全文获取类型
收费全文 | 300577篇 |
免费 | 21998篇 |
国内免费 | 77篇 |
专业分类
322652篇 |
出版年
2018年 | 3920篇 |
2017年 | 3763篇 |
2016年 | 4734篇 |
2015年 | 4654篇 |
2014年 | 6071篇 |
2013年 | 8680篇 |
2012年 | 10013篇 |
2011年 | 10509篇 |
2010年 | 7481篇 |
2009年 | 6481篇 |
2008年 | 9384篇 |
2007年 | 9642篇 |
2006年 | 9191篇 |
2005年 | 8615篇 |
2004年 | 8715篇 |
2003年 | 8389篇 |
2002年 | 8216篇 |
2001年 | 12685篇 |
2000年 | 12271篇 |
1999年 | 9565篇 |
1998年 | 3014篇 |
1997年 | 2881篇 |
1996年 | 2645篇 |
1995年 | 2419篇 |
1992年 | 7423篇 |
1991年 | 7608篇 |
1990年 | 7587篇 |
1989年 | 7370篇 |
1988年 | 6868篇 |
1987年 | 6483篇 |
1986年 | 5989篇 |
1985年 | 6144篇 |
1984年 | 4921篇 |
1983年 | 4124篇 |
1982年 | 2847篇 |
1981年 | 2506篇 |
1980年 | 2424篇 |
1979年 | 4598篇 |
1978年 | 3572篇 |
1977年 | 3255篇 |
1976年 | 3196篇 |
1975年 | 3835篇 |
1974年 | 4223篇 |
1973年 | 4273篇 |
1972年 | 3773篇 |
1971年 | 3532篇 |
1970年 | 3033篇 |
1969年 | 3007篇 |
1968年 | 2783篇 |
1967年 | 2513篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
A A Sukhopiatkina O S Bat A V Levitskaia V G Potapova 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1985,(4):80-81
The study of the specific epidemiological and clinical features of Q fever revealed the existence of an active focus of infection among humans due to their contacts with agricultural animals in one of the districts of the region. The focus was manifested by group morbidity among the cattle-tending personnel of a dairy farm. The source of this infection was cattle. The infection was transferred mainly through the air. The disease took a moderately severe course. The study of the rickettsial contamination of humans, animals and ticks suggested the presence of the active epidemic process and made it possible to work out concrete antiepidemic measures. 相似文献
22.
23.
F F Dias M K Shaikh Y B Bhatt D C Modi V R Subramanyam 《The Journal of applied bacteriology》1986,60(4):271-275
Mutants of Bacillus amyloliquefaciens resistant to at least 10 micrograms/ml of tunicamycin were isolated and shown to be pleiotropic. The mutants were more resistant to streptomycin, chloramphenicol, kanamycin and neomycin than was the parent strain but less resistant to penicillin G and tetracycline. They were more autolytic, presumably due to an altered cell wall. The mutants produced reduced levels of amylase, penicillinase and both metal and serine protease besides having an enhanced sporulation frequency and being more motile. 相似文献
24.
V A Berezin E N Zhmarev I A Brodskaia G M Shevchenko L S Zashko 《Biulleten' eksperimental'no? biologii i meditsiny》1985,100(7):68-70
The content of neurospecific proteins S-100, GFA and D2 was measured in malignant cerebral tumors by electrophoresis with the use of monospecific antisera. Concomitant measurement of proteins S-100 and GFA is a more reliable diagnostic criterion as to the tumor histogenesis than study of each protein alone. D2 protein appeared to be the most stable specific marker. 相似文献
25.
26.
27.
T. B. Lapirova V. R. Mikryakova A. S. Mavrin G. A. Yinogradova 《Journal of Evolutionary Biochemistry and Physiology》2000,36(1):47-51
The paper presents data on a change in lysozyme content in tissues of spleen, liver and heart in fry of the Lena River sturgeon
exposed to the presence of sublethal concentrations of Hg2+, Cd2+, and Cu2+ under conditions of chronic experiment. It has been shown that the lysozyme content in fish tissues varies and has a phasic
character. The amplitude of fluctuations of this parameter depends on the moment of sampling, nature of the toxicant, and
structural-functional organization of the studied organs. 相似文献
28.
29.
Z Zhong A Toukdarian D Helinski V Knauf S Sykes J E Wilkinson C O'Bryne T Shea C DeLoughery R Caspi 《Applied and environmental microbiology》2001,67(12):5771-5779
An agar-degrading marine bacterium identified as a Microscilla species was isolated from coastal California marine sediment. This organism harbored a single 101-kb circular DNA plasmid designated pSD15. The complete nucleotide sequence of pSD15 was obtained, and sequence analysis indicated a number of genes putatively encoding a variety of enzymes involved in polysaccharide utilization. The most striking feature was the occurrence of five putative agarase genes. Loss of the plasmid, which occurred at a surprisingly high frequency, was associated with loss of agarase activity, supporting the sequence analysis results. 相似文献
30.
Y. Salas A. Márquez J. Canelón Y. Perazzo V. Colmenárez J. A. López 《Mycopathologia》2012,174(5-6):511-517
Pythium insidiosum is a pathogenic oomycete known since 1890 that causes pythiosis in mammals. In this report, seven P. insidiosum isolates were recovered from Venezuelan horses and were characterized. The strains were recovered from biopsied tissues and kunkers collected from granulomatous masses located on the hind limb and from a nodular lesion in the left upper eyelid, which decrease the ability of the horses to be used for working purposes. The methods used to identify P. insidiosum isolates were based on the production of sporangia and zoospores, histopathology and PCR assay. To further characterize these strains, portions of the 18S rRNA genes of the seven isolates were sequenced. The sequences showed high homology to previously described P. insidiosum DNA sequences available in GenBank. Similar studies based on the morphological, histological and molecular data identified the etiological agent in samples of granulomatous lesions in these equines as P. insidiosum. In America, the infection has been diagnosed more frequently in equines of Brazil, Colombia, Costa Rica and the United States of America. 相似文献