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   3976篇
  免费   466篇
  国内免费   225篇
  2024年   27篇
  2023年   103篇
  2022年   137篇
  2021年   240篇
  2020年   257篇
  2019年   368篇
  2018年   216篇
  2017年   155篇
  2016年   149篇
  2015年   176篇
  2014年   271篇
  2013年   278篇
  2012年   195篇
  2011年   181篇
  2010年   143篇
  2009年   129篇
  2008年   145篇
  2007年   148篇
  2006年   134篇
  2005年   132篇
  2004年   83篇
  2003年   65篇
  2002年   93篇
  2001年   46篇
  2000年   57篇
  1999年   46篇
  1998年   46篇
  1997年   28篇
  1996年   38篇
  1995年   54篇
  1994年   40篇
  1993年   37篇
  1992年   39篇
  1991年   37篇
  1990年   34篇
  1989年   34篇
  1988年   27篇
  1987年   18篇
  1986年   16篇
  1985年   27篇
  1984年   33篇
  1983年   19篇
  1982年   26篇
  1981年   24篇
  1980年   17篇
  1979年   21篇
  1978年   27篇
  1977年   17篇
  1976年   7篇
  1974年   9篇
排序方式: 共有4667条查询结果,搜索用时 62 毫秒
991.
992.
《Cell》2021,184(25):6101-6118.e13
  1. Download : Download high-res image (168KB)
  2. Download : Download full-size image
  相似文献   
993.
Four adult rumen-fistulated wether sheep were fed silages combined with barley. The silages consisted of 48% grasses, 28% legumes and 24% other forbs (GCF) or of pure grass (G). The swards received no mineral fertiliser. The dry matter (DM) and fibre contents were lower in GCF than in G. Crude protein content of DM in GCF and G were 145 g/kg and 102 g/kg respectively. DM content as ash, lipids and non-fibrous carbohydrates were rather similar in both silages. About 40g DM were offered per kg BW0.75 and day either as silage alone or as a mixture of silage and barley (60:40). Faecal N excretion was greater with GCF than with G. The proportion of faecal bacterial and endogenous debris N reached 75 and 73% when GCF or G was fed, respectively. Undigested dietary N represented about 20%, and water soluble N accounted for 5–6% of faecal N. GCF caused more urinary N than G. Barley reduced urinary N excretion when supplemented to GCF. No dietary influence on urinary non-urea nitrogenous compounds was shown. GCF caused higher urinary urea N excretion than G and barley reduced this fraction when replacing part of GCF. Based on the urinary urea N proportions, it is concluded that N intake exceeded N requirement for any of the four diets fed. Dietary supplementation of ruminally fermentable carbohydrates can reduce urinary N excretion and this improves the efficiency of utilisation of N in N-unfertilised biodiverse grassland/ruminant farming systems.  相似文献   
994.
Dimethylacetamide has been included in different extenders for the cryopreservation of semen from species with promising results. The objective of this study was to evaluate the use of dimethylacetamide (DMA) in different concentrations, associated or not with glycerol (GLY), for the cryopreservation of ovine semen, and its effects on in vitro sperm parameters and post-thaw in vivo fertility. Five semen samples of five adult Santa Ines sheep (n=25) were used. The collected ejaculates were divided among the seven treatments for subsequent cryopreservation. The treatments presented different concentrations of DMA and GLY, being divided as G1: GLY 6%; G2: DMA 3%; G3: GLY 5% + DMA 1%; G4: GLY 4% + DMA 2%; G5: GLY 3% + DMA 3%; G6: GLY 2% + DMA 4%; G7: GLY 1% + DMA 5%. %. Post-thawing of the straws, aliquots were evaluated for computerized sperm kinetics (CASA) and plasma membrane integrity, using fluorescent probes and flow cytometry. After the in vitro evaluation of the sperm parameters, in vivo testing was performed by laparoscopic artificial insemination of 72 females. The post-thaw total motility (%) evaluated by CASA were 51.4, 51.4, 50.1, 53.6, 52.3, 52.8 and 46.9, respectively, for the seven groups. And the plasma membrane integrity (%) were 19.7, 28.4, 22.3, 29.4, 24.3, 17.9 and 16.9, respectively. There were no differences (P> 0.05) between the treatments for the parameters of spermatic kinetics and membrane integrity. For females inseminated with semen from the control group (G1, GLY6%), the percentage of pregnant females was 36.1%, a result similar to that obtained with G3 treatment (GLY5% + DMA1%). In conclusion, dimethylacetamide, either alone or in combination with glycerol, can be used for cryopreservation of ovine semen.  相似文献   
995.
