全文获取类型
收费全文 | 165篇 |
免费 | 16篇 |
专业分类
181篇 |
出版年
2021年 | 3篇 |
2019年 | 2篇 |
2018年 | 3篇 |
2017年 | 6篇 |
2016年 | 5篇 |
2015年 | 10篇 |
2014年 | 6篇 |
2013年 | 9篇 |
2012年 | 6篇 |
2011年 | 10篇 |
2010年 | 4篇 |
2009年 | 4篇 |
2008年 | 8篇 |
2007年 | 7篇 |
2006年 | 7篇 |
2005年 | 11篇 |
2004年 | 10篇 |
2003年 | 5篇 |
2002年 | 2篇 |
2001年 | 2篇 |
1999年 | 2篇 |
1998年 | 5篇 |
1996年 | 2篇 |
1992年 | 2篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1972年 | 2篇 |
1970年 | 1篇 |
1967年 | 2篇 |
1965年 | 1篇 |
1964年 | 2篇 |
1962年 | 3篇 |
1960年 | 2篇 |
1958年 | 1篇 |
1955年 | 2篇 |
1950年 | 1篇 |
1949年 | 1篇 |
1943年 | 1篇 |
1940年 | 1篇 |
1939年 | 2篇 |
1938年 | 2篇 |
1937年 | 1篇 |
1936年 | 2篇 |
1932年 | 1篇 |
1924年 | 1篇 |
1921年 | 1篇 |
1920年 | 1篇 |
1918年 | 1篇 |
1916年 | 1篇 |
1915年 | 1篇 |
排序方式: 共有181条查询结果,搜索用时 0 毫秒
1.
Isolated testes of the locust Schistocerca gregaria were immersed in solutions of tritiated thymidine, cytidine, uridine, or arginine for short periods to study nucleic acid and protein synthesis during spermatogenesis. DNA synthesis in this tissue is completed prior to initiation of meiosis. Protein synthesis continues throughout the whole meiotic cycle as well as during spermatid development. Meiotic cells, except those in metaphase through early telophase, and early spermatids are also actively synthesizing RNA. The heteropycnotic X-chromosome does not produce RNA at any stage of spermatogenesis. The rates of protein and particularly RNA synthesis decrease as chromosome condensation progresses. Depression of RNA synthesis, however, is not always accompanied by cytologically detectable condensation of chromatin, since very little or no RNA is synthesized in spermatids in which chromatin condensation has barely begun. 相似文献
2.
3.
Jimenez EC Shetty RP Lirazan M Rivier J Walker C Abogadie FC Yoshikami D Cruz LJ Olivera BM 《Journal of neurochemistry》2003,85(3):610-621
A new class of Conus peptides, the I-superfamily of conotoxins, has been characterized using biochemical, electrophysiological and molecular genetic methods. Peptides in this superfamily have a novel pattern of eight Cys residues. Five peptides that elicited excitatory symptomatology, r11a, r11b, r11c, r11d and r11e, were purified from Conus radiatus venom; four were tested on amphibian peripheral axons and shown to elicit repetitive action potentials, consistent with being members of the 'lightning-strike cabal' of toxins that effect instant immobilization of fish prey. A parallel analysis of Conus cDNA clones revealed a new class of conotoxin genes that was particularly enriched (with 18 identified paralogues) in a Conus radiatus venom duct library; several C. radiatus clones encoded the excitatory peptides directly characterized from venom. The remarkable diversity of related I-superfamily peptides within a single Conus species is unprecedented. When combined with the excitatory effects observed on peripheral circuitry, this unexpected diversity suggests a corresponding molecular complexity of the targeted signaling components in peripheral axons; the I-conotoxin superfamily should provide a rich lode of pharmacological tools for dissecting and understanding these. Thus, the I-superfamily conotoxins promise to provide a significant new technology platform for dissecting the molecular components of axons. 相似文献
4.
5.
One of the most frequently given reasons for relinquishing a companion animal to an animal shelter is that the person or family is moving. Telephone interviews conducted with 57 caregivers who relinquished animal companions to a shelter in the midwestern United States covered details of the move, characteristics both of the caregivers and the animals, and efforts to avoid relinquishment. A human-nonhuman animal bonding scale also was administered. Although some participants had additional reasons for relinquishment, the majority had given up their pets solely because they were moving. Most had relatively low income, were moving for employment reasons, and were renting their homes. Landlord restrictions were an important factor in relinquishment. High scores on the bonding scale and spontaneous expressions of discomfort and sorrow suggest that external pressures overrode attachment to the animal and the pain of relinquishment. 相似文献
6.
