全文获取类型
收费全文 | 1028篇 |
免费 | 107篇 |
出版年
2023年 | 5篇 |
2021年 | 21篇 |
2020年 | 11篇 |
2019年 | 12篇 |
2018年 | 18篇 |
2017年 | 19篇 |
2016年 | 31篇 |
2015年 | 47篇 |
2014年 | 59篇 |
2013年 | 70篇 |
2012年 | 86篇 |
2011年 | 71篇 |
2010年 | 39篇 |
2009年 | 40篇 |
2008年 | 55篇 |
2007年 | 61篇 |
2006年 | 58篇 |
2005年 | 52篇 |
2004年 | 59篇 |
2003年 | 43篇 |
2002年 | 46篇 |
2001年 | 13篇 |
2000年 | 8篇 |
1999年 | 13篇 |
1998年 | 17篇 |
1997年 | 13篇 |
1995年 | 12篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1984年 | 6篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1979年 | 8篇 |
1976年 | 3篇 |
1974年 | 4篇 |
1972年 | 3篇 |
1969年 | 5篇 |
1966年 | 7篇 |
1961年 | 3篇 |
1960年 | 3篇 |
1937年 | 3篇 |
1936年 | 4篇 |
1935年 | 4篇 |
1931年 | 3篇 |
排序方式: 共有1135条查询结果,搜索用时 18 毫秒
11.
Uptake of 24Mg by excised pine roots: A preliminary study 总被引:1,自引:0,他引:1
Uptake of 24Mg by excised roots of Pinus sylvestris L. during up to 4 h long incubations in 99.9 atom % 24Mg (50 M) was measured by ICP-MS. A rapid initial uptake phase (30 min) was followed by a slower uptake. This was interpreted as a shift from a phase dominated by saturable ion exchange (free space uptake), to a non-saturable phase, during which the rate of uptake was 0.077±0.0.012 mol Mg g–1 (d.wt.) h–1. The metabolic uncoupler DNP (2,4-dinitrophenol) at 50 M decreased the Mg uptake rate by 35% only, but the effect of DNP was significant (p<0.01). Several problems related to a high variability in the experimental material were encountered, and further refinement of this approach in studies of plant Mg uptake is suggested. 相似文献
12.
The taxonomic importance of fatty acid composition at genus and sub-genus level was evaluated by analysing the fatty acid
composition of fourteen different Microcystis isolates and seven additional members of the order Chroococcales. Fatty acid composition proved to be consistent within isolates.
Isolates were clustered into two major groups, namely A and B. Group B contained all the Microcystis isolates and was further divided into subgroups of varying similarity indicating the existence of different taxa. The Microcystis isolates were characterised by a high content of polyunsaturated fatty acids (27–44%) and a low content of palmitoleate.
The test organisms were arranged in a scheme indicating their possible phylogenetic relationship based on fatty acid composition
and other phenotypic characteristics. According to our data the toxic strains, represented by different isolates, of Microcystis appear as a distinct group. Furthermore two dubious species namely Microcystis incerta and a Synechocystis sp. could clearly be reasigned to different genera. The results demonstrated that fatty acid composition is an effective
taxonomic tool in clarifying taxonomical problems of Microcystis isolates.
Department of Microbiology, University of the Orange Free State 相似文献
13.
Factors involved in capillary growth in the heart 总被引:6,自引:0,他引:6
Olga Hudlická Margaret D. Brown Helene Walter Jacqueline B. Weiss Anita Bate 《Molecular and cellular biochemistry》1995,147(1-2):57-68
Growth of capillaries in the heart occurs under physiological circumstances during endurance exercise training, exposure to high altitude and/or cold, and changes in cardiac metabolism or heart rate elicited by modification of thyroid hormone levels. Capillary growth in all these conditions can be linked with increased coronary blood flow, decreased heart rate, or both. This paper brings evidence that, although increased blood flow due to long-term administration of coronary vasodilators results in capillary growth, a long-term decrease in heart rate induced by electrical bradycardial pacing in rabbits and pigs, or by chronic administration of a bradycardic drug, alinidine, in rats, stimulates capillary growth with little or no change in coronary blood flow. Decreased heart rate results in increased capillary wall tension, increased end-diastolic volume and increased force of contraction, and thus stretch of the capillary wall. This could lead to release of various growth factors possibly stored in the capillary basement membrane. Correlation was found between capillary density (CD) and the levels of low molecular endothelial cell stimulating angiogenic factor (ESAF) both in rabbit and pig hearts with CD increased by pacing. There was no relation between expression of mRNA for basic fibroblast growth factor and CD in sham-operated and paced rabbit hearts. In contrast, mRNA for TGFß was increased in paced hearts, and the possible role of this factor in the regulation of capillary growth induced by bradycardia is discussed. 相似文献
14.
