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   3964篇
  免费   411篇
  国内免费   4篇
耳鼻咽喉   53篇
儿科学   78篇
妇产科学   71篇
基础医学   567篇
口腔科学   70篇
临床医学   324篇
内科学   793篇
皮肤病学   49篇
神经病学   405篇
特种医学   228篇
外科学   555篇
综合类   89篇
一般理论   1篇
预防医学   564篇
眼科学   34篇
药学   254篇
肿瘤学   244篇
  2021年   37篇
  2019年   49篇
  2018年   51篇
  2017年   43篇
  2016年   51篇
  2015年   49篇
  2014年   78篇
  2013年   97篇
  2012年   127篇
  2011年   139篇
  2010年   99篇
  2009年   73篇
  2008年   140篇
  2007年   158篇
  2006年   133篇
  2005年   154篇
  2004年   132篇
  2003年   139篇
  2002年   134篇
  2001年   101篇
  2000年   110篇
  1999年   115篇
  1998年   65篇
  1997年   60篇
  1996年   66篇
  1995年   60篇
  1994年   43篇
  1993年   46篇
  1992年   88篇
  1991年   99篇
  1990年   95篇
  1989年   93篇
  1988年   79篇
  1987年   89篇
  1986年   86篇
  1985年   90篇
  1984年   65篇
  1983年   66篇
  1982年   40篇
  1981年   43篇
  1980年   35篇
  1979年   69篇
  1978年   44篇
  1977年   41篇
  1976年   45篇
  1975年   39篇
  1973年   42篇
  1972年   32篇
  1971年   36篇
  1968年   36篇
排序方式: 共有4379条查询结果,搜索用时 31 毫秒
71.
The absolute granulocyte count (AGC) in 125 blood samples from patients with total white blood cell counts of less than 1,000/microliter was estimated using three different methods, which were then compared for efficiency and accuracy. The three methods were 25 cell differential counts using Wright's-stained blood smears, granulocyte percentage estimates from WBC counting chambers, and combined narrow- and wide-angle light-scatter characteristics determined on a flow cytometer. A survey of clinical laboratories at University Hospital Cancer Centers revealed that the smear differential was the most-often-used method in those laboratories even when less than 25 cells could be counted. Consequently the data obtained from the counting chamber and flow cytometer methods were compared to the smear differential "standard" using linear regression, and outliers were identified. There was good correlation between AGC determined by smear differential and WBC counting chamber (correlation coefficient .911) and excellent correlation between the AGC determined by smear differential and the flow cytometer method (correlation coefficient .970). The flow cytometer method used in this investigation required minimal specimen preparation, and test results were available at a rate of 60 seconds/sample. The ease of sample preparation, speed, and statistical reliability of test results makes the flow cytometer an attractive alternate method of determining granulocyte counts on leukopenic patients as compared to the stained blood smear differential.  相似文献   
72.
A frontal lobe neoplasm in a 25-year-old Caucasian man showed the typical histological pattern of a "polar spongioblastoma." Immunoperoxidase staining for glial fibrillary acidic protein (GFAP) was negative while silver stains in paraffin-embedded tissue, and electron microscopy displayed neoplastic cells with neuritic processes. Ultrastructurally there were microtubules, synapses and dense-core neurosecretory granules, all features of a neuroblastic neoplasm. It is suggested that this new growth with its polar spongioblastic appearance is, in fact, a moderately malignant primary cerebral neuroblastoma.  相似文献   
73.
Archives of Sexual Behavior - Compersion is a well-known term in polyamorous communities that connotes the positive emotion an individual may experience in relation to their partner’s...  相似文献   
74.
Lack of expression of the fragile X mental retardation protein (FMRP) results in mental retardation and macroorchidism, seen as the major pathological symptoms in fragile X patients. FMRP is a cytoplasmic RNA- binding protein which cosediments with the 60S ribosomal subunit. Recently, two proteins homologous to FMRP were discovered: FXR1 and FXR2. These novel proteins interact with FMRP and with each other and they are also associated with the 60S ribosomal subunit. Here, we studied the expression pattern of the three proteins in brain and testis by immunohistochemistry. In adult brain, FMR1, FXR1 and FXR2 proteins are coexpressed in the cytoplasm of specific differentiated neurons only. However, we observed a different expression pattern in fetal brain as well as in adult and fetal testis, suggesting independent functions for the three proteins in those tissues during embryonic development and adult life.   相似文献   
75.
