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   7661篇
  免费   325篇
  国内免费   27篇
耳鼻咽喉   34篇
儿科学   121篇
妇产科学   112篇
基础医学   881篇
口腔科学   100篇
临床医学   481篇
内科学   2022篇
皮肤病学   221篇
神经病学   521篇
特种医学   318篇
外国民族医学   2篇
外科学   1479篇
综合类   29篇
一般理论   1篇
预防医学   140篇
眼科学   56篇
药学   391篇
中国医学   20篇
肿瘤学   1084篇
  2023年   63篇
  2022年   96篇
  2021年   143篇
  2020年   95篇
  2019年   112篇
  2018年   129篇
  2017年   106篇
  2016年   145篇
  2015年   143篇
  2014年   195篇
  2013年   250篇
  2012年   390篇
  2011年   523篇
  2010年   264篇
  2009年   220篇
  2008年   446篇
  2007年   482篇
  2006年   411篇
  2005年   476篇
  2004年   476篇
  2003年   433篇
  2002年   393篇
  2001年   111篇
  2000年   129篇
  1999年   140篇
  1998年   110篇
  1997年   102篇
  1996年   116篇
  1995年   91篇
  1994年   83篇
  1993年   56篇
  1992年   98篇
  1991年   91篇
  1990年   78篇
  1989年   56篇
  1988年   87篇
  1987年   57篇
  1986年   44篇
  1985年   42篇
  1984年   42篇
  1981年   25篇
  1980年   36篇
  1979年   49篇
  1978年   32篇
  1977年   36篇
  1975年   33篇
  1974年   26篇
  1968年   27篇
  1967年   28篇
  1966年   26篇
排序方式: 共有8013条查询结果,搜索用时 15 毫秒
81.
Twin and family studies had shown that genetic factors are important determinants of bone mass. Multiple genes might be involved. One candidate gene, the reversion-induced LIM gene (RIL), is a PDZ and LIM-domain-containing protein and has been localized within the cytokine cluster of chromosome 5 (5q31.1). In a genetic study of 370 adult Japanese women, we investigated the correlation between radial bone mineral density (BMD) and a genetic variation (−3333T→C) of the 5'-flanking region of RIL gene. A significant association was identified between the RIL variation −3333T→C and radial BMD (r=0.15, P=0.003). The variation of the RIL locus may be an important determinant of osteoporosis.  相似文献   
82.
Our research group aims to develop an osteochondral composite using type II collagen gel with hydroxyapatite (HAp) deposited on one side. Soaking gels in Ca2+ and phosphate solution is indispensable to HAp deposition, so relationships between cell behavior and Ca2+ concentration were examined in two- and three-dimensional cultures. The present results indicate that 2-4 mM Ca2+ is suitable for proliferation and survival of osteoblasts, whereas slightly higher concentrations (6-8 mM) favor osteoblast differentiation and matrix mineralization in both 2- and 3-dimensional cultures. Higher concentrations (>10 mM) are cytotoxic. Purely from the perspective of calcium deposition, higher concentrations lead to increased accumulation of Ca2+. Culturing cells in phosphate-containing gel in media with Ca2+ also leads to time-dependent formation of HAp in the gel. Considering the viability of embedded cells, culturing scaffolds in media with Ca2+ concentrations around 5mM is useful for both HAp deposition and osteoblast behavior.  相似文献   
83.
Responses of saccade-depressed (SD) and saccade-excited (SE) cells in the striate cortex to eye movements of alert cats under presentation of a visual pattern were studied under reinforcement of the eye movements with rewards of water. These responses were compared to those on passive displacement of the visual pattern reproducing the movements of the retinal image occurring during eye movements while eye movements were suppressed by withdrawal of reinforcement. Passive displacement of the visual pattern produced in the SD cells depression closely resembled the depression occurring during eye movements under presentation of the visual pattern, in time course as well as in amplitude. Both the saccade depression and the depression due to passive movement of the visual pattern were nonselective to the direction of eye movements. Saccade excitation of the SE cells frequently contained two components occurring at 20 and 80 ms after the onsets of eye movements. Passive displacement of the visual pattern produced in the SE cells excitation comparable with the early component of the saccade excitation. These findings suggest that saccade depression in the SD cells and the early component of the saccade excitation in the SE cells are related to retinal reafference of eye movement. During presentation of visual patterns, saccade excitation in the SE cells was closely related to parameters of eye movements, such as direction, amplitude, duration, and velocity. The correlations were completely lost or strongly reduced in darkness. Lines of evidence were provided that the saccade excitation of the SE cells in darkness or the later component of the saccade excitation under presentation of a visual pattern represents efference copy signals of eye movement transferred to the striate cortex through the Clare-Bishop (CB) cortex. Excitation comparable with saccade excitation in darkness occurred in synchrony with activities of the oculomotor nuclei even after retrobulbar paralysis of eye movement, indicating that the excitation is related to efference copy signals rather than proprioceptive reafference of eye movement.(ABSTRACT TRUNCATED AT 400 WORDS)  相似文献   
84.
