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   273748篇
  免费   15758篇
  国内免费   7726篇
耳鼻咽喉   3509篇
儿科学   8715篇
妇产科学   3147篇
基础医学   19342篇
口腔科学   6843篇
临床医学   32579篇
内科学   45869篇
皮肤病学   3303篇
神经病学   13852篇
特种医学   26264篇
外国民族医学   42篇
外科学   37863篇
综合类   26724篇
现状与发展   29篇
预防医学   16719篇
眼科学   7546篇
药学   25905篇
  92篇
中国医学   4885篇
肿瘤学   14004篇
  2023年   2766篇
  2022年   5905篇
  2021年   12493篇
  2020年   6963篇
  2019年   12697篇
  2018年   7413篇
  2017年   6556篇
  2016年   8459篇
  2015年   11455篇
  2014年   20877篇
  2013年   18111篇
  2012年   21535篇
  2011年   18858篇
  2010年   17074篇
  2009年   16671篇
  2008年   15552篇
  2007年   15497篇
  2006年   13407篇
  2005年   9419篇
  2004年   5618篇
  2003年   4569篇
  2002年   3666篇
  2001年   3024篇
  2000年   2729篇
  1999年   1893篇
  1998年   2270篇
  1997年   2128篇
  1996年   1791篇
  1995年   1779篇
  1994年   1696篇
  1993年   1333篇
  1992年   1448篇
  1991年   1297篇
  1990年   1300篇
  1989年   1233篇
  1988年   1170篇
  1987年   1026篇
  1986年   830篇
  1985年   1770篇
  1984年   1936篇
  1983年   1376篇
  1982年   1497篇
  1981年   1455篇
  1980年   1236篇
  1979年   1060篇
  1978年   808篇
  1977年   815篇
  1976年   692篇
  1974年   468篇
  1973年   444篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The immunoreactivity of apolipoprotein B (apo B) in plasma obtained from 238 unrelated black African male subjects from the People's Republic of Congo was analysed by non-competitive Enzyme Linked-Immunosorbent Assay (ELISA) with monoclonal BIP 45 anti-LDL antibody. The polymorphism detected by BIP 45 monoclonal antibody is identical to the Ag(c,g) polymorphism. Antibody BIP 45 distinguishes three apo B allotypes (immunophenotypes) encoded by the two allelic genes apo B Ag(c) and apo B Ag(g). Because of co-dominant transmission, genotypes may be inferred from allotypes, and it has been shown that BIP 45 binds strongly to the Ag(c) factor and only weakly to the allelic Ag(g) factor. Analysis of the Congolese plasma samples indicated that 67.65% of them bound BIP 45 with low affinity (Ag(c-,g+) genotype), 28.15% with intermediate affinity (Ag(c+,g+) genotype) and 4.20% with high affinity (Ag(c+,g-) genotype). According to the Hardy-Weinberg equilibrium, this corresponds to gene frequencies of 0.817 and 0.183 for the type Ag(g)/Ag(c) alleles, respectively. After adjustment for age and body-mass index, it was found that the Ag(c) allele decreases the apo B level by 9.62 mg/dl and that the Ag(g) allele increases apo B by 0.43 mg/dl. Therefore, as much as 4.30% of the genetic variance for apo B level could be accounted for by the Ag(c,g) gene locus.  相似文献   
992.
OBJECTIVE: To describe pelvic sonographic findings in girls as old as 7 years, to compare prepubertal girls with girls who had isolated thelarche or central precocious puberty, and to verify the accuracy of sonographic variables for distinguishing prepubertal girls from girls with central precocious puberty. METHODS: Ninety-six prepubertal girls and 2 reference groups (8 girls with isolated thelarche and 8 with idiopathic central precocious puberty) were included. Ovaries were classified morphologically as homogeneous, paucicystic, macrocystic, multicystic, and having isolated cysts. Receiver operating characteristic curves were used to choose the best cutoff points. RESULTS: Chronologic and bone age were correlated with uterine length, area, and volume and ovarian volume in prepubertal girls (P < .0001). Ovarian morphologic characteristics in prepubertal girls differed significantly from those of the reference groups (P < .0001). The best cutoff points were uterine length of 4.0 cm, uterine area of 4.5 cm2, uterine volume of 3.0 cm3, and ovarian volume of 1.0 cm3. CONCLUSIONS: Uterine and ovarian growth are proportional to age in prepubertal girls. Mean ovarian volume greater than 1 cm3 showed 100% sensitivity and specificity for discriminating between prepubertal girls and girls with central precocious puberty. Microcysts are common in prepubertal girls, but the presence of 6 or more follicles up to 10 mm in diameter may suggest central precocious puberty in girls younger than 8 years.  相似文献   
993.
