全文获取类型
收费全文 | 2751篇 |
免费 | 343篇 |
国内免费 | 2篇 |
专业分类
3096篇 |
出版年
2022年 | 21篇 |
2021年 | 38篇 |
2020年 | 24篇 |
2019年 | 27篇 |
2018年 | 37篇 |
2017年 | 36篇 |
2016年 | 43篇 |
2015年 | 98篇 |
2014年 | 86篇 |
2013年 | 143篇 |
2012年 | 155篇 |
2011年 | 154篇 |
2010年 | 87篇 |
2009年 | 94篇 |
2008年 | 132篇 |
2007年 | 110篇 |
2006年 | 106篇 |
2005年 | 101篇 |
2004年 | 120篇 |
2003年 | 111篇 |
2002年 | 96篇 |
2001年 | 62篇 |
2000年 | 84篇 |
1999年 | 63篇 |
1998年 | 44篇 |
1997年 | 24篇 |
1996年 | 26篇 |
1995年 | 19篇 |
1994年 | 30篇 |
1993年 | 25篇 |
1992年 | 46篇 |
1991年 | 43篇 |
1990年 | 89篇 |
1989年 | 78篇 |
1988年 | 60篇 |
1987年 | 42篇 |
1986年 | 41篇 |
1985年 | 32篇 |
1984年 | 32篇 |
1983年 | 25篇 |
1982年 | 29篇 |
1981年 | 28篇 |
1980年 | 20篇 |
1979年 | 29篇 |
1978年 | 21篇 |
1976年 | 17篇 |
1975年 | 28篇 |
1974年 | 21篇 |
1973年 | 23篇 |
1971年 | 18篇 |
排序方式: 共有3096条查询结果,搜索用时 13 毫秒
101.
Michael M. Lipsky Talia R. Sheridan Richard O. Bennett Eric B. May 《In vitro cellular & developmental biology. Plant》1986,22(6):360-362
Summary Comparisons were made of attachment and viability of rainbow trout (Salmo gairdneri) hepatocytes in short-term (2 days), primary culture on plastic, collagen-coated or extracellular matrix (ECM) coated dishes.
Hepatocyte isolation routinely yielded cells with good viability (96%). Cells plated on ECM attached with high efficiency
(93%) in contrast to cells cultured on plastic or collagen (∼20%). The cells plated on ECM flattened out and formed monolayers,
while the cells on plastic and collagen rounded up and formed multi-cell aggregates in suspension. Viability of cells in all
substrates remained high over the 2 day culture period. ECM is the first substrate to support trout-hepatocyte attachment
in primary culture. Differentiated liver function was maintained in cells cultured on ECM as evidence by the induction of
tyrosine aminotransferase by hydrocortisone (200%).
This work was supported in part by research grant R809599010 from the U. S. Environmental Protection Agency.
Editor's Statement This paper reports improved methods for culture of trout liver-derived cells that make in vitro investigations
of fish metabolism, carcinogenesis and chemical toxicity more feasible than previously applied techniques. Recent interest
in fish as models for study and indicators of effects of envionmental and food-related toxins make this work timely, poarticularly
since many of the compounds of interest are primarily metabolized by hepatocytes or act on liver as a major target. David
W. Barnes 相似文献
102.
Agrobacterium -mediated transformation of embryogenic cell suspensions of the banana cultivar Rasthali (AAB) 总被引:9,自引:0,他引:9
T. R. Ganapathi N. S. Higgs P. J. Balint-Kurti C. J. Arntzen G. D. May J. M. Van Eck 《Plant cell reports》2001,20(2):157-162
A protocol was developed for establishing embryogenic suspension cultures from in vitro-grown, thin shoot-tip sections of
the banana cultivar Rasthali. The best medium for callus induction was an MS-based medium supplemented with 2 mg/l 2,4-D and
0.2 mg/l zeatin. The callus was transferred to liquid medium to establish embryogenic cell suspensions. These cultures were
subsequently used for Agrobacterium-mediated transformation. The Agrobacterium tumefaciens strain EHA105 containing the binary vector pVGSUN with the als gene as a selectable marker and an intron-containing the gusA gene as a reporter gene was used for transformations. The herbicide Glean was used as a selection agent. Two hundred putative
transformants were recovered, of which a set of 16 was tested by histochemical analysis for GUS expression and by Southern
blot analysis with a probe for the gusA gene. The plants were positive for GUS expression and integration of the gusA gene. Two of the transformants were grown to maturity under greenhouse conditions. Bananas were harvested to test GUS expression
by histochemical analysis. The fruit from both transgenics tested positive for GUS expression.
