全文获取类型
收费全文 | 1982篇 |
免费 | 156篇 |
专业分类
2138篇 |
出版年
2023年 | 6篇 |
2022年 | 26篇 |
2021年 | 32篇 |
2020年 | 24篇 |
2019年 | 31篇 |
2018年 | 49篇 |
2017年 | 29篇 |
2016年 | 58篇 |
2015年 | 87篇 |
2014年 | 86篇 |
2013年 | 144篇 |
2012年 | 148篇 |
2011年 | 143篇 |
2010年 | 109篇 |
2009年 | 98篇 |
2008年 | 143篇 |
2007年 | 127篇 |
2006年 | 114篇 |
2005年 | 117篇 |
2004年 | 107篇 |
2003年 | 91篇 |
2002年 | 87篇 |
2001年 | 13篇 |
2000年 | 20篇 |
1999年 | 24篇 |
1998年 | 25篇 |
1997年 | 17篇 |
1996年 | 14篇 |
1995年 | 12篇 |
1994年 | 18篇 |
1993年 | 13篇 |
1992年 | 13篇 |
1991年 | 10篇 |
1990年 | 12篇 |
1989年 | 9篇 |
1988年 | 7篇 |
1987年 | 3篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 10篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1975年 | 2篇 |
1974年 | 4篇 |
1964年 | 2篇 |
排序方式: 共有2138条查询结果,搜索用时 0 毫秒
991.
992.
Fontanesi L Speroni C Buttazzoni L Scotti E Dall'Olio S Davoli R Russo V 《Molecular biology reports》2012,39(1):109-115
We genotyped single nucleotide polymorphisms (SNPs) in 5 cathepsin or cystatin genes (cathepsin F, CTSF; cathepsin L, CTSL; cathepsin S, CTSS; cathepsin Z, CTSZ; cystatin B, CSTB) in two groups of Italian Duroc pigs: the first group (n. 100) was chosen using a selective genotyping approach with extreme
estimated breeding value (EBV) for visible intermuscular fat (VIF); the second group (n. 218) was made of performance-tested
Duroc pigs not selected by any criteria. CTSL marker showed a tendency towards association (P < 0.10) with VIF (first group) and back fat thickness (BFT) and average daily gain (ADG; second group). In the second group,
the CTSL polymorphism was associated with weight of lean cuts (LC; P < 0.05). Additive effects for all mentioned traits in the second group was significant (P < 0.05). The results we obtained in the Italian Duroc pigs confirmed the results and the direction of the effects already
reported for the Italian Large White breed. 相似文献
993.
Prada N Nasi M Troiano L Roat E Pinti M Nemes E Lugli E Ferraresi R Ciacci L Bertoni D Biagioni O Gibertoni M Cornia C Meschiari L Gramazio E Mariotti M Consolo U Balli F Cossarizza A 《Immunity & ageing : I & A》2005,2(1):4-8
BACKGROUND: Down's syndrome (DS) is characterized by several immunological defects, especially regarding T cell compartment. DS is considered the best example of accelerated ageing in humans. Direct observations of the thymus have shown that in DS this organ undergoes severe histological and morphological changes. However, no data on its capacity to generate T cells are present in the literature. Here, using a new technology based upon real time PCR, we have investigated the capacity of the thymus to produce and release newly generated T lymphocytes (the so called "recent thymic emigrants", RTE) in children with DS. METHODS: We studied 8 children affected by DS, aged 2-7 years, compared with 8 age- and sex-matched healthy controls. Flow cytometry was used to determine different lymphocytes subsets. Real time PCR with the Taqman system was used to quantify the amount of RTE, i.e. peripheral blood lymphocytes that express the T cell receptor rearrangement excision circles (TREC). RESULTS: In comparison with control children, those with DS had a significant lower number of TREC+ peripheral blood cells. Moreover, in DS children but not in controls, a strong negative correlation between age and the levels of TREC+ cells was found. CONCLUSIONS: The direct measure of thymic output indicates that the impairment of the organ results in a reduced production of newly generated T cells. This observation could suggest that cytokines able to modulate thymic function, such as interleukins, could be useful to improve the functionality of the organ and to treat the immunodeficiency present in DS subjects. 相似文献
994.
Deregowski V Gazzerro E Priest L Rydziel S Canalis E 《The Journal of biological chemistry》2006,281(10):6203-6210
Notch proteins are transmembrane receptors that control cell-fate decisions. Upon ligand binding, Notch receptors undergo proteolytic cleavage leading to the release of their intracellular domain (NICD). Overexpression of NICD impairs osteoblastogenesis, but the mechanisms are not understood. We examined consequences of the constitutive activation of Notch 1 in ST-2 cells. Notch opposed the effects of bone morphogenetic protein (BMP)-2 and Wnt 3a on alkaline phosphatase activity (APA). BMP-2 induced the phosphorylation of Smad 1/5/8 and the transactivation of a BMP/Smad-responsive construct (12xSBE-Oc-pGL3), but the effect was not modified by Notch. BMP-2 had minimal effects on the phosphorylation of the mitogen-activated protein kinases ERK, p38, and JNK, in the absence or presence of NICD. Notch overexpression decreased the transactivating effect of Wnt 3a, cytoplasmic beta-catenin levels, and Wnt-dependent gene expression. Transfection of a mutant beta-catenin expression construct, or the use of a glycogen synthase kinase 3beta inhibitor to stabilize beta-catenin, partially blocked the inhibitory effect of NICD on Wnt signaling and on APA. HES-1 or Groucho1/TLE1 RNA interference enhanced basal and induced Wnt/beta-catenin signaling opposing NICD effects, but only HES-1 silencing enhanced Wnt 3a effects on APA. In conclusion, NICD overexpression prevents BMP-2 and Wnt biological effects by suppressing Wnt but not BMP signaling. HES-1 appears to mediate effects of Notch on osteoblastogenesis. 相似文献
995.
