全文获取类型
收费全文 | 2971篇 |
免费 | 419篇 |
国内免费 | 2篇 |
专业分类
3392篇 |
出版年
2023年 | 37篇 |
2022年 | 100篇 |
2021年 | 168篇 |
2020年 | 68篇 |
2019年 | 88篇 |
2018年 | 91篇 |
2017年 | 73篇 |
2016年 | 119篇 |
2015年 | 195篇 |
2014年 | 175篇 |
2013年 | 193篇 |
2012年 | 249篇 |
2011年 | 216篇 |
2010年 | 129篇 |
2009年 | 112篇 |
2008年 | 154篇 |
2007年 | 117篇 |
2006年 | 131篇 |
2005年 | 103篇 |
2004年 | 99篇 |
2003年 | 75篇 |
2002年 | 79篇 |
2001年 | 40篇 |
2000年 | 40篇 |
1999年 | 20篇 |
1998年 | 20篇 |
1997年 | 19篇 |
1996年 | 21篇 |
1995年 | 13篇 |
1994年 | 24篇 |
1993年 | 23篇 |
1992年 | 26篇 |
1991年 | 22篇 |
1990年 | 32篇 |
1989年 | 24篇 |
1988年 | 18篇 |
1987年 | 13篇 |
1986年 | 18篇 |
1985年 | 15篇 |
1984年 | 17篇 |
1980年 | 12篇 |
1979年 | 13篇 |
1978年 | 10篇 |
1977年 | 11篇 |
1976年 | 9篇 |
1974年 | 11篇 |
1972年 | 9篇 |
1971年 | 12篇 |
1969年 | 9篇 |
1968年 | 9篇 |
排序方式: 共有3392条查询结果,搜索用时 11 毫秒
51.
Chromosomal instability and delayed apoptosis in long-term T-lymphocyte cultures irradiated with carbon ions and x rays 总被引:1,自引:0,他引:1
In this study, we examined genomic instability induced by 250 kV X rays and 100 MeV/nucleon carbon ions in long-term lymphocyte cultures from two healthy donors. Two biological end points, delayed apoptosis and chromosomal instability, were studied in descendants of cells irradiated with three different doses of the particular radiation up to 22 population doublings. The delayed apoptosis showed no clear dependence on radiation dose, culture time or radiation quality. A persistent significant increase in the rate of apoptosis up to 36 days after X irradiation was observed for a dose of 4 Gy in donor 1 only. For both donors and radiations, de novo aberration yields were significantly increased in comparison to control values up to day 36. For both radiations, chromosome-type aberrations were seen more frequently than chromatid-type aberrations in both donors up to 22 days postirradiation. In both donors, carbon ions were more effective than X rays with respect to the induction of chromosome instability. A dose of 0.25 Gy of carbon ions corresponding to 1.4 ion traversals per cell nucleus was effective in the induction of instability in our cell system. 相似文献
52.
Pot I Measday V Snydsman B Cagney G Fields S Davis TN Muller EG Hieter P 《Molecular biology of the cell》2003,14(2):460-476
Kinetochore proteins contribute to the fidelity of chromosome transmission by mediating the attachment of a specialized chromosomal region, the centromere, to the mitotic spindle during mitosis. In budding yeast, a subset of kinetochore proteins, referred to as the outer kinetochore, provides a link between centromere DNA-binding proteins of the inner kinetochore and microtubule-binding proteins. Using a combination of chromatin immunoprecipitation, in vivo localization, and protein coimmunoprecipitation, we have established that yeast Chl4p and Iml3p are outer kinetochore proteins that localize to the kinetochore in a Ctf19p-dependent manner. Chl4p interacts with the outer kinetochore proteins Ctf19p and Ctf3p, and Iml3p interacts with Chl4p and Ctf19p. In addition, Chl4p is required for the Ctf19p-Ctf3p and Ctf19p-Iml3p interactions, indicating that Chl4p is an important structural component of the outer kinetochore. These physical interaction dependencies provide insights into the molecular architecture and centromere DNA loading requirements of the outer kinetochore complex. 相似文献
53.
