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   64740篇
  免费   4753篇
  国内免费   151篇
耳鼻咽喉   849篇
儿科学   1753篇
妇产科学   1628篇
基础医学   10667篇
口腔科学   1693篇
临床医学   6154篇
内科学   13036篇
皮肤病学   979篇
神经病学   6092篇
特种医学   2696篇
外国民族医学   45篇
外科学   8312篇
综合类   533篇
一般理论   85篇
预防医学   5079篇
眼科学   1230篇
药学   4671篇
中国医学   162篇
肿瘤学   3980篇
  2022年   483篇
  2021年   1053篇
  2020年   666篇
  2019年   938篇
  2018年   1146篇
  2017年   803篇
  2016年   964篇
  2015年   1120篇
  2014年   1397篇
  2013年   2386篇
  2012年   3102篇
  2011年   3196篇
  2010年   2280篇
  2009年   1912篇
  2008年   2865篇
  2007年   3019篇
  2006年   2999篇
  2005年   2841篇
  2004年   2891篇
  2003年   2629篇
  2002年   2687篇
  2001年   2174篇
  2000年   2224篇
  1999年   1995篇
  1998年   884篇
  1997年   742篇
  1996年   656篇
  1995年   676篇
  1994年   559篇
  1993年   609篇
  1992年   1458篇
  1991年   1401篇
  1990年   1344篇
  1989年   1333篇
  1988年   1108篇
  1987年   1112篇
  1986年   1048篇
  1985年   965篇
  1984年   701篇
  1983年   653篇
  1982年   459篇
  1981年   441篇
  1980年   380篇
  1979年   628篇
  1978年   375篇
  1977年   358篇
  1975年   376篇
  1974年   414篇
  1973年   350篇
  1972年   345篇
排序方式: 共有10000条查询结果,搜索用时 628 毫秒
991.
An IUD (TCu220C) was inserted in 82 women during low-transverse cesarean section. No untoward effect on puerperal morbidity or lactation was observed and no serious complications occurred in this series. At 12 months the rates were zero for pregnancy and 7.7 for expulsion; the latter figure is comparable to that reported after immediate postplacental insertion of the same IUD model. Intracesarean IUD insertion is a procedure that deserves further promotion.
Resumen A 82 mujeres se les insertó un DIU (TCu220C) durante una cesárea transversa en el segmento bajo. No se observaron efectos adversos en la morbilidad puerperal y la lactancia y no ocurrieron complicaciones serias en esta serie. A los 12 meses la tasa de embarazos fue de cero y de 7,7 la de expulsiones; esta última cifra es comparable a la registrada después de la inserción postparto inmediato del mismo modelo du DIU. Por lo tanto, la inserción intracesárea de DIU se considera un procedimiento que merece mayor promoción.

Résumé Un dispositif intra-utérin (TCu220C) a été mis en place chez 82 femmes au cours d'une césarienne transverse basse. On a noté aucune répercussion défavorable sur la morbidité post-puerpérale ni sur l'allaitement et aucune complication sérieuse est apparue dans cette série. Au bout de douze mois, les fréquences étaient de zéro pour les grossesses et de 7,7 pour les expulsions. Les chiffres ultérieurs sont comparables à ce qui a été publié après insertion post-placentaire immédiate du même modèle de DIU. La mise en place d'un DIU au cours de la césarienne est une méthode qui mérite d'être plus largement répandue.
  相似文献   
992.
A comparative study was made of three differently loaded Multiload intrauterine contraceptive devices. The IUDs were used by 450 women for 3 years unless the device was removed earlier. The reasons for IUD removal (pregnancy, bleeding and/or pain, and other) were recorded, and the data analyzed after 1 year and after 3 years using the log-rank method. No statistically significant differences could be found among the three devices either in rate of pregnancy nor IUD removal for any reason.
Resumen Se hizo un estudio comparativo de tres anticonceptivos intrauterinos Multiload con tres cargas diferentes. Durante tres años, 450 mujeres usaron los DIU a menos que el dispositivo hubiera sido quitado antes. Las razones para la remoción de los DIU (embarazo, sangrado y/o dolor y otras) fueron registradas y los datos se analizaron después de l año y de 3 años, usando el método log-rank. No se pudo encontrar ninguna diferencia estadísticamente significativa entre los tres dispositivos sea en la tasa de embarazos o en la remoción de los DIU por cualquier razón.

