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   9682篇
  免费   967篇
  国内免费   334篇
耳鼻咽喉   52篇
儿科学   114篇
妇产科学   83篇
基础医学   1600篇
口腔科学   168篇
临床医学   1107篇
内科学   1264篇
皮肤病学   145篇
神经病学   536篇
特种医学   568篇
外国民族医学   2篇
外科学   670篇
综合类   1507篇
预防医学   983篇
眼科学   114篇
药学   914篇
  4篇
中国医学   504篇
肿瘤学   648篇
  2024年   28篇
  2023年   196篇
  2022年   384篇
  2021年   530篇
  2020年   478篇
  2019年   391篇
  2018年   335篇
  2017年   346篇
  2016年   355篇
  2015年   373篇
  2014年   584篇
  2013年   590篇
  2012年   500篇
  2011年   555篇
  2010年   466篇
  2009年   455篇
  2008年   445篇
  2007年   460篇
  2006年   435篇
  2005年   386篇
  2004年   361篇
  2003年   313篇
  2002年   275篇
  2001年   239篇
  2000年   166篇
  1999年   175篇
  1998年   121篇
  1997年   126篇
  1996年   100篇
  1995年   102篇
  1994年   88篇
  1993年   66篇
  1992年   60篇
  1991年   49篇
  1990年   53篇
  1989年   46篇
  1988年   47篇
  1987年   50篇
  1986年   40篇
  1985年   51篇
  1984年   32篇
  1983年   22篇
  1982年   21篇
  1981年   20篇
  1980年   20篇
  1979年   8篇
  1978年   9篇
  1977年   6篇
  1976年   7篇
  1974年   5篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
目的筛选与涎腺腺样囊性癌转移相关的候选基因,并对其中的候选基因进行初步的验证。方法用限制片段差异显示PCR技术(restriction fragments differential display PCR, RFDD-PCR)建立涎腺腺样囊性癌高、低转移细胞株(ACC-M、ACC-2)的表达谱。对两个表达谱的片段进行比较,通过生物信息学的分析,初步筛选出候选基因。用半定量逆转录PCR技术对筛选出的基因进行初步验证。结果RFDD-PCR方法共获得5420个基因片段,其中包含12个基质金属蛋白酶(matrix metalloproteinase,MMP)基因。半定量逆转录PCR方法发现MMP2、MMP7、MMP9、MMP14、MMP15、MMP24在ACC-M和ACC-2中的表达存在明显差异。结论构建了ACC-M和ACC-2细胞株的表达谱,为寻找目的基因奠定了基础。发现MMP2、MMP7、MMP9和MMP15与涎腺腺样囊性癌的发生、发展、转移有关,不同肿瘤细胞的转移能力可能与不同的MMPs家族基因相关。  相似文献   
72.
Unsharp masking is a widely used image-enhancement method in medical imaging. Hardware-based solutions can be developed to support high computational demand for unsharp masking, but they suffer from limited flexibility. Software solutions can easily incorporate new features and modify key parameters, such as filtering kernel size, but they have not been able to meet the fast computing requirement. Modern programmable mediaprocessors can meet both fast computing and flexibility requirements, which will benefit medical image computing. In this article, we present fast adaptive unsharp masking on two leading mediaprocessors or high-end digital signal processors, Hitachi/Equator Technologies MAP-CA and Texas Instruments TMS320C64x. For a 2k × 2k 16-bit image, our adaptive unsharp masking with a 201 × 201 boxcar kernel takes 225 ms on a 300-MHz MAP-CA and 74 ms on a 600-MHz TMS320C64x. This fast unsharp masking enables technologists and/or physicians to adjust parameters interactively for optimal quality assurance and image viewing.  相似文献   
73.
糖尿病大鼠视网膜基因表达谱差异的初步分析   总被引:5,自引:1,他引:5  
目的 建立大鼠正常视网膜和糖尿病8周视网膜基因表达谱,比较两者差异,初步分析糖尿病视网膜病变的相关基因。方法 通过限制片段差异显示 PCR( restriction fragments differential display-PCR,RFDD-PCR)获得正常大鼠视网膜及8周糖尿病大鼠视网膜组织转录组片段。应用Fraent Analysis等软件,对差异片段进行生物信息学分析,初步确定糖尿病视网膜病变相关基因/表达序列标签( expression sequence tag, Ksr)。结果 获得有意义的片段共3639个,有差异的片段840个,占表达数的23.08%。其中包括5个视觉传导相关基因,13个兴奋性神经递质受体基因和3个抑制性神经递质受体基因。糖尿病8周大鼠视网膜Rhodopsin kinase,β-arrestin,Phosducin, rod photoreceptor cGMP-gated channel 和 Rpe65的表达下调,离子型谷氨酸受体iGluR1-4下调,代谢性谷氨酸受体及γ-氨基丁酸受体各亚型则普遍上调,而甘氨酸受体表达无变化。结论 糖尿病8周大鼠神经视网膜已受到累及,其基因表达模式的改变,可能与糖尿病早期视功能损害有关。  相似文献   
74.
The proximal and distal growth plates of the principal long bones do not contribute equally to longitudinal growth. Most forelimb elongation occurs at the shoulder and wrist, while most hindlimb growth occurs at the knee. This study examined whether insulin‐like growth factor‐I (IGF‐I), a potent growth regulator, could underlie this variation via differential receptor expression. The spatiotemporal distribution of the IGF‐I receptor (IGF‐IR) was mapped in hindlimb growth plates (overall and within regional zones) from immature mice using immunohistochemistry. Growth activity was assessed by size/morphology of the growth plate and proliferating cell nuclear antigen (PCNA) expression. Both IGF‐IR and PCNA staining declined considerably with age in the proximal femur and distal tibia (hip and ankle), but expression remained high in the more active distal femur and proximal tibia (knee) throughout growth. Growth plate size decreased with age in all sites, but the absolute and relative decline in IGF‐IR in the hips and ankles of older mice indicated a site‐specific loss of IGF‐I sensitivity in these less active regions. These results suggest that regulation of the IGF‐IR may at least partially mediate differential long bone growth, thereby providing a local mechanism for altering skeletal proportions absent modification of systemic hormone levels. Anat Rec, 2007. © 2007 Wiley‐Liss, Inc.  相似文献   
75.