Gildas Bourdais Deirdre H. McLachlan Lydia M. Rickett Ji Zhou Agnieszka Siwoszek Heidrun Hweker Matthew Hartley Hannah Kuhn Richard J. Morris Dan MacLean Silke Robatzek 《Traffic (Copenhagen, Denmark)》2019,20(2):168-180
Expansion of gene families facilitates robustness and evolvability of biological processes but impedes functional genetic dissection of signalling pathways. To address this, quantitative analysis of single cell responses can help characterize the redundancy within gene families. We developed high‐throughput quantitative imaging of stomatal closure, a response of plant guard cells, and performed a reverse genetic screen in a group of Arabidopsis mutants to five stimuli. Focussing on the intersection between guard cell signalling and the endomembrane system, we identified eight clusters based on the mutant stomatal responses. Mutants generally affected in stomatal closure were mostly in genes encoding SNARE and SCAMP membrane regulators. By contrast, mutants in RAB5 GTPase genes played specific roles in stomatal closure to microbial but not drought stress. Together with timed quantitative imaging of endosomes revealing sequential patterns in FLS2 trafficking, our imaging pipeline can resolve non‐redundant functions of the RAB5 GTPase gene family. Finally, we provide a valuable image‐based tool to dissect guard cell responses and outline a genetic framework of stomatal closure. 相似文献
54.
Telomere length reveals cumulative individual and transgenerational inbreeding effects in a passerine bird 下载免费PDF全文
Kat Bebbington Lewis G. Spurgin Eleanor A. Fairfield Hannah L. Dugdale Jan Komdeur Terry Burke David S. Richardson 《Molecular ecology》2016,25(12):2949-2960
Inbreeding results in more homozygous offspring that should suffer reduced fitness, but it can be difficult to quantify these costs for several reasons. First, inbreeding depression may vary with ecological or physiological stress and only be detectable over long time periods. Second, parental homozygosity may indirectly affect offspring fitness, thus confounding analyses that consider offspring homozygosity alone. Finally, measurement of inbreeding coefficients, survival and reproductive success may often be too crude to detect inbreeding costs in wild populations. Telomere length provides a more precise measure of somatic costs, predicts survival in many species and should reflect differences in somatic condition that result from varying ability to cope with environmental stressors. We studied relative telomere length in a wild population of Seychelles warblers (Acrocephalus sechellensis) to assess the lifelong relationship between individual homozygosity, which reflects genome‐wide inbreeding in this species, and telomere length. In juveniles, individual homozygosity was negatively associated with telomere length in poor seasons. In adults, individual homozygosity was consistently negatively related to telomere length, suggesting the accumulation of inbreeding depression during life. Maternal homozygosity also negatively predicted offspring telomere length. Our results show that somatic inbreeding costs are environmentally dependent at certain life stages but may accumulate throughout life. 相似文献
55.