7.
Gbotosho GO Sowunmi A Okuboyejo TM Happi CT Michael OS Folarin OA Adewoye EO 《Memórias do Instituto Oswaldo Cruz》2011,106(5):562-569
Anaemia in falciparum malaria is associated with an increased risk of gametocyte carriage, but its effects on transmission have not been extensively evaluated in malarious children. Plasmodium falciparum gametocyte carriage, emergence, clearance, population sex ratios (SR) (defined as the proportion of gametocytes that are male), inbreeding rates and temporal changes in SR were evaluated in 840 malarious children. Gametocyte carriage pre-treatment was at a level of 8.1%. Anaemia at enrolment was an independent risk factor for gametocyte carriage post-treatment. The emergence of gametocytes seven days post-treatment was significantly more frequent in anaemic children (7/106 vs. 10/696, p = 0.002). In the initially detected gametocytes, the proportion of children with a male-biased SR (MBSR) (> 0.5) was significantly higher in anaemic children (6/7 vs. 3/10, p = 0.027). Pre-treatment SR and estimated inbreeding rates (proportion of a mother's daughters fertilised by her sons) were similar in anaemic and non-anaemic children. Pre-treatment SR became more female-biased in non-anaemic children following treatment. However, in anaemic children, SR became male-biased. Anaemia was shown to significantly increase gametocyte emergence and may significantly alter the SR of emerging gametocytes. If MBSR is more infective to mosquitoes at low gametocytaemia, then these findings may have significant implications for malaria control efforts in endemic settings where malaria-associated anaemia is common. 相似文献
8.
Anton Pauw Sunshine A. Van Bael Halton A. Peters Steven D. Allison José L. C. Camargo Miguel Cifuentes-Jara Aurlstela Conserva Teresa Garcia Restom Tamara Heartsill-Scalley Scott A. Mangan Gabriela Nunez-lturri Elsie Rivera-Ocasio Mark Rountree Susanne Vetter Carolina Volkmer de Castllho 《Biotropica》2004,36(3):410-413
9.
A number of thrombin mutants have been constructed to investigate the role of Trp96 and the β-insertion loop for the specificity of thrombin. Thrombin(60D) consists of the replacement of the β-insertion loop (14 amino acid residues from 59 to 63, including a 9-residue insertion at position 60) with the corresponding four residues in trypsin, Tyr-Lys-Ser-Gly; thrombin(GGG) is a smaller loop mutation in which the residues Tyr60APro60BPro60CTrp60D Asp60ELys60F of the β-insertion loop were replaced by Gly-Gly-Gly; thrombin(96S) consists of a point mutation Trp96→Ser; and thrombin(GGG/96S) is the double mutant incorporating both changes. Thrombin(96S) clots fibrinogen ~3 times more slowly than thrombin, with the two β-insertion loop mutants, thrombin(GGG) and thrombin(GGG/96S), reacting ~3000- and 1300-fold more slowly, respectively. The specificity constant k cat/K m for the cleavage of fibrinopeptide A and fibrinopeptide B by thrombin(96S) was 2.6 and 0.35 μM?1 s?1 respectively, compared to 10 and 2.5 μM?1 s?1 for wild-type recombinant thrombin, respectively. Kinetic constants were determined for the hydrolysis of H-D-phenylalanyl-L-pipecolyl-L-arginine-p-nitroaniline. The Michaelis constant K m increased ~6-fold for thrombin(96S) and >200-fold for thrombin(GGG) and thrombin(GGG/96S) when compared to wild-type recombinant thrombin, while the catalytic constant k cat remained approximately the same. All mutants were more susceptible to inhibition by BPTI than wild-type recombinant thrombin. Clearly, the β-insertion loop is important for thrombin activity. But the mutation of Trp96→Ser can compensate somewhat for the loss of binding at the β-insertion loop. The deletion of the hydrophobic interaction between Trp96 and Pro60BPro60C appears to decrease the stability of the β-insertion loop, thereby causing a decrease in binding efficiency. 相似文献
10.