全文获取类型
收费全文 | 654篇 |
免费 | 87篇 |
国内免费 | 9篇 |
出版年
2019年 | 7篇 |
2018年 | 14篇 |
2017年 | 7篇 |
2016年 | 6篇 |
2015年 | 25篇 |
2014年 | 19篇 |
2013年 | 22篇 |
2012年 | 30篇 |
2011年 | 29篇 |
2010年 | 29篇 |
2009年 | 20篇 |
2008年 | 16篇 |
2007年 | 20篇 |
2006年 | 27篇 |
2005年 | 8篇 |
2004年 | 27篇 |
2003年 | 12篇 |
2002年 | 22篇 |
2001年 | 22篇 |
2000年 | 16篇 |
1999年 | 14篇 |
1998年 | 11篇 |
1997年 | 11篇 |
1996年 | 9篇 |
1994年 | 11篇 |
1992年 | 8篇 |
1991年 | 16篇 |
1990年 | 12篇 |
1989年 | 11篇 |
1988年 | 15篇 |
1987年 | 13篇 |
1986年 | 12篇 |
1985年 | 18篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 16篇 |
1977年 | 10篇 |
1976年 | 13篇 |
1975年 | 12篇 |
1974年 | 10篇 |
1973年 | 9篇 |
1971年 | 7篇 |
1970年 | 7篇 |
1968年 | 9篇 |
1967年 | 11篇 |
1966年 | 8篇 |
1965年 | 6篇 |
1961年 | 5篇 |
排序方式: 共有750条查询结果,搜索用时 358 毫秒
1.
R. L. Orozco M. D. Redwood P. Yong I. Caldelari F. Sargent L. E. Macaskie 《Biotechnology letters》2010,32(12):1837-1845
Escherichia coli strains MC4100 (parent) and a mutant strain derived from this (IC007) were evaluated for their ability to produce H2 and organic acids (OAs) via fermentation. Following growth, each strain was coated with Pd(0) via bioreduction of Pd(II).
Dried, sintered Pd-biomaterials (‘Bio-Pd’) were tested as anodes in a proton exchange membrane (PEM) fuel cell for their ability
to generate electricity from H2. Both strains produced hydrogen and OAs but ‘palladised’ cells of strain IC007 (Bio-PdIC007) produced ~threefold more power as compared to Bio-PdMC4100 (56 and 18 mW respectively). The power output used, for comparison, commercial Pd(0) powder and Bio-Pd made from Desulfovibrio desulfuricans, was ~100 mW. The implications of these findings for an integrated energy generating process are discussed. 相似文献
2.
3.
Mammographic changes following reduction mammaplasty 总被引:2,自引:0,他引:2
Mammographic findings after reduction mammaplasty may be similar to those seen with carcinoma. A knowledge of the expected mammographic alterations would be helpful in differentiating postoperative changes from those seen with carcinoma of the breast. Accordingly, the clinical records and mammograms of patients who underwent reduction mammaplasty at the Dartmouth-Hitchcock Medical Center between March of 1977 and July of 1985 were analyzed. Forty-two patients had at least one mammographic examination following reduction mammaplasty. Periareolar soft-tissue changes and inferior pole alterations were present in almost all examinations of patients during the first 6 months after operation, but they decreased during the next few years. Asymmetrical densities were present in approximately half the patients throughout the follow-up period but decreased in degree. Parenchymal calcifications occurred later; few x-rays showed these calcifications during the first year, but 50 percent were apparent after 2 years. Evidence of fat necrosis occurred in approximately 10 percent. Four patients had biopsies for suspicious densities. Chronic inflammation and inclusion cyst were reported. We believe that changes after reduction mammaplasty are predictable and can usually be differentiated from those associated with cancer. 相似文献
4.
5.
