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   1804篇
  免费   119篇
  2023年   8篇
  2022年   10篇
  2021年   37篇
  2020年   15篇
  2019年   42篇
  2018年   44篇
  2017年   27篇
  2016年   41篇
  2015年   80篇
  2014年   110篇
  2013年   129篇
  2012年   135篇
  2011年   150篇
  2010年   92篇
  2009年   87篇
  2008年   120篇
  2007年   114篇
  2006年   108篇
  2005年   108篇
  2004年   106篇
  2003年   79篇
  2002年   67篇
  2001年   13篇
  2000年   10篇
  1999年   14篇
  1998年   17篇
  1997年   12篇
  1996年   10篇
  1995年   16篇
  1994年   14篇
  1993年   9篇
  1992年   10篇
  1991年   7篇
  1990年   5篇
  1989年   5篇
  1988年   6篇
  1987年   3篇
  1986年   4篇
  1985年   5篇
  1984年   11篇
  1983年   4篇
  1982年   8篇
  1981年   3篇
  1980年   3篇
  1979年   6篇
  1978年   3篇
  1976年   2篇
  1975年   4篇
  1972年   2篇
  1970年   2篇
排序方式: 共有1923条查询结果,搜索用时 31 毫秒
71.
In recent years, special attention has been paid to the A3 adenosine receptor (A3AR) as a possible pharmacological target to treat intestinal inflammation. In this work, it was set up a novel method to quantify the concentration of a promising anti-inflammatory agent inside and outside of intestinal barrier using the everted gut sac technique. The compound chosen for the present study is one of the most potent and selective A3AR agonist reported so far, named AR 170 (N6-methyl-2-phenylethynyl-5′-N-methylcarboxamidoadenosine). In order to evaluate the intestinal absorption of AR 170 the radioligand binding assay in comparison with HPLC-DAD was used. Results showed that the compound is absorbed via passive diffusion by paracellular pathway. The concentrations determined in the serosal (inside the sac) fluid by radioligand binding assay are in good agreement with those obtained through the widely used HPLC/MS protocol, demonstrating the reliability of the method. It is worthwhile to note that the radioligand binding assay allows detecting very low concentrations of analyte, thus offering an excellent tool to measure the intestinal absorption of receptor ligands. Moreover, the AR 170 quantity outside the gut sac and the interaction with A3AR could presuppose good topical anti-inflammatory effects of this compound.  相似文献   
72.
The biotechnology for in vitro embryo production is becoming increasingly popular, being applied to humans and domestic animals. Embryo development can be achieved with either 20% or 5% oxygen tension. The extracellular vesicles (EVs) are secreted by different cell types and carry bioactive materials. Our objective was to determine the secretion pattern and micro RNA (miRNA) contents of EVs released in the bovine embryo culture environment—embryo and cumulus cell monolayer—on Days 3 and 7 of in vitro culture under two different oxygen tensions: High (20%) and low (5%). The EVs were isolated from the medium and analyzed to determine size, concentration, and miRNA levels. EVs concentration in low oxygen tension increased on Day 3 and decreased on Day 7. Additionally, altered EV miRNAs derived from the embryo‐cumulus culture medium were predicted to regulate survival and proliferation‐related pathways on Days 3 and 7. Moreover, miR‐210 levels decreased in EVs isolated from the culture medium under high oxygen tension suggesting that this miRNA can be used as a marker for normoxia since it is associated with low oxygen tension. In summary, this study provides knowledge of the oxygen tension effects on EVs release and content, and potentially, on cell‐to‐cell communication during in vitro bovine embryo production.  相似文献   
73.
It is a widely held belief that environmental contaminants contribute to the decline of amphibian populations. By spending most of their early life in water and later stages on the land, amphibians face a constant risk of exposure to pesticides and other chemical pollutants in both aquatic and terrestrial environments. This review presents an overview of the studies carried out in Italian amphibians to highlight hazardous effects of bioaccumulation of chemical pollutants in juveniles and adults in various contaminated environments. Further, the studies in the laboratory setting assessing the effects of chemical pollutants on reproductive and developmental processes are reported. These studies and their relative references have been summarized in a tabular form. Three prominent contaminant groups were identified: herbicides, insecticides, and fungicides; and only a few works reported the effects of other chemical pollutants. Each pollutant group has been delegated to a section. All through the literature survey, it is seen that interest in this topic in Italy is very recent and sparse, where only a few anuran and caudata species and only some chemical pollutants have been studied.  相似文献   
74.
