全文获取类型
收费全文 | 6609篇 |
免费 | 927篇 |
专业分类
7536篇 |
出版年
2021年 | 85篇 |
2018年 | 74篇 |
2016年 | 111篇 |
2015年 | 179篇 |
2014年 | 191篇 |
2013年 | 256篇 |
2012年 | 246篇 |
2011年 | 257篇 |
2010年 | 166篇 |
2009年 | 170篇 |
2008年 | 216篇 |
2007年 | 245篇 |
2006年 | 203篇 |
2005年 | 220篇 |
2004年 | 222篇 |
2003年 | 184篇 |
2002年 | 228篇 |
2001年 | 201篇 |
2000年 | 201篇 |
1999年 | 147篇 |
1998年 | 97篇 |
1997年 | 71篇 |
1996年 | 96篇 |
1995年 | 78篇 |
1994年 | 75篇 |
1993年 | 88篇 |
1992年 | 158篇 |
1991年 | 133篇 |
1990年 | 154篇 |
1989年 | 146篇 |
1988年 | 124篇 |
1987年 | 118篇 |
1986年 | 119篇 |
1985年 | 117篇 |
1984年 | 119篇 |
1983年 | 92篇 |
1982年 | 97篇 |
1981年 | 93篇 |
1980年 | 68篇 |
1979年 | 103篇 |
1978年 | 94篇 |
1977年 | 88篇 |
1976年 | 103篇 |
1975年 | 101篇 |
1974年 | 85篇 |
1973年 | 94篇 |
1972年 | 84篇 |
1971年 | 73篇 |
1970年 | 59篇 |
1969年 | 61篇 |
排序方式: 共有7536条查询结果,搜索用时 0 毫秒
81.
C. R. Ricketts E. J. L. Lowbury J. C. Lawrence M. Hall M. D. Wilkins 《BMJ (Clinical research ed.)》1970,2(5707):444-446
To clarify tthe mechanism by which local application of silver compounds protects burns against infection, an ion-specific electrode was used to measùre the concentration of silver ions in solutions. By this method it was shown that in burn dressings silver ions were reduced to a very low level by precipitation as silver chloride. The antibacterial effect was found to depend on the availability of silver ions from solution in contact with precipitate. Between 10-5 and 10-6 molar silver nitrate solution in water was rapidly bactericidal. The minimal amount of silver nitrate causing inhibition of respiration of skin in tissue culture was about 25 times the minimal concentration of silver nitrate that inhibited growth of Pseudomonas aeruginosa. 相似文献
82.
83.
The stoicheiometry of electron transfer by bacterial and plant ferredoxins 总被引:5,自引:1,他引:4 下载免费PDF全文
1. The number of electrons carried by ferredoxins from spinach, the blue-green alga Anacystis nidulans, the anaerobic bacterium Clostridium welchii and the photosynthetic bacterium Chromatium was determined. 2. Ferredoxins were reduced by illuminated chloroplasts, and the stoicheiometry of the reoxidation in the dark of the ferredoxins by NADP and benzyl viologen was measured. 3. Spinach and A. nidulans ferredoxins were found to be one-electron carriers, and Cl. welchii and Chromatium ferredoxins were two-electron carriers. 相似文献
84.
Food specimens (490) in nine categories were examined for total aerobic plate count and numbers and types of coliform organisms, including the enteropathogenic Escherichia coli (EEC). The total counts were compared with various suggested standards, and a limit of 100,000/g appeared to be a realistic goal, except for certain food types with a high level of natural flora. Plate counts in VRB were compared to counts obtained by isolation by enrichment in LST Broth, and the latter method produced a higher percentage of isolations. The presence of E. coli was determined by use of EC Medium incubated at 44.5 +/- 0.1 C. Only 40.4% of the positive EC tubes, however, contained E. coli. It appeared that a limit of 10 coliform organisms per g as a suggested standard could be met with several types of foods. Isolation of EEC was obtained only three times, or in 0.6% of the specimens. 相似文献
85.
Aflatoxin B1 Uptake by Flavobacterium aurantiacum and Resulting Toxic Effects 总被引:5,自引:1,他引:4 下载免费PDF全文
Removal of aflatoxin B(1) from liquid cultures by resting and growing cells of Flavobacterium aurantiacum NRRL B-184 was studied. Spectrophotometic and thin-layer techniques served as aflatoxin assays. Cells grown in the presence of 5 ppm or higher levels of aflatoxin developed aberrant morphological forms. These toxin concentrations partially inhibited growth, and the nature of the inhibition suggested that aflatoxin interfered with cell wall synthesis. Incubation of 1.0 x 10(11) resting cells per milliliter with 7.0 mug/ml of aflatoxin B(1) during a 4-hr period facilitated complete toxin removal from a buffered aqueous medium. Autoclaved cells and cell wall preparations could remove a fraction of the aflatoxin of a test system. However, the toxin removed by autoclaved cells and cell walls could be extracted by washing with water but the aflatoxin B(1) removed by intact cells could not be extracted into the liquid phase. The uptake of aflatoxin B(1) by resting cells was sensitive to temperature and pH. Ruptured preparations of F. aurantiacum were not able to remove or modify the aflatoxin in an aqueous solution. 相似文献
86.
Wesley S. Moore F. William Blaisdell Albert D. Hall 《The Western journal of medicine》1964,100(2):92-96
The presenting manifestations of polycythemia vera are often complications involving the vascular system. These include myocardial infarction, cerebro-vascular accidents and ischemic changes in the extremities.The concept of increased atherogenesis in cases of polycythemia vera has been questioned. A possible mechanism by which small, otherwise subclinical atheromatous plaques produce ischemic symptoms in patients with polycythemia vera is discussed. The blood in polycythemic patients has been shown to have an increased viscosity resulting in a prolonged circulation time. If a small atheromatous plaque is present in association with increased blood viscosity, this combination may well produce ischemic symptoms. This explains why treatment of polycythemia vera, with restoration of blood to normal viscosity, often reverses the patient''s ischemic symptoms.Two cases of polycythemia vera here reported, in which the presenting manifestations were gangrenous extremities, emphasize the need for prompt diagnosis and treatment of polycythemia vera. In the first case, early recognition and treatment of polycythemia vera successfully reversed the ischemic changes in the extremities, while failure of early recognition and treatment in the second case resulted in two major amputations. 相似文献
87.
88.
Spent mycelia of Blakeslea trispora recovered from a previous fermentation enhanced carotene production by mated cultures of the same organism. Peak yields of 107 to 142 mg of carotene per 100 ml of medium were achieved in 6 days. β-Carotene constituted 92% of the total carotenoids produced. The enhancing substance was found present in an aqueous extract of the mycelium. Part of its activity was due to an organic acid fraction. Other microbial cells, molds, yeasts, and bacteria were also capable of enhancing carotene production. 相似文献
89.
One hundred and twelve patients with far advanced, inoperable neoplastic disease were treated by a method utilizing the simultaneous administration of the pyrimidine antagonist, 5-fluorouracil, and ionizing irradiation to an estimated tumor dose of 2,000 roentgen units. Seventy-seven of them had periods of objective regression of tumor of three months or more.The data presented suggest that either there may be an additive effect when the two modes of therapy are used simultaneously or one mode of therapy may potentiate the antitumor effect of the other. 相似文献
90.