全文获取类型
收费全文 | 333998篇 |
免费 | 39436篇 |
国内免费 | 202篇 |
专业分类
373636篇 |
出版年
2016年 | 3818篇 |
2015年 | 5110篇 |
2014年 | 5930篇 |
2013年 | 8793篇 |
2012年 | 10895篇 |
2011年 | 11244篇 |
2010年 | 7122篇 |
2009年 | 6198篇 |
2008年 | 9835篇 |
2007年 | 10149篇 |
2006年 | 9573篇 |
2005年 | 9239篇 |
2004年 | 8947篇 |
2003年 | 8921篇 |
2002年 | 8574篇 |
2001年 | 12343篇 |
2000年 | 12659篇 |
1999年 | 9980篇 |
1998年 | 3974篇 |
1997年 | 4077篇 |
1996年 | 4119篇 |
1995年 | 3815篇 |
1994年 | 3837篇 |
1993年 | 3758篇 |
1992年 | 8503篇 |
1991年 | 8241篇 |
1990年 | 8014篇 |
1989年 | 7922篇 |
1988年 | 7459篇 |
1987年 | 7411篇 |
1986年 | 6864篇 |
1985年 | 7067篇 |
1984年 | 6037篇 |
1983年 | 5420篇 |
1982年 | 4377篇 |
1981年 | 4197篇 |
1980年 | 3817篇 |
1979年 | 6162篇 |
1978年 | 4872篇 |
1977年 | 4637篇 |
1976年 | 4437篇 |
1975年 | 4789篇 |
1974年 | 5224篇 |
1973年 | 5109篇 |
1972年 | 4692篇 |
1971年 | 4260篇 |
1970年 | 3738篇 |
1969年 | 3762篇 |
1968年 | 3367篇 |
1967年 | 2893篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Cyanobacteria are prominent constituents of the marine biosphere that account for a significant percentage of oceanic primary productivity. In an effort to resolve how open-ocean cyanobacteria persist in regions where the Fe concentration is thought to be limiting their productivity, we performed a number of Fe stress experiments on axenic cultures of marine Synechococcus spp., Crocosphaera sp., and Trichodesmium sp. Through this work, we determined that all of these marine cyanobacteria mount adaptive responses to Fe stress, which resulted in the induction and/or repression of several proteins. We have identified one of the Fe stress-induced proteins as an IdiA homologue. Genomic observations and laboratory data presented herein from open-ocean Synechococcus spp. are consistent with IdiA having a role in cellular Fe scavenging. Our data indicate that IdiA may make an excellent marker for Fe stress in open-ocean cyanobacterial field populations. By determining how these microorganisms respond to Fe stress, we will gain insight into how and when this important trace element can limit their growth in situ. This knowledge will greatly increase our understanding of how marine Fe cycling impacts oceanic processes, such as carbon and nitrogen fixation. 相似文献
103.
K. H. Jang J. W. Seo K. B. Song C. H. Kim S. K. Rhee 《Bioprocess and biosystems engineering》1999,21(5):453-458
Secretion of levansucrase from Zymomonas mobilis in Escherichiacoli by glycine supplement was investigated. A significant amount of levansucrase (about 25% of total activity) was found in intact whole-cells. Cell fractionation experiments showed that levansucrase was found both in the periplasmic space and in the cytoplasmic fraction of E. coli. None or only trace amounts of levansucrase was detected in the extracellular culture broth at 24 h of cultivation and it accrued with the increasing concentration of glycine in the culture medium and duration of the culture period. Optimal glycine concentration for the maximum secretion of levansucrase was in the range of 0.8-1%, in which approximately 20-50% of levansucrase was released into the extracellular fraction at 24 h of cultivation, although glycine retarded the bacterial growth. 相似文献
104.
N. Yamada W. Murata Y. Yamaguchi K.-I. Fujita A. Ogita T. Tanaka 《Letters in applied microbiology》2021,72(4):390-398
Amphotericin B (AmB), a typical polyene macrolide antifungal agent, is widely used to treat systemic mycoses. In the present study, we show that the fungicidal activity of AmB was enhanced by benzyl isothiocyanate (BITC), a cruciferous plant-derived compound, in the budding yeast, Saccharomyces cerevisiae. In addition to forming a molecular complex with ergosterol present in fungal cell membranes to form K+-permeable ion channels, AmB has been recognized to mediate vacuolar membrane disruption resulting in lethal effects. BITC showed no effect on AmB-induced plasma membrane permeability; however, it amplified AmB-induced vacuolar membrane disruption in S. cerevisiae. Furthermore, the BITC-enhanced fungicidal effects of AmB significantly decreased cell viability due to the disruption of vacuoles in the pathogenic fungus Candida albicans. The application of the combinatorial antifungal effect of AmB and BITC may aid in dose reduction of AmB in clinical antifungal therapy and consequently decrease side effects in patients. These results also have significant implications for the development of vacuole-targeting chemotherapy against fungal infections. 相似文献
105.
106.
107.
Use of restriction endonucleases and exonuclease III to expose halogenated pyrimidines for immunochemical staining 总被引:1,自引:0,他引:1
We describe an enzymatic procedure for exposure of single-stranded DNA (ssDNA) containing the halogenated pyrimidines (HdUrd) bromodeoxyuridine (BrdUrd) or iododeoxyuridine (IdUrd) in single cells to antibodies that bind to HrdUrd only in ssDNA. Production of ssDNA was accomplished by digesting the DNA using either restriction endonucleases alone or endonucleases followed by exonuclease III. The enzymatic production of ssDNA was maximal when 0.1 N HCl or 0.1 M citric acid plus Triton X-100 was added to extract nuclear proteins prior to enzymatic denaturation. The restriction endonucleases Bam HI, Dde I, Eco RI, and Hind III produced significant ssDNA when used alone to allow binding of detectable amounts of the anti-HdUrd antibody IU-4 in Chinese hamster ovary cells labeled with 10 microM BrdUrd or 10 microM IdUrd. However, these treatments did not expose sufficient ssDNA to allow binding of IU-1, an anti-HdUrd antibody with lower binding affinity. IU-4 binding was most intense after treatment with Eco RI. Treatment with exonuclease III following endonuclease digestion allowed substantially more IU-4 binding. 相似文献
108.
W A Van Sickle H G Wilcox A Nasjletti 《Biochemical and biophysical research communications》1986,139(2):416-423
The objective of this study was to determine if the apoprotein or lipid constituents of high density lipoproteins (HDL) mediate HDL-induced prostacyclin synthesis in the Langendorff-perfused rabbit heart. Acetylation, acetoacetylation, or partial removal by trypsin digestion of HDL apoprotein did not reduce the ability of the lipoprotein to stimulate cardiac prostacyclin synthesis. Delipidated apoproteins were less effective in stimulating cardiac prostacyclin synthesis in comparison to intact HDL. In contrast, protein-free lipid vesicles, made from HDL lipids, caused a pronounced stimulation of cardiac prostacyclin synthesis. These results suggest that HDL apoproteins, in their native state, are not essential for HDL-induced cardiac prostacyclin synthesis. The stimulation of cardiac prostacyclin synthesis by HDL may depend on the lipoprotein's lipid rather than on its apoprotein constituents. 相似文献
109.
110.