Clinical, light- and electron microscopic, and immunohistochemical findings of a 44-year-old woman with progressive multifocal leukoencephalopathy were presented. Autopsy revealed a wide distribution of the demyelinating lesion in the cerebrum, cerebellum, brain stem and spinal cord, and intranuclear inclusion bodies and papova-like virions in transmission electron microscopy in the nuclei of oligodendrocytes. SV40 antigen was immunohistochemically detected in these inclusion bodies. The widespread extension of the lesions seemed to correlate with the duration of the patient's illness. The prolongation of the clinical course in this case may be dependent upon the lack of serious underlying diseases except for a small nodule of thyroid carcinoma, SV40 infection rather than JC virus infection and/or improved care of that kind of patient.  相似文献   
85.
Well-differentiated colorectal adenocarcinomas are subclassified into carcinoma with high-grade atypia (CAH) and carcinoma with low-grade atypia (CAL) based on their cellular atypia. It is proposed that CAH and CAL are different in histologic prognostic factors and that the former should be regarded as carcinoma with high-grade malignancy and the latter as low-grade malignancy. In this study, the differences in cell-proliferative activity between CAH and CAL were examined using a monoclonal antibody to the proliferating cell nuclear antigen (PCNA). The PCNA index and mitotic index of 27 early colorectal carcinomas (9 CAL, 5 CAH, and 13 carcinomas with mixed low- and highgrade atypia) was evaluated in relation to their depth of invasion. In intra-mucosal lesions, both indices were higher in CAH (78%, 0.89%) than in CAL (68%, 0.47%; P <0.01). In lesions invading into the submucosa, the PCNA and mitotic indices were also higher in CAH (7596, 0.65%) than in CAL (35%, 0.19%; P <0.01). A significant correlation was observed between the PCNA index and the mitotic index in the mucosal lesions (P<0.05). These results indicate that CAH has a higher proliferative activity than CAL, and support the current authors' proposal that CAH is a high-grade malignancy and CAL a low-grade malignancy.  相似文献   
86.
The correlation of p53 protein overexpression and the K-ras codon 12 mutatlon wlth histologlc type, grade of cytologic atypla, depth of lnvasion and other histologlc prognostic factors was studied In paraffin sectlons from 43 ductectatic-and 70 solid-type pancreatic ductal carcinomas. Overexpression of p53 was found in 23.3% (10143) of ductectatic carcinomas (17.2% of intraductal and 35.7% of lnvaslve carclnomas) and in 61.4% (43/70) of solid carcinomas. In ductectatic cancers, p53 overexpression was detected In 14.8% (4/27) of carcinomas wlth lowgrade atypla (CAL), 50.0% (5110) of carcinomas wlth high-grade atypla (CAH) and in 16.7% (In) of mixed low- and hlgh-grade cancers. In the last group, expression was restricted to an area of CAH. In solld cancers, p53 overexpression did not dlffer by histologic type or grade. Overexpresslon of p53 and K-ras mutatlons did not correlate with histologlc prognostic factors (lymphatic, venous and perineural Invasion, and lymph node metastasls) in ductectatlc and solld cancers or depth of invasion of solld carclnomas. Our data suggest that p53 alteratlon occurs at an early intraductal stage of solld carcinoma, irrespectlve of cellular atypla, but Is low in ductectatic CAL and becomes hlgher In ductectatlc CAH. K-ras mutatlon, present In a high percentage of tumors of all groups and not correlating with the factors above, showed no changes In frequency with tumor progression.  相似文献   
87.
