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991.
992.
Enhanced somatic embryogenesis and plant regeneration have been obtained using young leaf bases of naked oat (Avena nuda) as explants by including salicylic acid (SA) and carrot embryogenic callus extracts (CECE) in media. A 5- and 4-fold improvement
was achieved in somatic embryogenesis and plant regeneration on the corresponding media supplemented with 0.5 mM SA and CECE
as compared to control, respectively. Some physiological and biochemical changes were assayed in both embryogenic callus (EC)
and non-embryogenic callus (NEC). The results indicated that superoxide dismutase activity was stimulated and catalases and
ascorbate peroxidase activities were inhibited, while the O2
- (superoxide anion) content was reduced and the hydrogen peroxide level was promoted in EC compared with NEC. Reduced malondialdehyde
content and relative electrolyte leakage were also detected in EC. 相似文献
993.
The amyloid-beta rise and gamma-secretase inhibitor potency depend on the level of substrate expression 总被引:2,自引:0,他引:2
Burton CR Meredith JE Barten DM Goldstein ME Krause CM Kieras CJ Sisk L Iben LG Polson C Thompson MW Lin XA Corsa J Fiedler T Pierdomenico M Cao Y Roach AH Cantone JL Ford MJ Drexler DM Olson RE Yang MG Bergstrom CP McElhone KE Bronson JJ Macor JE Blat Y Grafstrom RH Stern AM Seiffert DA Zaczek R Albright CF Toyn JH 《The Journal of biological chemistry》2008,283(34):22992-23003
The amyloid-beta (Abeta) peptide, which likely plays a key role in Alzheimer disease, is derived from the amyloid-beta precursor protein (APP) through consecutive proteolytic cleavages by beta-site APP-cleaving enzyme and gamma-secretase. Unexpectedly gamma-secretase inhibitors can increase the secretion of Abeta peptides under some circumstances. This "Abeta rise" phenomenon, the same inhibitor causing an increase in Abeta at low concentrations but inhibition at higher concentrations, has been widely observed. Here we show that the Abeta rise depends on the beta-secretase-derived C-terminal fragment of APP (betaCTF) or C99 levels with low levels causing rises. In contrast, the N-terminally truncated form of Abeta, known as "p3," formed by alpha-secretase cleavage, did not exhibit a rise. In addition to the Abeta rise, low betaCTF or C99 expression decreased gamma-secretase inhibitor potency. This "potency shift" may be explained by the relatively high enzyme to substrate ratio under conditions of low substrate because increased concentrations of inhibitor would be necessary to affect substrate turnover. Consistent with this hypothesis, gamma-secretase inhibitor radioligand occupancy studies showed that a high level of occupancy was correlated with inhibition of Abeta under conditions of low substrate expression. The Abeta rise was also observed in rat brain after dosing with the gamma-secretase inhibitor BMS-299897. The Abeta rise and potency shift are therefore relevant factors in the development of gamma-secretase inhibitors and can be evaluated using appropriate choices of animal and cell culture models. Hypothetical mechanisms for the Abeta rise, including the "incomplete processing" and endocytic models, are discussed. 相似文献
994.
SeO(2) induces apoptosis with down-regulation of Bcl-2 and up-regulation of P53 expression in both immortal human hepatic cell line and hepatoma cell line 总被引:10,自引:0,他引:10
An immortal human hepatic cell line HL-7702 and human hepatoma cell line SMMC-7721 were treated with 3-30 microM SeO(2). SeO(2) at 30 microM markedly inhibited cell proliferation and viability, and prompted apoptosis of both normal hepatic and hepatoma cells after 48h treatment. SeO(2) could also down-regulate the Bcl-2 level, greatly in HL-7702 and slightly in SMMC-7721 cells, but up-regulate wild type P53 level a little in HL-7702 and significantly in SMMC-7721 cells. The Bcl-2/P53 value was closely correlated with the apoptotic rate as well as SeO(2) concentrations. 相似文献
995.
996.
实时观测根瘤及根系形态对于豆科植物研究具有重要意义, 但目前还缺乏一个便于观测根系、高效结瘤、适宜生长且经济实用的豆科植物培养体系。以蒺藜苜蓿(Medicago truncatula)为植物材料, 建立了一种可实时观测根瘤及根系形态的纸袋水培法, 并与其它常用方法进行对比。结果表明, 依赖于石英砂等固体介质栽培蒺藜苜蓿对根瘤和根系形态的实时观测造成障碍, 而水培和喷雾培养等方法的根瘤菌接种效率不高, 且不便观测侧根发育情况。采用纸袋水培法探讨了褪黑素对蒺藜苜蓿根系发育的影响, 发现褪黑素具有降低根瘤形成效率、抑制侧根伸长、增加侧根数目以及增大侧根与主根之间夹角等作用。因此, 纸袋水培法能够高效接种根瘤菌且为实时无损伤观测根瘤及根系形态提供了可能, 是一种适用于豆科植物简单有效的培养方法。 相似文献
997.
