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   7798篇
  免费   380篇
  国内免费   85篇
耳鼻咽喉   25篇
儿科学   304篇
妇产科学   221篇
基础医学   943篇
口腔科学   128篇
临床医学   696篇
内科学   1915篇
皮肤病学   145篇
神经病学   599篇
特种医学   743篇
外科学   1033篇
综合类   64篇
一般理论   8篇
预防医学   489篇
眼科学   106篇
药学   362篇
  2篇
中国医学   4篇
肿瘤学   476篇
  2023年   31篇
  2022年   49篇
  2021年   100篇
  2020年   91篇
  2019年   124篇
  2018年   126篇
  2017年   114篇
  2016年   137篇
  2015年   164篇
  2014年   236篇
  2013年   338篇
  2012年   468篇
  2011年   550篇
  2010年   372篇
  2009年   355篇
  2008年   443篇
  2007年   540篇
  2006年   413篇
  2005年   465篇
  2004年   389篇
  2003年   337篇
  2002年   314篇
  2001年   96篇
  2000年   55篇
  1999年   68篇
  1998年   195篇
  1997年   225篇
  1996年   192篇
  1995年   149篇
  1994年   164篇
  1993年   141篇
  1992年   49篇
  1991年   55篇
  1990年   58篇
  1989年   67篇
  1988年   69篇
  1987年   65篇
  1986年   69篇
  1985年   66篇
  1984年   41篇
  1983年   31篇
  1982年   42篇
  1981年   42篇
  1980年   37篇
  1979年   11篇
  1978年   17篇
  1977年   28篇
  1976年   27篇
  1975年   18篇
  1974年   8篇
排序方式: 共有8263条查询结果,搜索用时 0 毫秒
91.
We studied the potential of both stereoisomers of 17-[123I]iodovinyloestradiol (E- andZ-[123I]IVE) and of 11-methoxy-17-[123I]iodovinyloestradiol (E-andZ-[123I]MIVE) as suitable radioligands for the imaging of oestrogen receptor(ER)-positive human breast tumours. The 17-[123I]iodovinyloestradiols were prepared stereospecifically by oxidative radio-iododestannylation of the corresponding 17-tri-n-butylstannylvi-nyloestradiol precursors. Competitive binding studies were performed in order to determine the relative binding affinity (RBA) of the unlabelled 17-iodovinyloes-tradiols for the ER in both human MCF-7 breast tumour cells and rat uterine tissue, compared with that of diethylstilboestrol (DES). Target tissue uptake, retention and uptake selectivity of their123I-labelled analogues were studied in immature female rats. All four 17-iodovi-nyloestradiols showed high affinity for the ER in human MCF-7 cells, as well as rat uterus. Their RBA for the ER showed the following order of decreasing potency: RBA of DES >Z-IVE >Z-MIVE >E-MIVE E-IVE. Neither of these 17-iodovinyloestradiols showed any significant binding to the sex hormone binding globulin in human plasma. The biodistribution studies showed ER-mediated uptake in the uterus, ovaries and pituitary, that ofE- andZ-[123I]MIVE being higher than that ofE- andZ-[123I]IVE. High target-to-non-target tissue uptake ratios, especially at longer periods after injection (up to 24 h), were exhibited by both isomers of [123I]MIVE. The uterus-to-blood uptake ratio was higher forE-[123I]MIVE. However, the uterus-to-fat uptake ratio appeared to be higher for theZ-isomer of [123I]MIVE, especially at 24 h after injection. Metabolic properties and temperature effects, which play a more important role in vivo, probably cause the discrepancies seen between in vitro and in vivo binding results. On the basis of their in vitro binding properties and in vivo distribution characteristics we conclude thatE- andZ-[123I]MIVE could be suitable radioligands for the diagnostic imaging of ER in human breast cancer. Therefore, further studies with these radioligands in mature normal and tumour-bearing rats are warranted.  相似文献   
