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   10945篇
  免费   1046篇
  国内免费   5篇
  2022年   79篇
  2021年   145篇
  2020年   92篇
  2019年   101篇
  2018年   149篇
  2017年   136篇
  2016年   223篇
  2015年   413篇
  2014年   450篇
  2013年   583篇
  2012年   720篇
  2011年   717篇
  2010年   500篇
  2009年   443篇
  2008年   631篇
  2007年   613篇
  2006年   566篇
  2005年   580篇
  2004年   626篇
  2003年   552篇
  2002年   572篇
  2001年   131篇
  2000年   140篇
  1999年   179篇
  1998年   179篇
  1997年   79篇
  1996年   104篇
  1995年   82篇
  1994年   103篇
  1993年   109篇
  1992年   125篇
  1991年   103篇
  1990年   163篇
  1989年   123篇
  1988年   120篇
  1987年   98篇
  1986年   94篇
  1985年   81篇
  1984年   99篇
  1983年   72篇
  1982年   94篇
  1981年   101篇
  1980年   63篇
  1979年   75篇
  1978年   60篇
  1977年   57篇
  1976年   51篇
  1975年   53篇
  1974年   48篇
  1973年   45篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
Cell lines derived from the small intestine that reflect authentic properties of the originating intestinal epithelium are of high value for studies on mucosal immunology and host microbial homeostasis. A novel immortalization procedure was applied to generate continuously proliferating cell lines from murine E19 embryonic small intestinal tissue. The obtained cell lines form a tight and polarized epithelial cell layer, display characteristic tight junction, microvilli and surface protein expression and generate increasing transepithelial electrical resistance during in vitro culture. Significant up-regulation of Cxcl2 and Cxcl5 chemokine expression upon exposure to defined microbial innate immune stimuli and endogenous cytokines is observed. Cell lines were also generated from a transgenic interferon reporter (Mx2-Luciferase) mouse, allowing reporter technology-based quantification of the cellular response to type I and III interferon. Thus, the newly created cell lines mimic properties of the natural epithelium and can be used for diverse studies including testing of the absorption of drug candidates. The reproducibility of the method to create such cell lines from wild type and transgenic mice provides a new tool to study molecular and cellular processes of the epithelial barrier.  相似文献   
23.
Informational interventions (e.g., awareness campaigns, carbon footprint calculators) are built on the assumption that informing the public about the environmental consequences of their actions should result in increased pro-environmental intentions and behavior. However, empirical support for this reasoning is mixed. In this paper, we argue that informational interventions may succeed in improving people’s knowledge about the negative environmental consequences of one’s actions, but this knowledge will not gain motivational force if people do not consider protecting the environment an important personal value. In an experiment, we measured individual differences in value priorities, and either presented participants a movie clip that portrayed the negative environmental consequences of using bottled water, or a control movie. As predicted, we found that the environmental movie improved recipients’ knowledge of the negative environmental impact of bottled water, but this knowledge only resulted in concomitant changes in intentions and acceptability of related policies among participants who strongly endorsed biospheric (i.e. environmental) values, while having no effect on those who care less about the environment. Interestingly, the results suggest that although informational interventions are perhaps not always successful in directly affecting less environmentally-conscious recipients, they could still have beneficial effects, because they make those who strongly care about the environment more inclined to act on their values.  相似文献   
24.
The goal of this study was to assess the relationship between Aβ deposition and white matter pathology (i.e., white matter hyperintensities, WMH) on microstructural integrity of the white matter. Fifty-seven participants (mean age: 78±7 years) from an ongoing multi-site research program who spanned the spectrum of normal to mild cognitive impairment (Clinical dementia rating 0–0.5) and low to high risk factors for arteriosclerosis and WMH pathology (defined as WMH volume >0.5% total intracranial volume) were assessed with positron emission tomography (PET) with Pittsburg compound B (PiB) and magnetic resonance and diffusion tensor imaging (DTI). Multivariate analysis of covariance were used to investigate the relationship between Aβ deposition and WMH pathology on fractional anisotropy (FA) from 9 tracts of interest (i.e., corona radiata, internal capsule, cingulum, parahippocampal white matter, corpus callosum, superior longitudinal, superior and inferior front-occipital fasciculi, and fornix). WMH pathology was associated with reduced FA in projection (i.e., internal capsule and corona radiate) and association (i.e., superior longitudinal, superior and inferior fronto-occipital fasciculi) fiber tracts. Aβ deposition (i.e., PiB positivity) was associated with reduced FA in the fornix and splenium of the corpus callosum. There were interactions between PiB and WMH pathology in the internal capsule and parahippocampal white matter, where Aβ deposition reduced FA more among subjects with WMH pathology than those without. However, accounting for apoE ε4 genotype rendered these interactions insignificant. Although this finding suggests that apoE4 may increase amyloid deposition, both in the parenchyma (resulting in PiB positivity) and in blood vessels (resulting in amyloid angiopathy and WMH pathology), and that these two factors together may be associated with compromised white matter microstructural integrity in multiple brain regions, additional studies with a longitudinal design will be necessary to resolve this issue.  相似文献   
25.
