全文获取类型
收费全文 | 8052篇 |
免费 | 675篇 |
国内免费 | 4篇 |
出版年
2023年 | 33篇 |
2022年 | 55篇 |
2021年 | 172篇 |
2020年 | 79篇 |
2019年 | 126篇 |
2018年 | 152篇 |
2017年 | 124篇 |
2016年 | 216篇 |
2015年 | 385篇 |
2014年 | 511篇 |
2013年 | 604篇 |
2012年 | 673篇 |
2011年 | 677篇 |
2010年 | 429篇 |
2009年 | 414篇 |
2008年 | 537篇 |
2007年 | 519篇 |
2006年 | 510篇 |
2005年 | 472篇 |
2004年 | 432篇 |
2003年 | 390篇 |
2002年 | 389篇 |
2001年 | 64篇 |
2000年 | 61篇 |
1999年 | 84篇 |
1998年 | 90篇 |
1997年 | 54篇 |
1996年 | 46篇 |
1995年 | 49篇 |
1994年 | 43篇 |
1993年 | 38篇 |
1992年 | 27篇 |
1991年 | 21篇 |
1990年 | 24篇 |
1989年 | 28篇 |
1988年 | 16篇 |
1987年 | 26篇 |
1986年 | 22篇 |
1985年 | 13篇 |
1984年 | 7篇 |
1983年 | 15篇 |
1982年 | 11篇 |
1981年 | 9篇 |
1980年 | 20篇 |
1979年 | 12篇 |
1978年 | 10篇 |
1977年 | 10篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1974年 | 8篇 |
排序方式: 共有8731条查询结果,搜索用时 162 毫秒
1.
2.
Seabirds are affected by changes in the marine ecosystem. The influence of climatic factors on marine food webs can be reflected in long-term seabird population changes. We modelled the survival and recruitment of the Mediterranean storm petrel (Hydrobates pelagicus melitensis) using a 21-year mark-recapture dataset involving almost 5000 birds. We demonstrated a strong influence of prebreeding climatic conditions on recruitment age and of rainfall and breeding period conditions on juvenile survival. The results suggest that the juvenile survival rate of the Mediterranean subspecies may not be negatively affected by the predicted features of climate change, i.e., warmer summers and lower rainfall. Based on considerations of winter conditions in different parts of the Mediterranean, we were able to draw inferences about the wintering areas of the species for the first time. 相似文献
3.
4.
Nathalie Jeanray Rapha?l Marée Benoist Pruvot Olivier Stern Pierre Geurts Louis Wehenkel Marc Muller 《PloS one》2015,10(1)
Zebrafish is increasingly used to assess biological properties of chemical substances and thus is becoming a specific tool for toxicological and pharmacological studies. The effects of chemical substances on embryo survival and development are generally evaluated manually through microscopic observation by an expert and documented by several typical photographs. Here, we present a methodology to automatically classify brightfield images of wildtype zebrafish embryos according to their defects by using an image analysis approach based on supervised machine learning. We show that, compared to manual classification, automatic classification results in 90 to 100% agreement with consensus voting of biological experts in nine out of eleven considered defects in 3 days old zebrafish larvae. Automation of the analysis and classification of zebrafish embryo pictures reduces the workload and time required for the biological expert and increases the reproducibility and objectivity of this classification. 相似文献
5.
Jean-Michel Panoff Bouachanh Thammavongs Jean-Marie Laplace Axel Hartke Philippe Boutibonnes Yanick Auffray 《Cryobiology》1995,32(6)
The physiology of the cold-shock response in Lactococcus lactis subsp. lactis IL1403 at a subzero temperature, and cold-induced adaptation to heat shock, were investigated. Preincubation of cells at 8°C led to the development of cryotolerance, i.e., an enhanced capacity to survive exposure to freezing temperature (-20°C). Pretreatment with chemicals considered to be chaotropic agents did not induce cryotolerance or, in contrast, led to a decrease in survival capacity at -20°C. Interestingly, preincubation at 8°C led also to thermololerance to a 52°C challenge, but preincubation of cells at 42°C for 30 min did not improve their capacity to survive freezing-thawing exposure. These results demonstrate that cold- and heat-shock responses are physiologically linked by a complex relation. Furthermore, food processing at low temperature before subzero or heat treatment may need to be reconsidered. 相似文献
6.
Summary Bacterial strains identified as Klebsiella pneumonia and Corynebacterium sp. degraded in few hours a great part of pure tara (Caesalpinia spinosa) tannin or crude water extract of tara pods powder. Large amounts of gallic acid were recovered during some experiments reaching 55 % of the theoretical yield in the best case. The feasibility of gallic acid production by a biotechnological process is discussed. 相似文献
7.
8.
9.
10.
Depressive symptoms during pregnancy are common and may have impact on the developing child. Selective serotonin reuptake inhibitors (SSRIs) are the most prescribed antidepressant treatment, but unfortunately, these treatments can also negatively affect the behavioral development and health of a child during pregnancy. In addition, serotonin (5-HT) exerts neurotrophic actions with thus far not fully known effects in the offspring. The neurotrophic growth factor (NGF) is involved in neuronal cell survival and differentiation, and altered placenta levels have been found to increase the risk for pregnancy complications, similar to those found in women treated with SSRIs. We therefore investigated whether the NGF signaling pathway was altered in the placenta from women treated with SSRIs (n = 12) and compared them with placenta from depressed (n = 12) and healthy mothers (n = 12). Results from immunohistochemical stainings revealed that placental NGF protein levels of SSRI-treated women were increased in both trophoblasts and endothelial cells compared with depressed and control women. In addition, downstream of the NGF receptor TrkA, increased levels of the signaling proteins ROCK2 and phosphorylated Raf-1 were found in stromal cells and a tendency towards increased levels of ROCK2 in trophoblasts and endothelial cells in SSRI-treated women when compared to healthy controls. SSRI-treated women also displayed increased levels of phosphorylated ROCK2 in all placental cell types studied in comparison with depressed and control women. Interestingly, in placental endothelial cells from depressed women, NGF levels were significantly lower compared to control women, but ROCK2 levels were increased compared with control and SSRI-treated women. Taken together, these results show that the NGF signaling and downstream pathways in the placenta are affected by SSRI treatment and/or antenatal depression. This might lead to an altered placental function, although the clinical relevance of our findings still needs to be investigated. 相似文献