全文获取类型
收费全文 | 11158篇 |
免费 | 1063篇 |
国内免费 | 8篇 |
专业分类
12229篇 |
出版年
2021年 | 105篇 |
2018年 | 107篇 |
2017年 | 92篇 |
2016年 | 178篇 |
2015年 | 268篇 |
2014年 | 314篇 |
2013年 | 446篇 |
2012年 | 534篇 |
2011年 | 562篇 |
2010年 | 394篇 |
2009年 | 346篇 |
2008年 | 515篇 |
2007年 | 569篇 |
2006年 | 553篇 |
2005年 | 560篇 |
2004年 | 573篇 |
2003年 | 505篇 |
2002年 | 548篇 |
2001年 | 119篇 |
2000年 | 96篇 |
1999年 | 157篇 |
1998年 | 163篇 |
1997年 | 118篇 |
1996年 | 133篇 |
1995年 | 114篇 |
1994年 | 160篇 |
1993年 | 127篇 |
1992年 | 109篇 |
1991年 | 108篇 |
1990年 | 108篇 |
1989年 | 110篇 |
1988年 | 99篇 |
1987年 | 99篇 |
1986年 | 93篇 |
1985年 | 125篇 |
1984年 | 136篇 |
1983年 | 118篇 |
1982年 | 170篇 |
1981年 | 191篇 |
1980年 | 180篇 |
1979年 | 109篇 |
1978年 | 146篇 |
1977年 | 132篇 |
1976年 | 111篇 |
1975年 | 92篇 |
1974年 | 124篇 |
1973年 | 120篇 |
1972年 | 79篇 |
1970年 | 81篇 |
1969年 | 78篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
A study of 10 infants in severe metabolic acidemia (pH below 7) led to the conclusion that the clinical signs—hyperventilation, coma or lethargy, peripheral vascular collapse, a significantly palpable liver, and abdominal distension—may all be directly related to the metabolic acidemia. In five of 10 infants, an initial erroneous diagnosis of congestive heart failure or pneumonia was made. Dramatic clinical improvement followed correction of the acidemia with rapid intravenous administration of sodium bicarbonate. This rapid administration of sodium bicarbonate was safe, provided hypocalcemia was recognized and treated in its early stages. In severe metabolic acidemia the measurement of blood bicarbonate alone does not reflect adequately the magnitude of the acid-base derangement and repeated measurements of hydrogen ion concentration, Pco2 and bicarbonates are needed to evaluate and treat such infants correctly. 相似文献
82.
83.
84.
85.
New localities in southern Illinois have yielded a flora consisting of 9 taxa. The plant remains occur in sandstones of the Chester Series and consist of casts, molds, and flattened impressions. The most important elements in the flora are: Archaeocalamites radiatus, Lepidodendron volkmannianum, Stigmaria ficoides, Rhynchogonium fayettevillense, and an unnamed Trigonocarpus. Stems probably referable to Lepidodendron veltheimii and Dictyoxylon also occur, as do numerous casts of the Knorria and Bergeria types. The range of features found in specimens of Lepidodendron volkmannianum allows some revision to be made of several species previously described by White in the Wedington Sandstone flora of northwest Arkansas, with which the present flora is closely comparable. The difficulties in making precise correlations with Upper Mississippian floras in other parts of the world are discussed. The necessity for critical re-examination of existing described collections and of undertaking more extensive field-work in the Mississippian of N. America is emphasized. 相似文献
86.
87.
Steroid Lysis of Protoplasts and Effects of Stabilizers and Steroid Antagonists 总被引:1,自引:1,他引:0 下载免费PDF全文
Six synthetic antimicrobial steroids were examined for indications of their mechanism of action. Dequadin acetate, cetyl pyridinium chloride (CPC), and sodium deoxycholate were studied for comparison. Aerated cells of Sarcina lutea were washed, suspended in 1.06 M sucrose, and converted to protoplasts with 20 mug/ml of lysozyme. Lysis was measured optically at 650 mmu as a decrease in optical density. Screening tests with 50 mug/ml of each compound showed five steroids and CPC to be lytic. Protoplasts were strongly protected from lysis by pretreatment with 0.001 to 0.004 M spermine tetrahydrochloride. Other polyamines, such as spermidine phosphate, were less protective, and putrescine was ineffective. Uranyl nitrate (5 x 10(-4) M) rapidly agglutinated protoplasts and protected them from rupture by the lytic agents. Similar studies with 0.001 to 0.004 M Mg(++) showed varying degrees of protection, which, in most cases, was only temporary. Steroidal lysis did not appear to be related to chelation, since ethylenediaminetetraacetate did not cause lysis alone and antagonized some lytic compounds. Lecithin, Tween 80, Tween 20, and Span 20 at 0.05% exhibited certain effects on protoplast stability. Span 20 strongly prevented lysis by steroids. Tween 20 alone quickly caused protoplast rupture. Lecithin and Tween 80, which also caused lysis alone, interfered with lytic steroids and CPC. The test compounds were both inhibitory and lethal to cells of Sarcina lutea. The results suggest that direct action on cell membranes may be chiefly responsible for the antimicrobial properties of the steroids. 相似文献
88.
Agar-Gel Precipitin-Inhibition Technique for C-Reactive Protein Determinations: III. Quantitation of C-Reactive Protein in Serum Specimens 下载免费PDF全文
A quantitative C-reactive protein serological procedure has been developed. By use of this method, which is performed in agar-gel plates, from 2 to 654 μg of C-reactive protein per ml of titrated human serum can be detected. The method is based on the inhibition of a specific C-reactive protein antigen-antibody precipitate formed in agar-gel by the minimal reactive dilutions of each reagent in 48 hr. It is simple, sensitive, and readily reproducible. 相似文献
89.
Donald H. Williams 《CMAJ》1967,96(14):1040-1044
Five basic forms of continuing educational endeavour by physicians are listed in rank order. These components constitute an indivisible unit bound together by self-learning. The scholarly habit of planned daily reading and study in a home library-sanctuary as an integral part of a physician''s workday heads the list. Day-to-day informal and formal colleague-association in patient care in the community and teaching hospital, in group practice and by consultation is the present major form of continuing educational endeavour. Emphasized is the sabbatical return every three to five years for three months at least to the teaching hospital to reinforce scholarly motivation and attitudes and to acquire new skills and knowledge. Attendance at scientific sessions of learned professional societies and short courses should be accompanied by presession and post-session guided reading to be undertaken in the physician''s home library-sanctuary. 相似文献
90.
In order to ascertain the prevalence of chronic respiratory disease in residents of a rural town and to determine the relative importance of tobacco smoking and air pollution, a survey was conducted of 726 persons living at Chilliwack, British Columbia, in May and June, 1963. Over 95% of a random sample of adults was interviewed and performed simple tests of respiratory function. The sample was selected from a commercial census. An analysis of the demographic characteristics of the sample indicated that the group, aged 25 to 74 years, was reasonably representative for detailed study of chronic respiratory disease. 相似文献