全文获取类型
收费全文 | 3300篇 |
免费 | 344篇 |
国内免费 | 1篇 |
出版年
2022年 | 16篇 |
2021年 | 34篇 |
2020年 | 28篇 |
2019年 | 47篇 |
2018年 | 52篇 |
2017年 | 47篇 |
2016年 | 75篇 |
2015年 | 111篇 |
2014年 | 122篇 |
2013年 | 166篇 |
2012年 | 197篇 |
2011年 | 199篇 |
2010年 | 142篇 |
2009年 | 127篇 |
2008年 | 144篇 |
2007年 | 137篇 |
2006年 | 148篇 |
2005年 | 143篇 |
2004年 | 120篇 |
2003年 | 138篇 |
2002年 | 132篇 |
2001年 | 104篇 |
2000年 | 101篇 |
1999年 | 88篇 |
1998年 | 43篇 |
1997年 | 34篇 |
1996年 | 40篇 |
1995年 | 37篇 |
1994年 | 36篇 |
1993年 | 38篇 |
1992年 | 76篇 |
1991年 | 49篇 |
1990年 | 43篇 |
1989年 | 54篇 |
1988年 | 29篇 |
1987年 | 42篇 |
1986年 | 48篇 |
1985年 | 36篇 |
1984年 | 33篇 |
1983年 | 36篇 |
1982年 | 25篇 |
1981年 | 31篇 |
1980年 | 19篇 |
1979年 | 24篇 |
1978年 | 28篇 |
1977年 | 21篇 |
1975年 | 23篇 |
1974年 | 19篇 |
1973年 | 18篇 |
1972年 | 16篇 |
排序方式: 共有3645条查询结果,搜索用时 15 毫秒
991.
992.
993.
Anna Maria Holmb?ck Michelle M Porter David Downham Jesper L Andersen Jan Lexell 《Journal of applied physiology》2003,95(6):2416-2424
The aim was to investigate determinants of ankle dorsiflexor muscle (DF) strength and size in moderately active young men and women (n = 30; age 20-31 yr). Concentric (Con) and eccentric (Ecc) strength were measured isokinetically. Magnetic resonance imaging was used to determine the muscle cross-sectional area (CSA). Multiple biopsies were obtained from the tibialis anterior muscle to determine total numbers, areas (Area I and II) and proportions (Prop I and II) of type I and II fibers, respectively, and relative contents of myosin heavy chain (MHC) isoforms MHC1, MHC2a, and MHC2x. Women had lower Con and Ecc strength (24 and 27%; P < 0.01), smaller CSA (19%; P < 0.001), lower Ecc DF specific strength (strength/CSA) (10%; P < 0.01), and smaller Area I and Area II (21 and 31%; P < 0.01) than men. Prop I, MHC1, estimated total number of fibers, and Con DF specific strength were similar for both sexes. Con DF strength was up to 72% determined by CSA and Prop I, and Ecc DF strength was up to 81% determined by CSA, Prop I, and sex; variables other than CSA explained at most 9%. Body weight and fiber areas explained >50% of the variation in CSA. In conclusion, CSA was the predominant determinant of DF strength, CSA was to a great extent determined by the body weight and the sizes of muscle fibers, and sex differences in Ecc specific strength require further study. 相似文献
994.
Todd C. LaJeunesse Georgina Lambert Robert A. Andersen Mary Alice Coffroth David W. Galbraith 《Journal of phycology》2005,41(4):880-886
Using flow cytometric analysis of fluorescence, we measured the genome sizes of 18 cultured “free‐living” species and 29 Symbiodinium spp. isolates cultured from stony corals, gorgonians, anemones, jellyfish, and giant clams. Genome size directly correlated with cell size, as documented previously for most eukaryotic cell lines. Among the smallest of dinoflagellates, Symbiodinium spp. (6–15 μm) possessed the lowest DNA content that we measured (1.5–4.8 pg·cell?1). Bloom‐forming or potentially harmful species in the genera Alexandrium, Karenia, Pfiesteria, and Prorocentrum possessed genomes approximately 2 to 50 times larger in size. A phylogenetic analysis indicated that genome/cell size has apparently increased and decreased repeatedly during the evolution of dinoflagellates. In contrast, genome sizes were relatively consistent across distantly and closely related Symbiodinium spp. This may be the product of intracellular host habitats imposing strong selective pressures that have restricted symbiont size. 相似文献
995.
