全文获取类型
收费全文 | 1602304篇 |
免费 | 146207篇 |
国内免费 | 1438篇 |
专业分类
1749949篇 |
出版年
2021年 | 18201篇 |
2019年 | 16184篇 |
2018年 | 19475篇 |
2017年 | 18313篇 |
2016年 | 29197篇 |
2015年 | 42733篇 |
2014年 | 50836篇 |
2013年 | 76933篇 |
2012年 | 46231篇 |
2011年 | 37595篇 |
2010年 | 47374篇 |
2009年 | 47552篇 |
2008年 | 34532篇 |
2007年 | 33678篇 |
2006年 | 36405篇 |
2005年 | 37743篇 |
2004年 | 36573篇 |
2003年 | 33945篇 |
2002年 | 31876篇 |
2001年 | 47784篇 |
2000年 | 45187篇 |
1999年 | 41876篇 |
1998年 | 27119篇 |
1997年 | 26833篇 |
1996年 | 26136篇 |
1995年 | 24288篇 |
1994年 | 23910篇 |
1993年 | 23190篇 |
1992年 | 35476篇 |
1991年 | 34081篇 |
1990年 | 32605篇 |
1989年 | 33051篇 |
1988年 | 30222篇 |
1987年 | 29006篇 |
1986年 | 27320篇 |
1985年 | 28814篇 |
1984年 | 27074篇 |
1983年 | 23930篇 |
1982年 | 22686篇 |
1981年 | 21685篇 |
1980年 | 20276篇 |
1979年 | 23226篇 |
1978年 | 20915篇 |
1977年 | 19646篇 |
1976年 | 18918篇 |
1975年 | 19015篇 |
1974年 | 19857篇 |
1973年 | 20108篇 |
1972年 | 17355篇 |
1971年 | 15765篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Li Zhang Mark Morrison Páraic ó Cuív Paul Evans Claire M. Rickard 《Journal of bacteriology》2012,194(23):6639
In recent years, Staphylococcus epidermidis has become a major nosocomial pathogen and the most common cause of intravascular catheter-related bacteremia, which can increase morbidity and mortality and significantly affect patient recovery. We report a draft genome sequence of Staphylococcus epidermidis AU12-03, isolated from an intravascular catheter tip. 相似文献
993.
This Perspective addresses one of the major puzzles of adipogenesis in adipose tissue, namely its resistance to cellular stress. It introduces a concept of “density” of integrin binding sites in extracellular matrix, proposes a cellular signaling explanation for the observed effects of matrix elasticity and of cell shape on mesenchymal stem cell differentiation, and discusses how specialized integrin binding sites in collagen IV-containing matrices guard two pivotal physiological and evolutionary processes: stress-resistant adipogenesis in adipose tissues and preservation of pluripotency of mesenchymal stem-like cells in their storage niches. Finally, it proposes strategies to suppress adipogenesis in adipose tissues. 相似文献
994.
995.
Larisa R. G. DeSantis Jessica R. Scott Blaine W. Schubert Shelly L. Donohue Brian M. McCray Courtney A. Van Stolk Amanda A. Winburn Michael A. Greshko Mackie C. O’Hara 《PloS one》2013,8(8)
The analysis of dental microwear is commonly used by paleontologists and anthropologists to clarify the diets of extinct species, including herbivorous and carnivorous mammals. Currently, there are numerous methods employed to quantify dental microwear, varying in the types of microscopes used, magnifications, and the characterization of wear in both two dimensions and three dimensions. Results from dental microwear studies utilizing different methods are not directly comparable and human quantification of wear features (e.g., pits and scratches) introduces interobserver error, with higher error being produced by less experienced individuals. Dental microwear texture analysis (DMTA), which analyzes microwear features in three dimensions, alleviates some of the problems surrounding two-dimensional microwear methods by reducing observer bias. Here, we assess the accuracy and comparability within and between 2D and 3D dental microwear analyses in herbivorous and carnivorous mammals at the same magnification. Specifically, we compare observer-generated 2D microwear data from photosimulations of the identical scanned areas of DMTA in extant African bovids and carnivorans using a scanning white light confocal microscope at 100x magnification. Using this magnification, dental microwear features quantified in 2D were able to separate grazing and frugivorous bovids using scratch frequency; however, DMTA variables were better able to discriminate between disparate dietary niches in both carnivorous and herbivorous mammals. Further, results demonstrate significant interobserver differences in 2D microwear data, with the microwear index remaining the least variable between experienced observers, consistent with prior research. Overall, our results highlight the importance of reducing observer error and analyzing dental microwear in three dimensions in order to consistently interpret diets accurately. 相似文献
996.
997.
Fourteen regularly cycling female rhesus monkeys were observed daily for menstruation and bled from the saphenous vein at regular intervals throughout the study. Plasma samples were assayed by RIA for progesterone levels. The animals were divided into 3 subgroups. The first (n=5) received daily subcutaneous injections of 1000 IU hCG from the 18th to 36th day following onset of menstruation. The second (n=7) received the same hCG treatment and was also implanted subcutaneously from the 18th to 40th days with 1.2 mg [Des-gly10, DTrp6, ProNHEt9] LHRH contained in cholesterol matrix pellets. The third (n=2) was untreated. Intermenstrual interval was significantly extended by hCG treatment. The extension was partially overcome by the LHRH agonist. The hCG-induced elevation in plasma progesterone to peak values over 17ng/ml was blocked by the LHRH agonist to give mean values not significantly different from control luteal phase levels. Plasma estradiol levels were unaffected by hCG or LHRH agonist. 相似文献
998.
999.
Reactions of cis-[PtCl(NH(3))(CyNH(2))(OH(2))](+) (Cy=cyclohexyl) with thione-containing single-stranded oligonucleotides d(T(8)XT(8)) and d(XT(16)) (X=(s6)I or (s4)U) and the mononucleotides 4-thiouridine ((s4)UMP) and 6-mercaptoinosine ((s6)IMP) have been studied in aqueous solution at pH 4.1. The reaction kinetics was followed using HPLC methodology as a function of ionic strength in the interval 5.0 mM相似文献
1000.
The distribution of sodium-potassium-activated adenosinetriphosphatase (Na+-K+-ATPase) in the alveolar portion of rat lungs was examined by indirect immunofluorescence with the use of a mouse monoclonal anti-rat Na+-K+-ATPase and by ultrastructural cytochemistry using p-nitrophenylphosphate as substrate. The reaction was inhibitable by 10 mM ouabain or by the omission of K+ from the reaction mixture. Cysteine or levamisole was used to inhibit alkaline phosphatase activity. By immunofluorescence, staining was confined to cuboidal cells in alveolar spaces. These were tentatively identified as type II pneumocytes. By ultrastructural cytochemistry reaction product was present on the cytoplasmic side of the basolateral membranes of type II pneumocytes. No reaction product was observed in type I pneumocytes or in endothelium. These results indicate that type II pneumocytes contain more Na+-K+-ATPase, an enzyme important in vectorial electrolyte transport, than type I pneumocytes or endothelial cells. More sensitive methods, however, are required to determine the amounts and distribution of this enzyme in type I pneumocytes and pulmonary vascular endothelial cells. 相似文献