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   2664篇
  免费   108篇
  国内免费   11篇
耳鼻咽喉   73篇
儿科学   58篇
妇产科学   27篇
基础医学   377篇
口腔科学   51篇
临床医学   160篇
内科学   594篇
皮肤病学   7篇
神经病学   297篇
特种医学   153篇
外科学   447篇
综合类   5篇
一般理论   1篇
预防医学   115篇
眼科学   5篇
药学   176篇
中国医学   5篇
肿瘤学   232篇
  2023年   8篇
  2022年   20篇
  2021年   28篇
  2020年   17篇
  2019年   28篇
  2018年   28篇
  2017年   29篇
  2016年   49篇
  2015年   47篇
  2014年   51篇
  2013年   85篇
  2012年   136篇
  2011年   154篇
  2010年   90篇
  2009年   85篇
  2008年   141篇
  2007年   150篇
  2006年   153篇
  2005年   166篇
  2004年   159篇
  2003年   178篇
  2002年   188篇
  2001年   39篇
  2000年   17篇
  1999年   35篇
  1998年   55篇
  1997年   51篇
  1996年   43篇
  1995年   28篇
  1994年   34篇
  1993年   36篇
  1992年   43篇
  1991年   38篇
  1990年   35篇
  1989年   29篇
  1988年   33篇
  1987年   30篇
  1986年   17篇
  1985年   26篇
  1984年   29篇
  1983年   19篇
  1982年   14篇
  1981年   18篇
  1980年   18篇
  1979年   9篇
  1978年   15篇
  1977年   16篇
  1974年   9篇
  1970年   6篇
  1957年   6篇
排序方式: 共有2783条查询结果,搜索用时 15 毫秒
41.
Cancers are characterized by invasive growth and distant metastasis. Cancer cells not only destroy the pre-existing extracellular matrix, but cancer invasion per se usually induces new matrix formation by activation of stromal cells; that is, desmoplastic reaction. This process includes both matrix production and degradation; that Is, the remodeling process. The similarity between desmoplastic reactions in cancer stroma and the wound healing process has already been pointed out, and it has been well documented that matrix-degrading processes are actively involved In the wound healing process. A recent study revealed that most matrix-degrading enzymes, generally considered to be one of the main mechanisms of cancer invasion and metastasis, are originated from stromal cells. Based on these preconditions, the present review postulates that the abundant expression of matrix-degrading enzymes by fibroblasts, coupled with the abundant expression of type I procollagen, is involved in the matrix remodeling processes occurring in cancer stroma; that is, the mechanism similar to the wound healing process. Next, macrophages distributed along the invasive margin are known to express matrix-degrading enzymes/factors. Data from past studies of colon carcinoma indicate that the tissue expression of matrix metalloproteinase-9 and urokinase-type plas-mlnogen activator receptor Is inversely associated with simultaneous liver metastasis and infiltrating growth pattern. Previous clinicopathologic data have indicated that immune/Inflammatory cells are one of the factors for a favorable prognosis. This suggests that the expression of matrix-degrading enzymes/factors by these host cells may be involved in host immune/inflammatory reactions, and that the net function of these cells can be defensive towards the host. Data from past studies of colon carcinoma on the expression of the intercellular adhesion molecule-1 suggest that the interaction between macrophages, lymphocytes, and the phenotypes of venules distributed along the Invasive margin, further support the pro-inflammatory milieu there. Therefore, the matrix degradation process in cancer tissue is multifunctional: besides the Involvement in cancer invasion and metastasis, the matrix degradation process is also involved in the tissue remodeling process and in the immune/inflammatory reaction occurring in the stroma.  相似文献   
42.
We investigated exocytosis of PC12 cells using two-photon excitation imaging and extracellular polar tracers (TEP imaging) at the basal region of PC12 cells adjacent to the glass cover slip. TEPIQ (two-photon extracellular polar-tracer imaging-based quantification) analysis revealed that most exocytosis was mediated by large dense-core vesicles (LVs) with a mean diameter of 220 nm, and that exocytosis of LVs occurred slowly with a mean latency of ∼7 s even though exocytosis was induced with large increases in cytosolic Ca2+ concentration by uncaging of a caged-Ca2+ compound. We also found that 97% of exocytic LVs remained poised at the plasma membrane, 72% maintained their fusion pores in an open conformation for more than 30 s, and 76% triggered sequential compound exocytosis of vesicles that were located deeper in the cytosol. Sequential compound exocytosis by PC12 cells was confirmed by electron microscopic investigation with photoconversion of diaminobenzidine by FM1-43 (a polar membrane tracer). Our data suggest that pre-stimulus docking of LVs to the plasma membrane does not necessarily hasten the fusion reaction, while docking and resulting stability of exocytic LVs facilitates sequential compound exocytosis, and thereby allowing mobilization of deep vesicles.  相似文献   
43.
Summary: Light‐induced reversible changes in elasticity of semi‐interpenetrating network (semi‐IPN) films bearing azobenzene moieties were achieved under both ultraviolet (UV) and visible light irradiation. The semi‐IPN film was prepared by a cationic copolymerization of azobenzene‐containing vinyl ethers in a linear polycarbonate (PC) film as a matrix. When the irradiation was switched on and off, the semi‐IPN film showed rapid reversible deformation with the same behavior occurring over a range of wavelengths, including both the UV and visible regions. The observed reversible deformation of the film was attributed to the decrease in the film's elasticity, which was assumed to be caused by the frequent transcis cycling isomerization of azobenzene moieties taking place during the UV and visible light irradiation. This cycling makes it difficult for the azobenzene groups to aggregate, thus hindering their ability to function as pseudo‐crosslinking points.

