全文获取类型
收费全文 | 21282篇 |
免费 | 1076篇 |
国内免费 | 2949篇 |
专业分类
25307篇 |
出版年
2024年 | 54篇 |
2023年 | 267篇 |
2022年 | 421篇 |
2021年 | 517篇 |
2020年 | 493篇 |
2019年 | 665篇 |
2018年 | 537篇 |
2017年 | 565篇 |
2016年 | 624篇 |
2015年 | 779篇 |
2014年 | 1082篇 |
2013年 | 1470篇 |
2012年 | 987篇 |
2011年 | 1092篇 |
2010年 | 915篇 |
2009年 | 1165篇 |
2008年 | 1264篇 |
2007年 | 1335篇 |
2006年 | 1231篇 |
2005年 | 1229篇 |
2004年 | 1085篇 |
2003年 | 1059篇 |
2002年 | 828篇 |
2001年 | 686篇 |
2000年 | 561篇 |
1999年 | 536篇 |
1998年 | 563篇 |
1997年 | 437篇 |
1996年 | 428篇 |
1995年 | 423篇 |
1994年 | 364篇 |
1993年 | 278篇 |
1992年 | 265篇 |
1991年 | 209篇 |
1990年 | 181篇 |
1989年 | 128篇 |
1988年 | 148篇 |
1987年 | 102篇 |
1986年 | 69篇 |
1985年 | 63篇 |
1984年 | 58篇 |
1983年 | 28篇 |
1982年 | 36篇 |
1981年 | 15篇 |
1980年 | 17篇 |
1979年 | 10篇 |
1978年 | 11篇 |
1977年 | 5篇 |
1976年 | 7篇 |
1972年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
971.
Furuhata S Ando K Oki M Aoki K Ohnishi S Aoyagi K Sasaki H Sakamoto H Yoshida T Ohnami S 《Molecular and cellular biochemistry》2007,298(1-2):125-138
Among the many tissue stem or progenitor cells recently being unveiled, endothelial progenitor cells (EPCs) have attracted
particular attention, not only because of their cardinal role in vascular biology and embryology but also because of their
potential use in the therapeutic development of a variety of postnatal diseases, including cardiovascular and peripheral vascular
disorders and cancer. The aim of this study is to provide some basic and comprehensive information on gene expression of EPCs
to characterize the cells in molecular terms. Here, we focus on EPCs derived from CD34-positive mononuclear cells of human
umbilical cord blood. The EPCs were purified and expanded in culture and analyzed by a high-density oligonucleotide microarray
and real-time RT-PCR analysis. We identified 169 up-regulated and 107 down-regulated genes in the EPCs compared with three
differentiated endothelial cells of human umbilical vein endothelial cells (HUVEC), human lung microvascular endothelial cells
(LMEC) and human aortic endothelial cells (AoEC). It is expected that the obtained list include key genes which are critical
for EPC function and survival and thus potential targets of EPC recognition in vivo and therapeutic modulation of vasculogenesis
in cancer as well as other diseases, in which de novo vasculogenesis plays a crucial role. For instance, the list includes
Syk and galectin-3, which encode protein tyrosine kinase and β-galactoside-binding protein, respectively, and are expressed higher in EPCs than
the three control endothelial cells. In situ hybridization showed that the genes were expressed in isolated cells in the fetal
liver at E11.5 and E14.5 of mouse development. 相似文献
972.
973.
Summary. Abaxial epidermal cells of developing faba bean (Vicia faba) cotyledons are modified to a transfer cell morphology and function. In contrast, the adaxial epidermal cells do not form
transfer cells but can be induced to do so when excised cotyledons are cultured on an agar medium. The first fenestrated layer
of wall ingrowths is apparent within 24 h of cotyledon exposure to culture medium. The time course of wall ingrowth formation
was examined further. By 2 h following cotyledon excision, a 350 nm thick wall was deposited evenly over the outer periclinal
walls of adaxial epidermal cells and densities of cytoplasmic vesicles increased. After 3 h in culture, 10% of epidermal cells
contained small projections of wall material on their outer periclinal walls. Thereafter, this percentage rose sharply and
reached a maximum of 90% by 15 h. Continuous culture of cotyledons on a medium containing 6-methyl purine (an inhibitor of
RNA synthesis) completely blocked wall ingrowth formation. In contrast, if exposure to 6-methyl purine was delayed for 1 h
at the start of the culture period, the adaxial epidermal cells were found to contain small wall ingrowths. Treating cotyledons
for 1 h with 6-methyl purine at 15 h following cotyledon excision halted further wall ingrowth development. We conclude that
transfer cell induction is rapid and that signalling and early events leading to wall ingrowth formation depend upon gene
expression. In addition, these gene products have a high turnover rate.
Correspondence and reprints: School of Environmental and Life Sciences, Biology Building, University of Newcastle, Callaghan,
NSW 2308, Australia. 相似文献
974.
