全文获取类型
收费全文 | 12713篇 |
免费 | 1020篇 |
国内免费 | 9篇 |
专业分类
13742篇 |
出版年
2021年 | 138篇 |
2020年 | 86篇 |
2019年 | 116篇 |
2018年 | 143篇 |
2017年 | 118篇 |
2016年 | 221篇 |
2015年 | 410篇 |
2014年 | 457篇 |
2013年 | 636篇 |
2012年 | 759篇 |
2011年 | 742篇 |
2010年 | 537篇 |
2009年 | 455篇 |
2008年 | 661篇 |
2007年 | 660篇 |
2006年 | 620篇 |
2005年 | 620篇 |
2004年 | 605篇 |
2003年 | 606篇 |
2002年 | 555篇 |
2001年 | 201篇 |
2000年 | 186篇 |
1999年 | 202篇 |
1998年 | 211篇 |
1997年 | 145篇 |
1996年 | 156篇 |
1995年 | 129篇 |
1994年 | 125篇 |
1993年 | 137篇 |
1992年 | 163篇 |
1991年 | 121篇 |
1990年 | 142篇 |
1989年 | 117篇 |
1988年 | 132篇 |
1987年 | 121篇 |
1986年 | 109篇 |
1985年 | 123篇 |
1984年 | 169篇 |
1983年 | 129篇 |
1982年 | 147篇 |
1981年 | 116篇 |
1980年 | 117篇 |
1979年 | 110篇 |
1978年 | 117篇 |
1977年 | 129篇 |
1976年 | 98篇 |
1975年 | 91篇 |
1974年 | 112篇 |
1973年 | 83篇 |
1972年 | 78篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
C R Lazarus A Abu-Bakar R L West J L Oblinger 《Applied and environmental microbiology》1977,33(1):217-218
When a tissue removal rinse technique was compared to the moist-swab contact method, significantly greater numbers of bacteria were recovered from beef carcasses, especially when the flora exceeded log10 4.5/6.45 cm2. Secondary treatment of the removed surface tissue by blending resulted in a significantly greater number of bacteria being recovered than when the same sample was swabbed and/or rinsed. Data indicate that blending of the carcass surface tissue provides a more representative value of the true microbial flora. 相似文献
92.
Summary Total lipids were extracted from 161 redpolls (Acanthis spp.) collected each month of the year from October 1962 to September 1963, in interior Alaska. A lipid index (Weight of ether extract x100/live body weight) was calculated for each sample. Lipids were also extracted from sections of pectoral muscle, livers and hearts representing each month.Body weight and lipid index were significantly positively correlated being highest in January and lowest in September. Total lipid content was significantly inversely correlated with air temperature; the high autumn and spring pre-migratory lipid peaks of migratory species were only weakly expressed in the redpolls. Liver lipid showed a significant annual variation being highest in December and lowest in August, while lipid from heart and pectoral muscle did not vary seasonally.Five birds were held in captivity during spring and summer at a constant temperature of 22°C. Food consumption was 5.1 g/day or 22.4 kcal. The caloric value of the most extensively utilized natural food, birch seed (Betula papyrifera), was determined (5.4–5.5 kcal/g dry wt). When esophageal diverticulae are full (2.0 g wet wt) of birch seeds, the resulting energy yield may sustain an individual for only a fraction of a 24 h winter day in contrast to other arctic herbivores (e.g. ptarmigan, Lagopus sp.) in which a full crop may suffice for the full 24 h period. 相似文献
93.
94.
Roger L. Crumley 《The Western journal of medicine》1977,126(3):184-189
Treatment techniques for airway obstruction in croup and epiglottitis are reviewed in the medical literature. Series totaling 295 nasotracheal intubations, and 591 tracheostomies were reviewed. There were two deaths attributable to airway complications in 126 patients in whom nasotracheal intubation was carried out. In three patients subglottic granulation tissue and subglottic stenoses developed from short-term nasotracheal intubation. There were no subglottic stenoses or tracheal stenoses reported in the 591 tracheostomies. From this review, it would seem feasible to use nasotracheal intubation for short-term airway treatment in croup and epiglottitis. The increasing occurrence of laryngeal and tracheal complications with long-term intubation suggests that tracheostomy be considered in such cases. 相似文献
95.
Brian Greenway M J Iqbal P J Johnson Roger Williams 《BMJ (Clinical research ed.)》1983,286(6359):93-95
The detection of high activities of two sex-steroid biosynthetic enzymes—aromatase and 5-alpha-reductase—in pancreatic carcinoma tissue suggested the possibility that these enzymes may influence the circulating concentrations of sex-steroid hormones. Mean serum testosterone concentrations in 22 men and women with exocrine carcinoma of the pancreas were significantly lower than those in 20 healthy controls and 27 patients with other known malignancies, who were of similar age and sex composition. Low serum testosterone concentrations may be due to uptake by and metabolism within the tumour; alternatively, patients with low androgen concentrations may be at greater risk of developing pancreatic carcinoma. 相似文献
96.