Urothelial carcinoma (UC) is the most common bladder tumour. Proper treatment requires tumour resection for diagnosing its grade (aggressiveness) and stage (invasiveness). White‐light cystoscopy and histopathological examination are the gold standard procedures for clinical and histopathological diagnostics, respectively. However, cystoscopy is limited in terms of specificity, histology requires long tissue processing, both procedures rely on operator's experience. Multimodal optical spectroscopy can provide a powerful tool for detecting, staging and grading bladder tumours in a fast, reliable and label‐free modality. In this study, we collected fluorescence, Raman and reflectance spectra from 50 biopsies obtained from 32 patients undergoing transurethral resection of bladder tumour using a multimodal fibre‐probe. Principal component analysis allowed distinguishing normal from pathological tissues, as well as discriminating tumour stages and grades. Each individual spectroscopic technique provided high specificity and sensitivity in classifying all tissues; however, a multimodal approach resulted in a considerable increase in diagnostic accuracy (≥95%), which is of paramount importance for tumour grading and staging. The presented method offers the potential for being applied in cystoscopy and for providing an automated diagnosis of UC at the clinical level, with an improvement with respect to current state‐of‐the‐art procedures.   相似文献   
75.
Invasive animals depend on finding a balanced nutritional intake to colonize, survive, and reproduce in new environments. This can be especially challenging during situations of fluctuating cold temperatures and food scarcity, but phenotypic plasticity may offer an adaptive advantage during these periods. We examined how lifespan, fecundity, pre‐oviposition periods, and body nutrient contents were affected by dietary protein and carbohydrate (P:C) ratios at variable low temperatures in two morphs (winter morphs WM and summer morphs SM) of an invasive fly, Drosophila suzukii. The experimental conditions simulated early spring after overwintering and autumn, crucial periods for survival. At lower temperatures, post‐overwintering WM lived longer on carbohydrate‐only diets and had higher fecundity on low‐protein diets, but there was no difference in lifespan or fecundity among diets for SM. As temperatures increased, low‐protein diets resulted in higher fecundity without compromising lifespan, while high‐protein diets reduced lifespan and fecundity for both WM and SM. Both SM and WM receiving high‐protein diets had lower sugar, lipid, and glycogen (but similar protein) body contents compared to flies receiving low‐protein and carbohydrate‐only diets. This suggests that flies spend energy excreting excess dietary protein, thereby affecting lifespan and fecundity. Despite having to recover from nutrient depletion after an overwintering period, WM exhibited longer lifespan and higher fecundity than SM in favorable diets and temperatures. WM exposed to favorable low‐protein diet had higher body sugar, lipid, and protein body contents than SM, which is possibly linked to better performance. Although protein is essential for oogenesis, WM and SM flies receiving low‐protein diets did not have shorter pre‐oviposition periods compared to flies on carbohydrate‐only diets. Finding adequate carbohydrate sources to compensate protein intake is essential for the successful persistence of D. suzukii WM and SM populations during suboptimal temperatures.  相似文献   
76.
Recently, there are controversial opinions on the presence of Mycoplasmas/Ureaplasmas as colonizers or pathogens, and on the use of a targeted therapy. This study aimed to characterize Mycoplasmas/Ureaplasmas infections in reproductive age women, including the acquisition of sexually transmitted (ST) pathogens and poor birth outcomes. A total of 646 healthy Italian women fulfilled the inclusion criteria including 521 infertile women, 65 pregnant women, and 60 fertile women with identified risk factors and symptomatic for vaginitis/cervicitis. Multiplex and quantitative molecular techniques and direct automatic DNA sequencing were performed to assess the genome structure of Mycoplasma/Ureaplasma species and ST infected pathogens. Ureaplasma parvum serovar 3 represented the predominant colonizer of the urogenital tract of this series and the unique species significantly associated with ST pathogens coinfection (p < 0.01). U. parvum load >104 bacteria/ml, suggestive of active infection, has been measured only in asymptomatic high-risk human papillomavirus infected women (24.3%) and in 40% of women with idiopathic infertility. To note, 16% of the follicular fluid from these idiopathic women resulted infected with U. parvum. In conclusion, the present study focused the attention on U. parvum serovar 3 as emerging microorganism in sexually active women that may have the benefit of targeted therapy.  相似文献   
77.
