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   6815篇
  免费   360篇
  国内免费   48篇
耳鼻咽喉   71篇
儿科学   93篇
妇产科学   75篇
基础医学   902篇
口腔科学   265篇
临床医学   461篇
内科学   1733篇
皮肤病学   97篇
神经病学   558篇
特种医学   373篇
外科学   1141篇
综合类   39篇
一般理论   2篇
预防医学   223篇
眼科学   154篇
药学   408篇
中国医学   6篇
肿瘤学   622篇
  2023年   28篇
  2022年   80篇
  2021年   131篇
  2020年   54篇
  2019年   100篇
  2018年   108篇
  2017年   99篇
  2016年   108篇
  2015年   115篇
  2014年   143篇
  2013年   225篇
  2012年   355篇
  2011年   401篇
  2010年   230篇
  2009年   213篇
  2008年   372篇
  2007年   390篇
  2006年   346篇
  2005年   394篇
  2004年   330篇
  2003年   358篇
  2002年   359篇
  2001年   165篇
  2000年   166篇
  1999年   185篇
  1998年   89篇
  1997年   53篇
  1996年   54篇
  1995年   56篇
  1994年   56篇
  1993年   49篇
  1992年   112篇
  1991年   117篇
  1990年   125篇
  1989年   111篇
  1988年   109篇
  1987年   120篇
  1986年   100篇
  1985年   108篇
  1984年   51篇
  1983年   57篇
  1982年   33篇
  1981年   26篇
  1979年   47篇
  1978年   27篇
  1977年   38篇
  1974年   26篇
  1972年   20篇
  1970年   19篇
  1969年   20篇
排序方式: 共有7223条查询结果,搜索用时 15 毫秒
71.
Leiomyosarcoma of the scrotum is a rare tumor. Up to 1999, only 29 cases have been reported in the literature worldwide. A 27-year-old man presented with a mass on the left side of the scrotum which had been painless and had gradually enlarged over the previous 10 years. During the following 3 months, however, it became painful and he was then referred to our hospital. Physical examination revealed a solid mass on the left side of the scrotum, measuring 7 cm in diameter, which was not adhering to the testis or to the vas deferens. The tumor was surgically resected. The histological examination confirmed the diagnosis of well differentiated leiomyosarcoma. Adjuvant therapy was considered unnecessary. The follow-up at 41 months revealed no local recurrence or distant metastasis.  相似文献   
72.
BACKGROUND: Little is known about the biological nature of T4 esophageal carcinoma growth signals and host defenses. METHODS: Paraffin-embedded sections from 78 patients with T2 to T4 esophageal squamous cell carcinoma who underwent operation were analyzed with immunohistochemistry. RESULTS: Positive cyclin A showed a significantly greater increase in T4 tumors than in those of other stages, and negative p27 showed a significantly greater decrease in T4 tumors than in large T3 stage tumors (tumor size > or = 4.0 cm). Patients with low-grade tumor-infiltrating lymphocyte (TIL) density showed a significantly greater decrease in T4 than in T2. The combination of p27 and cyclin A was a significant independent prognostic factor among T and N factors in multivariate analysis. TIL density was an independent prognostic factor among immunonutritional variables such as serum albumin concentration and the number of total blood lymphocytes. CONCLUSIONS: T4 esophageal squamous cell carcinoma has a poor prognosis, which is associated with increased p27-negative and cyclin A-positive growth signals in the tumor and with low TIL density in the host.  相似文献   
73.
Takenaka M  Iida H  Iida M  Dohi S 《Anesthesiology》2000,92(5):1376-1384
BACKGROUND: Systemic dexmedetomidine (DXM) attenuates the cerebral vasodilation induced by hypercapnia and decreases the cerebral blood flow response to hypoxia. We determined whether lumbar intrathecal DXM affected the cerebrovascular reactivity to hypercapnia and hypoxia. METHODS: Rabbits (n = 55) anesthetized with pentobarbital were prepared for measurement of pial vessel diameters using a closed cranial window preparation. The first study evaluated the response to hypercapnia after intrathecal administration of DXM (2 microg/kg; n = 7) or normal saline (n = 8). The second evaluated the response to hypercapnia after intrathecal DXM in the presence of yohimbine (20 microg/kg followed by DXM 2 microg/kg; n = 7). The third evaluated the response to mild or moderate hypoxia after intrathecal DXM (2 microg/kg; n = 7) or normal saline (n = 7). The hypercapnic responses were also examined in the presence of systemic DXM (2, 10 microg/kg; n = 6), topical DXM (10-8 m, 10-6 m; n = 6) and of intrathecal clonidine (2 microg/kg; n = 7). RESULTS: The pial arteriolar dilator response to hypercapnia was significantly attenuated after intrathecal administration of DXM. Pretreatment with yohimbine completely blocked the decreased reactivity to hypercapnia. Intrathecal clonidine, although less than DXM, also attenuate the hypercapnic response. Intrathecal DXM did not affect the vasodilation of pial arterioles induced by mild or moderate hypoxia. The systemic DXM 10 microg/kg and topical DXM 10-6 m, but not systemic 2 microg/kg and topical 10-8 m, attenuated hypercapnic vasodilation of pial arterioles. CONCLUSIONS: The presence of alpha2-adrenoceptor agonist administered intrathecally into the lumbar spinal region attenuates hypercapnic but not hypoxic cerebral vasodilation, probably via a stimulation of central alpha2-adrenergic receptors of the central nervous system.  相似文献   
74.
