全文获取类型
收费全文 | 1504篇 |
免费 | 92篇 |
出版年
2021年 | 11篇 |
2018年 | 20篇 |
2017年 | 13篇 |
2016年 | 25篇 |
2015年 | 38篇 |
2014年 | 39篇 |
2013年 | 77篇 |
2012年 | 79篇 |
2011年 | 89篇 |
2010年 | 48篇 |
2009年 | 49篇 |
2008年 | 82篇 |
2007年 | 86篇 |
2006年 | 94篇 |
2005年 | 81篇 |
2004年 | 96篇 |
2003年 | 72篇 |
2002年 | 80篇 |
2001年 | 27篇 |
2000年 | 20篇 |
1999年 | 22篇 |
1998年 | 25篇 |
1997年 | 19篇 |
1996年 | 17篇 |
1995年 | 9篇 |
1994年 | 17篇 |
1993年 | 20篇 |
1992年 | 14篇 |
1991年 | 15篇 |
1990年 | 15篇 |
1989年 | 13篇 |
1987年 | 18篇 |
1986年 | 9篇 |
1985年 | 13篇 |
1984年 | 15篇 |
1983年 | 14篇 |
1982年 | 22篇 |
1981年 | 18篇 |
1980年 | 15篇 |
1979年 | 13篇 |
1978年 | 12篇 |
1976年 | 8篇 |
1975年 | 14篇 |
1974年 | 8篇 |
1973年 | 7篇 |
1971年 | 9篇 |
1970年 | 7篇 |
1969年 | 8篇 |
1968年 | 10篇 |
1966年 | 7篇 |
排序方式: 共有1596条查询结果,搜索用时 15 毫秒
1.
Hartmut Seliger Michael Hinz Sigalit Gura Boa Nitzan Shlomo Margel 《Nucleosides, nucleotides & nucleic acids》2013,32(6-7):1305-1307
Abstract The use of composite beads consisting of a 6 μm polystyrene core with 30 nm surface-bound silica particles to routine automatic oligodeoxynucleotide (ODN) synthesis is described. 相似文献
2.
Mouse polyclonal and monoclonal antibody to scrapie-associated fibril proteins. 总被引:59,自引:12,他引:47 下载免费PDF全文
R J Kascsak R Rubenstein P A Merz M Tonna-DeMasi R Fersko R I Carp H M Wisniewski H Diringer 《Journal of virology》1987,61(12):3688-3693
Antibody response in mice to scrapie-associated fibril proteins (protease-resistant proteins [PrPs]) was generated to different epitopes depending on the source of antigen. Mice responded differently to PrPs isolated from scrapie-infected animals of homologous (mouse) versus heterologous (hamster) species. An enzyme-linked immunosorbent assay established to monitor this antibody response in mice immunized with PrPs was unable to detect such a response in scrapie-infected mice. A monoclonal antibody (MAb), 263K 3F4, derived from a mouse immunized with hamster 263K PrPs reacted with hamster but not mouse PrPs. MAb 263K 3F4 also recognized normal host protein of 33 to 35 kilodaltons in brain tissue from hamsters and humans but not from bovine, mouse, rat, sheep, or rabbit brains. This is the first demonstration of epitope differences on this host protein in different species. The defining of various epitopes on PrP through the use of MAbs will lead to a better understanding of the relationship of PrPs to their host precursor protein and to the infectious scrapie agent. 相似文献
3.
A PvuII RFLP detected in the human prion protein (PrP) gene. 总被引:4,自引:1,他引:3
4.
