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   207981篇
  免费   4791篇
  国内免费   581篇
耳鼻咽喉   2837篇
儿科学   7723篇
妇产科学   6075篇
基础医学   26558篇
口腔科学   6127篇
临床医学   16254篇
内科学   39311篇
皮肤病学   5026篇
神经病学   12874篇
特种医学   11155篇
外国民族医学   97篇
外科学   31053篇
综合类   1110篇
一般理论   1篇
预防医学   16651篇
眼科学   4393篇
药学   14043篇
  2篇
中国医学   149篇
肿瘤学   11914篇
  2021年   493篇
  2018年   3858篇
  2017年   4152篇
  2016年   3527篇
  2015年   5220篇
  2014年   4818篇
  2013年   4097篇
  2012年   10813篇
  2011年   5750篇
  2010年   2763篇
  2009年   4451篇
  2008年   2974篇
  2007年   3761篇
  2006年   3929篇
  2005年   11995篇
  2004年   13474篇
  2003年   8920篇
  2002年   4073篇
  2001年   4427篇
  2000年   1774篇
  1999年   5945篇
  1998年   635篇
  1992年   6930篇
  1991年   7171篇
  1990年   7406篇
  1989年   6978篇
  1988年   6512篇
  1987年   6277篇
  1986年   5999篇
  1985年   5271篇
  1984年   3619篇
  1983年   2937篇
  1982年   1018篇
  1981年   782篇
  1980年   849篇
  1979年   3840篇
  1978年   2376篇
  1977年   1789篇
  1976年   1567篇
  1975年   2475篇
  1974年   3113篇
  1973年   2741篇
  1972年   2765篇
  1971年   2748篇
  1970年   2562篇
  1969年   2471篇
  1968年   2246篇
  1967年   2176篇
  1966年   1906篇
  1965年   1134篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
Both acidic (aFGF) and basic (bFGF) fibroblast growth factors have been shown to be present in the adult rat ventral mesencephalon and to exert effects on cultured mesencephalic cells. In the present study we have examined the expression of aFGF and bFGF in the rat ventral mesencephalon at various stages of development. bFGF was present at all ages examined [embryonic day 16 (E16) to postnatal day 90 (P90)]. In contrast, aFGF was not detectable at embryonic and early postnatal ages, but was observed at later (P20, P60, P90) postnatal stages. These data suggest that aFGF and bFGF may have functions in mesencephalic dopamine neurones in different stages of development.  相似文献   
962.
The possibility to use the colorimetric MTT assay for measuring proliferation and cell death of human peripheral blood lymphocytes (PBL) was studied. In a range from 100,000-800,000 cells/well a linear correlation between the optical signal (OD signal at 570 nm) and the cell number was found. It is necessary to incubate the cells with the MTT at least 2 hours. After stimulation by different PHA concentrations a very good correlation between [3H] thymidine incorporation and MTT assay was found. A comparison of daunomycin cytotoxicity, measurement by trypan blue exclusion and MTT assay, gave also a good correlation between both methods. It can be pronounced that the MTT assay is a suitable method to measure cell proliferation and cell death of human PBL. The assay is easy to handle, a large number of probes can be assayed in a relatively short time and no radioactivity is necessary. For the measurement of the colored product a common ELISA reader can be used.  相似文献   
963.
Hepatic encephalopathy is ameliorated by drugs acting on the central GABAA-benzodiazepine receptor complex. To investigate whether these effects are specific for hepatic encephalopathy or just reflect a nonspecific arousal reaction, various benzodiazepine antagonists like flumazenil or with inverse agonistic properties (Ro 15-4513, Ro 15-3505) were studied in uremic encephalopathy in rats after bilateral ureteral ligation (n = 20) and compared with hepatic encephalopathy caused by thioacetamide-induced acute liver failure (n = 33). As soon as the animals developed clear signs of metabolic encephalopathy, their motor activity was recorded in an animal activity meter for 10 min. Furthermore, a composite score was calculated by grading various behavioral signs from 0 = absent to 3 = apparently normal. Rats were then injected with coded preparations of Ro 15-4513 (0.5, 2.5 and 5 mg/kg body wt intraperitoneally), flumazenil (2.5, 10, 25 and 40 mg/kg), Ro 15-3505 (10 mg/kg) or vehicle, and the measurements were repeated. The code was broken after the completion of the study. Pretreatment motor activity was decreased both in hepatic and uremic encephalopathy (20.7 +/- 6.4 [S.E.M.] and 41.3 +/- 37.1 movements/10 min). In hepatic encephalopathy motor activity and the composite score were improved both by 5 mg/kg Ro 15-4513 (by 293%, p less than 0.05) and by 10 mg/kg Ro 15-3505 (by 509%, p greater than 0.01), whereas vehicle and flumazenil had no effects. In uremic encephalopathy neither drug was effective in improving the neurobehavioral status.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
964.
