全文获取类型
收费全文 | 10138篇 |
免费 | 668篇 |
国内免费 | 2篇 |
出版年
2023年 | 57篇 |
2022年 | 132篇 |
2021年 | 268篇 |
2020年 | 141篇 |
2019年 | 201篇 |
2018年 | 232篇 |
2017年 | 223篇 |
2016年 | 355篇 |
2015年 | 522篇 |
2014年 | 585篇 |
2013年 | 732篇 |
2012年 | 790篇 |
2011年 | 767篇 |
2010年 | 544篇 |
2009年 | 413篇 |
2008年 | 572篇 |
2007年 | 534篇 |
2006年 | 558篇 |
2005年 | 475篇 |
2004年 | 489篇 |
2003年 | 421篇 |
2002年 | 402篇 |
2001年 | 135篇 |
2000年 | 86篇 |
1999年 | 107篇 |
1998年 | 93篇 |
1997年 | 94篇 |
1996年 | 67篇 |
1995年 | 41篇 |
1994年 | 52篇 |
1993年 | 46篇 |
1992年 | 49篇 |
1991年 | 44篇 |
1990年 | 38篇 |
1989年 | 38篇 |
1988年 | 34篇 |
1987年 | 31篇 |
1986年 | 29篇 |
1985年 | 35篇 |
1984年 | 35篇 |
1983年 | 32篇 |
1982年 | 38篇 |
1981年 | 32篇 |
1980年 | 31篇 |
1979年 | 21篇 |
1977年 | 16篇 |
1976年 | 15篇 |
1975年 | 15篇 |
1974年 | 13篇 |
1973年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
611.
The Su(Hw) chromatin insulator protein alters double-strand break repair frequencies in the Drosophila germ line 总被引:3,自引:0,他引:3
P element-induced double-strand breaks (DSBs) on the X chromosome of Drosophila melanogaster were repaired up to four times more frequently when functional Su(Hw) chromatin insulator protein was removed from all genomic
binding sites. Simultaneous comparisons of interallelic gap repair frequencies at two target loci on the X chromosome confirmed that a Su(Hw) binding site nested within a template had no effect on DSB repair efficiency. The results
suggest that the genome-wide homology search of broken ends for homologous template sequences is affected because it is the
only step in the recombinational repair process with an apparent genome-wide interaction. We propose that the searching 3′-hydroxy
ends gain a higher degree of freedom for the search in a su(Hw) mutant background.
Received: 22 September 1999; in revised form: 17 December 1999 / Accepted: 28 December 1999 相似文献
612.
Intracellular Signal Triggered by Cholera Toxin in Saccharomyces boulardii and Saccharomyces cerevisiae
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Rogelio L. Brando Ieso M. Castro Eduardo A. Bambirra Sheila C. Amaral Luciano G. Fietto Maria Jos M. Tropia Maria Jos Neves Raquel G. Dos Santos Newton C. M. Gomes Jacques R. Nicoli 《Applied microbiology》1998,64(2):564-568
As is the case for Saccharomyces boulardii, Saccharomyces cerevisiae W303 protects Fisher rats against cholera toxin (CT). The addition of glucose or dinitrophenol to cells of S. boulardii grown on a nonfermentable carbon source activated trehalase in a manner similar to that observed for S. cerevisiae. The addition of CT to the same cells also resulted in trehalase activation. Experiments performed separately on the A and B subunits of CT showed that both are necessary for activation. Similarly, the addition of CT but not of its separate subunits led to a cyclic AMP (cAMP) signal in both S. boulardii and S. cerevisiae. These data suggest that trehalase stimulation by CT probably occurred through the cAMP-mediated protein phosphorylation cascade. The requirement of CT subunit B for both the cAMP signal and trehalase activation indicates the presence of a specific receptor on the yeasts able to bind to the toxin, a situation similar to that observed for mammalian cells. This hypothesis was reinforced by experiments with 125I-labeled CT showing specific binding of the toxin to yeast cells. The adhesion of CT to a receptor on the yeast surface through the B subunit and internalization of the A subunit (necessary for the cAMP signal and trehalase activation) could be one more mechanism explaining protection against the toxin observed for rats treated with yeasts. 相似文献
613.
