全文获取类型
收费全文 | 3663篇 |
免费 | 213篇 |
国内免费 | 6篇 |
专业分类
3882篇 |
出版年
2022年 | 22篇 |
2021年 | 43篇 |
2019年 | 26篇 |
2018年 | 32篇 |
2017年 | 27篇 |
2016年 | 54篇 |
2015年 | 82篇 |
2014年 | 102篇 |
2013年 | 300篇 |
2012年 | 182篇 |
2011年 | 204篇 |
2010年 | 127篇 |
2009年 | 117篇 |
2008年 | 174篇 |
2007年 | 185篇 |
2006年 | 180篇 |
2005年 | 189篇 |
2004年 | 173篇 |
2003年 | 182篇 |
2002年 | 160篇 |
2001年 | 90篇 |
2000年 | 78篇 |
1999年 | 80篇 |
1998年 | 36篇 |
1997年 | 53篇 |
1996年 | 36篇 |
1995年 | 30篇 |
1994年 | 32篇 |
1993年 | 34篇 |
1992年 | 62篇 |
1991年 | 57篇 |
1990年 | 48篇 |
1989年 | 47篇 |
1988年 | 42篇 |
1987年 | 47篇 |
1986年 | 39篇 |
1985年 | 54篇 |
1984年 | 42篇 |
1983年 | 28篇 |
1982年 | 41篇 |
1981年 | 35篇 |
1980年 | 26篇 |
1979年 | 27篇 |
1978年 | 34篇 |
1977年 | 16篇 |
1975年 | 21篇 |
1974年 | 20篇 |
1973年 | 20篇 |
1970年 | 17篇 |
1969年 | 17篇 |
排序方式: 共有3882条查询结果,搜索用时 15 毫秒
41.
Poly(ADP-ribose) polymerase cDNAs have been isolated from different classes of animals. Cloning of genes from lower eukaryotes has allowed us to investigate directly the biological functions of poly(ADP-ribosyl)ationin vivo. The conservation of specific regions among mammals, chicken,Xenopus laevis, andDrosophila melanogaster reveals the essential structural elements required for recognition of breaks in DNA and for catalytic activity. Cys, His and basic residues in the zinc-finger consensus region are conserved. The carboxyl terminal region corresponding to an NAD-binding domain is strongly conserved. The dinucleotide-binding consensus sequence and 1-A-2, Rossmann fold structure, and -sheet structures are completely conserved from mammals to insect. InDrosophila, a putative leucine-zipper motif has been identified, and other poly(ADP-ribose) polymerases also contain an -helical, amphipathic structure in the auto-modification domain. In this article, we review the recent structural analyses of the functional domains of poly(ADP-ribose) polymerase in phylogenetically divergent species, and discuss the implications of structural conservation for its biological functions.Abbreviations aa
amino acid(s)
-
D. melanogaster
Drosophila melanogaster
- PARP
poly(ADP-ribose) polymerase [EC 2.4.2.30]
- PCR
polymerase chain reaction
-
X. laevis
Xenopus laevis 相似文献
42.
43.
Nambara Eiji; Keith Kallie; McCourt Peter; Naito Satoshi 《Plant & cell physiology》1994,35(3):509-513
An Arabidopsis thaliana mutant that produces green seeds thatare highly insensitive to exogenous ABA, non-dormant and severelydesiccation intolerant was isolated from a population of fastneutron-irradiated seeds. Molecular and genetic analysis ofthis mutant shows that these phenotypes are caused by an internaldeletion of approximately one third of the ABI3 gene. Thereforeabi3 mutants with the above phenotypes are representative ofnull alleles at this locus. (Received December 3, 1993; Accepted January 22, 1994) 相似文献
44.
Koichi Suzuki Misa Iwata Shigenori Ito Kiyoshi Matsui Atsuko Uchida Yasuhiko Mizoi 《Human genetics》1994,94(2):129-135
The “a” subunit of human coagulation factor XIII (F13A) exhibits genetic polymorphism defined by four common alleles, F13A*1A, *1B, *2A, and *2B. We have previously suggested on the basis of the isoelectric focusing patterns of the four allele products that point mutations at two separate sites and one intragenic crossing over might be involved in the genes of F13A polymorphism. Here, we report nucleotide substitutions associated with F13A polymorphism. A C/T transition of the second nucelotide of codon 564 in exon 12 is responsible for the difference between F13A*1A and *1B and that between F13A*2A and *2B, and a set of two base changes in codons 650 and 651 in exon 14 leads to the differences between F13A*1A and *2A and those between F13A*1B and *2B. The four combinations of the point mutations at the two exons thus correspond to the four alleles, two of which were generated by the point mutations from ancestral monomorphic gene. The results suggest strongly that intragenic crossing over must be involved in the genesis of the fourth allele. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) methods discriminating these base changes in exons 12 and 14 are also presented. 相似文献
45.
