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Summary
Bacillus thuringiensis var.kurstaki (HD-1)_was grown as a continuous phased culture in a cyclone fermentor. During the time course of the continuous phased cultivation (CPC), the culture was sampled to determine the efficiency of sporulation and parasporal crystal formation. Concurrently, plasmid DNA was extracted and resolved on agarose gels. The plasmid profile remained constant throughout 328 h of cultivation. However, during the same time period, asporogenous, acrystalliferous variants increased from<1% to>90% of the cells harvested. Our data suggests that the disappearance of parasporal crystals inB. thuringiensis var.kurstaki (HD-1) during CPC occurs independent of plasmid copy but may be due to defective sporulation. 相似文献
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Roy E. Weber Frank B. Jensen Raymond P. Cox 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1987,157(2):145-152
Summary The allosteric effects of the erythrocytic nucleoside triphosphates (NTP) and of proton concentrations were investigated by precise measurement of Hb–O2 equilibria of tench hemoglobin (including extreme, high and low saturation ranges) and analysed in terms of the MWC two state model and the Adair four step oxygenation theory.At low concentrations (NTP/Hb ratio=1.0, and pH>7.3) ATP, GTP and protons decrease Hb–O2 affinity by increasing the allosteric constantL and reducingK
T, the association constant1 of the deoxy, tense state of the Hb, without significantly affecting that (K
R) of the oxy state, increasing the free energy of cooperativity (G). High concentrations of these effectors, however, also reduceK
R. The greater sensitivity of the half-saturation O2 tension (P
50) of the Hb to GTP than to ATP at the same concentration, correlates with greater effects of GTP on bothK
T andK
R. The pH and NTP dependence of the four Adair association constants and the calculated fractional populations of Hb molecules in different stages of oxygenation show that the autochthonous NTP effectors and protons stabilize the T structure and postpone the TR transition basic to cooperativity in fish Hb.The possible implications of the findings for aquatic respiration are discussed.Abbreviations
ATP
adenosine triphosphate
-
DPG
2,3-diphosphoglycerate (glycerate-2,3-bisphosphate)
-
GTP
guanosine triphosphate
-
IHP
inositol hexaphosphate
-
NTP
nucleoside triphosphates
In this paperK
T andK
R are defined as theassociation equilibrium constants instead of dissociation constants (as originally defined by Monod et al. 1965) to facilitate comparison with the Adair constants 相似文献
46.
用云南山楂(Crataegus scabrifolia(Franch.)Rehd.)成年树茎尖和实生芽两种不同发育阶段的材料为外殖体,诱导它们休眠芽萌动,丛生芽条并诱导芽条生根。实验结果如下:1.以成年态的云南山楂侧芽为外植体,培养在附加IAA 0.1—0.5mg/l+6-BA 1-2mg/l的MS培养基上可诱导芽的萌发;将芽继代培养在附加0.5—1mg/l 6-BA的SH或MS培养基上,40天后芽数增殖4—6倍;将芽条截下置于1/2MS培养基上,附加不同浓度的IAA或IBA,可得到50—80%的生根率。2.以实生芽为外殖体,在相同条件下,则20天后芽数增殖便可获4—6倍;98%以上生根。结果表明:云南山楂的幼年态要比成年态易脱分化和再分化。 相似文献
47.
Purification and properties of formylglutamate amidohydrolase from Pseudomonas putida. 总被引:4,自引:3,他引:1 下载免费PDF全文
Formylglutamate amidohydrolase (FGase) catalyzes the terminal reaction in the five-step pathway for histidine utilization in Pseudomonas putida. By this action, N-formyl-L-glutamate (FG) is hydrolyzed to produce L-glutamate plus formate. Urocanate, the first product in the pathway, induced all five enzymes, but FG was able to induce FGase alone, although less efficiently than urocanate did. This induction by FG resulted in the formation of an FGase with electrophoretic mobility identical to that of the FGase induced by urocanate. A 9.6-kilobase-pair HindIII DNA fragment containing the P. putida FGase gene was cloned into the corresponding site on plasmid pBEU1 maintained in Escherichia coli. Insertion of the fragment in either orientation on the vector resulted in expression, but a higher level was noted in one direction, suggesting that the FGase gene can be expressed from either of two vector promoters with different efficiencies or from a single vector promoter in addition to a less efficient Pseudomonas promoter. FGase was purified 1,110-fold from the higher-expression clone in a yield of 10% through six steps. Divalent metal ions stimulated activity, and among those tested (Co, Fe, Zn, Ca, Ni, Cd, Mn, and Mg), Co(II) was the best activator, followed by Fe(II). FGase exhibited a Km of 14 mM for FG and a specific activity of 100 mumol/min per mg of protein in the presence of 5 mM substrate and 0.8 mM CoCl2 at 30 degrees C. The enzyme was maximally active in the range of pH 7 to 8. FGase was found to be a monomer of molecular weight 50,000. N-Acetyl-L-glutamate was not a substrate for the enzyme, but both it and N-formyl-L-aspartate were competitive inhibitors of formylglutamate hydrolysis, exhibiting Ki values of 6 and 9 mM, respectively. The absence of FGase activity as an integral part of histidine breakdown in most other organisms and the somewhat uncoordinated regulation of FGase synthesis with that of the other hut enzymes in Pseudomonas suggest that the gene encoding its synthesis may have evolved separately from the remaining hut genes. 相似文献
48.
