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61.
Morphogenesis of the foetal membranes and placenta of the root-rat (Tachyoryctes splendens (Rüppel))
The morphogenesis of the foetal membranes and placenta of the root-rat Tachyoryctes splendens was studied by light microscopy. Implantation of the blastocyst is antimesometrial. The mode of implantation is secondary interstitial and the decidual reaction is similar to that in other rodents. Amniogenesis is by cavitation with a temporary open epamniotic cavity. Inversion of the yolk sac is complete but the disappearance of the parietal segment occurs relatively late. With the breakdown of both the decidua capsularis and parietalis, the yolk sac wall near the margins of the placenta becomes bathed in a pool of maternal blood and tissue debris resembling the haemophagous organ. The yolk sac villi are well vascularized. The allantoic cavity is persistent up to the limb bud stage. The definitive placenta is haemochorial and shows conspicuous endodermal sinuses or placental pits. 相似文献
62.
SecA protein: Autoregulated initiator of secretory precursor protein translocation across theE. coli plasma membrane 总被引:10,自引:0,他引:10
Donald B. Oliver Robert J. Cabelli Gregory P. Jarosik 《Journal of bioenergetics and biomembranes》1990,22(3):311-336
Several classes ofsecA mutants have been isolated which reveal the essential role of this gene product forE. coli cell envelope protein secretion. SecA-dependent,in vitro protein translocation systems have been utilized to show that SecA is an essential, plasma membrane-associated, protein translocation factor, and that SecA's ATPase activity appears to play an essential but as yet undefined role in this process. Cell fractionation studies suggested that SecA protein is in a dynamic state within the cell, occurring in soluble, peripheral, and integral membraneous states. These data have been used to argue that SecA is likely to promote the initial insertion of secretory precursor proteins into the plasma membrane in a manner dependent on ATP hydrolysis. The protein secretion capability of the cell has been shown to translationally regulatesecA expression with SecA protein serving as an autogenous repressor, although the exact mechanism and purpose of this regulation need to be defined further. 相似文献
63.
Claude Penel Thomas Gaspar Michèle Crèvecoeur Claire Kevers Hubert Greppin 《Physiologia plantarum》1990,79(2):250-254
Ca2+ and Mn2+ activate the conversion of 1-aminocyclopropane-1-carboxylic acid (ACC) by root microsomes of Vicia lens as they do in other similar systems. The preparation of microsomes in the presence of Mn2+ greatly increases their ability to convert ACC into ethylene, without addition of Mn2+ in the reaction mixture. Ca2+ does not have this property. The effect could not be attributed to Mn2+ entrapping into membrane vesicles (sonication followed by repelleting had no effect) but, possibly, in part to Mn2+ -mediated binding to microsomes of a soluble factor favouring the conversion of ACC to C2 H4 . Although no direct correlation could be established in vitro between ethylene-forming-enzyme (EFE) and peroxidase activities, some soluble peroxidases might be this soluble factor. Mn2+ favoured attachment to membranes of some peroxidase activity from the soluble fraction and from commercial HRP and lipoxygenase. This binding effect of Mn2+ cannot be readily distinguished from its role in the generation of a chain of free radicals and in redox mechanisms. 相似文献
64.
蜂毒肽在磷脂膜上取向的高效液相色谱和质谱研究 总被引:1,自引:0,他引:1
利用脂质体模型系统研究了跨膜电位对蜂毒肽在磷脂磷上取向的影响,采用高效液相色谱与质谱技术相结合方法,分析了蜂毒肽与磷脂膜作用后的胰蛋白酶酶解产物,结果发现,当蜂毒肽分子与没有跨膜电位的脂质体结合后,它的所有酶切位点都能够酶有效切断,当蜂毒肽与带负向膜电全的脂质体结合后,其N端的一个酶切位点被封闭,从而说明跨膜电位造成了蜂毒肽在膜上的重瓣取向。 相似文献
65.
A liquid chromatography stationary phase containing immobilized membranes obtained from a cell line that expresses the human organic cation transporter (hOCT1-IAM) has been used to study the binding of the enantiomers of propranolol, atenolol, pseudoephedrine, and alpha-methylbenzylamine to the immobilized hOCT1. Frontal displacement chromatography was used to determine the binding affinities (K(d) values), and the data demonstrate that there was an enantioselective difference in the K(d) values of the enantiomers of propranolol, atenolol, and pseudoephedrine, while alpha-methylbenzylamine did not significantly bind to the transporter. Competitive inhibition studies with the cell line used to create the chromatographic column demonstrated that, for the enantiomers of propranolol, the ratio of the chromatographically determined K(d) values [K(d (+)-(R)-propranolol)/K(d (-)-(S)-propranolol) = 2.98] reflected an enantioselective difference in the functional activity of the two enantiomers [IC(50 (+)-(R)-propranolol)/IC(50 (-)-(S)-propranolol) = 2.75]. The chromatographically determined K(d) values were used to construct an initial pharmacophore which contains a hydrogen bond donating site that appears to be responsible for the observed enantioselectivity. 相似文献
66.
