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   2439篇
  免费   177篇
  国内免费   5篇
耳鼻咽喉   14篇
儿科学   42篇
妇产科学   19篇
基础医学   269篇
口腔科学   45篇
临床医学   139篇
内科学   765篇
皮肤病学   24篇
神经病学   231篇
特种医学   69篇
外科学   501篇
综合类   7篇
预防医学   55篇
眼科学   58篇
药学   91篇
中国医学   4篇
肿瘤学   288篇
  2023年   28篇
  2022年   42篇
  2021年   92篇
  2020年   63篇
  2019年   66篇
  2018年   95篇
  2017年   63篇
  2016年   67篇
  2015年   83篇
  2014年   102篇
  2013年   105篇
  2012年   187篇
  2011年   185篇
  2010年   100篇
  2009年   91篇
  2008年   139篇
  2007年   149篇
  2006年   132篇
  2005年   149篇
  2004年   144篇
  2003年   121篇
  2002年   124篇
  2001年   24篇
  2000年   25篇
  1999年   25篇
  1998年   27篇
  1997年   14篇
  1996年   23篇
  1995年   17篇
  1994年   14篇
  1993年   18篇
  1992年   16篇
  1991年   11篇
  1990年   6篇
  1989年   8篇
  1988年   7篇
  1987年   7篇
  1986年   9篇
  1985年   3篇
  1984年   5篇
  1983年   2篇
  1982年   5篇
  1981年   4篇
  1980年   6篇
  1979年   2篇
  1978年   4篇
  1977年   5篇
  1976年   3篇
  1975年   2篇
  1969年   1篇
排序方式: 共有2621条查询结果,搜索用时 31 毫秒
21.
Aquaporins (AQPs) are water channel proteins that permit osmotically driven water movement. To determine their dynamics in pulmonary oedema, we examined the expression of mRNA and protein for AQP1, AQP3, AQP4, and AQP5 in the lungs of normal and thiourea-treated rats. In the thiourea group, lung water content increased significantly (vs. controls) with the peak at around 4 h. Semi-quantitative RT-PCR showed that AQP3 mRNA in the thiourea group rose significantly, peaking at around 4–8 h. The expression of AQP1, AQP4, AQP5, ENaC and CFTR mRNA each decreased significantly some time after the peak in lung water content. Immunoblot analysis showed that glycosylated AQP3 protein was increased 4–10 h after treatment. Expression of the other AQP proteins was not significantly altered, except for that of AQP4. Immunohistochemical examination revealed that AQP1 was expressed in endothelia, AQP3 in the basal cells of the large airways and in cuboidal cells in the bronchioles, AQP4 in the basolateral membrane of airway cells and AQP5 in type-I pneumocytes. Our results suggest that AQP3 is expressed not only in large airways, but also in bronchioles, and is related to water movement in pulmonary oedema.  相似文献   
22.
Few studies have reviewed the roles of perfusion magnetic resonance (MR) imaging in the histopathological examination of meningiomas. We analyzed the relationships between radiological findings on perfusion MR imaging and pathological characteristics such as origin of the tumor, mitotic activity, pathological subtype, and perifocal edema formation. The subjects were 21 surgical cases of meningioma preoperatively evaluated by perfusion MR imaging. A region of interest (ROI) was set inside of the tumor, and perifocal edema of the same size, cerebral blood volume (CBV), and cerebral blood flow (CBF) on perfusion MR and diffusion-weighted (DW) imaging were analyzed. These radiological data were evaluated in comparison with histopathological characteristics. On perfusion MR imaging, the average ratio of CBV against the contralateral side was 6.43 (1.13–20.0) and that of CBF was 7.73 (1.34–11.3). There was no significant relationship with perfusion MR imaging data, tumor volume, or perifocal edema volume. However, the large peritumoral edema group often had a higher CBV and CBF than the non-large peritumoral edema group. The skull base group had a significantly higher CBV and lower signal intensity on DW images than the non-skull base group. Signal intensity on DW images was higher in grade II or III than in grade I. Perfusion MR imaging data revealed that the higher ratio of peritumoral edema against tumor size was associated with higher blood flow and blood volume under intratumoral circulatory conditions, and that skull base meningioma had a higher blood volume than non-skull base meningioma.  相似文献   
23.
