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   8042篇
  免费   315篇
  国内免费   39篇
耳鼻咽喉   103篇
儿科学   106篇
妇产科学   118篇
基础医学   996篇
口腔科学   211篇
临床医学   457篇
内科学   1941篇
皮肤病学   74篇
神经病学   611篇
特种医学   252篇
外科学   1561篇
综合类   38篇
一般理论   1篇
预防医学   203篇
眼科学   51篇
药学   793篇
中国医学   13篇
肿瘤学   867篇
  2023年   27篇
  2022年   74篇
  2021年   131篇
  2020年   58篇
  2019年   98篇
  2018年   147篇
  2017年   96篇
  2016年   138篇
  2015年   153篇
  2014年   217篇
  2013年   271篇
  2012年   442篇
  2011年   468篇
  2010年   277篇
  2009年   251篇
  2008年   436篇
  2007年   462篇
  2006年   467篇
  2005年   525篇
  2004年   468篇
  2003年   484篇
  2002年   481篇
  2001年   104篇
  2000年   120篇
  1999年   132篇
  1998年   139篇
  1997年   116篇
  1996年   92篇
  1995年   127篇
  1994年   92篇
  1993年   89篇
  1992年   108篇
  1991年   102篇
  1990年   89篇
  1989年   91篇
  1988年   93篇
  1987年   92篇
  1986年   69篇
  1985年   79篇
  1984年   49篇
  1983年   51篇
  1982年   39篇
  1981年   46篇
  1980年   36篇
  1979年   32篇
  1978年   26篇
  1977年   28篇
  1976年   30篇
  1975年   28篇
  1974年   21篇
排序方式: 共有8396条查询结果,搜索用时 14 毫秒
71.
We examined the expression levels of microRNAs (miRNAs; miRs) in colorectal tumors (63 cancer specimens and 65 adenoma specimens) compared to adjacent non-tumorous tissues. Decreased expression of miR-143 and -145 was frequently observed in the adenoma and cancer samples. As the down-regulation of miR-143 and -145 was observed even in the early phase of adenoma formation, their decreased expression would appear to contribute mainly to the initiation of tumorigenesis. For clinical application, we added aromatic benzene-pyridine (BP-type) analogs to the 3'-overhang region of the RNA-strand and changed the sequences of the passenger strand in the miR-143 duplex (miR-143BPs), leading to greater activity and increased resistance to nuclease. The cell growth inhibitory effect of the chemically modified miR-143BPx in vitro was greater than that of the endogenous miR-143. The modified miR-143BPx showed a significant tumor-suppressive effect on xenografted tumors of human colorectal cancer DLD-1 cells. These findings suggest that miR-143 and -145 are important onco-related genes for the initiation of colorectal tumor development and that chemically modified miR-143BPx may be a candidate for an RNA medicine for the treatment of colorectal tumors.  相似文献   
72.
Phthalate esters and phosphate esters in samples of indoor air from 27 houses in the Tokyo Metropolitan area were quantified using gas chromatograph/mass spectrometer and gas chromatograph/flame photometric detector after adsorption on to charcoal and solvent extraction. The median concentrations of diethyl phthalate, dibutyl phthalate (DBP), butylbenzyl phthalate, dicyclohexyl phthalate and diethylhexyl phthalate were 0.10, 0.39, 0.01, 0.07 and 0.11 microg/m(3), respectively. The median concentrations of tributyl phosphate, tris(2-chloroethyl) phosphate, triphenyl phosphate and tris(2-butoxyethyl) phosphate were less than 0.001 microg/m(3). DBP was detected at the highest concentration (6.18 microg/m(3)) in a new residential housing. This research indicated that exposure to phthalate esters through inhalation of air from the indoor environment is as important as dietary intake of phthalate esters, and can contribute to daily intake to a much greater extent than has been assumed hitherto.  相似文献   
73.
This study concerns the immunohistochemical localization of S-100 alpha, S-100 beta, and whole brain S-100 (wbS-100) in testicular large-cell calcifying Sertoli cell tumor (LCCSCT). We examined 8 LCCSCTs (7 benign and 1 malignant), 6 Sertoli cell tumors not otherwise specified (SCTs-NOS), 6 Leydig cell tumors (LCTs), 5 ovarian Sertoli-Leydig cell tumors (SLCTs), and 7 gonadoblastomas (GBLs). The 8 LCCSCTs showed immunoreactivity for S-100 alpha, S-100 beta, and wbS-100. Five of the 6 LCTs and the Leydig cell components in the ovarian SLCTs stained positively for S-100 alpha and wbS-100 but were negative for S-100 beta. SCTs-NOS and the Sertoli cell components in the SLCTs occasionally showed focal and weak/moderate positivity for S-100 alpha, S-100 beta, and wbS-100. Sex cord cells of the GBLs were positive for S-100 beta and wbS-100 and negative for S-100 alpha. Germ cell elements of the GBLs were negative for S-100 alpha, S-100 beta, and wbS-100. In nonneoplastic testicular parenchyma adjacent to the above-mentioned tumors, there was S-100 alpha reactivity in Leydig cells, rete testis, and a few Sertoli cells. S-100 beta reactivity was seen in a few Sertoli cells, Schwann cells, and some endothelial cells. WbS-100 reactivity was present in Leydig cells, a few Sertoli cells, rete testis, Schwann cells, and some endothelial cells. The results indicate that S-100 alpha and S-100 beta can potentially be used as immunohistochemical markers for LCCSCT, especially when differentiating it from LCT, which may mimic LCCSCT on routine histopathology. Although the biological significance of both S-100 subunits expression in LCCSCT remains unknown, these notable calcium-binding proteins may be associated with the characteristic calcification in LCCSCT through regulation of calcium levels in the tumor cells.  相似文献   
74.
