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   8543篇
  免费   438篇
  国内免费   57篇
耳鼻咽喉   64篇
儿科学   187篇
妇产科学   64篇
基础医学   1139篇
口腔科学   181篇
临床医学   508篇
内科学   2439篇
皮肤病学   112篇
神经病学   689篇
特种医学   304篇
外科学   1548篇
综合类   32篇
预防医学   218篇
眼科学   200篇
药学   506篇
中国医学   26篇
肿瘤学   821篇
  2023年   37篇
  2022年   87篇
  2021年   128篇
  2020年   74篇
  2019年   112篇
  2018年   122篇
  2017年   111篇
  2016年   155篇
  2015年   180篇
  2014年   190篇
  2013年   223篇
  2012年   416篇
  2011年   467篇
  2010年   231篇
  2009年   250篇
  2008年   408篇
  2007年   515篇
  2006年   458篇
  2005年   525篇
  2004年   514篇
  2003年   540篇
  2002年   521篇
  2001年   171篇
  2000年   165篇
  1999年   192篇
  1998年   177篇
  1997年   138篇
  1996年   148篇
  1995年   124篇
  1994年   99篇
  1993年   87篇
  1992年   135篇
  1991年   133篇
  1990年   120篇
  1989年   99篇
  1988年   96篇
  1987年   73篇
  1986年   83篇
  1985年   77篇
  1984年   76篇
  1983年   59篇
  1982年   45篇
  1981年   66篇
  1980年   40篇
  1979年   52篇
  1978年   36篇
  1977年   38篇
  1976年   24篇
  1975年   27篇
  1974年   31篇
排序方式: 共有9038条查询结果,搜索用时 0 毫秒
1.
In Cryptococcus neoformans the DNA content of cells having tiny buds varied rather widely, depending on growth phases and strains used. Typically, buds of C. neoformans emerged soon after initiation of DNA synthesis in the early exponential phase. However, bud emergence was delayed to G2 during transition to the stationary phase, and in the early stationary phase budding scarcely occurred, although roughly half of the cells completed DNA synthesis. The timing of budding in C. neoformans was shifted to later cell cycle points with progression of the growth phase of the culture. Similarly, a deficit in oxygen was demonstrated to delay the timing of budding, prolong the G2 phase and cause accumulation of cells after DNA synthesis, but before commitment to budding. The C. neoformans homologue of the main cell cycle control gene CDC28/Cdc2 was isolated using degenerate RT-PCR. The full-length coding region was then amplified using primers to target the regions around the start and stop codons. The gene was called CnCdk1 and was found to have high homologies to S. cerevisiae CDC28 and S. pombe cdc2. To determine its function, its ability to rescue S. cerevisiae cdc28-temperature sensitive mutants was tested. S. cerevisiae cdc28-4 and cdc28-1N strains transformed with the pYES2-CnCdk1 construct exhibited growth at the restrictive temperature. Results of the sequence analysis and the ability of CnCdk1 to complement the S. cerevisiae cdc28-ts mutations support its assumed role as the CDC28/cdc2 homologue in C. neoformans.  相似文献   
2.
Two-color flow cytometry was carried out to determine the correlation between cell-mediated immunity and the levels of proteinuria in 30 patients with membranous nephropathy. Lymphocyte subpopulations were measured by two-color flow cytometry using various monoclonal antibodies of the Leu series. Clinically, the patients were divided into four stages as follows: 1. untreated nephrotic stage, 2. prednisolone (PSL) treated nephrotic stage, 3. persistent proteinuric stage (incomplete remission, ICR) and 4. complete remission (CR). Two-color flow cytometry showed a significant decrease in Leu 2a+15+ (suppressor T) cells and relative increase in Leu 3a+8+ (suppressor inducer T) cells in the untreated nephrotic stage. The mean Leu 3a+8-/Leu 2a+15+ (helper/suppressor) cell ratio was normalized in the persistent proteinuric stage or complete remission after treatment with PSL. Patients with membranous nephropathy showed a significant elevation of Leu 2a+DR+ cells after treatment with PSL. The abnormalities of suppressor T cells and suppressor inducer T cells in the peripheral blood appear to reflect the levels of proteinuria in patients with membranous nephropathy. It was concluded that PSL might stimulate Leu 2a positive cells and then increase the number of Leu 2a+15+ cells in the peripheral blood of patients with membranous nephropathy.  相似文献   
3.
OBJECTIVE: To examine the influence of in-season injury prevention training on hip and knee kinematics during a landing task. DESIGN: Longitudinal pre-post intervention study. SETTING: Testing sessions were conducted in a biomechanics research laboratory. PARTICIPANTS: Eighteen female soccer players between the ages of 14 and 17 participated in this study. All subjects were healthy with no current complaints of lower extremity injury. INTERVENTIONS: Testing sessions were conducted prior to and following a season of soccer practice combined with injury prevention training. MAIN OUTCOME MEASUREMENTS: During each testing session three-dimensional kinematics were collected while each subject performed a drop landing task. Peak hip and knee joint angles were measured during the early deceleration phase of landing and compared between pre- and post-training using paired t-tests. RESULTS: Following a season of soccer practice combined with injury prevention training, females demonstrated significantly less hip internal rotation (7.1 degrees vs. 1.9 degrees; P = 0.01) and significantly greater hip abduction (-4.9 degrees vs. -7.7 degrees; P = 0.02). No differences in knee valgus or knee flexion angles were found post-season. CONCLUSIONS: Female soccer players exhibited significant changes in hip kinematics during a landing task following in-season injury prevention training. Our results support the premise that a season of soccer practice combined with injury prevention training is effective in altering lower extremity motions that may play a role in predisposing females to ACL injury.  相似文献   
4.
