全文获取类型
收费全文 | 3970篇 |
免费 | 317篇 |
出版年
2021年 | 32篇 |
2020年 | 25篇 |
2019年 | 30篇 |
2018年 | 40篇 |
2017年 | 34篇 |
2016年 | 67篇 |
2015年 | 116篇 |
2014年 | 127篇 |
2013年 | 164篇 |
2012年 | 197篇 |
2011年 | 210篇 |
2010年 | 138篇 |
2009年 | 134篇 |
2008年 | 196篇 |
2007年 | 221篇 |
2006年 | 161篇 |
2005年 | 169篇 |
2004年 | 175篇 |
2003年 | 189篇 |
2002年 | 185篇 |
2001年 | 67篇 |
2000年 | 46篇 |
1999年 | 66篇 |
1998年 | 61篇 |
1997年 | 26篇 |
1996年 | 44篇 |
1995年 | 43篇 |
1994年 | 35篇 |
1993年 | 41篇 |
1992年 | 36篇 |
1991年 | 48篇 |
1990年 | 41篇 |
1989年 | 49篇 |
1988年 | 41篇 |
1987年 | 38篇 |
1986年 | 29篇 |
1985年 | 39篇 |
1984年 | 43篇 |
1983年 | 45篇 |
1982年 | 50篇 |
1981年 | 46篇 |
1980年 | 37篇 |
1979年 | 36篇 |
1978年 | 49篇 |
1977年 | 31篇 |
1976年 | 25篇 |
1974年 | 37篇 |
1973年 | 56篇 |
1972年 | 30篇 |
1971年 | 33篇 |
排序方式: 共有4287条查询结果,搜索用时 15 毫秒
61.
C S Tsai S N Evan P J Asselberg R R McGregor D B Fowler 《The International journal of biochemistry》1983,15(11):1321-1328
Pyruvate kinase has been purified from codfish muscle. The ratio of phosphotransferase and oxalacetate decarboxylase activities remains relatively constant throughout purification steps. These two activities are dependent as well as sensitive to sulfhydryl reagents. In the presence of dithioerythritol, only one molecular form of pyruvate kinase is detected. However, the enzyme exists as four pseudoisozymes in the presence of 2-mercaptoethanol. The pseudoisozymes of codfish pyruvate kinase are interconvertible under the influence of sulfhydryl reagents. 相似文献
62.
B. R. Malcolm 《Biopolymers》1983,22(1):319-322
Electron diffraction photographs of poly (α-aminoisobutyric acid) treated with dichloracetic acid are shown to be consistent with space group R3c. This is strong evidence for a hexagonal cell in which right- and left-handed 310-helices form a honeycomb structure. It appears that the dichloracetic acid molecules are located in the centers of the holes. 相似文献
63.
David S. Gullion T. Elaine Adamson Malcolm S. M. Watts 《The Western journal of medicine》1983,138(4):582-588
The Professional Competence Assurance Program (PROCAP) is an individualized educational program that examines physicians'' performance in ambulatory practice. It uses medical record review to identify deficiencies in the care process that guides development of the educational intervention. Medical care is reassessed one year later. This program was used with 51 private practitioners to assess the care of 1,229 hypertensive patients. The educational program included a computer printout comparing one physician''s performance with that of peers, readings targeted to management problems, and a conference call or group seminar with an expert stressing issues relevant to each physician''s performance. Postintervention assessment showed that physicians prescribed beta-blockers (P<.01) and vasodilators (P<.01) more often. Improvement (P<.05) occurred in the control of diastolic blood pressure (≤90 mm of mercury) and in several other criteria. These results show that well-designed, individualized continuing medical education addressing specific deficiencies can change physicians'' performance and patients'' intermediate outcome. 相似文献
64.
65.
