全文获取类型
收费全文 | 2183篇 |
免费 | 91篇 |
国内免费 | 52篇 |
出版年
2023年 | 25篇 |
2022年 | 16篇 |
2021年 | 42篇 |
2020年 | 48篇 |
2019年 | 72篇 |
2018年 | 88篇 |
2017年 | 34篇 |
2016年 | 35篇 |
2015年 | 44篇 |
2014年 | 156篇 |
2013年 | 161篇 |
2012年 | 90篇 |
2011年 | 118篇 |
2010年 | 66篇 |
2009年 | 83篇 |
2008年 | 92篇 |
2007年 | 80篇 |
2006年 | 70篇 |
2005年 | 83篇 |
2004年 | 53篇 |
2003年 | 58篇 |
2002年 | 40篇 |
2001年 | 41篇 |
2000年 | 39篇 |
1999年 | 25篇 |
1998年 | 33篇 |
1997年 | 34篇 |
1996年 | 19篇 |
1995年 | 18篇 |
1994年 | 18篇 |
1993年 | 15篇 |
1992年 | 15篇 |
1991年 | 14篇 |
1990年 | 24篇 |
1989年 | 15篇 |
1987年 | 16篇 |
1986年 | 8篇 |
1985年 | 28篇 |
1984年 | 32篇 |
1983年 | 33篇 |
1982年 | 42篇 |
1981年 | 41篇 |
1980年 | 45篇 |
1979年 | 45篇 |
1978年 | 37篇 |
1977年 | 41篇 |
1976年 | 29篇 |
1975年 | 17篇 |
1974年 | 16篇 |
1973年 | 20篇 |
排序方式: 共有2326条查询结果,搜索用时 15 毫秒
1.
Activity, control and primer requirements of starch phosphorylase in developing barley endosperm were investigated. Phosphorylase was detected in endosperm extracts from 3 days after anthesis. Unprimed activity was predominant between 2 and 10 days after anthesis, when it constituted 70–80% of total activity, but this proportion declined rapidly as the grain developed. The existence of at least 2 isoenzymes was indicated by studies of pH dependence and phosphate inhibition, and was further supported by acrylamide gel electrophoresis and column chromatography using DEAE-cellulose. The two isoenzymes which ere possibly both glyco proteins, appear in barley endosperm soon after anthesis. One appears capable of unprimed activity, and may be associated with the initiation of a-1,2 glucans, which then serve as primers for starch synthetase. This disappears by 13–15 days after anthesis. The other isoenzyme is capable of some unprimed activity but undergoes modification between 15 and 20 days after anthesis, resulting in the loss of unprimed activity. The relevance of the results to initiation of starch synthesis and to starch synthetase in amyloplasts is discussed. 相似文献
2.
Inhibition of the Bacterial Cell Wall Synthesis in vitro by Enduracidin,a New Polypeptide Antibiotic
Michio Matsuhashi Ikuko Ohara Yoshihiro Yoshiyama 《Bioscience, biotechnology, and biochemistry》2013,77(1):134-137
Adenosine 5′-phosphosulfate (APS) kinase from a thermophilic bacterium, Bacillus st ear other mophilus, was purified to apparent homogeneity. The apparent molecular weight was 50 kDa, consisting of two 26-kDa subunits. The enzyme was very thermostable and lacked cysteine and methionine residues. Enzyme activity was more stimulated with Mn2 + , Zn2 +, or Co2 + than with Mg2 + and the Km for ATP and APS were 220 µM and 42 µM, respectively. 相似文献
3.
The intrinsic activity of the C‐terminal catalytic (C) domain of cyclic guanosine monophosphate (cGMP)‐dependent protein kinases (PKG) is inhibited by interactions with the N‐terminal regulatory (R) domain. Selective binding of cGMP to cyclic nucleotide binding (CNB) domains within the R‐domain disrupts the inhibitory R–C interaction, leading to the release and activation of the C‐domain. Affinity measurements of mammalian and plasmodium PKG CNB domains reveal different degrees of cyclic nucleotide affinity and selectivity; the CNB domains adjacent to the C‐domain are more cGMP selective and therefore critical for cGMP‐dependent activation. Crystal structures of isolated CNB domains in the presence and absence of cyclic nucleotides reveal isozyme‐specific contacts that explain cyclic nucleotide selectivity and conformational changes that accompany CNB. Crystal structures of tandem CNB domains identify two types of CNB‐mediated dimeric contacts that indicate cGMP‐driven reorganization of domain–domain interfaces that include large conformational changes. Here, we review the available structural and functional information of PKG CNB domains that further advance our understanding of cGMP mediated regulation and activation of PKG isozymes. 相似文献
4.
A method is described for the subcellular fractionation of goldfish xanthophores. The procedure produces relatively pure fractions of caroteniod droplets, pterinosomes, cytosol and what appears to be plasma membrane. The presence of a distinct pattern of proteins is shown to be associated with the carotenoid droplets. Treatment of the xanthophores with ACTH affects the buoyant density of some carotenoid droplets and stimulates the phosphorylation of a polypeptide associated with the carotenoid droplets. 相似文献
5.
