全文获取类型
收费全文 | 97060篇 |
免费 | 7694篇 |
国内免费 | 32篇 |
出版年
2021年 | 833篇 |
2018年 | 1300篇 |
2017年 | 1212篇 |
2016年 | 1634篇 |
2015年 | 1726篇 |
2014年 | 2082篇 |
2013年 | 2961篇 |
2012年 | 3238篇 |
2011年 | 3341篇 |
2010年 | 2488篇 |
2009年 | 2098篇 |
2008年 | 3044篇 |
2007年 | 2998篇 |
2006年 | 2824篇 |
2005年 | 2659篇 |
2004年 | 2654篇 |
2003年 | 2543篇 |
2002年 | 2364篇 |
2001年 | 4397篇 |
2000年 | 4152篇 |
1999年 | 3223篇 |
1998年 | 1042篇 |
1997年 | 1034篇 |
1996年 | 916篇 |
1995年 | 834篇 |
1993年 | 829篇 |
1992年 | 2442篇 |
1991年 | 2453篇 |
1990年 | 2456篇 |
1989年 | 2204篇 |
1988年 | 2064篇 |
1987年 | 1977篇 |
1986年 | 1824篇 |
1985年 | 1818篇 |
1984年 | 1495篇 |
1983年 | 1295篇 |
1982年 | 929篇 |
1981年 | 873篇 |
1979年 | 1435篇 |
1978年 | 1126篇 |
1977年 | 1015篇 |
1976年 | 973篇 |
1975年 | 1156篇 |
1974年 | 1255篇 |
1973年 | 1337篇 |
1972年 | 1184篇 |
1971年 | 1042篇 |
1970年 | 924篇 |
1969年 | 955篇 |
1968年 | 836篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
911.
The nucleotide sequence of the G6-amylase gene from alkalophilic Bacillus sp. H-167 was determined. The open reading frame of the gene consisted of 2865 base pairs, encoding 955 amino acids. The NH2-terminal amino acid sequence analysis of the G6-amylase indicated that the enzyme had a single peptide of 33 amino acid residues and the mature enzyme was composed of 922 amino acids, giving a molecular mass of 102,598. Identity of the NH2-terminal amino acid sequences among each component of the multiform G6-amylase suggested the proteolytic processing of the COOH-terminal side of the enzyme. The DNA sequence and the deduced amino acid sequence of the G6-amylase gene showed no homology with those of other bacterial alpha-amylases although the consensus amino acid sequences of the active center were well conserved. 相似文献
912.
Enumeration and presumptive identification of some functional groups of bacteria in the rumen of dairy cows fed grass silage-based diets 总被引:5,自引:0,他引:5
Abstract Samples of rumen ingesta from two rumen-fistulated dairy cows fed grass silage-based diets were examined for numbers and types of bacteria that developed colonies on rumen fluid-agar media designated to support the growth of (a) a wide range of species, (b) cellulolytic bacteria, (c) lactate-fermenting bacteria, (d) non-fermentative bacteria. The most numerous species was Bacteroides ruminicola followed by Butyrivibrio fibrisolvens . The most abundant cellulolytic species were Eubacterium cellulosolvens and Ruminococcus flavefaciens. Megasphaera elsdenii and Selenomonas ruminantium were important lactate fermenters but an unidentified bacterium that grew poorly on maintenance medium was by far the most numerous among bacteria isolated from lactate-containing medium. One strain remained sufficiently viable to show that it fermented lactate to propionate and acetate. 相似文献
913.
The polymerase chain reaction for Mycoplasma pulmonis 总被引:2,自引:0,他引:2
R Harasawa K Koshimizu T Uemori O Takeda K Asada I Kato 《Microbiology and immunology》1990,34(4):393-395
In vitro DNA amplification by polymerase chain reaction was examined to detect Mycoplasma pulmonis. A pair of synthetic oligonucleotide primers was constructed, and used to amplify a unique sequence of M. pulmonis DNA. Amplified products were detected by agarose gel electrophoresis and verified by blot hybridization with a synthetic oligonucleotide probe. This system detected cellular DNA of M. pulmonis but not M. arthritidis or M. neurolyticum, and thus appears to be useful for M. pulmonis diagnosis. 相似文献
914.
