全文获取类型
收费全文 | 4797篇 |
免费 | 372篇 |
国内免费 | 1篇 |
专业分类
5170篇 |
出版年
2023年 | 26篇 |
2022年 | 68篇 |
2021年 | 124篇 |
2020年 | 55篇 |
2019年 | 77篇 |
2018年 | 98篇 |
2017年 | 86篇 |
2016年 | 152篇 |
2015年 | 261篇 |
2014年 | 245篇 |
2013年 | 331篇 |
2012年 | 421篇 |
2011年 | 396篇 |
2010年 | 249篇 |
2009年 | 195篇 |
2008年 | 306篇 |
2007年 | 300篇 |
2006年 | 264篇 |
2005年 | 257篇 |
2004年 | 242篇 |
2003年 | 218篇 |
2002年 | 237篇 |
2001年 | 42篇 |
2000年 | 34篇 |
1999年 | 47篇 |
1998年 | 52篇 |
1997年 | 45篇 |
1996年 | 19篇 |
1995年 | 35篇 |
1994年 | 31篇 |
1993年 | 34篇 |
1992年 | 25篇 |
1991年 | 14篇 |
1990年 | 16篇 |
1989年 | 18篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1986年 | 8篇 |
1985年 | 15篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 17篇 |
1981年 | 10篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1976年 | 10篇 |
1973年 | 4篇 |
1972年 | 4篇 |
1969年 | 5篇 |
排序方式: 共有5170条查询结果,搜索用时 15 毫秒
71.
João Afonso Baptista Monica Truninger 《The journal of the Royal Anthropological Institute》2022,28(2):556-576
Doing research on fishery commodities in Portugal led us to an enigma: for a dead fish to be fresco (fresh) it must be alive. This paradox manifests at a popular, commercial, and legal level. It denotes the interruption of the difference between being dead and being alive in the commodity form. In Portugal, we suggest, the commercialization of peixe fresco (fresh fish) is based on the production and consumption of edible ‘zombis’: seafood corpses technologically and symbolically crafted as undead. An open concept, ‘edible zombis’ is part of an experimental vocabulary that foregrounds the productive agency of undeadness, both biological and commercial, in the seafood economic complex. It relates to the ordinary practice of necromancy in the commodity-based world. Edible zombis are commodity fetishes that fetishize their producers and consumers, suspending them from the capitalist system in which they live. 相似文献
72.
Feyisara Eyiwumi Oni Niels Geudens Joseph T. Onyeka Oluwatoyin Faith Olorunleke Ayodeji Ekundayo Salami Olumide Owolabi Omoboye Anthony Arguelles Arias Amayana Adiobo Stefaan De Neve Marc Ongena José C. Martins Monica Höfte 《Environmental microbiology》2020,22(12):5137-5155
Pseudomonas isolates from tropical environments have been underexplored and may form an untapped reservoir of interesting secondary metabolites. In this study, we compared Pseudomonas and cyclic lipopeptide (CLP) diversity in the rhizosphere of a cocoyam root rot disease (CRRD) suppressive soil in Boteva, Cameroon with those from four conducive soils in Cameroon and Nigeria. Compared with other soils, Boteva andosols were characterized by high silt, organic matter, nitrogen and calcium. Besides, the cocoyam rhizosphere at Boteva was characterized by strains belonging mainly to the P. koreensis and P. putida (sub)groups, with representations in the P. fluorescens, P. chlororaphis, P. jessenii and P. asplenii (sub)groups. In contrast, P. putida isolates were prominent in conducive soils. Regarding CLP diversity, Boteva was characterized by strains producing 11 different CLP types with cocoyamide A producers, belonging to the P. koreensis group, being the most abundant. However, putisolvin III-V producers were the most dominant in the rhizosphere of conducive soils in both Cameroon and Nigeria. Furthermore, we elucidated the chemical structure of putisolvin derivatives—putisolvin III-V, and described its biosynthetic gene cluster. We show that high Pseudomonas and metabolic diversity may be driven by microbial competition, which likely contributes to soil suppressiveness to CRRD. 相似文献
73.