S Kim S Urs F Massiera P Wortmann R Joshi Y-R Heo B Andersen H Kobayashi M Teboul G Ailhaud A Quignard-Boulangé A Fukamizu B H Jones J H Kim N Moustaid-Moussa 《Hormones et métabolisme》2002,34(11-12):721-725
To address the role of angiotensinogen (agt) in lipid metabolism and its potential endocrine effects in vivo, we studied the effects of high-fat diet (HFD) on adult, 28-week-old agt knockout (KO) mice compared to wild type (WT) mice. Recent studies (Massiera et al., 2001) have demonstrated that reexpression of agt in adipose tissue of KO mice normalized adiposity, blood pressure, and kidney abnormalities. We therefore used microarray analysis to investigate changes in gene expression profile in kidneys of KO vs. Tg-KO mice, where agt expression is restricted to adipose tissue. Body weight, adiposity and insulin levels were significantly decreased (p < 0.05) in KO mice on a chow diet (CD) compared to WT mice, while circulating leptin levels were similar. On a high-fat diet, KO mice exhibited significantly lower bodyweight (p < 0.05), adiposity (p < 0.05), leptin, and insulin levels (p < 0.05) compared to WT mice. In agreement with previously reported changes in kidney histology, agt KO mice displayed altered expressions of genes involved in blood pressure regulation and renal function, but these levels were corrected by reexpression of agt in adipose tissue. Collectively, these findings further document important endocrine roles of adipocyte agt, in part via regulation of lipid metabolism and kidney homeostasis. 相似文献
996.
John H. Loughrin Thomas R. Hamilton-Kemp Roger A. Andersen David F. Hildebrand 《Physiologia plantarum》1991,83(3):492-496
The volatile profiles from flowers of Nicotiana sylvestris and N. suaveolens were investigated by means of dynamic headspace sampling and capillary gas chromatography. Under conditions of light/dark entrainment both species emitted phenylpropanoid-derived volatiles (e.g. benzyl alcohol, methyl benzoate) with maximum emission occurring during the dark period. Emission of these compounds was demonstrated to be circadian by continuance of rhythmicity under conditions of constant light and subsequent re-entrainment to a new light/dark cycle. In contrast, emission of the sesquiterpene hydrocarbon, caryophyllene, from N. sylvestris followed no apparent pattern. The emission of monoterpene hydrocarbons from flowers of N. suaveolens showed diurnal differences only under conditions of light/dark entrainment. 相似文献
997.
Robert A. Andersen 《Nordic Journal of Botany》1989,8(6):653-669
The first flagellum of Hibberdia magna comb. nov. bears mastigonemes that have both short and long lateral filaments attached to the tubular shaft. The second flagellum is very short (ca. 850 nm) and is directed posteriorly approximately 160° from the first flagellum. Three microtubular flagellar roots (R1, R2 and R4) and a rhizoplast (= striated root) are present. The R1 root consists of four microtubules that arise near the right surface of the first flagellum basal body; the R1 root extends to the dorsal side of the cell and then curves back along the left side of the cell. Cytoskeletal microtubules are nucleated from the R1 root including one loose cluster of cytoskeletal microtubules that extends down the left side of the cell adjacent to the contractile vacuole. The R2 root is a single microtubule that arises along the left surface of the first flagellum basal body and extends to the left side of the cell. The R4 root consists of three microtubules that arise along the left side of the second flagellum basal body. A helical band wraps around two microtubules at the proximal end of the R4 root. Two of the three R4 root microtubules extend along the left side of the second flagellum, curve around to the right side of that flagellum and terminate. No R3 root was found. The orientation of the basal bodies of Hibberdia gen. nov. is similar to that of the Xanthophyceae and Oomycetes. There are apparent homologies in the R1, R2 and R4 roots of Hibberdia and these and other protists, but only Hibberdia lacks a R3 root. Three long flagella are present in preprophase but later one is endocytosized and the axoneme extends to the posterior of the cell. During metaphase the nuclear envelope is more or less intact except at the poles; the flagellar apparatuses are at the poles and the spindle microtubules originate near the basal bodies. Two stages are known in the life history: 1) a capsoidlike state with non-swimming flagellate cells inside a colonial gel, and 2) a free-swimming single-celled monad state. Vegetative cell division occurs in both stages. The flagellar apparatus, the cell division process and the life history combined with the previously described unique light-harvesting antheraxanthin make H. magna distinct from other algae. A new genus, Hibberdia gen. nov., a new family, Hibberdiaceae fam. nov. and a new order, Hibberdiales, ord. nov. are described. 相似文献
998.
