全文获取类型
收费全文 | 2164篇 |
免费 | 154篇 |
专业分类
2318篇 |
出版年
2022年 | 13篇 |
2021年 | 20篇 |
2020年 | 10篇 |
2019年 | 12篇 |
2018年 | 24篇 |
2017年 | 23篇 |
2016年 | 41篇 |
2015年 | 64篇 |
2014年 | 78篇 |
2013年 | 98篇 |
2012年 | 113篇 |
2011年 | 87篇 |
2010年 | 51篇 |
2009年 | 63篇 |
2008年 | 89篇 |
2007年 | 110篇 |
2006年 | 79篇 |
2005年 | 71篇 |
2004年 | 71篇 |
2003年 | 95篇 |
2002年 | 81篇 |
2001年 | 83篇 |
2000年 | 95篇 |
1999年 | 60篇 |
1998年 | 27篇 |
1997年 | 33篇 |
1996年 | 30篇 |
1995年 | 39篇 |
1994年 | 14篇 |
1993年 | 27篇 |
1992年 | 56篇 |
1991年 | 54篇 |
1990年 | 46篇 |
1989年 | 37篇 |
1988年 | 37篇 |
1987年 | 44篇 |
1986年 | 51篇 |
1985年 | 26篇 |
1984年 | 29篇 |
1983年 | 33篇 |
1982年 | 13篇 |
1981年 | 28篇 |
1980年 | 14篇 |
1979年 | 26篇 |
1978年 | 17篇 |
1977年 | 10篇 |
1976年 | 15篇 |
1973年 | 11篇 |
1971年 | 10篇 |
1970年 | 8篇 |
排序方式: 共有2318条查询结果,搜索用时 0 毫秒
91.
92.
Biodegradation of low-molecular-weight halogenated hydrocarbons by methanotrophic bacteria 总被引:5,自引:0,他引:5
R S Hanson H C Tsien K Tsuji G A Brusseau L P Wackett 《FEMS microbiology reviews》1990,7(3-4):273-278
Low-molecular-weight halogenated hydrocarbons are susceptible to degradation by anaerobic and aerobic bacteria. The methanotrophic bacterium Methylosinus trichosporium 0B3b degrades trichloroethylene more rapidly than other bacteria examined to date. Expression of soluble methane monooxygenase (MMO) is correlated with high rates of biodegradation. An analysis of 16 S rRNA sequences of 11 ribosomal RNAs from type I, type II and type X methanotrophs and methanol-utilizing bacteria have revealed four clusters of phylogenetically related methylotrophs. This information may be useful for the identification and enumeration of methylotrophs in bioreactors and other environments during remediation of contaminated waters. 相似文献
93.
Eiji Takita Katsunori Kohda Hajime Tomatsu Shigeru Hanano Kanami Moriya Tsutomu Hosouchi Nozomu Sakurai Hideyuki Suzuki Atsuhiko Shinmyo Daisuke Shibata 《DNA research》2013,20(6):583-592
Ligation, the joining of DNA fragments, is a fundamental procedure in molecular cloning and is indispensable to the production of genetically modified organisms that can be used for basic research, the applied biosciences, or both. Given that many genes cooperate in various pathways, incorporating multiple gene cassettes in tandem in a transgenic DNA construct for the purpose of genetic modification is often necessary when generating organisms that produce multiple foreign gene products. Here, we describe a novel method, designated PRESSO (precise sequential DNA ligation on a solid substrate), for the tandem ligation of multiple DNA fragments. We amplified donor DNA fragments with non-palindromic ends, and ligated the fragment to acceptor DNA fragments on solid beads. After the final donor DNA fragments, which included vector sequences, were joined to the construct that contained the array of fragments, the ligation product (the construct) was thereby released from the beads via digestion with a rare-cut meganuclease; the freed linear construct was circularized via an intra-molecular ligation. PRESSO allowed us to rapidly and efficiently join multiple genes in an optimized order and orientation. This method can overcome many technical challenges in functional genomics during the post-sequencing generation. 相似文献
94.