Introduction

Total Lymphocyte Count (TLC) has been found to be an inexpensive and useful marker for staging disease, predicting progression to AIDS and death and monitoring response to ART. However, the correlation between TLC and CD4 has not been consistent. Access to HAART is expanding in Kampala, Uganda, yet there are no published data evaluating the utility of TLC as inexpensive surrogate marker of CD4 cell count to help guide therapeutic decisions.

Objective

To evaluate clinical illnesses and total lymphocyte count (TLC) as surrogate markers of the CD4 cell count in HIV infected persons being considered for ART.

Methods

A total of 131 patients were enrolled and evaluated by clinical assessment, TLC and CD4 count. Clinical illnesses and TLC dichotomized at various cut-point values were used to determine the sensitivity, specificity, and positive and negative predictive values (PPV and NPV) for the diagnosis of CD4 count <200 cells/mm3 among 100 participants fulfilling criteria for WHO clinical stage 2 and 3.

Results

A strong correlation was observed between TLC and CD4 (r = 0.73, p<0.0001). For all clinical syndromes, except pulmonary tuberculosis, the positive predictive values (PPV) for a CD4 count <200 cells/mm3 were high (>80%) but the negative predictive values (NPV) were low. Using the WHO recommended TLC cut-off of 1200 cells/mm3 to diagnose a CD4 less than 200 cells/mm3, the PPV was 100%, and the NPV was 32%.

