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   11370篇
  免费   706篇
  国内免费   127篇
耳鼻咽喉   198篇
儿科学   74篇
妇产科学   135篇
基础医学   2087篇
口腔科学   325篇
临床医学   946篇
内科学   1852篇
皮肤病学   454篇
神经病学   1044篇
特种医学   640篇
外科学   1566篇
综合类   35篇
一般理论   2篇
预防医学   463篇
眼科学   278篇
药学   1237篇
中国医学   151篇
肿瘤学   716篇
  2024年   7篇
  2023年   77篇
  2022年   292篇
  2021年   475篇
  2020年   200篇
  2019年   304篇
  2018年   358篇
  2017年   276篇
  2016年   389篇
  2015年   502篇
  2014年   650篇
  2013年   729篇
  2012年   1043篇
  2011年   982篇
  2010年   621篇
  2009年   527篇
  2008年   741篇
  2007年   729篇
  2006年   642篇
  2005年   557篇
  2004年   446篇
  2003年   385篇
  2002年   315篇
  2001年   218篇
  2000年   188篇
  1999年   129篇
  1998年   59篇
  1997年   45篇
  1996年   31篇
  1995年   27篇
  1994年   20篇
  1993年   17篇
  1992年   34篇
  1991年   31篇
  1990年   31篇
  1989年   22篇
  1988年   16篇
  1987年   16篇
  1986年   8篇
  1985年   8篇
  1984年   10篇
  1983年   3篇
  1982年   4篇
  1981年   4篇
  1979年   7篇
  1978年   5篇
  1977年   5篇
  1976年   5篇
  1969年   2篇
  1968年   3篇
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
81.
82.
Retinal pigment epithelial (RPE) cells transdifferentiate in culture, a transition which is accompanied by a shift in biological activity. The present study investigates whether transforming growth factor (TGF)-beta has the same effects on morphologically transformed RPE cells that it has on primary RPE cells. It also evaluates the autocrine and paracrine activities of TGF-beta s synthesized by RPE cells as well as the anti-TGF-beta effect of mannose-6-phosphate (M-6-P). RPE cells were subcultured at the sixth passage to induce morphological change. The effect of second passaged RPE-conditioned medium (CM) on DNA synthesis was evaluated by the incorporation of 3H-thymidine in rabbit subconjunctival fibroblasts (SCFs) and primary RPE cells. The presence of TGF-beta in RPE-CM was determined using immunoblotting analysis. And the inhibitory effect of M-6-P on cell proliferation mediated by RPE-CM was also analyzed using 3H-thymidine incorporation into DNA. TGF-beta 1, TGF-beta 2, and TGF-beta 3 inhibited the proliferation of the primary cultures of RPE cells in a dose-dependent manner, but the spindle-shaped sixth passaged RPE cells were not inhibited by these growth factors. The medium conditioned by RPE cells stimulated the proliferation of SCFs and inhibited the proliferation of primary RPE cells, in a manner similar to TGF-beta. When this medium was precipitated with either anti-TGF-beta 1, anti-TGF-beta 2, or anti-TGF-beta 3 antibodies, all three TGF-beta s, with an apparent molecular size of 25 kDa, were detected. Mannose-6-phosphate significantly blocked the effect of RPE-CM on cell proliferation. These findings indicate that RPE cells produce biologically functional TGF-beta s and that M-6-P can block the inhibitory effect of RPE-CM on cell proliferation.  相似文献   
83.
Kwon BM  Jung HJ  Lim JH  Kim YS  Kim MK  Kim YK  Bok SH  Bae KH  Lee IR 《Planta medica》1999,65(1):74-76
Fifteen lignans were isolated from the fruits of SCHIZANDRA CHINENSIS, the leaves of MACHILUS THUNBERGII, and the flower buds of MAGNOLIA DENUDATA. They were identified as gomisins, schizandrin, wuweizisu, schizantherin, licarins, and machilin, which inhibited rat liver ACAT with IC (50) values of 25-200 microM. Comisin N is the most potent inhibitor with IC (50) value of 25 microM in these lignans.  相似文献   
84.
Three 1,2-benzothiazine derivatives were synthesized, and their analgesic/anti-inflammatory efficacy and their effects on gastric irritation were evaluated. Among the three compounds, 39 exhibited the most potent analgesic action, but the effect was weaker than that of piroxicam. Nonetheless, the compound showed 4 times more potent analgesic action with less gastric damage than did ibuprofen. These compounds did not show anti-inflammatory effect at an oral dose of 5 mg/kg.  相似文献   
85.