Dry seeds of anoxia-tolerant lotus ( Nelumbo nucifera Gaertn= Nelumbium speciosum Willd.) have green shoots with plastids containing chlorophyll, so photosynthesis starts even in seedlings germinated under water, namely hypoxia. Here we investigated antioxidative enzyme changes in N. nucifera seedlings responding to oxygen deficiency. The activity of superoxide dismutase (SOD; EC 1.15.1.1), dehydroascorbate reductase (DHAR; EC 1.8.5.1) and glutathione reductase (GR; EC 1.6.4.2) were lower in seedlings germinated under water (submerged condition) in darkness (SD seedlings) than those found in seedlings germinated in air and darkness (AD seedlings). In contrast, ascorbate peroxidase (APX; EC 1.11.1.11) activity was higher in SD seedlings and the activity of catalase (EC 1.11.1.6) and monodehydroascorbate reductase (MDAR; EC 1.6.5.4) in SD seedlings was nearly the same as in AD seedlings. When SD seedlings were exposed to air, the activity of SOD, DHAR and GR increased, while the activity of catalase and MDAR decreased. Seven electrophoretically distinct SOD isozymes were detectable in N. nucifera . The levels of plastidic Cu,Zn-SODs and Fe-SOD in SD seedlings were comparable with those found in AD seedlings, which may reflect the maintenance of green plastids in SD seedlings as well as in AD seedlings. These results were substantially different from those previously found in rice seedlings germinated under water. 相似文献
95.
We here show an example of morphological novelties, which have evolved from insect wings into the specific structures controlling social behaviour in an ant species. Most ant colonies consist of winged queen(s) and wingless workers. In the queenless ponerine ant Diacamma sp. from Japan, however, all female workers have a pair of small thoracic appendages, called gemmae, which are homologous to the forewings and acts as an organ regulating altruism expression. Most workers, whose gemmae are clipped off by other colony members, become nonreproductive helpers, while only a single individual with complete gemmae becomes functionally reproductive. We examined histologically the development of gemmae, and compared it with that of functional wings in males. Female larvae had well-developed wing discs for both fore- and hindwings. At pupation, however, the wing discs started to evaginate and later degenerate. The hindwing discs completely degenerated, while the degeneration of forewing discs was incomplete, leading to the formation of gemmae. The degeneration process involved apoptotic cell death as confirmed by TUNEL assay. In addition, glandular cells differentiated from the epithelial cells of the forewing buds after completion of pupation. The mechanism of developmental transition from wing to gemma can be regarded as an evolutionary gain of new function, which can be seen in insect appendages and vertebrate limbs.Edited by P. Simpson 相似文献
96.
Cloning, sequencing, and expression of the gene encoding an intracellular beta-D-xylosidase from Streptomyces thermoviolaceus OPC-520 总被引:1,自引:0,他引:1
Tsujibo H Takada C Tsuji A Kosaka M Miyamoto K Inamori Y 《Bioscience, biotechnology, and biochemistry》2001,65(8):1824-1831
The intracellular beta-xylosidase was induced when Streptomyces thermoviolaceus OPC-520 was grown at 50 degrees C in a minimal medium containing xylan or xylooligosaccharides. The 82-kDa protein with beta-xylosidase activity was partially purified and its N-terminal amino acid sequence was analyzed. The gene encoding the enzyme was cloned, sequenced, and expressed in Escherichia coli. The bxlA gene consists of a 2,100-bp open reading frame encoding 770 amino acids. The deduced amino acid sequence of the bxlA gene product had significant similarity with beta-xylosidases classified into family 3 of glycosyl hydrolases. The bxlA gene was expressed in E. coli, and the recombinant protein was purified to homogeneity. The enzyme was a monomer with a molecular mass of 82 kDa. The purified enzyme showed hydrolytic activity towards only p-nitrophenyl-beta-D-xylopyranoside among the synthetic glycosides tested. Thin-layer chromatography analysis showed that the enzyme is an exo-type enzyme that hydrolyze xylooligosaccharides, but had no activity toward xylan. High activity against pNPX occurred in the pH range 6.0-7.0 and temperature range 40-50 degrees C. 相似文献
97.
