全文获取类型
收费全文 | 124360篇 |
免费 | 5724篇 |
国内免费 | 76篇 |
出版年
2021年 | 604篇 |
2018年 | 1508篇 |
2017年 | 1607篇 |
2016年 | 3762篇 |
2015年 | 7737篇 |
2014年 | 7470篇 |
2013年 | 7750篇 |
2012年 | 7487篇 |
2011年 | 4877篇 |
2010年 | 3890篇 |
2009年 | 3572篇 |
2008年 | 2975篇 |
2007年 | 2913篇 |
2006年 | 2725篇 |
2005年 | 8804篇 |
2004年 | 7470篇 |
2003年 | 5597篇 |
2002年 | 3158篇 |
2001年 | 1575篇 |
2000年 | 710篇 |
1999年 | 1961篇 |
1998年 | 917篇 |
1997年 | 622篇 |
1992年 | 2303篇 |
1991年 | 2331篇 |
1990年 | 2339篇 |
1989年 | 2268篇 |
1988年 | 2221篇 |
1987年 | 2060篇 |
1986年 | 1855篇 |
1985年 | 1953篇 |
1984年 | 1407篇 |
1983年 | 1089篇 |
1982年 | 808篇 |
1981年 | 695篇 |
1980年 | 622篇 |
1979年 | 1261篇 |
1978年 | 981篇 |
1977年 | 814篇 |
1976年 | 807篇 |
1975年 | 1032篇 |
1974年 | 1180篇 |
1973年 | 1197篇 |
1972年 | 1079篇 |
1971年 | 1028篇 |
1970年 | 917篇 |
1969年 | 919篇 |
1968年 | 807篇 |
1967年 | 820篇 |
1966年 | 642篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Sixteen raptors and three hooded crows were infected experimentally with Francisella tularensis biovar palaearctica. The birds were infected parenterally or per os. One goshawk, one sparrow hawk and one hooded crow died during the experimental period, and the remaining 16 birds were killed 14-77 days after the first infection. Francisella tularensis was not isolated from any bird. Antibody levels against F. tularensis measured in nine birds varied from 0 to 1:1,280. In one goshawk with a titer of 1:1,280, positive fluorescent antibody reactions against F. tularensis were seen in the liver and spleen. These results are similar to those found by other authors indicating that raptors and corvids are normally resistant to infections with F. tularensis. 相似文献
992.
V S Rusinov O M Grindel' E V Sharova M A Kulikov V N Kaliuzhny? 《Zhurnal vysshe? nervno? deiatelnosti imeni I P Pavlova》1988,38(2):207-218
The data are given of the analysis of the low-frequency EEG component (LF EEG--0.2--2.0 Hz) of 34 healthy subjects and 36 patients examined in dynamics in the acute period after operations: ablation of a tumour localized at the level of the diencephalon and the level of the brainstem. The LF EEGs were analyzed by a special program: auto- and crosscorrelation functions and power spectra were estimated. In the norm LF EEGs were characterized by mosaics, various frequencies and periodicity in various cortical areas, they appeared with interhemispheric asymmetry, depended on the EEG type--dominance or lack of the alpha-rhythm. In patients in the post-operative period the LF EEGs were changed; in favourable terminations, at first the period of oscillations and the coefficient of correlation increased, then they tended to normalization. In unfavourable terminations, with gross pathological foci in these areas, the LF EEGs acquired a synchronized character, with a higher frequency than in the norm. 相似文献
993.
Study was carried out on 232 white rats, male and female, fixed in a hammock and subjected to painful stimulation of the tail. The first impulse of pain vocalization was analyzed. The rats were divided into three groups--with intact brain, with inactivated left or right hemisphere. The first impulses of rats pain vocalizations may be divided into short screams with 40-140 ms duration and long squeals of 140-420 ms duration. Unilateral cortex inactivation led to a reduction of the latency, increase of the peak amplitude and change of the per cent both of the pain screams and pain squeals. After elimination of the left hemisphere as compared with that of the right one, a shorter latency and a greater per cent of the pain screams was observed and a smaller per cent of pain squeals. The obtained data testify to the dominance of the left hemisphere in the control of pain vocalizations in rats. 相似文献
994.
Monoclonal antibodies localize events in the folding, assembly, and intracellular transport of the influenza virus hemagglutinin glycoprotein 总被引:26,自引:0,他引:26
We used monoclonal antibodies that recognize monomeric and/or trimeric forms of the influenza virus hemagglutinin (HA) to study biosynthesis of this integral membrane protein in influenza virus-infected cells. We find the following: First, the globular head of the HA folds into its mature conformation in the endoplasmic reticulum prior to the assembly of HA monomers into trimers. Second, trimerization begins within 1 to 2 min following synthesis, with a half-time of approximately 5 min. Third, trimerization occurs only after the HA has been transported from the endoplasmic reticulum. Fourth, newly formed trimers are sensitive to acid-induced conformational alterations associated with viral fusion activity. 相似文献
995.
