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991.
992.
Changes in the level of 1-(malonylamino)-cyclopropane-1-carboxylic acid (MACC) were determined in 6 winter wheat cultivars during cold hardening at 4°C. The cultivars differed by one degree of frost resistance within the range of degree II to VII of the COMECON scale. The time-course of changes in MACC level showed a similar pattern in all 6 cultivars; i.e. increase till day 6, no changes for the next 10 days, and then a steady decrease till the end of the hardening period. There was little difference between the final and the initial levels. The increase of MACC level, expressed as per cent of the original level, was not directly correlated with either the degree of frost resistance of the actual percentage of survival. In some cultivars. mean errors exceeded the difference in MACC accumulation between cultivars closest on the resistance scale.
The fate of MACC during the second half of hardening and after transfer of plants to 25°C was studied in cultivars Bezostaya and San Pastore. During the second half of the hardening period the level of MACC decreased in the leaves of both cultivars, but increased significantly in the roots. Within two days of transfer of the hardened plants to 25°C, the MACC level in leaves increased again, while that in the roots decreased. This finding, together with the preliminary evidence of very low MACC metabolism, strongly suggest that MACC accumulates in roots during the hardening period and when transferred to 25°C, it moves from roots to leaves. 相似文献
The fate of MACC during the second half of hardening and after transfer of plants to 25°C was studied in cultivars Bezostaya and San Pastore. During the second half of the hardening period the level of MACC decreased in the leaves of both cultivars, but increased significantly in the roots. Within two days of transfer of the hardened plants to 25°C, the MACC level in leaves increased again, while that in the roots decreased. This finding, together with the preliminary evidence of very low MACC metabolism, strongly suggest that MACC accumulates in roots during the hardening period and when transferred to 25°C, it moves from roots to leaves. 相似文献
993.
Shoots of two species of moss, Plagiomnium undulatum (Hedw.) Kop. and Plagiomnium affine (Funck) Kop., were subjected to freezing at various temperatures. After thawing, the activities of different photosynthetic reactions were determined in relation to the ages of the leaves. Analysis of the fast kinetics of chlorophyll-a fluorescence of individual leaves showed that young and old tissues were considerably less frost tolerant than mature ones. In principle, the pattern of freeze inactivation of photosynthetic reactions resembles that observed in higher plants. The decreases in the amplitude of Fv (variable fluorescence) and the ratio of Fv to Fm (maximum fluorescence) with increasing freezing stress reflect a progressive inactivation of photosystem II (PSII)-mediated electron transport, i.e. inhibition of photoreaction to photochemistry and-or electron donation to the photochemical reaction, and thus a decline in the potential photochemical efficiency of PSII. The insignificant change in the F0 (constant fluorescence) level during progressive decline of Fv indicates that the excitation-energy transfer between antenna pigments and from those to reaction centres of PSII was little impaired by lethal freezing stress. Sugar analyses of various stem sections showed that ontogenetic variation in the frost tolerance of leaves cannot be attributed to differences in the cellular levels of sucrose, glucose and fructose.Abbreviations and Symbols DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- Fm
maximum fluorescence
- F0
constant (initial) fluorescence
- Fv
variable fluorescence 相似文献
994.
An iduronate-rich dermatan sulphate fraction was found to contain variants with high affinity for human low density lipoprotein. Digestion of a dermatan sulphate-lipoprotein complex with chondroitinase-ABC afforded fragments that contained between 10 and 20 disaccharide repeats. In this fragment half of the uronate residues were iduronate-sulphate. The non-sulphated iduronate-bearing repeats were interspersed among the repeats containing sulpho-iduronate. This feature is similar to that observed with heparin-related glycans having high affinity for lipoproteins. 相似文献
995.
WILLIAM BLOCK 《Ecological Entomology》1982,7(1):1-8
Abstract. 1. Mean supercooling points of eleven species of arthropods (three Collembola, seven Acari and one Diptera) ranged from -6.2 to -9.4°C (high group), and from -17.7 to -31.0°C (low group). The majority of individuals in the high group had food in their gut systems.
2. Freezing was lethal to all species examined except larval Belgica antarctica Jacobs (Chironomidae).
3. Glucose, glycerol and mannitol were found in low concentrations in extracts of Ctyptopygus antarcticus Willem (Collembola) and larvae of B. antarcrica; it is udikely that these substances had a major effect on the supercooling of either species.
4. Two Collembola species possessed significantly ( P< 0.05) lower supercooling points at locations on the Antarctic Pensinsula than at Signy Island, South Orkney Islands. The converse was observed for two species of Acari.