Hydatid cysts of central nervous system are rare and comprise only 2% to 3% of all hydatid cysts reported. Orbital localization is very uncommon and has been reported less than 1 % of all hydatid diseases. The primary treatment of hydatid disease is surgical. The most important complication of the surgical treatment is secondary hydatidosis due to spillage of the cyst contents. Because of the difficulties of the orbital localization, total extirpation of the cysts without rupture is almost impossible. Preventing spontaneous rupture of the cysts during surgery and postoperative antihelmintic treatment should be taken into consideration in these cases.This study includes four cases who underwent surgery for orbital hydatid cysts. Radiological characteristics, operative technique and postoperative medical therapy are discussed.  相似文献   
994.
This study addresses the question of whether the normal range for distribution of local cerebral blood flow (lCBF) in adults can be transferred to the 4- to 15-year-old age group. Twenty-three children (age: 4–15 years; mean 11±3 years, group I) and 10 adults (age: 27–56 years; mean 45±10 years, group II) without evidence of cerebrovascular disease or other brain diseases underwent technetium-99m ethyl cysteinate dimer single-photon emission tomography. Counts in cortical and subcortical regions of interest (ROIs) were related to those in cerebellar ROIs (= 100%). Relative cortical activity in group I exceeded that in group II, particularly in left parietal (107.6%±9.8% vs 84.1%±12.4%), left frontal (97.7%±6.7% vs 79.4%±8.9%) and left temporal areas (99.7%±7.4% vs 84.9%±10.1%) and in the cingulate cortex (112.1%±9.1% vs 95.9%±10.1%, P<0.05). Cerebral activity uptake per injected dose was inversely correlated with age in 19 children of group I (r = –0.77, P<0.001). In group I, there was also an inverse correlation between age and the relative local count density in the parietal (r = –0.42 to –0.57), frontal (r = –0.48), temporal (r = –0.42 to –0.58) and occipital cortex (r = –0.44). In these cortical regions relative counts differed when subgroups of children aged 4–10 and 11–15 years were analysed. It is concluded that there are systematic differences between 4- to 15-year-old children and adults with regard to normal lCBF. Diagnostic use of perfusion agents has to consider age-adjusted normal flow maps; normal ranges should be determined separately for the age groups 4–10 and 11–15 years. Received 23 March and in revised form 11 July 1997  相似文献   
995.
Angioedema of the oropharynx and hypopharynx due to oral angiotensin-converting enzyme (ACE) inhibitors is a potentially life-threatening event and has not been well described in the radiology literature. A retrospective review of the clinical and radiologic findings in three patients with angioedema due to ACE inhibitor use was performed.Our subgroup of patients treated with ACE inhibitors presented with varying degrees of dysphagia, dyspnea, and facial swelling. Plain radiographic findings included enlargement of the epiglottis, aryepiglottic folds, and prevertebral and submental soft tissue. Computed tomography confirmed extensive retropharyngeal and subcutaneous edema. Clinical symptoms resolved in each case in 24–48 hours with cessation of the ACE inhibitor and concomitant steriod therapy.Our cases demonstrate the typical clinical and radiographic presentation of neck angioedema in the setting of ACE inhibitor use. As ACE inhibitors are increasingly being used as first-line agents in the treatment of hypertension, we caution that neck angioedema may be encountered with increased frequency in adults. Early recognition and immediate intervention result in rapid resolution of this potentially life-threatening event.  相似文献   
996.
Summary The antiproteinuric effect of the antiplatelet agent dipyridamole has been assessed after inhibiton of thromboxane B2 (TxB2) synthesis in 8 patients with confirmed membranous glomerulonephritis. There were three study periods, each of 30 days, and 45 days apart, namely a washout period, treatment with dipyridamole 300 mg/d, and dipyridamole 225 mg/d plus aspirin 150 mg/d. On Days 1 and 30 of each study period serum and urine creatinine, 24-h excretion of protein, creatinine clearance, platelet aggregometry on whole blood and serum TxB2 were measured. Treatment with dipyridamole alone or with aspirin produced significant inhibition of platelet aggregation and a fall in 24-h protein excretion; the latter amounted to 54% with dipyridamole alone and 56 % with dipyridamole plus aspirin (NS). Dipyridamole plus aspirin caused an 82 % reduction in serum TxB2.  相似文献   
997.
