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   7565篇
  免费   536篇
  国内免费   32篇
耳鼻咽喉   84篇
儿科学   256篇
妇产科学   102篇
基础医学   976篇
口腔科学   79篇
临床医学   868篇
内科学   1302篇
皮肤病学   56篇
神经病学   676篇
特种医学   368篇
外科学   1058篇
综合类   197篇
现状与发展   1篇
一般理论   3篇
预防医学   797篇
眼科学   164篇
药学   678篇
中国医学   32篇
肿瘤学   436篇
  2023年   38篇
  2022年   46篇
  2021年   114篇
  2020年   80篇
  2019年   107篇
  2018年   118篇
  2017年   103篇
  2016年   98篇
  2015年   126篇
  2014年   179篇
  2013年   250篇
  2012年   371篇
  2011年   388篇
  2010年   254篇
  2009年   224篇
  2008年   373篇
  2007年   419篇
  2006年   341篇
  2005年   330篇
  2004年   332篇
  2003年   295篇
  2002年   302篇
  2001年   259篇
  2000年   237篇
  1999年   208篇
  1998年   108篇
  1997年   82篇
  1996年   94篇
  1995年   108篇
  1994年   64篇
  1993年   74篇
  1992年   176篇
  1991年   158篇
  1990年   138篇
  1989年   115篇
  1988年   116篇
  1987年   113篇
  1986年   90篇
  1985年   123篇
  1984年   102篇
  1983年   80篇
  1982年   51篇
  1981年   54篇
  1980年   46篇
  1979年   75篇
  1978年   51篇
  1977年   43篇
  1974年   46篇
  1973年   32篇
  1972年   33篇
排序方式: 共有8133条查询结果,搜索用时 0 毫秒
71.
Technical developments in MR angiography   总被引:6,自引:0,他引:6  
CE MRA has evolved rapidly since the early studies by Prince et al [3]. Whereas many of the procedures in clinical use today rely heavily on the use of gadolinium contrast agents and standard. Fourier transform acquisition techniques, advances will have a significant impact on MRA by shortening the acquisition time, improving the reproducibility of the image-acquisition techniques, and improving spatial resolution or SNR. From a technical basis, shorter acquisition times associated with fast gradients are likely to improve spatial resolution and allow for acquisition of MR images over large FOVs. In addition, alternative k-space sampling techniques, such as parallel imaging and PR, are expected to further reduce acquisition time, while maintaining or improving spatial resolution. The approval and subsequent use of new contrast agents will also have a beneficial impact on the image quality of contrast-enhanced MRA applications. It is likely that these contrast agents will be coupled with advanced acquisition techniques to improve spatial resolution and technical success rates of MRA examinations.  相似文献   
72.
BACKGROUND: Murine hindlimb reperfusion injury (I/R), is initiated by activation of the classical pathway of complement. Complement receptor-2 knockout mice (Cr2-/-) are protected from I/R injury due to defective B-1 cells with a resulting deficient natural immunoglobulin M (IgM) repertoire. Cr2-/- and wild type (WT) mice were studied to isolate the antibody or antibodies responsible for initiation of I/R. METHODS: IgM-secreting B-1 cell clones were produced with hybridoma technology from WT cells. Of 21 clones tested in murine I/R models, only 1 clone, CM22, was found to restore injury in protected mice. Cr2-/- mice reconstituted with IgM from individual clones, WT serum, or saline were subjected to 2 hours hindlimb ischemia and 3 hours reperfusion and compared with WT. RESULTS: Muscle injury in Cr2-/- mice reconstituted with CM22 was similar to injury in WT mice reconstituted with saline and Cr2-/- mice reconstituted with WT serum. This injury was 137% greater (P < .05) than in both Cr2-/- mice reconstituted with saline and those reconstituted with a different IgM clone, CM31. IgM and C3 deposition was found only on injured muscle of WT mice or Cr2-/- mice reconstituted with CM22 or WT serum. CONCLUSION: A single clone of self-reactive IgM, CM22, can initiate complement-dependent I/R injury.  相似文献   
73.
Immunologic heterogeneity of diffuse large cell lymphoma   总被引:2,自引:0,他引:2  
The cellular lineage of 57 diffuse large-cell lymphomas (DLCLs) was determined using a panel of monoclonal antibodies directed against lineage-restricted and -associated T, B, and monocyte antigens. The majority (82%) were of B cell lineage as determined by the expression of sig and/or B1, with the remaining 16% being of T cell lineage and 2%, of monocyte-myeloid lineage. By the expression of other B cell- restricted and -associated antigens, two major and two minor subgroups could be identified. These subgroups expressed the following phenotypes: (1) B1+B4+sIG+B2- (51%); (2) B1+B4+sIg+B2+ (29%); (3) B1+B4+sIg-B2+ (10%); and (4) B1+B4-sIg+B2- (10)%. The morphology of transformed lymphocytes, the weak to absent expression of the early B cell antigens B2 and sIgD, and the absence of the late B cell differentiation antigens PCA-1 and PC-1 suggested that these tumors were the neoplastic counterparts of normal B cells at the mid-stages of differentiation. Further support for the notion that B-DLCLs correspond to transformed B lymphocytes was concluded from the observation that B cells could be identified in normal spleen that expressed the cell surface phenotype and morphological appearance of the majority of B- DLCLs.  相似文献   
74.
The genes for four components (C) of complement in the human major histocompatibility complex (HLA) have been aligned previously in a series of overlapping cosmid cloned inserts. Those inserts, which contained the two C4 genes C4A and C4B, hybridized with human adrenal mRNA, indicating that they contain a gene expressed in the adrenal. The mRNA fraction of 2.4 kilobases (kb) hybridizes with genomic DNA of 4.5 kb, which is duplicated and lies about 1.5 kb 3' of both the C4A and the C4B complement genes. Sequencing of a 430-base section and comparison with the published cDNA sequence of bovine cytochrome P-450 21-hydroxylase, peptide sequences of porcine 21-hydroxylase, and a cDNA sequence of a rat liver cytochrome P-450 identified the gene as coding for human steroid 21-hydroxylase [steroid,hydrogen-donor:oxygen oxidoreductase (21-hydroxylating), EC 1.14.99.10]. Mapping of the gene was helped by use of a synthetic oligonucleotide based on the bovine cDNA sequence.  相似文献   
75.

