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991.
Acyltransferase-catalyzed cleavage of arachidonic acid from phospholipids and transfer to lysophosphatides in lymphocytes and macrophages 总被引:2,自引:0,他引:2
The cleavage of fatty acyl moieties from phospholipids was compared in intact cells and homogenates of mouse lymphocytes (thymocytes, spleen cells) and macrophages. Liberation of free arachidonic acid during incubations of intact cells was only detectable in the presence of albumin. Homogenization of prelabeled thymocytes and further incubation of these homogenates at 37 degrees C resulted in a pronounced decrease of phospholipid degradation and cleavage of arachidonoyl residues, while further incubation of homogenates from prelabeled macrophages produced a greatly increased phospholipid degradation. Homogenates of macrophages but not those of thymocytes contain substantial activities of phospholipase A2 detectable using exogenous radiolabeled substrates. These findings indicate that in thymocytes cleavage of arachidonic acid from phosphatidylcholine is an active process that is not catalyzed by phospholipase A2. Addition of CoA and lysophosphatidylethanolamine to prelabeled thymocyte homogenates induced a fast breakdown of phosphatidylcholine and transfer of arachidonic acid to phosphatidylethanolamine, as in seen during incubations of intact thymocytes or macrophages. The transfer is restricted to arachidonic acid and does not require addition of ATP. Sodium cholate, a known inhibitor of the acyl-CoA:lysophosphatide acyltransferase, completely inhibited this transfer reaction. These results suggest that the CoA-mediated, ATP-independent breakdown of phosphatidylcholine and transfer of arachidonic acid is catalyzed by the acyl-CoA:lysophosphatide acyltransferase operating in reverse. 相似文献
992.
993.
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995.
A new bacterial uricase for uric acid determination 总被引:7,自引:0,他引:7
J L Mahler 《Analytical biochemistry》1970,38(1):65-84
996.
997.
998.
Molecular dynamics (MD) simulations of phosphatidylinositol (4,5)-bisphosphate (PIP2) and phosphatidylinositol (3,4,5)-trisphosphate (PIP3) in 1-palmitoyl 2-oleoyl phosphatidylcholine (POPC) bilayers indicate that the inositol rings are tilted ∼40° with respect to the bilayer surface, as compared with 17° for the P-N vector of POPC. Multiple minima were obtained for the ring twist (analogous to roll for an airplane). The phosphates at position 1 of PIP2 and PIP3 are within an Ångström of the plane formed by the phosphates of POPC; lipids in the surrounding shell are depressed by 0.5-0.8 Å, but otherwise the phosphoinositides do not substantially perturb the bilayer. Finite size artifacts for ion distributions are apparent for systems of ∼26 waters/lipid, but, based on simulations with a fourfold increase of the aqueous phase, the phosphoinositide positions and orientations do not show significant size effects. Electrostatic potentials evaluated from Poisson-Boltzmann (PB) calculations show a strong dependence of potential height and ring orientation, with the maxima on the −25 mV surfaces (17.1 ± 0.1 Å for PIP2 and 19.4 ± 0.3 Å for PIP3) occurring near the most populated orientations from MD. These surfaces are well above the background height of 10 Å estimated for negatively charged cell membranes, as would be expected for lipids involved in cellular signaling. PB calculations on microscopically flat bilayers yield similar maxima as the MD-based (microscopically rough) systems, but show less fine structure and do not clearly indicate the most probable regions. Electrostatic free energies of interaction with pentalysine are also similar for the rough and flat systems. These results support the utility of a rigid/flat bilayer model for PB-based studies of PIP2 and PIP3 as long as the orientations are judiciously chosen. 相似文献
999.
H Zitzer H H H?nck D B?chner D Richter H J Kreienkamp 《The Journal of biological chemistry》1999,274(46):32997-33001
By using the yeast two-hybrid system we identified a novel protein from the human brain interacting with the C terminus of somatostatin receptor subtype 2. This protein termed somatostatin receptor interacting protein is characterized by a novel domain structure, consisting of six N-terminal ankyrin repeats followed by SH3 and PDZ domains, several proline-rich regions, and a C-terminal sterile alpha motif. It consists of 2185 amino acid residues encoded by a 9-kilobase pair mRNA; several splice variants have been detected in human and rat cDNA libraries. Sequence comparison suggests that the novel multidomain protein, together with cortactin-binding protein, forms a family of cytoskeletal anchoring proteins. Fractionation of rat brain membranes indicated that somatostatin receptor interacting protein is enriched in the postsynaptic density fraction. The interaction of somatostatin receptor subtype 2 with its interacting protein was verified by overlay assays and coimmunoprecipitation experiments from transfected human embryonic kidney cells. Somatostatin receptor subtype 2 and the interacting protein display a striking overlap of their expression patterns in the rat brain. Interestingly, in the hippocampus the mRNA for somatostatin receptor interacting protein was not confined to the cell bodies but was also observed in the molecular layer, suggesting a dendritic localization of this mRNA. 相似文献
1000.
Jürgen Sühnel 《Bulletin of mathematical biology》1998,60(2):197-213
A possible experimental design for combination experiments is to compare the doseresponse curve of a single agent with the
corresponding curve of the same agent using either a fixed amount of a second one or a fixed dose ratio. No interaction is
then often defined by a parallel shift of these curves. We have performed a systematic study for various types of doseresponse
relations both for the dose-additivity (Loewe additivity) and for the independence (Bliss independence) criteria for defining
zero interaction. Parallelism between doseresponse curves of a single agent and those of the same agent in the presence of
a fixed amount of another one is found for the Loewe-additivity criterion for linear doseresponse relations. For nonlinear
relations, one has to differentiate between effect parallelism (parallel shift on the effect scale) and dose parallelism (parallel
shift on the dose scale). In the case of Loewe additivity, zero-interaction dose parallelism is found for power, Weibull,
median-effect and logistic doseresponse relations, given that special parameter relationships are fulfilled. The mechanistic
model of competitive interaction exhibits dose parallelism but not effect parallelism for Loewe additivity. Bliss independence
and Loewe additivity lead to identical results for exponential doseresponse curves. This is the only case for which dose parallelism
was found for Bliss independence. Parallelism between single-agent doseresponse relations and Loewe additivity mixture relations
is found for examples with a fixed doseratio design. However, this is again not a general property of the design adopted but
holds only if special conditions are fulfilled. The comparison of combination doseresponse curves with single-agent relations
has to be performed taking into account both potency and shape parameters. The results of this analysis lead to the conclusion
that parallelism between zero interaction combination and single-agent doseresponse relations is found only for special cases
and cannot be used as a general criterion for defining zero-interaction in combined-action assessment even if the correct
potency shift is taken into account. 相似文献