LOH studies provide evidence for the implication of novel TSGs in human tumours. The p arm of chromosome 8 has been reported to harbour tumour suppressor genes (TSGs) which are very likely to be involved in the development of colon, lung, bladder and hepatocellular carcinomas. In addition, the c-myc proto-oncogene which is located on the 8q arm, has been found to be overexpressed in SCCHN. In the present study we have investigated the incidence of loss of heterozygosity (LOH) in chromosome 8 in 37 tumour specimens of squamous cell carcinomas of the head and neck (SCCHN), using a bank of 11 polymorphic microsatellite markers. The aim of this work was to assess whether there was an 8p TSG(s) in SCCHN, as reported in other tumours and also to investigate whether other areas of chromosome 8 exhibit a high LOH. A relatively high incidence of LOH was found for the markers D8S87 (29%) on 8p12 and ANK1 (20%) on 8p21.2-p11. These two markers are located in the area in which TSG(s) for other cancers have been previously described. When the data on D8S87 and ANK1 were analyzed together it was found that 13/35 (37%) of the SCCHN specimens had a loss at one or other of these markers, thus indicating that a putative TSG(s) in this region may play a role in the development of the SCCHN. No correlation was found between the LOH data and any of the clinicopathological parameters. We also investigated the incidence of c-myc amplification in 144 SCCHN specimens but only 4% were found to have an amplified c-myc allele, thus indicating that the overexpression of c-myc in SCCHN was not the result of gene amplification.  相似文献   
76.
This study computed life table probabilities of contraceptive failure, discontinuation of use, and return to contraceptive use in the US. Data were obtained from the 1995 National Survey of Family Growth (NSFG) among a nationally representative sample of 6867 contraceptive use intervals contributed by women 15-45 years old who began use or resumed use after discontinuation during 1991-95. Analysis was based on Kaplan-Meier product-limit single decrement life table probability methods. Findings indicate that the risk of failure during typical use of reversible methods was 9% within 1 year of starting. Women with continuous lifetime use will experience 1.8 contraceptive failures. Failure rates were 7% for the pill, 9% for the male condom, 8% for the diaphragm, 20% for periodic abstinence, and 15% for spermicides. Failure rates reflect imperfect use. 31% of women discontinued use within 6 months of starting use. 44% discontinued within 12 months. Women using reversible methods continuously will discontinue use nearly 10 times during the reproductive period. Most women resumed use shortly after discontinuation. Low income women had higher risk of unintended pregnancy for all methods and the pill and lower risk of resumption after discontinuation. Hispanics had a higher risk of contraceptive failure for all methods and the condom. Black women had a higher risk of discontinuation of oral pills and condoms.  相似文献   
77.
Oh JD  Vaughan CL  Chase TN 《Brain research》1999,821(2):433-442
Sensitization of striatal N-methyl-d-aspartate (NMDA) receptors has been implicated in the pathogenesis of the response alterations associated with dopaminomimetic treatment of parkinsonian animals and patients. To determine whether serine phosphorylation of NMDA receptor subunits by activation of Ca2+/calmodulin-dependent protein-kinase II (CaMKII) contributes to this process, we examined the effects of unilateral nigrostriatal ablation with 6-hydroxydopamine and subsequent treatment with levodopa, SKF 38393 (D1-preferring dopamine agonist), or quinpirole (D2-preferring agonist) on motor responses and phosphorylation states. Three weeks of twice-daily levodopa administration to rats shortened the duration of their rotational response to levodopa or SKF 38393 challenge, but prolonged the duration of quinpirole-induced rotation. At the same time, levodopa treatment elevated serine phosphorylation of striatal NR2A (p<0.02), but not that of NR2B subunits, without associated changes in subunit protein levels. Chronic treatment with SKF 38393 increased NR2A (p<0.0001) but decreased NR2B (p<0.004) serine phosphorylation. In contrast, chronic quinpirole treatment had no effect on NR2A but increased NR2B phosphorylation (p<0.0001). The acute intrastriatal injection of the CaMKII inhibitor KN93 (1.0 micrograms) not only normalized the levodopa-induced motor response alterations but also attenuated the D1 and D2 receptor-mediated serine phosphorylation of NR2A and NR2B subunits, respectively (p<0.02). These results suggest that a CaMKII-mediated rise in serine phosphorylation of NMDA receptor subunits induced by intermittent stimulation of D1 or D2 dopaminergic receptors contributes to the apparent enhancement in striatal NMDA receptor sensitivity and thus to the dopaminergic response plasticity in levodopa-treated parkinsonian rats.  相似文献   
78.