Amy M. Gancarz-Kausch Gabrielle L. Schroeder Clarisse Panganiban Danielle Adank Monica S. Humby Michael A. Kausch Stewart D. Clark David M. Dietz 《PloS one》2013,8(12)
The addicted phenotype is characterized as a long-lasting, chronically relapsing disorder that persists following long periods of abstinence, suggesting that the underlying molecular changes are stable and endure for long periods even in the absence of drug. Here, we investigated Transforming Growth Factor-Beta Type I receptor (TGF-β R1) expression in the nucleus accumbens (NAc) following periods of withdrawal from cocaine self-administration (SA) and a sensitizing regimen of non-contingent cocaine. Rats were exposed to either (i) repeated systemic injections (cocaine or saline), or (ii) self-administration (cocaine or saline) and underwent a period of forced abstinence (either 1 or 7 days of drug cessation). Withdrawal from cocaine self-administration resulted in an increase in TGF-β R1 protein expression in the NAc compared to saline controls. This increase was specific for volitional cocaine intake as no change in expression was observed following a sensitizing regimen of experimenter-administered cocaine. These findings implicate TGF-β signaling as a novel potential therapeutic target for treating drug addiction. 相似文献
74.
Marra M Salzano G Leonetti C Porru M Franco R Zappavigna S Liguori G Botti G Chieffi P Lamberti M Vitale G Abbruzzese A La Rotonda MI De Rosa G Caraglia M 《Biotechnology advances》2012,30(1):302-309
Zoledronic acid (ZOL) is a drug whose potent anti-cancer activity is limited by its short plasma half-life and rapid uptake and accumulation within bone. We have recently proposed new delivery systems to avoid ZOL accumulation into the bone, thus improving extra-skeletal bioavailability. In this work, we have compared the technological and anti-cancer features of either ZOL-containing self-assembly PEGylated nanoparticles (NPs) or ZOL-encapsulating PEGylated liposomes (LIPO-ZOL). ZOL-containing NPs showed superior technological characteristics in terms of mean diameter, size distribution, and ZOL encapsulation efficiency, compared to LIPO-ZOL. Moreover, the anti-cancer activity of NPs in nude mice xenografted with prostate cancer PC3 cells was higher than that one induced by LIPO-ZOL. In addition, NPs induced the complete remission of tumour xenografts and an increase of survival time higher than that one observed with LIPO-ZOL. It has also to be considered that PC3 tumour xenografts were almost completely resistant to the anti-cancer effects induced by free ZOL. Both nanotechnological products did not induce toxic effects not affecting the mice weight nor inducing deaths. Moreover, the histological examination of some vital organs such as liver, kidney and spleen did not find any changes in terms of necrotic effects or modifications in the inflammatory infiltrate. On the other hand, NPs but not LIPO-ZOL caused a statistically significant reduction of the tumour associated macrophages (TAM) in tumour xenografts. This effect was paralleled by a significant increase of both necrotic and apoptotic indexes. The effects of the NPs were also higher in terms of neo-angiogenesis inhibition. These results suggest the future preclinical development of ZOL-encapsulating NPs in the treatment of human cancer. 相似文献
75.
González JF Degrassi G Devescovi G De Vleesschauwer D Höfte M Myers MP Venturi V 《Journal of Proteomics》2012,75(18):5911-5919
Xanthomonas oryzae pv. oryzae (Xoo) is the second most important rice pathogen, causing a disease called bacterial leaf blight. Xoo colonizes and infects the vascular tissue resulting in tissue necrosis and wilting causing significant yield losses worldwide. In this study Xoo infected vascular fluid (xylem sap) was recovered and analyzed for secreted Xoo proteins. Three independent experiments resulted in the identification of 324 different proteins, 64 proteins were found in all three samples which included many of the known virulence-associated factors. In addition, 10 genes encoding for the identified proteins were inactivated and one mutant displayed statistically a significant loss in virulence when compared to the wild type Xoo, suggesting that a new virulence-associated factor has been revealed. The usefulness of this approach in understanding the lifestyle and unraveling the virulence-associated factors of phytopathogenic vascular bacteria is discussed. 相似文献
76.
