全文获取类型
收费全文 | 995789篇 |
免费 | 117340篇 |
国内免费 | 520篇 |
出版年
2016年 | 11176篇 |
2015年 | 16449篇 |
2014年 | 19147篇 |
2013年 | 26984篇 |
2012年 | 30509篇 |
2011年 | 30525篇 |
2010年 | 20775篇 |
2009年 | 19409篇 |
2008年 | 27728篇 |
2007年 | 28620篇 |
2006年 | 26778篇 |
2005年 | 25840篇 |
2004年 | 25810篇 |
2003年 | 24957篇 |
2002年 | 24414篇 |
2001年 | 42265篇 |
2000年 | 42712篇 |
1999年 | 34483篇 |
1998年 | 13293篇 |
1997年 | 13854篇 |
1996年 | 13261篇 |
1995年 | 12626篇 |
1994年 | 12471篇 |
1993年 | 12242篇 |
1992年 | 29420篇 |
1991年 | 28443篇 |
1990年 | 27972篇 |
1989年 | 27144篇 |
1988年 | 25183篇 |
1987年 | 24515篇 |
1986年 | 22694篇 |
1985年 | 22823篇 |
1984年 | 19040篇 |
1983年 | 16698篇 |
1982年 | 13314篇 |
1981年 | 11915篇 |
1980年 | 11352篇 |
1979年 | 18591篇 |
1978年 | 14769篇 |
1977年 | 13438篇 |
1976年 | 12660篇 |
1975年 | 13763篇 |
1974年 | 14851篇 |
1973年 | 14742篇 |
1972年 | 13344篇 |
1971年 | 12395篇 |
1970年 | 10620篇 |
1969年 | 10114篇 |
1968年 | 9052篇 |
1967年 | 8101篇 |
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
991.
992.
993.
Thirteen polymorphic microsatellite loci were developed for blowflies for use in studies of genetic differentiation in wild populations of Lucilia illustris, to detect the possible occurrence of bottlenecks and to study changes in genetic variation in laboratory populations of Lucilia sericata following artificial bottlenecks. In this preliminary study it was revealed that heterozygosity was lower than expected in wild populations and genetic variation had been lost in the laboratory population despite being kept at a large size. 相似文献
994.
995.
996.
Orthostatic reflexes were examined at 375 m and after 60 min of exposure in a hypobaric chamber at 3660 m using a 20-min 70 degrees head-up tilt (HUT) test. Mean arterial blood pressure, R wave-R wave interval (RRI), and mean cerebral blood flow velocity (MFV) were examined with coarse-graining spectral analysis. Of 14 subjects, 7 at 375 m and 12 at 3660 m were presyncopal. Immediately on arrival to high altitude, breathing frequency and MFV increased, and endtidal PCO2, RRI, RRI complexity, and the parasympathetic nervous system indicator decreased. MFV was similar in HUT at both altitudes. The sympathetic nervous system indicator increased with tilt at 3660 m, whereas parasympathetic nervous system indicator decreased with tilt at both altitudes. Multiple regression analysis of supine variables from either 375 or 3660 m and the time to presyncope at 3660 m indicated that, after 1 h of exposure, increased presyncope at altitude was the result of 1). ineffective peripheral vasoconstriction, despite increased cardiac sympathetic nervous system activity with HUT, and 2). insufficient cerebral perfusion owing to cerebral vasoconstriction as the result of hypoxic hyperventilation-induced hypocapnia. 相似文献
997.