Ronidazole (1-methyl-5-nitroimidazole-2-methanol carbamate) is reductively metabolized by liver microsomal and purified NADPH-cytochrome P-450 reductase preparations to reactive metabolites that covalently bind to tissue proteins. Kinetic experiments and studies employing immobilized cysteine or blocked cysteine thiols have shown that the principal targets of protein alkylation ara cysteine thiols. Furthermore, ronidazole specifically radiolabelled with 14C in the 4,5-ring, N-methyl or 2-methylene positions give rise to equivalent apparent covalent binding suggesting that the imidazole nucleus is retained in the bound residue. In contrast, the carbonyl-14C-labeled ronidazole gives approx. 6--15-fold less apparent covalent binding indicating that the carbamoyl group is lost during the reaction leading to the covalently bound metabolite. The conversion of ronidazole to reactive metabolite(s) is quantitative and reflects the amazing efficiency by which this compound is activated by microsomal enzymes. However, only about 5% of this metabolite can be accounted for as protein-bound products under the conditions employed in these studies. Consequently, approx. 95% of the reactive ronidazole metabolite(s) can react with other constituents in the reaction media such as other thiols or water. Based on these results, a mechanism is proposed for the metabolic activation of ronidazole. 相似文献
97.
The purpose of this study was to learn wether a number of Ca2+ antagonists were effective in reducing contractile response of the isolated ileum of the sensitized and normal guinea pig. Contractions of the normal ileum in response to LTD4, acetylcholine, histamine, and potassium chloride were obtained before and after verapamil, diltiazen and papaverine. Ovalbumin-induced contractions of the ovalbumin-sensitized ileum were obtained in the presence of the three Ca2+ antagonists. In the normal ileum, all the Ca2+ antagonists were highly effective in diminishing the contractile responses to LTD4, acetylcholine, histamine and potassium chloride. In the sensitized ileum, ovalbumin-evoked contractions, with subsequent release of a potent contractile mediator (presumably SRS-A), were Ca2+-dependent since verapamil, diltiazem and papaverine caused a concentration-related reduction of contractions. Thus, the influx of extracellular Ca2+ plays a key role in the contractile responses of the normal and sensitized guinea pig ileum when stimulated by various potent agonists acting on specific receptors or on the cell membrane. 相似文献
98.
A numerical taxonomic study of species of Vibrio isolated from the aquatic environment and birds in Kent, England 总被引:4,自引:3,他引:1
A numerical taxonomic study has been carried out to confirm the identity of strains of the family Vibrionaceae isolated during an ecological study. A total of 237 strains were studied including 148 from the aquatic environment, 6 from estuarine birds, 1 from sheep faeces, and 61 control cultures. Duplicates of 21 of the strains were randomly selected and included to estimate test and operator error. Taxonomic resemblance was estimated on the basis of 148 characters using Euclidean distance. The taxonomic position of some strains was reevaluated using the pattern difference coefficient. Strains were clustered by three methods, all of which gave similar results. The estimated average probability of test error was 1.5%. Strains previously identified as Vibrio anguillarum fell into four distinct phenons corresponding to V. anguillarum biovar I, ' V. anguillarum biovar II', V. diazotrophicus , and strains pathogenic to oyster larvae. The latter group characteristically degraded xanthine and probably represents a new species. The phenon corresponding to V. cholerae included the type strain, strains of human origin, and strains isolated in the United Kingdom from birds and the aquatic environment. Some strains of V. cholerae were luminous. Other phenons were identified as V. metschnikovii, V. fluvialis , and Aeromonas spp. 相似文献
99.
We have previously shown that several agents which interfere with binding of ligands to the mannose-glycoprotein receptor on macrophages can inhibit zymosan-induced lysosomal enzyme secretion. Here we show that mannose only reduces the association of zymosan with macrophages during the first hour of exposure; after longer periods of uptake no effect is detectable. We have previously shown that mannose reduces surface binding of zymosan, probably by interfering selectively with binding to the mannose receptor. The present inhibition of association of zymosan with macrophages during short exposures can be entirely explained by this reduction of binding. Macrophages must therefore internalize zymosan at sites in addition to the mannose receptor. In contrast to macrophages the murine macrophage-like cell line P388D1 is lacking the mannose-glycoprotein receptor. Accordingly we find that binding of zymosan to P388D1 is much slighter than to macrophages and is unaffected by mannose or mannose-6-phosphate. The spontaneous lysosomal enzyme secretion of P388D1 is also unaffected by mannose. The data on macrophages confirm our previous suggestion that agents interfering with the mannose receptor inhibit the induction of lysosomal enzyme secretion by acting directly on the receptor. The data on P388D1 cells support this assertion by excluding effects at later steps in the secretory pathway. 相似文献
100.
W. A. Schroeder Darleen Powars Joan B. Shelton J. Roger Shelton J. B. Wilson T. H. J. Huisman Antranik A. Bedros 《Biochemical genetics》1982,20(11-12):1175-1187
After a boy of Mexican-American descent became jaundiced during treatment of a serious urinary tract infection with an oxidant drug, an extensive hematological examination was made. The important finding was the presence of Hb-Leiden to the extent of less than 3% or about a tenth of the usual percentage. Although inclusion bodies are present in the erythrocytes at all times, his hematological parameters have remained normal. The genetic basis for the unusually small amount of Hb-Leiden in the propositus may be due to the Hb-Leiden gene in an anti-Lepore configuration, that is, and Hb-Leiden gene in cis to the normal β and δ genes. 相似文献