75.
BACKGROUND: Recent laboratory studies have suggested that cadmium is an estrogenic compound and may be a potential risk factor for breast cancer. METHODS: We investigated the relationship between urinary cadmium concentrations and serum concentrations of estrone, testosterone, and dehydroepiandrosterone sulfate in 164 postmenopausal Japanese women. RESULTS: There was a significant positive association between the urinary cadmium and serum testosterone levels after controlling for age and body mass index. The mean testosterone level was 28% higher in women with high urinary cadmium (> or = 3.00 microg/g creatinine) than in those with low urinary cadmium (< 2.00 microg/g creatinine). Urinary cadmium was not significantly associated with serum estrone and dehydroepiandrosterone sulfate levels. Additional adjustment for smoking, alcohol and reproductive factors including known risk factors for breast cancer did not substantially alter the results. CONCLUSION: Data suggested that cadmium exposure is associated with increased testosterone levels. As high testosterone levels have been associated with the risk of breast cancer, the involvement of cadmium exposure in breast cancer risk should be evaluated in future studies.  相似文献   
76.
OBJECT: Patients with subarachnoid hemorrhage (SAH) in whom angiography does not demonstrate diagnostic findings sometimes suffer recurrent disease and actually harbor undetected cerebral aneurysms. The management strategy for such cases remains controversial, but technological advances in spiral computerized tomography (CT) angiography are changing the picture. The purpose of this prospective study was to examine how spiral CT angiography can contribute to the detection of cerebral aneurysms that cannot be visualized on angiography. METHODS: In 134 consecutive patients with SAH, a prospective search for the source of bleeding was performed using digital subtraction (DS) and spiral CT angiography. In 21 patients in whom initial DS angiography yielded no diagnostic findings, spiral CT angiography was performed within 3 days. Patients in whom CT angiography provided no diagnostic results underwent second and third DS angiography sessions after approximately 2 weeks and 6 months, respectively. Six patients with perimesencephalic SAH were included in the 21 cases. Six of the other 15 patients had small cerebral aneurysms detectable by spiral CT angiography, five involving the anterior communicating artery and one the middle cerebral artery. Two patients in whom initial angiograms did not demonstrate diagnostic findings proved to have a ruptured dissecting aneurysm of the vertebral artery; in one case this was revealed at autopsy and in the other during the second DS angiography session. A third DS angiography session revealed no diagnostic results in 13 patients. CONCLUSIONS: Spiral CT angiography was useful in the detection of cerebral aneurysms in patients with SAH in whom angiography revealed no diagnostic findings. Anterior communicating artery aneurysms are generally well hidden in these types of SAH cases. A repeated angiography session was warranted in patients with nonperimesencephalic SAH and in whom initial angiography revealed no diagnostic findings, although a third session was thought to be superfluous.  相似文献   
77.
