全文获取类型
收费全文 | 5217篇 |
免费 | 360篇 |
国内免费 | 1篇 |
出版年
2023年 | 36篇 |
2022年 | 77篇 |
2021年 | 132篇 |
2020年 | 92篇 |
2019年 | 109篇 |
2018年 | 122篇 |
2017年 | 101篇 |
2016年 | 177篇 |
2015年 | 286篇 |
2014年 | 314篇 |
2013年 | 391篇 |
2012年 | 478篇 |
2011年 | 401篇 |
2010年 | 282篇 |
2009年 | 239篇 |
2008年 | 326篇 |
2007年 | 319篇 |
2006年 | 285篇 |
2005年 | 238篇 |
2004年 | 203篇 |
2003年 | 206篇 |
2002年 | 166篇 |
2001年 | 47篇 |
2000年 | 47篇 |
1999年 | 44篇 |
1998年 | 28篇 |
1997年 | 29篇 |
1996年 | 37篇 |
1995年 | 31篇 |
1994年 | 24篇 |
1993年 | 28篇 |
1992年 | 33篇 |
1991年 | 29篇 |
1990年 | 25篇 |
1989年 | 19篇 |
1988年 | 20篇 |
1987年 | 14篇 |
1986年 | 16篇 |
1985年 | 17篇 |
1984年 | 11篇 |
1983年 | 8篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 10篇 |
1979年 | 12篇 |
1978年 | 9篇 |
1976年 | 4篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1973年 | 8篇 |
排序方式: 共有5578条查询结果,搜索用时 15 毫秒
1.
2.
Sequence complexity and diversity of polyadenylated RNA molecules transcribed in human myeloid cells
3.
Amy Chapman Gonzalo Gonzales Wayne R. Burrowes Paul Assanah Bernadette Iannone Michael K. Leung George B. Stefano 《Cellular and molecular neurobiology》1984,4(2):143-155
In Mytilus and Leucophaea the high-affinity binding site density is significantly lower in old animals than in young animals, whereas the low-affinity site density remains unchanged. In Mytilus the estimated met-enkephalin and met-enkephalin-Arg6-Phe7 levels are significantly higher in old than in young animals. In Leucophaea only the met-enkephalin level can be determined, and it is also higher in old animals. The decrease in the high-affinity binding site density and the corresponding increase in endogenous enkephalin levels suggest the existence of an opioid compensatory mechanism associated with the aging process. In Mytilus there is a demonstrated decrease with age in intraganglionic dopamine levels in response to applied opiates. In addition, the inhibition of dopamine-stimulated adenylate cyclase activity by opiates also decreases in older animals. In Leucophaea the sex difference in opioid binding densities diminishes with age. 相似文献
4.
5.
6.
Food subsidies have the potential to modify ecosystems and affect the provision of goods and services. Predictable Anthropogenic Food Subsidies (PAFS) modify ecosystems by altering ecological processes and food webs. The global concern over the effects of PAFS in ecosystems has led to development of environmental policies aimed at curbing the production or ultimately banning of PAFS. However, the effects of reducing or banning PAFS are not known. We explore the consequences of PAFS removal in a marine ecosystem under two scenarios: 1) gradual reduction, or 2) an abrupt ban, using a mass balance model to test these hypotheses–The reduction or loss of PAFS will: i) modify trophic levels and food webs through effects on foraging by opportunistic species, ii) increase the resilience of opportunistic species to food shortages, and iii) modify predator–prey interactions through shifts in prey consumption. We found that PAFS lower the trophic levels of opportunistic scavengers and increase their food pathways. Scavengers are able to switch prey when PAFS are reduced gradually but they decline when PAFS are abruptly banned. PAFS reduction to a certain minimal level causes a drop in the ecosystem’s stability. We recommend gradual reduction of PAFS to a minimal level that would maintain the ecosystem’s stability and allow species exploiting PAFS to habituate to the food subsidy reduction. 相似文献
7.
Cristina Cereda Emanuela Leoni Pamela Milani Orietta Pansarasa Giuliano Mazzini Stefania Guareschi Elena Alvisi Andrea Ghiroldi Luca Diamanti Stefano Bernuzzi Mauro Ceroni Emanuela Cova 《PloS one》2013,8(10)
Several lines of evidence support the hypothesis of a toxic role played by wild type SOD1 (WT-SOD1) in the pathogenesis of sporadic amyotrophic lateral sclerosis (SALS). In this study we investigated both distribution and expression profile of WT-SOD1 in leukocytes from 19 SALS patients and 17 healthy individuals. Immunofluorescence experiments by confocal microscopy showed that SOD1 accumulates in the nuclear compartment in a group of SALS subjects. These results were also confirmed by western blot carried out on soluble nuclear and cytoplasmic fractions, with increased nuclear SOD1 level (p<0.05). In addition, we observed the presence of cytoplasmic SOD1 aggregates in agreement with an increased amount of the protein recovered by the insoluble fraction. A further confirmation of the overall increased level of SOD1 has been obtained from single cells analysis using flow cytometry as cells from SALS patients showed an higher SOD1 protein content (p<0.05). These findings add further evidence to the hypothesis of an altered WT-SOD1 expression profile in peripheral blood mononuclear cells (PBMCs) from patients with ALS suggesting that WT-SOD1 species with different degrees of solubility could be involved in the pathogenesis of the disease. 相似文献
8.
9.
Pirjo Rajaniemi‐Wacklin Anne Rantala Maria. A. Mugnai Silvia Turicchia Stefano Ventura Jarka Komrkov Liisa Lepist Kaarina Sivonen 《Journal of phycology》2006,42(1):226-232
In this study, the first reported isolates of the genera Snowella and Woronichinia were characterized by 16S rRNA gene sequencing and morphological analysis. Phylogenetic studies and sequences for these genera were not available previously. By botanical criteria, the five isolated strains were identified as Snowella litoralis (Häyrén) Komárek et Hindák Snowella rosea (Snow) Elenkin and Woronichinia naegeliana (Unger) Elenkin. This study underlines the identification of freshly isolated cultures, since the Snowella strains lost the colony structure and were not identifiable after extended laboratory cultivation. In the 16S rRNA gene analysis, the Snowella strains formed a monophyletic cluster, which was most closely related to the Woronichinia strain. Thus, our results show that the morphology of the genera Snowella and Woronichinia was in congruence with their phylogeny, and their phylogeny seems to support the traditional botanical classification of these genera. Furthermore, the genera Snowella and Woronichinia occurred commonly and might occasionally be the most abundant cyanobacterial taxa in mainly oligotrophic and mesotrophic Finnish lakes. Woronichinia occurred frequently and also formed blooms in eutrophic Czech reservoirs. 相似文献
10.