  相似文献   

44.
The present study tested whether a gene-transfer based upon the retrograde axonal transport of the lacZ adenovirus is effective in the spinal descending tracts of the adult mouse. A small volume of a replication-defective recombinant adenovirus encoding E. coli beta-galactosidase was injected into the upper lumbar cord, and, seven days later, the mice were transcardially perfused by a fixative solution. X-gal staining of coronal or sagittal sections of the spinal cord and the brain revealed that many sites of origin for rubrospinal, vestibulospinal, and reticulospinal tracts were retrogradely labeled, whereas few of the corticospinal tract neurons were retrogradely labeled. Ependymal cells surrounding the central canal of the spinal cord, which were located far from the injection site, showed a high expression of beta-galactosidase activity. Motoneurons around the injection site were strongly stained by X-gal staining, and their axons in the ventral root were anterogradely labeled. Afferent fibers in the dorsal root were labeled by the transganglionic transport of beta-galactosidase. To examine the efficacy of the uptake and retrograde transport of HRP and adenovirus, we injected a mixed solution of 10% HRP and recombinant adenovirus. The number of HRP-labeled corticospinal neurons overwhelmed the number of X-gal stained ones, while the numbers of HRP-labeled rubrospinal and subcoeruleus-spinal neurons were smaller in comparison with the numbers of beta-galactosidase-positive counterparts. The present study revealed that the origins for the spinal descending tracts except for corticospinal neurons could be efficiently gene-transferred by the retrograde infection of a recombinant adenovirus. Such a difference in efficacy of retrograde infection among the spinal descending tracts is practically important when an adenovirus-mediated gene transfer is designed to treat certain neurological diseases affecting the spinal descending tracts.  相似文献   
45.
Cigarette smoke condensate (CSC) was separated into severalfractions and each was tested for an inhibitory effect on theearly antigen (EA) of Epstein-Barr virus (EBV) which can beinduced by 12-0-tetradecanoylphorbol-13-acetate (TPA) in Rajicells. Two diastereoisomers of 2,7,11-cembratriene-4,6-diol(- and ß-CBT) were isolated from the neutral fractionsof CSC and these showed potent inhibitory effects on the inductionof EBV-EA by TPA. The doses of - and ß-CBT requiredfor 50% inhibition of EBV-EA induction by TPA were 7.7 and 6.7µg/ml, respectively, which are comparable with those ofretinoic acid, a potent inhibitor of induction of epideral ornithinedecarboxylase (ODC) activity and tumor promotion by TPA in mice.Application of - and ß-CBT to mouse skin prior totreatment with TPA inhibited TPA-induced ODC activity. The degreeof inhibition was dependent on the dose and application of 16.5µmol/mouse of - and ß-CBT resulted in a 50 and40% reduction, respectively, of the maximum of the ODC activityinduced as a result of treatment with TPA. In initiation-promotionexperiments, -CBT markedly inhibited the promoting effect ofTPA on skin tumor formation in mice which were initiated with7,12-dimethylbenz[a]anthracene, but ß-CBT was foundto be less effective. Application of 3.3 µmol of -CBT40 min prior to treatment with TPA (1 µg) resulted ina 53% reduction in the number of papillomas per mouse. Our presentdata suggest that EBV-EA inhibition assay using Raji cells iseffective for the first screening of inhibitors of tumor promotion,and provide evidence that CSC contains antitumor-promoting agentsin addition to carcinogenic and tumor-promoting agents alreadyreported.  相似文献   
46.
