全文获取类型
收费全文 | 1068760篇 |
免费 | 117001篇 |
国内免费 | 409篇 |
出版年
2018年 | 10176篇 |
2017年 | 9649篇 |
2016年 | 13537篇 |
2015年 | 17882篇 |
2014年 | 21037篇 |
2013年 | 30570篇 |
2012年 | 33974篇 |
2011年 | 34923篇 |
2010年 | 23804篇 |
2009年 | 22141篇 |
2008年 | 31201篇 |
2007年 | 32387篇 |
2006年 | 30246篇 |
2005年 | 29148篇 |
2004年 | 28713篇 |
2003年 | 27739篇 |
2002年 | 27195篇 |
2001年 | 46019篇 |
2000年 | 45608篇 |
1999年 | 36480篇 |
1998年 | 13342篇 |
1997年 | 13682篇 |
1996年 | 12997篇 |
1995年 | 12545篇 |
1994年 | 12180篇 |
1993年 | 12287篇 |
1992年 | 30712篇 |
1991年 | 30164篇 |
1990年 | 29242篇 |
1989年 | 28741篇 |
1988年 | 26322篇 |
1987年 | 25454篇 |
1986年 | 23754篇 |
1985年 | 23760篇 |
1984年 | 19739篇 |
1983年 | 17152篇 |
1982年 | 13130篇 |
1981年 | 11829篇 |
1980年 | 11152篇 |
1979年 | 18645篇 |
1978年 | 14775篇 |
1977年 | 13312篇 |
1976年 | 12774篇 |
1975年 | 14192篇 |
1974年 | 15050篇 |
1973年 | 14933篇 |
1972年 | 13551篇 |
1971年 | 12292篇 |
1970年 | 10573篇 |
1969年 | 10341篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Tom P. Moorhouse Cecilia A. L. Dahlsj? Sandra E. Baker Neil C. D'Cruze David W. Macdonald 《PloS one》2015,10(10)
Tourism accounts for 9% of global GDP and comprises 1.1 billion tourist arrivals per annum. Visits to wildlife tourist attractions (WTAs) may account for 20–40% of global tourism, but no studies have audited the diversity of WTAs and their impacts on the conservation status and welfare of subject animals. We scored these impacts for 24 types of WTA, visited by 3.6–6 million tourists per year, and compared our scores to tourists’ feedback on TripAdvisor. Six WTA types (impacting 1,500–13,000 individual animals) had net positive conservation/welfare impacts, but 14 (120,000–340,000 individuals) had negative conservation impacts and 18 (230,000–550,000 individuals) had negative welfare impacts. Despite these figures only 7.8% of all tourist feedback on these WTAs was negative due to conservation/welfare concerns. We demonstrate that WTAs have substantial negative effects that are unrecognised by the majority of tourists, suggesting an urgent need for tourist education and regulation of WTAs worldwide. 相似文献
12.
Maximilian Schmid Bianca Dufner Julius Dürk Konstanze Bedal Kristina Stricker Lukas Ali Prokoph Christoph Koch Anja K. Wege Henner Zirpel Ger van Zandbergen Rupert Ecker Bogdan Boghiu Uwe Ritter 《PloS one》2015,10(10)
Characterization of host-pathogen interactions is a fundamental approach in microbiological and immunological oriented disciplines. It is commonly accepted that host cells start to change their phenotype after engulfing pathogens. Techniques such as real time PCR or ELISA were used to characterize the genes encoding proteins that are associated either with pathogen elimination or immune escape mechanisms. Most of such studies were performed in vitro using primary host cells or cell lines. Consequently, the data generated with such approaches reflect the global RNA expression or protein amount recovered from all cells in culture. This is justified when all host cells harbor an equal amount of pathogens under experimental conditions. However, the uptake of pathogens by phagocytic cells is not synchronized. Consequently, there are host cells incorporating different amounts of pathogens that might result in distinct pathogen-induced protein biosynthesis. Therefore, we established a technique able to detect and quantify the number of pathogens in the corresponding host cells using immunofluorescence-based high throughput analysis. Paired with multicolor staining of molecules of interest it is now possible to analyze the infection profile of host cell populations and the corresponding phenotype of the host cells as a result of parasite load. 相似文献
13.
Mathias Kaiser Benedikt Kirsch Hannah Hauser Désirée Schneider Ingrid Seu?-Baum Francisco M. Goycoolea 《PloS one》2015,10(10)
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
14.
15.
16.
17.
18.
19.