5. It is suggested that whilst gross climatic and also micro-habitat conditions may influence the cold hardiness of such arthropods, especially seasonally, their full supercooling ability is rarely tested. 相似文献
2. Freezing was lethal to all species examined except larval Belgica antarctica Jacobs (Chironomidae).
3. Glucose, glycerol and mannitol were found in low concentrations in extracts of Ctyptopygus antarcticus Willem (Collembola) and larvae of B. antarcrica; it is udikely that these substances had a major effect on the supercooling of either species.
4. Two Collembola species possessed significantly ( P< 0.05) lower supercooling points at locations on the Antarctic Pensinsula than at Signy Island, South Orkney Islands. The converse was observed for two species of Acari.
5. It is suggested that whilst gross climatic and also micro-habitat conditions may influence the cold hardiness of such arthropods, especially seasonally, their full supercooling ability is rarely tested. 相似文献
996.
A. J. Lawson J. K. Gong K. R. Case D. M. Gersten H. B. Bosmann 《Cell biochemistry and biophysics》1982,4(1):47-61
Circulating erythrocytes from rats were examined up to 30 weeks post whole-body exposures of 1.0 R for alterations in the
expression of net negative surface charge as measured by whole-cell microelectrophoresis in saline sorbitol. Erythrocyte electrophoretic
mobility was determined in an apparatus composed of a horizontal transilluminated cylindrical chamber, equipped with a reversible,
blacked platinum electrode, immersed in a water bath maintained at 25.0±0.1°C (Rank Brothers). In two separate experiments,
recurrent decreases in the expression of net negative surface charge occurred at 10, 17, and 30 weeks post-irradiation. At
these times distribution analyses of recorded erythrocyte electrophoretic mobility (EEPM) values revealed a skewing of the
normally distributed EEPM population values to lower EEPM. Total sialic acid content released from hydrolyzed erythrocyte
membrane preparations revealed no significant differences between erythrocytes from sham and irradiated animals. In vivo post-irradiation
labeling of erythrocytes with diisopropyl-[32P] phosphorofluoridate at 4 and 33 weeks (separate experiments) indicated only a minor abbreviated erythrocyte life span at
33 weeks. Therefore, effects from low dose (1.0 R) whole-body irradiation would appear to include a recurrent defect in the
expression of the net negative surface charge. 相似文献
997.
Nonenzymatic galactosylation of human LDL decreases its metabolism by human skin fibroblasts 总被引:1,自引:0,他引:1
J Sasaki V Arora G L Cottam 《Biochemical and biophysical research communications》1982,108(2):791-796
Incubation of human LDL with galactose in vitro resulted in a glycosylated-LDL containing radiolabel covalently attached to apo B. The rate of radiolabel incorporation was proportional to the time of incubation and concentration of carbohydrate. The rate of incorporation of galactose into apo B was higher than with glucose or mannose. The nonenzymatic glycosylation of LDL decreased its uptake and metabolism by the high affinity, receptor dependent process for LDL in normal human skin fibroblasts. 相似文献
998.
Apolipoprotein-E degradation in human very low density lipoproteins by plasma protease(s): chemical and biological consequences 总被引:1,自引:0,他引:1
W A Bradley E B Gilliam A M Gotto S H Gianturco 《Biochemical and biophysical research communications》1982,109(4):1360-1367
Serine proteases coisolate with human very low density lipoproteins (VLDL) which degrade apolipoprotein E and cause hypertriglyceridemic VLDL to lose the ability to interact with the LDL receptor of human skin fibroblasts. We identified proteolytic fragments of apolipoprotein-E in isolated VLDL which can be produced by the action of thrombin on purified apoE. There are two major thrombin cleavage products: Mr ~ 22,000 (E-22) and Mr ~ 12,000 (E-12), the N- and C-terminal fragments, respectively, of apoE. We conclude that the structural integrity and the ability of VLDL to interact with cell receptors are a function of not only VLDL constituents but also of the extent to which VLDL apoprotein E has been degraded. 相似文献
999.
Summary Seedlings of a broad based population of alfalfa, (Medicago sativa L.), were visually selected for 2 generations (cycles) in an acid Cecil soil (pH=4.8). Simultaneously, 2 generations of selections
were made in a limed Cecil soil (pH=6.2) amended with phosphorus.
When tested in acid soil (pH=4.8) with added P, the cycle 2 acid selections yielded significantly more top yield than either
the limed selections or the original seed. When grown in the limed soil (pH=6.2) without added P, the acid selections yielded
significantly less. There were no significant differences among selections in other soil conditions (pH=4.8, no P added and
pH=6.2, P added). Root weight and length and nodule fresh weight correlated well with top yield in all treatments.
The yield of the 10 parent varieties and polycrossed seed of their cycle 1 acid and cycle 1 limed selections were compared
under two soil conditions (acid and limed). The results of this test indicate that some varieties were more responsive to
acid soil selection than other. Overall, none of the 10 varieties showed any decreases in total top yield due to one cycle
of selection in either the acid or limed soil conditions. 相似文献
1000.