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   5178篇
  免费   395篇
  国内免费   7篇
  2023年   18篇
  2022年   36篇
  2021年   85篇
  2020年   51篇
  2019年   70篇
  2018年   77篇
  2017年   87篇
  2016年   148篇
  2015年   234篇
  2014年   272篇
  2013年   316篇
  2012年   371篇
  2011年   361篇
  2010年   229篇
  2009年   257篇
  2008年   332篇
  2007年   304篇
  2006年   338篇
  2005年   297篇
  2004年   305篇
  2003年   289篇
  2002年   262篇
  2001年   68篇
  2000年   43篇
  1999年   63篇
  1998年   58篇
  1997年   32篇
  1996年   38篇
  1995年   39篇
  1994年   44篇
  1993年   38篇
  1992年   39篇
  1991年   28篇
  1990年   22篇
  1989年   24篇
  1988年   22篇
  1987年   13篇
  1986年   21篇
  1985年   22篇
  1984年   27篇
  1983年   14篇
  1982年   14篇
  1981年   16篇
  1980年   18篇
  1979年   11篇
  1978年   15篇
  1977年   15篇
  1976年   14篇
  1975年   10篇
  1974年   9篇
排序方式: 共有5580条查询结果,搜索用时 22 毫秒
191.

Background

As the World Health Organization grading system for gastroenteropancreatic-neuroendocrine tumors (GEP-NETs) may not always correlate with tumor progression, it is imperative that other independent predictors of tumor progression be established. To identify such predictors, we conducted a retrospective histopathological study of hindgut NETs, obtained from endoscopic procedures, and used statistical analyses to evaluate predictive factors.

Methods

We first obtained clinicopathological data of cases of hindgut NETs. Tissue sections from tumor samples were prepared and subjected to pathological examination. In particular, we calculated the microvessel density (MVD) and lymphatic microvessel density (LMVD) values, and performed appropriate statistical analyses.

Results

A total of 42 cases of hindgut NETs were selected for the study, 41 from the rectum and 1 from the sigmoid colon. Based on the Ki-67 labeling index, 34 cases were classified as NET G1 tumors and 8 as NET G2 tumors. MVD values ranged from 1.4/mm2 to 73.9/mm2 and LMVD values from 0/mm2 to 22.9/mm2. MVD and LMVD were identified as risk factors for venous and lymphatic invasion of hindgut NETs. Moreover, MVD positively correlated with the maximum diameter of the tumor.

Conclusions

Tumor progression of NETs may cause angiogenesis and lymphangiogenesis, via an unknown mechanism, as well as lymphovascular invasion. Angiogenesis likely plays an important role in occurrence and progression in the initial phase of hindgut NETs.
  相似文献   
192.
Aspergillus species are among the most important filamentous fungi from the viewpoints of industry, pathogenesis, and mycotoxin production. Fungal cells are exposed to a variety of environmental stimuli, including changes in osmolality, temperature, and pH, which create stresses that primarily act on fungal cell walls. In addition, fungal cell walls are the first interactions with host cells in either human or plants. Thus, understanding cell wall structure and the mechanism of their biogenesis is important for the industrial, medical, and agricultural fields. Here, we provide a systematic review of fungal cell wall structure and recent findings regarding the cell wall integrity signaling pathways in aspergilli. This accumulated knowledge will be useful for understanding and improving the use of industrial aspergilli fermentation processes as well as treatments for some fungal infections.  相似文献   
193.
The room temperature (RT) processability of the photoactive layers in polymer solar cells (PSCs) from halogen‐free solvent along with their highly reproducible power conversion efficiencies (PCEs) and intrinsic thickness tolerance are extremely desirable for the large‐area roll‐to‐roll (R2R) production. However, most of the photoactive materials in PSCs require elevated processing temperatures due to their strong aggregation, which are unfavorable for the industrial R2R manufacturing of PSCs. These limiting factors for the commercialization of PSCs are alleviated by synthesizing random terpolymers with components of (2‐decyltetradecyl)thiophen‐2‐yl)naphtho[1,2‐c:5,6‐c′]bis[1,2,5]thiadiazole and bithiophene substituted with methyl thiophene‐3‐carboxylate (MTC). In contrast to the temperature‐dependent PNTz4T polymer, the resulting random terpolymers (PNTz4T‐MTC) show better solubility, slightly reduced crystallinity and aggregation, and weaker intermolecular interaction, thus enabling PNTz4T‐MTC to be processed at RT from a halogen‐free solvent. Particularly, the PNTz4T‐5MTC‐based photoactive layer exhibits an excellent PCE of 9.66%, which is among the highest reported PCEs for RT and ecofriendly halogen‐free solvent processed fullerene‐based PSCs, and a thickness tolerance with a PCE exceeding 8% from 100 to 520 nm. Finally, large‐area modules fabricated with the PNTz4T and PNTz4T‐5MTC polymer have shown 4.29% and 6.61% PCE respectively, with an area as high as 54.45 cm2 in air.  相似文献   
194.
195.
Feral Horse (Equus caballus) impacts in northern Kosciuszko National Park, New South Wales, Australia are directly occurring in habitat of the nationally threatened Broad‐toothed Rat (Mastacomys fuscus). This species is endemic primarily to the mountain regions of south‐eastern mainland Australia and Tasmania, with a disjunct population at Barrington Tops. The Broad‐toothed Rat's preferred habitat is being increasingly impacted by browsing and trampling associated with the expansion of feral horse populations. This study surveyed 180 sites supporting preferred habitat for this species to determine Broad‐toothed Rat presence and relative abundance in relation to the level of feral horse impacts within the reserve. There was a significant negative relationship between feral horse impacts and both Broad‐toothed Rat presence and abundance. No scats were identified at localities where feral horse impacts were severe, and at moderate horse impact sites, there was a proportion (34%) without scats found. Locations with low horse impacts had little impact on Broad‐toothed Rat occurrence. As feral horse populations increase, Broad‐toothed Rat populations may be further impacted. Such impacts will be due to the loss of vegetation cover from feral horse trampling and grazing, making animals more vulnerable to predation by predators or impacting on their ability to disperse to more suitable habitat. Habitat remnants and vegetation corridors along drainage lines require protection from feral horses to prevent localized extinctions of Broad‐toothed Rat.  相似文献   
196.
197.
198.
199.
200.
This review promotes the value of isolated hepatocytes in modern Drug Discovery programmes and outlines how increased understanding, particularly in the area of in vitro-in vivo extrapolation (IVIVE), has led to more widespread use. The importance of in vitro metabolic intrinsic clearance data for predicting in vivo clearance has been acknowledged for several years and the greater utility of hepatocytes, compared with hepatic microsomes and liver slices, for this application is discussed. The application of hepatocytes in predicting drug-drug interactions (DDIs) resulting from reversible and irreversible (time-dependent) inhibition is relatively novel but affords the potential to study both phase I and phase II processes together with any impact of drug efflux and/or uptake (cellular accumulation). Progress in this area is reviewed along with current opinions on the comparative use of primary hepatocytes and higher throughput reporter gene-based systems for studying cytochrome P450 (CYP) induction. The appreciation of the role of transporter proteins in drug disposition continues to evolve. The study of hepatic uptake using isolated hepatocytes and the interplay between drug transport and metabolism with respect to both clearance and DDIs and subsequent IVIVE is also considered.  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