全文获取类型
收费全文 | 6912篇 |
免费 | 478篇 |
国内免费 | 395篇 |
专业分类
7785篇 |
出版年
2024年 | 24篇 |
2023年 | 129篇 |
2022年 | 208篇 |
2021年 | 223篇 |
2020年 | 293篇 |
2019年 | 256篇 |
2018年 | 240篇 |
2017年 | 204篇 |
2016年 | 172篇 |
2015年 | 226篇 |
2014年 | 487篇 |
2013年 | 448篇 |
2012年 | 383篇 |
2011年 | 481篇 |
2010年 | 343篇 |
2009年 | 312篇 |
2008年 | 309篇 |
2007年 | 263篇 |
2006年 | 269篇 |
2005年 | 236篇 |
2004年 | 189篇 |
2003年 | 187篇 |
2002年 | 155篇 |
2001年 | 133篇 |
2000年 | 117篇 |
1999年 | 103篇 |
1998年 | 90篇 |
1997年 | 111篇 |
1996年 | 94篇 |
1995年 | 83篇 |
1994年 | 90篇 |
1993年 | 73篇 |
1992年 | 53篇 |
1991年 | 86篇 |
1990年 | 73篇 |
1989年 | 62篇 |
1988年 | 48篇 |
1987年 | 39篇 |
1986年 | 34篇 |
1985年 | 55篇 |
1984年 | 73篇 |
1983年 | 57篇 |
1982年 | 64篇 |
1981年 | 54篇 |
1980年 | 33篇 |
1979年 | 39篇 |
1978年 | 14篇 |
1977年 | 14篇 |
1976年 | 17篇 |
1973年 | 14篇 |
排序方式: 共有7785条查询结果,搜索用时 0 毫秒
1.
《Cell reports》2020,30(1):112-123.e4
- Download : Download high-res image (131KB)
- Download : Download full-size image
2.
Defective transducing phages carrying aroG, the structural gene for phenylalanine (phe)-inhibitable phospho-2-keto-heptonate aldolase (EC 4.1.2.15; previously known as 3-deoxy-D-arabinoheptulosonate-7-phosphate synthetase[phe]), have been isolated, and DNA from two of these phages has been used to construct a restriction map of the region from att lambda to aroG. A 7.6-kb PstI-HindIII fragment from one of these phages was cloned into pBR322 and shown to contain aroG. The location of aroG within the 7.6 kb was established by subcloning and Tn3 transpositional mutagenesis. A fragment carrying the aroG promoter and operator has been cloned into a high copy number promoter-cloning vector (pMC489), and the resulting aroGpo-LacZ' (alpha) fusion subcloned in a low copy number vector. Strains with this fusion on the low copy number vector exhibit negative regulation of beta-galactosidase expression by both phenylalanine and tryptophan and positive regulation by tyrosine in a tyrR+ background. 相似文献
3.
S. L. GLOCKLING FLS G. W. BEAKES 《Botanical journal of the Linnean Society. Linnean Society of London》2001,136(3):329-338
Two new species of Haptoglossa , one zoosporic, H. northumbrica , and one aplanosporic, H. polymorphs, , were isolated from samples of manure and horse dung in north-east England. The zoosporic H. northumbrica is morphologically similar to H. dickii but differs in having slightly smaller infection gun cells with a unique internal arrangement of cones in the apical missile chamber. The thallus of the aplanosporic H. polymorpha is similar to H. heteromorpha but produces three different types of aplanospore. The smaller cysts either develop into broad, arcuate gun cells or form curved adhesive cells that have a rounded base. These curved adhesive cells have very different internal ultrastructural organization. The large cysts develop into infection cells that are morphologically similar to the curved adhesive cells, but their internal structure has not yet been observed. 相似文献
4.
F. Hubert M.-H. Rodier A. Minoza V. Portet-Sulla E. Cateau K. Brunet 《Letters in applied microbiology》2021,72(1):82-89
Candida auris is an emerging species responsible for life-threatening infections. Its ability to be resistant to most systemic antifungal classes and its capacity to persist in a hospital environment have led to health concerns. Currently, data about environmental reservoirs are limited but remain essential in control of C. auris spread. The aim of our study was to explore the interactions between C. auris and two free-living amoeba (FLA) species, Vermamoeba vermiformis and Acanthamoeba castellanii, potentially found in the same water environment. Candida auris was incubated with FLA trophozoites or their culture supernatants. The number of FLA and yeasts was determined at different times and transmission electron microscopy (TEM) was performed. Supernatants of FLAs promoted yeast survival and proliferation. Internalization of viable C. auris within both FLA species was also evidenced by TEM. A water environmental reservoir of C. auris can therefore be considered through FLAs and contamination of the hospital water networks would consequently be possible. 相似文献
5.
The photon flux autocorrelation function of a fluorescent label attached to a bacterial motor shaft is calculated for the case in which the bacterial motor is considered to be actively but idly rotating. It is shown that even when the fluorescent label has a very short lifetime, fluorescence correlation spectroscopy should provide a useful tool for determining the rate of revolution of the bacterial motor under various solution conditions. 相似文献
6.
Summary In comparison to cassava grown in monoculture the root infection of cassava with vesicular-arbuscular mycorrhiza was increased by crop rotation with grain legumes in the field. This was also found when cassava was intercropped with legumes and fertilized. A possible specificity of mycorrhizal fungi to increase the yield of one species more than the other when grown in association, is discussed. 相似文献
7.
Abstract Both the intracellular and the extracellular concentration of cyclic AMP increases logarithmically in synchronously growing cultures of Escherichia coli . Thus, cyclic AMP by itself cannot regulate growth and division of the bacterium during the cell cycle. 相似文献
8.
Abstract A short-term oral administration of live Saccharomyces cerevisiae cells, strain Sillix Hansen DSM 1883, resulted in enhanced resistance of mice toward infections with K. pneumoniae, S. pneumoniae and S. pyogenes A produced by intranasal inoculation. Yeast pre-treatment also increased the efficacy of antibiotic therapy in bacterial infections and of antiviral drugs in viral infections. Yeast treatment of animals stimulated phagocytosis, activated the complement system and induced interferon which are likely to represent the main mechanisms of action whereby pretreatment of mice with live S. cerevisiae cells increases resistance to infection. It is concluded that preventive administration of live Saccharomyces cerevisiae cells should be used for increasing resistance to bacterial infections, in particular of the respiratory tract, or to viral infections, as well as an adjunct to antibiotic and antiviral drug therapy. 相似文献
9.
Pierre Bongrand Gilles Bouvenot Robert Bartolin J Jeanne Tatossian Bernard Bruguerolle 《Chronobiology international》1988,5(1):81-83
Eleven male subjects were investigated to detect a possible circadian rhythm of the polymorphonuclear phagocytosis. Both cell activity and serum opsonins were studied for numerical detection of granulocytes having ingested at least one particle and for the mean number of ingested particles per cell. No significant temporal differences (ANOVA and cosinor) were found. 相似文献
10.