Diurnal oscillations of steady-state mRNA levels encoding the chlorophyll a/b-binding proteins were monitored inLycopersicon esculentum, Glycine max, Phaseolus vulgaris, P. aureus, P. coccineus, Pisum sativum, Sinapis alba, Hordeum vulgare,
Triticum aestivum andZea mays. In these plant speciescab mRNA accumulation increases and decreases periodically indicating i) that the expression of the genes for chlorophyll a/b-binding
proteins (cab genes) is controlled by a circadian rhythm, and ii) that the rhythm is widely distributed among monocotyledonous and dicotyledonous
plant species. A detailed characterization of the pattern ofcab mRNA expression in tomato leaves shows that the amplitude of the oscillation is dependent on i) the developmental stage of
the leaves, ii) the circadian phase and duration of light and iii) the circadian phase and duration of darkness. In addition
to the chlorophyll a/b-binding proteins, genes coding for other cellular functions were examined for cyclic variations of
their mRNA levels. The analysis includes genes involved in i) carbon metabolism (e.g. phosphoenolpyruvate carboxylase, pyruvate
orthophosphate dikinase, alpha amylase, fructose-1,6-bisphosphate aldolase, triosephosphate isomerase), ii) photosynthesis
(large and small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase, QB-binding protein, reaction-center protein of photosystem I) and iii) other physiological or morphological reactions (e.g.
ubiquitin, actin). However, no periodic fluctuation pattern was detected for the mRNA levels of these genes in tomato and
maize leaves. 相似文献
5.
The increased expiration of ethane and pentane by mice treated with hepatotoxic doses of acetaminophen suggests the possibility of oxidant mechanisms associated with the necrosis. However, studies in rats are not consistent with oxidant stress mechanisms causing the damage, because acetaminophen given to rats does not increase GSSG efflux, a sensitive index of intrahepatic oxidant stress. To compare the extent of oxidant stress generated by acetaminophen in mice versus rats, hepatic content and biliary efflux of GSSG and GSH in mice have been examined. Bile was collected from anesthetized male ICR mice before and after intraperitoneal administration of acetaminophen (325 mg/kg, 2.15 mmol/kg), t-butyl hydroperoxide (TBHP) (1.5 mmol/kg), diethyl maleate (400 mg/kg, 2.33 mmol/kg, in corn oil) or saline (control) and GSH and GSSG were measured by the enzymatic recycling method of Tietze. An increase in biliary GSSG efflux was produced by t-butyl hydroperoxide, but not by the other agents. Biliary GSH/GSSG ratios decreased in acetaminophen-treated animals, presumably reflecting the marked depletion of hepatic GSH, since a similar decrease was observed with non-hepatotoxic doses of diethyl maleate. The failure of acetaminophen to increase the hepatic content or biliary efflux of GSSG in ICR mice is not consistent with the view that oxidant stress mechanisms cause the damage, despite the increases in alkanes expired after acetaminophen administration in this specific animal model. 相似文献
6.
In pulse-chase experiments ([35S]Met as radioactive label) 4 intracellular forms of the alpha-subunit (apparent molecular weights of 11, 16.5, 19.5, and 23.4 kDa) were observed whereas almost no label was incorporated into the beta-subunit. The 23.4 kDa form was secreted as free alpha-subunit, the others were precursors of the alpha-subunit contained in secreted human choriogonadotropin. The rate-limiting step seemed to be the processing of the 19.5 kDa precursor by alpha-mannosidase II. 8-bromo-cAMP increased the total amount of intracellular forms of the alpha-subunit and accelerated significantly the velocity of all glycosylation steps. It seemed to cause a higher efficacy of the alpha-mannosidase II reaction. In the presence of 8-bromo-cAMP intracellular as well as extracellular alpha-subunits showed a higher sialic acid content. 相似文献
7.
Hartmut Köttig Gerhard Rottner Karl-Friedrich Beck Michael Schweizer Eckhart Schweizer 《Molecular & general genetics : MGG》1991,226(1-2):310-314
Summary The fatty acid synthetase (FAS) gene FAS1 of the alkane-utilizing yeast Yarrowia lipolytica was cloned and sequenced. The gene is represented by an intron-free reading frame of 6228 by encoding a protein of 2076 amino acids and 229980 Da molecular weight. This protein exhibits a 58% sequence similarity to the corresponding Saccharomyces cerevisiae FAS -subunit. The sequential order of the five FAS1-encoded enzyme domains, acetyl transferase, enoyl reductase, dehydratase and malonyl/palmityl-transferase, is co-linear in both organisms. This finding agrees with available evidence that the functional organization of FAS genes is similar in related organisms but differs considerably between unrelated species. In addition, previously reported conflicting data concerning the 3 end of S. cerevisiae FAS1 were re-examined by genomic and cDNA sequencing of the relevant portion of the gene. Thereby, the translational stop codon was shown to lie considerably downstream of both published termination sites. The S. cerevisiae FAS1 gene thus has a corrected length of 6153 by and encodes a protein of 2051 amino acids and 228667 Da molecular weight. 相似文献
8.