92.
Summary The creatine kinase (CK) activity of the serum of 33 male and 24 female patients with tibial shaft fractures has been assayed. In 40 of the 57 patients the CK level surpassed the maximal normal limit of 1.7 tkat/l. Patients with fractures due to direct violence had significantly higher levels than those with fractures due to indirect violence. When the fracture was displaced the CK level was more often abnormal than when there was no displacement. Patients with extensive swelling of the injured leg had significantly higher levels than patients with minor or no swelling. CK determinations could be used to quantify muscle injury.
Zusammenfassung Die Serum-Kreatinkinase (CK)-Werte von 33 männlichen and 24 weiblichen Patienten mit einer Tibiadiaphysenfraktur wurden gemessen. Bei 40 von 57 Patienten lag der Serum-CK-Spiegel über dem oberen Normalwert von 1,7 kat/l. Bei Patienten mit Frakturen, verursacht durch ein direktes Trauma, wurden signifikant höhere Serum-CK-Werte gemessen als bei Patienten mit Frakturen, entstanden durch ein indirektes Trauma. Der Serum-CK-Spiegel war öfter erhöht bei Patienten mit einer Fraktur mit Fehlstellung, verglichen mit Patienten mit einer Fraktur ohne Fehlstellung. Patienten mit einer außergewöhnlichen Schwellung des geschädigten Beines hatten signifikant höhere Serum-CK-Werte als Patienten mit geringer oder keiner Schwellung. Die Serum-CK kann dazu benutzt werden, den Muskelschaden quantitativ zu beurteilen.
  相似文献   
93.
The toxicity of four trimethyltin concentrations to stage I zoeae of the fiddler crab,Uca pugilator, was tested at temperatures of 10°C, 20°C and 28°C and salinities of 10, 20 and 30. Stepwise multiple regression of the probit of mortality data produced a formula from which productive response surfaces were generated. 24 hr LC 50's in 30 salinity at 10°C was 12 ppm, at 20°C 3.35 ppm and 0.61 ppm at 28°C. Corresponding 48 hr LC 50's were about one-tenth of these values. An increase in temperature and a decrease in salinity sharply increased trimethyltin toxicity in fiddler crab zoeae.Contribution No. 1226, Center for Environmental and Estuarine Studies, University of Maryland  相似文献   
94.
95.
Objective: The combination of transvaginal sonography and serum hCG measurement is reliable in the diagnosis of ectopic pregnancy (EP) in spontaneous pregnancies. In patients who became pregnant through IVF-ET, transfer of multiple embryos after IVF could be responsible for the different performance of these tests. We evaluated the discriminative capacity of transvaginal sonography in combination with hCG measurement in the diagnosis of EP after IVF-ET.

