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991.
Pereira L Gonçalves J Franco-Duarte R Silva J Rocha T Arnold C Richards M Macaulay V 《Molecular biology and evolution》2007,24(3):868-874
The first complete mitochondrial DNA (mtDNA) sequences (approximately 16,569 bp) in 20 patients with asthenozoospermia and a comparison with 23 new complete mtDNA sequences in teratoasthenozoospermic individuals, confirmed no sharing of specific polymorphisms or specific mitochondrial lineages between these individuals. This is strong evidence against the accepted claim of a major role played by mtDNA in male fertility, once supported by haplogroup association studies based on the screening of hypervariable region I. The hypothesis of maternally driven selection acting in male reproductive success must thus be treated with caution. 相似文献
992.
It has been proposed that proteins fold by a process called "Zipping and Assembly" (Z&A). Zipping refers to the growth of local substructures within the chain, and assembly refers to the coming together of already-formed pieces. Our interest here is in whether Z&A is a general method that can fold most of sequence space, to global minima, efficiently. Using the HP model, we can address this question by enumerating full conformation and sequence spaces. We find that Z&A reaches the global energy minimum native states, even though it searches only a very small fraction of conformational space, for most sequences in the full sequence space. We find that Z&A, a mechanism-based search, is more efficient in our tests than the replica exchange search method. Folding efficiency is increased for chains having: (a) small loop-closure steps, consistent with observations by Plaxco et al. 1998;277;985-994 that folding rates correlate with contact order, (b) neither too few nor too many nucleation sites per chain, and (c) assembly steps that do not occur too early in the folding process. We find that the efficiency increases with chain length, although our range of chain lengths is limited. We believe these insights may be useful for developing faster protein conformational search algorithms. 相似文献
993.
The aim of the present work is to relate functional differences of voltage-gated K(+) (K(v)), hyperpolarization-activated cyclic nucleotide-gated (HCN), and cyclic nucleotide gated (CNG) channels to differences in their amino acid sequences. By means of combined bioinformatic sequence analyses and homology modelling, we suggest that: (1) CNG channels are less voltage-dependent than K(v) channels since the charge of their voltage sensor, the S4 helix, is lower than that of K(v) channels and because of the presence of a conserved proline in the S4-S5 linker, which is quite likely to uncouple S4 from S5 and S6. (2) In HCN channels, S4 features a higher net positive charge with respect to K(v) channels and an extensive network of hydrophobic residues, which is quite likely to provide a tight coupling among S4 and the neighboring helices. We suggest insights on the gating of HCN channels and the reasons why they open with membrane hyperpolarization and with a significantly longer time constant with respect to other channels. 相似文献
994.
Wang SW Parhar K Chiu KJ Tran A Gangoiti P Kong J Gonzalez M Salh B Duronio V Steinbrecher UP Gómez-Muñoz A 《Cellular signalling》2007,19(8):1772-1783
995.
Walz HA Wierup N Vikman J Manganiello VC Degerman E Eliasson L Holst LS 《Cellular signalling》2007,19(7):1505-1513
cAMP signaling is important for the regulation of insulin secretion in pancreatic beta-cells. The level of intracellular cAMP is controlled through its production by adenylyl cyclases and its breakdown by cyclic nucleotide phosphodiesterases (PDEs). We have previously shown that PDE3B is involved in the regulation of nutrient-stimulated insulin secretion. Here, aiming at getting deeper functional insights, we have examined the role of PDE3B in the two phases of insulin secretion as well as its localization in the beta-cell. Depolarization-induced insulin secretion was assessed and in models where PDE3B was overexpressed [islets from transgenic RIP-PDE3B/7 mice and adenovirally (AdPDE3B) infected INS-1 (832/13) cells], the first phase of insulin secretion, occurring in response to stimulation with high K(+) for 5 min, was significantly reduced ( approximately 25% compared to controls). In contrast, in islets from PDE3B(-/-) mice the response to high K(+) was increased. Further, stimulation of isolated beta-cells from RIP-PDE3B/7 islets, using successive trains of voltage-clamped depolarizations, resulted in reduced Ca(2+)-triggered first phase exocytotic response as well as reduced granule mobilization-dependent second phase, compared to wild-type beta-cells. Using sub-cellular fractionation, confocal microscopy and transmission electron microscopy of isolated mouse islets and INS-1 (832/13) cells, we show that endogenous and overexpressed PDE3B is localized to insulin granules and plasma membrane. We conclude that PDE3B, through hydrolysis of cAMP in pools regulated by Ca(2+), plays a regulatory role in depolarization-induced insulin secretion and that the enzyme is associated with the exocytotic machinery in beta-cells. 相似文献
996.
