全文获取类型
收费全文 | 149702篇 |
免费 | 144470篇 |
国内免费 | 29624篇 |
出版年
2019年 | 2776篇 |
2018年 | 3304篇 |
2017年 | 3227篇 |
2016年 | 5093篇 |
2015年 | 8666篇 |
2014年 | 8306篇 |
2013年 | 8017篇 |
2012年 | 7600篇 |
2011年 | 5281篇 |
2010年 | 6650篇 |
2009年 | 11563篇 |
2008年 | 4559篇 |
2007年 | 4424篇 |
2006年 | 3383篇 |
2005年 | 9398篇 |
2004年 | 8061篇 |
2003年 | 5863篇 |
2002年 | 4186篇 |
2001年 | 5202篇 |
1999年 | 8100篇 |
1998年 | 9120篇 |
1997年 | 9205篇 |
1996年 | 8527篇 |
1995年 | 8811篇 |
1994年 | 8219篇 |
1993年 | 7851篇 |
1992年 | 9587篇 |
1991年 | 9711篇 |
1990年 | 10623篇 |
1989年 | 9786篇 |
1988年 | 9060篇 |
1987年 | 8044篇 |
1986年 | 7391篇 |
1985年 | 6834篇 |
1984年 | 5110篇 |
1983年 | 4059篇 |
1982年 | 3991篇 |
1981年 | 3632篇 |
1980年 | 3513篇 |
1979年 | 4329篇 |
1978年 | 3732篇 |
1977年 | 3507篇 |
1976年 | 3338篇 |
1975年 | 3174篇 |
1974年 | 3457篇 |
1973年 | 3468篇 |
1972年 | 3760篇 |
1971年 | 3515篇 |
1970年 | 3164篇 |
1969年 | 3219篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
UV mutability of Salmonella typhimurium LT2 was eliminated in the presence of a multicopy plasmid carrying the Escherichia coli lexA+ gene. This result suggests that inducible, SOS-like functions are required for UV mutagenesis in S. typhimurium. S. typhimurium strains carrying either point or deletion mutations in topA had previously been shown to lose their mutability by UV or methyl methanesulfonate (K. Overbye and P. Margolin, J. Bacteriol. 146:170-178, 1981; K. Overbye, S. M. Basu, and P. Margolin, Cold Spring Harbor Symp. Quant. Biol. 47:785-791, 1983). Mitomycin C induction of the phi(mucB'-lacZ') fusion (a DNA damage-inducible locus carried on plasmid pSE205) in S. typhimurium topA was normal, suggesting that RecA is activated in topA mutants. These observations lead us to deduce that S. typhimurium has at least one DNA damage-inducible locus in addition to recA that is required for UV mutability. 相似文献
932.
933.
934.
Linear mapping of tryptophan residues in Vesiculovirus M and N proteins by partial chemical cleavage. 总被引:3,自引:2,他引:1
Nonlimit chemical cleavage at tryptophan residues of protein labeled at the amino terminus afforded a simple procedure for generating specific fragments and for mapping tryptophan positions. A comparison of the matrix (M) and nucleocapsid (N) proteins of four members of the Vesiculovirus group by this procedure suggests considerable conservation of tryptophan number and location in the four serotypes examined. 相似文献
935.
A strain of Lactobacillus plantarum which was unable to produce manganese (Mn)catalase (ATCC 8014) grew somewhat more rapidly and to a slightly higher plateau density than did an Mn catalase-positive strain (ATCC 14421), and this was the case during aerobic or anaerobic growth. However, when maintenance of viability was measured during the stationary phase of the growth cycle, the advantage provided by Mn catalase was obvious. Thus, the viability of ATCC 14431 was undiminished over 21 h of aerobic incubation, during the stationary phase, whereas that of ATCC 8014 decreased by seven orders of magnitude. Addition of catalase to the medium or growth in the presence of hemin, which allows catalase synthesis, protected ATCC 8014 against this loss of viability. Suppression of Mn catalase within ATCC 14431 by treatment with NH2OH caused the cells to lose viability when exposed to 4 mM H2O2. 相似文献
936.
A M Dunning R Houlston J Frosteg?rd J Revill J Nilsson A Hamsten P Talmud S Humphries 《Biochimica et biophysica acta》1991,1096(3):231-237
We have searched for sequence differences in the region of the apolipoprotein B (apo B) gene encoding amino acids 3130-3630 in eight individuals with reduced affinity of low density lipoprotein (LDL) for the normal LDL-receptor. All individuals were hypercholesterolaemic and were selected either on the basis of reduced fractional catabolic rate (FCR) of autologous LDL or substantially reduced binding of their LDL to normal LDL-receptors determined by an in vitro cell growth assay using the U937 macrophage-like cell line. Segments of the apo B gene were amplified by the polymerase chain reaction. Using a combination of cloning and sequencing the amplified fragment, together with chemical cleavage mismatch analysis, no sequence differences were identified in this region of the gene. We therefore conclude that variation outside the region of the apo B gene that codes for amino acids 3130-3630 must be responsible for the reduced LDL clearance in these patients. 相似文献
937.
C Haux A Larsson M L Sj?beck G Lithner 《Comparative biochemistry and physiology. A, Comparative physiology》1987,86(4):729-732
Intra-lake variations in physiological parameters, representing haematology, plasma ion composition and carbohydrate metabolism, were investigated in perch (Perca fluviatilis), inhabiting a comparatively unpolluted lake. Provided the perch were subjected to a standardized procedure for capture, handling, recovery after capture, and sampling, only few and minor differences were observed in 21 parameters investigated when 3 groups were compared to a control group of perch. It is concluded that the experimental design used is suitable for the examination of the physiological status of perch in the field. 相似文献
938.
V I Popova L M Va?ner I I Gorshkova O A Gromova V V Liakhovich 《Biokhimii?a (Moscow, Russia)》1985,50(1):53-62
The previously described, iodine-labeled alkylating stable nitroxyl radicals located at different distances between the N-O. group and the iodine atom were used for a comparative study of the structure of microsomal cytochromes P-450 and P-448 active centers. The radicals were shown to change the optical spectra of Fe3+ located in the active site of the enzyme that are similar to those induced by cytochrome P-450 substrates. Some differences in the type of the radicals binding to control, phenobarbital- and 3-methylcholanthrene-induced microsomes were revealed. The alkylating radical substrate analogs covalently bound to microsomal cytochrome P-450 in the vicinity of the active center, resulting in the inhibition of oxidation of type I and II substrates (e. g., aniline and naphthalene). The value of the spectral binding constant (Ks) for naphthalene in the presence of the radical covalently bound to the cytochrome P-450 active center showed a tendency to increase. Using the ESR technique, the interaction between Fe3+ and the radical localized in the active site of cytochrome P-450 was demonstrated. The contribution of Fe3+ to the relaxation of the radicals covalently bound to cytochrome P-450 was evaluated from the values of the spin label ESR spectra saturation curves at 77K. The distances between the N-O. group of these radicals and Fe3+ in the enzyme active center for the three types of microsomes were determined. The data obtained point to structural peculiarities of the active center of cytochrome P-450, depending on the microsomal type. 相似文献
939.
940.
Body measurements of squirrel populations are described. The relation between body length and body weight was examined and factors causing individual or seasonal variation in body weight were studied. 相似文献