Design: Prospective cohort study.

Setting and Patient(s): Consecutive patients, pregnant through IVF-ET, who presented with clinically suspected EP.

Intervention(s): Transvaginal sonography, serum hCG measurement at 6, 9, and 15 days after ET and after a negative transvaginal sonography.

Main Outcome Measure(s): Ectopic pregnancy confirmed at laparoscopy.

Result(s): Between September 1993 and May 1996, 86 women were included in the study, of whom 24 had an EP. Transvaginal sonography identified 46 intrauterine pregnancies and 5 EPs, but serum hCG could not diagnose EPs in patients in whom transvaginal sonography did not show a gestational sac. Serum hCG measurement 9 days after ET could identify pregnancy failure with 100% specificity at a cut-off value of 18 IU/L, but it could not identify patients with EP with enough certainty to justify immediate treatment.

Conclusion(s): We recommend single serum hCG measurement 9 days after ET to discriminate between viable and nonviable pregnancies. Transvaginal sonography can be postponed until 5 weeks after ET, except for patients with abdominal pain and/or vaginal bleeding, or patients with a serum hCG level of <18 IU/L.  相似文献   

96.
Diwan  BA; Anderson  LM; Ward  JM 《Carcinogenesis》1997,18(10):2009-2014
Tamoxifen (TAM) is widely used as adjuvant breast cancer therapy after surgery and as a chemopreventive agent in women of child-bearing age. However, TAM therapy has been shown to result in an increased incidence of endometrial carcinoma in women. The present study was designed to investigate the effects of TAM (5 mg/kg and 7.5 mg/kg body wt) given i.g. to pregnant CD-1 mice (1x/day, days 12 through 18 of gestation) on their female offspring. Progressive proliferative hyperplasia of the oviduct was frequently seen in TAM-exposed offspring, reaching 100% incidence by 52 weeks in both treatment groups. These females also developed progressive proliferative uterine lesions, including moderate/severe cystic endometrial hyperplasia (34-50%) and polypoid adenomas (27-30%) between 53 and 78 weeks. Deciduomas (15%) occurred at young ages (12 and 24 weeks) while leiomyomas (14%), a malignant leiomyosarcoma, and ovarian granulosa cell tumors (14%), were found between 72 and 78 weeks. Our findings thus suggest a strong association between transplacental TAM and reproductive tract abnormalities in female CD-1 mice.   相似文献   
97.
Persistent hyperinsulinemic hypoglycaemia of infancy (PHHI) is the most frequent cause of hypoglycaemia in infancy. Clinical presentation is heterogeneous, with variable onset of hypoglycaemia and response to diazoxide, and presence of sporadic or familial forms. Underlying histopathological lesions can be focal or diffuse. Focal lesions are characterised by focal hyperplasia of pancreatic islet-like cells, whereas diffuse lesions implicate the whole pancreas. The distinction between the two forms is important because surgical treatment and genetic counselling are radically different. Focal lesions correspond to somatic defects which are totally cured by limited pancreatic resection, whereas diffuse lesions require a subtotal pancreatectomy exposing to high risk of diabetes mellitus. Diffuse lesions are due to functional abnormalities involving several genes and different transmission forms. Recessively inherited PHHI have been attributed to homozygote mutations for the beta-cell sulfonylurea receptor (SUR1) or the inward-rectifying potassium-channel (Kir6.2) genes. Dominantly inherited PHHI can implicate the glucokinase gene, particularly when PHHI is associated with diabetes, the glutamate dehydrogenase gene when hyperammonaemia is associated, or another locus.  相似文献   
98.
OBJECTIVE: Because survival from admission to discharge does not provide parents and physicians information about future life expectancy in the premature neonate, we characterized the actuarial survival, defined as the future life expectancy from a given postnatal age, in a large inborn population of premature infants < 30 weeks' gestation. STUDY DESIGN: We determined daily actuarial survival of 1925 inborn infants (23 to 29 weeks' gestation) admitted to the Baylor Affiliated Nurseries from July 1986 through December 1994, stratified by 100-g birth weight and by 1-week gestational-age intervals. RESULTS: In the 501- to 600-g birth weight stratum, actuarial survival improved from 31% at birth, to 61% on day of life 7, and then to 75% on day of life 28; in the 901- to 1000-g birth weight stratum, actuarial survival improved from 88%, to 94%, and then to 98% throughout the same times, respectively. Similar trends were obtained when data were stratified by gestational age. CONCLUSIONS: Survival in the smallest infants improves dramatically during the first few days of life, but there is a significant risk for late death in the smallest of these infants.  相似文献   
99.
OBJECTIVE: The ketogenic diet is a high-fat, low-protein, low-carbohydrate diet developed in the 1920s for the treatment of children with difficult to control seizures. Despite advances in both the pharmacotherapy and the surgery of epilepsy, many children continue to have difficult-to-control seizures. This prospective study sought to determine the ketogenic diet's effectiveness and tolerability in children refractory to today's medications. METHODS: One hundred fifty consecutive children, ages 1 to 16 years, virtually all of whom continued to have more than two seizures per week despite adequate therapy with at least two anticonvulsant medications, were prospectively enrolled in this study, treated with the ketogenic diet, and followed for a minimum of 1 year. Seizure frequency was tabulated from patients' daily seizure calendars and seizure reduction calculated as percentage of baseline frequency. Adverse events and reasons for diet discontinuation were recorded. RESULTS: The children (mean age, 5.3 years), averaged 410 seizures per month before the diet, despite an exposure to a mean of 6.2 antiepileptic medications. Three months after diet initiation, 83% of those starting remained on the diet and 34% had >90% decrease in seizures. At 6 months, 71% still remained on the diet and 32% had a >90% decrease in seizures. At 1 year, 55% remained on the diet and 27% had a >90% decrease in seizure frequency. Most of those discontinuing the diet did so because it was either insufficiently effective or too restrictive. Seven percent stopped because of intercurrent illness. CONCLUSIONS: The ketogenic diet should be considered as alternative therapy for children with difficult-to-control seizures. It is more effective than many of the new anticonvulsant medications and is well tolerated by children and families when it is effective.  相似文献   
100.
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