The aim of this study was to investigate the roles of microRNA-383 (miRNA-383) in progression of non–small cell lung cancer (NSCLC) and the potential mechanism. The expressions of miR-383 and Wnt1 protein were detected in lung cancer tissues and cells by quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot analysis. After the transfection of miR-383 mimics, si-Wnt1 or miR-383+Wnt1, the viability and apoptosis of NSCLC cells were detected by cell counting kit-8 and terminal deoxynucleotidyl transferase–mediated dUTP nick-end labeling, respectively. The interaction between miR-383 and Wnt1 was investigated by luciferase activity and Western blot analysis. Cells stably transfected with miR-383 mimics were inoculated into the right axillary of nude mice by subcutaneous injection. The tumor volume and weight were measured, and the expressions of miR-383, Wnt1, β-catenin, and cyclin D1 were detected by qRT-PCR and Western blot analysis. The expression of miR-383 was significantly decreased, and the level of Wnt1 was significantly increased (P < 0.05) in lung cancer tissues and cells. Upregulation of miR-383 or inhibition of Wnt1 expression inhibited the cell viability and induce apoptosis in NSCLC cells. Moreover, Wnt1 was the target gene of miR-383, and its overexpression weakened the regulatory effect of miR-383 on cell viability and apoptosis in NSCLC cells. Besides, the addition of miR-383 decreased the tumor volume and size and inhibited the expressions of Wnt1, β-catenin, and cyclin D1 at the protein level in nude mice. Collectively, miR-383 induced apoptosis and inhibited cell viability as well as tumorigenic capacity in nude mice via regulating the Wnt/β-catenin signaling pathway.  相似文献   
996.
《Biomarkers》2013,18(5):455-462
Purpose: To explore serum superoxide dismutase (SOD) for predicting radiation pneumonitis (RP) in non-small cell lung cancer patients following chemoradiotherapy.

Methods: Serum levels for SOD were measured by enzyme-linked immunosorbent assays prior to radiation therapy (Pre-RT) and post 40 Gy/4 weeks during the treatment (Pos-RT).

Results: SOD concentrations after delivery of 40 Gy/4 weeks was associated with the development of RP. The best predictive ability of SOD was observed for a cut-off value of 56 unit/ml, with a sensitivity of 0.80 (95% CI 0.28–0.99), and a specificity of 0.67 (95% CI 0.43–0.65) (p = 0.040).

Conclusion: Serum SOD may be a potential predictor for RP, which need to be further verified.  相似文献   
997.
Schistosomula of Schistosoma mansoni newly transformed from cercariae by either the mechanical or skin penetration procedures, as well as 5-day-old schistosomula recovered from the lungs of mice, were tested for their ability to activate the human alternative complement pathway. Newly transformed larvae prepared by both methods, although less active than cercariae, were found to activate the pathway to a comparable degree as judged by the consumption of fluid phase C3 and factor B and the conversion of native C3 into a component with a more anodal electrophoretic mobility. The alternative pathway activating capacity could not be blocked or enhanced by pretreating the larvae with purified IgG or F(ab′)2 fragments prepared from human sera containing antibodies directed against schistosomula. In contrast to newly transformed parasites, 5-day-old schistosomula recovered from mouse lungs failed to activate the alternative pathway as judged by either the C3 or B consumption assays or the C3 conversion assay. This developmental change could not be reversed by treating lung stage larvae with neuraminidase and heparinase, enzymes which are known to alter the activating capacity of other particulate substances or with chondroitinase ABC or trypsin.  相似文献   
998.
