全文获取类型
收费全文 | 1150159篇 |
免费 | 129800篇 |
国内免费 | 1184篇 |
出版年
2018年 | 14251篇 |
2017年 | 13796篇 |
2016年 | 16779篇 |
2015年 | 20535篇 |
2014年 | 23436篇 |
2013年 | 32732篇 |
2012年 | 39316篇 |
2011年 | 43257篇 |
2010年 | 29811篇 |
2009年 | 27641篇 |
2008年 | 37687篇 |
2007年 | 39735篇 |
2006年 | 32398篇 |
2005年 | 32126篇 |
2004年 | 31245篇 |
2003年 | 30009篇 |
2002年 | 29004篇 |
2001年 | 46132篇 |
2000年 | 46248篇 |
1999年 | 37089篇 |
1998年 | 14569篇 |
1997年 | 14819篇 |
1996年 | 14146篇 |
1995年 | 13145篇 |
1994年 | 12950篇 |
1993年 | 13010篇 |
1992年 | 31088篇 |
1991年 | 30298篇 |
1990年 | 29575篇 |
1989年 | 29029篇 |
1988年 | 26515篇 |
1987年 | 25583篇 |
1986年 | 23924篇 |
1985年 | 23905篇 |
1984年 | 20223篇 |
1983年 | 17558篇 |
1982年 | 13723篇 |
1981年 | 12427篇 |
1980年 | 11703篇 |
1979年 | 19153篇 |
1978年 | 15402篇 |
1977年 | 13970篇 |
1976年 | 13175篇 |
1975年 | 14454篇 |
1974年 | 15565篇 |
1973年 | 15400篇 |
1972年 | 14159篇 |
1971年 | 13094篇 |
1970年 | 10724篇 |
1969年 | 10444篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
The intellectual property rights debate focuses on the flow of germplasm from developing tropical countries to developed temperate nations. Few investigators have addressed the converse. We discuss the abundance and importance of introduced plants in pharmacopoeias of northern South America. Introduced species commonly are employed as medicines throughout the region and include at least 216 Eurasian, North American, African, and Pacific species. Among the Shuar of lowland Ecuador, four introduced plants (Citrus aurantium, Cymbopogon citratus, Saccharum officinarum, and Zingiber officinale) are included in their most commonly prescribed remedies. The widespread use of introduced plants is due, in part, to the medicinal value of plants whose primary use is for food (e.g., Musa X paradisiacal Similarly, many introduced ornamentals also have therapeutic value (e.g., Hedychium coronarium). Other species have been introduced specifically as medicines (e.g., Aloe vera). Restrictions on the flow of germplasm and plant knowledge may protect the economic interests of governments and national industry. If applied bilaterally, however, constraints on the movement of plants will limit the continued evolution of traditional medicinal systems in areas where they are most needed. 相似文献
993.
The chloroform-methanol extractable lipids of the Gram-negative fresh-water bacteria Arcocella aquatica NO-502 and Flectobacillus major FM were found to contain an unusual ninhydrin-positive glycolipid. It was purified by two-stage silica gel-column chromatography. By the use of IR and (1)H-NMR spectroscopy, mass spectrometry and chemical-degradation experiment, the lipid was established to be 1-O-monoglycosyl ceramide, the carbohydrate moiety of which was the alpha-pyranose-ring form of 7-desoxy-7-amino-D-manno-heptulosonic acid, or 1-hydroxycarbonyl-6-deoxy-6-amino-alpha-D-mannopyranose. The ceramide portion consisted mainly (by 95% in the A. aquatica glycolipid and 80% in the F. major glycolipid) of 2-N-(2'-D-hydroxy-13'-methyltetradecanoyl)-15-methyl-4(E)-hexad ecasph ingenine. The minor molecular species differed from the major one only in fatty acid structure. The glycolipid accounted for 8 and 11% of the total lipids extracted from A. aquatica NO-502 and F. major FM cells, respectively. 相似文献
994.
Murine Cytomegalovirus m02 Gene Family Protects against Natural Killer Cell-Mediated Immune Surveillance
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Sofia A. Oliveira Se-Ho Park Peter Lee Albert Bendelac Thomas E. Shenk 《Journal of virology》2002,76(2):885-894
The murine cytomegalovirus m02 gene family encodes putative type I membrane glycoproteins named m02 through m16. A subset of these genes were fused to an epitope tag and cloned into an expression vector. In transfected and murine cytomegalovirus-infected cells, m02, m04, m05, m06, m07, m09, m10, and m12 localized to cytoplasmic structures near the nucleus, whereas m08 and m13 localized to a filamentous structure surrounding the nucleus. Substitution mutants lacking the m02 gene (SMsubm02) or the entire m02 gene family (SMsubm02-16) grew like their wild-type parent in cultured cells. However, whereas SMsubm02 was as pathogenic as the wild-type virus, SMsubm02-16 was markedly less virulent. SMsubm02-16 produced less infectious virus in most organs compared to wild-type virus in BALB/c and C57BL/6J mice, but it replicated to wild-type levels in the organs of immunodeficient gamma(c)/Rag2 mice, lacking multiple cell types including natural killer cells, and in C57BL/6J mice depleted of natural killer cells. These results argue that one or more members of the m02 gene family antagonize natural killer cell-mediated immune surveillance. 相似文献
995.
Haploid plants were regenerated in vitro from unpollinated ovules of niger (Guizotia abyssinica (L. f.) (Cass.) on Murashige and Skoog nutrient medium (MS) supplemented with 10 μM naphthaleneacetic acid or 10 μM NAA +
1.5 μM kinetin and 30 g/l sucrose. Gamborg (B5) medium was the best for plant regeneration (in comparison with MS, Nitsch
and Nitsch (NN), and Chu (N6) media) from cultured ovules, and 6.66 and 7.33 ovules of JNC-6 and Ootacamund cultivars were
involved in direct plant regeneration on this medium. Matured ovules (ovules collected one day before anthesis or on the day
of anthesis) only responded to cultural regimes and involved in direct plantlet development. Cytological preparation of root
tips and chloroplast counts in the guard cells of leaf stomata of regenerated plants confirmed their haploid nature.
This text was submitted by the authors in English. 相似文献
996.
997.
The use of the probiotic Acylact in combination with Viferone containing human recombinant interferon-alpha 2 in the treatment of intestinal dysbacteriosis in children with insulin-dependent diabetes mellitus (IDDM) was shown to be highly efficient. Elimination of microecologic disorders in the intestine was accompanied in all the children by immune rearrangements. The quantity of secretory and serum immunoglobulins and complement increased and the white blood cell chemiluminescence proved to be higher. The correction of the immune status of the children with IDDM resulted in a certain decrease of glycemia. The data are indicative of the fact that such a treatment of intestinal dysbacteriosis in children with IDDM is promising. 相似文献
998.
999.
1000.
Air transport can move patients safely and rapidly over long distances. However, changes in altitude can have disastrous effects because diminished ambient air pressure may allow gases in closed spaces and tissues to expand rapidly. Even pressurized commercial aircraft do not maintain sea-level pressure: cabin pressures equal to those at yp to 8000 ft may be experienced, diminishing oxygen tension in proportion. Air transport is absolutely contraindicated for patients with untreated pneumothorax, gas gangrene, or air trapped in the cranium and those who have recently undergone abdominal surgery. Special considerations including a planned low-altitude flight are warrented for patients who are anemic, in respiratory or cardiac distress, or immobilized in casts, or who have been engaged in underwater diving immediately before the flight. 相似文献