mesenteric artery of the rabbit. Rauwolscine, known as an antagonist at 2-adrenoceptors, did not induce contraction itself but interacted with angiotensin to produce a facilitated response of the vascular tissue. In the presence of rauwolscine, the contractile response of the tissue to angiotensin was markedly enhanced. The degree of facilitation appeared to be dependent on the rauwolscine concentration used rather than that of angiotensin. Moreover, rauwolscine induced a concentration-dependent increase in tension (pD2=6.8) in the presence of even subcontractile concentrations of angiotensin (10–10 mol/l). This effect was not attributable to an indirect action involving presynaptic catecholamines, as revealed by the use of tissue strips from animals pretreated with reserpine or after chemical sympathectomy. Furthermore, an interaction via the prostaglandin system was excluded by negative results obtained with indomethacin. The agonistic effect of rauwolscine was significantly attenuated by phentolamine (1/2) but not by prazosin (1) or phenoxybenzamine when applied for only a short time. The 2-antagonist BDF 6143 behaved like rauwolscine whereas the 1-antagonist corynanthine, a stereoisomer of rauwolscine, did not. The results indicate that the rauwolscine effect is mediated by a receptor with 2-characteristics. In general, angiotensin appears to interfere with some process which determines the expression of a drug's intrinsic effect.This study was supported by a grant of the Deutsche Forschungsgemeinschaft  相似文献   
1000.
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