全文获取类型
收费全文 | 20826篇 |
免费 | 1605篇 |
国内免费 | 26篇 |
专业分类
22457篇 |
出版年
2023年 | 111篇 |
2022年 | 160篇 |
2021年 | 322篇 |
2020年 | 247篇 |
2019年 | 276篇 |
2018年 | 468篇 |
2017年 | 442篇 |
2016年 | 592篇 |
2015年 | 739篇 |
2014年 | 925篇 |
2013年 | 1164篇 |
2012年 | 1642篇 |
2011年 | 1591篇 |
2010年 | 915篇 |
2009年 | 714篇 |
2008年 | 1151篇 |
2007年 | 1274篇 |
2006年 | 1072篇 |
2005年 | 1036篇 |
2004年 | 959篇 |
2003年 | 906篇 |
2002年 | 829篇 |
2001年 | 434篇 |
2000年 | 438篇 |
1999年 | 293篇 |
1998年 | 225篇 |
1997年 | 180篇 |
1996年 | 175篇 |
1995年 | 184篇 |
1994年 | 167篇 |
1993年 | 143篇 |
1992年 | 159篇 |
1991年 | 149篇 |
1990年 | 146篇 |
1989年 | 130篇 |
1988年 | 134篇 |
1987年 | 108篇 |
1986年 | 107篇 |
1985年 | 120篇 |
1984年 | 117篇 |
1983年 | 116篇 |
1982年 | 120篇 |
1981年 | 114篇 |
1980年 | 91篇 |
1979年 | 102篇 |
1978年 | 99篇 |
1977年 | 98篇 |
1976年 | 82篇 |
1974年 | 72篇 |
1973年 | 64篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Reindeer calves (n = 632) were slaughtered in November/December (n = 476) or in January (n = 156). Dressed weights and amount of perirenal fat were recorded, and the reproductive organs were collected. A separate group of 130 reindeer calves were weighed at 7 months of age and were followed up with repeated weighings and pregnancy examinations up to 21 months. The onset of puberty and the pregnancy rate were significantly influenced by body weight and the amount of perirenal fat. Approximately 60 g of perirenal fat and 22 kg dressed weight were found at the lower limits for pregnancy. A total of 222 (35%) animals had reached puberty and 126 (20%) were pregnant when examined after slaughter. Animals which conceived during their first autumn showed only a moderate weight gain the following year, and the calf mortality rate in these animals was 47.4%. It was concluded that calf pregnancies are common among the reindeer of Southern Norway and that measures need to be taken to prevent them. 相似文献
22.
23.
Glutamate dehydrogenase preparations from several sources have been shown to have suffered limited proteolysis during purification. This proteolysis has been previously shown to involve removal of the N-terminal tetrapeptide and to result in changes in the regulatory properties of the enzyme. In the present work the previously unidentified N-terminal residue of the unproteolysed enzyme from ox brain and liver is shown to be cysteine. The thiol group of this residue is masked in the native enzyme but it becomes accessible after reduction. Exposure of solutions of the unproteolysed enzyme to air oxidation causes large changes in its sensitivity to inhibition by the antipsychotic drug perphenazine, GTP and by high concentrations of NADH. No such changes occurred in the behaviour of preparations of the enzyme that had suffered proteolysis during purification under these conditions.Special issue dedicated to Dr. Santiago Grisolia. 相似文献
24.
25.
26.
Gauthier Janel Lacroix Renée Coté Alain Doyon Julien Drolet Michel 《Applied psychophysiology and biofeedback》1985,10(2):139-159
In order to assess the relative effectiveness of finger warming and temporal blood volume pulse reduction biofeedback in the treatment of migraine, 22 female migraine patients were assigned to one of three experimental conditions: temporal artery constriction feedback, finger temperature feedback, or waiting list. Biofeedback training consisted of 12 sessions over a 6-week period. All patients completed 5 weeks of daily self-monitoring of headache activity (frequency, duration, and intensity) and medication before and after treatment. Treatment credibility was assessed at the end of Sessions 1, 6, and 12. Results showed that temporal constriction and finger temperature biofeedback were equally effective in controlling migraine headaches and produced greater benefits than the waiting list condition. Power analyses indicated that very large sample sizes would have been required to detect any significant differences between the two treatment groups. No significant relationships were found between levels of therapeutic gains and levels of thermal or blood volume pulse self-regulation skills. Likewise, treatment outcome was not found to be related to treatment credibility. Further analyses revealed that changes in headache activity and medication were associated with changes in vasomotor variability. Because blood volume pulse variability was not significantly affected by biofeedback training, questions about its role in the therapeutic mechanism are raised.This research was supported in part by grants from the Quebec Ministry of Education and the Quebec Ministery of Social Affairs to the first author, and an award from the Medical Research Council of Canada to the second author. The authors are indebted to Drs. Frank Andrasik, Howard Barbaree, Edward Blanchard, Martin Ford, and Patrick McGrath, as well as to two anonymous reviewers, for their helpful comments on an earlier draft of this paper. 相似文献
27.
28.
Study of the effect of phenformin on the blood glucose level in normal subjects before and during 70 hours of starvation showed a statistically significant hypoglycaemic effect after 40 hours of starvation. This effect was not due to increased glucose utilization.Another finding in this study was a statistically significant decrease in total urinary nitrogen excretion during starvation in subjects given phenformin. These findings show that the hypoglycaemic effect of phenformin in starved normal subjects is due to inhibition of gluconeogenesis. 相似文献
29.
Summary Eight newSalmonella types are described.S. houten, 43; Z4, Z23 :−, was isolated from a frog,S.tuindorp, 43: Z4, Z32: −,S. vleuten, 44: fg: −,S.zeist, 18: Z10: Z6, andS.soesterberg. 21: Z4, Z23: −, were isolated from lizards.
S. kralingen (8), 20: y: Z6, was isolated from peanuts andS. assen, 21: a: −, was isolated from a swine. All these strains were isolated in the Netherlands.
S.mim, 13, 22: a: 1,6, was isolated from a rat in Ghana. 相似文献
30.
Out of 12,472 strains ofSalmonella isolated in the Netherlands in 1962, 1365, or 10.94%, were found to be resistant to tetracycline or chloramphenicol or to both. Compared with the findings of the preceding years (1958/59:2.08%, 1960:1.29%, 1961:3.96%) this is a considerable increase. Of these 1365 strains, 1285, or 94.1%, were resistant to tetracycline and 46, or 3.4%, were resistant to chloramphenicol. The remaining 34 strains, or 2.5%, were resistant to both drugs.Among allSalmonella strains isolated in 1962, 5517 belonged to the speciesS. typhi murium. Of these, 1203 or 21.8%, were resistant to tetracycline. The resistance rates of strains originating from human patients, calves, pigs, other animals and other materials were 24.4%, 37.1%, 15.0%, 8.0% and 5.7% respectively.Factors which may possibly have contributed to the greatly increased frequency of drug resistance inS. typhi murium are: (1) the rapid spread of the use of tetracycline for therapeutic, prophylactic and nutritive purposes, and (2) the possibility of an episome-mediated transfer of drug resistance from relatively harmless intestinal bacteria, such asE. coli, toS. typhi murium. 相似文献