全文获取类型
收费全文 | 21409篇 |
免费 | 1986篇 |
国内免费 | 1620篇 |
专业分类
25015篇 |
出版年
2024年 | 50篇 |
2023年 | 245篇 |
2022年 | 630篇 |
2021年 | 945篇 |
2020年 | 767篇 |
2019年 | 869篇 |
2018年 | 938篇 |
2017年 | 729篇 |
2016年 | 952篇 |
2015年 | 1358篇 |
2014年 | 1506篇 |
2013年 | 1653篇 |
2012年 | 1944篇 |
2011年 | 1709篇 |
2010年 | 1082篇 |
2009年 | 943篇 |
2008年 | 1125篇 |
2007年 | 987篇 |
2006年 | 868篇 |
2005年 | 718篇 |
2004年 | 696篇 |
2003年 | 647篇 |
2002年 | 599篇 |
2001年 | 438篇 |
2000年 | 343篇 |
1999年 | 346篇 |
1998年 | 188篇 |
1997年 | 189篇 |
1996年 | 174篇 |
1995年 | 165篇 |
1994年 | 139篇 |
1993年 | 122篇 |
1992年 | 142篇 |
1991年 | 132篇 |
1990年 | 106篇 |
1989年 | 95篇 |
1988年 | 73篇 |
1987年 | 68篇 |
1986年 | 54篇 |
1985年 | 47篇 |
1984年 | 34篇 |
1983年 | 35篇 |
1982年 | 25篇 |
1981年 | 23篇 |
1980年 | 12篇 |
1979年 | 18篇 |
1978年 | 18篇 |
1975年 | 9篇 |
1974年 | 9篇 |
1972年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
991.
细胞色素P450(CYP)能催化各种内源性及外源性化合物的代谢,与多种肿瘤发生有关.其中CYP1A1参与多种前致癌物和致突变物的代谢活化,CYP1B1被认为在许多人癌细胞中特异性表达,参与药物的氧化代谢和前药的活化.CYP1A1和1B1已成为靶向抗肿瘤前药研究的新靶点.相继有大量相关研究报道,本文就近年来文献报道的CYP 1A1和1B1靶向抗肿瘤前药研究进展. 相似文献
992.
993.
现代生物医药的发展越来越依赖大分子药物的开发与应用,其中蛋白质药物所占的比重越来越高,生产需求进一步加大.重组蛋白质技术作为一种方便的蛋白质生产来源,日益得到广泛运用.重组蛋白质纯化过程中往往使用到融合亲和纯化标签,然而这些冗余的标签在蛋白质精细化生产中,尤其是作为蛋白质医药存在时,是必须被予以去除的.切割蛋白酶发挥着不可替代的作用.本文就现有的各种常用切割蛋白酶进行比较和总结,为重组蛋白质生产与科研者提供参考. 相似文献
994.
995.
Jian Wen Wang Li Ping Zheng Ben Zhang Ting Zou 《Applied microbiology and biotechnology》2009,85(2):285-292
This work examined the accumulation of artemisinin and related secondary metabolism pathways in hairy root cultures of Artemisia annua L. induced by a fungal-derived cerebroside (2S,2′R,3R,3′E,4E,8E)-1-O-β-d-glucopyranosyl-2-N-(2′-hydroxy-3′-octadecenoyl)-3-hydroxy-9-methyl-4,8-sphingadienine. The presence of the cerebroside induced nitric oxide
(NO) burst and artemisinin biosynthesis in the hairy roots. The endogenous NO generation was examined to be involved in the
cerebroside-induced biosynthesis of artemisinin by using NO inhibitors, N
ω-nitro-l-arginine methyl ester and 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide. The gene expression and activity
of 3-hydroxy-3-methylglutaryl CoA reductase and 1-deoxy-d-xylulose 5-phosphate synthase were stimulated by the cerebroside, but more strongly by the potentiation of NO. While the
mevalonate pathway inhibitor, mevinolin, only partially inhibited the induced artemisinin accumulation, the plastidic 2-C-methyl-d-erythritol 4-phosphate pathway inhibitor, fosmidomycin, nearly arrested artemisinin accumulation induced by cerebroside and
the combination elicitation with an NO donor, sodium nitroprusside (SNP). With the potentiation by SNP at 10 μM, the cerebroside
elicitor stimulated artemisinin production in 20-day-old hairy root cultures up to 22.4 mg/l, a 2.3-fold increase over the
control. These results suggest that cerebroside plays as a novel elicitor and the involvement of NO in the signaling pathway
of the elicitor activity for artemisinin biosynthesis. 相似文献
996.