Dynamics of Persistent TT Virus Infection, as Determined in Patients Treated with Alpha Interferon for Concomitant Hepatitis C Virus Infection 下载免费PDF全文
Fabrizio Maggi Mauro Pistello Marialinda Vatteroni Silvano Presciuttini Santino Marchi Patrizia Isola Claudia Fornai Sabina Fagnani Elisabetta Andreoli Guido Antonelli Mauro Bendinelli 《Journal of virology》2001,75(24):11999-12004
TT virus (TTV) is a recently identified widespread DNA virus of humans that produces persistent viremia in the absence of overt clinical manifestations. In an attempt to shed light on the dynamics of chronic infection, we measured the levels of TTV in the plasma of 25 persistently infected patients during the first 3 months of alpha interferon (IFN-alpha) treatment for concomitant hepatitis C virus (HCV) infection. The first significant decline of TTV loads was observed at day 3 versus day 1 for HCV. Subsequently, the loads of TTV became progressively lower in most patients, but some initial responders relapsed before the end of the follow-up, suggesting that at least in some subjects the effects of IFN on TTV can be very short-lived. No correlation between the responses of TTV and HCV to therapy was found. Fitting the viremia data obtained during the first week of treatment into previously developed mathematical models showed that TTV sustains very active chronic infections, with over 90% of the virions in plasma cleared and replenished daily and a minimum of approximately 3.8 x 10(10) virions generated per day. Low levels of TTV were occasionally detected in the peripheral blood mononuclear cells of patients who had cleared plasma viremia, thus corroborating previous results showing that these cells may support TTV replication and/or persistence. 相似文献
996.
Florence has a tradition of Natural Philosophy, and since as early as the sixteenth century fossils were collected by the Granduke. The Museum of Natural History of the University of Florence houses today collections that belonged to Nicolas Steno, when fossils were for the first time used as documents to reconstruct Earth history. Natural philosophers and geologists, both Italian and foreigners, continued to study fossils collected in Tertiary strata of Tuscany until the nineteenth century, when the first speculations on the origin of species were proposed. Charles Darwin himself mentions fossil vertebrates that are today on show in our museum. In the last years, this part of the history of science has been proposed to the public. The aim was to foster an understanding of the centrality of fossils in two cultural revolutions, the discovery of deep time and the birth of evolutionary theory–connected among themselves and with the emergence of geology. Dedicated volumes, public conferences, guided visits to the collections, and field trips to paleontological sites have attracted an attentive and responsive public, showing that the history of science can help deliver modern evolutionary thinking. Other activities aimed at students of all ages have also shown that the interaction between schools, university teachers, and museum personnel is vital to form the mind of future generations on the reality of the evolution of natural systems. 相似文献
997.
998.
Palazzo E Marconi A Truzzi F Dallaglio K Petrachi T Humbert P Schnebert S Perrier E Dumas M Pincelli C 《Journal of cellular physiology》2012,227(3):1017-1025
Neurotrophins (NTs) belong to a family of growth factors that play a critical role in the control of skin homeostasis. NTs act through the low-affinity receptor p75NTR and the high-affinity receptors TrkA, TrkB, and TrkC. Here we show that dermal fibroblasts (DF) and myofibroblasts (DM) synthesize and secrete all NTs and express NT receptors. NTs induce differentiation of DF into DM, as shown by the expression of α-SMA protein. The Trk inhibitor K252a, TrkA/Fc, TrkB/Fc, or TrkC/Fc chimera prevents DF and DM proliferation. In addition, p75NTR siRNA inhibits DF proliferation, indicating that both NT receptors mediate DF proliferation induced by endogenous NTs. Autocrine NTs also induce DF migration through p75NTR and Trk, as either silencing of p75NTR or Trk/Fc chimeras prevent this effect, in absence of exogenous NTs. Finally, NGF or BDNF statistically increase the tensile strength in a dose dependent manner, as measured in a collagen gel through the GlaSbox device. Taken together, these results indicate that NTs exert a critical role on fibroblast and could be involved in tissue re-modeling and wound healing. 相似文献
999.
Olaf Kinzel Daniela Fattori Paolo Ingallinella Elisabetta Bianchi Antonello Pessi 《Journal of peptide science》2003,9(6):375-385
The synthesis of a high affinity mannose receptor ligand, appropriately functionalized for chemoselective ligation with an antigen or DNA-binding moieties is described. By a combination of solid- and solution-phase chemistry a versatile synthesis of the target structure was accomplished. Examples of subsequent ligation reactions are described. 相似文献
1000.