OBJECTIVES: The purpose of the present study was to compare the effect of vitamin K(2) on cortical and cancellous bones in orchidectomized young rats. METHODS: Forty male Sprague-Dawley rats, 6 weeks of age, were randomized by stratified weight method into four groups with 10 rats in each group: baseline controls (BLC), age-matched controls (AMC), orchidectomy (ORX), and ORX+vitamin K(2) administration (K). Vitamin K(2) (menatetrenone) was administered subcutaneously twice a week at dose of 30 mg/kg each. The experimental period was 8 weeks, and cortical and cancellous bone histomorphometry was performed on the tibial shaft and the proximal tibia, respectively. RESULTS: Cortical area (Ct Ar) and cancellous bone volume (BV/TV) were significantly greater in the AMC group than in the BLC group. Ct Ar was significantly lower in the ORX group than in the AMC group, and cancellous BV/TV was also significantly lower in the ORX group than in the AMC group as a result of significantly increased eroded surface (ES/BS). Although Ct Ar in the ORX+K group did not differ significantly from that in the ORX group, cancellous BV/TV was significantly greater in the ORX+K group than in the ORX group, but still significantly lower than in the AMC group. This protective effect of vitamin K(2) on cancellous bone was attributable to normalizing increased ES/BS. CONCLUSIONS: Vitamin K(2) appears to act more strongly on cancellous bone than on cortical bone in ORX young rats. High dose vitamin K(2) could partially prevent the reduction of cancellous bone gain by normalizing raised bone resorption in ORX young rats.  相似文献   
88.
Little information is available on the clinical characteristics of infectious complications that occur in the early period after reduced-intensity stem cell transplantation (RIST). We retrospectively investigated the clinical features of neutropenic fever and infectious episodes within 30 days after RIST in 76 patients who had received fluoroquinolones as part of their antibacterial prophylaxis. Preparative regimens included cladribine 0.66 mg/kg or fludarabine 180 mg/m2 plus busulfan 8 mg/kg. All but 1 patient survived 30 days after transplantation, and 75 patients (99%) became neutropenic within a median duration of 9 days. Neutropenic fever was observed in 29 patients (38%), and bacterial infection was confirmed in 15 (20%) of these, including bacteremia (n = 13), bacteremia plus pneumonia (n = 1), and urinary tract infection (n = 1). The causative organisms were gram-positive (n = 9) and gram-negative organisms (n = 7), with a mortality rate of 6%. Neither viral nor fungal infection was documented. Multivariate analysis showed that the presence of neutropenia at the initiation of preparative regimens was an independent risk factor for subsequent documented bacterial infections (P =.026; 95% confidence interval, 1.25-35.1). We conclude that neutropenic fever and bacteremia remain common complications in RIST.  相似文献   
89.
The α subunit of a GTP-blndlng protein, Go, was investigated in pulmonary neuroendocrine neoplasms and fetal tissues of the lung by an immunohistochemlcal method. Positive immunostaining for the α subunit of Go (Goα) was found predominantly on the cell membrane and found occasionally in the cytoplasm. Typical carcinoids were all positively stained (9/9), and small cell carcinoma showed weaker and less frequent staining (5 positive cases in 10). Atypical carcinoids were variously stained (3/4). The tendency for obvious neuroendocrine differentiation to be immunohistochemically determined in typical carcinoids and not in small cell carcinoma is also true of staining for neuron specific enolase (NSE), chromogranin A (CG-A) and synaptophysin. In the lung, Goα-immunostaining was positive not only in nerve tissues but also in the airway epithelium. In the fetal lung, serial sections immunostained for NSE, CG-A and Goα confirmed that Goα-immunoreactive cells belong to the neuroendocrine cell population. The biological significance of Goα is unclear in normal and neoplastic lung tissues, but Goα is a useful marker of neuroendocrine cells and neoplasms of the lung.  相似文献   
90.
We generated transgenic mice expressing osteopontin (OPN) under the control of the alpha(1)-antitrypsin promoter. These mice (OPN-T mice) expressed OPN mRNA in liver and kidney, and released a large amount of plasma OPN, which increased after stimulation with turpentine oil. Before sensitization, the number of CD4+ T cells in lymph nodes was significantly higher in OPN-T than nontransgenic mice, and that in spleen was slightly higher, whereas that of CD8+ T cells was no different between OPN-T and nontransgenic mice. After sensitization, the CD4+ T cell numbers in spleen increased significantly, while there were almost no changes in the CD8+ T cells in lymph nodes and spleen. The intensity of contact hypersensitivity responses to 2,4-dinitrofluorobenzene (DNFB) was obviously enhanced in OPN-T mice. In the delayed-type hypersensitivity (DTH) model elicited by DNFB, the number of CD8+ T cells among DNFB-2,4,6-trinitrobenzenesulfonic acid (TNBS)-peritoneal exudate cells was significantly higher in OPN-T than nontransgenic mice, while there was almost no difference in that of CD4+ T cells. Adoptive transfer experiments revealed that the enhanced reactivity is carried by CD4+ and CD8+ T cells, respectively, although the ability of transferring DTH was significantly lower in CD8+ than in CD4+ T cells. The enhancement of CD8+ T cell migration was observed in OPN-T mice. These results suggest that OPN induces a proliferation of effector CD4+ and CD8+ cells in cell-mediated reactions and plays a role in the migration of CD8+ T cells.  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