Bin Su Sébastien Wurtzer Marie-Anne Rameix-Welti Dominic Dwyer Sylvie van der Werf Nadia Naffakh Fran?ois Clavel Béatrice Labrosse 《PloS one》2009,4(12)
Background
The major role of the neuraminidase (NA) protein of influenza A virus is related to its sialidase activity, which disrupts the interaction between the envelope hemagglutin (HA) protein and the sialic acid receptors expressed at the surface of infected cells. This enzymatic activity is known to promote the release and spread of progeny viral particles following their production by infected cells, but a potential role of NA in earlier steps of the viral life cycle has never been clearly demonstrated. In this study we have examined the impact of NA expression on influenza HA-mediated viral membrane fusion and virion infectivity.Methodology/Principal Findings
The role of NA in the early stages of influenza virus replication was examined using a cell-cell fusion assay that mimics HA-mediated membrane fusion, and a virion infectivity assay using HIV-based pseudoparticles expressing influenza HA and/or NA proteins. In the cell-cell fusion assay, which bypasses the endocytocytosis step that is characteristic of influenza virus entry, we found that in proper HA maturation conditions, NA clearly enhanced fusion in a dose-dependent manner. Similarly, expression of NA at the surface of pseudoparticles significantly enhanced virion infectivity. Further experiments using exogeneous soluble NA revealed that the most likely mechanism for enhancement of fusion and infectivity by NA was related to desialylation of virion-expressed HA.Conclusion/Significance
The NA protein of influenza A virus is not only required for virion release and spread but also plays a critical role in virion infectivity and HA-mediated membrane fusion. 相似文献997.
998.
Cytochrome bc1 complex catalyzes the reaction of electron transfer from ubiquinol to cytochrome c (or cytochrome c2) and couples this reaction to proton translocation across the membrane. Crystallization of the Rhodobacter sphaeroides bc1 complex resulted in crystals containing only three core subunits. To mitigate the problem of subunit IV being dissociated from the three-subunit core complex during crystallization, we recently engineered an R. sphaeroides mutant in which the N-terminus of subunit IV was fused to the C-terminus of cytochrome c1 with a 14-glycine linker between the two fusing subunits, and a 6-histidine tag at the C-terminus of subunit IV (c1-14Gly-IV-6His). The purified fusion mutant complex shows higher electron transfer activity, more structural stability, and less superoxide generation as compared to the wild-type enzyme. Preliminary crystallization attempts with this mutant complex yielded crystals containing four subunits and diffracting X-rays to 5.5 Å resolution. 相似文献
999.
用离子交换高效液相层析(HPLC)分离并同步测定脑组织腺苷酸环化酶(AC)反应生成的cAMP,从而直接测定AC活性。100℃加热1min终止AC反应后,混合物在0℃放置2h。在此期间,反应体系中残留的ATP水解酶将反应混合物中大部分剩余的ATP水解除去。用二氯甲烷抽提除去罂粟碱等干扰物质,使混合物中的cAMP同蓁物质在Shim-Pak WAX-1阴离子交换HPLC术上基线分离,并可定量测定,用此方 相似文献
1000.
Jiu-Xiang Xie Gong-Hua Lin Cui-Xia Liu Chuan-Hua Yang Xiao-Gong Deng Xue-Feng Cui Bang Li Tong-Zuo Zhang Jian-Ping Su 《Acta theriologica》2014,59(2):337-345
Subterranean herbivores affect the plant community by plant consumption and burrowing activities. However, diet selection of subterranean herbivores has not been studied in detail in complex natural fields, mainly for lack of an accurate method to determine diet species, frequency, and biomass. Plateau zokors' (Eospalax baileyi) caching habit for the long inclement winter makes it possible to solve this problem. We studied the diet composition and biomass in caches and vicinity of plateau zokors' burrow systems. We found that plateau zokors are dietary generalist but show a significant selection among the available food items, plant parts, functional groups, organ types, and habitats. These results suggested that plateau zokors strictly selected their diet and were able to adjust their foraging strategy according to the different conditions of food abundance and quality. Plateau zokors' selective foraging can directly reduce the proportion of toxicity forbs; plateau zokors can be recognized as an important element to influence the alpine meadow plant community and cattle husbandry. 相似文献