Factorial experimental design was used to study the protective effects of Zn and Cu on cadmium-metallothionein(CdMT)-induced nephrotoxicity in male Wistar rats. In the factorial design two levels of Zn (0 and 25 mg/kg body weight), two levels of Cu (0 and 12.5 mg/kg), and two levels of CdMT (0.1 and 0.4 mg of Cd/kg) were used as varied factors. The factorial design was complemented with a center point with all three variables at an intermediate setting, i.e., Zn at 12.5 mg/kg, Cu at 6.25 mg/kg, and CdMT at 0.25 mg Cd/kg. Each of the nine combinations of settings was administered to one of nine groups with six rats in each. Zn and Cu were injected sc 24 hr prior to the injection of CdMT. The concentrations of protein and Ca in urine and Ca in renal cortex were used as effects. The relationship between the experimental design settings and the effects were modeled with multiple regression. The multiple regression analysis revealed that for the high dose of CdMT (i) the enhanced values of protein in urine caused by CdMT injection could be more efficiently reduced by Zn than by Cu, and (ii) excessive Ca in urine and renal cortex could be more efficiently reduced by Cu than by Zn. No significant synergism or antagonism between Cu and Zn was found. These models can be used to estimate the dose levels of Zn and Cu which will reduce the toxic effects of CdMT. The treatment of 20.4 mg/kg Zn, for example, will reduce the effects of 0.4 mg Cd/kg as CdMT on protein in urine, and 2.8 mg/kg Cu will reduce the Ca in urine to the levels of those caused by 0.25 mg Cd/kg (no Zn and Cu). Similarly, the effect of 0.4 mg Cd/kg on Ca level in renal cortex can be reduced to that of 0.28 mg Cd/kg as CdMT by 7.98 mg Cu/kg, which is three times as efficient as Zn. The obtained results might be of importance in understanding the mechanism of cadmium toxicity and the potential risk to the health of the population exposed to cadmium occupationally or environmentally.  相似文献   
965.
966.
The finding of large quantities of blood group A-active oligosaccharides in the feces of a blood group A breast-fed infant motivated a search for the origin of these compounds. Using an affinity chromatographic technique, the nature of A-active oligosaccharides in human milk is demonstrated. The amounts of A-active tetrasaccharide (A-tetra) and the Lewis b-active lacto-N-difucohexaose I (LND-I) varied between 19-375 mg/L for A-tetra and 14-710 mg/L for LND-I. Using the same technique, the amounts of A-tetra and LND-I in milk samples from five women of different blood groups were compared with those in the feces of their breast-fed infants. The A-tetra was present only in feces from infants of blood group A or AB mothers and the amount per 24 h corresponded roughly to that in a I-L portion of milk. One of the milk samples was also analyzed for the presence of larger A-active oligosaccharides (A-pentasaccharide, A-hexasaccharide, and A-heptasaccharide). Their amounts were much less as compared to the amounts present in feces. These results indicate that milk is a possible source for the smallest A-tetrasaccharide found in the feces of breast-fed infants, while the larger A-active oligosaccharides might be the result of an intestinal metabolic modification.  相似文献   
967.
