全文获取类型
收费全文 | 20386篇 |
免费 | 1889篇 |
国内免费 | 13篇 |
专业分类
22288篇 |
出版年
2023年 | 121篇 |
2022年 | 300篇 |
2021年 | 563篇 |
2020年 | 266篇 |
2019年 | 388篇 |
2018年 | 435篇 |
2017年 | 340篇 |
2016年 | 586篇 |
2015年 | 985篇 |
2014年 | 1020篇 |
2013年 | 1399篇 |
2012年 | 1597篇 |
2011年 | 1565篇 |
2010年 | 967篇 |
2009年 | 844篇 |
2008年 | 1212篇 |
2007年 | 1192篇 |
2006年 | 1073篇 |
2005年 | 1015篇 |
2004年 | 914篇 |
2003年 | 852篇 |
2002年 | 823篇 |
2001年 | 197篇 |
2000年 | 153篇 |
1999年 | 178篇 |
1998年 | 168篇 |
1997年 | 140篇 |
1996年 | 116篇 |
1995年 | 110篇 |
1994年 | 116篇 |
1993年 | 112篇 |
1992年 | 119篇 |
1991年 | 107篇 |
1990年 | 97篇 |
1989年 | 85篇 |
1988年 | 92篇 |
1987年 | 72篇 |
1986年 | 66篇 |
1985年 | 89篇 |
1984年 | 96篇 |
1983年 | 62篇 |
1982年 | 81篇 |
1981年 | 72篇 |
1980年 | 67篇 |
1979年 | 77篇 |
1978年 | 54篇 |
1977年 | 60篇 |
1976年 | 65篇 |
1975年 | 70篇 |
1973年 | 55篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
52.
53.
55.
Mathew Alexander Vadas 《Immunogenetics》1980,11(1):215-223
Parasite infestations offer fertile ground for investigation of the relationship between immunity, disease and the major histocompatibility complex (MHC). However, due to the complexities of parasite life cycles and the success of parasites in evading the immune response, immune reactions against the parasite often do not parallel protective immunity, and immunity does not imply lack of disease. — An additional level of complexity is introduced in some forms of parasite immunity by accessory effector cells, e. g., macrophages and eosinophils, that need to be activated for maximal effectiveness, and the activated form of these cells may partly compensate for a deficiency in specific immune responses. — It is not surprising, therefore, that polygenic effects operate in parasite immunity and reports linking non-MHC genes with parasite immunity far out number those linking MHC genes with it. From the reports that do link MHC genes with parasite immunity, two areas emerge that are interesting. First, the increased incidence of certainHLA genes in people with schistosomiasis who develop hepatosplenic disease may pinpoint individuals at risk of morbidity and direct early treatment to them. Second, mechanisms that intimately involve MHC products but are not linked to a particular MHC haplotype, may indicate newer areas in the investigation of parasite immunity. 相似文献
56.
Variations in the chemical flavour composition of three cultivars of cabbage were determined for plants of different horticultural histories. In some i 相似文献
57.
Bacteria able to use at least one of 13 ionic alkylphosphonates of O-alkyl or O,O-dialkyl alkylphosphonates as phosphorus sources were isolated from sewage and soil. Four of these isolates used 2-aminoethylphosphonic acid (AEP) as a sole carbon, nitrogen, and phosphorus source. None of the other phosphonates served as a carbon source for the organisms. One isolate, identified as Pseudomonas putida, grew with AEP as its sole carbon, nitrogen, and phosphorus source and released nearly all of the organic phosphorus as orthophosphate and 72% of the AEP nitrogen as ammonium. This is the first demonstration of utilization of a phosphonoalkyl moiety as a sole carbon source. Cell-free extracts of P. putida contained an inducible enzyme system that required pyruvate and pyridoxal phosphate to release orthophosphate from AEP; acetaldehyde was tentatively identified as a second product. Phosphite inhibited the enzyme system. 相似文献
58.
59.
R. McN. Alexander 《Journal of Zoology》1983,201(3):363-376
Pachyornis , which is extinct, was a huge bird with massively thick leg bones. These have been measured, to assess their strength. A mathematical model is used to calculate the forces that must have acted on them, when Pachyornis ran. Hence it is shown that the stresses likely to have acted on them are similar in magnitude to the stresses experienced (in stenuous activities) by bones of modem birds and mammals. The femur and tarsometatanus, however, seem disproportionately strong in comparison with the tibiotanus. 相似文献
60.
Characterization of the calmodulin binding domain of neuromodulin. Functional significance of serine 41 and phenylalanine 42. 总被引:14,自引:0,他引:14
E R Chapman D Au K A Alexander T A Nicolson D R Storm 《The Journal of biological chemistry》1991,266(1):207-213
Neuromodulin (also designated P-57, GAP-43, B-50) is a major presynaptic substrate for protein kinase C. Phosphorylation of neuromodulin decreases its affinity for calmodulin, suggesting that neuromodulin may function to bind and concentrate calmodulin at specific sites within neurons, releasing calmodulin locally in response to phosphorylation by protein kinase C (Alexander, K. A., Cimler, B. M., Meier, K. E., and Storm, D. R. (1987) J. Biol. Chem. 262, 6108-6113). In the present study, we have constructed and characterized several mutant neuromodulins to demonstrate that the amino acid sequence 39-56 is required for calmodulin binding, and that this domain contains the sole in vitro protein kinase C phosphorylation site at serine 41. We also demonstrate that the adjacent phenylalanine 42, interacts hydrophobically with calmodulin. These hydrophobic interactions may be disrupted by the introduction of negative charge at serine 41, and thereby regulate the neuromodulin/calmodulin binding interactions. The sensitivity of the neuromodulin/calmodulin binding interaction to negative charge at serine 41 was determined by substitution of serine 41 with an aspartate or an asparagine residue. The asparagine mutant retained its affinity for calmodulin-Sepharose while the aspartate mutant did not adsorb to calmodulin-Sepharose. We conclude that protein kinase C phosphorylation of neuromodulin abolishes calmodulin binding by introducing negative charges within the calmodulin binding domain at a position adjacent to the phenylalanine. 相似文献