Humoral hypercalcemia of malignancy (HHM) in neoplastic syndrome has been most commonly reported in squamous cell carcinoma. Gallbladder carcinoma with HHM is uncommon. In this report, we describe a male case of gallbladder carcinoma with marked hypercalcemia and a high level of serum parathyroid hormone-related peptide (PTHrP). An immunohistochemical examination using PTHrP was also positive.  相似文献   
5.
6.
O Koide  S Iwai  K Baba  H Iri 《Cancer》1987,60(6):1325-1330
The identification of atypical testicular germ cells is often difficult by by routine histologic examination. By immunohistochemical detection of placental alkaline phosphatase (PLAP) and by periodic acid Schiff staining of glycogen, atypical germ cells were easily identified in testicular samples. Forty-one fetal and adult testes were used for a preliminary study, and 121 testes from infants and adults with either cryptorchidism or germ cell tumors were studied for the presence of atypical germ cells. Two types of clear germ cells were differentiated histochemically, and one with PLAP-positive cell surfaces and glycogen-rich cytoplasm was considered to be atypical. The alkaline phosphatase of atypical germ cells appeared to be similar to that found in a few germ cells of early fetal testes. The atypical germ cells seemed to be multi-potential malignant cells capable of developing not only into seminoma but also into other germ cell tumors. Only in yolk sac tumor of infants were the atypical germ cells absent from tumor-adjacent seminiferous tubules.  相似文献   
7.
OBJECTIVE: The aim of this study was to evaluate the relationship between the degree of conversion (DC) of composites and the light intensity using LED-curing units and also to determine the amount of exposure required to achieve optimal curing. METHOD: The light outputs of light-curing units and the depths of cure of composites exposed to these units were determined using the methods outlined in modified ISO standards, ISO/TS10650 and ISO 4049, respectively. The distributions of DC in composites were investigated by IR spectra of microareas obtained at various depths from the irradiated surface of thin specimens cut out from the cured composites. IR spectra were measured using a Fourier transform infrared spectrometer equipped with a microscopic unit. DC was calculated from the changes in the amount of C=C double bonds in the IR spectra. RESULTS: The light intensity at various depths through the cured composite was calculated from the attenuation coefficient of each material, obtained from the linear relationship between the depth of cure and the logarithm of the amount of exposure, which is defined as the product of the irradiance and irradiation time. There was a third or fourth order regression relationship between DC and the logarithm of total light energy at a particular depth. SIGNIFICANCE: The minimum light energy required to produce a saturated DC was about 1000 s mW/cm2.  相似文献   
8.
OBJECTIVES: Vesicoureteral reflux (VUR) is the most common congenital urinary tract anomaly. This disease can pose a major threat to the kidneys as twenty percent of patients with endstage renal disease are reported to have VUR. Although genetic studies for uroplakin III (UPIII) have been reported recently, no study has focused on UPIII gene expression in VUR patients. We describe here the up-regulation of UPIII mRNA in exfoliated urinary cells from primary VUR patients. METHODS: A real-time RT-PCR for UPIII mRNA was performed on exfoliated urothelial cells from 18 primary VUR and 38 control samples. UPIII mRNA copies were calculated for each sample. The statistical differences were assessed by the Mann-Whitney U test. Receiver operator characteristic curves were constructed for analysis of the diagnostic values. RESULTS: UPIII mRNA was found to be up-regulated to a greater extent in VUR than in control exfoliated urinary cells (mean +/- SE: 497.0 +/- 178.5 copies vs. 69.0 +/- 10.0 copies, respectively, P < 0.001). In evaluating the measurement of urinary UPIII mRNA as a screening test for VUR, the sensitivity was 77.8% and the specificity was 76.3% by the best diagnostic cutoff point. CONCLUSIONS: This is the first report demonstrating up-regulation of UPIII in mRNA levels in VUR patients. We submit that the quantitative measurement of urinary UPIII mRNA has a potential of developing into the first non-invasive screening test for VUR.  相似文献   
9.
A new method of determining urinary polyamine concentration was compared with other techniques, namely, high pressure liquid chromatography (HPLC) and a polyamine test-enzyme kit. The values obtained by the new method, HPLC, and polyamine test-enzyme kit correlated well for all the fractions: diamine, spermidine and spermine. The correlation between the new method and the polyamine test-enzyme kit gave r = 0.9702, y = 1.1359x + 5.1266 (n = 48).  相似文献   
10.
We present herein the rare case of a young man who was found to have a solitary tumor in the right upper lobe of his lung by a routine chest X-ray. The tumor was removed by thoracoscopic surgery, and pathological examinations confirmed the diagnosis of a primary lymphangioma of the lung. A brief review of the available literature on this extremely rare type of benign tumor follows the case report.  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