Using sucrose density gradient centrifugation in a vertical rotor, we have separated three major binding components contained in hepatic cytosols from C57BL/6 mice and Sprague-Dawley rats. Using this preparative method we have obtained, after a 3-h run of 2.4 ml of crude cytosol from 1,4-bis[2-(3,5-dichlorodipyridyloxy)]benzene-treated C57BL/6 mice (approximately 50 mg of protein: 10,000 fmol of Ah receptor) 50 and 75% yields of isolated Ah receptor and carcinogen-binding protein (4 S binding protein), respectively. Both binding components may be kept at -70 degrees C for several months without loss of activity. A third binding component, which did not sediment in a sucrose density gradient (5-20%), even after a 4-h run at 63,000 rpm, was recovered from the top fractions of gradients. When applied to Sephacryl S-300 columns this component was eluted in the void fraction. Resistant to the direct degradative action of nucleases and proteases, this large complex was sequentially converted to its subcomponents by lipoprotein-lipase, proteinase K, and phospholipases. Only the phospholipases are able to abolish the binding capacity of this light density component (LDC) for [3H]2,3,7,8-tetrachlorodibenzo-p-dioxin: hence, we conclude that phospholipids are the true binders of this radioligand. In vitro, this lipoprotein irreversibly binds many hydrophobic radioligands (2,3,7,8-tetrachlorodibenzo-p-dioxin,3-methylcholanthrene, benzo(a)pyrene, 7,12-dimethylbenz(a)anthracene, and dexamethasone). Using single vertical spin density gradient ultracentrifugation, the major part (80%) of LDC was characterized as a very low-density lipoprotein, and a minor part (20%) as a low-density lipoprotein. This conclusion was supported by the size of LDC particles (about 25-75 nm) observed in electron microscopy. 相似文献
49.
50.
Interleukin 2 up-regulates its own production 总被引:2,自引:0,他引:2
J Hu C Vaquero S Huet A Bernard G Sterkers 《Journal of immunology (Baltimore, Md. : 1950)》1987,139(12):4109-4115
It has been previously reported that a combination pair of anti-CD2 monoclonal antibodies (mAb) T11(2)+T11(3) induces a strong proliferation of T cells, which does not require the involvement of accessory cells and exogenous interleukin 2 (IL-2). More recently, we have shown that the requirement for optimal T cell proliferation depends on the combination pairs of anti-CD2 mAb used. Among them, anti-GT2+T11(1) mAb do not allow optimal proliferation of TA4 helper cloned T cells due, at least in part, to a low level of IL-2 production. This observation offered us the opportunity to study the effect of IL-2 on its own production. We show here that stimulation of cloned TA4 cells with anti-GT2+T11(1) mAb induces only a marginal level of IL-2 production. By contrast, significantly higher levels of IL-2 activity are detected in the culture supernatant of TA4 cells preincubated with recombinant IL-2 (rIL-2) before stimulation with anti-GT2+T11(1) mAb. This effect is dose-dependent over a wide range (5 to 50 IU/ml) of rIL-2 concentrations added during preincubation time. In addition, it is not due to carryover of rIL-2 bound during the preincubation time, or to lesser IL-2 consumption by these cells, or to increasing numbers of IL-2-producing cells induced by exogenous IL-2. Moreover, the observation was confirmed with IL-2 mRNA. Although neither rIL-2 nor anti-GT2+T11(1) mAb alone could induce a significant production of IL-2, rIL-2 appears to up-regulate its own production when the TA4 cells are activated by the anti-CD2 mAb-mediated second signal. 相似文献