Kevin Huvaere Mogens L Andersen Michael Storme Jan Van Bocxlaer Leif H Skibsted Denis De Keukeleire 《Photochemical & photobiological sciences》2006,5(10):961-969
Photooxidation of sulfur-containing amino acids and derivatives readily occurs upon visible-light irradiation in the presence of flavins. The sulfur moiety seems pivotal for interaction, as was determined from kinetic analyses using laser flash photolysis spectroscopy. After photooxidation, the resulting radical intermediates were characterized by addition to a spin trap, followed by electron paramagnetic resonance spectroscopy and evaluation of the coupling constants. The presence of the proposed radical intermediates was strongly supported by the identification of the reaction products using mass spectrometry. Accordingly, feasible degradation pathways for various sulfur-containing amino acids and derivatives were proposed. It was finally proven that flavin-induced photoproduction of sulfhydryl radicals and recombination with a 3-methylbut-2-enyl radical, derived from the photodegradation of hop-derived isohumulones, are decisive in the formation of beer lightstruck flavor. 相似文献
999.
We have studied the distribution and methylation of CpG islands on human chromosomes, using the novel technique of self-primed
in situ labeling (SPRINS). The SPRINS technique is a hybrid of the two techniques primed in situ labeling (PRINS) and nick
translation in situ. SPRINS detects chromosomal DNA breaks, as in nick translation in situ, and not annealed primers, as is
the case in PRINS. We analyzed in situ-generated DNA breaks induced by the restriction enzymes HpaII and MspI. These restriction enzymes enable the detection of chromosomal CpG islands. Both HpaII- and MspI-SPRINS produce a banding pattern resembling R-banding, indicating a higher level of CpG islands in R-positive bands than
in R-negative bands. Our SPRINS banding observations also indicate differences in sequence copy number in the satellites of
homologous acrocentric chromosomes. Furthermore, a comparison of homologous HpaII-SPRINS-banded X chromosomes of females from lymphocyte cultures grown without methotrexate or bromodeoxyuridine revealed
methylation difference between them. The same comparison of homologous X chromosomes from the cell line GM01202D, which has
four X chromosomes, one active and three inactive, revealed the active X chromosome to be hypermethylated.
Received: 5 February 1998; in revised form: 8 May 1998 / Accepted: 11 May 1998 相似文献
1000.
The effects of apomorphine (0.05, 0.1, and 1.0 mg/kg, s.c.) on K+-evoked dopamine release were studied through the use of in vivo microdialysis in the neostriatum of developing and adult rats. Fifteen-minute samples were collected from urethane-anesthetized rats 5, 10–11, 21–22, 35–36 days of age, and adults, and quantified by high performance liquid chromatography with electrochemical detection. Apomorphine attenuated K+-evoked dopamine release in all age groups, suggesting that the dopamine autoreceptor modulating release in the neostriatum is functional by 5 days of age. A dose-response effect of apomorphine was observed in all age groups except at 5 and 10 days of age. Absolute levels of extracellular dopamine were significantly lower at 5 and 10 days of age compared with the other ages, and the effectiveness of a high-K+ artificial cerebrospinal fluid to evoke dopamine release increased with age. 相似文献