Resumé On a conduit une étude pour comparer 3 DIU multichargés, de charge différente. Ces DIU ont été utilisés par 450 femmes pendant 3 ans, sauf retrait plus précoce. On a relevé les motifs de retrait du DIU (grossesse, hémorragie et/ou douleurs et autres motifs) et analysé les données au bout de 1 an et de 3 ans, par la méthode des rangs logarithmiques. Aucune différence statistiquement significative n'a été constatée entre les 3 DIU; ni sur le plan du taux de grossesse ni sur celui du taux de retrait, pour un motif quelconque.
  相似文献   
993.
As CT is often the initial imaging method in the evaluation of suspected complications of abdominal aortic aneurysm, especially rupture of the aneurysm, it is important to be aware of other less common complications that can be detected by CT. A patient with an aortocaval fistula and renal venous hypertension is discussed. The constellation of CT findings that suggest this diagnosis is described as is the angiographic correlation. Awareness of these CT findings, including early equivalent enhancement of the inferior vena cava and aorta; enlarged, poorly functioning kidney; and perirenal "cobwebs," will lead to the appropriate confirmatory angiographic studies.  相似文献   
994.
A seroepidemiological study was performed on HTLV-III, T. pallidum, C. trachomatis and Hepatitis B virus (HBV), in Butare, Rwanda, among 33 female prostitutes, 25 male customers of prostitutes, and 60 male and female controls. As compared with female controls the prostitutes had a higher prevalence of antibodies to HTLV-III (29/33 versus 4/33, p<0.001), T. pallidunz (TPHA: 27/33 versus 6/33, p<0.001; RPR: 19/33 versus 233, p<0.001; FTA-Abs: 27/33 versus 5/33, p<0:001) and C. trachomatis (IgG IF: 31/33 versus 13/33, p<0.001). HBV serological markers were more often detected in the prostitutes than in the female controls (31/33 versus 18/33, p<0.001) although HBs antigen carriage rate was similar in both groups. As compared with male controls, the male customers of prostitutes had more frequently detectable antibodies to HTLV-III (7/25 versus 2/27, p = 0.05), and a positive RPR (10/25 versus 1/27, p<0.01). Among the 118 individuals studied, odds ratios and trend analysis disclosed a significant association between HTLV-III seropositivity and a positive TPHA, RPR, FTA-Abs, Chlamvdia IgG IF test and serological markers to HBV. No association was found between HTLV-III seropositivity and IIBs Ag carriage. This study suggests that HTLV-III has to be considered as an infectious agent transmitted among promiscuous Central African heterosexuals by sexual contact and/or parenteral contact with unsterile needles used for STD treatments.  相似文献   
995.
During a 1-year period, a prospective ultrasound (US) study of the biliary tract was performed in 41 neonates receiving total parenteral nutrition (TPN). Gallbladder sludge appeared in 18 neonates (44%) after a mean period of 10 days of TPN. The occurrence of this abnormality seems related to three main factors: prematurity with immaturity of the enterohepatic circulation of bile acids, duration of TPN, and lack of enteral nutrition. In five neonates (12%), an evolution of sludge to "sludge balls" was observed. Two neonates (5%) went on to develop uncomplicated gallstones and a spontaneous resolution occurred in one of them 6 months after the examination. This finding suggests conservative management in such cases. However, since cholecystitis or biliary tract obstruction are classical complications in older children, a US survey of neonates receiving TPN is useful to follow the abnormal gallbladder content, and rapid introduction of enteral feeding is advisable.  相似文献   
996.
The averaged lambda wave elicited by saccadic eye movements across a checkerboard pattern has been reported to differ from checkerboard reversal evoked reponses, even when the electroencephalographic responses were corrected for the artefact caused by the movement of the dipole moment of the eye itself. Because of these differences it was suggested that the recording of the lambda wave might provide extra information in pathological circumstances. We performed experiments in which the parameters of the pattern (high contrast checkerboard pattern, 20 checks, large field 72 × 72 degrees) shift across the retina were carefully adjusted. For instance, eye movements were made across an integer and odd number of checks in order to mimic the pattern reversal. Furthermore, the timing of the pattern movement in the pattern reversal condition was adjusted so as to simulate the saccadic eye movement. The results seem to suggest that the reported dissimilarities between pattern reversal and eye movement evoked responses can be accounted for by the small differences of the retinal shift in the two conditions.  相似文献   
997.
