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   6856篇
  免费   501篇
  国内免费   6篇
  2023年   45篇
  2022年   112篇
  2021年   186篇
  2020年   110篇
  2019年   122篇
  2018年   190篇
  2017年   145篇
  2016年   240篇
  2015年   332篇
  2014年   344篇
  2013年   481篇
  2012年   565篇
  2011年   566篇
  2010年   332篇
  2009年   300篇
  2008年   394篇
  2007年   443篇
  2006年   376篇
  2005年   351篇
  2004年   292篇
  2003年   292篇
  2002年   261篇
  2001年   79篇
  2000年   61篇
  1999年   58篇
  1998年   58篇
  1997年   59篇
  1996年   40篇
  1995年   38篇
  1994年   39篇
  1993年   40篇
  1992年   28篇
  1991年   29篇
  1990年   27篇
  1989年   25篇
  1988年   26篇
  1987年   20篇
  1986年   20篇
  1985年   17篇
  1984年   32篇
  1983年   16篇
  1982年   19篇
  1981年   18篇
  1980年   19篇
  1979年   11篇
  1978年   17篇
  1977年   15篇
  1975年   16篇
  1973年   7篇
  1972年   8篇
排序方式: 共有7363条查询结果,搜索用时 175 毫秒
91.
T. Binder  H. Rieth 《Mycopathologia》1965,27(1-2):17-25
Resumen 1) Se analizan las historias clínicas de 100 personas histoplasmino-positivas. 61% de ellas son histoplasmino-positivas y tuberculinonegativas, 39% histoplasmino y tuberculino-positivas.2) Se habían sacado radiografías de los pulmones a 38 de los 100 pacientes, encontrándose calcificaciones en 22, sea en un 58% de ellos.3) Se describen 4 casos: 3 de ellos con una historia y con signos radiológicos que hacen evidente que han tenido una histoplasmosis; un caso es consideredo como una histoplasmosis en evolución.4) En todos los casos se trata de formas benignas de histoplasmosis.
Summary 1) Analysis of the clinical histories of 100 histoplasmin-positive reactors: 61% are histoplasmin-positive and tuberculin-negative, 39% histoplasmin- and tuberculin-positive.2) Lung X-rays have been taken of 38 of the 100 patients. In 22 X-rays (58%) calcifications are present.3) 4 cases are described: 3 of them with a history and with radiological symptoms, that make it evident, that they have had a histoplasmosis; one case is considered as a histoplasmosis in evolution.4) All cases are benign forms of histoplasmosis.

Zusammenfassung 1) Die Krankengeschichten von 100 histoplasmin-positiven Patienten werden analysiert. 61% davon sind histoplasmin-positiv und tuberkulin-negativ, 39% histoplasmin- und tuberkulin-positiv.2) Von 38 der 100 Patienten wurden Lungenroentgenbilder aufgenommen. In 22 Aufnahmen (58%) fanden sich Verkalkungen.3) 4 Fälle werden beschrieben: bei dreien machen es Krankengeschichte und Roentgenbefund evident, dass sie eine Histoplasmose durchgemacht haben; ein Fall wird als akute Histoplasmose angesehen.4) Bei allen Fällen handelt es sich um eine gutartige Form der Histoplasmose.


Read in the meeting of the First Congress of the International Society for Tropical Dermatology, Naples, June 8–13, 1964.  相似文献   
92.

Parkinson’s disease (PD) signs and symptoms regularly include tremor. Interestingly, the nucleoside guanosine (GUO) has already proven to be effective in reducing reserpine-induced tremulous jaw movements (TJMs) in rodent models, thus becoming a promising antiparkinsonian drug. Here, we aimed at revealing the mechanism behind GUO antiparkinsonian efficacy by assessing the role of adenosine A1 and A2A receptors (A1R and A2AR) on GUO-mediated anti-tremor effects in the reserpinized mouse model of PD. Reserpinized mice showed elevated reactive oxygen species (ROS) production and cellular membrane damage in striatal slices assessed ex vivo and GUO treatment reversed ROS production. Interestingly, while the simultaneous administration of sub-effective doses of GUO (5 mg/kg) and SCH58261 (0.01 mg/kg), an A2AR antagonist, precluded reserpine-induced TJMs, these were ineffective on reverting ROS production in ex vivo experiments. Importantly, GUO was able to reduce TJM and ROS production in reserpinized mouse lacking the A2AR, thus suggesting an A2AR-independent mechanism of GUO-mediated effects. Conversely, the administration of DPCPX (0.75 mg/kg), an A1R antagonist, completely abolished both GUO-mediated anti-tremor effects and blockade of ROS production. Overall, these results indicated that GUO anti-tremor and antioxidant effects in reserpinized mice were A1R dependent but A2AR independent, thus suggesting a differential participation of adenosine receptors in GUO-mediated effects.