In the last few years a group of verotoxinogenic E. coli bacteria has been defined as a causative agent of hemorrhagic colitis and haemolytic uremic syndrome. The corresponding toxins (verotoxins, Shiga-like-toxins) released from these bacteria play a key role in the pathogenesis and are responsible for the severity of the respective illness. Therefore, besides the clinical and other paraclinical investigations the detection of SLT-producing E. coli or of the corresponding toxins directly in the stool as early as possible has to be included into strategies for diagnostics and therapy. Moreover, it is necessary to avoid the release of huge amounts of toxins (e.g. by antibiotic therapy) and to take care for suitable measures to neutralize or eliminate the toxins. First isolations of enterohaemorrhagic E. coli (EHEC, VTEC) in stool samples from patients suffering from diarrhoeal diseases and HUS in the vicinity of Wernigerode demonstrate the necessity for further bacteriological and epidemiological investigations in order to evaluate frequency and importance of these EHEC bacteria in the pediatric praxis.  相似文献   
968.
Ocular motility in thalidomide embryopathy   总被引:1,自引:0,他引:1  
Twenty-one individuals, aged 28 to 29 years, with documented thalidomide embryopathy were examined in Sweden. The most noteworthy ophthalmologic finding was the high prevalence of incomitant horizontal strabismus, primarily of the Duane syndrome type. Less frequently seen were cases of both marked abduction and adduction limitation similar to a gaze paresis with no observable fissure changes, as well as a few cases of isolated abduction weakness or inferior oblique under-action. There were many examples of aberrant lacrimation, facial nerve palsy, and ear anomalies combined with horizontal incomitant forms of strabismus. Ear and facial nerve palsies are known to occur with ingestion of thalidomide early in the sensitive period (approximately days 21 to 26 after conception).  相似文献   
969.
The subjects in the study were 114 persons receiving a disability pension or referred for disability assessment. They were placed in two groups of 57 persons each, one with marked cervicobrachial syndrome and the other without. The latter group was chosen by the method of equivalent pairs with regard to sex and age. All subjects underwent a clinical examination and a standardized questionnaire was completed. The questionnaire pertained to the state of health, focussing on the amount and type of physical burdening at the workplace and on activities outside the workplace. Sixty-five percent of the subjects were aged from 51 to 60 years. A statistically significant difference was established between earlier occupation and cervicobrachial syndrome. Cervicobrachial syndrome was found in 31.6% of unskilled workers and 12.3% of the controls (P < 0.05). A forced body posture during work was recorded in 74% of the subjects with the syndrome and in 50% of the control subjects (P < 0.05). Repetitive movements at work were reported by a large number of subjects with cervicobrachial syndrome (71.9:49.1%; P < 0.05) who also claimed to strain the arms (84.2:61.4%; P < 0.05) and burden the cervical spine (68.5:40.4%; P < 0.05) during household activities to a significantly greater extent than the controls. A possible preventive approach to the occurrence and progression of cervicobrachial syndrome is discussed.  相似文献   
970.
The incidence of lymphoid malignancies (acute leukemias and myelomatosis excluded) during 1969-1987 in the County of Uppsala was calculated on the basis of the regional cancer register and local registers from the only oncological, hematological, dermatological and pathological departments in this well-defined geographical area. Of the 774 patients included, 639 had histopathological specimens available, all of which were re-examined. Seventy-nine patients were diagnosed on the basis of bone marrow investigations (greater than 70% re-examined, all had a low-grade non-Hodgkin's lymphoma = NHL) and 54 on fine-needle aspiration biopsies (not re-examined). Seventy-nine of the lymphoma diagnoses were based on autopsy specimens. The overall age standardized incidence was 16.2/100,000/year (NHL: 13.6, Hodgkin's disease = HD: 1.5) according to the Swedish 1970 census (according to world standard population: 10.2); male: 20.9 (12.9) and female: 12.4 (7.9). The annual change in trend was +3.0% +/- 2.6 (NHL: +3.6% +/- 2.4, HD: no change). The omission of the 54 'fine needle cases' led to an overall incidence of 15.0 (9.7) and an annual change in trend of +3.5% +/- 1.9. Among the histopathological specimens, an NHL was found in 524 patients and HD in 69. In 46 registered patients, the diagnosis malignant lymphoma was wrong. The diagnosis changed to NHL in 43 patients registered as HD.  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