C Forestier E Moreno J Pizarro-Cerda J P Gorvel 《Journal of immunology (Baltimore, Md. : 1950)》1999,162(11):6784-6791
In this study, we detailed in a time-dependent manner the trafficking, the recycling, and the structural fate of Brucella abortus LPS in murine peritoneal macrophages by immunofluorescence, ELISA, and biochemical analyses. The intracellular pathway of B. abortus LPS, a nonclassical endotoxin, was investigated both in vivo after LPS injection in the peritoneal cavity of mice and in vitro after LPS incubation with macrophages. We also followed LPS trafficking after infection of macrophages with B. abortus strain 19. After binding to the cell surface and internalization, Brucella LPS is routed from early endosomes to lysosomes with unusual slow kinetics. It accumulates there for at least 24 h. Later, LPS leaves lysosomes and reaches the macrophage cell surface. This recycling pathway is also observed for LPS released by Brucella S19 following in vitro infection. Indeed, by 72 h postinfection, bacteria are degraded by macrophages and LPS is located inside lysosomes dispersed at the cell periphery. From 72 h onward, LPS is gradually detected at the plasma membrane. In each case, the LPS present at the cell surface is found in large clusters with the O-chain facing the extracellular medium. Both the antigenicity and heterogenicity of the O-chain moiety are preserved during the intracellular trafficking. We demonstrate that LPS is not cleared by macrophages either in vitro or in vivo after 3 mo, exposing its immunogenic moiety toward the extracellular medium. 相似文献
998.
A. Franz B. Ronacher 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2002,188(4):261-271
The vast majority of animals are poikilotherms, and thus face the problem that the temperature of their nervous systems rather smoothly follows the temperature changes imposed by their environment. Since basic properties of nerve cells, e.g., the time constants of ion channels, strongly depend on temperature, a temperature shift likely affects the processing of the temporal structure of sensory stimuli. This can be critical in acoustic communication systems in which time patterns of signals are decisive for recognition by the receiver. We investigated the temperature dependence of the responses of locust auditory receptors and interneurons by varying the temperature of the experimental animals during intracellular recordings. The resolution of fast amplitude modulations of acoustic signals was determined in a gap detection paradigm. In auditory receptors and local (second order) interneurons, temporal resolution was improved at higher temperatures. This gain could be attributed to a higher precision of spike timing. In a third-order neuron, a rise in temperature affected the interactions of inhibition and excitation in a complex manner, also resulting in a better resolution of gaps in the millisecond range. 相似文献
999.
A phosphotransferase-dependent aryl-β-glucoside uptake and utilisation system (abg) was isolated from the ruminal Clostridium (“C. longisporum”). The system is composed of three genes, abgG, abgF and abgA, and a number of regulatory regions, including terminator/antiterminator type stem-loop structures preceding the abgG and abgF genes. Similarity analysis of the proteins encoded by these genes indicated that they were responsible for the regulation
of the abg system through antitermination (AbgG), the uptake and phosphorylation of aryl-β-glucosides (AbgF) and the hydrolysis of the
intracellular phosphorylated glycosides (AbgA). Experimental evidence for the functions of AbgF and AbgA was obtained. Although
it was not possible to demonstrate any function for AbgG, a promoter 5′ to the abgG gene was identified which was responsible for expression of the downstream genes. The abg system is remarkably similar to operons from the gram negative Enterobacteriaceae, both in the coding and non-coding regulatory
regions.
Received: 3 April 1997 / Accepted: 8 September 1997 相似文献
1000.
Liposomes composed of soybean phosphatidylcholine were peroxidized using the reagent sodium hypochlorite or the myeloperoxidase-hydrogen peroxide-Cl- system. Linoleic acid hydroperoxide previously prepared from linoleic acid by means of lipoxidase was incorporated into liposomes. The yield of thiobarbituric acid reactive substances (TBARS) continuously increased with higher amounts of hydroperoxide groups after the initiation of lipid peroxidation by hypochlorous acid producing systems. The accumulation of TBARS was inhibited by scavengers of free radicals such as butylated hydroxytoluene and by the scavengers of hypochlorous acid, taurine and methionine. Lipid peroxidation was also prevented by sodium azide or chloride free medium in the myeloperoxidase-hydrogen peroxide-Cl- system. Here we show for the first time that the reaction of hypochlorous acid with a biologically relevant hydroperoxide yields free radicals able to cause further oxidation of lipid molecules. 相似文献