Green callus obtained from leaves of the CAM-inducible plant Kalanchoe blossfeldiana cv. Montezuma has previously been shown to perform C3-type photosynthesis under 16-h days and to shift to crassulacean acid metabolism (CAM) under 9-h days. The utilization of photoperiodic regimes (i.e. night interruptions by 30 min red light) established that CAM induction in the callus was under the control of phytochrome, as shown by measurements of CAM criteria: phosphoenolpyruvate carboxylase activity and malic acid pools. Short-term responsiveness of the callus cells to phytochrome modulations by monochromatic radiations was also established by the rapid changes observed in the diameter of the callus-derived protoplasts. These results provide further evidence that whole plant correlations are not necessary for phytochrome operativity.Abbreviations CAM
crassulacean acid metabolism
- PAL
phenylalanine ammonia lyase (EC 4.3.1.5)
- PAR
photosynthetically active radiations
- PEPC
phosphoenolpyruvate carboxylase (EC 4.1.1. 31)
- Rubisco
ribulose 1,5 bisphosphate carboxylase (EC 4.1.1.39) 相似文献
915.
Bovine serum albumin, free of deoxyribonuclease activity, was obtained in our laboratory using ion-exchange chromatography followed by acetylation. Chromatography on four different resins (DEAE-52, P-11, hydroxylapatite and Q Sepharose fast-flow) was examined. Fractions from Q Sepharose chromatography, eluted with a linear gradient 0-1.0 M NaCl and subsequently acetylated, proved to be the most effective method for obtaining deoxyribonuclease-free bovine serum albumin. 相似文献
916.
A systematic study of agarose gel electrophoresis of double-stranded RNA in the kilobase range of sizes was performed. The dsRNA to dsDNA relative mobility was found to depend on gel concentration: in low density gels RNA moves slower and in high density gels - faster than DNA of the same molecular size. The electrophoretic differences were interpreted within the reptation theory to be mainly due to the molecular stiffness differences. The dsRNA persistence length was roughly estimated to be about twice as great as that of DNA. 相似文献
917.
P V Belan O N Osipenko A V Tepikin 《Comp. Biochem. Physiol. C, Comp. Pharmacol. Toxicol.》1990,96(1):45-47
1. Cytoplasmic Ca2+ concentration ICaIin and membrane potential of single Helix pomatia neurons was studied by Fura-2 fluorescence measurement and conventional current clamp methods. 2. Intracellular injection of inositol-1,4,5-trisphosphate (IP3) and nonhydrolysable GTP analogue (Gpp/NH/p) led to a rise of ICaIin; in contrast, GTP injection did not cause significant ICaIin changes. 3. We suggest that both IP3 and Gpp/NH/p directly activated Ca release from intracellular stores. 相似文献
918.
919.
The human metallothionein gene complex on chromosome 16 has been remapped to 16q13 using high-resolution in situ hybridization. The complex is not disrupted by the rearrangement breakpoint on the long arm of chromosome 16 in patients with myelomonocytic leukemia with abnormal eosinophils, as had been previously reported. The locus order on 16q is cen-MT-FRA16B-D16S4-inversion breakpoint-HP-tel. 相似文献
920.
A simultaneous increase is found in the level of protein synthesis and the major regulatory glycolytic enzyme, phosphofructokinase (PFK), in early phytohemagglutinin exposure of human lymphocytes. The induction of DNA synthesis is demonstrated to be a much later event. This indicates that the increase of glycolysis in mitogen-stimulated cells precedes cell proliferation, but occurs simultaneously with a general increase in protein synthesis. Chemical inhibitors are used to clarify the interrelationship of protein synthesis, glycolytic enzymes levels, and DNA synthesis. Inhibition of protein synthesis with cycloheximide in the mitogen-exposed lymphocytes prevents any increase in PFK levels, implicating protein synthesis as a cause for the increased glycolysis. Cycloheximide also prevents entry into S phase in mitogen-stimulated lymphocytes which may be due to inhibition of the synthesis of enzymes necessary for DNA synthesis, such as DNA polymerase. Aphidicolin, a specific DNA polymerase inhibitor, is found to have no effect on the increase in protein synthesis and PFK levels that precedes DNA synthesis. The increase in glycolysis in mitogen-stimulated lymphocytes occurs simultaneously with, and is dependent upon, increased protein synthesis, and precedes DNA synthesis and lymphocyte proliferation; thus, the high glycolytic rate of mitogen-stimulated cells is not merely a secondary manifestation of rapid cell proliferation as has been previously reported. 相似文献