甜高粱茎秆糖锤度配合力的测定 总被引:3,自引:0,他引:3
曹文伯 《植物遗传资源学报》2002,3(4):23-27
经测定,本试验各参试甜高梁品种茎秆糖锤度性状的配合力效应及其相对效应值存在显著差别。在亲本不育系中以 Tx625A 为最高(4.44、45.16%);在亲本恢复系中以4035为最高(2.01、20.44%)。由于双亲的交互作用,各组合之特殊配合力相对效应值,以 Tx622A×4034最高,为28.99%,其次是 Tx625A×4008,为19.83%。说明在应用三系选育甜高粱杂交种时,为了获得高锤度的组合,特殊配合力相对效应值高是重要的指标,关键在于亲本的选择及其组配方式。 相似文献
998.
Flash photolysis investigations of horse heart metmyoglobin bound with NO (Mb(3+)NO) reveal the kinetics of water entry and binding to the heme iron. Photodissociation of NO leaves the sample in the dehydrated Mb(3+) (5-coordinate) state. After NO photolysis and escape, a water molecule enters the heme pocket and binds to the heme iron, forming the 6-coordinate aquometMb state (Mb(3+)H2O). At longer times, NO displaces the H2O ligand to reestablish equilibrium. At 293 K, we determine a value k(w) approximately 5.7 x 10(6) s(-1) for the rate of H2O binding and estimate the H2O dissociation constant as 60 mM. The Arrhenius barrier height H(w) = 42 +/- 3 kJ/mol determined for H2O binding is identical to the barrier for CO escape after photolysis of Mb(2+)CO, within experimental uncertainty, consistent with a common mechanism for entry and exit of small molecules from the heme pocket. We propose that both processes are gated by displacement of His-64 from the heme pocket. We also observe that the bimolecular NO rebinding rate is enhanced by 3 orders of magnitude both for the H64L mutant, which does not bind water, and for the H64G mutant, where the bound water is no longer stabilized by hydrogen bonding with His-64. These results emphasize the importance of the hydrogen bond in stabilizing H2O binding and thus preventing NO scavenging by ferric heme proteins at physiological NO concentrations. 相似文献
999.
An attempt has been made to obtain intact individual keratin filaments of various levels from micron cortical, micron macrofibril to nano intermediate filament and polypeptide alpha-helix from the human hair shaft. The feasibility of this initiative has been largely demonstrated by finding that there is a longitudinal seam/zipper on the cuticle of the human hair shaft, which can be unzipped by certain solvents such as performic acid and urea, allowing one to use an anatomical approach to separate intact individual micron/nano filaments. Micron cortical and macrofibril filaments have been obtained. It is also found that the cortical filaments are twisted together to form a yarn, giving rise to the strength for the hair shaft; and that individual cortical filaments are often 2-2 paired in a similar structure to the double helix. 相似文献
1000.
目的 :观察利多卡因和硫喷妥钠对生后 2 2d大鼠培养海马脑片的实验型缺血后神经元损伤的影响。方法 :将培养的SD大鼠海马脑片实验型缺血 (缺氧缺糖 ) 1 0min ,给药组在缺血前 1 0min给予 1 0nmol/L、1 0 0nmol/L的利多卡因或 2 50nmol/L、60 0nmol/L的硫喷妥钠 ,缺血后换用正常培养基继续培养 7d ,并用荧光染料PropidiumIo dide(PI)连续观察海马CA1区和齿状回神经元的损伤。结果 :缺血后第 1d缺血组即出现神经元损伤高峰 ,CA1区和齿状回的PI指数显著增加 (P <0 .0 1 ) ;直至缺血后第 7d其损伤指数仍显著高于缺血前水平 (P <0 .0 1 )。两浓度的利多卡因和硫喷妥钠均可降低缺血后CA1区和齿状回神经元损伤的程度 (P <0 .0 1 ) ,并可将CA1区和齿状回的神经元损伤高峰推迟至缺血后第 3d。结论 :利多卡因和硫喷妥可减轻缺血后海马CA1区和齿状回的神经元损伤 ,推迟神经元的损伤高峰。 相似文献