24.
Basophils produce interleukins (IL)-4 in response to various stimuli and may contribute to type 2 immune responses to various infections and allergens. We found that resting basophils freshly isolated from mice produce IL-4 in response to IL-3 but not to high-affinity Fc receptor (FcεRI) cross-linking (CL), yet both required the immunoreceptor tyrosine-based activation motif (ITAM) containing adaptor Fc receptor γ-chain (FcRγ), while basophils activated in vitro by IL-3 become responsive to FcεRI CL. Acquisition of responsiveness to FcεRI CL occurred upon infection with Trichinella spiralis or administration of superantigen. Because cultured basophils return to a quiescent state upon starvation with IL-3 with surface FcεRI levels unchanged, this acquisition is reversible and probably reflects intracellular events requiring protein synthesis. Interestingly, similar activation-associated acquisition was observed for responsiveness to other stimuli, including CD200R3 CL, which is known to signal via DAP-12, and the allergen protease papain. This acquisition of responsiveness to FcεRI CL was inhibited by Jak inhibitor. Thus, the IL-3 signal bifurcates downstream of Jak, into two distinct pathway, one leading to IL-4 production and the other to render basophils competent to respond to stimuli dependent on ITAM-containing adaptors DAP12 and FcRγ for IL-4 production.  相似文献   
25.
The procedure of aspiration biopsy cytology by fine needle aspiration (ABC) is as option in establishing definitive diagnoses for breast cancers. In this series, a needle size of 21G was considered most suitable for ABC as well as flow cytometric DNA analysis. Histograms from fresh samples aspirated by fine needle clearly delineated a sharp peak in G&sup0;G(1) phases and also a better CV was obtained than with paraffin-embedded preparations. In addition, fresh samples gave more reliable DI and suggested the value of measuring nuclear DNA contents. It is believed that the prognoses of breast cancers are closely associated with DNA ploidy patterns. In this sense, flow cytometric DNA analysis of fresh samples of ABC is regarded as important in clinical use.  相似文献   
26.
A multiclinic double-blind controlled study was performed on the effects of MAP in both inpatients and outpatients with AMT as control drug.
  • 1 Subjects consisted of 41 male and 45 female patients suffering from various types of depression. MAP was assigned to 42 cases and AMT to 44 cases. Of these patients, 14 MAP cases and 10 AMT cases were subsequently dropped for a variety of reasons to obtain 28 MAP cases and 34 AMT cases as evaluable.
  • 2 The global improvement ratings were compared and found not significantly different for any week between the two treatments.
  • 3 The global improvement ratings by the characteristic features of patients did not show any significant difference in any items studied between the two treatments.
  • 4 The symptomatic improvement ratings (on the Hamilton R.S. for assessment by the physician) indicated that AMT was more effective on “anxiety (psychic).”
  • 5 The symptomatic improvement ratings (on the Beck self-assessment scale by the patient) indicated that MAP was more effective on “work” and AMT on “pathos”, “feeling of satisfaction”, “withdrawal” and “loss of libido.”
  • 6 During the treatment period, 74.3 percent of the MAP group and 76.9 percent of the AMT group of patients showed some side effects or accompanying symptoms, with no significant difference recognized between the two treatments. Itemwise, however, the incidence of tremor was significantly lower (p-=0.06) in the MAP group. Moreover, the MAP group tended to be less liable to such anti-cholinergic side effects as dry mouth, constipation, trouble of accommodation, urinary disturbance and palpitation.
  • 7 On the basis of the above findings, it is concluded that MAP is as effective against depression as AMT and less liable to the anticholinergic side effects. It is, therefore, a very useful antidepressant.
  相似文献   
27.
