全文获取类型
收费全文 | 11936篇 |
免费 | 1218篇 |
国内免费 | 1267篇 |
出版年
2024年 | 49篇 |
2023年 | 208篇 |
2022年 | 453篇 |
2021年 | 690篇 |
2020年 | 507篇 |
2019年 | 650篇 |
2018年 | 581篇 |
2017年 | 427篇 |
2016年 | 623篇 |
2015年 | 892篇 |
2014年 | 978篇 |
2013年 | 961篇 |
2012年 | 1123篇 |
2011年 | 938篇 |
2010年 | 646篇 |
2009年 | 562篇 |
2008年 | 580篇 |
2007年 | 470篇 |
2006年 | 414篇 |
2005年 | 340篇 |
2004年 | 321篇 |
2003年 | 297篇 |
2002年 | 258篇 |
2001年 | 177篇 |
2000年 | 134篇 |
1999年 | 149篇 |
1998年 | 78篇 |
1997年 | 75篇 |
1996年 | 62篇 |
1995年 | 59篇 |
1994年 | 57篇 |
1993年 | 58篇 |
1992年 | 87篇 |
1991年 | 70篇 |
1990年 | 65篇 |
1989年 | 54篇 |
1988年 | 40篇 |
1987年 | 38篇 |
1986年 | 33篇 |
1985年 | 35篇 |
1984年 | 28篇 |
1983年 | 19篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1980年 | 14篇 |
1977年 | 9篇 |
1972年 | 11篇 |
1971年 | 9篇 |
1970年 | 9篇 |
1969年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
通过DEAE-SephadexA-50,DEAE-SepharoseCL-6B,MonoQ (FPLC)三步离子交换柱层析,纯化得到一新的纤维蛋白原溶酶,在碱性聚丙烯酰胺凝胶电泳和SDS-聚丙烯酰胺凝胶电泳上均呈单一的蛋白带。分子量为2600,等电点pl4.7;它是一个糖蛋白,含糖量6.4%,其中中性糖0.3%,已糖胺4.9%,唾液酸1.2%。烙铁头蛇毒纤维蛋白原溶酶TMVFg由187个氨基酸组成,含有较高的酸性氨基酸,此外甘氨酸含量也较高。TMVFg热稳定性强,而酸不稳定,在280 nm处具有典型的蛋白吸收峰,在无离子水中紫外消光系数E0.1%/280 nm=1.558。纯化的TMVFg具有较强的精氨酸酯酶活力,对苯甲酰-L-精氨酸乙酯(BAEE)的Km值为1.4×10[-3]M。TMVFg的活性受苯甲基丹磺酰氟(PMSF)抑制;乙二胺四乙酸(EDTA)对活性无影响。TMVFg不能使纤维蛋白原凝固,但能水解纤维蛋白原α、β链。纤溶实验表明TMVFg具有激活纤溶作用。纯化的烙铁头蛇毒纤维蛋白原溶酶对酪蛋白无作用,无出血活性,因而与凝血酶样酶、出血毒素及β-纤维蛋白原溶酶(OUYANG et al.,1977)明显不同。 相似文献
42.
P M Anderson W V Johnson J J Korte X F Xiong Y C Sung J A Fuchs 《The Journal of biological chemistry》1988,263(12):5674-5680
Cyanase is an inducible enzyme in Escherichia coli that catalyzes the reaction of cyanate with bicarbonate resulting in the decomposition of cyanate to ammonia and bicarbonate. In this study, the role of the single sulfhydryl group in each of the eight identical subunits of cyanase was investigated. Tetranitromethane, methyl methanethiosulfonate, N-ethylmaleimide, and Hg2+ all reacted with the sulfhydryl group to give derivatives which had reduced activities and which dissociated reversibly to inactive dimer. Association of inactive dimer to active octamer was facilitated by the presence of azide (cyanate analog) and bicarbonate, increased temperature and enzyme concentration, and presence of phosphate. Nitration of tyrosine residues by tetranitromethane occurred only in the absence of azide and bicarbonate, suggesting that at least some of the tyrosine residues become exposed when octamer dissociates to dimer. Site-directed mutagenesis was used to prepare a mutant enzyme in which serine was substituted for cysteine. The mutant enzyme was catalytically active and had properties very similar to native enzyme, except that it was less stable to treatment with urea and to high temperatures. These results establish that in native cyanase the sulfhydryl group per se is not required for catalytic activity, but it may play a role in stabilizing octameric structure, and that octameric structure is required for catalytic activity. 相似文献
43.
Uniformly fatty livers from orotic acid-fed rats secreted almost no very low density lipoproteins (VLDL) but normal amounts of nascent high density lipoproteins (HDL) accumulated in perfusates. When lecithin:cholesterol acyltransferase (LCAT) was inhibited, nascent HDL were uniformly discoidal and lacked cholesteryl esters. Lipid and apoprotein compositions of nascent HDL from normal and fatty livers were similar whether LCAT was inhibited or not. Apolipoprotein B-100 was not detected in perfusates of uniformly fatty livers, but small amounts of apolipoprotein B-48 were present in HDL2 fractions. Nascent lipoproteins were not seen in Golgi compartments, but lipid-rich particles were clearly evident in endoplasmic reticulum cisternae adjacent to the cis face of the Golgi complex, suggesting that orotic acid blocks VLDL secretion by preventing translocation of nascent particles from the endoplasmic reticulum to the cis Golgi compartment. The accumulation of normal amounts of discoidal HDL in liver perfusates despite virtual absence of triglyceride-rich lipoproteins in Golgi secretory compartments, the space of Disse, and the perfusate is inconsistent with the concept that nascent HDL are exclusively a product of surface remnants cast off during lipolysis of chylomicrons and VLDL. 相似文献
44.
45.
46.
光合能量代谢对C_3植物光呼吸的调节作用 总被引:1,自引:0,他引:1
C_3植物光呼吸与光合作用关系受光合能量代谢状况的调节。在外界无CO_2和照光条件下,贮藏性光合产物经某种转化途径能“回迁”光合与光呼吸碳循环并显著地受到光合能量代谢的影响。在无CO_2或低CO_2浓度、高光强条件下,此碳素“回迁”过程对协调光合能量代谢与光合碳素代谢平衡,可能起重要作用。 相似文献
47.
西藏金发藓科植物,已知有7属,30种,4变种;其中新种5个,新变种3个。从水平分布看,大多集中雅鲁藏布江流域附近,因该流域是印度板块北缘与欧亚大陆南缘的缝合线,因而金发藓科植物得以高度集中。本文讨论了该科在本区的地理分布和区系成份的分析等问题,并讨论了青藏高原的隆起对该群藓类的影响。 相似文献
48.
49.
50.