Monica G. Turner William H. Romme Erica A. H. Smithwick Daniel B. Tinker Jun Zhu 《Ecosystems》2011,14(7):1081-1095
Following fire, fine-scale variation in early successional vegetation and soil nutrients may influence development of ecosystem structure and function. We studied conifer forests burned by stand-replacing wildfire in Greater Yellowstone (Wyoming, USA) to address two questions: (1) How do the variability and spatial structure of aboveground cover and soil nitrogen availability change during the first 4 years following stand-replacing fire? (2) At fine scales (2–20 m), are postfire soil inorganic N pools and fluxes related to aboveground cover? Aboveground cover, soil N pools, and annual net N transformations were measured from 2001 to 2004 using a spatially explicit sampling design in four 0.25-ha plots that burned during summer 2000. Within-stand variability (coefficient of variation) in postfire live vegetative cover declined with time since fire, whereas variability in bare mineral soil, charred litter and fresh litter was greatest 2-3 years postfire. The soil nitrate pool was more variable than the soil ammonium pool, but annual net nitrification was less variable than annual net N mineralization. Spatial structure (quantified by semivariograms) was observed in some aboveground cover variables (for example, graminoids and fresh litter), but there was little spatial structure in soil N variables and no obvious congruence in spatial scales of autocorrelation for soil N and aboveground cover. Significant Spearman correlations (at the sample point) indicated that aboveground cover and soil N were coupled following severe fire, and the dominant influence was from aboveground cover to soil N, rather than from soil N to vegetation. Initial patterns of fire severity and re-vegetation contributed to fine-scale heterogeneity in soil N availability for at least 4 years after severe fire. 相似文献
77.
Parthenolide sensitizes cells to X-ray-induced cell killing through inhibition of NF-kappaB and split-dose repair 总被引:2,自引:0,他引:2
Mendonca MS Chin-Sinex H Gomez-Millan J Datzman N Hardacre M Comerford K Nakshatri H Nye M Benjamin L Mehta S Patino F Sweeney C 《Radiation research》2007,168(6):689-697
Human cancers have multiple alterations in cell signaling pathways that promote resistance to cytotoxic therapy such as X rays. Parthenolide is a sesquiterpene lactone that has been shown to inhibit several pro-survival cell signaling pathways, induce apoptosis, and enhance chemotherapy-induced cell killing. We investigated whether parthenolide would enhance X-ray-induced cell killing in radiation resistant, NF-kappaB-activated CGL1 cells. Treatment with 5 microM parthenolide for 48 to 72 h inhibited constitutive NF-kappaB binding and cell growth, reduced plating efficiency, and induced apoptosis through stabilization of p53 (TP53), induction of the pro-apoptosis protein BAX, and phosphorylation of BID. Parthenolide also enhanced radiation-induced cell killing, increasing the X-ray sensitivity of CGL1 cells by a dose modification factor of 1.6. Flow cytometry revealed that parthenolide reduced the percentage of X-ray-resistant S-phase cells due to induction of p21 waf1/cip1 (CDKN1A) and the onset of G1/S and G2/M blocks, but depletion of radioresistant S-phase cells does not explain the observed X-ray sensitization. Further studies demonstrated that the enhancement of X-ray-induced cell killing by parthenolide is due to inhibition of split-dose repair. 相似文献
78.
