全文获取类型
收费全文 | 4770篇 |
免费 | 382篇 |
国内免费 | 2篇 |
专业分类
5154篇 |
出版年
2023年 | 19篇 |
2022年 | 37篇 |
2021年 | 71篇 |
2020年 | 55篇 |
2019年 | 82篇 |
2018年 | 72篇 |
2017年 | 83篇 |
2016年 | 142篇 |
2015年 | 223篇 |
2014年 | 253篇 |
2013年 | 304篇 |
2012年 | 368篇 |
2011年 | 340篇 |
2010年 | 238篇 |
2009年 | 184篇 |
2008年 | 265篇 |
2007年 | 241篇 |
2006年 | 243篇 |
2005年 | 222篇 |
2004年 | 249篇 |
2003年 | 224篇 |
2002年 | 208篇 |
2001年 | 56篇 |
2000年 | 40篇 |
1999年 | 66篇 |
1998年 | 57篇 |
1997年 | 56篇 |
1996年 | 59篇 |
1995年 | 39篇 |
1994年 | 26篇 |
1993年 | 42篇 |
1992年 | 36篇 |
1991年 | 34篇 |
1990年 | 21篇 |
1989年 | 27篇 |
1988年 | 37篇 |
1987年 | 25篇 |
1986年 | 37篇 |
1985年 | 30篇 |
1984年 | 26篇 |
1983年 | 31篇 |
1982年 | 19篇 |
1981年 | 20篇 |
1980年 | 13篇 |
1979年 | 26篇 |
1978年 | 21篇 |
1977年 | 22篇 |
1976年 | 21篇 |
1974年 | 14篇 |
1973年 | 23篇 |
排序方式: 共有5154条查询结果,搜索用时 8 毫秒
81.
Summary To optimize culture conditions and gain a more reliable culturing system for studies of metabolic properties of neuronal cells,
a simplified perfusion chamber was developed. It consists of two parts: a perfusion block and a standard plastic culture dish.
To confirm the suitability of this chamber for continuous culturing of anchorage-dependent cells, the growth and morphology
of the four neuronal cell lines glioma C6 and glioma 138MG, neuroblastoma C1300, clones N1E115 and N18 were followed for 4
d using both traditional and perfusion techniques. A marked increase in growth and a decrease in the degree of morphological
differentiation were obtained with the latter technique compared to the former.
This work was supported by grants from the National Swedish Board for Technical Development (Grant 81-5009), the Swedish Work
Environmental Foundation (Grant 76-53), and Ollie and Elof Ericssons Foundation for Scientific Research. 相似文献
82.
The macrobenthic fauna associated withFucus at a station in the Kiel Fjord was investigated from June 1978 until June 1979. The predominant group in number as well as in biomass were gammarids. They formed, together with the isopodsIdotea spp., approximately 95 % of the total average annual biomass. The total dry weight of all macrobenthic animals (excl.Littorina spp.) increased from 1.9 g per kgFucus in May to about 16 g in June–August, and dropped to 8.3 g in September. Winter average dry weight values were only about 6 % of the summer values. 相似文献
83.
84.
Elevation of Taurine in Hippocampal Extracellular Fluid and Cerebrospinal Fluid of Acutely Hypoosmotic Rats: Contribution by Influx from Blood? 总被引:3,自引:2,他引:1
Anders Lehmann Christian Carlström Erlend A. Nagelhus† Ole Petter Ottersen† 《Journal of neurochemistry》1991,56(2):690-697
Previous work has demonstrated that there is a selective increase in extracellular taurine in the brain during acute water intoxication. One aim of the present study was to investigate whether plasma taurine contributes to this increase. To this end, the concentrations of taurine, other amino acids, and ethanolamine (EA) were measured in plasma and CSF of urethane-anesthetized rats injected with 150 ml/kg body weight of distilled water. Blood pressure, blood gases, and pH, as well as plasma and CSF osmolality, were also measured. The CSF level of albumin was quantitated to study the function of the blood-CSF barrier. In separate experiments, hippocampal microdialysis was performed to determine the effects of acute plasma hypoosmolality on extracellular amino acids. Finally, the effect of water injection on hippocampal specific gravity and tissue amino acids was assessed. Blood gases and pH were essentially unchanged after water administration. Mean arterial blood pressure increased to peak levels approximately 50 mm Hg above control. Plasma osmolality decreased rapidly, whereas the depression of CSF osmolality was slower and less pronounced. The average volume of the hippocampus increased by 8%. Water injection was accompanied by a 25-fold elevation of taurine in plasma, whereas phosphoethanolamine (PEA) and EA increased moderately. A small fraction of the increase in plasma taurine might derive from blood cells because dilution of blood in vitro led to doubled plasma levels of the amino acid. Taurine, PEA, and EA increased consistently in CSF and hippocampal microdialysates. Plasma hypoosmolality transiently opened the blood-CSF barrier is reflected by augmented CSF concentrations of albumin.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
85.
Orchid pollination biology 总被引:1,自引:0,他引:1
Anders Nilsson L 《Trends in ecology & evolution》1992,7(8):255-259
Orchids display many unsurpassed floral specializations, as both rewarders and frauds in their interaction with animal pollinators. Accumulating evidence indicates that their floral evolution is driven by pollinator traits and that expenditure for maximized sexual reproduction is parcelled out over their lifetimes in strategies for coping with pollinator and resource limitations. Recent advances in orchid pollination biology center mainly on floral evolutionary processes, pseudocopulation and other deceptive pollination systems, and flower and fruit production in relation to costs of sexual reproduction. 相似文献
86.
Summary The effective diffusion coefficient of ethanol in a 4 %(w/v) agarose gel at 25°C was measured using a diaphragm diffusion
cell. The reproducibility was very good; a standard deviation of only 2% was obtained. The mean value (9.5×10−6 cm2/s) agreed well with available theory and previous investigations. 相似文献
87.
88.
Graham V. Brown Ross L. Coppel Helena Vrbova Raelene J. Grumont Robin F. Anders 《Experimental parasitology》1982,53(2):279-284
Proteins of erythrocytic stages of Plasmodium falciparum were biosynthetically labeled at different times during the first cycle of in vitro synchronous cultivation after collection from patients in the Madang region of Papua New Guinea. Proteins were immunoprecipitated with a pool of hyperimmune serum collected in the region then analyzed by sodium dodecyl sulfate-gel electrophoresis. Antigens were recognized in all life cycle stages but the majority of antigens, particularly those of high molecular weight, were present in the mature forms of the parasite. 相似文献
89.
Summary The reasons behind the absence of the prawn Palaemon adspersus and the presence of P. squilla in rockpools and on bare sand bottoms were studied. Some maximal abundances in different habitats are given. Introduction experiments into natural and artificial rockpools and measurements of tolerance towards low oxygen levels showed that nocturnal hypoxia excluded P. adspersus which was significantly more sensitive to oxygen depletion. Respiration rates measured by the closed-bottle method showed no interspecific difference.On bare sand bottoms P. aspersus was probably excluded by predators, since predator exclusion experiments in cages and predator inclusion experiments in containers showed that P. adaspersus was more vulnerable to predation than P. squilla.The costs for being able to cope with a wide array of habitat in P. squilla are probably balanced by the benefits of access to habitats such as intertidal rockpools, very shallow bottoms and deeper sand bottoms. Tolerance towards abiotic factors extends its habitat range upwards into shallower waters, and tolerance towards biotic factors, i.e. predation, extends it downwards. 相似文献
90.