全文获取类型
收费全文 | 1585篇 |
免费 | 113篇 |
出版年
2023年 | 9篇 |
2022年 | 14篇 |
2021年 | 26篇 |
2020年 | 22篇 |
2019年 | 18篇 |
2018年 | 39篇 |
2017年 | 26篇 |
2016年 | 43篇 |
2015年 | 83篇 |
2014年 | 85篇 |
2013年 | 92篇 |
2012年 | 147篇 |
2011年 | 99篇 |
2010年 | 58篇 |
2009年 | 67篇 |
2008年 | 77篇 |
2007年 | 72篇 |
2006年 | 71篇 |
2005年 | 75篇 |
2004年 | 54篇 |
2003年 | 44篇 |
2002年 | 35篇 |
2001年 | 36篇 |
2000年 | 41篇 |
1999年 | 21篇 |
1998年 | 19篇 |
1997年 | 19篇 |
1996年 | 18篇 |
1994年 | 9篇 |
1993年 | 9篇 |
1992年 | 21篇 |
1991年 | 11篇 |
1990年 | 13篇 |
1989年 | 13篇 |
1988年 | 11篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1984年 | 8篇 |
1982年 | 7篇 |
1980年 | 11篇 |
1979年 | 10篇 |
1975年 | 9篇 |
1974年 | 7篇 |
1973年 | 12篇 |
1972年 | 9篇 |
1971年 | 11篇 |
1969年 | 11篇 |
1968年 | 8篇 |
1965年 | 7篇 |
1958年 | 6篇 |
排序方式: 共有1698条查询结果,搜索用时 46 毫秒
1.
2.
3.
Andrea Schneider Manuela Ruppert Oliver Hendrich Thomas Giang Maite Ogueta Stefanie Hampel Marvin Vollbach Ansgar Büschges Henrike Scholz 《PloS one》2012,7(12)
The decision to move towards a mating partner or a food source is essential for life. The mechanisms underlying these behaviors are not well understood. Here, we investigated the role of octopamine – the invertebrate analogue of noradrenaline – in innate olfactory attraction to ethanol. We confirmed that preference is caused via an olfactory stimulus by dissecting the function of the olfactory co-receptor Orco (formally known as OR83b). Orco function is not required for ethanol recognition per se, however it plays a role in context dependent recognition of ethanol. Odor-evoked ethanol preference requires the function of Tbh (Tyramine β hydroxalyse), the rate-limiting enzyme of octopamine synthesis. In addition, neuronal activity in a subset of octopaminergic neurons is necessary for olfactory ethanol preference. Notably, a specific neuronal activation pattern of tyraminergic/octopaminergic neurons elicit preference and is therefore sufficient to induce preference. In contrast, dopamine dependent increase in locomotor activity is not sufficient for olfactory ethanol preference. Consistent with the role of noradrenaline in mammalian drug induced rewards, we provide evidence that in adult Drosophila the octopaminergic neurotransmitter functions as a reinforcer and that the molecular dissection of the innate attraction to ethanol uncovers the basic properties of a response selection system. 相似文献
4.
Arthroscopic surgery causes considerably less soft tissue damage than conventional surgery. As the result of the development of an optical system employed with a chip camera and a video chain arthroscopic knee surgery can be ideally documented with excellent picture quality. Besides the advantage of soft-tissue sparing procedures, diagnosis is substantially improved and operative procedures can be kept to a minimum. This means, in particular in the case of meniscus procedures, that only the damaged areas are removed, this minimising changes to the biomechanics of the knee. The technical equipment, the arthroscopic surgery technic and the advantages of the knee arthroscopy are discussed. 相似文献
5.
6.
Anubha Sagar Carolin Klemm Lara Hartjes Stefanie Mauerer Ger van Zandbergen Barbara Spellerberg 《PloS one》2013,8(4)
S. agalactiae (group B streptococci, GBS) is a major microbial pathogen in human neonates and causes invasive infections in pregnant women and immunocompromised individuals. The S. agalactiae β-hemolysin is regarded as an important virulence factor for the development of invasive disease. To examine the role of β-hemolysin in the interaction with professional phagocytes, the THP-1 monocytic cell line and human granulocytes were infected with a serotype Ia S. agalactiae wild type strain and its isogenic nonhemolytic mutant. We could show that the nonhemolytic mutants were able to survive in significantly higher numbers than the hemolytic wild type strain, in THP-1 macrophage-like cells and in assays with human granulocytes. Intracellular bacterial multiplication, however, could not be observed. The hemolytic wild type strain stimulated a significantly higher release of Tumor Necrosis Factor-α than the nonhemolytic mutant in THP-1 cells, while similar levels of the chemokine Interleukin-8 were induced. In order to investigate bacterial mediators of IL-8 release in this setting, purified cell wall preparations from both strains were tested and found to exert a potent proinflammatory stimulus on THP-1 cells. In conclusion, our results indicate that the β-hemolysin has a strong influence on the intracellular survival of S. agalactiae and that a tightly controlled regulation of β-hemolysin expression is required for the successful establishment of S. agalactiae in different host niches. 相似文献
7.
