全文获取类型
收费全文 | 1286篇 |
免费 | 115篇 |
专业分类
1401篇 |
出版年
2023年 | 7篇 |
2022年 | 19篇 |
2021年 | 36篇 |
2020年 | 18篇 |
2019年 | 25篇 |
2018年 | 28篇 |
2017年 | 28篇 |
2016年 | 35篇 |
2015年 | 46篇 |
2014年 | 47篇 |
2013年 | 79篇 |
2012年 | 77篇 |
2011年 | 89篇 |
2010年 | 38篇 |
2009年 | 37篇 |
2008年 | 47篇 |
2007年 | 76篇 |
2006年 | 47篇 |
2005年 | 39篇 |
2004年 | 50篇 |
2003年 | 34篇 |
2002年 | 31篇 |
2001年 | 34篇 |
2000年 | 29篇 |
1999年 | 26篇 |
1998年 | 13篇 |
1997年 | 12篇 |
1995年 | 9篇 |
1994年 | 11篇 |
1993年 | 7篇 |
1992年 | 26篇 |
1991年 | 28篇 |
1990年 | 25篇 |
1989年 | 26篇 |
1988年 | 14篇 |
1987年 | 12篇 |
1986年 | 12篇 |
1985年 | 16篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 16篇 |
1978年 | 17篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1973年 | 7篇 |
1972年 | 10篇 |
1971年 | 9篇 |
1966年 | 7篇 |
排序方式: 共有1401条查询结果,搜索用时 15 毫秒
41.
A novel technique to overcome browning in tissue culture 总被引:13,自引:0,他引:13
Experiments conducted using Dioscorea alata L. revealed that an exudate from the cut end of the explants was responsible for browning of the culture medium. Browning did not affect growth of roots and shoots when explants were cultured in a large volume of medium, but in a small volume it was lethal. Sealing the cut ends with paraffin wax was found to control browning by preventing exudation. This simple technique permitted establishment of cultures in a small volume of medium in about 90 percent of the cases, while in unsealed cultures lethal browning was recorded in 80 percent of the cases. The advantages of this technique over other methods of controlling browning are discussed. 相似文献
42.
Prevalence of gene sequences coding for hypervariable regions of Opa (protein II) in Neisseria gonorrhoeae 总被引:3,自引:0,他引:3
G. F. Brooks L. Olinger C. J. Lammel K. S. Bhat C. A. Calvello M. L. Palmer J. S. Knapp R. S. Stephens 《Molecular microbiology》1991,5(12):3063-3072
Opas (protein IIs) are a family of surface-exposed proteins of Neisseria gonorrhoeae. Each strain of N. gonorrhoeae has multiple (10-11) genes encoding for Opas. Identifiable elements in opa genes include the coding repeat within the signal sequence, conserve 5' and 3' regions, and hypervariable regions (HV1 and HV2) located within the structural gene. N. gonorrhoeae strains appear to have many biological properties in common that are either HV-region-mediated or associated with the presence of specific HV regions, suggesting that HV regions could be found in many clinical isolates. Oligonucleotides from three source strains representing three conserved regions of opa, 12 HV1 regions, and 14 HV2 regions were used by dot blot analysis to probe 120 clinical isolates of N. gonorrhoeae. The probe for the coding repeat hybridized to all 120 strains, the 3' conserved-region probe reacted with 98% of the strains, and the 5' conserved-region probe with 90% of the strains. Nine HV1 probes hybridized to 3.3-39.2% of the strains, and 13 of the HV2 probes hybridized to 1.7-25% of the isolates. Analysis of the number of probes that hybridized to each of the isolates showed that 19% did not hybridize with any of the HV1 probes and 25% did not hybridize with any of the HV2 probes. Approximately three-quarters of the isolates hybridized with one, two or three of the HV1 probes or one, two or three of the HV2 probes; 89% of the isolates hybridized to least one HV1 or one HV2 probe. The data indicate that some genes encoding HV regions of N. gonorrhoeae Opa proteins are widely distributed in nature. 相似文献
43.
Analysis of the Gal3 Signal Transduction Pathway Activating Gal4 Protein-Dependent Transcription in Saccharomyces Cerevisiae 总被引:12,自引:2,他引:10
下载免费PDF全文
![点击此处可从《Genetics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The Saccharomyces cerevisiae GAL/MEL regulon genes are normally induced within minutes of galactose addition, but gal3 mutants exhibit a 3-5-day induction lag. We have discovered that this long-term adaptation (LTA) phenotype conferred by gal3 is complemented by multiple copies of the GAL1 gene. Based on this result and the striking similarity between the GAL3 and GAL1 protein sequences we attempted to detect galactokinase activity that might be associated with the GAL3 protein. By both in vivo and in vitro tests the GAL3 gene product does not appear to catalyze a galactokinase-like reaction. In complementary experiments, Escherichia coli galactokinase expressed in yeast was shown to complement the gal1 but not the gal3 mutation. Thus, the complementation activity provided by GAL1 is not likely due to galactokinase activity, but rather due to a distinct GAL3-like activity. Overall, the results indicate that GAL1 encodes a bifunctional protein. In related experiments we tested for function of the LTA induction pathway in gal3 cells deficient for other gene functions. It has been known for some time that gal3gal1, gal3gal7, gal3gal10, and gal3 rho- are incapable of induction. We constructed isogenic haploid strains bearing the gal3 mutation in combination with either gal15 or pgi1 mutations: the gal15 and pgi1 blocks are not specific for the galactose pathway in contrast to the gal1, gal7 and gal10 blocks. The gal3gal5 and gal3pgi1 double mutants were not inducible, whereas both the gal5 and pgi1 single mutants were inducible. We conclude that, in addition to the GAL3-like activity of GAL1, functions beyond the galactose-specific GAL1, GAL7 and GAL10 enzymes are required for the LTA induction pathway. 相似文献
44.