  相似文献   
93.
A multidisciplinary approach was carried out in order to study the biodeterioration and the associated microbiome of a XVIII Century wax seal coloured with minium. A small wax seal fragment was observed by scanning electron microscopy combined with energy dispersive spectroscopy in non-destructive mode. The same object was analysed by Raman and Fourier-transform infrared spectroscopy. The identification of the microbiota growing on the seal was performed with both a culture-dependent strategy, combined with hydrolytic assays, and high-throughput sequencing using the MinION platform. The whole bacterial 16S rRNA gene and the fungal markers ITS and 28S rRNA were targeted. It was observed that the carnauba wax coloured with lead tetroxide (minium) was covered by a biofilm consisting of a network of filaments and other structures of microbial origin. The culture-dependent and culture-independent investigations showed the presence of a complex microbiota composed mainly by fungal members, which demonstrated interesting properties related to lipids and lead processing. The formation of lead soaps and secondary biogenic minerals was also described.  相似文献   
94.
95.
Journal of Physiology and Biochemistry - Many deleterious consequences for health of excessive fat accumulation are due to visceral fat. Browning of visceral fat is mainly cold dependent and has...  相似文献   
96.
The efficiency of protected areas (PAs) has often been questioned due to global decline of biodiversity. Invertebrates, especially insects, have been historically underrepresented in conservation studies. Our study focuses on hoverflies, an important group of insect pollinators and proven to be good bioindicators. Research was focused in Serbia, one of Europe's hotspots of hoverfly diversity, with a long tradition of hoverfly research, which provided sufficient information for achieving our aims: identifying areas of high hoverfly diversity, evaluating the efficiency of PAs and prime hoverfly areas (PHAs) in the conservation of hoverflies, determining how well they cover the distribution of hoverfly species, especially those of conservation concern, and testing the importance of the size of the area for conservation of hoverfly diversity. We applied weighting of the species to help stress the importance of species of conservation concern. The results indicated that PHAs cover the areas with high hoverfly diversity better than PA networks, especially when it comes to species of conservation concern. Generalized linear model results showed that the area size was a significant predictor of number of species in both PA and PHA. This indicates that area size is key when designating new areas important for conservation, but there are also other factors that need to be taken into account, such as habitat quality or suitability. Studies like this are useful in aiding designation of new areas important for conservation of certain species and in identifying sampling gaps, which could potentially aim future research in that direction.  相似文献   
97.
Probiotics and Antimicrobial Proteins - This study aimed to characterize, evaluate toxicity and optimize the conditions for the growth and production of bacteriocin-like substances by Lactobacillus...  相似文献   
98.
Amino Acids - The polyamine (PA) metabolism is involved in cell proliferation and differentiation. Increased cellular PA levels are observed in different types of cancers. Products of PA oxidation...  相似文献   
99.
Purpose

Obsolescence, as premature end of use, increases the overall number of products produced and consumed, and thereby can increase the environmental impact. Measures to decrease the effects of obsolescence by altering the product or service design have the potential to increase use time (defined as the realized active service life) of devices, but can themselves have (environmental) drawbacks, for example, because the amount of material required for production increases. As such, paying special attention to methodological choices when assessing such measures and strategies using life cycle assessment (LCA) needs is crucial.

Methods

Open questions and key aspects of obsolescence, including the analysis of its effects and preventative measures, are discussed against the backdrop of the principles and framework for LCA given in ISO 14040/44, which includes guidance on how to define a useful functional unit and reference flow in the context of real-life use time.

Results and discussion

The open and foundational requirements of ISO 14040/14044 already form an excellent basis for analysis of the phenomenon obsolescence and its environmental impact in product comparisons. However, any analysis presumes clear definition of the goal and scope phase with special attention paid to aspects relevant to obsolescence: the target product and user group needs to be placed into context with the analysed “anti-obsolescence” measures. The reference flow needs to reflect a realized use time (and not solely a technical lifetime when not relevant for the product under study). System boundaries and types of data need to be chosen also in context of the anti-obsolescence measure to include, for example, the production of spare parts to reflect repairable design and/or manufacturer-specific yields to reflect high-quality manufacturing.

Conclusions

Understanding the relevant obsolescence conditions for the product system under study and how these may differ across the market segment or user types is crucial for a fair and useful comparison and the evaluation of anti-obsolescence measures.

  相似文献   
100.
Acoustic phenotypic variation is of major importance for speciation and the evolution of species diversity. Whereas selective and stochastic forces shaping the acoustic divergence of signaling systems are well studied in insects, frogs, and birds, knowledge on the processes driving acoustic phenotypic evolution in mammals is limited. We quantified the acoustic variation of a call type exchanged during agonistic encounters across eight distinct species of the smallest‐bodied nocturnal primate radiation, the Malagasy mouse lemurs. The species live in two different habitats (dry forest vs. humid forest), differ in geographic distance to each other, and belong to four distinct phylogenetic clades within the genus. Genetically defined species were discriminated reliably on the phenotypic level based on their acoustic distinctiveness in a discriminant function analysis. Acoustic variation was explained by genetic distance, whereas differences in morphology, forest type, or geographic distance had no effect. The strong impact of genetics was supported by a correlation between acoustic and genetic distance and the high agreement in branching pattern between the acoustic and molecular phylogenetic trees. In sum, stochastic factors such as genetic drift best explained acoustic diversification in a social communication call of mouse lemurs.  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