Synthesis and gas permeation measurements of several types of polymers from methylstyrene derivatives containing mono-and bis(trialkylsilyl) group(s) were carried out. Upon radical homo-and co-polymerization of silicon-containing monomers high-molecular-weight polymers were obtained. Results from gas permeation measurements showed that these types of silicon-containing polymers exhibit fairly high oxygen permselectivity (ratio of oxygen and nitrogen permeation coefficients P/P = 3,1 ? 4,6), keeping the oxygen permeation coefficients (P) in the range of between 1,4 · 10?9 and 4,5·10?9 cm3 (STP) · cm · cm?2 · s?1 · cmHg?1. From time lag measurements, it was found that permeation coefficients are dependent on the solubility of gases in the membranes rather than on diffusivity. Actually, the oxygen solubility coefficients increase with increasing silicon content in the polymers. Permselectivity of oxygen against nitrogen is governed by polymer constitution rather than by silicon content.  相似文献   
75.
BACKGROUND: The urinary leukotriene E4 (U-LTE4) concentration is significantly increased in patients with aspirin-intolerant asthma (AIA). However, the relationship between the clinicopathogenetic factors of asthma and the U-LTE4 concentration remains undetermined. OBJECTIVE: We sought to examine the clinical features of asthmatic patients with increased excretion levels of U-LTE4 (hyperleukotrienuria). METHODS: We measured the U-LTE4 concentrations in 137 asthmatic patients (including 64 patients with AIA) who were in clinically stable condition. A U-LTE4 concentration of 150 pg/mg creatinine or greater (mean U-LTE4 + 3 SDs of normal healthy control subjects) was indicative of hyperleukotrienuria. RESULTS: The basal concentration of U-LTE4 was significantly higher in the patients with AIA than in those with aspirin-tolerant asthma (ATA; median, 227.2 vs 90.3 pg/mg creatinine; P <.01). Compared with normal leukotrienuria in the patients with AIA, hyperleukotrienuria in the patients with AIA was associated with older age and decrease in pulmonary function. On the other hand, compared with normal leukotrienuria in the patients with ATA, hyperleukotrienuria in the patients with ATA was associated with severe asthma and chronic hyperplastic rhinosinusitis with nasal polyposis (CHRS/NP), which are well-known symptoms of the aspirin triad, as well as hypereosinophilia and anosmia. The patients with ATA with CHRS/NP excreted U-LTE4 at significantly high concentrations. There were significant decreases in the U-LTE4 concentrations before and after the sinus surgery in both the AIA and ATA groups (P <.05). CONCLUSION: Cysteinyl leukotrienes are not strictly associated with aspirin intolerance itself but rather with clinical features, such as CHRS/NP, that are similar to those seen in AIA. CHRS/NP might be involved in cysteinyl leukotriene overproduction in asthmatic patients.  相似文献   
76.
S-adenosylhomocysteine hydrolase is a prospective target for developing new anti-malarial drugs. Inhibition of the hydrolase results in an anti-cellular effect due to the suppression of adenosylmethionine-dependent transmethylations. Based on the crystal structure of Plasmodium falciparum S-adenosylhomocysteine hydrolase which we have determined recently, we performed mutational analyses on P. falciparum and human enzymes. Cys59 and Ala84 of the parasite enzyme, and the equivalent residues on the human enzyme, Thr60 and Gln85, were examined. Mutations of Cys59 and Thr60 caused dramatic impact on inhibition by 2-fluoronoraristeromycin without significant effect both on its kinetic parameters and on inhibition constant against noraristeromycin. In addition, the impact was independent from the electronegativity of the side chain of the substituting residue. These results showed that steric hindrance between a functional group at the 2-position of an adenine nucleoside inhibitor and Thr60 of the human enzyme, not an electrostatic effect, contributed to inhibitor selectivity.  相似文献   
77.
Squamous differentiation is the most common histological variation in urothelial carcinoma (UC). However, the clinical significance of squamous differentiation in upper urinary tract UC is unclear. To investigate the significance of squamous differentiation, hematoxylin and eosin stained slides from 140 patients with upper urinary tract UC who underwent nephroureterectomy were reviewed by a single pathologist and the presence of squamous differentiation was recorded. Squamous differentiation was observed in 23 out of 140 studied cases (16%). Squamous differentiation significantly correlated with several adverse prognostic factors including histological grade 3 tumors, presence of lymphovascular invasion, concomitant carcinoma in situ, advanced tumor stage, and occurrence of lymph node metastasis. The Kaplan-Meier and univariate Cox regression analyses revealed that the presence of squamous differentiation was significantly associated with shorter metastasis-free survival [log-rank P = 0.030; univariate hazard ratio (HR), 2.30; 95% confidence interval (CI), 1.06-4.99], cancer-specific survival (log-rank P = 0.0024; univariate HR 3.34; 95% CI, 1.47-7.85), and overall survival (log-rank P = 0.018; univariate HR 2.39; 95% CI, 1.13-5.06) after nephroureterectomy. However, in multivariate analyses, squamous differentiation was not significantly associated with patient outcomes. These findings suggest that squamous differentiation is associated with disease progression, but is not an independent predictor of a worse prognosis in patients with upper urinary tract UC.  相似文献   
78.