D R Tocher J Carr J R Sargent 《Comparative biochemistry and physiology. B, Comparative biochemistry》1989,94(2):367-374
1. The incorporation and metabolism of (n-3) and (n-6) polyunsaturated fatty acids (PUFA) supplemented to growing cultures were studied in rainbow trout (RTG-2) and turbot (TF) cell lines. 2. A fatty acid concentration of 20 microM considerably altered the fatty acid composition of the cells without affecting lipid class composition or the appearance of cytoplasmic lipid droplets. 3. Both cell lines exhibited considerable delta 6 desaturase activities. 4. Whereas delta 5 desaturase activity was expressed in RTG-2 cells, delta 4 desaturase activity was absent and, conversely, delta 4 desaturase activity was expressed in TF cells, but there was an apparent deficiency in the C18 to C20 elongase multi-enzyme complex. 5. The delta 6 desaturase activity in both cell lines showed little preference between 18:2(n-6) and 18:3(n-3) but the delta 5 desaturase activity of RTG-2 cells and the delta 4 desaturase activity of TF cells showed a preference for (n-3)PUFA. 6. Two fish oil concentrates were assessed for their ability to generate fatty acid compositions in the cell lines more closely resembling those of intact fish tissues. 相似文献
6.
The thermostable tailspike endorhamnosidase of bacteriophage P22 has been investigated by laser Raman spectroscopy to determine the protein's secondary structure and the basis of its thermostability. The conformation of the native tailspike, determined by Raman amide I and amide III band analyses, is 52 to 61% beta-sheet, 24 to 27% alpha-helix, 15 to 21% beta-turn and 0 to 10% other structure types. The secondary structure of the wild-type tailspike, as monitored by the conformation-sensitive Raman amide bands, was stable to 80 degrees C, denatured reversibly between 80 and 90 degrees C, and irreversibly above 90 degrees C. The purified native form of a temperature-sensitive folding mutant (tsU38) contains secondary structures virtually identical to those in the wild-type in aqueous solution at physiological conditions (0.05 M-Na+ (pH 7.5], at both permissive (20 degrees C) and restrictive (40 degrees C) temperatures. This supports previous results showing that the mutational defect at 40 degrees C affects intermediates in the folding pathway rather than the native structure. At temperatures above 60 degrees C the wild-type and mutant forms were distinguishable: the reversible and irreversible denaturation thresholds were approximately 15 to 20 degrees C lower in the mutant than in the wild-type protein. The irreversible denaturation of the mutant tailspikes led to different aggregation/polymerization products from the wild-type, indicating that the mutation altered the unfolding pathway. In both cases only a small percentage of the native secondary structure was altered by irreversible thermal denaturation, indicating that the aggregated states retain considerable native structure. 相似文献
7.
8.
An overview of the secondary structure of the V4 region of eukaryotic small-subunit ribosomal RNA. 总被引:3,自引:2,他引:1 下载免费PDF全文
The V4 region of the small subunit (18S) ribosomal RNA was examined in 72 different sequences representing a broad sample eukaryotic diversity. This domain is the most variable region of the 18S rRNA molecule and ranges in length from ca. 230 to over 500 bases. Based upon comparative analysis, secondary structural models were constructed for all sequences and the resulting generalized model shows that most organisms possess seven helices for this region. The protists and two insects show from one to as many as four helices in addition to the above seven. In this report, we summarize secondary structure information presented elsewhere for the V4 region, describe the general features for helical and apical regions, and identify signature sequences useful in helix identification. Our model generally agrees with other current concepts; however, we propose modifications or alternative structures for the start of the V4 region, the large protist inserts, and the sector that may possibly contain a pseudoknot. 相似文献
9.
10.
J M Berman T M Chen R Sargent S H Buck P Shea E F Heminger R J Broersma 《FEBS letters》1988,237(1-2):76-80
Two analogs of rat atrial natriuretic factor, rANF7-28-NH2 and [Mpr7,Ala20,D-Arg27]rANF7-27-NH2, were prepared by the solid-phase method. These peptides had 2-fold and 7-fold less affinity, respectively, than rANF1-28 in binding to membranes prepared from cultured aortic smooth muscle cells, and both peptides were 5-fold less potent than rANF1-28 in relaxing serotonin-contracted rabbit aortic rings. rANF7-28-NH2 was rapidly degraded by rat kidney homogenates but [Mpr7,Ala20,D-Arg27]rANF7-27-NH2 had enhanced stability against rat kidney homogenate degradation. However, this in vitro stability did not translate into an extended duration of action in vivo. 相似文献