全文获取类型
收费全文 | 7644篇 |
免费 | 638篇 |
国内免费 | 11篇 |
出版年
2023年 | 69篇 |
2022年 | 60篇 |
2021年 | 178篇 |
2020年 | 128篇 |
2019年 | 189篇 |
2018年 | 226篇 |
2017年 | 217篇 |
2016年 | 279篇 |
2015年 | 397篇 |
2014年 | 401篇 |
2013年 | 521篇 |
2012年 | 605篇 |
2011年 | 584篇 |
2010年 | 370篇 |
2009年 | 305篇 |
2008年 | 395篇 |
2007年 | 396篇 |
2006年 | 342篇 |
2005年 | 326篇 |
2004年 | 257篇 |
2003年 | 230篇 |
2002年 | 266篇 |
2001年 | 172篇 |
2000年 | 216篇 |
1999年 | 161篇 |
1998年 | 58篇 |
1997年 | 40篇 |
1996年 | 38篇 |
1995年 | 58篇 |
1994年 | 46篇 |
1993年 | 36篇 |
1992年 | 81篇 |
1991年 | 66篇 |
1990年 | 62篇 |
1989年 | 71篇 |
1988年 | 48篇 |
1987年 | 42篇 |
1986年 | 46篇 |
1985年 | 50篇 |
1984年 | 35篇 |
1983年 | 30篇 |
1982年 | 16篇 |
1981年 | 24篇 |
1979年 | 24篇 |
1978年 | 22篇 |
1977年 | 16篇 |
1976年 | 17篇 |
1974年 | 11篇 |
1973年 | 12篇 |
1972年 | 13篇 |
排序方式: 共有8293条查询结果,搜索用时 15 毫秒
1.
Xiaojing Dang Thu Giang Tran Thi Guanshan Dong Hui Wang Wisdom Mawuli Edzesi Delin Hong 《Planta》2014,239(6):1309-1319
Key message
Twenty-seven QTLs were identified for rice seed vigor, in which 16 were novel QTLs. Fifteen elite parental combinations were designed for improving seed vigor in rice.Abstract
Seed vigor is closely related to direct seeding in rice (Oryza sativa L.). Previous quantitative trait locus (QTL) studies for seed vigor were mainly derived from bi-parental segregating populations and no report from natural populations. In this study, association mapping for seed vigor was performed on a selected sample of 540 rice cultivars (419 from China and 121 from Vietnam). Population structure was estimated on the basis of 262 simple sequence repeat (SSR) markers. Seed vigor was evaluated by root length (RL), shoot length (SL) and shoot dry weight in 2011 and 2012. Abundant phenotypic and genetic diversities were found in the studied population. The population was divided into seven subpopulations, and the levels of linkage disequilibrium (LD) ranged from 10 to 80 cM. We identified 27 marker–trait associations involving 18 SSR markers for three traits. According to phenotypic effects for alleles of the detected QTLs, elite alleles were mined. These elite alleles could be used to design parental combinations and the expected results would be obtained by pyramiding or substituting the elite alleles per QTL (apart from possible epistatic effects). Our results demonstrate that association mapping can complement and enhance previous QTL information for marker-assisted selection and breeding by design. 相似文献2.
3.