Nishikawa K Biewener AA Aerts P Ahn AN Chiel HJ Daley MA Daniel TL Full RJ Hale ME Hedrick TL Lappin AK Nichols TR Quinn RD Satterlie RA Szymik B 《Integrative and comparative biology》2007,47(1):16-54
Neuromechanics seeks to understand how muscles, sense organs,motor pattern generators, and brain interact to produce coordinatedmovement, not only in complex terrain but also when confrontedwith unexpected perturbations. Applications of neuromechanicsinclude ameliorating human health problems (including prosthesisdesign and restoration of movement following brain or spinalcord injury), as well as the design, actuation and control ofmobile robots. In animals, coordinated movement emerges fromthe interplay among descending output from the central nervoussystem, sensory input from body and environment, muscle dynamics,and the emergent dynamics of the whole animal. The inevitablecoupling between neural information processing and the emergentmechanical behavior of animals is a central theme of neuromechanics.Fundamentally, motor control involves a series of transformationsof information, from brain and spinal cord to muscles to body,and back to brain. The control problem revolves around the specifictransfer functions that describe each transformation. The transferfunctions depend on the rules of organization and operationthat determine the dynamic behavior of each subsystem (i.e.,central processing, force generation, emergent dynamics, andsensory processing). In this review, we (1) consider the contributionsof muscles, (2) sensory processing, and (3) central networksto motor control, (4) provide examples to illustrate the interplayamong brain, muscles, sense organs and the environment in thecontrol of movement, and (5) describe advances in both roboticsand neuromechanics that have emerged from application of biologicalprinciples in robotic design. Taken together, these studiesdemonstrate that (1) intrinsic properties of muscle contributeto dynamic stability and control of movement, particularly immediatelyafter perturbations; (2) proprioceptive feedback reinforcesthese intrinsic self-stabilizing properties of muscle; (3) controlsystems must contend with inevitable time delays that can simplifyor complicate control; and (4) like most animals under a varietyof circumstances, some robots use a trial and error processto tune central feedforward control to emergent body dynamics. 相似文献
79.
Kumar A Redondo-Muñoz J Perez-García V Cortes I Chagoyen M Carrera AC 《Molecular and cellular biology》2011,31(10):2122-2133
Class I(A) phosphoinositide 3-kinases (PI3Ks) are heterodimeric enzymes composed of a p85 regulatory and a p110 catalytic subunit that induce the formation of 3-polyphosphoinositides, which mediate cell survival, division, and migration. There are two ubiquitous PI3K isoforms p110α and p110β that have nonredundant functions in embryonic development and cell division. However, whereas p110α concentrates in the cytoplasm, p110β localizes to the nucleus and modulates nuclear processes such as DNA replication and repair. At present, the structural features that determine p110β nuclear localization remain unknown. We describe here that association with the p85β regulatory subunit controls p110β nuclear localization. We identified a nuclear localization signal (NLS) in p110β C2 domain that mediates its nuclear entry, as well as a nuclear export sequence (NES) in p85β. Deletion of p110β induced apoptosis, and complementation with the cytoplasmic C2-NLS p110β mutant was unable to restore cell survival. These studies show that p110β NLS and p85β NES regulate p85β/p110β nuclear localization, supporting the idea that nuclear, but not cytoplasmic, p110β controls cell survival. 相似文献
80.
Shafat I Ben-Arush MW Issakov J Meller I Naroditsky I Tortoreto M Cassinelli G Lanzi C Pisano C Ilan N Vlodavsky I Zunino F 《Journal of cellular and molecular medicine》2011,15(9):1857-1864
Heparanase is an endoglycosidase that specifically cleaves heparan sulphate side chains of heparan sulphate proteoglycans, activity that is strongly implicated in cell migration and invasion associated with tumour metastasis, angiogenesis and inflammation. Heparanase up-regulation was documented in an increasing number of human carcinomas, correlating with reduced post-operative survival rate and enhanced tumour angiogenesis. Expression and significance of heparanase in human sarcomas has not been so far reported. Here, we applied the Ewing's sarcoma cell line TC71 and demonstrated a potent inhibition of cell invasion in vitro and tumour xenograft growth in vivo upon treatment with a specific inhibitor of heparanase enzymatic activity (compound SST0001, non-anticoagulant N-acetylated, glycol split heparin). Next, we examined heparanase expression and cellular localization by immunostaining of a cohort of 69 patients diagnosed with Ewing's sarcoma. Heparanase staining was noted in all patients. Notably, heparanase staining intensity correlated with increased tumour size (P = 0.04) and with patients' age (P = 0.03), two prognostic factors associated with a worse outcome. Our study indicates that heparanase expression is induced in Ewing's sarcoma and associates with poor prognosis. Moreover, it encourages the inclusion of heparanase inhibitors (i.e. SST0001) in newly developed therapeutic modalities directed against Ewing's sarcoma and likely other malignancies. 相似文献