全文获取类型
收费全文 | 441426篇 |
免费 | 33896篇 |
国内免费 | 1060篇 |
出版年
2018年 | 17153篇 |
2017年 | 16014篇 |
2016年 | 13553篇 |
2015年 | 7688篇 |
2014年 | 7831篇 |
2013年 | 11322篇 |
2012年 | 17294篇 |
2011年 | 26940篇 |
2010年 | 21785篇 |
2009年 | 17122篇 |
2008年 | 21996篇 |
2007年 | 24177篇 |
2006年 | 10123篇 |
2005年 | 10758篇 |
2004年 | 10341篇 |
2003年 | 10120篇 |
2002年 | 9433篇 |
2001年 | 13094篇 |
2000年 | 13132篇 |
1999年 | 10172篇 |
1998年 | 3756篇 |
1997年 | 3911篇 |
1996年 | 3810篇 |
1995年 | 3400篇 |
1994年 | 3312篇 |
1993年 | 3324篇 |
1992年 | 8306篇 |
1991年 | 8248篇 |
1990年 | 7840篇 |
1989年 | 7804篇 |
1988年 | 7189篇 |
1987年 | 6907篇 |
1986年 | 6291篇 |
1985年 | 6480篇 |
1984年 | 5441篇 |
1983年 | 4567篇 |
1982年 | 3561篇 |
1981年 | 3283篇 |
1980年 | 3089篇 |
1979年 | 5129篇 |
1978年 | 3996篇 |
1977年 | 3856篇 |
1976年 | 3539篇 |
1975年 | 3970篇 |
1974年 | 4369篇 |
1973年 | 4292篇 |
1972年 | 4483篇 |
1971年 | 4172篇 |
1970年 | 3243篇 |
1969年 | 3155篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
991.
F. A. R. Stammers 《BMJ (Clinical research ed.)》1957,2(5044):555-558
992.
ANN H. SZYSZKO BESSEMARIE L. PRAZAK CHARLES F. EHRET WILLIAM J. EISLER JOHN J. WILLE 《The Journal of eukaryotic microbiology》1968,15(4):781-785
SYNOPSIS. A multi-unit automatic sampling device for investigation of microbial growth under a wide variety of conditions is described. The kinetics of asynchronous population growth for batch cultures of Tetrahymena pyriformis (W) at several temperatures show that there are 2 distinct growth phases: an exponential ultradian growth phase that is strongly temperature dependent and a non-stationary growth phase, the infradian phase, that shows little or no temperature dependence over the range from 15–27 C. 相似文献
993.
The polar lipids of the autotrophically grown, obligately anaerobic, photosynthetic bacterium Chromatium strain D were separated by paper chromatography. Four major phospholipids were identified: lysophosphatidylethanolamine, phosphatidylethanolamine, phosphatidylglycerol, and cardiolipin. In addition, three glycolipids were observed and characterized, namely, monoglucosyldiglyceride, which is found in other biological systems, and (mannosyl, glucosyl)-diglyceride and (dimannosyl, glucosyl)-diglyceride, which heretofore have not been observed in nature. 相似文献
994.
995.
996.
Competition for sulphur in a grass-clover association 总被引:2,自引:0,他引:2
Summary A 3 × 3 factorial experiment with nitrogen and sulphur fertilizers was carried out on a grass-clover association in an area where there is little if any cyclic return of sulphur. In the absence of sulphur, grass took up 98 per cent of the total uptake of sulphur, and nitrogen fixation by associated clover was negligible. In the absence of fertilizer nitrogen, dressings of sulphur as gypsum stimulated clover growth; at a low rate of application of sulphur, nitrogen fertilizer increased grass growth and clover was suppressed. This suppression was largely overcome with a higher dressing of sulphur. Sulphur therefore must be added to the group of elements (phosphorus, nitrogen and potassium) for which grass may compete intensely when grown with clover and when nitrogen fertilizers are applied to a grass-clover association adequate supplies of sulphur must be assured in order to minimise suppression of clover. Sulphate of ammonia may stimulate clover growth under these conditions. Solubility of gypsum was low in a dry season and residual effects were pronounced. 相似文献
997.
Tau, sigma, and delta. A family of repeated elements in yeast 总被引:16,自引:0,他引:16
We report here the isolation and structure of a new repeated DNA element, tau. This element, from Saccharomyces cerevisiae, is 371 base pairs long and is flanked on either end by the same invertedly repeated sequence found at the ends of some Ty and sigma elements in yeast, copia elements in Drosophila and spleen necrosis virus. The tau inverted repeats are themselves flanked by a 5-base pair directly repeated genomic sequence that is present only once in a cognate tau-allele. These structural characteristics, the presence of multiple copies of tau in the genome, and the isolation of tau+ and tau- allelic pairs suggest that tau may be capable of transposition either alone or in association with some larger element. Detailed sequence analysis of the tau, sigma, and delta elements revealed that all three contain significant regions of homology, suggesting that they are probably members of a single family derived from a common progenitor. 相似文献
998.
999.
Background
Arsenic contamination is widespread throughout the world and this toxic metalloid is known to cause cancers of organs such as liver, kidney, skin, and lung in human. In spite of a recent surge in arsenic related studies, we are still far from a comprehensive understanding of arsenic uptake, detoxification, and sequestration in plants. Crambe abyssinica, commonly known as 'abyssinian mustard', is a non-food, high biomass oil seed crop that is naturally tolerant to heavy metals. Moreover, it accumulates significantly higher levels of arsenic as compared to other species of the Brassicaceae family. Thus, C. abyssinica has great potential to be utilized as an ideal inedible crop for phytoremediation of heavy metals and metalloids. However, the mechanism of arsenic metabolism in higher plants, including C. abyssinica, remains elusive. 相似文献1000.
G. P. Polovinko O. N. Yaroslavtseva Z. A. Teshebaeva V. Yu. Kryukov 《Contemporary Problems of Ecology》2010,3(5):515-521
The paper studies mycobiota of the dead insects in West Siberia, Primorsky krai, and Kyrgyzstan. Ascomycetes anamorphs of
13 genera are revealed. In all regions Beauveria bassiana (Bals.-Criv.) Vuill. dominated comprising on average 68% of the total number of isolates. The fungus hosts list the insects
of 7 orders and 32 families with Coleoptera, Lepidoptera, and Hemiptera dominating. The rarely found entomopathogens include
Tolypocladium inflatum Gams (primarily on Lepidoptera), Metarhizium anisopliae (Metschn.) Sorokin (on Coleoptera). The mortality rate of the insects due to micromycetes is observed mainly on enzootic
level. The study of the pathogenic properties of the dominating species (B. bassiana) show the absence of specificity of its environmental isolates for a number of representatives of Orthoptera, Lepidoptera,
Coleoptera, and Diptera. 相似文献