The influence of moulded hay (Alternaria alternata, Epicoccum nigrum, Mucor racemosus, Ulocladium chartarum) and the efficiency of Vitamin B1 substitution to cope these effects on rumen protozoa was investigated using the longterm rumen simulation technique (RUSITEC) for about 25 days. Moulded hay affected medium-sized protozoa to a different extent (Alternaria alternata: ?16 %, Epicoccum nigrum: ?27 %, Mucor racemosus: ?9 %, Ulocladium chartarum: +2 %). The vitamin B1 substitution had positive effects during the feeding of Mucor racemosus and Ulocladium chartarum. 相似文献
8.
Hildemar Scholz 《Plant Systematics and Evolution》1987,155(1-4):277-282
The syntypes ofBromus madritensis var.delilei
Boiss. comprise two different elements: specimens ofB. haussknechtii
Boiss. and ofB. fasciculatus
C. Presl s.l. By its lectotypification and on the basis of new morphological characters, the validation ofB. fasciculatus subsp.delilei (Boiss.)H. Scholz 1971 was substantiated. This subspecies represents the eastern marginal segregate of the south-Mediterranean species.B. fasciculatus var.alexandrinus
Thell. is a minor variant of the typical subspecies.Dedicated to Prof.K. H. Rechinger on the occasion of his 80th birthday. 相似文献
9.
Photon reemission in the ultraweak intensity range that is observed after irradiation of cell suspensions with light, reveals characteristic differences between normal human amnion cells and transformed Wish cells from the same parental tissue. The reemission kinetics, approximated best by a hyperbolical process, were studied as a function of cell density, showing that: malignant Wish cells have a photon storage capacity that is not improved by increasing the cell density; and that normal amnion cells exhibit a photon storage capacity that strongly increases with increasing cell density. The interpretation of this effect and the nature of the emitter are discussed. 相似文献
10.
The influence of human T lymphocytes expressing the enzyme dipeptidyl peptidase IV (DPP IV) was investigated with respect to human peripheral B-lymphocyte differentiation. B cells stimulated with pokeweed mitogen in the presence of DPP IV-positive T cells produced high amounts of immunoglobulin. Moderate amounts of immunoglobulin could be measured when B cells were cultured in the presence of DPP IV-negative T cells. DPP IV defines a T-cell subset partially overlapping the subsets characterized by the differentiation antigens Leu 3a (helper/inducer) and Leu 2a (suppressor/cytotoxic). DPP IV-positive T cells exert, in contrast to DPP IV-negative T cells, high interleukin-2 activity after stimulation with phytohemagglutinin and pokeweed mitogen. To further functionally characterize DPP IV-positive and DPP IV-negative T cells, the helper effects of Leu 3a-positive T-cell subsets, differing in DPP IV expression, were investigated in pokeweed mitogen- and Staphylococcus aureus-driven B-cell differentiation systems. After pokeweed mitogen stimulation, immunoglobulin production was markedly reduced when B cells were cultured in the presence of Leu 3a-positive T cells expressing DPP IV (DPP IV+/Leu 3a+). In contrast, high amounts of immunoglobulin were produced in cultures with Leu 3a-positive but DPP IV-negative T cells (DPP IV-/Leu 3a+). This difference in immunoglobulin production of B cells cultured with DPP IV+/Leu 3a+ and DPP IV-/Leu 3a+ T cells could not be observed in Staphylococcus aureus-stimulated cultures. Here, both T-cell subsets supported terminal differentiation of B cells. We conclude that in the pokeweed mitogen-driven culture systems, DPP IV+/Leu 3a+ and DPP IV-/Leu 3a+ T cells may differ in the production of growth and/or differentiation factors distinct from interleukin-2. 相似文献