    
The liver is a major site for synthesis and catabolism of plasma proteins. Albumin has various binding sites for anionic drugs, 1acid glycoprotein possesses a single binding site for cationic drugs. In spite of extensive protein binding, the liver can efficiently remove drags from the circulation. Intrahepatic dissociation of the drag-protein complex may involve dissociation-limited debinding under non-equilibrium conditions or surface interaction-facilitated dissociation phenomena. During liver or renal disease and acute-phase conditions plasma protein binding of drugs may be affected. Changes in the unbound drag fraction do not always result in proportional changes in clearance or distribution volume. Potential changes in the unbound concentration in steady-state as well as the fluctuations in total plasma levels depend on the extent of protein binding of a drug, the relative change in the unbound drug fraction, type of clearance, the size of the distribution volume, route of administration as well as concomitant changes in intrinsic (cellular) clearance function. Optimization of dosage regimens for certain drags and interpretation of liver function tests with diagnostic dyes may largely benefit from determination of the unbound rather than the total concentration of the drags involved.Part of this work was supported by Grant 900-521-078 from MEDICON, which is subsidized by The Netherlands' Organization of Pure Research.  相似文献   
998.
A "two-site" immunoradiometric assay (IRMA) which allows the direct estimation of human CRH (hCRH) in plasma is described. Using this IRMA, basal levels of CRH in normal subjects ranged from 2-28 pg/mL [mean, 15 +/- 7 (+/- SD) pg/mL; n = 58]. Values in men and women were similar. Plasma CRH values within this range were also found in patients with Cushing's syndrome, Addison's disease, and Nelson's syndrome, with no correlation between plasma CRH and ACTH levels in these patients. Elevated plasma CRH levels were found in pregnant women near term [1462 +/- 752 (+/- SD) pg/mL; n = 55], and the dilution curve of this CRH-like immunoreactivity paralleled the IRMA standard curve. After its immunoadsorption from maternal plasma, this CRH-like material eluted on reverse phase high performance liquid chromatography with a retention time identical to that of synthetic CRH and had equipotent bioactivity with the synthetic peptide in the perfused anterior pituitary cell bioassay. Circulating CRH was not detected in Wistar rats, even after adrenalectomy and subsequent ether stress. Synthetic hCRH was degraded by fresh human plasma relatively slowly; 65% of added CRH remained after 1 h of incubation at 37 C. Degradation was inhibited by heat treatment (54 C; 1 h), cold treatment (4 C; 4 h), or freezing and thawing. Loss of synthetic rat CRH occurred more rapidly when fresh rat plasma was used; only 20% of added CRH remained under the same conditions. The inability to measure CRH in peripheral rat plasma may be due to the presence of active CRH-degrading enzymes which fragment the CRH molecule into forms not recognized by the CRH IRMA.  相似文献   
999.
Cardiac dysrhythmias are easy. Unlike the lung (which has formidable neuroendocrine, metabolic, and respiratory responsibilities), the heart is simple. It is an innervated muscular pump. A resting Purkinje or ventricular muscle cell membrane maintains a charge of about 90 millivolts. The five phases of a cardiac action potential are similar to the action potential in skeletal muscle, however, the cardiac action potential lasts a hundred times longer. When sodium specific "fast" channels and calcium specific "slow" channels open, positive ions rush into the myocardial cell, thus causing rapid membrane depolarization. In order to produce an action potential, some stimulus must decrease the membrane potential from -90 millivolts to "threshold" or -60 millivolts. Purkinje fibers do not have a stable phase for diastolic potential. These fibers continuously depolarize during diastole. Hypoxemia or hypokalemia may exacerbate this diastolic depolarization, thus promoting "hyperexcitability" or "automatic" ectopy. When myocardium is damaged, characteristically with myocardial ischemia, rapid conduction of cardiac impulses may be slowed dramatically. Very slow impulses may course through muscle such that by the time the activation wave front returns to the initiating site, this origin has had a chance to repolarize. This is the basis for re-entrant dysrhythmias. All cardiac dysrhythmias are automatic, re-entrant or both.  相似文献   
1000.
Drechslera maydis, the causal agent of Southern corn leaf blight, and Drechslera sorghicola, the causal agent of leaf spot on Johnson grass, produce a series of phytotoxic sesterterpenoids. These sesterterpenoids belong to the ophiobolin family. One of them, ophiobolin I, was characterized by x-ray diffraction and served as a crucial reference compound for characterizing four other ophiobolins. All of the ophiobolins studied produce characteristic lesions on host plants at concentrations of 1 mM to 1 μM. The ophiobolin characterized as 6-epiophiobolin A is selectively toxic to corn bearing Texas-male-sterile (Tms) cytoplasm when assayed in a dark CO2 fixation assay. It is plausible that these ophiobolins had a role in the 1970 corn-blight epidemic in North America.  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