Metabolism of Plant Polysaccharides by Leucoagaricus gongylophorus, the Symbiotic Fungus of the Leaf-Cutting Ant Atta sexdens L.
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Clia Gomes De Siqueira Maurício Bacci Jr. Fernando Carlos Pagnocca Odair Correa Bueno Maria Jos Aparecida Hebling 《Applied microbiology》1998,64(12):4820-4822
Atta sexdens L. ants feed on the fungus they cultivate on cut leaves inside their nests. The fungus, Leucoagaricus gongylophorus, metabolizes plant polysaccharides, such as xylan, starch, pectin, and cellulose, mediating assimilation of these compounds by the ants. This metabolic integration may be an important part of the ant-fungus symbiosis, and it involves primarily xylan and starch, both of which support rapid fungal growth. Cellulose seems to be less important for symbiont nutrition, since it is poorly degraded and assimilated by the fungus. Pectin is rapidly degraded but slowly assimilated by L. gongylophorus, and its degradation may occur so that the fungus can more easily access other polysaccharides in the leaves. 相似文献
614.
Lilia Gonzalez-Ceron Mario H Rodriguez Robert A Wirtz Barbara J Sina Olga L Palomeque Jose A Nettel Victor Tsutsumi 《Experimental parasitology》1998,90(3):203-211
Gonzalez-Ceron, L., Rodriguez, M. H., Wirtz, R. A., Sina, B. J., Palomeque, O. L., Nettel, J. A., and Tsutsumi, V. 1998.Plasmodium vivax:A monoclonal antibody recognizes a circumsporozoite protein precursor on the sporozoite surface.Experimental Parasitology90, 203–211. The major surface circumsporozoite (CS) proteins are known to play a role in malaria sporozoite development and invasion of invertebrate and vertebrate host cells.Plasmodium vivaxCS protein processing during mosquito midgut oocyst and salivary gland sporozoite development was studied using monoclonal antibodies which recognize different CS protein epitopes. Monoclonal antibodies which react with the CS amino acid repeat sequences by ELISA recognized a 50-kDa precursor protein in immature oocyst and additional 47- and 42-kDa proteins in older oocysts. A 42-kDa CS protein was detected after initial sporozoite invasion of mosquito salivary glands and an additional 50-kDa precursor CS protein observed later in infected salivary glands. These data confirm previous results with otherPlasmodiumspecies, in which more CS protein precursors were detected in oocysts than in salivary gland sporozoites. A monoclonal antibody (PvPCS) was characterized which reacts with an epitope found only in the 50-kDa precursor CS protein. PvPCS reacted with allP. vivaxsporozoite strains tested by indirect immunofluorescent assay, homogeneously staining the sporozoite periphery with much lower intensity than that produced by anti-CS repeat antibodies. Immunoelectron microscopy using PvPCS showed that the CS protein precursor was associated with peripheral cytoplasmic vacuoles and membranes of sporoblast and budding sporozoites in development oocysts. In salivary gland sporozoites, the CS protein precursor was primarily associated with micronemes and sporozoite membranes. Our results suggest that the 50-kDa CS protein precursor is synthesized intracellularly and secreted on the membrane surface, where it is proteolytically processed to form the 42-kDa mature CS protein. These data indicate that differences in CS protein processing in oocyst and salivary gland sporozoites development may occur. 相似文献
615.
A biological ricefield in northern Italy, without periodic dry spells in its growing cycle and therefore more familiar to naturally humid zones, was studied for its heleoplankton community. The biocoenosis reached a greater level of complexity than reported in literature. In particular, the seasonal succession of Cladocerans, the dominant group throughout the study period, was analyzed. Wlassicsia pannonica (Daday, 1904; Anomopoda Macrothricidae), is new to Italy; its morphology is compared to that of other populations of the same species and its biological cycle is compared with that of other dominant Cladocerans. 相似文献
616.
617.