Received: 22 February 2000 / Revision received: 2 October 2000 / Accepted: 5 October 2000 相似文献
103.
104.
Chronic pain appears to be associated with brain gray matter reduction in areas ascribable to the transmission of pain. The morphological processes underlying these structural changes, probably following functional reorganisation and central plasticity in the brain, remain unclear. The pain in hip osteoarthritis is one of the few chronic pain syndromes which are principally curable. We investigated 20 patients with chronic pain due to unilateral coxarthrosis (mean age 63.25±9.46 (SD) years, 10 female) before hip joint endoprosthetic surgery (pain state) and monitored brain structural changes up to 1 year after surgery: 6–8 weeks, 12–18 weeks and 10–14 month when completely pain free. Patients with chronic pain due to unilateral coxarthrosis had significantly less gray matter compared to controls in the anterior cingulate cortex (ACC), insular cortex and operculum, dorsolateral prefrontal cortex (DLPFC) and orbitofrontal cortex. These regions function as multi-integrative structures during the experience and the anticipation of pain. When the patients were pain free after recovery from endoprosthetic surgery, a gray matter increase in nearly the same areas was found. We also found a progressive increase of brain gray matter in the premotor cortex and the supplementary motor area (SMA). We conclude that gray matter abnormalities in chronic pain are not the cause, but secondary to the disease and are at least in part due to changes in motor function and bodily integration. 相似文献
105.
El-Sofany Walaa I. Osman Dalia Ahmed A. Mahran Asma M. May El-Manawaty A. El-Sayed Wael A. 《Russian Journal of Bioorganic Chemistry》2020,46(5):873-873
Russian Journal of Bioorganic Chemistry - erratum 相似文献
106.
Burns KL Gelbaum LT Sullards MC Bostwick DE May SW 《The Journal of biological chemistry》2005,280(17):16550-16558
Iso-coenzyme A is an isomer of coenzyme A in which the monophosphate is attached to the 2'-carbon of the ribose ring. Although iso-CoA was first reported in 1959 (Moffatt, J. G., and Khorana, H. G. (1959) J. Am. Chem. Soc. 81, 1265-1265) to be a by-product of the chemical synthesis of CoA, relatively little attention has been focused on iso-CoA or on acyl-iso-CoA compounds in the literature. We now report structural characterizations of iso-CoA, acetyl-iso-CoA, acetoacetyl-iso-CoA, and beta-hydroxybutyryl-iso-CoA using mass spectrometry (MS), tandem MS, and homonuclear and heteronuclear NMR analyses. Although the 2'-phosphate isomer of malonyl-CoA was recently identified in commercial samples, previous characterizations of iso-CoA itself have been based on chromatographic analyses, which ultimately rest on comparisons with the degradation products of CoA and NADPH or have been based on assumptions regarding enzyme specificity. We describe a high performance liquid chromatography methodology for separating the isomers of several CoA-containing compounds. We also report here the first examples of iso-CoA-containing compounds acting as substrates in enzymatic acyl transfer reactions. Finally, we describe a simple synthesis of iso-CoA from CoA, which utilizes beta-cyclodextrin to produce iso-CoA with high regioselectivity, and we demonstrate a plausible mechanism that accounts for the existence of iso-CoA isomers in commercial preparations of CoA-containing compounds. We anticipate that these results will provide methodology and impetus for investigating iso-CoA compounds as potential pseudo-substrates or inhibitors of the >350 known CoA-utilizing enzymes. 相似文献
107.