Ken Hirano Yuichiro Yoshida Tomomi Ishido Naoji Moriya Yoshiyuki Mizushina Mitsuru Ishikawa 《Analytical biochemistry》2010,405(2):160-199
In the present study, we investigated mammalian polymerases that consecutively incorporate various fluorophore-labeled nucleotides. We found that rat DNA polymerase β (pol β) consecutively incorporated fluorophore-labeled nucleotides to a greater extent than four bacterial polymerases, Sequenase Version 2.0, VentR (exo-), DNA polymerase IIIα and the Klenow fragment, and the mammalian polymerases DNA polymerase α and human DNA polymerase δ, under mesophilic conditions. Furthermore, we investigated the kinetics of correct or mismatched incorporation with labeled nucleotides during synthesis by rat pol β. The kinetic parameters Km and kcat were measured and used for evaluating: (i) the discrimination against correct pair incorporation of labeled nucleotides relative to unlabeled nucleotides; and (ii) the fidelity for all nucleotide combinations of mismatched pairs in the presence of labeled or unlabeled nucleotides. We also investigated the effect of fluorophore-labeled nucleotides on terminal deoxynucleotidyl transferase activity of rat pol β. We have demonstrated for the first time that mammalian pol β can consecutively incorporate various fluorophore-labeled dNTPs. These findings suggest that pol β is useful for high-density labeling of DNA probes and single-molecule sequencing for high-speed genome analysis. 相似文献
98.
Komine A Suenaga M Nakao K Tsuji T Tomooka Y 《Biochemical and biophysical research communications》2007,355(3):758-763
In order to investigate tooth development, several cell lines of the dental epithelium and ectomesenchyme have been established. However, no attempt has been reported to regenerate teeth with cell lines. Here, we have established several clonal cell lines of the dental epithelium from a p53-deficient fetal mouse. They expressed specific markers of the dental epithelium such as ameloblastin and amelogenin. A new method has been developed to bioengineer tooth germs with dental epithelial and mesenchymal cells. Reconstructed tooth germs with cell lines and fetal mesenchymal cells were implanted under kidney capsule. The germs regenerated teeth with well-calcified structures as seen in natural tooth. Germs without the cell lines developed bone. This is the first success to regenerate teeth with dental epithelial cell lines. They are useful models in vitro for investigation of mechanisms in morphogenesis and of cell lineage in differentiation, and for clinical application for tooth regeneration. 相似文献
99.
Cloning and molecular characterization of a cubilin-related serine proteinase from the hard tick Haemaphysalis longicornis 总被引:3,自引:0,他引:3
Miyoshi T Tsuji N Islam MK Kamio T Fujisaki K 《Insect biochemistry and molecular biology》2004,34(8):799-808
Serine proteinases are one of the largest proteolytic families of enzymes, and have diverse cellular activities in mammalian tissues. We report here the cloning and molecular characterization of a cDNA encoding the serine proteinase of the hard tick Haemaphysalis longicornis (HlSP). The HlSP cDNA is 1570 bp long and the deduced precursor protein consists of 464 amino acids with a predicted molecular mass of 50.4 kDa and a pI of 8.2. The preprotein, consisting of 443 amino acids, was predicted to include a complement C1r/C1s, Uegf, and bone morphogenic protein-1 domain, a low-density lipoprotein receptor class A domain, and a catalytic domain. HlSP sequence analysis showed high similarity to serine proteinases reported from arthropods and vertebrate animal species. Two-dimensional immunoblot analysis revealed endogenous HlSP in adult tick extracts at 50 kDa. Endogenous HlSP was also expressed in all lifecycle stages of H. longicornis. Immunohistochemical studies detected the endogenous enzyme in the midgut epithelial cells of an adult tick. The Escherichia coli-expressed recombinant HlSP was demonstrated to degrade bovine serum albumin and hydrolyze the substrate Bz-L-Arg-pNA at the rate of 30.2 micromol/min/mg protein. Further, HlSP expression was up-regulated during a blood-feeding process, indicating its involvement in the digestion of host blood components. 相似文献
100.
When growth-arrested 3Y1 cells (Fischer rat fibroblasts) were exposed to 3 X 10(-5) M colchicine, they entered S phase after a 12-h lag period which is the same as that in serum-stimulated cells. The expression of genes such as c-fos, c-myc, JE, KC, ornithine decarboxylase, and histone H3, analyzed by Northern blotting, increased in a cell-cycle dependent manner after colchicine treatment. The increased level of mRNAs was much smaller in colchicine-stimulated cells than in serum-stimulated cells, corresponding to the lower frequency of the former cells entering S phase. The course of the prereplicative phase seems to be similar in terms of the expression of cell cycle-dependent genes in cells stimulated with colchicine and in those stimulated with serum. 相似文献