全文获取类型
收费全文 | 111125篇 |
免费 | 13293篇 |
国内免费 | 412篇 |
专业分类
124830篇 |
出版年
2021年 | 749篇 |
2018年 | 1000篇 |
2017年 | 969篇 |
2016年 | 1263篇 |
2015年 | 1566篇 |
2014年 | 1961篇 |
2013年 | 2491篇 |
2012年 | 2894篇 |
2011年 | 2842篇 |
2010年 | 1903篇 |
2009年 | 1874篇 |
2008年 | 2399篇 |
2007年 | 2376篇 |
2006年 | 2368篇 |
2005年 | 2167篇 |
2004年 | 2110篇 |
2003年 | 2140篇 |
2002年 | 2117篇 |
2001年 | 9665篇 |
2000年 | 9526篇 |
1999年 | 7206篇 |
1998年 | 1623篇 |
1997年 | 1794篇 |
1996年 | 1588篇 |
1995年 | 1421篇 |
1994年 | 1314篇 |
1993年 | 1253篇 |
1992年 | 4800篇 |
1991年 | 4536篇 |
1990年 | 3999篇 |
1989年 | 4019篇 |
1988年 | 3618篇 |
1987年 | 3089篇 |
1986年 | 2788篇 |
1985年 | 2688篇 |
1984年 | 1974篇 |
1983年 | 1733篇 |
1982年 | 1233篇 |
1981年 | 988篇 |
1980年 | 916篇 |
1979年 | 1762篇 |
1978年 | 1368篇 |
1977年 | 1200篇 |
1976年 | 1029篇 |
1975年 | 1150篇 |
1974年 | 1169篇 |
1973年 | 1165篇 |
1972年 | 1034篇 |
1971年 | 958篇 |
1970年 | 823篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
942.
I Edfors-Lilja U Gustafsson Y Duval-Iflah H Ellergren M Johansson R K Juneja L Marklund L Andersson 《Animal genetics》1995,26(4):237-242
The loci encoding the porcine intestinal receptors for Escherichia coli K88ab and K88ac (K88abR and K88acR) were firmly assigned to chromosome 13 by linkage analysis using a three-generation pedigree. The linear order of these loci and seven other markers on chromosome 13 was determined by multipoint analyses. The K88abR and K88acR loci were tightly linked with the K88abR locus localized 7·4 cM (sex average) proximal to the transferrin locus. The results, together with previous reports from two other groups, provide an unequivocal assignment of the K88 receptor loci to chromosome 13, and reject a previous assignment to chromosome 4. Pigs possessing the receptor had a slightly higher specific IgG response to the K88 antigen after an intramuscular immunization with an E. coli vaccine. 相似文献
943.
Plasmids containing a Pseudomonas sp. strain 109 extracellular lipase gene (lipL) lacking NH2-terminal sequence and a lipase modulator gene (limL) lacking the NH2-terminal hydrophobic region were constructed and expressed independently in Escherichia coli by using the T7 promoter expression vector system. Recombinant LipL (rLipL) was produced as inclusion bodies, whereas recombinant LimL (rLimL) was present as a soluble protein. During in vitro renaturation of the purified rLipL inclusion bodies after they had been dissolved in 8 M urea, addition of rLimL was essential to solubilize and modulate rLipL. The solubility and activity of rLipL were influenced by the rLimL/rLipL molar ratio; the highest level of solubility was obtained at an rLimL/rLipL ratio of 4:5, whereas the highest activity level was obtained at an rLimL/rLipL ratio of 4:1. After renaturation, rLipL and rLimL were coprecipitated with anti-rLipL antibody, indicating the formation of an rLipL-rLimL complex. Activity of the native lipase purified from Pseudomonas sp. strain 109 was also inhibited by rLimL. By Western blotting (immunoblotting) with anti-rLimL antibody, native LimL was detected in Pseudomonas cells solubilized by sarcosyl treatment. LimL was purified from Pseudomonas sp. strain 109, and the NH2-terminal amino acid sequence was determined to be NH2-Leu-Glu-Pro-Ser-Pro-Ala-Pro-. We propose that to prevent membrane degradation, LimL weakens lipase activity inside the cell, especially in the periplasm, in addition to modulating lipase folding. 相似文献
944.
The cut locus encodes a homeobox protein that is localized in the nuclei of a variety of tissues and is required for proper morphogenesis of those tissues. Cut protein is required in embryonic and adult external sensory organs, where its absence results in conversion of the organs to chordotonal organs. Expression of cut also occurs in the Malpighian tubules, spiracles, central nervous system, and a number of other tissues. Gypsy transposon insertions upstream of the cut promoter block expression in subsets of these tissues. The effect of the gypsy insertions is polar, with those farthest from the promoter affecting the fewest tissues. The hypothesis that gypsy insertions block a series of tissue-specific enhancer elements that are distributed over a region of 80 kb upstream of the promoter predicts the location of the enhancers for cut expression in each of the tissues in which it is active in embryos. DNA fragments from this region drive expression of a reporter gene in each of the embryonic tissues in which endogenous cut gene is expressed. Each tissue has its own enhancer, and none of the enhancers require the activity of the endogenous cut gene to function. 相似文献
945.
946.
Ubiquitous and neuronal DNA-binding proteins interact with a negative regulatory element of the human hypoxanthine phosphoribosyltransferase gene. 总被引:2,自引:2,他引:0 下载免费PDF全文
D E Rincn-Limas F Amaya-Manzanares M L Nio-Rosales Y Yu T P Yang P I Patel 《Molecular and cellular biology》1995,15(12):6561-6571
947.
948.
949.
Dall'Olio Fabio; Mariani Erminia; Tarozzi Andrea; Meneghetti Alessandra; Chiricolo Mariella; Lau Joseph T. Y.; Facchini Andrea 《Glycobiology》1997,7(4):507-513
The extent of processing of N-linked oligosaccharides and thesialylation of the target cell membranes has been positivelycorrelated with resistance to lysis mediated by NK cells, buta conclusive evidence has never been reached. Colon cancer tissuesexpress an increased activity of ß-ga-lactoside 相似文献
950.
OBJECTIVE: To test the efficacy of a graded aerobic exercise programme in the chronic fatigue syndrome. DESIGN: Randomised controlled trial with control treatment crossover after the first follow up examination. SETTING: Chronic fatigue clinic in a general hospital department of psychiatry. SUBJECTS: 66 patients with the chronic fatigue syndrome who had neither a psychiatric disorder nor appreciable sleep disturbance. INTERVENTIONS: Random allocation to 12 weeks of either graded aerobic exercise or flexibility exercises and relaxation therapy. Patients who completed the flexibility programme were invited to cross over to the exercise programme afterwards. MAIN OUTCOME MEASURE: The self rated clinical global impression change score, "very much better" or "much better" being considered as clinically important. RESULTS: Four patients receiving exercise and three receiving flexibility treatment dropped out before completion. 15 of 29 patients rated themselves as better after completing exercise treatment compared with eight of 30 patients who completed flexibility treatment. Analysis by intention to treat gave similar results (17/33 v 9/33 patients better). Fatigue, functional capacity, and fitness were significantly better after exercise than after flexibility treatment. 12 of 22 patients who crossed over to exercise after flexibility treatment rated themselves as better after completing exercise treatment 32 of 47 patients rated themselves as better three months after completing supervised exercise treatment 35 of 47 patients rated themselves as better one year after completing supervised exercise treatment. CONCLUSION: These findings support the use of appropriately prescribed graded aerobic exercise in the management of patients with the chronic fatigue syndrome. 相似文献