Increased Respiration Through Cytochrome d Enhances Microaerobic N2Fixation in Klebsiella Pneumoniae
Nitrogenase activity was increased in a Klebsiella pneumoniae strain (FN27) producing higher amounts of cytochrome d than the wild-type strain. The increased production of cytochrome d in FN27 showed a positive effect on nitrogenase activity in cells cultured with glucose as carbon source at 1 kPa oxygen but a negative effect at higher O2concentrations. In cells cultured with pyruvate as carbon source, FN27 expressed higher activity of nitrogenase at all oxygen tensions tested when compared to the wild-type strain. This analysis shows that the over production of cytochrome d terminal oxidase improves nitrogen fixation in certain culture conditions. 相似文献
618.
Cláudio M. Gomes Alice Faria João C. Carita Joaquim Mendes Manuela Regalla Paula Chicau Harald Huber Karl O. Stetter M. Teixeira 《Journal of biological inorganic chemistry》1998,3(5):499-507
Seven-iron ferredoxins from the thermoacidophilic archaea Acidianus ambivalens, A. infernus, Metalosphaera prunae and Sulfolobus metallicus were extensively characterised, allowing study of their expression under aerobic and anaerobic growth conditions as well
as the putative role in thermal stability of a recently described zinc centre. The archaeon S. metallicus was found to express, under the same growth conditions, two ferredoxins in almost identical amounts, a novelty among Archaea. Most interestingly, these two ferredoxins differ at the N-terminal amino acid sequence in that one has a zinc binding motif
(FdA) and the other does not (FdB); in agreement with these findings, FdA contains a zinc ion and FdB does not. These two
ferredoxins have identical thermal stabilities, indicating that the zinc atom is not determinant in the protein thermostability.
Further, the presence of the additional zinc centre does not interfere with the redox properties of the iron-sulfur clusters
since their reduction potentials are almost identical. From the other three archaea, independently of the growth mode in respect
to oxygen, only a single zinc-containing ferredoxin was found. EPR studies on the purified proteins, both in the oxidised
and dithionite reduced states, allowed the identification of one [3Fe-4S]1+/0 centre and one [4Fe-4S]2+/1+ centre in all proteins studied. The complete sequence of A. ambivalens ferredoxin is reported. Together with the data gathered in this study, the properties of the seven-iron ferredoxins from
Sulfolobales so far known are re-discussed.
Received: 10 June 1998 / Accepted: 25 June 1998 相似文献
619.
Selection of Gβ Subunits with Point Mutations That Fail to
Activate Specific Signaling Pathways In Vivo: Dissecting Cellular
Responses Mediated by a Heterotrimeric G Protein in Dictyostelium
discoideum
下载免费PDF全文
![点击此处可从《Molecular biology of the cell》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Tian Jin Mario Amzel Peter N. Devreotes Lijun Wu 《Molecular biology of the cell》1998,9(10):2949-2961
In Dictyostelium discoideum, a unique Gβ subunit is required for a G protein–coupled receptor system that mediates a variety of cellular responses. Binding of cAMP to cAR1, the receptor linked to the G protein G2, triggers a cascade of responses, including activation of adenylyl cyclase, gene induction, actin polymerization, and chemotaxis. Null mutations of the cAR1, Gα2, and Gβ genes completely impair all these responses. To dissect specificity in Gβγ signaling to downstream effectors in living cells, we screened a randomly mutagenized library of Gβ genes and isolated Gβ alleles that lacked the capacity to activate some effectors but retained the ability to regulate others. These mutant Gβ subunits were able to link cAR1 to G2, to support gene expression, and to mediate cAMP-induced actin polymerization, and some were able to mediate to chemotaxis toward cAMP. None was able to activate adenylyl cyclase, and some did not support chemotaxis. Thus, we separated in vivo functions of Gβγ by making point mutations on Gβ. Using the structure of the heterotrimeric G protein displayed in the computer program CHAIN, we examined the positions and the molecular interactions of the amino acids substituted in each of the mutant Gβs and analyzed the possible effects of each replacement. We identified several residues that are crucial for activation of the adenylyl cyclase. These residues formed an area that overlaps but is not identical to regions where bovine Gtβγ interacts with its regulators, Gα and phosducin. 相似文献
620.