Involvement of nuclear factor-kappaB (NF-kappaB) in cell survival and proliferation of multiple myeloma has been well established. In this study we observed that NF-kappaB is constitutively activated in all human myeloma cell lines, thus confirming the previous studies. In addition, we found the phosphorylation of p65 subunit of NF-kappaB in addition to the phosphorylation of IkappaBalpha and the activation of NF-kappaB DNA binding and that various target genes of NF-kappaB including bcl-x(L), XIAP, c-IAP1, cyclin D1, and IL-6 are up-regulated. We then examined the effect of a novel IkappaB kinase inhibitor, 2-amino-6-[2-(cyclopropylmethoxy)-6-hydroxyphenyl]-4-piperidin-4-yl nicotinonitrile (ACHP). When myeloma cells were treated with ACHP, the cell growth was efficiently inhibited with IC(50) values ranging from 18 to 35 mumol/L concomitantly with inhibition of the phosphorylation of IkappaBalpha/p65 and NF-kappaB DNA-binding, down-regulation of the NF-kappaB target genes, and induction of apoptosis. In addition, we observed the treatment of ACHP augmented the cytotoxic effects of vincristine and melphalan (l-phenylalanine mustard), conventional antimyeloma drugs. These findings indicate that IkappaB kinase inhibitors such as ACHP can sensitize myeloma cells to the cytotoxic effects of chemotherapeutic agents by blocking the antiapoptotic nature of myeloma cells endowed by the constitutive activation of NF-kappaB.  相似文献   
28.
PURPOSE: Receptor activator of nuclear factor-kappaB ligand (RANKL) is a key mediator of osteoclastogenesis. Because certain types of tumor cells aberrantly express RANKL, and because bone destruction also develops in B-cell lymphomas of bone origin, we investigated RANKL expression and the mechanisms of osteoclastogenesis in B-lymphoid neoplasms. EXPERIMENTAL DESIGN AND RESULTS: Immunohistochemistry of bone specimens resected from patients with primary B-cell lymphoma of bone with bone destruction revealed that lymphoma cells express RANKL as well as vascular endothelial cell growth factor (VEGF). The tumor cells isolated from the bone specimens enhanced osteoclastogenesis in vitro. In contrast, B-cell lymphoma infiltrating to the bone marrow without bone destruction did not express RANKL. Both RANKL and VEGF were expressed by a portion of B-lymphoid cell lines, including Daudi and IM-9. These RANKL-expressing tumor cells enhanced osteoclastogenesis from RAW264.7 cells and human monocyte-derived preosteoclasts in the absence of stromal cells/osteoblasts in a RANKL-dependent manner. Furthermore, conditioned media from Daudi cells enhanced transmigration of preosteoclasts that was inhibited by anti-VEGF antibody, suggesting that tumor cell-derived VEGF mediates recruitment of osteoclast precursors. Moreover, cocultures of B-lymphoid cell lines with osteoclasts enhanced the growth of B-lymphoid cells. CONCLUSIONS: Some malignant B cells aberrantly express functional RANKL as well as VEGF to enhance osteoclastogenesis. The coexpression of RANKL and VEGF may also contribute to the close cellular interactions with osteoclastic cells, thereby forming a vicious cycle between osteoclastic bone destruction and tumor expansion in bone.  相似文献   
29.
We investigated the effect of propofol anesthesia on the level of interstitial dopamine in vivo awake free moving and anesthetized rats brain striatum using microdialysis techniques. Rats were implanted a microdialysis probe to right striatum of the brain and administered intravenously 20 mg.kg-1 of propofol for induction and followed by continuous infusion at 12.5, 25 and 50 mg.kg-1.hr-1 up to 1 hour. The microdialysis probe was perfused with artificial cerebrospinal fluid and dialysates from the probe were determined every 20 minutes by high performance liquid chromatography and electrochemical detection. Propofol anesthesia reduced the amount of dopamine derived from dialysate, but no prolonged increases of dopamine metabolites were observed, as we demonstrated in previous investigation for halothane, isoflurane or sevoflurane anesthesia. We hypothesize that the characteristics of propofol anesthesia for dopamine and its metabolites might contribute to low incidence of postoperative nausea and vomiting in its clinical use.  相似文献   
30.
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