全文获取类型
收费全文 | 3976篇 |
免费 | 215篇 |
国内免费 | 2篇 |
专业分类
4193篇 |
出版年
2021年 | 29篇 |
2020年 | 22篇 |
2019年 | 27篇 |
2018年 | 51篇 |
2017年 | 29篇 |
2016年 | 58篇 |
2015年 | 102篇 |
2014年 | 103篇 |
2013年 | 279篇 |
2012年 | 198篇 |
2011年 | 161篇 |
2010年 | 99篇 |
2009年 | 126篇 |
2008年 | 206篇 |
2007年 | 218篇 |
2006年 | 204篇 |
2005年 | 225篇 |
2004年 | 200篇 |
2003年 | 196篇 |
2002年 | 187篇 |
2001年 | 65篇 |
2000年 | 65篇 |
1999年 | 75篇 |
1998年 | 60篇 |
1997年 | 29篇 |
1996年 | 45篇 |
1995年 | 43篇 |
1994年 | 44篇 |
1993年 | 43篇 |
1992年 | 87篇 |
1991年 | 63篇 |
1990年 | 36篇 |
1989年 | 57篇 |
1988年 | 62篇 |
1987年 | 58篇 |
1986年 | 35篇 |
1985年 | 46篇 |
1984年 | 33篇 |
1983年 | 41篇 |
1982年 | 32篇 |
1981年 | 50篇 |
1980年 | 27篇 |
1979年 | 39篇 |
1978年 | 22篇 |
1976年 | 28篇 |
1974年 | 25篇 |
1973年 | 21篇 |
1970年 | 25篇 |
1968年 | 26篇 |
1967年 | 20篇 |
排序方式: 共有4193条查询结果,搜索用时 0 毫秒
111.
112.
Distribution of ribonucleic acid coliphages in raw sewage from treatment plants in Japan. 总被引:4,自引:2,他引:2 下载免费PDF全文
To determine the transmission cycle of ribonucleic acid (RNA) coliphages in their natural habitats, we investigated the distribution patterns of RNA phages in raw sewage collected from treatment plants in various localities in Japan. Most of the sewage samples contained group II and III phages. Samples from treatment plants in Sapporo, Tokyo, and Toyama contained appreciable amounts of group I phages in addition to the group II and III phages. As a whole, raw sewage from treatment plants in Japan contained RNA phages of the three groups in the ratio 1:2:5, group I/II/III. Based on the distribution patterns of RNA phages in sewage from domestic drainage in Japan proper (group II/III, 3:1), in animal feces and sewage from slaughter houses (mostly group I), and in human feces (group II/III, 1:1), it can be reasonably said that group I phages tend to be introduced from animal sources and group II and III phages tend to be introduced from human sources. Raw sewage from treatment plants in Japan consists mainly of human feces, sewage from domestic drainage, and industrial wastewater, and, in part, from slaughter houses. In fact, sewage from slaughter houses together with that from human sources flowed into the treatment plants of Tokyo as far as we could confirm. 相似文献
113.
Excess recA protein, a protein essential to general genetic recombination in Escherichia coli, promotes a sequence of formation and dissociation of D-loops from negative superhelical closed circular double-stranded DNA (form I DNA) and homologous single-stranded fragments in the presence of excess ATP, resulting in inactivation of the form I DNA without apparent damage to the DNA. The dissociation of D-loops is accompanied by hydrolysis of ATP to ADP that apparently depends on homologous DNA molecules (homology-dependent ATP hydrolysis). However, at a lower concentrations of ATP, we observed anomalous kinetics in the formation and dissociation of D-loops; as the concentration of ATP was decreased, there was a progressively smaller dissociation of D-loops and a faster resynthesis in the second phase, without changing the rate of the first formation of D-loops. This anomaly might suggest that, as the increase in the amount of ADP relative to that of ATP, dissociation form I DNA is stimulated before formation of D-loops is inhibited. We found that addition of ADP inhibited competitively both formation and dissociation of D-loops and that the latter process was more sensitive to the inhibition than was the former process. Addition of a sufficient amount of ADP to inhibit both formation and dissociation of D-loops, cessation of homology-dependent hydrolysis of ATP, or incubation at low temperature resulted in reactivation of form I DNA that had been inactivated by the sequence. In the presence of an ATP-regenerating system, we confirmed our previous result that limiting the amount of recA protein also causes anomalous kinetics in the formation and dissociation of D-loops. These observations indicate that the formation and dissociation of D-loops and the inactivation and reactivation of form I DNA make a circular reaction sequence. 相似文献
114.
Nucleotide sequences of two aspartic acid tRNAs from rat liver and rat ascites hepatoma 总被引:7,自引:0,他引:7
Y Kuchino N Shindo-Okada N Ando S Watanabe S Nishimura 《The Journal of biological chemistry》1981,256(17):9059-9062
115.
