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161.
162.
Li J Sun L Xu C Yu F Zhou H Zhao Y Zhang J Cai J Mao C Tang L Xu Y He J 《生物化学与生物物理学报(英文版)》2012,44(4):300-306
The activation of molecular chaperone heat-shock protein 90 (Hsp90) is dependent on ATP binding and hydrolysis, which occurs in the N-terminal domains of protein. Here, we have determined three crystal structures of the N-terminal domain of human Hsp90 in native and in complex with ATP and ATP analog, providing a clear view of the catalytic mechanism of ATP hydrolysis by Hsp90. Additionally, the binding of ATP leads the N-terminal domains to be an intermediate state that could be used to partially explain why the isolated N-terminal domain of Hsp90 has very weak ATP hydrolytic activity. 相似文献
163.
Xiaomin Tang Weidong Bao Wenli Zhang Zhukuan Cheng 《植物学报(英文版)》2007,49(6):953-960
To develop reliable techniques for chromosome identification is critical for cytogenetic research, especially for genomes with a large number and smaller-sized chromosomes. An efficient approach using bacterial artificial chromosome (BAC) clones as molecular cytological markers has been developed for many organisms. Herein, we present a set of chromosomal arm-specific molecular cytological markers derived from the gene-enriched regions of the sequenced rice genome. All these markers are able to generate very strong signals on the pachytene chromosomes of Oryza sativa L. (AA genome) when used as fluorescence in situ hybridization (FISH) probes. We further probed those markers to the pachytene chromosomes of O. punctata (BB genome) and O. officinalis (CC genome) and also got very strong signals on the relevant pachytene chromosomes. The signal position of each marker on the related chromosomes from the three different rice genomes was pretty much stable, which enabled us to identify different chromosomes among various rice genomes. We also constructed the karyotype for both O. punctata and O. officinalis with the BB and CC genomes, respectively, by analysis of 10 pachytene cells anchored by these chromosomal arm-specific markers. 相似文献
164.
西洋参(Panax Quinquefolium L.)种胚需经形态后熟和生理后熟后才能萌发.经过激素(GA100ppm+KT50ppm+BA20ppm)处理的西洋参种子,在后熟过程中鲜重增加,β—淀粉酶活性增强,过氧化物酶活性保持较高水平.在生理后熟期,可溶性蛋白量逐渐增多.激素处理加速了胚体内物质的分解和合成,促使胚迅速发育和分化,缩短了种胚完成形态和生理后熟的时间,使种子提早一年萌发. 相似文献
165.
The precise physiological causes that result in reduced development of oocytes after heat shock (HS) are not clear. In this study, apoptosis, heat shock protein70 (hsp70), and in vitro development of porcine oocytes were evaluated after HS. Porcine cumulus-oocyte complexes (COCs) were subjected to in vitro maturation for 42 h. The matured oocytes were then heated at 41.5 degrees C for 0 h (control, C0h), 1 h (HS1h), 2 h (HS2h), or 4 h (HS4h). An additional group of oocytes was cultured for 4 h without HS (control, C4h). In Experiment 1, expression of hsp70 was detected by Western-blotting and no difference between controls and HS groups was observed. In Experiment 2, apoptosis of matured oocytes after HS was examined by Annexin V-FITC and TUNEL. No significant TUNEL-positive signals were detected in the heated oocytes compared to the controls, but the intensity of Annexin V-FITC labeling among different groups increased with length of HS and in vitro culture (P<0.05). Oocytes were parthenogenetically activated by an electric pulse plus 6-DMAP (Experiment 3). Mean (+/-S.E.M.) embryonic development in HS2h (cleavage: 42+/-29%; blastocyst: 11+/-10%) and HS4h (cleavage: 36+/-28%; blastocyst: 11+/-8%) were decreased when compared to those in C0h (cleavage: 63+/-12%; blastocyst: 24+/-14%) and C4h (cleavage: 66+/-8%; blastocyst: 21+/-11%). Numbers of blastocysts with TUNEL-positive signals were similar among groups, but the signals increased before the eight-cell stage in HS groups (P<0.05). In conclusion, developmental competence of matured pig oocytes was compromised after heat shock, but it was not closely associated with the expression of oocyte hsp70. However, there may be a link between apoptosis and developmental competence of porcine oocytes. 相似文献
166.