Lateral transperitoneal laparoscopic adrenalectomy   总被引:7,自引:0,他引:7  
Several laparoscopic approaches to the adrenal gland have been described. The lateral transperitoneal approach has several distinct advantages when contrasted with other techniques for laparoscopic adrenalectomy (LA). We present our technique and results obtained in 50 consecutive transperitoneal LAs. We review 50 consecutive laparoscopic adrenalectomies (28 female, 19 male) performed from 1993 to 1998. S.J. Shichman or R.E. Sosa was either the primary surgeon or the first assistant for all cases. The lateral transperitoneal approach described below was used in all cases. Indications for adrenalectomy included Cushing's syndrome (13), aldosteronoma (15), pheochromocytoma (7), nonfunctioning adenoma (11), hyperplasia (2), and 1 case each of Carney's syndrome and metastasis to the adrenal gland. We performed 5 bilateral, 22 left, and 18 right laparoscopic adrenalectomies. The average time needed for bilateral adrenalectomy was 503 min (range 298–690 min); for left adrenalectomy, 227 min (range 121–337 min); and for right LA, 210 min (range 135–355 min). We demonstrated a yearly trend in lower operative times. The largest adrenal gland removed measured 13.8 × 6.7 × 3.5 cm. Intraoperative blood loss was low. Only one patient received a blood transfusion. Conversion to open adrenalectomy was not required. Postoperative analgesic requirements were low. The average length of stay was 3.8 days for bilateral LA and 3 days for unilateral LA. Complications occurred in 5 patients (2 wound infections, 2 hematomas, and 1 pleural effusion). There was no mortality. Lateral transperitoneal adrenalectomy is a safe and efficient technique for the removal of functional and nonfunctional adrenal masses. This technique is associated with low morbidity, a minimal postoperative analgesic requirement, and a short hospital stay and, in our opinion, is more versatile than the retroperitoneal approach.  相似文献   
79.
The elasticity of tissues subjected to repeated deformation is provided by the presence of elastic fibers in the extracellular matrix (ECM). The most abundant component of elastic fibers is elastin, whose soluble precursor is tropoelastin. To establish the role elastin plays in the bladder, this study describes the biosynthetic, histologic, and physiologic consequences of expression of an isoform of rat tropoelastin in transgenic mouse bladder. The polymerase chain reaction (PCR) was used to determine expression of a rat tropoelastin minigene in transgenic mice. Histochemical methods were used to demonstrate changes in elastic fibers in frozen sections of bladder. Cystometric analysis was carried out in transgenic and non-transgenic mice, prior to and after 3 weeks of partial outlet obstruction. The PCR assay demonstrated that bladder tissue of transgenic mice expressed rat tropoelastin mRNA, whereas non-transgenes did not. Increased deposition of elastic fibers was demonstrated with the Verhoeff-van Gieson stain. Bladders of transgenic animals were more compliant than bladders of their non-transgenic littermates. Partial outlet obstruction resulted in increased bladder volume and more compliant bladders in non-transgenic mice. In contrast, the bladder volume and compliance in transgenes was almost unchanged by obstruction. This study demonstrates that normal elastic fiber assembly is prerequisite for the compliant properties of the bladder wall. Moreover, the response of the bladder to obstruction is critically influenced by elastin synthesis.  相似文献   
80.
From 1948, when WHO was established, the Organisation has relied on the assessed contributions of its member states for its regular budget. However, since the early 1980s the WHO World Health Assembly has had a policy of zero real growth for the regular budget and has had to rely increasingly, therefore, on attracting additional voluntary contributions, called extrabudgetary funds (EBFs). Between 1984-85 and 1992-93 the real value of the EBFs apparently increased by more than 60% and in the 1990-91 biennium expenditure of extrabudgetary funds exceeded the regular budget for the first time. All WHO programmes, except the Assembly and the Executive Board, receive some EBFs. However, three cosponsored and six large regular programmes account for about 70% of these EBFs, mainly for vertically managed programmes in the areas of disease control, health promotion and human reproduction. Eighty percent of all EBFs received by WHO for assisted activities have been contributed by donor governments, with the top 10 countries (in Europe, North America and Japan) contributing about 90% of this total, whereas the UN funds and the World Bank have donated only about 6% of the total to date. By contrast, about 70% of the regular budget expenditure has been for organisational expenses and for the support of programmes in the area of health systems. Despite the fact that the more successful programmes are heavily reliant on EBFs, there are strong indications that donors, particularly donor governments, are reluctant to maintain the current level of funding without major reforms in the leadership and management of the Organisation. This has major implications for WHO's international role as the leading UN specialised agency for health.  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