Summary We tested whether larval black flies actively control the positioning of their feeding appendages (labral fans), and if so, whether their posture represents a balance between the conflicting demands of drag and feeding. We compared the postures of live larvae with the postures of larvae killed by heat-shock in three different flow regimes in a laboratory experiment; we assumed that the postures of heat-killed larvae approximated a passive response to drag. The average height of the labral fans above the bed declined significantly in faster flows, and was significantly greater in live than dead larvae. There was also a significant interaction effect, since the difference between the fan heights of live and dead larvae was greater in slower flows. Two mechanisms may contribute to this result. Larvae in slower flows have to increase their fan heights more than larvae living in faster flows to achieve comparable increases in velocity and thus particle flux. In addition, muscular strength may limit the feeding postures larvae can assume. The fan heights of live larvae also varied depending on the concentration of food particles: larvae exposed to low food concentrations held their fans higher above the bed than did larvae exposed to high food concentrations in the same flow regime. This change in posture is due neither to an uneven particle concentration in the boundary layer nor to added drag from particles trapped in the labral fans. Collectively, our results indicate that these suspension feeders actively control their feeding posture, and suggest that these varying postures represent a dynamic balance between the conflicting needs of minimizing drag and maximizing feeding. 相似文献
9.
Inhibition of early steps of de novo fatty-acid biosynthesis by different xenobiotica 总被引:1,自引:0,他引:1
The importance of the early steps of de novo fatty-acid biosynthesis is discussed in terms of rate-limiting enzymic reactions with respect to their inhibition by xenobiotics. The inhibitory spectra of allicin as an inhibitor of the acetyl-CoA-synthase, two classes of graminicides (cyclohexane-1,3-diones and aryloxyphenoxypropionic acids) as inhibitors of acetyl-CoA-carboxylase, and the two antibiotics cerulenin and thiolactomycin, which affect the condensing step in fatty-acid biosynthesis, are compared. 相似文献
10.
Gerd Wallukat Gyorgy Nemecz Tibor Farkas Hartmut Kuehn Albert Wollenberger 《Molecular and cellular biochemistry》1991,102(1):35-47
Incubation of rocker-cultured neonatal rat heart cells with 3 mM L(+)-lactate led to a sharp increase in the sensitivity of cardiomyocytes to the beta-adrenergic agonist isoprenaline, as measured by their chronotropic response. This effect was accompanied by a reduction in the arachidonic acid content of the total phospholipids. The phospholipase A2-activator melittin as well as free arachidonic acid induced this supersensitivity to the same degree. On the other hand, the L(+)-lactate-evoked supersensitivity could be blocked by the phospholipase A2 inhibitors mepacrine and n-bromophenacyl-bromide, suggesting an involvement of phospholipase A2 in the process of beta-adrenergic sensitization. The sensitizing action of arachidonic acid was blocked by the lipoxygenase inhibitors esculetin and nordihydroguaiaretic acid, but not by the cyclooxygenase inhibitor indomethacin. Supersensitivity was likewise evoked by 15-S-hydroxyeicosatetraenoic acid (15-S-HETE), but not by 5-S-HPETE or 5-S-HETE. These findings suggest that the phospholipase A2-15-lipoxygenase pathway plays a role in the induction of beta-adrenergic supersensitivity in the cultured cardiomyocytes and point to a new physiological role of the lipoxygenase product 15-S-HETE.Abbreviations NDGA
nordihydroguaiaretic acid
- HETE
hydroeicosatetraenoic acid
- HPETE
hydroperoxyeicosatetraenoic acid 相似文献