全文获取类型
收费全文 | 2425篇 |
免费 | 231篇 |
国内免费 | 1篇 |
专业分类
2657篇 |
出版年
2023年 | 14篇 |
2022年 | 29篇 |
2021年 | 54篇 |
2020年 | 30篇 |
2019年 | 42篇 |
2018年 | 42篇 |
2017年 | 38篇 |
2016年 | 82篇 |
2015年 | 130篇 |
2014年 | 133篇 |
2013年 | 162篇 |
2012年 | 165篇 |
2011年 | 199篇 |
2010年 | 132篇 |
2009年 | 110篇 |
2008年 | 120篇 |
2007年 | 162篇 |
2006年 | 103篇 |
2005年 | 119篇 |
2004年 | 130篇 |
2003年 | 131篇 |
2002年 | 109篇 |
2001年 | 36篇 |
2000年 | 17篇 |
1999年 | 30篇 |
1998年 | 23篇 |
1997年 | 21篇 |
1996年 | 18篇 |
1995年 | 20篇 |
1994年 | 19篇 |
1993年 | 21篇 |
1992年 | 16篇 |
1991年 | 21篇 |
1990年 | 17篇 |
1989年 | 19篇 |
1988年 | 13篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 8篇 |
1983年 | 9篇 |
1982年 | 5篇 |
1981年 | 17篇 |
1980年 | 8篇 |
1979年 | 10篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1974年 | 12篇 |
1973年 | 4篇 |
1971年 | 4篇 |
排序方式: 共有2657条查询结果,搜索用时 0 毫秒
1.
2.
Kirsten Skamstrup Hansen Stefan Vieths Helle Vestergaard Per Stahl Skov Carsten Bindslev-Jensen Lars K. Poulsen 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2001,756(1-2)
The aim of the study was to investigate the possibility of a seasonal variation in reactivity to apples in 27 birch pollen allergic patients. Before and during the birch pollen season 1998, the patients were subjected to double-blind, placebo-controlled food challenges (DBPCFCs) with grated fresh Golden Delicious apple followed by an open food challenge with whole fresh apple. The clinical reactions elicited during the challenges were evaluated both by the patients and the investigators. Moreover, the skin reactivity and the in vitro reactivity to apple were evaluated by skin prick test (SPT), leukocyte histamine release (HR), measurement of specific IgE, and immunoblotting experiments. The sensitivity of the DBPCFC, when compared with the result of the open challenge, was 0.74 (14/19) before the season and 0.80 (16/20) during the season. None of the patients reacted to the blinded challenge without a subsequent reaction to the open challenge. One placebo reaction was registered both before and in season, but not in the same patient. The patient scores of the first positive challenges, and the maximal scores of each combined blinded and open challenge session, were significantly increased during the pollen season (P<0.05). The scores of the open challenge were significantly higher than the scores of the DBPCFC both before the season and during the in-season challenges (P<0.05). Specific IgE against Golden Delicious increased during season (P<0.05), while neither SPT, HR, nor immunoblotting experiments could confirm an increase in reactivity. In conclusion, the results of the oral challenge tests indicated an increase in clinical reactivity to apples during the birch pollen season in birch pollen allergic individuals. 相似文献
3.
D W Frederiksen 《Biochemistry》1979,18(9):1651-1656
Porcine aortic myosin is a smooth muscle contractile protein similar to its striated muscle counterpart. Electrophoresis in sodium dodecyl sulfate indicates that the molecule consists of three classes of subunits with polypeptide chain molecular weights of 192,000, 19,000, and 15,000. At 277 nm the absorption spectrum gives an extinction coefficient for aortic myosin of 0.558 cm2/mg; the circular dichroism spectrum of the protein indicates that aortic myosin contains about 70% of its residues in the alpha-helical configuration. Amino acid analysis shows that the smooth muscle myosin has significantly more arginine and leucine and significantly less valine and isoleucine than rabbit skeletal muscle myosin. Other studies yielded these data: Vapp = 0.716 mL/g [eta] = 0.213 mL/mg, S20, w = 5.84 x 10(-13)S. Similar studies with rabbit skeletal muscle myosin indicate that Vapp = 0.711 mL/g and S20, w = 6.36 x 10(-13)S. These properties suggest that aortic myosin, like skeletal muscle myosin, behaves hydrodynamically like a rigid rod. 相似文献
4.