167.
Screening and isolation of an organic solvent-tolerant bacterium for high-yield production of organic solvent-stable protease 总被引:1,自引:0,他引:1
Forty-three strains were screened from crude oil-contaminated samples by toluene and cyclohexane enrichment in medium. Ten of these strains demonstrated high protease activity on skim-milk agar. Among them, the PT121 isolate, identified as Pseudomonas aeruginosa, was selected based on its extracellular protease stability in the presence of hydrophilic organic solvents. The crude protease also retained most of its activity up to at least 14 days in the presence of various organic solvents at 50% concentration, and the protease activity in production medium was 10,876U/ml after 72h incubation. This protease showed high activity as a catalyst for aspartame precursor Cbz-Asp-Phe-NH2 synthesis in the presence of 50% dimethylsulfoxide (DMSO). 相似文献
168.
169.
Halohydrin dehalogenase (HheC) from Agrobacterium radiobacter AD1 catalyzes the reversible intramolecular nucleophilic displacement of a halogen by a hydroxyl group in vicinal haloalcohols, producing the corresponding epoxides. The enzyme displays high enantioselectivity toward some aromatic halohydrins. To understand the kinetic mechanism and enantioselectivity of the enzyme, steady-state and pre-steady-state kinetic analysis was performed with p-nitro-2-bromo-1-phenylethanol (PNSHH) as a model substrate. Steady-state kinetic analyses indicated that the k(cat) of the enzyme with the (R)-enantiomer (22 s(-1)) is 3-fold higher than with the (S)-enantiomer and that the K(m) for the (R)-enantiomer (0.009 mM) is about 45-fold lower than that for the (S)-enantiomer, resulting in a high enantiopreference for the (R)-enantiomer. Product inhibition studies revealed that HheC follows an ordered Uni Bi mechanism for both enantiomers, with halide as the first product to be released. To identify the rate-limiting step in the catalytic cycle, pre-steady-state experiments were performed using stopped-flow and rapid-quench methods. The results revealed the existence of a pre-steady-state burst phase during conversion of (R)-PNSHH, whereas no such burst was observed with the (S)-enantiomer. This indicates that a product release step is rate-limiting for the (R)-enantiomer but not for the (S)-enantiomer. This was further examined by doing single-turnover experiments, which revealed that during conversion of the (R)-enantiomer the rate of bromide release is 21 s(-1). Furthermore, multiple turnover analyses showed that the binding of (R)-PNSHH is a rapid equilibrium step and that the rate of formation of product ternary complex is 380 s(-1). Taken together, these findings enabled the formulation of an ordered Uni Bi kinetic mechanism for the conversion of (R)-PNSHH by HheC in which all of the rate constants are obtained. The high enantiopreference for the (R)-enantiomer can be explained by weak substrate binding of the (S)-enantiomer and a lower rate of reaction at the active site. 相似文献
170.
用免疫细胞化学和原位杂交技术探讨G、D细胞及胃泌素mRNA与肠化生的关系。标本来自胃镜活检的胃粘膜。结果显示,在与大肠化生区相邻的胃粘膜,G细胞突变消失,假幽门腺化生也缺乏G细胞,而淖肠化生仍保留少数G细胞;D细胞不仅见于小肠化生,而且也出现在假幽门腺化生以及某些大肠化生区。胃泌素mRNA仅限于G细胞分布区,未出现在大肠化生区和假幽门腺化生区,G细胞及胃泌素mRNA在大肠化生区的消失,可能由于局部杯状细胞分泌的硫酸粘蛋白改变了局部的微环境,从而影响了G细胞的分化与发育,至于假幽门腺化生区G细胞及胃泌素mRNA消失的原因还不清楚,应继续研究。 相似文献