The purpose of this study was to assess the impact of an educational intervention on medical students' attitudes toward social and sexual contact with patients by doctors from three medical specialties (general practice, obstetrics/gynaecology and psychiatry). Medical students from two consecutive fifth year classes at one medical school participated in one 3 hour session that included instruction on the standards of the profession that prohibit doctor–patient sexual contact. Students were assigned to either intervention groups or control groups and responded to an anonymous questionnaire (overall response rate 66·8% ; n=141). As many as 14·5% of control group students thought it was (sometimes or usually) appropriate for general practitioners to date their own patients and at least 3% thought it appropriate for members of any of these three medical specialties to engage in sexual contact with their own patients. However, there were no significant differences in attitudes toward hugging, dating or sexual contact with current patients between those who had attended the seminar and the control groups. The session significantly influenced attitudes regarding obstetrician/gynaecologists and psychiatrists hugging and having sexual contact with former patients. These findings are discussed in relation to a need for expansion of such instruction.  相似文献   
998.
Flow dynamics through spinal needles   总被引:2,自引:0,他引:2  
We examined the flow pattern produced when liquid dye was actively injected into a fluid medium at various flows through five different commonly used spinal needles. At all flows, the Whitacre-type needles produced a directional stream exiting at an angle from the longitudinal axis. At intermediate rates the stream developed tracks which disappeared at faster rates. The Quincke needle always produced an undeviated stream of dye and did not form tracks at any flow rate. When a perspex plate (representing the spinal cord) was interposed in front of the needle, the dispersion of dye was always unidirectional from the Whitacre needle and bidirectional from the Quincke needle. The dye adhered to the surface of the plate as a concentrated film at slow rates and at faster rates it dispersed turbulently for both types of needle.  相似文献   
999.
Metastases of differentiated thyroid cancer may show different uptake patterns for fluorine-18 fluorodeoxyglucose and [131I]NaI. FDG positron emission tomography (PET), iodine-131 whole-body scintigraphy (131I WBS) and magnetic resonance imaging were performed in 58 unselected patients, and spiral computed tomography (CT) of the lung in 25 patients. Thirty-eight patients presented with papillary carcinomas, 15 patients with follicular carcinomas and five patients with variants of follicular carcinoma. Primary tumour stage (pT) was pT1 in 3, pT2 in 19, pT3 in 11 and pT4 in 25 cases. For the detection of metastases, FDG PET was found to have a sensitivity of 50%, 131I WBS a sensitivity of 61%, and the two methods combined a sensitivity of 86%. When FDG PET was limited to patients with elevated thyroglobulin (Tg) levels and negative 131I WBS, the sensitivity of this algorithm was 82%. Of the 21 patients with lymph node metastases, seven presented with FDG uptake but no iodine uptake. In four of them, a second FDG hot spot appeared in a lymph node metastasis of normal size. Five of the seven patients underwent surgery. None of the eight patients with pulmonary metastases smaller than 1 cm exhibited FDG uptake, while five of them had iodine uptake. All had positive results on spiral CT. In conclusion, FDG PET cannot be substituted for 131I WBS. If the Tg level is elevated and 131I WBS is negative, FDG PET can be used to detect lymph node metastases and complements anatomical imaging. A spiral CT of the lung is useful to exclude pulmonary metastases before planning a dissection of iodine-negative lymph node metastases. Received 2 May and in revised form 8 July 1997  相似文献   
1000.
Although alcoholism is a known risk factor for osteoporosis, there are few published reports on alcoholism-associated bone loss. To study alcoholism-associated bone loss, this study used a dual X-ray absorptiometry (DXA) densitometer to measure lumbar and femoral bone mineral density (BMD) in a previously little-studied population: 32 relatively healthy, nonhospitalized, Caucasian, alcoholic men with a period of abstinence longer than that previously studied (median abstinence 4.0 months, range 3 days–36 months). DXA is a new, highly precise densitometric method with many advantages over the methods used in previous studies. The subjects had statistically significant bone loss at three sites: lumbar spine, femoral neck, and Ward's triangle (multiple correction adjusted two-tailed P < 0.008). Compared to the mean BMD of sex-, age-, and race-matched norms, the subjects' average femoral neck, Ward's triangle, and lumbar BMDs were, respectively, 0.56, 0.69, and 0.57 standard deviations (SDs) below the normative values.This study was partially funded by a National Institutes of Health Short Term Research Training Grant (PHSHL 07491) to K.C.  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