全文获取类型
收费全文 | 23160篇 |
免费 | 2188篇 |
国内免费 | 2篇 |
专业分类
25350篇 |
出版年
2023年 | 80篇 |
2022年 | 184篇 |
2021年 | 379篇 |
2020年 | 210篇 |
2019年 | 289篇 |
2018年 | 357篇 |
2017年 | 320篇 |
2016年 | 629篇 |
2015年 | 1024篇 |
2014年 | 1070篇 |
2013年 | 1297篇 |
2012年 | 1695篇 |
2011年 | 1493篇 |
2010年 | 971篇 |
2009年 | 942篇 |
2008年 | 1219篇 |
2007年 | 1270篇 |
2006年 | 1150篇 |
2005年 | 1116篇 |
2004年 | 1049篇 |
2003年 | 1070篇 |
2002年 | 987篇 |
2001年 | 378篇 |
2000年 | 289篇 |
1999年 | 366篇 |
1998年 | 286篇 |
1997年 | 219篇 |
1996年 | 204篇 |
1995年 | 210篇 |
1994年 | 185篇 |
1993年 | 190篇 |
1992年 | 257篇 |
1991年 | 237篇 |
1990年 | 203篇 |
1989年 | 198篇 |
1988年 | 204篇 |
1987年 | 158篇 |
1986年 | 160篇 |
1985年 | 172篇 |
1984年 | 181篇 |
1983年 | 127篇 |
1982年 | 136篇 |
1981年 | 112篇 |
1980年 | 105篇 |
1979年 | 124篇 |
1978年 | 88篇 |
1977年 | 101篇 |
1974年 | 117篇 |
1972年 | 80篇 |
1970年 | 82篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
Se-Chan Kim Alexander Ghanem Heidi Stapel Klaus Tiemann Pascal Knuefermann Andreas Hoeft Rainer Meyer Christian Grohé Anne A Knowlton Georg Baumgarten 《BMC physiology》2007,7(1):5
Backgound
It has been reported that Toll-like receptor 4 (TLR4) deficiency reduces infarct size after myocardial ischemia/reperfusion (MI/R). However, measurement of MI/R injury was limited and did not include cardiac function. In a chronic closed-chest model we assessed whether cardiac function is preserved in TLR4-deficient mice (C3H/HeJ) following MI/R, and whether myocardial and systemic cytokine expression differed compared to wild type (WT). 相似文献12.
M. von Balthazar K. Raunsgaard Pedersen E. M. Friis 《Plant Systematics and Evolution》2005,255(1-2):55-75
A charcoalified fossil flower bud of a new genus and species (Teixeiria lusitanica) is described from the Early Cretaceous of Portugal. The flower is actinomorphic and unisexually male. At the base of the
bud there are several bracts of different sizes, which are followed by sepal-like and petal-like tepals. Bracts and perianth
organs seem to be arranged spirally and to exhibit transitions between different organ categories. The androecium has numerous
stamens in two sizes, but with unclear arrangement. Pollen is small and tricolpate with a perforate tectum and a densely columellate
infratectal layer. No carpels or remains of carpels could be observed on the floral axis. Teixeiria lusitanica shows most affinities to members of Ranunculales. There are also some similarities with Berberidopsis (Berberidopsidaceae, Berberidopsidales) and members of the Saxifragales (Hamamelidaceae and Daphniphyllaceae). 相似文献
13.
14.
15.
Three specimens of Ayapana triplinervis (Vahl) R.M. King & H. Rob from Reunion Island (Indian Ocean) collected at two distant locations (North of the island; samples 1 and 2, South of the island; sample 3), in different growth phases (flowering; samples 1 and 3, vegetative; sample 2) were investigated for their leaf essential oil composition. This study reports the chemical character of this species on the island and investigates the relationship between essential oil composition, developmental stage and geographic location. Analysis by GC–FID and GC–MS enabled us to identify and quantify a total of 39 constituents accounting for 97.1–98.0% of the oils. The three essential oil samples, all obtained by hydrodistillation, showed a high percentage of the aromatic compound thymohydroquinone dimethyl ether (89.9–92.8%). All other minor components remained more or less unchanged both qualitatively and quantitatively with respect to the stage of growth. On the contrary, variations were observed with geographic distribution. The geographical variation of the chemical composition of the volatile oil of A. triplinervis from several sites in the world is also briefly discussed. 相似文献
16.