Roubina Tatavosian Chao Yu Zhen Huy Nguyen Duc Maggie M. Balas Aaron M. Johnson Xiaojun Ren 《The Journal of biological chemistry》2015,290(47):28038-28054
Epigenetic complexes play an essential role in regulating chromatin structure, but information about their assembly stoichiometry on chromatin within cells is poorly understood. The cellular assembly stoichiometry is critical for appreciating the initiation, propagation, and maintenance of epigenetic inheritance during normal development and in cancer. By combining genetic engineering, chromatin biochemistry, and single-molecule fluorescence imaging, we developed a novel and sensitive approach termed single-molecule chromatin immunoprecipitation imaging (Sm-ChIPi) to enable investigation of the cellular assembly stoichiometry of epigenetic complexes on chromatin. Sm-ChIPi was validated by using chromatin complexes with known stoichiometry. The stoichiometry of subunits within a polycomb complex and the assembly stoichiometry of polycomb complexes on chromatin have been extensively studied but reached divergent views. Moreover, the cellular assembly stoichiometry of polycomb complexes on chromatin remains unexplored. Using Sm-ChIPi, we demonstrated that within mouse embryonic stem cells, one polycomb repressive complex (PRC) 1 associates with multiple nucleosomes, whereas two PRC2s can bind to a single nucleosome. Furthermore, we obtained direct physical evidence that the nucleoplasmic PRC1 is monomeric, whereas PRC2 can dimerize in the nucleoplasm. We showed that ES cell differentiation induces selective alteration of the assembly stoichiometry of Cbx2 on chromatin but not other PRC1 components. We additionally showed that the PRC2-mediated trimethylation of H3K27 is not required for the assembly stoichiometry of PRC1 on chromatin. Thus, these findings uncover that PRC1 and PRC2 employ distinct mechanisms to assemble on chromatin, and the novel Sm-ChIPi technique could provide single-molecule insight into other epigenetic complexes. 相似文献
4.
Yasmin Husaini Glen P. Lockwood Trung V. Nguyen Vicky Wang-Wei Tsai Mohammad G. Mohammad Pamela J. Russell David A. Brown Samuel N. Breit 《PloS one》2015,10(2)
The divergent TGF-β superfamily member, macrophage inhibitory cytokine-1 (MIC-1/GDF15), is overexpressed by most cancers, including prostate cancer (PCa). Whilst its circulating levels are linked to cancer outcome, the role MIC-1/GDF15 plays in cancer development and progression is incompletely understood. To investigate its effect on PCa development and spread, we have used TRAMP prostate cancer prone mice bearing a germline deletion of MIC-1/GDF15 (TRAMPMIC-/-). On average TRAMPMIC-/- mice died about 5 weeks earlier and had larger prostatic tumors compared with TRAMP mice that were wild type for MIC-1/GDF15 (TRAMPMIC+/+). Additionally, at the time of death or ethical end point, even when adjusted for lifespan, there were no significant differences in the number of mice with metastases between the TRAMPMIC+/+ and TRAMPMIC-/- groups. However, consistent with our previous data, more than twice as many TRAMP mice overexpressing MIC-1/GDF15 (TRAMPfmsmic-1) had metastases than TRAMPMIC+/+ mice (p<0.0001). We conclude that germ line gene deletion of MIC-1/GDF15 leads to increased local tumor growth resulting in decreased survival consistent with an overall protective role for MIC-1/GDF15 in early primary tumor development. However, in advancing disease, as we have previously noted, MIC-1/GDF15 overexpression may promote local invasion and metastatic spread. 相似文献
5.
Christopher A. Emerling Hieu T. Huynh Minh A. Nguyen Robert W. Meredith Mark S. Springer 《Proceedings. Biological sciences / The Royal Society》2015,282(1819)
Retinal opsin photopigments initiate mammalian vision when stimulated by light. Most mammals possess a short wavelength-sensitive opsin 1 (SWS1) pigment that is primarily sensitive to either ultraviolet or violet light, leading to variation in colour perception across species. Despite knowledge of both ultraviolet- and violet-sensitive SWS1 classes in mammals for 25 years, the adaptive significance of this variation has not been subjected to hypothesis testing, resulting in minimal understanding of the basis for mammalian SWS1 spectral tuning evolution. Here, we gathered data on SWS1 for 403 mammal species, including novel SWS1 sequences for 97 species. Ancestral sequence reconstructions suggest that the most recent common ancestor of Theria possessed an ultraviolet SWS1 pigment, and that violet-sensitive pigments evolved at least 12 times in mammalian history. We also observed that ultraviolet pigments, previously considered to be a rarity, are common in mammals. We then used phylogenetic comparative methods to test the hypotheses that the evolution of violet-sensitive SWS1 is associated with increased light exposure, extended longevity and longer eye length. We discovered that diurnal mammals and species with longer eyes are more likely to have violet-sensitive pigments and less likely to possess UV-sensitive pigments. We hypothesize that (i) as mammals evolved larger body sizes, they evolved longer eyes, which limited transmittance of ultraviolet light to the retina due to an increase in Rayleigh scattering, and (ii) as mammals began to invade diurnal temporal niches, they evolved lenses with low UV transmittance to reduce chromatic aberration and/or photo-oxidative damage. 相似文献
6.