Plant and Soil - The aims of this research were: i) to compare Cr, Cu, Ni and Pb concentrations in Quercus ilex L. leaves collected at urban/industrial and urban areas; ii) to investigate the main...  相似文献   
78.
Plant Molecular Biology - Overexpression of BoMYB29 gene up-regulates the aliphatic glucosinolate pathway in Brassica oleracea plants increasing the production of the anti-cancer metabolite...  相似文献   
79.
Excitatory amino acids (EAAs) are found present in the nervous and reproductive systems of animals. Numerous studies have demonstrated a regulatory role for Glutamate (Glu), d -aspartate ( d -Asp) and N-methyl- d -aspartate (NMDA) in the control of spermatogenesis. EAAs are able to stimulate the Glutamate receptors, including the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR). Here in, we assess expression of the main AMPAR subunits, GluA1 and GluA2/3, in the mouse testis and in spermatogonial GC-1 cells. The results showed that both GluA1 and GluA2/3 were localized in mouse testis prevalently in spermatogonia. The subunit GluA2/3 was more highly expressed compared with GluA1 in both the testis and the GC-1 cells. Subsequently, GC-1 cells were incubated with medium containing l -Glu, d -Glu, d -Asp or NMDA to determine GluA1 and GluA2/3 expressions. At 30 minutes and 2 hours of incubation, EAA-treated GC-1 cells showed significantly higher expression levels of both GluA1 and GluA2/3. Furthermore, p-extracellular signal-regulated kinase (ERK), p-Akt, proliferating cell nuclear antigen (PCNA), and Aurora B expressions were assayed in l -Glu-, d -Glu-, and NMDA-treated GC-1 cells. At 30 minutes and 2 hours of incubation, treated GC-1 cells showed significantly higher expression levels of p-ERK and p-Akt. A consequent increase of PCNA and Aurora B expressions was induced by l -Glu and NMDA, but not by d -Glu. Our study demonstrates a direct effect of the EAAs on spermatogonial activity. In addition, the increased protein expression levels of GluA1 and GluA2/3 in EAA-treated GC-1 cells suggest that EAAs could activate ERK and Akt pathways through the AMPAR. Finally, the increased PCNA and Aurora B levels may imply an enhanced proliferative activity.  相似文献   
80.
Extreme weather events are predicted to increase as a result of climate change, yet amphibian responses to extreme disturbance events remain understudied, especially in the Neotropics. Recently, an unprecedented windstorm within a protected Costa Rican rainforest opened large light gaps in sites where we have studied behavioral responses of diurnal strawberry poison frogs (Oophaga pumilio) to ultraviolet radiation for nearly two decades. Previous studies demonstrate that O. pumilio selects and defends perches where ultraviolet radiation (UV‐B) is relatively low, likely because of the lethal and sublethal effects of UV‐B. In this natural experiment, we quantified disturbance to O. pumilio habitat, surveyed for the presence of O. pumilio in both high‐disturbance and low‐disturbance areas of the forest, and assessed UV‐B levels and perch selection behavior in both disturbance levels. Fewer frogs were detected in high‐disturbance habitat than in low‐disturbance habitat. In general, frogs were found vocalizing at perches in both disturbance levels, and in both cases, in significantly lower UV‐B levels relative to ambient adjacent surroundings. However, frogs at perches in high‐disturbance areas were exposed to UV‐B levels nearly 10 times greater than males at perches in low‐disturbance areas. Thus, behavioral avoidance of UV‐B may not reduce the risks associated with elevated exposure under these novel conditions, and similarly, if future climate and human‐driven land‐use change lead to sustained analogous environments.  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