Purpose

Our objective was to compare open and endovascular aortic aneurysm repair with respect to postoperative delirium.

Methods

After Institutional Ethics Review Board approval, we conducted a retrospective review of all patients who underwent abdominal and thoraco-abdominal aortic aneurysm repair surgery at Toronto General Hospital during June 2006 to December 2007. Patients were classed into either the OPEN or the endovascular (EVAR) group based on the type of surgery and were assessed for the presence of delirium after surgery. The NEECHAM Confusion Scale and the validated chart review instrument were used for diagnosis of delirium. Patients with dementia and/or abnormal levels of consciousness preoperatively were excluded.

Results

There were 256 patients included in the study, 149 (58%) in the OPEN group and 107 (42%) in the EVAR group. Patients in the EVAR group were considerably older, 74 (10) yr vs 68 (9) yr, and they had shorter duration of surgery, 150 [119, 180] min vs 200 [165, 260] min, respectively, P?<?0.0001. Postoperative delirium was present in 43 (29%) patients in the OPEN group and 14 (13%) patients in the EVAR group (95% confidence interval [CI], 22 to 36 vs 95% CI, 7 to 19, respectively; P?=?0.003). Hospital length of stay was 8.3 [6.6, 13.4] days in the OPEN group and 4.5 [3.1, 6.4] days in the EVAR group, P?<?0.0001.

Conclusions

Perioperative management of patients undergoing endovascular aortic aneurysm repair was associated with lower rates of delirium after surgery than that of patients undergoing open aortic aneurysm repair.  相似文献   
76.
Carroll  R; Gombergh  R 《Radiology》1987,163(3):822-823
Ultrasound scanning of the pelvis with an empty bladder permits a true frontal view of the uterus to be easily obtained. This view is comparable to the en face view seen at hysterography performed with contrast material. Good definition both of the endometrium and the uterine wall makes this the optimal method for the evaluation of an intrauterine contraceptive device.  相似文献   
77.
Bello L  Lucini V  Giussani C  Carrabba G  Pluderi M  Scaglione F  Tomei G  Villani R  Black PM  Bikfalvi A  Carroll RS 《Neurosurgery》2003,52(1):177-85; discussion 185-6
OBJECTIVE: The biological features of malignant gliomas include high cell proliferation, extensive local infiltration of tumor cells into normal brain, and marked neovascularization. alphavbeta3 integrin is highly expressed in malignant gliomas and plays a role in glioma growth. This article investigates the in vitro and in vivo effects of a synthetic alphavbeta3 integrin inhibitor called IS20I on human malignant gliomas. METHODS: The in vitro effects of IS20I were studied by performing adhesion assays, competition studies, semi-in vivo angiogenic assays, and migration and proliferation assays. For the in vivo experiments, IS20I was administered systemically in nude mouse intracranial and subcutaneous malignant glioma models. RESULTS: IS20I reacted selectively to alphavbeta3 integrin in glioma cells and tissues. In vitro, IS20I strongly inhibited angiogenesis and simultaneously exhibited potent antimitotic and antimigratory effects on numerous tumor and endothelial cell lines. In addition, at high concentrations, IS20I induced endothelial and tumor cell apoptosis. In vivo, when IS20I was administered intraperitoneally in subcutaneous and intracranial nude mouse glioma models, it potently reduced malignant glioma growth. Inhibition levels of 76 and 82% were observed at concentrations of 1 and 5 mg/kg, respectively, in the U87 intracranial model. The suppression of tumor growth is associated with a decrease in tumor vascularity, an increase in apoptosis, and a decrease in tumor cell proliferation. CONCLUSION: This work expands the understanding of the effects of anti-alphavbeta3 integrin inhibitors on malignant gliomas. In addition to direct proapoptotic and antiangiogenic effects, IS20I inhibits tumor and endothelial cell proliferation and migration, resulting in a potent inhibition of glioma growth in vivo.  相似文献   
78.
79.
To define the optimal methods of diagnosis and repair of ureteral and renal pelvic injuries, we reviewed the records of 18 patients with 19 collecting system injuries (16 penetrating, three blunt). Hematuria was absent in five of 16 patients. Intravenous urography was diagnostic of ureteral injury in three and normal or nondiagnostic in eight. Retrograde pyelography was performed in only one patient and was diagnostic of bilateral ureteral injury. Treatment consisted of primary repair (minimal or no debridement and closure) in 11 injuries, ureteroureterostomy (debridement and reanastomosis) in six, ureteroneocystostomy in one, and transureteroureterostomy in one. Ureteral stents were placed in 12 injuries, nephrostomy catheter in one, and both in two. Four patients had no form of diversion. Followup was available for 14 patients; serum creatinine values were normal in each. Results of imaging studies in 13 were normal in 11; one showed mild caliectasis and one a resolving urinoma. Both intravenous urography and initial urinalysis may be unreliable indicators of ureteral and renal pelvic injury, and high suspicion mandates exploration. Usually the urinary tract can be satisfactorily reconstructed. Satisfactory urinary diversion can be achieved in most cases with an internal ureteral stent.  相似文献   
80.
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