全文获取类型
收费全文 | 2197篇 |
免费 | 158篇 |
出版年
2023年 | 7篇 |
2022年 | 26篇 |
2021年 | 46篇 |
2020年 | 34篇 |
2019年 | 51篇 |
2018年 | 49篇 |
2017年 | 54篇 |
2016年 | 72篇 |
2015年 | 107篇 |
2014年 | 106篇 |
2013年 | 151篇 |
2012年 | 187篇 |
2011年 | 135篇 |
2010年 | 125篇 |
2009年 | 88篇 |
2008年 | 118篇 |
2007年 | 114篇 |
2006年 | 127篇 |
2005年 | 91篇 |
2004年 | 98篇 |
2003年 | 73篇 |
2002年 | 86篇 |
2001年 | 41篇 |
2000年 | 52篇 |
1999年 | 23篇 |
1998年 | 24篇 |
1997年 | 20篇 |
1996年 | 15篇 |
1995年 | 22篇 |
1994年 | 17篇 |
1993年 | 18篇 |
1992年 | 23篇 |
1991年 | 18篇 |
1990年 | 16篇 |
1989年 | 15篇 |
1988年 | 14篇 |
1987年 | 9篇 |
1986年 | 10篇 |
1985年 | 11篇 |
1983年 | 4篇 |
1981年 | 6篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1974年 | 3篇 |
1973年 | 5篇 |
1972年 | 5篇 |
1971年 | 7篇 |
1969年 | 4篇 |
1968年 | 6篇 |
1966年 | 4篇 |
排序方式: 共有2355条查询结果,搜索用时 484 毫秒
141.
Erland Bth Montserrat Díaz-Ravia sa Frostegrd Colin D. Campbell 《Applied microbiology》1998,64(1):238-245
The effects of heavy-metal-containing sewage sludge on the soil microbial community were studied in two agricultural soils of different textures, which had been contaminated separately with three predominantly single metals (Cu, Zn, and Ni) at two different levels more than 20 years ago. We compared three community-based microbiological measurements, namely, phospholipid fatty acid (PLFA) analysis to reveal changes in species composition, the Biolog system to indicate metabolic fingerprints of microbial communities, and the thymidine incorporation technique to measure bacterial community tolerance. In the Luddington soil, bacterial community tolerance increased in all metal treatments compared to an unpolluted-sludge-treated control soil. Community tolerance to specific metals increased the most when the same metal was added to the soil; for example, tolerance to Cu increased most in Cu-polluted treatments. A dose-response effect was also evident. There were also indications of cotolerance to metals whose concentration had not been elevated by the sludge treatment. The PLFA pattern changed in all metal treatments, but the interpretation was complicated by the soil moisture content, which also affected the results. The Biolog measurements indicated similar effects of metals and moisture to the PLFA measurements, but due to high variation between replicates, no significant differences compared to the uncontaminated control were found. In the Lee Valley soil, significant increases in community tolerance were found for the high levels of Cu and Zn, while the PLFA pattern was significantly altered for the soils with high levels of Cu, Ni, and Zn. No effects on the Biolog measurements were found in this soil. 相似文献
142.
Cross-fostering technique can be defined as adoption of infants by adults of other species. This phenomenon is poorly investigated because very young animals have few opportunities to interact peacefully with non-conspecific adults, either in captivity or in natural conditions. This study describes the induction of cross-fostering in captivity between white tufted-ear (Callithrix jacchus) and black tufted-ear marmosets (Callithrix penicillata). We conclude that this technique can be very useful for preserving the life of rejected by parents or orphan infants, mainly in the case of species with low reproduction rate in captivity or those threatened by extinction, as well for investigating the environmental effects on the typical behavior of species (courtship, food preference, vocalization patterns, e.g.). 相似文献
143.
Francisco Tadeu Rantin Cecilia Del Rosario Guerra Ana Lúcia Kalinin Mogens Lesner Glass 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》1998,119(4):391
When exposed to severely hypoxic water, many teleosts skim the better oxygenated surface layer (aquatic surface respiration, ASR). Information is scarce concerning the thresholds triggering ASR and its cardio-respiratory consequences. To assess the ambient conditions leading to ASR and to evaluate its effects on cardio-respiratory function, we exposed specimens of Piaractus mesopotamicus to gradual hypoxia (water oxygen tension ranging from 120 to 10 torr) with or, alternatively, without access to the surface. Concurrently, ASR, cardiac and respiratory frequencies, O2 uptake and gill ventilation were monitored. With surface access, ASR developed below the critical tension for O2 uptake (34 torr) by normal gill ventilation. Moreover, the time spent in ASR increased with prolonged hypoxic exposure to a maximum of 95% of total time. Without surface access, the species exhibited hypoxic bradycardia, that had not occurred in the group with fully developed ASR. Even without ASR, P. mesopotamicus recovered readily from hypoxic exposure, showing that this species possesses a number of mechanisms to cope with environmental hypoxia. 相似文献
144.