Many conventional anticancer drugs display relatively poor selectivity for neoplastic cells, in particular for solid tumors. Furthermore, expression or development of drug resistance, increased glutathione transferases as well as enhanced DNA repair decrease the efficacy of these drugs. Research efforts continue to overcome these problems by understanding these mechanisms and by developing more effective anticancer drugs. Cyclophosphamide is one of the most widely used alkylating anticancer agents. Because of its unique activation mechanism, numerous bioreversible prodrugs of phosphoramide mustard, the active species of cyclophosphamide, have been investigated in an attempt to improve the therapeutic index. Solid tumors are particularly resistant to radiation and chemotherapy. There has been considerable interest in designing drugs selective for hypoxic environments prevalent in solid tumors. Much of the work had been centered on nitroheterocyclics that utilize nitroreductase enzyme systems for their activation. In this article, recent developments of anticancer prodrug design are described with a particular emphasis on exploitation of selective metabolic processes for their activation.  相似文献   
86.
In bioassay-guided search for inducible nitric oxide synthase (iNOS) inhibitory compounds from higher plants of South Korea, two beta-carboline alkaloids, 4-methoxy-1-vinyl-beta-carboline (1) and 4,8-dimethoxy-l-vinyl-beta-carboline (2) have been isolated from the cortex of Melia azedarach var. japonica. The structures of these compounds were elucidated on the basis of spectroscopic data. Compounds 1 and 2 showed marked inhibitory activity of iNOS on LPS- and interferon-gamma-stimulated RAW 264.7 cells.  相似文献   
87.
Primary spinal cord primitive neuroectodermal tumor (PNET) is a rare entity. In all, 13 cases have been reported in the literature, including 3 with intracranial seeding. A 3-month-old girl with involvement of the spinal cord below the mid-thoracic level is described. The brain MRI revealed findings indicative of seeding along the intracranial subarachnoid space. Biopsy, duraplasty and removal of laminotomy flap were done. In spite of a good response to the first cycle of postoperative 8-drugs-in-a-day chemotherapy, further treatment was refused. She died 21 days after the onset of leg weakness, which reveals the rapid progression of untreated cases. To our knowledge, this is the first case of spinal cord PNET with parenchymal involvement that has been described in an infant.  相似文献   
88.
The suprathreshold tonotopic organization of rat and guineapig auditory cortex was investigated using intrinsic signaloptical imaging through a thinned skull. Optical imaging revealedthat suprathreshold pure sine wave tone stimulation (25–40dB) evoked activity over large cortical areas that were tonotopicallyorganized. Three-dimensional surface plots of the activatedareas revealed "patchy" auditory-evoked activity consistingof numerous local peaks and valleys building to a maximum. Subsequentdetailed electrophysiological mapping in the same subjects confirmedthe localization of auditory-evoked activity based on opticalimaging, including responses to a test frequency at corticalloci more than 2 octaves away from the threshold-defined isofrequencycontour. The success of this technique in visualizing auditorycortex functional organization at suprathreshold stimulus levelswill allow for future investigations of auditory cortex frequencyrepresentation. including representational plasticity inducedby a variety of experimental manipulations.  相似文献   
89.
This unusual cystic lesion was previously described as a lesion that has features of both botryoid odontogenic cyst and mucoepidermoid tumor and later was named as glandular odontogenic cyst. An additional case is reported and its clinicopathologic features described. The name "mucoepidermoid odontogenic cyst" is proposed.  相似文献   
90.
BACKGROUND: Magnetic resonance imaging studies in schizophrenia have revealed abnormalities in temporal lobe structures, including the superior temporal gyrus. More specifically, abnormalities have been reported in the posterior superior temporal gyrus, which includes the Heschl gyrus and planum temporale, the latter being an important substrate for language. However, the specificity of the Heschl gyrus and planum temporale structural abnormalities to schizophrenia vs affective psychosis, and the possible confounding roles of chronic morbidity and neuroleptic treatment, remain unclear. METHODS: Magnetic resonance images were acquired using a 1.5-T magnet from 20 first-episode (at first hospitalization) patients with schizophrenia (mean age, 27.3 years), 24 first-episode patients with manic psychosis (mean age, 23.6 years), and 22 controls (mean age, 24.5 years). There was no significant difference in age for the 3 groups. All brain images were uniformly aligned and then reformatted and resampled to yield isotropic voxels. RESULTS: Gray matter volume of the left planum temporale differed among the 3 groups. The patients with schizophrenia had significantly smaller left planum temporale volume than controls (20.0%) and patients with mania (20.0%). Heschl gyrus gray matter volume (left and right) was also reduced in patients with schizophrenia compared with controls (13.1%) and patients with bipolar mania (16.8%). CONCLUSIONS: Compared with controls and patients with bipolar manic psychosis, patients with first-episode schizophrenia showed left planum temporale gray matter volume reduction and bilateral Heschl gyrus gray matter volume reduction. These findings are similar to those reported in patients with chronic schizophrenia and suggest that such abnormalities are present at first episode and are specific to schizophrenia.  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