BACKGROUND/OBJECTIVESOocyte lipid droplets play a crucial role in meiosis and embryo development. Biotin is associated with fatty acid synthesis and is the coenzyme for acetyl-CoA carboxylase (ACC). The effects of a biotin deficiency on the oocyte lipid metabolism remain unknown. This study examined the effects of a biotin deficiency and its replenishment on murine 1) oocyte lipid droplet levels, 2) ovary lipid metabolism, and 3) oocyte meiosis.MATERIALS/METHODSMice were divided into 3 groups: control, biotin deficient (BD), and recovery groups. The control and BD groups were fed a control diet or BD diet (0.004 or 0 g biotin/kg), respectively. The recovery group mice were fed a BD diet until day 21, and were then fed the control diet from days 22 to 64. This study then quantified the oocyte lipid droplet levels, assessed the oocyte mitochondrial function, and examined the ability of oocytes to undergo meiosis. Ovarian phosphorylated ACC (p-ACC), lipogenesis, β-oxidation, and ATP production-related genes were evaluated.RESULTSThe BD group showed a decrease in lipid droplets and mitochondrial membrane potential and increased p-ACC levels. In the recovery group, the hepatic biotin concentration, ovarian p-ACC levels, and mitochondrial membrane potential were restored to the control group levels. On the other hand, the quantity of lipid droplets in the recovery group was not restored to the control levels. Furthermore, the percentage of oocytes with meiotic abnormalities was higher in the recovery group than in the control group.CONCLUSIONSA biotin deficiency reduced the oocyte lipid droplet levels by downregulating lipogenesis. The decreased lipid droplets and increased oocyte meiosis failure were not fully restored, even though the biotin nutrition status and gene expression of lipid metabolism was resumed. These results suggest that a biotin deficiency remains robust and can be long-lasting. Biotin might play a crucial role in maintaining the oocyte quality.  相似文献   
78.
As part of a Hastings Center Report series of six articles on reproductive technologies around the world, three Japanese scholars report on the situation in their country. At present, artificial insemination and in vitro fertilization are offered to infertile married couples, and research is performed on early embryos up to 14 days after fertilization. Neither surrogate mothers nor donated gametes are used in Japan. Bai, Shirai, and Ishii identify several issues that they believe merit further public debate, among them the legal status of AID children, the experimental nature of in vitro fertilization, genetic manipulation of embryos, and gender selection. They summarize the findings of four opinion surveys that show a lack of consensus among the Japanese on the acceptability of reproductive technologies, which in the words of the authors "create a tension and a link between traditional belief and contemporary practice."  相似文献   
79.
Purpose: We evaluated the diagnostic performance of the texture features of dynamic contrast-enhanced (DCE) MRI for breast cancer diagnosis in which the discriminator was optimized, so that the specificity was maximized via the restriction of the negative predictive value (NPV) to greater than 98%.Methods: Histologically proven benign and malignant mass lesions of DCE MRI were enrolled retrospectively. Training and testing sets consist of 166 masses (49 benign, 117 malignant) and 50 masses (15 benign, 35 malignant), respectively. Lesions were classified via MRI review by a radiologist into 4 shape types: smooth (S-type, 34 masses in training set and 8 masses in testing set), irregular without rim-enhancement (I-type, 60 in training and 14 in testing), irregular with rim-enhancement (R-type, 56 in training and 22 in testing), and spicula (16 in training and 6 in testing). Spicula were immediately classified as malignant. For the remaining masses, 298 texture features were calculated using a parametric map of DCE MRI in 3D mass regions. Masses were classified into malignant or benign using two thresholds on a feature pair. On the training set, several feature pairs and their thresholds were selected and optimized for each mass shape type to maximize specificity with the restriction of NPV > 98%. NPV and specificity were computed using the testing set by comparison with histopathologic results and averaged on the selected feature pairs.Results: In the training set, 27, 12, and 15 texture feature pairs are selected for S-type, I-type, and R-type masses, respectively, and thresholds are determined. In the testing set, average NPV and specificity using the selected texture features were 99.0% and 45.2%, respectively, compared to the NPV (85.7%) and specificity (40.0%) in visually assessed MRI category-based diagnosis.Conclusion: We, therefore, suggest that the NPV of our texture-based features method described performs similarly to or greater than the NPV of the MRI category-based diagnosis.  相似文献   
80.
From the stem bark of Ekebergia capensis, 10 new triterpenoid compounds, ekeberins A (1), B (2), C1 (3), C2 (4), C3 (5), D1 (6), D2 (7), D3 (8), D4 (9), and D5 (10), were isolated together with 17 known compounds. The structures of these new compounds were elucidated on the basis of the results of spectroscopic analysis, and the absolute configuration of compounds 6-10 were determined by partial synthesis from known compounds and using the Mosher ester method. Several of these compounds were screened in vitro against both chloroquine (CQ)-sensitive and -resistant Plasmodium falciparum isolates and were found to exhibit moderate antiplasmodial activity, with compounds 20 (7-deacetoxy-7-oxogedunin) and 27 (2-hydroxymethyl-2,3,22,23-tetrahydroxy-2,6,10,15,19,23-hexamethyl-6,10,14,18-tetracosatetraene) showing IC50 values of 6 and 7 microM, respectively. Compound 27 at a dose of 500 mg/kg showed moderate parasitemia suppression of 52.9% against P. berghei NK 65 in a mouse model.  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