A Sóoki-Tóth G Bánfalvi J Sz?ll?si E Kirsten M Staub F Antoni E Kun 《Experimental cell research》1989,184(1):44-52
Thymic cells were isolated at intervals of between 0 and 144 h from mice that received one intraperitoneal injection of emetine (33 mg/kg), and thymus weight, incorporation of [14C]leucine into proteins and [3H]thymidine into DNA in intact thymic cells, as well as initial rates of protein ADP-ribosylation in permeabilized cells [A. Sóoki-Tóth, F. Asghari, E. Kirsten, and E. Kun (1987) Exp. Cell Res. 170, 93] were simultaneously monitored. The effect of emetine as an inhibitor of protein synthesis [F. Antoni, N. G. Luat, I. Csuka, I. Oláh, A. Sóoki-Tóth, and G. Bánfalvi (1987) Int. J. Immunopharmacol. 9, 333] corresponds to the induction of sequential cellular events, such as cell exit and remigration, by other antimitotic agents [C. Penit and F. Vasseur (1988) J. Immunol. 140, 3315] and produces an activation of proliferation of cells reentering into this organ. Proliferation, as demonstrated by a large increase in DNA synthesis and entrance into S phase, was kinetically related to an apparent increase in poly(ADP-ribose) polymerase activity in thymic cells and a highly significant in vitro ADP-ribosylation of histone H3. Since no DNA fragmentation occurred in thymic cells, as tested by a fluorometric technique [C. Birnboim and J. J. Jevac (1981) Cancer Res. 41, 1889], it is probable that a selective activation of poly(ADP-ribose) polymerase may have been induced in cells that undergo differentiation and proliferation while repopulating the thymus. 相似文献
5.
Steen Kølvraa Torben A. Kruse P. K. A. Jensen Kirsten H. Linde Søren R. Vestergaard Lars Bolund 《Human genetics》1986,74(3):284-287
Summary EDA (ectodermal dysplasia, anhidrotic) is an X-linked recessive disorder characterized by hypohidrosis, hypoor anodontia, and hypotrichosis. A possible linkage between the gene for EDA and a number of restriction fragment length polymorphisms (RFLPs) spread over the X chromosome was investigated in two Danish families segregating EDA. No recombination between the gene for EDA and our probe pTAK8, which detects a two allele polymorphism in the region Xp11-q12, was found in nine informative meiotic events (seven of which are phase known), giving a maximal lod score of 2.41 at a recombination fraction of 0.00. This juxtacentromeric location of the gene for EDA agrees well with the linkage data obtained with the other markers used in this study. 相似文献
6.
7.
8.
The profundal zone of Lake Esrom, Denmark has a dense population of Chironomus anthracinus, which survives 2–4 months of oxygen depletion each summer during stratification. The metabolism of 3rd and 4th instar larvae was examined in regard to variation in biomass and temperature. Respiration at air saturation was described by a curvilinear multiple regression relating oxygen consumption to individual AFDW and temperature. At 10 °C and varying oxygen regimes the O2 consumption and CO2 production of 4th instar larvae were almost unaltered from saturation to about 3 mg O2 l–1, but decreased steeply below this level. The respiratory quotient increased from 0.82 at saturation to about 3.4 at oxygen concentrations near 0.5 mg O2 l–1. This implied a shift from aerobic to partially anaerobic metabolism. At 0.5 mg O2 l–1 the total energy production equalled 20% of the rate at saturation of which more than one third was accounted for by anaerobic degradation of glycogen. This corresponded to a daily loss of 12 µg mg AFDW–1 or approximately 5% of the body reserves. At unchanged metabolic rate the glycogen store would last three weeks, but long term oxygen deficiency causes a further suppression of the energy metabolism in C. anthracinus. 相似文献
9.
Signe Frederiksen 《Nordic Journal of Botany》1994,14(1):3-6
Hybrid plants were obtained in an intergeneric cross between Taenìatherum caputmedusae (2n = 2x = 14) and Triticum aestívum (2n = 6x = 42). The chromosome number was as expected 2n = 28. Morphologically the offspring looked like Triticum aestívum . Analysis of meiotic metaphase I showed an unexpected high number of bi- and trivalents which is ascribed to homoeologous pairing of chromosomes from T. aestivum . It is concluded that the genome of Taeniatherum has effects on the pairing regulation system present in T. aestívum . 相似文献
10.