A new simple and sensitive in-vitro method for the diagnosis of type 1 (IgE-mediated) hypersensitivity in man is described. Sliced human skin is passively sensitized by reaginic serum from allergic patients and the presence of antigen-specific IgE on the sensitized slices is detected by assay of antigen-evoked histamine release. Serum from 12 out of 14 patients with clinical respiratory allergy and positive skin tests gave significant antigen-specific histamine release. This method, which is essentially an in-vitro model of the Prausnitz-Küstner reaction, should prove of value in the diagnosis of human reaginic hypersensitivity in man. 相似文献
66.
Of 16 metal cations tested on agar medium, only copper and iron stimulated mycelial growth of Endothia parasitica in relatively high concentrations. Similarly enhanced growth was produced in high (32%) glucose concentrations and also when the fungus was grown on cellophane placed over the agar surface. E. parasitica secreted large amounts of oxalate that precipitated primarily as calcium oxalate at the periphery of the fungal colony, causing an opaque halo in the medium. Mycelial growth was retarded greatly when calcium oxalate accumulated, but retardation was reversed by copper and iron salts that prevented accumulation of the calcium oxalate crystals. E. parasitica grew well on media containing copper oxalate and copper-calcium oxalate but grew poorly with calcium oxalate as the carbon source and was inhibited by sodium oxalate in the medium. The specificity by which only copper and iron salts stimulated mycelial growth suggested that the metal and oxalate ions interact to form specific oxalate complexes that reverse the inhibition of simple oxalate salts. This probably accounts for enhanced growth in the presence of otherwise toxic levels of metals and oxalate. The stimulation did not occur in liquid cultures. 相似文献
67.
Biophysical and Biochemical Studies on Rhinovirus and Poliovirus II. Chemical and Hydrodynamic Analysis of the Rhinovirion 总被引:2,自引:2,他引:0
Chemical analysis of rhinovirus 14 revealed a ribonucleic acid (RNA) content of 29.8% and a high adenylic acid content (35%). A partial specific volume of 0.682 cm3/g was obtained for the rhinovirion. Rhinovirus and poliovirus had identical sedimentation coefficients of 158S. A diffusion coefficient of 1.71 × 10−7 cm2/sec was consistent with a hydrated diameter of 25 nm for the rhinovirion. The calculated molecular weights of the rhinovirion and its genome were 7.1 × 106 and 2.1 × 106 daltons, respectively. Sedimentation analysis of infectious RNA confirmed the similarity of the molecular size of the poliovirus and rhinovirus genomes. 相似文献
68.
Isolation, Mapping, and Characterization of Trehalaseless Mutants of Neurospora crassa 总被引:4,自引:0,他引:4
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Alfred S. Sussman M. Kerry Garrett Malcolm Sargent Shih-An Yu 《Journal of bacteriology》1971,108(1):59-68
Mutant strains of Neurospora crassa that lack trehalase and are unable to grow on trehalose were isolated, and the gene (tre) was positioned on the right arm of linkage group I. Maltase and beta-galactosidase activities are almost identical in tre(-) strains, whereas that of invertase was reduced by more than half and those of acid phosphatase and amylase were somewhat increased. Heterocaryons between standard and trehalaseless strains yield less than one-tenth the activity of the former. In addition, strains with duplications heterozygous for trehalase produce less than 1% of the activity of the standard strain. An inhibitor of trehalase has been found in tre(-) strains; its sensitivity to heat and proteolysis, and its nondialyzability suggest that this substance is a protein. The mig gene, which determines the rate of migration of trehalase on acrylamide gels, has been shown to be less than 1 map unit away from the tre gene. 相似文献
69.
70.
Serial sections of the rectal valve in Aphelenchoides blastophthorus Franklin and the oesophago-intestinal valve in Thornenema wickeni Yeates were examined electron microscopically. Each valve when closed appears as a convoluted path of closely apposed (10 nm) pairs of three-layered cell membranes. Both valves serve to stop intestinal leakage, open briefly and rapidly by forcible dilatation and are closed by pressure from surrounding tissues, helped perhaps by intermolecular forces. 相似文献