We propose a cellular automaton model of solid tumour growth, in which each cell is equipped with a micro-environment response network. This network is modelled using a feed-forward artificial neural network, that takes environmental variables as an input and from these determines the cellular behaviour as the output. The response of the network is determined by connection weights and thresholds in the network, which are subject to mutations when the cells divide. As both available space and nutrients are limited resources for the tumour, this gives rise to clonal evolution where only the fittest cells survive. Using this approach we have investigated the impact of the tissue oxygen concentration on the growth and evolutionary dynamics of the tumour. The results show that the oxygen concentration affects the selection pressure, cell population diversity and morphology of the tumour. A low oxygen concentration in the tissue gives rise to a tumour with a fingered morphology that contains aggressive phenotypes with a small apoptotic potential, while a high oxygen concentration in the tissue gives rise to a tumour with a round morphology containing less evolved phenotypes. The tissue oxygen concentration thus affects the tumour at both the morphological level and on the phenotype level. 相似文献
975.
目的: 原核表达盐穗木(Halostachys caspica C. A. Mey.)金属硫蛋白HcMT并探究其抗氧化活性。方法: 构建原核表达载体pET-32a-HcMT,转化至大肠杆菌Escherichia coli BL21,加入Zn2+胁迫培养(终浓度为200 μmol/L),分离纯化得到Zn-HcMT,测定Zn-HcMT自由基清除活性和总抗氧化能力,制备复合物Zn-HcMT/TiO2并做FTIR表征。结果: 通过原核表达获得融合蛋白Zn-HcMT,对·OH、O2·-、DPPH自由基具有较强的清除活性,对·OH、O2·-的IC50分别为0.386 mg/mL、0.038 mg/mL。融合蛋白浓度为0.01 mg/mL时,对DPPH清除率达(37.43 ± 0.006 8)%,浓度为0.3mg/mL时TEAC(trolox-equivalent antioxidant capacity)值为(1.023 ± 0.01)mmol/L,融合蛋白还原力A700为0.142 ± 0.055,FTIR图谱同时表现了Zn-HcMT和TiO2吸收特性。结论: Zn-HcMT具有良好的清除ROS活性及较强的抗氧化能力,在化妆品领域有潜在应用前景。 相似文献
976.
Molecular pharming relies on the integration of foreign genes into a plant system for production of the desired recombinant protein. The speed, scalability, and lack of contaminating human pathogens highlights plants as an enticing and feasible system to produce diverse protein-based products, including vaccines, antibodies, and enzymes. However, limitations of expression levels, host defense responses, and production irregularities underscore distinct areas for improvement within the molecular pharming pipeline. Within the past five years, mass spectrometry-based proteomics has begun to address these critical areas and show promise in advancing our understanding of the complex biological systems driving molecular pharming. Further, opportunities to leverage comprehensive proteome profiling have surfaced to meet good manufacturing practice regulations and move biopharmaceuticals derived from plants into mainstream production. 相似文献
977.
VPAC2在CHO细胞的表达及鉴定 总被引:1,自引:0,他引:1
PAC2是垂体腺苷酸环化酶激活多肽(Pituitary adenylate cyclase activating polypeptide,PACAP)和血管活性肠肽(vasoactive intestinal peptide,VIP)的共同受体,介导多种重要生物学功能。为获得稳定特异表达VPAC2的中国仓鼠卵巢(Chinesehamsterovary,CHO)细胞,将pcDNA-VPAC2表达载体转染CHO细胞,G418筛选转染阳性克隆,PACAP38标准品诱导阳性克隆细胞的胞内cAMP生成,筛选出对PACAP38最为敏感的阳性单克隆细胞株(VPAC2-CHO),运用RT-PCR、Westernblot和免疫荧光法检测VPAC2受体表达情况,利用VPAC2受体特异激动剂通过竞争性结合试验和促进胞内第二信使cAMP生成的活性检测实验证实,VPAC2-CHO特异表达有功能的VPAC2。Scatchard作图分析显示VPAC2-CHO的VPAC2受体密度为(1.1±0.2)pmol/mg膜蛋白,PACAP38与VPAC2的解离常数Kd值为(0.55±0.10)nmol/L。特异表达VPAC2受体细胞系的构建为深入研究该受体理化性质、生物学功能以及筛选、开发VPAC2受体新型特异激动剂和拮抗剂等研究奠定了基础。 相似文献
978.
基于载体的RNA干涉介导人核受体hLRH-1的表达抑制实验研究 总被引:2,自引:1,他引:2
为探讨经RNA干涉法诱导人核受体hLRH-1的表达抑制的可行性,通过设计并构建能表达靶向人核受体hLRH-1基因的siRNAs的干涉载体pShLRH-1.1和pShLRH-1.2,经脂质体介导法转染人肝癌细胞BEL-7402,RT-PCR法鉴定hLRH-1基因的表达抑制效应,同时以同样方法分析焦磷酸法呢酯合成酶基因的表达情况。瞬时转染后分析结果表明,所构建的干涉载体pShLRH-1.1和pShLRH-1.2均能在细胞水平有效诱导hLRH-1基因的表达抑制,抑制率高达约80%;与未转染和空载体转染对照组相比,hLRH-1基因表达受抑的细胞中焦磷酸法呢酯合成酶基因的表达呈明显上调,提示hLRH-1可能在焦磷酸法呢酯合成酶基因的表达中起负调作用。 相似文献
979.
980.