A huge rectosigmoidal cancer which extended into the urinary bladder in a 64-year-old man is herein described. The tumor occupied the pelvic and lower abdominal cavities, while the rectosigmoid was totally obstructed. No hepatic or pulmonary metastasis was evident. The ventral and flank sides of the peritoneum in the right lower abdomen, right common iliac vessels, bilateral ureters, terminal ileum, cecum, ascending colon, and urinary bladder were all directly invaded by the tumor, but the aorta, sacrum, and lower rectum were free of cancer. Consequently, an anterior pelvic exenteration was carried out along with an ileal conduit and a right hemicolectomy. Immediately after the exenteration, intra-pelvic hyperthermochemotherapy was performed using a 46–47°C perfusate containing 40 g/ml of mitomycin C (MMC) and 200 g/ml of cisplatin (CDDP), for 90 min, in an attempt to prevent any further local recurrence. A right hemicolectomy and a permanent colostomy were done simultaneously with the hyperthermia treatment. After an uneventful postoperative course, the patient was prescribed adjuvant chemotherapy, i.e., two administrations of 17 mg/m2 and 21 mg/m2 of MMC, and ten doses of 710 mg/m2 of 5-fluorouracil (5-FU) followed by five doses of 535 mg/m2 of 5-FU. At the time of this writing, the patient is still alive without recurrence at 21 months after surgery.  相似文献   
47.
The localization of Cu/Zn- and Mn-superoxide dismutase (SOD) in breast cancer tissue (12 papillotubular carcinomas, 21 solid-tubular carcinomas, 16 scirrhous carcinomas, 1 medullary carcinoma, 1 secreting carcinoma, 1 lobular carcinoma, 1 Paget's disease) was investigated via an immunohistochemical technique using antihuman Cu/Zn- and Mn-SOD antibodies in 10%formalin fixed-paraffin embedded thin sections. Both SODs stained strongly in the normal breast gland, but not clearly in many cancer tissues. Furthermore, Cu/Zn-SOD stained more strongly in well differentiated tubular carcinomas than in poorly differentiated tubular carcinomas. It tended to stain less in tumors which recurred or had a poor outcome, and in tumors with a diploid pattern on DNA flow cytometry. Mn-SOD staining was similar to that of Cu/Zn-SOD, but no significant differences among subgroups was found, since the incidence of positively staining tumors was too small in all groups. The intensity of SOD staining seems to change in relation to cell proliferation and differentiation in breast carcinoma, and may be a prognostic indicator, since SOD decreased in poorly differentiated carcinoma and in tumors which developed distant metastasis. Thus, the localization of SOD in breast cancer tissue can provide useful information for cancer treatment.  相似文献   
48.
It has been known that the serum concentration of antipsychotics is varied according to individual case. There are several factors that may affect the plasma levels of antipsychotics; e.g., antipsychotic dose, body weight, interaction with other drugs, enzyme activity in the human liver, age and smoking. The enzyme cytochrome P450 2D6 (CYP2D6) is an important factor affecting the plasma levels of antipsychotics, because CYP2D6 is involved in the metabolism of these drugs. In this paper, we review the effect of several factors on plasma haloperidol concentration.  相似文献   
49.
Objective: To evaluate the effect of prednisolone plus low-dose aspirin (PSL/LDA) in women with autoimmune conditions who were enrolled in an IVF-ET program.

Design: A retrospective clinical study.

Setting: In vitro fertilization unit, Niigata University Hospital, Niigata, Japan.

Patient(s): Three hundred seven women who underwent IVF-ET between January 1996 and December 1997.

Intervention(s): Prednisolone (10 mg/d) and aspirin (81 mg/d) were administered to the women with autoantibodies who chose to participate.

Main Outcome Measure(s): Pregnancy and implantation rates with IVF-ET.

Result(s): Women undergoing IVF who had positive antinuclear antibodies, with or without antiphospholipid antibodies, had significantly lower pregnancy and implantation rates than did women without autoantibodies (14.8% versus 21.7% and 6.8% versus 10.4%, respectively). The administration of PSL/LDA to women with antinuclear antibodies significantly improved the outcome of IVF-ET (40.6% pregnancy rate and 20.3% implantation rate).

Conclusion(s): A high proportion of women who are undergoing IVF-ET have autoantibodies, which are associated with poor IVF outcomes. The administration of PSL/LDA to these women may improve their implantation rate.  相似文献   

50.
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