Michiya Sugimori Yumiko Hayakawa Bruce M. Boman Jeremy Z. Fields Miharu Awaji Hiroko Kozano Ryoi Tamura Seiji Yamamoto Toru Ogata Mitsuhiko Yamada Shunro Endo Masanori Kurimoto Satoshi Kuroda 《PloS one》2015,10(8)
Background
Accumulating evidence indicates that cancer stem cells (CSCs) drive tumorigenesis. This suggests that CSCs should make ideal therapeutic targets. However, because CSC populations in tumors appear heterogeneous, it remains unclear how CSCs might be effectively targeted. To investigate the mechanisms by which CSC populations maintain heterogeneity during self-renewal, we established a glioma sphere (GS) forming model, to generate a population in which glioma stem cells (GSCs) become enriched. We hypothesized, based on the clonal evolution concept, that with each passage in culture, heterogeneous clonal sublines of GSs are generated that progressively show increased proliferative ability.Methodology/Principal Findings
To test this hypothesis, we determined whether, with each passage, glioma neurosphere culture generated from four different glioma cell lines become progressively proliferative (i.e., enriched in large spheres). Rather than monitoring self-renewal, we measured heterogeneity based on neurosphere clone sizes (#cells/clone). Log-log plots of distributions of clone sizes yielded a good fit (r>0.90) to a straight line (log(% total clones) = k*log(#cells/clone)) indicating that the system follows a power-law (y = xk) with a specific degree exponent (k = −1.42). Repeated passaging of the total GS population showed that the same power-law was maintained over six passages (CV = −1.01 to −1.17). Surprisingly, passage of either isolated small or large subclones generated fully heterogeneous populations that retained the original power-law-dependent heterogeneity. The anti-GSC agent Temozolomide, which is well known as a standard therapy for glioblastoma multiforme (GBM), suppressed the self-renewal of clones, but it never disrupted the power-law behavior of a GS population.Conclusions/Significance
Although the data above did not support the stated hypothesis, they did strongly suggest a novel mechanism that underlies CSC heterogeneity. They indicate that power-law growth governs the self-renewal of heterogeneous glioma stem cell populations. That the data always fit a power-law suggests that: (i) clone sizes follow continuous, non-random, and scale-free hierarchy; (ii) precise biologic rules that reflect self-organizing emergent behaviors govern the generation of neurospheres. That the power-law behavior and the original GS heterogeneity are maintained over multiple passages indicates that these rules are invariant. These self-organizing mechanisms very likely underlie tumor heterogeneity during tumor growth. Discovery of this power-law behavior provides a mechanism that could be targeted in the development of new, more effective, anti-cancer agents. 相似文献56.
Munc13-4 is essential for cytolytic granules fusion and is mutated in a form of familial hemophagocytic lymphohistiocytosis (FHL3) 总被引:28,自引:0,他引:28
Feldmann J Callebaut I Raposo G Certain S Bacq D Dumont C Lambert N Ouachée-Chardin M Chedeville G Tamary H Minard-Colin V Vilmer E Blanche S Le Deist F Fischer A de Saint Basile G 《Cell》2003,115(4):461-473
Secretion of cytolytic granules content at the immunological synapse is a highly regulated process essential for lymphocyte cytotoxicity. This process requires the rapid transfer of perforin containing lytic granules to the target cell interface, followed by their docking and fusion with the plasma membrane. Defective cytotoxicity characterizes a genetically heterogeneous condition named familial hemophagocytic lymphohistiocytosis (FHL), which can be associated with perforin deficiency. The locus of a perforin (+) FHL subtype (FHL3), observed in 10 patients, was mapped to 17q25. This region contains hMunc13-4, a member of the Munc13 family of proteins involved in vesicle priming function. HMunc13-4 mutations were shown to cause FHL3. HMunc13-4 deficiency results in defective cytolytic granule exocytosis, despite polarization of the secretory granules and docking with the plasma membrane. Expressed tagged hMunc13-4 localizes with cytotoxic granules at the immunological synapse. HMunc13-4 is therefore essential for the priming step of cytolytic granules secretion preceding vesicle membrane fusion. 相似文献
57.
Klonowska A Clark ME Thieman SB Giles BJ Wall JD Fields MW 《Applied microbiology and biotechnology》2008,78(6):1007-1016
Desulfovibrio vulgaris Hildenborough is a well-studied sulfate reducer that can reduce heavy metals and radionuclides [e.g., Cr(VI) and U(VI)].
Cultures grown in a defined medium had a lag period of approximately 30 h when exposed to 0.05 mM Cr(VI). Substrate analyses
revealed that although Cr(VI) was reduced within the first 5 h, growth was not observed for an additional 20 h. The growth
lag could be explained by a decline in cell viability; however, during this time small amounts of lactate were still utilized
without sulfate reduction or acetate formation. Approximately 40 h after Cr exposure (0.05 mM), sulfate reduction occurred
concurrently with the accumulation of acetate. Similar amounts of hydrogen were produced by Cr-exposed cells compared to control
cells, and lactate was not converted to glycogen during non-growth conditions. D. vulgaris cells treated with a reducing agent and then exposed to Cr(VI) still experienced a growth lag, but the addition of ascorbate
at the time of Cr(VI) addition prevented the lag period. In addition, cells grown on pyruvate displayed more tolerance to
Cr(VI) compared to lactate-grown cells. These results indicated that D. vulgaris utilized lactate during Cr(VI) exposure without the reduction of sulfate or production of acetate, and that ascorbate and
pyruvate could protect D. vulgaris cells from Cr(VI)/Cr(III) toxicity.
