全文获取类型
收费全文 | 822篇 |
免费 | 87篇 |
国内免费 | 2篇 |
出版年
2022年 | 3篇 |
2021年 | 12篇 |
2020年 | 5篇 |
2019年 | 9篇 |
2018年 | 11篇 |
2017年 | 9篇 |
2016年 | 15篇 |
2015年 | 31篇 |
2014年 | 40篇 |
2013年 | 51篇 |
2012年 | 58篇 |
2011年 | 51篇 |
2010年 | 32篇 |
2009年 | 30篇 |
2008年 | 55篇 |
2007年 | 47篇 |
2006年 | 44篇 |
2005年 | 38篇 |
2004年 | 57篇 |
2003年 | 40篇 |
2002年 | 41篇 |
2001年 | 11篇 |
2000年 | 6篇 |
1999年 | 16篇 |
1998年 | 24篇 |
1997年 | 4篇 |
1996年 | 6篇 |
1995年 | 8篇 |
1994年 | 10篇 |
1993年 | 15篇 |
1992年 | 10篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 12篇 |
1986年 | 11篇 |
1985年 | 10篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1977年 | 6篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1970年 | 2篇 |
1969年 | 2篇 |
排序方式: 共有911条查询结果,搜索用时 78 毫秒
881.
Abstract ATP levels of three marine isolates (a Vibrio sp., Serratia marcescens , and an unidentified rodshaped organism) were measured during nutrient-limiting conditions for free-living bacteria or cells adhered to a glass/liquid interface. In all strains there was a higher content of ATP per biovolume (numbers × cell volume) for cells starved at the glass/liquid interface compared with those in the bulk phase. Leakage from viable cells and the formation of a conditioning film are suggested only partly to explain the elevated levels of ATP per biovolume at the surface. 相似文献
882.
HuanJun Li Yu-Jin Kim Liu Yang Ze Liu Jie Zhang Haotian Shi Guoqiang Huang Staffan Persson Dabing Zhang Wanqi Liang 《The Plant cell》2020,32(12):3961
The highly variable and species-specific pollen surface patterns are formed by sporopollenin accumulation. The template for sporopollenin deposition and polymerization is the primexine that appears on the tetrad surface, but the mechanism(s) by which primexine guides exine patterning remain elusive. Here, we report that the Poaceae-specific EXINE PATTERN DESIGNER 1 (EPAD1), which encodes a nonspecific lipid transfer protein, is required for primexine integrity and pollen exine patterning in rice (Oryza sativa). Disruption of EPAD1 leads to abnormal exine pattern and complete male sterility, although sporopollenin biosynthesis is unaffected. EPAD1 is specifically expressed in male meiocytes, indicating that reproductive cells exert genetic control over exine patterning. EPAD1 possesses an N-terminal signal peptide and three redundant glycosylphosphatidylinositol (GPI)-anchor sites at its C terminus, segments required for its function and localization to the microspore plasma membrane. In vitro assays indicate that EPAD1 can bind phospholipids. We propose that plasma membrane lipids bound by EPAD1 may be involved in recruiting and arranging regulatory proteins in the primexine to drive correct exine deposition. Our results demonstrate that EPAD1 is a meiocyte-derived determinant that controls primexine patterning in rice, and its orthologs may play a conserved role in the formation of grass-specific exine pattern elements. 相似文献
883.
Crystal structures of membrane lipids. 总被引:13,自引:0,他引:13
884.
885.
Abstract Starvation for different individual nutrients revealed various morphotypes of Vibrio sp. strain S14. Carbon or multiple-nutrient starved cells formed ultramicrocells with low respiratory activity and high culturability. In contrast, cells starved for nitrogen or phosphorus formed filaments or swollen rods with large inclusion bodies of PHB. These cells exhibited a 3–4 log decrease in culturability, nevertheless many were actively respiring and direct viable counts equalled at least 80% of the original number of cells. After 2–3 days of prolonged incubation, microcolonies appeared at approximately the same number of cells as at the onset of starvation. A nutrient-induced increase in respiratory activity, after 120 h of starvation, was instantaneous for cells starved for carbon or multiple-nutrients, but cells depleted of nitrogen or phosphorus exhibited a lag period of at least 3 h. 相似文献
886.
887.
Staffan Tamm 《Behavioural processes》1977,2(3):293-299
Social hierarchy was studied in two flocks (14 and 10 individuals, respectively) of captive jackdaws. Parent birds acquired high-ranking positions during the nesting period. Outside the breeding season the hierarchy seemed to be stable. Males generally dominated females. When the top-ranking male arrived at the feeding place it tended to supplant one of the feeding birds rather than choose an unoccupied site. 相似文献
888.
Anna K Jönsson Olav Spigset Micaela Tjäderborn Henrik Druid Staffan Hägg 《BMC clinical pharmacology》2009,9(1):7-5
Background
Pharmaceutical drug poisonings have previously been reported using single sources of information, either hospital data or forensic data, which might not reveal the true incidence. We therefore aimed to estimate the incidence of suspected fatal drug poisonings, defined as poisonings by pharmaceutical agents, by using all relevant case records from various sources in a Swedish population. 相似文献889.
Pulmonary response to group B streptococcal toxin in young lambs 总被引:1,自引:0,他引:1
Sandberg K.; Engelhardt B.; Hellerqvist C.; Sundell H. 《Journal of applied physiology》1987,63(5):2024-2030
Marked respiratory distress is seen in severe early onset group B beta-hemolytic streptococcal (GBS) disease in newborn infants. To investigate the pathophysiological effects of a polysaccharide toxin from GBS type III cultures, obtained from an infant who died from this disease, young chronically instrumented, unanesthetized lambs were studied with measurements of lung mechanics, lung volumes, ventilation, hemodynamics, and lung vascular permeability. Intravenously administered GBS toxin resulted in a biphasic response with an early threefold increase in total lung resistance, 40% decrease in dynamic lung compliance, and 30% increase in minute ventilation coinciding with hypoxemia, pulmonary hypertension, and fever. A second phase of the response followed consisting of less prominent changes in these variables as well as increased lung lymph protein clearance compatible with increased vascular permeability. The temporal close relationship between marked leukopenia and increased lung lymph thromboxane B2 concentrations to the simultaneously occurring pulmonary hypertension and changes in lung mechanics suggests that leukocytes and thromboxane A2 may be mediators of these GBS toxin-induced effects. 相似文献
890.
Dryas octopetala has heliotropic flowers, whose petals reflect the light on the pistils, thus warming them up. The effects of this reflection on seed formation and development were studied by measuring the pistil temperature of intact flowers, of flowers with petals removed, of shaded flowers, and of flowers constrained in such a way as always to be directed towards the zenith. In August, the seeds of these flowers were collected, counted and weighed. The temperature differences between the differently treated flowers were greates about noon, the flowers ranking as follows in ascending order of temperature: shaded flowers, flowers without petals, constrained flowers and intact flowers. The mean temperature differences between the gynoecia and the air, in degrees Celsius, were: 1.1, 1.8, 2.5 and 3.2, respectively. The same ranking was obtained for the different treatments, when arranged in order of ascending weight per seed, except that the positions of the shaded flowers and the flowers without petals were interchanged. The mean values of the weight per seed in milligrams were: 0.42, 0.48, 0.53 and 0.61 for the groups flowers without petals, shaded flowers, constrained flowers and intact flowers, respectively. 相似文献