The interaction of 2-macroglobulin (2M) with an alkaline serine proteinase (ALPase I) from alkalophilicBacillus sp. grown in an extraordinarily alkaline environment was investigated. Stoichiometry of the reaction showed that ALPase I bound to 2M in a molar ratio of about 21. The 2M-ALPase I complex showed about 80% of the proteinase activity shown by ALPase I in the hydrolysis of succinyl-l-alanyl-l-alanyl-l-prolyl-l-phenylalanyl-4-methyl-coumaryl-7-amide (Suc-Ala-Ala-Pro-Phe-MCA) and casein. The conformational changes in the 2M molecule caused by the complex formation at pH 7.5 were determined from electron micrographs and difference spectra. The antigenic activity of the 2M-ALPase I complex with the anti-ALPase I antiserum was found to be completely abolished. Immunoelectrophoresis of the complex incubated at pH 7.5 after 48 h showed no appreciable change, and the complex was recognized as exhibiting enhanced stability at pH 7.5. 相似文献
46.
47.
The effects of three forms of alginate (free acid, sodium and calcium salts) on ingestion and excretion of cholesterol in
the rat were studied. For two weeks, Male Sprague-Dawley rats were fed a cholesterol-rich diet containing 3% alginate from
the brown alga Ascophyllum nodosum. The food efficiency of the three types of alginate was: Na-alginate > Ca-alginate > alginic acid. A significant increase
in the weight of cecum was also observed in alginate diets. Alginate was not effective in preventing the elevation of serum
total cholesterol levels, although irregularly changing patterns were observed. The cholesterol level of liver showed a tendency
to decrease with alginate feeding, while fecal excretion of cholesterol increased. 相似文献
48.
Eiji Nitasaka Tsuneyuki Yamazaki M. M. Green 《Molecular & general genetics : MGG》1995,247(2):164-168
A large proportion of spontaneous mutations inDrosophila melanogaster strains of laboratory origin are associated with insertions of mobile DNA elements. As a first step toward determining whether spontaneous laboratory mutations are predictive for mutational events occurring in the wild, recessivebrown (bw) eye color mutants were isolated. By inbreeding the progeny of wild-caughtDrosophila melanogaster females,bw mutations were isolated from seven separate geographic sites distributed among Japan, California, Siberia and Hungary. Among a total of 14 mutations studied, no case of transposon mutagenesis was found. At least 4 mutations are associated with small deletions in thebw gene. The remainder are inseparable from wild-typebw by Southern analysis and are presumed to be basepair changes or very small indels. Although only two spontaneousbw mutants of laboratory origin have been analyzed molecularly, one is a mobile element insertion. 相似文献
49.
The authors established apoptosis resistant COS–1, myeloma, hybridoma, and Friend leukemia cell lines by genetically engineering cells, aiming at more efficient protein production by cell culture. COS–1 cells, which are most widely used for eukariotic gene expression, were transfected with human bcl–2 gene. Both bcl–2 and mock transfected COS–1 cells were cultured at low (0.2%) serum concentration for 9 days. The final viable cell number of the bcl–2 transfected cells was ninefold of that of the mock transfectants. Both bcl–2 and mock transfectants were further transfected with the vector pcDNA- containing SV40 ori and immunoglobulin gene for transiently expressing protein. The bcl–2 expressing COS–1 cells produced more protein than the mock transfected COS–1 cells after 4 days posttransfection.Mouse myeloma p3-X63-Ag.8.653 cells, which are widely used as the partner for preparing hybridoma, and hybridoma 2E3 cells were transfected with human bcl–2 gene. Both bcl–2 transfected myeloma and hybridoma survived longer than the corresponding original cells in batch culture. The bcl–2 transfected 2E3 cells survived 2 to 4 four days longer in culture, producing 1.5- to 4-fold amount of antibody in comparison with the mock transfectants.Coexpression of bag–1 with bcl–2 improved survival of hybridoma 2E3 cells more than bcl–2 expression alone. The bag–1 and bcl–2 coexpressing cells produced more IgG than the the cells expressing bcl–2 alone.Apoptosis of Friend murine erythroleukemia(F-MEL) cells was suppressed with antisense c-jun expression. The antisense c-jun expressing cells survived 16 days at non-growth state. 相似文献
50.
An algal suspension containing protoplasmic detritus [termed, single cell detritus (SCD)] was prepared from freeze-dried fronds
of Ulva and its dietary value to Artemia nauplii was tested after size fractionation. The dissolved fraction (<0.22 μm) ofthe
Ulva suspension contained ca. 48% of theoriginal protein in the Ulva, but had no dietaryvalue to Artemia, which is a suspension
feeder. In contrast, the fraction passing through a 100-μm meshand containing SCD of 2–14 μm in diameter, contributedto the
survival of Artemia. The fraction remaining on the 100 μm mesh was further incubated with and without the bacterium Pseudoalteromonas
espejiana strain AR06 FERM BP-5024. The bacterium degraded
Ulva forming new SCD over 106 mL -1 level as rapidly as by 16 h of incubation. The dietary
value of Ulva for Artemia growth was elevated over four times by the incubation. The protein content of the SCD
was approximately doubled by the attaching of bacteria, suggesting the enhanced Artemia growth is attributable to
the combined effect of the SCD and the bacteria. Development of a hatchery diet from Ulva , a resource with a low
commercial value, is suggested utilizing the degrading and attaching ability of P. espejiana.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献