The low density lipoprotein receptor-related protein 1 (LRP1) has been implicated in intracellular signaling functions as well as in lipid metabolism. Recent in vivo and in vitro studies suggest that LRP1 is a physiological modulator of the platelet-derived growth factor (PDGF) signaling pathway. Here we show that in mouse fibroblasts LRP1 modulates PDGF-BB signaling by controlling endocytosis and ligand-induced down-regulation of the PDGF receptor beta (PDGFRbeta). In LRP1-deficient fibroblasts, basal PDGFRbeta tyrosine kinase activity was derepressed, and PDGF-BB-induced endocytosis and degradation of PDGFRbeta were accelerated as compared with control cells. This was accompanied by rapid uptake of receptor-bound PDGF-BB into the cells and by attenuated ERK activation in response to PDGF-BB stimulation. Pulse-chase analysis indicated that the steady-state turnover rate of PDGFRbeta was also accelerated in LRP-deficient fibroblasts. The rapid degradation of PDGFRbeta in the LRP1-deficient fibroblasts was prevented by MG132 and chloroquine. Furthermore, the association of PDGFRbeta with c-Cbl, a ubiquitin E3-ligase, as well as the ligand-induced ubiquitination of PDGFRbeta were increased in LRP1-deficient fibroblasts. We show that LRP1 can directly interact with c-Cbl, suggesting a Sprouty-like role for LRP1 in regulating the access of the PDGFRbeta to the ubiquitination machinery. Thus, LRP1 modulates PDGF signaling by controlling ubiquitination and endocytosis of the PDGFRbeta. 相似文献
108.
Chi Fat Wong Hejingying Niu Jingwei Jiang Jun Li Charis May Ngor Chan Dennis Yiu Cheong Leung Frederick Chi Ching Leung 《Journal of bacteriology》2012,194(22):6326
Pseudomonas mendocina DLHK is an aerobic bacterium isolated from a biotrickling reactor which can remove nitric oxide, a common air pollutant from combustion exhaust gas. Here, we present the draft genome of Pseudomonas mendocina DLHK. 相似文献
109.
The highly divergent beta-tubulins of Aspergillus nidulans are functionally interchangeable 总被引:3,自引:1,他引:3 下载免费PDF全文
G S May 《The Journal of cell biology》1989,109(5):2267-2274
An internal 1.4-kb Bst EII fragment was used to disrupt the benA gene and establish heterokaryons. The heterokaryons demonstrated that the molecular disruption of benA results in a recessive benA null mutation. Conidia from a heterokaryon swell and germinate but cannot undergo nuclear division and are thus inviable. A chimeric beta-tubulin gene was constructed with the benA promoter driving the tubC structural gene. This chimeric gene construction was placed on a plasmid containing a selectable marker for Aspergillus transformation and the gene disrupting fragment of benA. Integration of this plasmid at benA by the internal gene disrupting fragment of benA simultaneously disrupts the benA gene and replaces it with the chimeric beta-tubulin gene, rescuing the benA null generated by the integration. Strains generated by this procedure contain only tubC beta-tubulin for all beta-tubulin functions. Strains having only tubC beta-tubulin are viable and exhibit no detectable microtubule dysfunction though they are more sensitive than wild-type strains to the antimicrotubule drug benomyl. It is concluded that the two beta-tubulin genes of Aspergillus nidulans, though highly divergent, are interchangeable. 相似文献
110.
Tran Tinh Hien Nguyen Thi Dung Nguyen Thanh Truong Ninh Thi Thanh Van Tran Nguyen Bich Chau Nguyen Van Minh Hoang Tran Thi Thu Nga Cao Thu Thuy Pham Van Minh Nguyen Thi Cam Binh Tran Thi Diem Ha Pham Van Toi To Song Diep James I. Campbell Elaine Stockwell Constance Schultsz Cameron P. Simmons Clare Glover Winnie Lam Filipe Marques James P. May Anthony Upton Ronald Budhram Gordon Dougan Jeremy Farrar Nguyen Van Vinh Chau Christiane Dolecek 《PloS one》2010,5(7)