Paul H. Ward Andrew F. Ippoliti Daniel H. Simmons James V. Maloney Jr 《The Western journal of medicine》1988,149(1):58-65
An edited summary of an Interdepartmental Conference arranged by the Department of Medicine of the UCLA School of Medicine, Los Angeles. The Director of Conferences is William M. Pardridge, MD, Professor of Medicine.Several specialists have recently recognized that gastrointestinal reflux causes complications resulting in significant disease. It causes discomfort, indigestion, esophagitis, Barrett''s esophagus, and carcinoma of the esophagus. Pediatricians attribute many early pulmonary problems, and even some sudden deaths in infants, to the reflux of gastric contents. Otolaryngologists now recognize that many cases of nonbacterial, nonspecific pharyngitis and laryngitis are due to the reflux of gastrc acid secretions. Contact granuloma and cancer of the larynx may, in some instances, be secondary to nocturnal reflux. Thoracic surgeons and pulmonologists believe chronic tracheobronchitis and some cases of pulmonary disease are attributable to recurrent bathing of the respiratory epithelium by aspirated gastric contents. An awareness of the many complications of gastrointestinal reflux should lead to a multidisciplined attack on the factors responsible for these diseases. 相似文献
996.
Of 124 staphylococcal strains isolated from sheep milk, 78 produced enterotoxin A, B, C, or D when evaluated by an enzyme-linked immunosorbent assay. Enterotoxins A and D, elaborated by 44 and 43 strains, respectively, showed the highest incidence. Enterotoxin production by coagulase-negative strains (one Staphylococcus cohnii, three S. epidermidis, five S. haemolyticus, and four S. xylosus) was detected. Linear and logarithmic-logarithmic regressions of optical density on enterotoxin concentration yielded the best-fitting equations for enterotoxin quantitation. A significantly higher incidence of enterotoxin producers and significantly higher levels of enterotoxins produced were recorded for coagulase-positive, thermostable nuclease-positive, hemolysis-positive, or mannitol-positive strains. Mannitol utilization was the best test for discriminating between enterotoxigenic and nonenterotoxigenic staphylococci. 相似文献
997.
N A Kocharova Iu A Knirel' N K Kochetkov E S Stanislavski? 《Bioorganicheskaia khimiia》1988,14(5):701-703
A polysaccharide isolated from the degraded lipopolysaccharides of P. aeruginosa serogroup O7 (Lányi--Bergan classification) was characterized by liquid chromatography, acid hydrolysis, and 1H and 13C NMR spectroscopy. It has molecular mass 15,000 and represents mainly a rhamnan of the structure----2)-alpha-D-Rha-(1----3)-alpha-D-Rha-(1----3)-alpha-D-Rha-(1 ----, identical to the structure of O-specific polysaccharides of Pseudomonas aeruginosa pvs morsprunorum and cerasi. Some minor constituents, such as glucose, mannose, an unknown sugar, and phosphate, are found in the polysaccharide preparation as well. Distribution of the rhamnan in some other P. aeruginosa serogroups is discussed and its identity to the common polysaccharide antigen of P. aeruginosa is suggested. 相似文献
998.
Summary In a mineral salts medium containing yeast extract, NH4Cl and glucose (50g/L), the pH range producing the fastest growth ofZ. mobilis was 5.5–6.5 with an apparent optimum at 6.5. At constant growth rate of 0.15hr–1, the specific rates of glucose utilization (qs) and ethanol production (qp) were relatively unaffected by pH over the range 7.0–5.5 but increased sharply as the pH was further decreased below 5.5 to 4.0. Under these conditions the ethanol yield was unaffected by pH over the range 4.0–6.5 but decreased markedly at pH of 7. 相似文献
999.
In a 3:1 scaled model of the human aorta models of the Omniscience, Bj?rk-Shiley Convexo-Concave, Bj?rk-Shiley Monostrut, Medtronic-Hall, Duromedics (Hemex) and the Saint Jude Medical heart valve prostheses are studied in steady flow representing the systolic peak flow phase. Detailed flow visualization experiments show flow separations at all inner ring surfaces as well as at most of the occluders. The resulting stagnation areas increase the risk of thrombus accumulation. Flow separations also stimulate vortex formation and turbulent mixing at the downstream jet boundaries and thus may intensify blood damage by turbulent shear stresses. The different influences of struts and occluder guides on the flow around the occluders are discussed. The effects of the individual valve components on the flow fields are analyzed and correlated with the resulting pressure losses. 相似文献
1000.
Purification of the growth-related protein p25 of the Ehrlich ascites tumor and analysis of its isoforms 总被引:2,自引:0,他引:2
1. Two of the three isoforms of the growth-related protein p25 of the Ehrlich ascites tumor have been purified to homogeneity by giant two-dimensional polyacrylamide gel electrophoresis. 2. Antibodies raised against the isoform p25/1 react also with isoforms p25/2 and p25/3. 3. Limited tryptic digestion of p25/1 and p25/2 resulted in similar oligopeptide patterns. Corresponding oligopeptides of both isoforms have identical amino acid sequences. 4. The isoforms p25/2 and p25/3 are phosphorylated derivatives of unphosphorylated p25/1. The phosphorus is bound to serine and a further unknown phosphorylation site. 相似文献