Jeffrey R. Vincent 《Ecological Research》2007,22(1):3-7
The most important message of Levin (Ecol Res 21:328–333, 2006) is that “Ecologists and economists have much incentive for
interaction.” Recent studies that account for evolutionary processes and local interactions support this view by obtaining
results that run counter to conventional wisdom within resource economics. A second major message of the article is that to
meet environmental challenges, humanity must develop social norms that enhance cooperative responses. Successful examples
of resource management systems back up norms with economic incentives: rewards for good behavior and punishments for bad.
Economic incentives are especially important if rapid and large changes in human behavior are desired. 相似文献
997.
Gaël Ruiz Vincent Gloaguen Robert Granet Annette Roy Aziza Mouradi-Givernaud François Louvet Pierre Krausz 《Journal of applied phycology》2007,19(1):1-13
The synthesis of hydrophobic plastic films was performed by acylation of agaroids with lauroyl chloride in the N,N-dimethylacetamide
homogeneous system. All the plastic films were characterized by FT-IR spectroscopy and their degrees of substitution (DS)
was deduced from their 1H-NMR spectra. In addition, thermomechanical feature of plastic films were analyzed and compared to those obtained from other
kinds of hydrophobic plastic films. Latin square design of experiments helped us to determine optimized experimental conditions
and identify the most important factors. Hence, mild conditions of acylation (90∘C, 1 eq/OH of lauroyl chloride, 1 eq/OH of
4-dimethylaminopyridine, 5,min) led to the production of highly substituted plastic films (DS = 3.62; maximum 4) with a high
weight yield (211%) displaying mechanical properties close to polyethylene low density. 相似文献
998.
Kao HT Sturgis S DeSalle R Tsai J Davis D Gruber DF Pieribone VA 《Marine biotechnology (New York, N.Y.)》2007,9(6):733-746
To gain a better understanding of the natural function of fluorescent proteins, we have undertaken quantitative analyses of these proteins in a single species of coral, Montastraea cavernosa, residing around Turneffe atoll, on the Belizean Barrier Reef. We identified at least 10 members of a fluorescent protein family in this species, which consist of 4 distinct spectral classes. As much as a 10-fold change in the overall expression of fluorescent proteins was observed from specimen to specimen, suggesting that fluorescent proteins are dynamically regulated in response to environmental or physiological conditions. We found that the expression of some proteins was inversely correlated with depth, and that groups of proteins were coordinately expressed. There was no relationship between the expression of fluorescent proteins and the natural coloration of the Montastraea cavernosa specimens in this study. These findings have implications for current hypotheses regarding the properties and natural function of fluorescent proteins. 相似文献
999.
Chiang LY Sheppard DC Bruno VM Mitchell AP Edwards JE Filler SG 《Cellular microbiology》2007,9(1):233-245
To identify Candida albicans genes whose proteins are necessary for host cell interactions and virulence, a collection of C. albicans insertion mutants was screened for strains with reduced capacity to damage endothelial cells in vitro. This screen identified CKA2. CKA2 and its homologue CKA1 encode the catalytic subunits of the protein kinase CK2. cka2delta/cka2delta strains of C. albicans were constructed and found to have significantly reduced capacity to damage both endothelial cells and an oral epithelial cell line in vitro. Although these strains invaded endothelial cells similarly to the wild-type strain, they were defective in oral epithelial cell invasion. They were also hypersusceptible to hydrogen peroxide, but not to high salt or to cell wall damaging agents. A cka1delta/cka1delta mutant caused normal damage to both endothelial cells and oral epithelial cells, and it was not hypersusceptible to hydrogen peroxide. However, overexpression of CKA1 in a cka2delta/cka2delta strain restored wild-type phenotype. Although the cka2delta/cka2delta mutant had normal virulence in the mouse model of haematogenously disseminated candidiasis, it had significantly attenuated virulence in the mouse model of oropharyngeal candidiasis. Therefore, Cka2p governs the interactions of C. albicans with endothelial and oral epithelial cells in vitro and virulence during oropharyngeal candidiasis. 相似文献
1000.
Germline mutagenesis mediated by <Emphasis Type="Italic">Sleeping Beauty</Emphasis>transposon system in mice
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Following the descovery of its transposition activity in mammalian culture systems, the Sleeping Beauty (SB) transposon has since been applied to achieve germline mutagenesis in mice. Initially, the transposition efficiency was found to be low in cultured systems, but its activity in germ cells was unexpectedly high. This difference in transposition efficiency was found to be largely dependent on chromosomal status of the host genomic DNA and transposon vector design. The SB transposon system has been found to be suitable for comprehensive mutagenesis in mice. Therefore, it is an effective tool as a forward genetics screen for tagged insertional mutagenesis in mice. 相似文献