Torosachrysone and two new naphthalenic lactones, isotoralactone and cassialactone, were isolated from the seeds of Cassia obtusifolia. Their structures were established as 9,10-dihydroxy-7-methoxy-3-methylene-1H-naphtho(2,3-c)dihydropyrone-1-one and 8-methoxy-4-methyl-1-oxo-4,10,11-trihydroxy-naphtho(2,3-c)oxepin, respectively. 相似文献
116.
Sumio Iwai Kazuo Nakata Teruyoshi Nagao Nobumaro Kawashima Susumu Matsuyama 《Planta》1981,152(5):478-480
Nine plants were produced from anthers of a somatic hybrid which had been obtained by fusion of Nicotiana tabacum L. and N. rustica L. protoplants. As determined by electrofocusing, the Fraction I protein of the original somatic hybrid had largesubunit polypeptides exclusively of the N. tabacum type. Two of the plants regenerated from anthers contained Fraction-I-protein large subunits exclusively of the N. rustica type. Since each plant was regenerated from a single cell, the somatic hybrid must have had cells containing both the N. tabacum and N. rustica chloroplast genome although the latter was not expressed. Possibilities to account for this non-expression of a chloroplast genome in the somatic hybrid are discussed. 相似文献
117.
Shukuko Ikawa Takehiko Shibata Tadahiko Ando Hiuga Saito 《Molecular & general genetics : MGG》1980,177(3):359-368
Summary We transformed B. subtilis 168 with DNA from B. subtilis IAM1231, IAM1192 and ATCC6633. When we examined the restriction activities of the transformants in vivo and in vitro using phage 105C we found the following: (1) Cells of either IAM1231 or IAM1192 have two modification and restriction systems (Bsu1231(1)-system and Bsu1231(II)-system in IAM1231, and Bsu1192(I)-system and Bsu1192(II)-systems in IAM1192), and cells of ATCC6633 have only one system (Bsu6633-system). (2) The restriction enzymes of all of these five systems are site-specific endonucleases. (3) The nucleotide sequence specificities of the enzymes involved in Bsu1231(I)-system, Bsu1192(I)-system and Bsu6633-system are the same; and those of Bsu1231(II)-system and Bsu1192(II)-system are the same. The sequence specificities of these two groups are different from each other and also different from those of the Bsu168-system of B. subtilis 168, the BsuR-system of B. subtilis R and the Bsu1247(I)-and Bsu1247(II)-systems which are systems of B. subtilis IAM1247. (4) Transformants possessing four different modification and restriction systems (Bsu1231(I)-, Bsu1247(I)-, BsuR- and Bsu168-systems) were constructed. (5) Transformation of two derivatives of 168 that were m
R
+
r
R
+
by DNA from IAM1231 produced 16 transformants that had the Bsu1231(II) restriction system, but had lost the BsuR system. Transformation of a derivative of 168 that was m
1247(II)
+
r
1247(II)
+
by DNA from m
1231(II)
+
r
1231(II)
+
-or m
R
+
r
R
+
-derivative of 168 produced about 100 each of transformants that had the Bsu1231(II)-restriction system or the BsuR-restriction system. But all these transformants lost the Bsu1247(II)-system. 相似文献
118.
Pure phloem sap from rice plant was collected by a method similarto the aphid technique using leafhoppers and planthoppers instead.A Yttrium-Aluminium Garnet laser was used to sever the insectstylets. Sap exuded from the plant through the stylet for upto 3 hr at a rate of 0.2 µl/hr. Analysis of the sap forsugars revealed that the only carbohydrate present was sucrose;its content was estimated to be 17% and remained at this levelfor 3 hr. (Received April 16, 1980; ) 相似文献
119.
The maximum leaf surface temperatures (MLSTs) of 126 species of higher plants were measured by means of an infrared thermometer,
in the Inland Sea area, southwest of Honshu-Island, Japan, where plants suffered from severe environmental conditions due
to an abnormally small amount of precipitation during the summer of 1978. The MLSTs of plants in the summer of 1978 were greater
than or equal to those of 1979, when the environmental conditions were not so severe.
The MLST measured in this study was 50.4 C for a non-succulent plant (Liriodendron), and 53.1 C for a succulent plant (Agave). Plants with different life forms appeared to have different MLSTs. The average of the MLSTs of conifers deciduous trees,
and evergreens were 36.4, 37.7, and 40.3 C, respectively. This order corresponds to the distribution of forests from high
to low, latitudes. Also the MLSTs were higher for woody plants than for herbaceous plants. Relatively high leaf temperatures
were observed for climbing plants, both herbaceous and woody.
Plants with narrow leaves had lower leaf surface temperatures than those with borad leaves. Herbaceous dicotyledonous plants
actively growing at the end of the summer of 1978, in full sun at Hiroshima Castle were exclusively those with relatively
high leaf temperatures. 相似文献
120.
The possible role of sophorolipids from Torulopsis bombicola was investigated in alkane fermentation. Sophorolipids and related model compounds specifically stimulated the growth of strains of Torulopsis yeasts on insoluble alkanes and may act as a specific growth factor. There may be more than one way for a yeast to be stimulated to incorporate alkanes for growth. 相似文献