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   4304篇
  免费   385篇
  2023年   25篇
  2022年   13篇
  2021年   81篇
  2020年   44篇
  2019年   65篇
  2018年   81篇
  2017年   59篇
  2016年   126篇
  2015年   245篇
  2014年   239篇
  2013年   253篇
  2012年   356篇
  2011年   325篇
  2010年   198篇
  2009年   178篇
  2008年   237篇
  2007年   266篇
  2006年   239篇
  2005年   225篇
  2004年   211篇
  2003年   203篇
  2002年   209篇
  2001年   51篇
  2000年   33篇
  1999年   46篇
  1998年   49篇
  1997年   35篇
  1996年   36篇
  1995年   29篇
  1994年   32篇
  1993年   31篇
  1992年   30篇
  1991年   26篇
  1990年   30篇
  1989年   29篇
  1988年   24篇
  1987年   20篇
  1986年   21篇
  1985年   26篇
  1984年   38篇
  1983年   28篇
  1982年   14篇
  1981年   18篇
  1979年   21篇
  1978年   16篇
  1977年   12篇
  1975年   9篇
  1974年   10篇
  1973年   12篇
  1969年   8篇
排序方式: 共有4689条查询结果,搜索用时 15 毫秒
1.
Capsaicin has known health beneficial and therapeutic properties. It is also able to enhance the permeability of drugs across epithelial tissues. Unfortunately, due to its pungency the oral administration of capsaicin is limited. To this end, we assessed the effect of nanoencapsulation of capsaicin, under the hypothesis that this would reduce its pungency. Core-shell nanocapsules with an oily core and stabilized with phospholipids were used. This system was used with or without chitosan coating. In this work, we investigated the in vitro release behavior of capsaicin-loaded formulations in different physiological media (including simulated saliva fluid). We also evaluated the influence of encapsulation of capsaicin on the cell viability of buccal cells (TR146). To study the changes in pungency after encapsulation we carried out a sensory analysis with a trained panel of 24 students. The in vitro release study showed that the systems discharged capsaicin slowly in a monotonic manner and that the chitosan coating had an effect on the release profile. The cytotoxic response of TR146 cells to capsaicin at a concentration of 500 μM, which was evident for the free compound, was reduced following its encapsulation. The sensory study revealed that a chitosan coating results in a lower threshold of perception of the formulation. The nanoencapsulation of capsaicin resulted in attenuation of the sensation of pungency significantly. However, the presence of a chitosan shell around the nanoformulations did not mask the pungency, when compared with uncoated systems.  相似文献   
2.
3.
Nowadays the activity of heart ectoenzymes, breaking up ATP, are determined in the undamaged tissue to eliminate the effect to the ATP of intracellular enzymes. Our aim is to study the activity of ecto-adenosine triphosphatase in the heart damaged by ischemia. It was established that the activity of ectoenzymes, breaking up ATP, may be measured in the tissue damaged by ischemia only in case when the cellular membrane becomes impermeable for the intracellular enzymes. The activity of adenosine triphosphatase is significantly reduced during the myocardial reperfusion after ischemia and appeared as one of the criteria by which we can assume the degree of the heart reperfusion damage.  相似文献   
4.
5.
6.
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   
7.
A water-soluble root extract of Angelica archangelica subsp. litoralis afforded, in addition to adenosine, coniferin and the two known dihydrofurocoumarin glycosides, apterin and 1′-O-β-d-glycopyranosyl-(S)-marmesin (marmesinin), two new dihydrofuranocoumarin glycosides, 1′-O-β-d-glucopyranosyl-(2S, 3R)-3-hydroxymarmesin, and 2′-β-d-glucopyranosyloxymarmesin. For the latter a 2S-configuration was demonstrated, the stereochemistry at position 1′ remaining undefined. Roots of A. silvestris similarly afforded 1′-O-β-d-glucopyranosyl-(2S, 3R)-3-hydroxymarmesin. By correlation with the aglycone 2S,3R)-3-hydroxymarmesin obtained in this work, the absolute configurations (2S,3R) were established for the known dihydrofurocoumarin diesters smirniorin and smirnioridin.  相似文献   
8.
9.
Abstract. The relationships between biogeographical patterns and local‐scale patterns based on microscale features, such as topoclimate, are well known in plant biogeography. Here we present a method of determining this correspondence using constrained ordination and correlations. We examined compositional gradients at two different scales, biogeographical chorotypes, and diversity. Compositional data (124 taxa × 113 plots) were sampled at four regularly spaced sites in south‐eastern Spain. Longitude (LONGI) was used as a spatial variable representing an east–west climate gradient, together with a radiation index (RADIN), elevation, and a disturbance indicator. All factors correlated with the compositional gradients, but the local‐topoclimate factor (RADIN) and the broad‐scale factor (LONGI) were most important. These two, spatially independent factors were both correlated with the two first ordination axes, and therefore should relate to the same general trend in species‐turnover. There was a significant Spearman's rank correlation between the species order along these two gradients. This is interpreted as an ecological self‐similar pattern, i.e. coenoclines repeating at different scales. A consistent order of species along local‐ and broad‐scale coenoclines may indicate that similar operational factors act at several scales, here related to moisture and temperature. The distribution of Mediterraneo–Macaronesian, Mediterraneo–Saharo–Arabian and Ibero–Maghribian species confirmed the correspondence between the broad‐ and local‐scale gradients. The former group decreases in number with increasing aridity along both gradients, whereas the two latter groups increase. A discordant pattern was found with south‐eastern Iberian endemics, but this may be explained by several of them being edaphic (saxicolous) specialists. There is a significant decrease in species richness with high radiation, but the expected increase along the longitudinal gradient from west (dry) to east (moist) was not statistically significant. This may be due to the correspondence between high richness and disturbance, both occurring in the middle of the broad‐scale gradient.  相似文献   
10.
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