J.D. Wall and M.W. Fields are both affiliated to the Virtual Institute of Microbial Stress and Survival ().
M.E. Clark and S.B. Thieman contributed equally to this work. 相似文献
58.
Matthias Albrecht David Kleijn Neal M. Williams Matthias Tschumi Brett R. Blaauw Riccardo Bommarco Alistair J. Campbell Matteo Dainese Francis A. Drummond Martin H. Entling Dominik Ganser G. Arjen de Groot Dave Goulson Heather Grab Hannah Hamilton Felix Herzog Rufus Isaacs Katja Jacot Philippe Jeanneret Mattias Jonsson Eva Knop Claire Kremen Douglas A. Landis Gregory M. Loeb Lorenzo Marini Megan McKerchar Lora Morandin Sonja C. Pfister Simon G. Potts Maj Rundlf Hillary Sardias Amber Sciligo Carsten Thies Teja Tscharntke Eric Venturini Eve Veromann Ines M.G. Vollhardt Felix Wckers Kimiora Ward Andrew Wilby Megan Woltz Steve Wratten Louis Sutter 《Ecology letters》2020,23(10):1488-1498
Floral plantings are promoted to foster ecological intensification of agriculture through provisioning of ecosystem services. However, a comprehensive assessment of the effectiveness of different floral plantings, their characteristics and consequences for crop yield is lacking. Here we quantified the impacts of flower strips and hedgerows on pest control (18 studies) and pollination services (17 studies) in adjacent crops in North America, Europe and New Zealand. Flower strips, but not hedgerows, enhanced pest control services in adjacent fields by 16% on average. However, effects on crop pollination and yield were more variable. Our synthesis identifies several important drivers of variability in effectiveness of plantings: pollination services declined exponentially with distance from plantings, and perennial and older flower strips with higher flowering plant diversity enhanced pollination more effectively. These findings provide promising pathways to optimise floral plantings to more effectively contribute to ecosystem service delivery and ecological intensification of agriculture in the future. 相似文献
59.
60.
Derivation and characterization of an efficiently myocarditic reovirus variant. 总被引:4,自引:11,他引:4 下载免费PDF全文
A reovirus variant, 8B, was isolated from a neonatal mouse which had been inoculated with a mixture of two reovirus strains: type 1 Lang (T1L) and type 3 Dearing (T3D) (E. A. Wenske, S.J. Chanock, L. Krata, and B. N. Fields, J. Virol. 56:613-616, 1985). 8B is a reassortant containing eight gene segments derived from the T1L parent and two gene segments derived from the T3D parent. Upon infection of neonatal mice, 8B produced a generalized infection characteristic of many reoviruses, but it also efficiently induced numerous macroscopic external cardiac lesions, unlike either of its parents. Microscopic examination of hearts from infected mice revealed myocarditis with necrotic myocytes and both polymorphonuclear and mononuclear cellular infiltration. Electron microscopy revealed viral arrays in necrotic myocytes and dystrophic calcification accompanying late lesions. Determination of viral titers in hearts from T1L-, T3D-, or 8B-infected mice indicated that growth was not the primary determinant of myocardial necrosis. Results from inoculations of athymic mice demonstrated that T cells were not a requirement for the 8B-induced myocarditis. Finally, 8B was more cytopathic than either of the parent viruses in cultured mouse L cells. Together, the data suggest that 8B-induced myocardial necrosis is due to a direct effect of reovirus on myocytes. Reovirus thus provides a useful model for the study of viral myocarditis. 相似文献