[Acyl CoA]monoacylglycerol acyltransferase 2 (MGAT2) is of interest as a target for therapeutic treatment of diabetes, obesity and other diseases which together constitute the metabolic syndrome. In this Letter we report our discovery and optimisation of a novel series of MGAT2 inhibitors. The development of the SAR of the series and a detailed discussion around some key parameters monitored and addressed during the lead generation phase will be given. The in vivo results from an oral lipid tolerance test (OLTT) using the MGAT2 inhibitor (S)-10, shows a significant reduction (68% inhibition relative to na?ve, p <0.01) in plasma triacylglycerol (TAG) concentration.  相似文献   
26.
Childhood obesity is becoming a topic of great concern due to the rising prevalence of this condition in North America. Studies conducted in the United States have indicated that the prevalence of obesity has increased dramatically over the past few decades. The purpose of this study was to estimate the prevalence of obesity in Canadian children between the ages of 5 and 12 years by examining data from two national and two regional surveys. The 85th percentiles of each of four anthropometric indices derived from large normative populations were used as diagnostic criteria for obesity. As expected, the resulting prevalences varied according to the criteria used. A significant increase in childhood obesity between the 1981 to 1988 national surveys was observed when the three indices which used skinfolds were applied. Weight-for-height percentiles did not indicate an increase in obesity in these samples. Regional samples showed a less than expected prevalence of obesity among the middle-class children and a higher than expected rate among the inner city boys. It can be concluded that there is a need for a defined criteria for identifying obesity in children in order to avoid confusion resulting from the wide variation in estimates of prevalence resulting from different standards and measurements. Using adiposity-based criteria for obesity it was clearly evident that the prevalence of obesity has increased in Canadian children.  相似文献   
27.
p21WAF1 is a well-characterized mediator of cell cycle arrest and may also modulate chemotherapy-induced cell death. The role of p21WAF1 in drug-induced cell cycle arrest and apoptosis of acute lymphoblastic leukemia (ALL) cells was investigated using p53-functional patient-derived xenografts (PDXs), in which p21WAF1 was epigenetically silenced in T-cell ALL (T-ALL), but not in B-cell precursor (BCP)-ALL PDXs. Upon exposure to diverse cytotoxic drugs, T-ALL PDX cells exhibited markedly increased caspase-3/7 activity and phosphatidylserine (PS) externalization on the plasma membrane compared with BCP-ALL cells. Despite dramatic differences in apoptotic characteristics between T-ALL and BCP-ALL PDXs, both ALL subtypes exhibited similar cell death kinetics and were equally sensitive to p53-inducing drugs in vitro, although T-ALL PDXs were significantly more sensitive to the histone deacetylase inhibitor vorinostat. Transient siRNA suppression of p21WAF1 in the BCP-ALL 697 cell line resulted in a moderate depletion of the cell fraction in G1 phase and marked increase in PS externalization following exposure to etoposide. Furthermore, stable lentiviral p21WAF1 silencing in the BCP-ALL Nalm-6 cell line accelerated PS externalization and cell death following exposure to etoposide and vorinostat, supporting previous findings. Finally, the Sp1 inhibitor, terameprocol, inhibited p21WAF1 expression in Nalm-6 cells exposed to vorinostat and also partially augmented vorinostat-induced cell death. Taken together, these findings demonstrate that p21WAF1 regulates the early stages of drug-induced apoptosis in ALL cells and significantly modulates their sensitivity to vorinostat.  相似文献   
28.
29.
30.
Body Talk: Rhetoric, Technology, Reproduction. Mary M. Lay. Laura J. Gurak. Clare Gravon. and Cynthia Myntii. eds. Madison: University of Wisconsin Press, 2000. xiii. 307 pp.  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