全文获取类型
收费全文 | 5103篇 |
免费 | 597篇 |
国内免费 | 1篇 |
专业分类
5701篇 |
出版年
2022年 | 41篇 |
2021年 | 74篇 |
2020年 | 41篇 |
2019年 | 47篇 |
2018年 | 60篇 |
2017年 | 66篇 |
2016年 | 105篇 |
2015年 | 161篇 |
2014年 | 184篇 |
2013年 | 234篇 |
2012年 | 303篇 |
2011年 | 282篇 |
2010年 | 194篇 |
2009年 | 140篇 |
2008年 | 226篇 |
2007年 | 230篇 |
2006年 | 220篇 |
2005年 | 208篇 |
2004年 | 171篇 |
2003年 | 218篇 |
2002年 | 175篇 |
2001年 | 178篇 |
2000年 | 160篇 |
1999年 | 142篇 |
1998年 | 91篇 |
1997年 | 73篇 |
1996年 | 70篇 |
1995年 | 67篇 |
1994年 | 58篇 |
1993年 | 61篇 |
1992年 | 110篇 |
1991年 | 93篇 |
1990年 | 87篇 |
1989年 | 74篇 |
1988年 | 77篇 |
1987年 | 54篇 |
1986年 | 81篇 |
1985年 | 72篇 |
1984年 | 52篇 |
1983年 | 57篇 |
1982年 | 47篇 |
1981年 | 47篇 |
1980年 | 53篇 |
1979年 | 44篇 |
1978年 | 42篇 |
1977年 | 31篇 |
1976年 | 41篇 |
1973年 | 39篇 |
1972年 | 31篇 |
1968年 | 34篇 |
排序方式: 共有5701条查询结果,搜索用时 15 毫秒
101.
102.
Nutritional factors controlling exocellular protease production by Pseudomonas aeruginosa. 总被引:12,自引:4,他引:8 下载免费PDF全文
A defined medium capable of supporting growth and exocellular protease production by clinical isolates of Pseudomonas aeruginosa has been developed. Control of protease production is effected by a mixture of three amino acids and glucose. 相似文献
103.
J W Jensen J D Springfield J S Schutzbach 《The Journal of biological chemistry》1980,255(23):11268-11272
An oligosaccharide-P-P-lipid has been isolated from porcine liver by extraction with organic solvents and purified by chromatography on silica gel and DEAE-cellulose. The purified oligosaccharide-lipid was shown to contain mannose and N-acetylglucosamine in an approximate ratio of 1:1 and our results suggest that the major oligosaccharide component in the preparation was a tetrasaccharide with the composition (Man)2 (GlcNAc)2. When the oligosaccharide-lipid was incubated with GDP-[14C]mannose and a solubilized enzyme preparation from rabbit liver in the presence of MgCl2, three radioactive products could be isolated. The oligosaccharides in the products could be identified as a penta-, a hexa-, and a heptasaccharide. These products were formed by the stepwise addition of mannose to the growing oligosaccharide chain and GDP-mannose was indicated as the glycosyl donor in each reaction. 相似文献
104.
New method for large-scale growth; and concentration of the Epstein-Barr viruses. 总被引:1,自引:0,他引:1 下载免费PDF全文
G P Shibley M Manousos K Munch I Zelljadt L Fisher S Mayyasi K Harewood R Stevens K E Jensen 《Applied microbiology》1980,40(6):1044-1048
Efficacious systems are described for the large-scale growth in tissue culture and concentration of infectious (P3HR-1) and transforming (B95-8) Epstein-Barr virus. Also recorded here are our updated procedures for growing stock cultures and protocols to harvest fluids containing biologically active virus which is infectious or transforming. Various methods of concentrating biologically active Epstein-Barr virus have been evaluated. Cellular debris can be removed efficiently and rapidly from culture harvest fluids by clarification through a JCF-Z continuous-flow rotor. Efficient and reliable virus concentration was achieved by molecular filtration with Millipore Pellicon cassettes, using flow rates to 10 liters/h to produce fivefold concentrates followed by pelletization in a fixed-angle rotor. Data from recent production lots showed an average infectivity titer for P3HR-1 virus of 10(4.5) early antigen units per ml (100-fold concentrate) and 10(5.7) transforming units per ml (200-fold concentrate) for B95-9 virus lots. 相似文献
105.
Cell-mediated immunity to viruses in hamsters 总被引:4,自引:0,他引:4
R M Zinkernagel A Althage F Jensen J W Streilein W R Duncan 《Federation proceedings》1978,37(7):2078-2081
106.
A survey of the sources of Clostridium botulinum type C toxin possibly utilized as food by aquatic birds in an epizootic area of avian botulism in northern Utah showed that living aquatic and terrestrial invertebrates normally found in close association with dead, decomposing birds commonly carried the toxin. Of 461 samples associated with 21 species of avian carcasses, 198 were toxin-positive. Invertebrate species not normally scavengers of vertebrate tissues were less commonly and less highly toxic, particularly when captured 30 cm or more from a carcass; six of 237 samples of such aquatic invertebrates low-level toxin. Of the species tested, blow fly larvae (Calliphoridae) were the most consistently and highly toxic, although others, particularly adult and larval stages of several species of beetles (Coleoptera), contained toxin at levels probably significant in the epizootiology of the disease. An estimated 0.05 to 0.25 g of the most toxic fly larvae or 15 g of the most toxic beetles tested carried a mediam lethal dose for an adult mallard duck. Examination of stomach contents of aquatic birds dead of botulism showed that some had consumed invertebrates. 相似文献
107.
L C Sieker L H Jensen T S Samy 《Biochemical and biophysical research communications》1976,68(2):358-362
The antitumor protein, neocarzinostatin, has been crystallized and examined by X-ray diffraction. Crystals of this globular protein are of space group P212121 with cell parameters a = 27.4Å, b = 33.9Åand c = 102.0Å. There is one molecule of approximately 27Ådiameter per asymmetric unit. Crystals soaked in a K2HgI4 solution give diffraction patterns significantly different from native crystal diffraction patterns. 相似文献
108.
Gudmund Skjåk Bræk Arne Jensen Åge Mohus 《Journal of experimental marine biology and ecology》1976,25(1):37-50
The combined effects of copper and zinc ions on the growth of three marine diatoms and one dinoflagellate in culture have been studied. The two metals were found to act synergistically to all algae except Phaeodactylum tricornutum Bohlin. With this species an antagonistic effect was observed. Addition of zinc ions reduced the inhibition of growth caused by the more toxic copper ions. Zinc toxicity to this alga increased at low concentration of magnesium, indicating a common route for divalent metal ions in general. 相似文献
109.
Eimeria stiedai or Eimeria tenella oocysts were incubated in aqueous cysteine hydrochloride (cysHCl) under carbon dioxide (CO2), aqueous cysHCl under air, water under CO2 or water under air, and analyzed for sulfhydryl (-SH) groups. The cysHCl-CO2 treatment produced more -SH groups than the other treatments and was effective in allowing activation of intact and sodium hypochlorite (NaOCl)-treated E. stiedai oocysts as well as NaOCl-treated E. tenella oocysts. The CO2-cysHCl complex may act directly on the oocyst wall, especially in the micropylar region, to unmask lipid-shielded disulfide bridges, which are reduced to -SH groups. The reduction apparently disturbs the protein superstructure of the oocyst wall, promotes opening of the micropyle, and changes the impermeable state of the sporulated oocyst. 相似文献
110.