Conclusion

Our data showed a good correlation between TLC and CD4 cell count. However, the WHO recommended TLC cutoff of 1200 did not identify the majority of WHO stage 2 and 3 patients with CD4 counts less than 200 cells/mm3. A more rational use of TLC counts is to treat all patients with WHO stage 2 and 3 who have a TLC <1200 and to limit CD4 counts to patients who are symptomatic but have TLC of >1200.  相似文献   
76.
As the soft copy reading and computer assisted diagnosis (CAD) in mammography become more and more important, the standardization of digital images becomes paramount. Telemammography and telemedicine requires the standardization for image characteristics, such as image resolution, bit-depth and intensity response. Soft copy reading and CAD in mammography are both dependent on the characteristics of the source of the digital data, either direct digital mammography or digitized screen-film mammography. An algorithm developed on images from one database may not perform well as on images from another database (with a different digitization). In this paper, we describe two methods based on a genetic algorithm and a nonlinear algorithm for standardization of digitized and digital mammography. The proposed standardization techniques are based on geometric and intensity transformations that are discovered using a set of calibration images. A set of transformation algorithm is used to search for the best standardization.  相似文献   
77.
目的:采用影像遗传学研究方法探索精神分裂症的影像遗传学特征。方法:在传统稀疏回归模型的基础上,改进 了其在不同范数条件下进行变量选择的能力,形成一种基于稀疏表示变量选择算法,并将该算法应用于208 个受试者的 41 236个功能磁共振成像数据和722 177个单核苷酸多态性数据的综合分析。通过对两类数据施加不同的权重因子,并 使用不同的Lp (p=0、0.5、1)范数分别对模型进行求解,筛选出两类数据在不同条件下的显著特征。结果:基因DAOA和 HTR2A在3种范数下均被筛选出。此外,在影像学数据方面,发现中央前回、枕上回、顶下缘角回、角回、内侧和旁扣带脑 回、后扣带回脑区与精神分裂症相关,此发现与先前精神分裂症的临床医学研究结果一致。结论:基于稀疏表示变量选择 方法应用于影像遗传学数据分析是一个有效可行的途径,为今后精神分裂症的影像遗传学研究提供了一种新的研究 思路。  相似文献   
78.
We retrospectively reviewed 74 fine-needle aspiration (FNA) cases of presumptive non-Hodgkin lymphoma (NHL). All the cases had cytology and core-needle biopsy and 53 cases had concurrent flow cytometric analysis. FNA (cytology and flow cytometry) and core-needle biopsy were evaluated independently. FNA was diagnostic of diffuse large B-cell lymphoma (DLBL) in 25% (13/53) of cases and small B-cell NHL in 15% (8/53) of cases, whereas core-needle biopsy was diagnostic of DLBL in 37% (27/74) of cases and small B-cell NHL in 8% (6/74) of cases. Subclassification of small B-cell NHL was reached in 3/6 cases by core-needle biopsy. Insufficient cases were observed in both FNA (47%; 25/53) and core-needle biopsy (28%; 21/74) groups. With the combination of FNA and core-needle biopsy, diagnostic cases of DLBL increased to 43% (32/74) and insufficient samples were reduced to 16% (12/74). There was no clear advantage in the diagnosis and classification of small B-cell NHL by adding core-needle biopsy to FNA (14%; 10/74). We conclude that core-needle biopsy is a useful adjunct to FNA in the diagnosis of DLBL and shall be encouraged. In small B-cell NHL, core-needle biopsy does not add to the diagnostic ability of FNA. Cases insufficient for diagnosis may be seen in both core-needle biopsy and FNA. A combined approach reduces the number of insufficient cases and is recommended in routine FNA practice.  相似文献   
79.
Dai L  Lü XH  Li ZH  Li R  Liu H  Liu YL  Hui YZ 《中华病理学杂志》2004,33(2):140-142
目的 探讨肾上皮性肿瘤的诊断及鉴别诊断。方法 对91例具有较完整病理资料的肾上皮性肿瘤进行了常规组织学观察,Mowy胶状铁染色及CD10、细胞角蛋白(CK)7、波形蛋白免疫组织化学染色。结果 91例肾上皮性肿瘤中肾透明细胞癌78例,占86%;肾乳头状癌8例,占9%;肾嫌色细胞癌4例,占4%;肾嗜酸细胞腺瘤1例,占1%。78例肾透明细胞癌中CD10、波形蛋白阳性分别为63例(81%)和69例(88%),主要表现为细胞膜阳性。74/78肾透明细胞癌CK7呈阴性,17/17 Mowy胶状铁染色阴性或呈灶状粗颗粒。肾嫌色细胞癌4例,CK7均呈胞膜阳性;Mowy胶状铁染色表现为胞质内蓝色细网状;4例CD10肿瘤细胞膜均阴性,波形蛋白阴性。肾嗜酸细胞腺癌1例CD10,CK7,波形蛋白,Mowy胶状铁染色均为阴性或不特异。结论 在常规诊断肾上皮性肿瘤有困难时免疫组织化学CD10,CK7,波形蛋白染色以及Mowy胶状铁染色对鉴别诊断有帮助。  相似文献   
80.
A new deconvolution algorithm (DCON) suitable for pharmacokinetic applications is presented. It requires that both the impulse and input responses, typically systemic drug levels, be well described by polyexponential equations. DCON has a wider range of applications than an earlier method (DECONV) from which it is derived. A FORTRAN program is provided, making implementation of the technique a simple matter. DCON is demonstrated to evaluate the GI bioavailability, defined as the rate and the extent of gastrointestinal drug release, of various ibuprofen dosage forms. The GI drug release kinetics exemplifies a pharmacokinetic system which cannot be evaluated using the previous deconvolution algorithm (DECONV) because of an initial zero drug level response. This limitation is not found in DCON. It is also demonstrated how the mean in vivo dissolution time MDT can be evaluated by deconvolution.  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