Truong Quoc Phong Do Thi Thu Ha Uwe Volker Elke Hammer 《Indian journal of microbiology》2015,55(2):219-230
Reports in recent years indicate that the increasing emergence of resistance to drugs be using to TB treatment. The resistance to them severely affects to options for effective treatment. The emergence of multidrug-resistant tuberculosis has increased interest in understanding the mechanism of drug resistance in M. tuberculosis and the development of new therapeutics, diagnostics and vaccines. In this study, a label-free quantitative proteomics approach has been used to analyze proteome of multidrug-resistant and susceptible clinical isolates of M. tuberculosis and identify differences in protein abundance between the two groups. With this approach, we were able to identify a total of 1,583 proteins. The majority of identified proteins have predicted roles in lipid metabolism, intermediary metabolism, cell wall and cell processes. Comparative analysis revealed that 68 proteins identified by at least two peptides showed significant differences of at least twofolds in relative abundance between two groups. In all protein differences, the increase of some considering proteins such as NADH dehydrogenase, probable aldehyde dehydrogenase, cyclopropane mycolic acid synthase 3, probable arabinosyltransferase A, putative lipoprotein, uncharacterized oxidoreductase and six membrane proteins in resistant isolates might be involved in the drug resistance and to be potential diagnostic protein targets. The decrease in abundance of proteins related to secretion system and immunogenicity (ESAT-6-like proteins, ESX-1 secretion system associated proteins, O-antigen export system and MPT63) in the multidrug-resistant strains can be a defensive mechanism undertaken by the resistant cell.
Electronic supplementary material
The online version of this article (doi:10.1007/s12088-015-0511-2) contains supplementary material, which is available to authorized users. 相似文献7.
8.
To clarify the ploidy and distribution of Lilium leichtlinii var. maximowiczii populations in Korea, we inspected several mountains and northern valleys and almost all of the sea coast of South Korea. We found nine diploid populations and 19 triploid populations. Many large and small populations were distributed around northern Chungcheongbook‐do and Gyunggi‐do and all over Kangwon‐do. The diploid plants were smaller than the triploid plants in almost all of their morphological characteristics. This is the second report of natural polyploid complexes of diploids and triploids in the genus Lilium. 相似文献
9.
Selected morphometrics of Heterorhabditis bacteriophora and seven species of Steinernema from in vivo culture were compared in relation to time of harvest. In addition, five Steinernema species were reared in vitro and their morphometrics were compared with those from in vivo culture. With in vivo culture, there was generally a negative linear relationship between body length of infective juveniles (IJ) and time of harvest. The distance from the anterior end to the excretory pore (EP) and the tail length (T) of IJ also varied with time of harvest. The E percentage (= EP/T x 100) was the least variable. Body lengths of IJ reared in vitro were much less than those of IJ reared in vivo. The study suggests that IJ harvested from in vivo culture within 1 week of emergence from cadavers are best for species identification. Infective juveniles from in vitro culture should not be used for species identification. 相似文献
10.
Interaction between corticosteroid binding globulin and activated leukocytes in vitro 总被引:1,自引:0,他引:1
G L Hammond C L Smith C M Underhill V T Nguyen 《Biochemical and biophysical research communications》1990,172(1):172-177
The interaction between human corticosteroid binding globulin and activated leukocytes is restricted to the granulocyte population, and is characterized by specific proteolytic cleavage of corticosteroid binding globulin which markedly reduces its steroid binding activity. A direct interaction between corticosteroid binding globulin and the activated cells appears to enhance this event, and does not involve cellular internalization of corticosteroid binding globulin or its proteolytic degradation products, which resemble those obtained after incubation of corticosteroid binding globulin with neutrophil elastase. These data suggest that corticosteroid binding globulin interacts with elastase on the surface of activated neutrophils, and may promote glucocorticoid delivery to these cells during inflammation. 相似文献