BackgroundAlthough healthcare databases are a valuable source for real-world oncology data, cancer stage is often lacking. We developed predictive models using claims data to identify metastatic/advanced-stage patients with ovarian cancer, urothelial carcinoma, gastric adenocarcinoma, Merkel cell carcinoma (MCC), and non-small cell lung cancer (NSCLC).MethodsPatients with ≥1 diagnosis of a cancer of interest were identified in the HealthCore Integrated Research Database (HIRD), a United States (US) healthcare database (2010–2016). Data were linked to three US state cancer registries and the HealthCore Integrated Research Environment Oncology database to identify cancer stage. Predictive models were constructed to estimate the probability of metastatic/advanced stage. Predictors available in the HIRD were identified and coefficients estimated by Least Absolute Shrinkage and Selection Operator (LASSO) regression with cross-validation to control overfitting. Classification error rates and receiver operating characteristic curves were used to select probability thresholds for classifying patients as cases of metastatic/advanced cancer.ResultsWe used 2723 ovarian cancer, 6522 urothelial carcinoma, 1441 gastric adenocarcinoma, 109 MCC, and 12,373 NSCLC cases of early and metastatic/advanced cancer to develop predictive models. All models had high discrimination (C > 0.85). At thresholds selected for each model, PPVs were all >0.75: ovarian cancer = 0.95 (95% confidence interval [95% CI]: 0.94–0.96), urothelial carcinoma = 0.78 (95% CI: 0.70–0.86), gastric adenocarcinoma = 0.86 (95% CI: 0.83–0.88), MCC = 0.77 (95% CI 0.68–0.89), and NSCLC = 0.91 (95% CI 0.90 – 0.92).ConclusionPredictive modeling was used to identify five types of metastatic/advanced cancer in a healthcare claims database with greater accuracy than previous methods.  相似文献   
999.
Lung cancer is one of the most frequently diagnosed malignant tumors and the main reason for cancer-related death around the world, whereas nonsmall cell lung cancer that consists two subtypes: lung adenocarcinoma (LUAD) and squamous cell carcinoma (LUSC) is responsible for an estimated 85% of all lung cancers. The current study aimed to explore gene expression and methylation differences between LUAD and LUSC. EdgeR was used to identify differentially regulated genes between normal and cancer in the LUAD and LUSC extracted from The Cancer Genome Atlas (TCGA), respectively, whereas SAM was used to find genes with differential methylation between normal and cancer in the LUAD and LUSC, respectively. Finally, Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis was performed to analyze the function which these genes enriched in. A total of 391 genes with opposite methylation patterns in LUAD and LUSC and four functional pathways were obtained (false discovery rate (FDR) < 0.1). These pathways mainly included fat digestion and absorption, phenylalanine metabolism, bile secretion, and so on, which were related to the airframe nutrition metabolic pathway. Moreover, two genes CTSE (cathepsin E) and solute carrier family 5 member 7 (SLC5A7) were also found, among which CTSE was overexpressed and hypomethylated in LUAD corresponding to normal lung tissues, whereas SLC5A7 showed the opposite in LUAD. In conclusion, this study investigated the differences between the gene expression and methylation patterns in LUAD and LUSC, and explored their different biological characteristics. Further understanding of these differences may promote the discovery and development of new, accurate strategies for the prevention, diagnosis, and treatment of lung cancer.  相似文献   
1000.
Evidence for close genetic linkage between the loci for serum albumin (ALB) and vitamin D binding protein (GC) in sheep is presented. No recombinants were found in 28 informative offspring of a single ram family. The recombination frequency between the two loci was estimated to be in the range of 0 to 10%. No sign of linkage was observed between the ALB-GC complex and transferrin.  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