F. Roch F. Serras F. J. Cifuentes M. Corominas B. Alsina M. Amorós A. López-Varea R. Hernández D. Guerra S. Cavicchi J. Baguñá A. García-Bellido 《Molecular genetics and genomics : MGG》1998,257(2):103-112
We have carried out screens for lethal mutations on the second chromosome of Drosophila melanogaster that are associated with abnormal imaginal disc morphologies, particularly in the wing disc. From a collection of 164 P element-induced mutations with a late larva/pupa lethal phase we have identified 56 new loci whose gene products are required for normal wing disc development and for normal morphology of other larval organs. Genetic mosaics of these 56 mutant lines show clonal mutant phenotypes for 23 cell-viable mutations. These phenotypes result from altered cell parameters. Causal relationships between disc and clonal phenotypes are discussed. 相似文献
145.
Uribe Xavier Torres Miguel Angel Capellades Montserrat Puigdomènech Pere Rigau Joan 《Plant molecular biology》1998,37(6):1069-1078
In the past few years many - and -tubulin genes of different organisms have been cloned and studied, and in most systems studied they constitute multigene families. In plants, most studies have been done in Arabidopsis thaliana and Zea mays. In this paper, the study of mRNA accumulation by in situ hybridization and the activity of three maize -tubulin gene promoters (tua1, tua2 and tua3) in transgenic tobacco plants are described. In maize, the expression of these three tubulin isotypes differ in the root and shoot apex and is associated with different groups of cells throughout the distinct stages of cell differentiation. In transgenic tobacco plants the promoters of the genes, fused to the uidA reporter gene (GUS), direct expression to the same tissues observed by in situ hybridization experiments. The tua1 promoter is mainly active in cortex-producing meristematic cells and in pollen, whereas tua3 is active in cells which are differentiating to form vascular bundles in the root and shoot apices. The accumulation of tua2 mRNA is detected by RNA blot in a similar form as tua1, but at a very much low level. In situ hybridization indicates that the tua2 mRNA specifically accumulates in the maize root epidermis. No GUS staining was detected in transgenic tobacco plants with the tua2 promoter. The difference in expression of the specific genes may be linked to processes where microtubules have different functions, suggesting that in plants, as in animals, there are differences in the function of the tubulin isotypes. 相似文献
146.
S Cavicchi D Guerra V Natali G Giorgi C Pezzoli L Villani 《Developmental genetics》1989,10(5):386-392
An analysis of the modifiers affecting the expression of the vg gene was performed. We selected for weak and strong expression of the vg mutant in F2 segregating populations obtained by crossing a vestigial stock with an Oregon laboratory stock (O) and with a wild strain (B) captured near Bologna, Italy. The selection for enlarged wings was more effective in the vg B population where wild wings appeared from the 10th generation. The assay of the three major chromosomes showed that the modifiers are located on chromosomes 2 and 3. The mutant imaginal disc cell death phenotype is evident in vg/vg strains that have a wild-type wing phenotype. It is suggested that the selected modifiers do not prevent cell death but induce regenerative growth. 相似文献
147.
Dionizio Ramos-Filho Gustavo Chicaybam Eduardo de-Souza-Ferreira Camila Guerra Martinez Eleonora Kurtenbach Gustavo Casimiro-Lopes Antonio Galina 《PloS one》2015,10(6)
High intensity interval training (HIIT) is characterized by vigorous exercise with short rest intervals. Hydrogen peroxide (H2O2) plays a key role in muscle adaptation. This study aimed to evaluate whether HIIT promotes similar H2O2 formation via O2 consumption (electron leakage) in three skeletal muscles with different twitch characteristics. Rats were assigned to two groups: sedentary (n=10) and HIIT (n=10, swimming training). We collected the tibialis anterior (TA-fast), gastrocnemius (GAST-fast/slow) and soleus (SOL-slow) muscles. The fibers were analyzed for mitochondrial respiration, H2O2 production and citrate synthase (CS) activity. A multi-substrate (glycerol phosphate (G3P), pyruvate, malate, glutamate and succinate) approach was used to analyze the mitochondria in permeabilized fibers. Compared to the control group, oxygen flow coupled to ATP synthesis, complex I and complex II was higher in the TA of the HIIT group by 1.5-, 3.0- and 2.7-fold, respectively. In contrast, oxygen consumed by mitochondrial glycerol phosphate dehydrogenase (mGPdH) was 30% lower. Surprisingly, the oxygen flow coupled to ATP synthesis was 42% lower after HIIT in the SOL. Moreover, oxygen flow coupled to ATP synthesis and complex II was higher by 1.4- and 2.7-fold in the GAST of the HIIT group. After HIIT, CS activity increased 1.3-fold in the TA, and H2O2 production was 1.3-fold higher in the TA at sites containing mGPdH. No significant differences in H2O2 production were detected in the SOL. Surprisingly, HIIT increased H2O2 production in the GAST via complex II, phosphorylation, oligomycin and antimycin by 1.6-, 1.8-, 2.2-, and 2.2-fold, respectively. Electron leakage was 3.3-fold higher in the TA with G3P and 1.8-fold higher in the GAST with multiple substrates. Unexpectedly, the HIIT protocol induced different respiration and electron leakage responses in different types of muscle. 相似文献
148.
149.
150.