17.
Alexander Wiedenmann Peter Dimroth Christoph von Ballmoos 《Molecular microbiology》2009,72(2):479-490
F1 F0 ATP synthases use the electrochemical potential of H+ or Na+ across biological membranes to synthesize ATP by a rotary mechanism. In bacteria, the enzymes can act in reverse as ATP-driven ion pumps creating the indispensable membrane potential. Here, we demonstrate that the F0 parts of a Na+ - and H+ -dependent enzyme display major asymmetries with respect to their mode of operation, reflected by the requirement of ∼100 times higher Na+ or H+ concentrations for the synthesis compared with the hydrolysis of ATP. A similar asymmetry is observed during ion transport through isolated F0 parts, indicating different affinities for the binding sites in the a/c interface. Together with further data, we propose a model that provides a rationale for a differential usage of membrane potential and ion gradient during ATP synthesis as observed experimentally. The functional asymmetry might also reflect an important property of the ATP synthesis mechanism in vivo . In Escherichia coli , we observed respiratory chain-driven ATP production at pH 7–8, while P -site pH values < 6.5 were required for ATP synthesis in vitro . This discrepancy is discussed with respect to the hypothesis that during respiration lateral proton diffusion could lead to significant acidification at the membrane surface. 相似文献
18.
19.
R. P. Pacumbaba J. G. Wutoh Sama Anne Eyango J. T. Tambong L. M. Nyochembeng 《Journal of Phytopathology》1992,135(4):265-273
Cocoyam is the second most important staple crop of Cameroon and root rot is a destructive disease of this plant. Pythium myriotylum (Pm), Fusarium solani (Fs), and Rhizoctonia solani (Rs) were isolated from the rhizosphere of root rot affected cocoyams and from the soil of a cocoyam experimental field plot temporarily devoid of same in Mamu, Cameroon. Pm was isolated from the above soil by the cocoyam leaf disc baits. Fs and Rs were also isolated from the same soils by the water dilution method and from the roots of diseased cocoyams but were always associated with mycelial growth of Pm. Pathogenicity of Pm and in combinations with Fs or Rs or Fs + Rs all developed cocoyam root rot disease (CRRD) symptoms on 3– and 7–month old cocoyam plantlets 2–7 days after inoculation. Symptoms included rotted roots and wilting with general chlorosis of inoculated plantlets. No symptoms of CRRD were noted on cocoyam plantlets inoculated with Fs, Rs, Fs + Rs, and distilled water. Results indicated that CRRD is not caused by several pathogens but only by Pm. Pm isolates from the soils and roots of diseased cocoyams and those maintained in the ROTREP laboratory have significantly bigger diameter of mycelial colony growth in 24 h–period at 31 °C on lima bean sucrose agar, V–8 juice sucrose agar, and potato sucrose agar than on potato dextrose agar and 2 % water agar. The cocoyam plantlets were raised axenically from tissue culture of explants in the laboratory. 相似文献
20.
In the mesenterium of rats it was found that an overacidity of the blood flowing in the area of microcirculation and caused by irrigation with acid media may be objectively represented in the clearing of venols measurable by means of video technique. The cause of this clearing process is the swelling of erythrocytes setting in at lower pH-values. According to in-vitro findings this swelling of erythrocytes will lead to an increase of the apparent viscosity of the blood fluid or blood cell suspension respectively in conformity with the increase of hematocrit connected with it. 相似文献