Probiotic effect of lactic acid bacteria in the feed on growth and survival of fry of Atlantic cod (Gadus morhua) 总被引:17,自引:0,他引:17
A growing concern for the high consumption of antibiotics in aquaculture has initiated a search for alternative methods of
disease control. Improved resistance against infectious diseases can be achieved by the use of probiotics. Probiotics are
live microorganisms supplemented in food or feed which give beneficial effects on the intestinal microbial balance. In the
present study a dry feed containing lactic acid bacteria (Carnobacterium divergens) isolated from Atlantic cod (Gadus morhua)intestines
was given to cod fry. After three weeks of feeding the fry was exposed to a virulent strain of Vibrio anguillarum. The death
rate was recorded during further three weeks of feeding with lactic acid bacteria supplemented feed. A certain improvement
of disease resistance was obtained, and at the end of the experiment lactic acid bacteria dominated the intestinal flora in
surviving fish given feed supplemented with lactic acid bacteria. No obvious growth inhibition of V. anguillarum was observed
in an in vitro mixed culture of this bacterium and the C. divergens isolated from cod intestines.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
15.
16.
Stefanie Possekel Anne Lombes Helene Ogier de Baulny Marie-Arnelle Cheval Michel Fardeau Bernhard Kadenbach Norma B. Romero 《Histochemistry and cell biology》1995,103(1):59-68
Despite the demonstration of a clear biochemical defect, the genetic alterations causing childhood forms of cytochromec oxidase (COX) deficiency remain unknown. The double genetic origin (nuclear and mitochondrial DNA), and the complexity of COX enzyme structure and regulation, indicate the need for genetic iinvestigations of the molecular structure of individual COX subunits. In the present study a new monoclonal antibody, which reacts exclusively with heart-type human COX subunit VIIa (VIIa-H), and other monoclonal antibodies against human COX subunits, were used in the immunohistochemical analysis of skeletal muscle from children with different forms of mitochondrial myopathy with COX deficiency. By immunohistochemical investigation a normal reaction was seenn with antibodies to COX subunits IV, Va+Vb, and VIa+VIc in all four cases, and in two cases with antibodies to COX VIIa-H and VIIa+VIIb. In muscle from a fatal infantile case with cardiac and skeletal muscle involvement, no immunohistochemical reaction was seen with the monoclonal antibody against the tissue-specific subunit VIIa-H. In muscle from an 11-year-old boy with exclusive muscular symptoms and signs, immunohistological reactions were absent with COX subunit VIIa-H and COX subunits VIIa+VIIb, and slightly decreased with COX subunit II, thus demonstrating a different molecular mechanism in each case. It is concluded that the molecular basis of COX deficiency in childhood may vary greatly between patients. 相似文献
17.
The wide-ranging neuronal actions of excitatory amino acids, such as glutamate, are thought to be mediated mainly by postsynaptic N-methyl-D-aspartate (NMDA) and non-NMDA receptors. We now report the existence of presynaptic glutamate receptors in isolated nerve terminals (synaptosomes) prepared from hippocampus, olfactory bulb, and cerebral cortex. Activation of these receptors by NMDA or non-NMDA agonists, in a concentration-dependent manner, resulted in Ca(2+)-dependent release of noradrenaline from vesicular transmitter stores. The NMDA-stimulated release was potentiated by glycine and was blocked by Mg2+ and selective NMDA antagonists. In contrast, release stimulated by selective non-NMDA agonists was blocked by 6-cyano-7-nitroquinoxaline-2,3- dione, but not by Mg2+ or NMDA antagonists. Our data suggest that the presynaptic glutamate receptors can be classified pharmacologically as both the NMDA and non-NMDA types. These receptors, localized on nerve terminals of the locus ceruleus noradrenergic neurons, may play an important role in interactions between noradrenaline and glutamate. 相似文献
18.