Mitochondrial DNA (mtDNA) from two breeds of cattle, viz., [Hariana (Bos indicus), Holstein (Bos taurus)] and Indian water buffalo (Bubalis bubalus), was analyzed using 13 restriction endonucleases which recognized an average of about 40 six-base sites. Polymorphism among
cattle was detected with six of these enzymes. The two Holstein differed at six sites, whereas the Hariana breed (Bos indicus) did not show any site polymorphism. Surprisingly, the Hariana type differed by only one site from one of the Holstein types.
The total size of buffalo mtDNA was estimated to be 16.4 kb. Polymorphism within the Murrah buffalo breed was observed with
respect to aBglI site. Scarcely any of the restriction fragments of buffalo mtDNA matched those of cattle mtDNA. 相似文献
45.
The fine needle aspiration (FNA) observations in a case of gynecomastia occurring in a mortician are described. The FNA smear showed cytomorphologic features typical of a gynecomastia. Morticians use an embalming cream that contains estrogens or estrogenlike compounds; these substances may be absorbed percutaneously and cause the development of gynecomastia. The mortician should be made aware of the potential risk of such an occupational exposure and development of the "embalmer's curse. "Recognition by the clinicians and cytopathologists of such an occurrence and its implications can help with the proper management. 相似文献
46.
Summary A method is described for computing the theoretical distribution of solutes around a root with root hairs. The P concentration profile around the primary root of a rape seedling with root hairs, growing in a low-P soil, showed considerably greater depletions than predicted by this method, using the relationship between P in soil and in solution obtained from a desorption isotherm experiment. This suggests an enhanced release of soil P into solution in the rhizosphere.Soil Science Laboratory, Department of Agricultural Science, University of Oxford 相似文献
47.
Farwa Basit Javaid Akhter Bhat Jiajun Han Yajing Guan Basit Latief Jan Awais Shakoor Saleh Alansi 《Saudi Journal of Biological Sciences》2022,29(5):3918-3928
Rice is the most important crop for the majority of population across the world with sensitive behavior toward heavy metals such as chromium (Cr) in polluted regions. Although, there is no information on the Cr resistance phenotyping in rice. Herein, two different groups of rice cultivars (normal, and hybrid) were used, each group with 14 different rice cultivars. Firstly, seed germination analysis was conducted by evaluating various seed germination indices to identify the rice cultivars with greatest seed germination vigor. Furthermore, exposure of chromium (Cr) toxicity to 28 different rice varieties (NV1-NV14, HV1-HV14) caused noticeable plant biomass reduction. Subsequently, NV2, NV6, NV10, NV12, NV13 (normal type), HV1, HV4, HV8, and HV9 (hybrid types) were pragmatic as moderately sensitive varieties, while NV3, NV4, NV9, and NV14 (normal type), HV3, HV6, HV7, and HV13 were observed as moderately tolerant. Although, NV7, and HV10 were ranked most sensitive cultivars, and NV11, and HV14 were considered as most tolerant varieties as compared to the other rice (both groups) genotypes. Afterward, Cr induced reduction in chlorophyll pigments were significantly lesser in HV14 relative to NV11, NV7, and especially HV10, and as a result HV14 modulated the total soluble sugar level as well as reduced ROS accumulation, and MDA contents production by stimulating the antioxidant defense mechanism conspicuously which further reduced the electrolyte leakage as well. Our outcomes provide support to explore the Cr tolerance mechanism in cereal crops as well as knowledge about rice breeding with increased tolerance against Cr stress. 相似文献
48.
Jensen KK Previs SF Zhu L Herath K Wang SP Bhat G Hu G Miller PL McLaren DG Shin MK Vogt TF Wang L Wong KK Roddy TP Johns DG Hubbard BK 《American journal of physiology. Endocrinology and metabolism》2012,302(2):E209-E217
The liver is a crossroad for metabolism of lipid and carbohydrates, with acetyl-CoA serving as an important metabolic intermediate and a precursor for fatty acid and cholesterol biosynthesis pathways. A better understanding of the regulation of these pathways requires an experimental approach that provides both quantitative metabolic flux measurements and mechanistic insight. Under conditions of high carbohydrate availability, excess carbon is converted into free fatty acids and triglyceride for storage, but it is not clear how excessive carbohydrate availability affects cholesterol biosynthesis. To address this, C57BL/6J mice were fed either a low-fat, high-carbohydrate diet or a high-fat, carbohydrate-free diet. At the end of the dietary intervention, the two groups received (2)H(2)O to trace de novo fatty acid and cholesterol synthesis, and livers were collected for gene expression analysis. Expression of lipid and glucose metabolism genes was determined using a custom-designed pathway focused PCR-based gene expression array. The expression analysis showed downregulation of cholesterol biosynthesis genes and upregulation of fatty acid synthesis genes in mice receiving the high-carbohydrate diet compared with the carbohydrate-free diet. In support of these findings, (2)H(2)O tracer data showed that fatty acid synthesis was increased 10-fold and cholesterol synthesis was reduced by 1.6-fold in mice fed the respective diets. In conclusion, by applying gene expression analysis and tracer methodology, we show that fatty acid and cholesterol synthesis are differentially regulated when the carbohydrate intake in mice is altered. 相似文献
49.
50.
Summary Representative strains of distinctly flagellated, but doubtfully motile, coryneform bacteria were isolated from the intestine of Indian earthworms. Their morphological, cultural, physiological and nutritional characters are described, and their taxonomic position discussed. 相似文献