全文获取类型
收费全文 | 3885篇 |
免费 | 201篇 |
出版年
2023年 | 11篇 |
2021年 | 44篇 |
2020年 | 29篇 |
2019年 | 26篇 |
2018年 | 60篇 |
2017年 | 54篇 |
2016年 | 80篇 |
2015年 | 121篇 |
2014年 | 130篇 |
2013年 | 235篇 |
2012年 | 213篇 |
2011年 | 216篇 |
2010年 | 127篇 |
2009年 | 122篇 |
2008年 | 194篇 |
2007年 | 224篇 |
2006年 | 198篇 |
2005年 | 214篇 |
2004年 | 187篇 |
2003年 | 171篇 |
2002年 | 178篇 |
2001年 | 117篇 |
2000年 | 113篇 |
1999年 | 94篇 |
1998年 | 49篇 |
1997年 | 67篇 |
1996年 | 27篇 |
1995年 | 24篇 |
1994年 | 33篇 |
1993年 | 29篇 |
1992年 | 69篇 |
1991年 | 59篇 |
1990年 | 55篇 |
1989年 | 50篇 |
1988年 | 77篇 |
1987年 | 49篇 |
1986年 | 35篇 |
1985年 | 28篇 |
1984年 | 32篇 |
1983年 | 21篇 |
1982年 | 27篇 |
1981年 | 10篇 |
1980年 | 14篇 |
1979年 | 21篇 |
1978年 | 23篇 |
1975年 | 17篇 |
1974年 | 13篇 |
1973年 | 21篇 |
1971年 | 13篇 |
1968年 | 9篇 |
排序方式: 共有4086条查询结果,搜索用时 187 毫秒
11.
The mitoplasts were prepared from bullfrog (Rana catesbeiana) liver mitochondria by treatment with digitonin and were then separated into the matrix and inner membrane fractions. The matrix fraction thus obtained was free of lysosomal contaminations and exhibited a distinct proteinase activity. pH dependency of the matrix proteinase activity measured in the presence and absence of iodoacetamide revealed that the matrix contained at least two kinds of proteinase, a major alkaline thiol proteinase having an optimal pH at 8.5 and a minor neutral proteinase having an optimal pH at 7.5. The major matrix proteinase activity was strongly inhibited by leupeptin, chymostatin, antipain and E64-C, an inhibitor of Ca2+-dependent thiol proteinase, while it was scarcely affected by diethylpyrocarbonate. The activity was also inhibited by DTNB and p-chloromercuribenzoate. Addition of hydrocarbon compounds such as ethylene glycol, glycerol, Triton X-100 and poly (ethylene glycol) to the reaction mixture was found to decrease the matrix proteinase activity. Neither cytochrome c nor glutamate dehydrogenase was hydrolyzed when subjected to the matrix proteinase activity in vitro. On the other hand, cytochrome c oxidase was effectively hydrolyzed, and the enzyme associated with the mitochondrial innermembrane fragments was partially hydrolyzed by the major matrix proteinase activity. 相似文献
12.
Heterochrony, an evolutionary change in developmental processes, is one of the major proximate causes of morphological diversity of organisms. It has been reported in the medaka Oryzias latipes that higher-latitude larvae have a genetic tendency to complete fin ray formation at larger body sizes, which results in relatively shorter anal and dorsal fins in adults. However, this latitudinal, heterochronic variation in fin length in the wild may be partially explained by latitudinal differences in thermal environments, if temperatures affect the timing of fin ray formation. Common-environment experiments revealed that the body size at which fin pterygiophore (a basal skeleton of fin rays) formation was completed was larger in higher-latitude larvae than in lower-latitude larvae at all temperatures examined, supporting the proposal that fin ray formation of the former is genetically delayed. However, phenotypic plasticity in response to temperature was also evident; lower temperatures caused delayed fin ray formation until a larger body size had been achieved in both high- and low-latitude larvae. These observations suggest that habitat temperatures also contribute to the latitudinal difference in the timing of fin development, magnifying phenotypic variation in fin length across latitudes. We discuss reasons for this positive covariance between genetic and environmental effects on the latitudinal, heterochronic variation, from the viewpoint of local adaptation and evolution of phenotypic plasticity. 相似文献
13.
When pregnant mice were fed biotin-deficient diets, cleft palate occurred more frequently in male fetuses than in female fetuses. Possible underlying mechanisms are speculated on, and some methodological problems in the analysis of sex-related differences in multiparous animals are discussed. 相似文献
14.
15.
16.
Masaru Manabe Tetsuhisa Goto Shinji Matsuura 《Bioscience, biotechnology, and biochemistry》2013,77(11):2003-2007
Aflatoxins Bl, B2, G1 and G2 were quantitatively detected by high-performance liquid chromatography on a 12 µl flow-cell in the fluorometric detector using the mobile phase of toluene system instead of chloroform, dichloromethane or methanol system. Various kinds of columns and mobile phases were tested, and fine mutual separation of all the four aflatoxins without quenching their fluorescence was achieved by using sHica gel column and toluene- ethyl acetate-formic acid-methanol (89.0: 7.5: 2.0: 1.5 v/v/v/v). The relationship between the fluorescence peak area and the amount injected was linear in the range of 0.3 ng to 120 ng. This method, as applied to food and feed extracts, is sensitive at the 10~20 ppb levels of the four kinds of aflatoxins. 相似文献
17.
18.
19.
Shingo Ishihara Jessica J. Bitner Greg H. Farley Eric T. Gillock 《Current microbiology》2013,66(4):337-343
We analyzed highly vancomycin-resistant Gram-positive bacteria isolated from the saliva of migratory songbirds captured, sampled, and released from a bird-banding station in western Kansas. Individual bacterial isolates were identified by partial 16S rRNA sequencing. Most of the bacteria in this study were shown to be Staphylococcus succinus with the majority being isolated from the American Robin. Some of these bacteria were shown to carry vanA, vanB, and vanC vancomycin-resistance genes and have the ability to form biofilms. One of the van gene-carrying isolates is also coagulase positive, which is normally considered a virulence factor. Other organisms isolated included Staphylococcus saprophyticus as well as Enterococcus gallinarum. Given the wide range of the American Robin and ease of horizontal gene transfer between Gram-positive cocci, we postulate that these organisms could serve as a reservoir of vancomycin-resistance genes capable of transferring to human pathogens. 相似文献
20.
Shingo Marumo Kazuya Sasaki Saburo Suzuki 《Bioscience, biotechnology, and biochemistry》2013,77(12):1931-1935
The relative stereochemistry of cervicarcin, an antitumor antibiotic, was determined as shown in 1, which represents the absolute stereochemistry also. 相似文献