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141.
Morphological transformations of bolaamphiphilic polydiacetylene (L-Glu-Bis-3) lipid assemblies from helical ribbons to vesicles and flat sheets through controlled doping are described, and the role of specific lipid dopants in these processes is discussed. Upon doping with cell surface receptor G(M1) ganglioside, fluid vesicular structures start to emerge, coexisting with the micro-crystalline helical ribbons. The vesicle formation is further facilitated and stabilized by the introduction of cholesterol into the system, presumably through surface curvature variation induced by inhomogeneous distribution and dynamic clustering of G(M1) and cholesterol within the doped assemblies. Extended helical ribbons are "truncated" into patches of flat sheets when a sufficient amount of Bis-1, a structurally compatible symmetric bolaamphiphilic diacetylene lipid, is doped. The results reaffirm the important roles of packing geometry and headgroup chirality in the formation of extended helical ribbon structures. The doped assemblies of bolaamphiphiles allow for capture of intermediate structures of morphological transformation using transmission electron microscopy (TEM). A vesicle-to-ribbon transformation mechanism via lateral reorganization within relatively fluid vesicular microstructures has been suggested. Understanding of the doping-induced transformation process provides useful information for the design of advanced materials where the microscopic morphology of material is crucial to its function. 相似文献
142.
Abu Dayyeh BK Quan TK Castro M Ruby SW 《The Journal of biological chemistry》2002,277(23):20221-20233
Pre-mRNA binding to the yeast U2 small nuclear ribonucleoprotein (snRNP) during prespliceosome formation requires ATP hydrolysis, the highly conserved UACUAAC box of the branch point region of the pre-mRNA, and several factors. Here we analyzed the binding of a radiolabeled 2'-O-methyl oligonucleotide complementary to U2 small nuclear RNA to study interactions between the UACUAAC box, U2 snRNP, and Prp5p, a DEAD box protein necessary for prespliceosome formation. Binding of the 2'-O-methyl oligonucleotide to the U2 snRNP in yeast cell extract was assayed by gel electrophoresis. Binding was rapid, enhanced by ATP, and dependent on the integrity and conformation of the U2 snRNP. It was also stimulated by Prp5p that was found to associate physically with U2 snRNP. In vitro heat inactivation of the temperature-sensitive prp5-1 mutant extract decreased oligonucleotide binding to U2 and the ATP enhancement of binding by 3-fold. Furthermore, the temperature-sensitive prp5-1 mutation maps to the ATP-binding motif I within the helicase-like domain. Thus the catalytic activity of Prp5p likely promotes a conformational change in the U2 snRNP. 相似文献
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Zhou Q Zhang L Fu XQ Chen GQ 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2002,780(1):161-169
A high-performance liquid chromatograph equipped with an evaporative light scattering detector (ELSD) (HPLC-ELSD) was used to assay the ceramides in yeast cells. The HPLC-ELSD method employed a cyanopropyl bonded column (CN column) that effectively separated the main interfering substance ergosterol without any derivatization process; most other interfering substances were also removed. The method can be applied for routine assay of ceramide content in yeast. 相似文献
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Teplova M Wilds CJ Wawrzak Z Tereshko V Du Q Carrasco N Huang Z Egli M 《Biochimie》2002,84(9):849-858
Selenium was incorporated into an oligodeoxynucleotide in the form of 2'-methylseleno-uridine (U(Se)). The X-ray crystal structure of the duplex left open bracket d(GCGTA)U(Se)d(ACGC) right open bracket (2) was determined by the multiwavelength anomalous dispersion (MAD) technique and refined to a resolution of 1.3 A, demonstrating that selenium can selectively substitute oxygen in DNA and that the resulting compounds are chemically stable. Since derivatization at the 2'-alpha-position with selenium does not affect the preference of the sugar for the C3'-endo conformation, this strategy is suitable for incorporating selenium into RNA. The availability of selenium-containing nucleic acids for crystallographic phasing offers an attractive alternative to the commonly used halogenated pyrimidines. 相似文献
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149.
Mingone CJ Gupte SA Quan S Abraham NG Wolin MS 《Experimental biology and medicine (Maywood, N.J.)》2003,228(5):535-539
Heme is a co-factor required for the stimulation of soluble guanylate cyclase (sGC) by nitric oxide (NO) and carbon monoxide, and sGC activation by these agents is inhibited by superoxide. Because heme promotes oxidant generation, we examined the influence of rat pulmonary microvascular endothelial cells (PMECs) with a stable human heme oxygenase-1 (HO-1) transfection and heme on oxidant generation and cGMP. Culture of PMEC with low serum heme decreased cGMP and the detection of peroxide with 10 microM 2',7'-dichlorofluorescin diacetate and increased HO-1 further decreased cGMP without altering the peroxide detection under these conditions. Under conditions where heme (30 microM) has been shown to stimulate cGMP production in PMECsby mechanisms involving NO and CO, heme increased the detection of peroxide in a PMEC-dependent manner and HO-1 transfection did not markedly alter the effects heme on peroxide detection. The addition of 1 microM catalase markedly inhibited the effects of heme on peroxide detection whereas increasing (0.1 mM ebselen) or decreasing (depleting glutathione with 7 mM diethylmaleate) rates of intracellular peroxide metabolism or inhibiting the biosynthesis of oxidants (with 10 microM diphenyliodonium or 0.1 mM nitro-L-arginine) had only modest effects. The detection of superoxide by 10 microM dihydroethidium from PMECs was not increased by exposure to heme. These actions of oxidant probes suggest that intracellular oxidants have a minimal influence on the response to heme. Thus, exposure of PMECs to heme causes a complex response involving an extracellular generation of peroxide-derived oxidant species, which do not appear to originate from increases in intracellular superoxide or peroxide. This enables heme and HO to regulate sGC through mechanisms involving NO and CO, which are normally inhibited by superoxide. 相似文献
150.
Cells of Candida krusei capable of producing phytase were immobilized in Ca-alginate gel beads and used for the preparation of myo-inositol phosphates. The immobilization yield was increased about 5-fold after the beads were treated for 96 h at pH 4.0, 4 degrees C. The increased yield was retained, even after 1 month, when the cells were kept at this temperature and pH. No shift in the pH optima of phytase of the immobilized cells was observed, compared with that of free cells. However, the optimum temperature for the enzyme of the immobilized cells was 55 degrees C, which was 15 degrees C higher than that of free cells. The degradation characteristics of the phytate in immobilized cells packed in a glass column (i.d. 1.2 cm, length 20 cm) were investigated. The variation in the composition of the products results from a change in the flow rate of phytate solution (5 mM). At a flow rate of 1.30 ml/min, a mixture of myo-inositol-2-monophosphate, myo-inositol-1,2,5-triphosphate and myo-inositol-1,2,5,6-tetrakisphosphate was produced, in which the latter two were physiologically active. Also, it was found by NMR analysis that the enzyme of this strain produced only one isomer of each of the inositol phosphates, with the exception of myo-inositol pentakisphosphate. Therefore, the pure isomers were easily isolated using ion-exchange chromatography. 相似文献