Gerda Tyrsted Pao-chang Chao Birgitte Munch-Petersen 《Molecular and cellular biochemistry》1987,76(1):27-34
Deoxycytidylate deaminase isolated from normal human lymphocytes and from mononuclear leucocytes from patients with acute lymphoblastic leukemia, chronic lymphocytic leukemia and acute monocytic leukemia has been characterized in regard to the substrate, dAMP and the allosteric regulators dCTP and dTTP. The enzymes exhibited sigmoidal initial velocity versus dCMP concentration whereas in the presence of the activator, dCTP, Michaelis-Menten kinetics were obtained.At saturating substrate concentrations dTTP acted as an allosteric inhibitor of the enzyme isolated from non-stimulated as well as from stimulated lymphocytes. However, the enzymes isolated from the leukemic cells had lost the allosteric regulation by dTTP.At low substrate concentrations the competitive inhibitor, dAMP, activated all the enzymes. This activation was abolished in the presence of dCTP which indicates that dAMP might be involved in the regulation of dCMP deaminase activity and thus influence the dCTP and dTTP pools under physiological conditions.Abbreviations dCMP deaminase
deoxycytidylate deaminase
- PHA
Phytohemagglutinin
- ALL
acute lymphoblastic leukemia
- CLL
chronic lymphocytic leukemia
- AMOL
acute monocytic leukemia
- WBC
white blood cells 相似文献
6.
7.
Karin Johannesen Joseph W. Depierre Anders Bergstrand Gustav Dallner Lars Ernster 《Biochimica et Biophysica Acta (BBA)/General Subjects》1977,496(1):115-135
Optimal conditions for the preparation of relatively pure microsomes and microsomal subfractions from rat lung have been determined. The most important of these conditions is homogenization of a 20% (w/v) suspension of lung tissue in 0.44 M sucrose/1% (w/v) bovine serum albumin with four up-and-down strokes at 440 rev./min in a Potter-Elvehjem homogenizer. The 10 000 × g supernatant prepared from this homogenate can be centrifuged at 105 000 × g to obtain total microsomes or subfractionated into rough and smooth microsomes on a Cs+-containing discontinuous sucrose gradient. The total, rough and smooth microsomes have been characterized in terms of their chemical composition, enzymatic activity, and morphology. These preparations should prove useful in studies of various enzymes in lung (e.g. benzpyrene monooxygenase, epoxide hydrase, enzymes of phospholipid and ascorbic acid synthesis) and in subfractionations designed to reveal heterogeneites in the lateral plane of the lung endoplasmic reticulum. 相似文献
8.
Horst Will Tatyana S. Levchenko Dmitri O. Levitsky Vladimir N. Smirnov Albert Wollenberger 《Biochimica et Biophysica Acta (BBA)/General Subjects》1978,543(2):175-193
Pigeon heart microsomes contain three minor size protein kinase substrates of minimal molecular weights of 22 000, 15 000, and 11 500, as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. When the microsomes were partially loaded with calcium oxalate and subjected to rate zonal and isopynic centrifugations in sucrose density gradient columns, the 22 000 and the 15 000 dalton proteins settled in the heaviest fraction, which was composed mainly of vesicles of sarcoplasmic reticular membranes; the 11 500 dalton protein was concentrated in the lightest fractions, which consisted chiefly of vesicles of sarcolemmal origin. During incubation of the membrane fractions with Mg[γ-32P]ATP significant amounts of 32P were incorporated into all these proteins. Incorporation of 32P into the 15 000 dalton protein was moderately and 32P incorporation into the 22 000 dalton protein was markedly enhanced in the presence of exogenous soluble cyclic AMP-dependent protein kinase and cyclic AMP. The phosphorylation of the three proteins was virtually unaffected by CA2+ concentrations up to 0.1 mM and by ethyleneglycol-bis(β-aminoethylether)-N,N′-tetraacetic acid in the absence of added Ca2+.Phosphorylation of the 22 000 and the 11 500 dalton proteins occurred mainly at serine residues. In the 15 000 dalton protein threonine residues were the main site of endogenous phosphorylation. Nearly equal amounts of [32P]-phosphate were incorporated into threonine and serine residues of this protein when phosphorylation was supported by exogenous cyclic AMP-dependent protein kinase and cyclic AMP.The 15 000 dalton protein could be removed from its membrane attachment by extraction with an acidic chloroform/methanol mixture. This step opens the way for the purification of this membrane-bound protein kinase substrate. 相似文献
9.
A Pierré M Richou F Lawrence M Robert-Géro P Vigier 《Biochemical and biophysical research communications》1977,76(3):813-819
An increase of methylase activity is often related to neoplastic transformation. SAH, the natural inhibitor of transmethylases, does not inhibit cell transformation induced by RSV, in contrast to one of its synthetic analogues, SIBA. This inefficiency was thought to be due to the rapid metabolism of SAH by transformed cells. We now show, that, on the contrary, 70 % of the added amount of SAH disappears in one hour in cell-free extracts of normal cell against only 14 % in extracts of transformed cells. This decreased rate of degradation occurred one day post infection. Cells infected with the non transforming RAV1 degrade SAH at the same rate as normal cells. A decrease of SAH-hydrolase and adenosine deaminase activity was also observed in infected cells. The decrease of the first enzyme seems to be related to the transformed state, whereas that of the second enzyme seems to depend only on infection, since it is also observed in cells infected with RAV1. 相似文献
10.
By SDS-polyacrylamide gel electrophoresis, mitochondrial proteins having covalently-bound flavin were analyzed. Mitochondria were prepared from the liver of rat injected with radioactive riboflavin. Radioactivity was found to be associated with four protein components. Their subunit molecular weights were 91,000, 72,000, 60,000 and 44,000. The first two components exhibited yellowish fluorescence on a gel under ultraviolet illumination. The component of the highest molecular weight seems to be a new protein containing covalently-bound flavin. 相似文献