Pilar Galan Helene Thibault Paul Preziosi Serge Hercberg 《Biological trace element research》1992,32(1-3):421-426
The relationship between iron status and capacity for IL-2 production by lymphocytes was assessed in 81 children from 6 mo
to 3 yr of age selected at random from a population with low socioeconomic status, undergoing free systematic examination
in four children's health centers in the Paris area. Iron deficiency was defined by the existence of at least two abnormal
values among the three indicators of iron status: serum ferritin level ≤12 μg/L, transferrin saturation <12%, and erythrocyte
protoporphyrin concentration >3 μg/g hemoglobin. According to this definition, 53 children were classified as iron deficient
and 28 as iron sufficient. No differences were observed between the iron-deficient and iron-sufficient groups in terms of
the IL-2 concentration without stimulation by PHA. IL-2 production by lymphocytes stimulated with PHA, as well as the stimulation
index (ratio of IL-2 concentration following stimulation by PHA to that of IL-2 concentration without stimulation by PHA)
were significantly lower in iron-deficient children. The reduction in IL-2 production by activated lymphocytes observed in
our study of iron-deficient children may be responsible for impairments in immunity found by other authors, particularly in
cell-mediated immunity. 相似文献
19.
Abla A. Creasey Helene S. Smith Adeline J. Hackett Kimie Fukuyama William L. Epstein Stewart H. Madin 《In vitro cellular & developmental biology. Plant》1979,15(5):342-350
Summary Three human melanoma cell lines derived from one primary and two metastatic tumors from three different patients were characterized
for growth properties usually associated with malignant transformation; these include cell morphology, growth rate, saturation
density, growth in semisolid media, colony-forming ability on contact-inhibited monolayers of normal fibroblasts and epithelial
cells, and tumorigenicity in immunosuppressed mice. Variations in expression of aberrant properties were evident among the
lines. One of the metastatic lines satisfied all the parameters of malignancy tested and the other showed a number of these
properties, whereas the primary essentially fulfilled only one. These results suggest that cultured melanoma cells reflect
the clinical variability often observed among melanoma patients and the metastatic melanoma seems to display a higher degree
of malignant transformation than the primary.
THis work was supported in part by USPHS Grant No. 5 T01 AI00332-06 from the National Institutes of Health, Contract E73-2001-N01-CP-3-3237
from the Virus Cancer Program of the National Cancer Institute, and USPHS Grant No. 0H00714-02 from the National Institute
for Occupational Safety and Health. 相似文献
20.
Drought‐stress and plant resistance affect herbivore performance and proteome: the case of the green peach aphid Myzus persicae (Hemiptera: Aphididae) 下载免费PDF全文
Jaime A. Verdugo Marie‐Helene Sauge Jean‐Philippe Lacroze Frederic Francis Claudio C. Ramirez 《Physiological Entomology》2015,40(4):265-276
Little is known about the simultaneous effects of drought stress and plant resistance on herbivorous insects. By subjecting the green peach aphid Myzus persicae Sulzer to well‐watered and drought‐stressed plants of both susceptible and resistant peach (Prunus persica), the effects of both stressors on aphid performance and proteomics are tested. Overall, the influence of the water treatment on aphid performance is less pronounced than the effect of host plant genetic resistance. On the susceptible cultivar, aphid survival, host acceptance and ability to colonize the plant do not depend on water treatment. On the resistant cultivar, aphid survival and ability to colonize are higher on drought‐stressed than on well‐watered plants. A study examining the pattern of protein expression aiming to explain the variation in aphid performance finds higher protein expression in aphids on the drought‐stressed susceptible cultivars compared with the well‐watered ones. In the susceptible cultivar, the regulated proteins are related to energy metabolism and exoskeleton functionality, whereas, in the resistant cultivar, the proteins are involved with the cytoskeleton. Comparison of the protein expression ratios for resistant versus susceptible plants reveals that four proteins are down‐regulated in well‐watered plants and 15 proteins are down‐regulated in drought‐stressed plants. Drought stress applied to the susceptible cultivar induces the regulation of proteins in M. persicae that enable physiological adaptation to maintain an almost unaltered aphid performance. By contrast, for aphids on the resistant cultivar subjected to drought stress, the down‐regulation of proteins responds to an induced host susceptibility effect. 相似文献