Study Objective

To evaluate a new magnetic resonance imaging (MRI) grading system for preoperative differentiation between benign and variant-type uterine leiomyomas including smooth muscle tumors of uncertain malignant potential (STUMPs).

Design

Retrospective analysis (Canadian Task Force classification III).

Setting

Teaching hospital (Teine Keijinkai Hospital).

Patients

Three-hundred thirteen patient medical records were retrospectively reviewed if treated for uterine myomas and diagnosed with variant type leiomyomas or STUMPs (n?=?27) or benign, typical leiomyomas (n?=?286) and treated between January 2012 and December 2014.

Intervention

Uterine myoma classifications using MRI findings according to a 5-grade system (grades I–V) based on 3 elements.

Measurements and Main Results

Uterine myoma MRI classifications were based on 3 elements: T2-weighted imaging (high or low), diffusion-weighted imaging (high or low), and apparent diffusion coefficient values (high or low; apparent diffusion coefficient?<?1.5?×?10?3 mm2/sec was considered low). Grades I to II were designated as typical or benign leiomyomas, grade III as degenerated leiomyomas, and grades IV to V as variant type leiomyomas or STUMPs. Accuracy levels were 98.9%, 100%, 94.3%, 58.8%, and 41.9% for grades I through V lesions, respectively. The grades were divided into 2 groups to discriminate benign leiomyomas and STUMPs (grades I–III were considered negative and grades IV–V positive). Grades IV to V scored 85.2% for sensitivity, 91.3% for specificity, 47.9% positive predictive value, 98.5% negative predictive value, a 9.745 positive likelihood ratio, and a .162 negative likelihood ratio.

Conclusion

This novel MRI grading system for uterine myomas may be beneficial in differentiating benign leiomyomas from STUMPs or variant type leiomyomas and could be a future effective presurgical assessment tool.  相似文献   
79.
80.
Cerebral autosomal dominant arteriopathy with subcortical infarcts and leucoencephalopathy (CADASIL) is one of the most common heritable causes of stroke and dementia in adults. The gene involved in the pathogenesis of CADASIL is Notch3; in which mutations affect the number of cysteine residues in its extracellular domain, causing its accumulation in small arteries and arterioles of the affected individuals. Besides the usual neurological and vascular findings that have been well-documented in CADASIL patients, this paper additionally reports multiple neoplastic lesions that were observed in an autopsy case of CADASIL patient; that could be related to Notch3 mutation. The patient was a 62 years old male, presented with a past history of neurological manifestations, including gait disturbance and frequent convulsive attacks. He was diagnosed as CADASIL syndrome with Notch3 Arg133Cys mutation. He eventually developed hemiplegia and died of systemic convulsions. Autopsy examination revealed-besides the vascular and neurological lesions characteristic of CADASIL- multiple neoplastic lesions in the body; carcinoid tumorlet and diffuse idiopathic pulmonary neuro-endocrine cell hyperplasia (DIPNECH) in the lungs, renal cell carcinoma (RCC), prostatic adenocarcinoma (ADC) and adenomatoid tumor of the epididymis. This report describes a spectrum of neoplastic lesions that were found in a case of CADASIL patient that could be related to Notch3 gene mutations.  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