We investigated molecular recognition of antibodies to membrane-antigens and extraction of the antigens out of membranes at the single molecule level. Using dynamic force microscopy imaging and enzyme immunoassay, binding of anti-sendai antibodies to sendai-epitopes genetically fused into bacteriorhodopsin molecules from purple membranes were detected under physiological conditions. The antibody/antigen interaction strength of 70-170 pN at loading rates of 2-50 nN/second yielded a barrier width of x = 0.12 nm and a kinetic off-rate (corresponding to the barrier height) of k(off) = 6s(-1), respectively. Bacteriorhodopsin unfolding revealed a characteristic intra-molecular force pattern, in which wild-type and sendai-bacteriorhodopsin molecules were clearly distinguishable in their length distributions, originating from the additional 13 amino acid residues epitope in sendai purple membranes. The inter-molecular antibody/antigen unbinding force was significantly lower than the force required to mechanically extract the binding epitope-containing helix pair out of the membrane and unfold it (126 pN compared to 204 pN at the same loading rate), meeting the expectation that inter-molecular unbinding forces are weaker than intra-molecular unfolding forces responsible for stabilizing native conformations of proteins. 相似文献
67.
Structural and functional link between the mitochondrial network and the endoplasmic reticulum 总被引:1,自引:0,他引:1
Carlotta Giorgi Diego De Stefani Angela Bononi Rosario Rizzuto Paolo Pinton 《The international journal of biochemistry & cell biology》2009,41(10):1817-1827
Mitochondrial and endoplasmic reticulum (ER) networks are fundamental for the maintenance of cellular homeostasis and for determination of cell fate under stress conditions. Recent structural and functional studies revealed the interaction of these networks. These zones of close contact between ER and mitochondria called MAM (mitochondria associated membranes) support communication between the two organelles including bioenergetics and cell survival. The existence of macromolecular complexes in these contact sites has also been revealed. In this contribution, we will review: (i) the ER and mitochondria structure and their dynamics, (ii) the basic principles of ER mitochondrial Ca2+ transport, (iii) the physiological/pathological role of this cross-talk. 相似文献
68.
Jean F. Emly Wendy A. Ratcliffe Elaine Green Sarah J. Bowden David A. Heath Ann Blight Susan Hughes John G. Ratcliffe 《生物化学与生物物理学报:疾病的分子基础》1992,1180(1):58-64
The molecular forms of parathyroid hormone-related protein (PTHRP) in conditioned media from the BEN human lung cancer cell line, rat parathyroid cells (PT-r) and human keratinocytes were studied by gel-filtraton chromatography with assay of PTHRP by immunoassays and bioassay. Immunoreactivity (1–86 and 1–34) and bioactivity (1–34) in conditioned media eluted as a coincident major peak (approx. molecular mass 19–22 kDa) and there was evidence of amino-terminal species in the molecular mass range 10–16 kDa in BEN and keratinocyte media. Western blotting of PTHRP affinity purified by monoclonal antibodies directed at regions 1–34 or 37–67, identified a major species in all cell cytosols and media with an apparent molecular mass of 24–25 kDa, consistently slighty larger than recombinant PTHRP(1–141) (mobility of 21 kDa) which may represent an intact or native form of PTHRP. Additional amino-terminal species were identified in medium from keratinocytes (16 and 7 kDa), BEN cells (18 and 14 kDa) and PT-R cells (17 kDa), suggesting that processing occurs at the C-terminus and within the mid-region to form a range of amino-terminal fragments. 相似文献
69.
Etienne Morel Sara Ghezzal Géraldine Lucchi Caroline Truntzer Jean-Paul Pais de Barros Françoise Simon-Plas Sylvie Demignot Chieko Mineo Philip W. Shaul Armelle Leturque Monique Rousset Véronique Carrière 《Biochimica et Biophysica Acta (BBA)/Molecular and Cell Biology of Lipids》2018,1863(2):199-211
Scavenger receptor Class B type 1 (SR-B1) is a lipid transporter and sensor. In intestinal epithelial cells, SR-B1-dependent lipid sensing is associated with SR-B1 recruitment in raft-like/ detergent-resistant membrane domains and interaction of its C-terminal transmembrane domain with plasma membrane cholesterol. To clarify the initiating events occurring during lipid sensing by SR-B1, we analyzed cholesterol trafficking and raft-like domain composition in intestinal epithelial cells expressing wild-type SR-B1 or the mutated form SR-B1-Q445A, defective in membrane cholesterol binding and signal initiation. These features of SR-B1 were found to influence both apical cholesterol efflux and intracellular cholesterol trafficking from plasma membrane to lipid droplets, and the lipid composition of raft-like domains. Lipidomic analysis revealed likely participation of d18:0/16:0 sphingomyelin and 16:0/0:0 lysophosphatidylethanolamine in lipid sensing by SR-B1. Proteomic analysis identified proteins, whose abundance changed in raft-like domains during lipid sensing, and these included molecules linked to lipid raft dynamics and signal transduction. These findings provide new insights into the role of SR-B1 in cellular cholesterol homeostasis and suggest molecular links between SR-B1-dependent lipid sensing and cell cholesterol and lipid droplet dynamics. 相似文献
70.