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91.
Elevated CO2 and drought alter tissue water relations of birch (Betula populifolia Marsh.) seedlings
The effect of increasing atmospheric CO2 concentrations on tissue water relations was examined in Betula populifolia, a common pioneer tree species of the northeastern U.S. deciduous forests. Components of tissue water relations were estimated from pressure volume curves of tree seedlings grown in either ambient (350 l l–1) or elevated CO2 (700 l l–1), and both mesic and xeric water regimes. Both CO2 and water treatment had significant effects on osmotic potential at full hydration, apoplasmic fractions, and tissue elastic moduli. Under xeric conditions and ambient CO2 concentrations, plants showed a decrease in osmotic potentials of 0.15 MPa and an increase in tissue elastic moduli at full hydration of 1.5 MPa. The decrease in elasticity may enable plants to improve the soil-plant water potential gradient given a small change in water content, while lower osmotic potentials shift the zero turgor loss point to lower water potentials. Under elevated CO2, plants in xeric conditions had osmotic potentials 0.2 MPa lower than mesic plants and decreased elastic moduli at full hydration. The increase in tissue elasticity at elevated CO2 enabled the xeric plants to maintain positive turgor pressures at lower water potentials and tissue water contents. Surprisingly, the elevated CO2 plants under mesic conditions had the most inelastic tissues. We propose that this inelasticity may enable plants to generate a favorable water potential gradient from the soil to the plant despite the low stomatal conductances observed under elevated CO2 conditions. 相似文献
92.
To elucidate how enriched CO2 atmospheres, soil fertility, and light availability interact to influence the long-term growth of tree seedlings, six co-occurring members of temperate forest communities including ash (Fraxinus americana L.), gray birch (Betula populifolia), red maple (Acer rubrum), yellow birch (Betula alleghaniensis), striped maple (Acer pensylvanicum), and red oak (Quercus rubra L.) were raised in a glasshouse for three years in a complete factorial design. After three years of growth, plants growing in elevated CO2 atmospheres were generally larger than those in ambient CO2 atmospheres, however, magnitudes of CO2-induced growth enhancements were contingent on the availability of nitrogen and light, as well as species identity. For all species, magnitudes of CO2-induced growth enhancements after one year of growth were greater than after three years of growth, though species' growth enhancements over the three years declined at different rates. These results suggest that CO2-induced enhancements in forest productivity may not be sustained for long periods of time. Additionally, species' differential growth responses to elevated CO2 may indirectly influence forest productivity via long-term species compositional changes in forests. 相似文献
93.
Seedlings of carob ( Ceratonia siliqua L. cv. Mulata) were used in two sets of experiments in order to evaluate; (1) the reciprocal effects of each nitrogen form on net uptake of nitrate and ammonium, and (2) the effect of earlier nitrogen nutrition on ammonium versus nitrate uptake. In the former group of experiments we studied the kinetics of nitrate and ammonium uptake as well as the interference of each of the two forms with net uptake of ammonium and nitrate by both nitrogen depleted and nitrogen fed carob seedlings. On the whole, nitrogen depletion led to increase in both affinity and Vmax of the system for both forms of nitrogen, at the same time as the effects of nitrate on uptake of ammonium and vice versa were concentration dependent. In the second group of experiments the effects of earlier nitrogen nutrition on nitrate and ammonium uptake were characterized, and in this case we observed that: (a) if only one form of N was supplied, ammonium was taken up in greater amounts than nitrate; (b) the presence of ammonium enhanced nitrate uptake; (c) ammonium uptake was inhibited by nitrate; (d) there was a significant effect of the earlier nitrogen nutrition on the response of the plants to a different nitrogen source. The latter was evident mainly as regards ammonium uptake by plants grown in ammonium nitrate. The interactions between nitrate and ammonium uptake systems are discussed on the basis of the adaptation to the nitrogen source during early growth. 相似文献
94.
Dario Grossberger Anne Marcuz Annette Fichtel Lisbeth Dudler Wayne R. Hein 《Immunogenetics》1993,37(3):222-226
The nucleotide sequences reported in this paper have been submitted to the GenBank database and have been assigned the accession numbers M94181-M94183. 相似文献
95.
96.
Callus cultures from 300 genotypes of alfalfa (Medicago sativa L.) were initiated from leaf, petiole, and internode explants placed on Blaydes medium containing 10.74 M -naphthaleneacetic acid, 11.42 M indole-3-acetic acid, and 9.29 M kinetin. Five genotypes produced somatic embryos. Upon transfer of these embryos to growth regulator-free Murashige and Skoog medium with B5 vitamins, new somatic embryos repeatedly formed directly on older somatic embryos without an intervening callus phase in a cycle lasting about 30 days. These cultures have been maintained for two years, during which time their embryogenic capacity has remained stable. New embryogenic cultures could be started repeatedly from these genotypes. The elimination of sugars from the medium could stop recurrent embryogenesis. Glucose, maltose, and fructose stimulated recurrent embryogenesis more effectively than sucrose. Sucrose was superior to lactose, while sorbitol and mannitol did not stimulate recurrent somatic embryogenesis. The absence of nicotinic acid in the medium, as long as sucrose was present, was lethal to embryos of three of the five tested genotypes. The ability of this system to propagate embryos exponentially offers potential for development of new gene transfer systems and application to artificial seed technology.Abbreviations NAA
-naphthaleneacetic acid
- RSE
recurrent somatic embryogenesis 相似文献
97.
The metabolism of sugar and malic acid by Leuconostoc oenos: effect of malic acid, pH and aeration conditions 总被引:1,自引:1,他引:0
M. Paula Firme M. Cristina Leitão M. Vitória San Romão 《Journal of applied microbiology》1994,76(2):173-181
The co-metabolism of sugars by Leuconostoc oenos was studied under different environmental conditions. Under aerobic conditions, growth and sugar metabolism were poorer than under CO2 or N2 atmosphere and acetic acid accumulated to a larger extent. Glycerol was found in the aerobic cultures while erythritol was detected under N2 or CO2 . When medium conditions make growth difficult (low pH, aerobic conditions, low nutrients), sugars were only slightly metabolized and growth was very slow while malic acid was rapidly and completely degraded, leading to an increase in the y ATP . Aeration effects on the malic acid degradation rate depended on the nutrients and carbon source in the medium. Malic acid clearly stimulated bacterial growth, allowing an increase in the molar growth yields and ATP production. The results suggest that under adverse conditions cells are not able to grow and malic degradation supplies additional energy production. 相似文献
98.
99.
Polarized secretion of IGF-I and IGF-I binding protein activity by cultured aortic endothelial cells
W. Robert Taylor Robert M. Nerem R. Wayne Alexander 《Journal of cellular physiology》1993,154(1):139-142
Insulin-like growth factor-I (IGF-I) secretion by the vascular endothelium has been proposed to play a role in the regulation of vascular smooth muscle cell proliferation. Because vascular smooth muscle cells are adjacent to the abluminal surface of the endothelium, we tested the hypothesis that secretion of IGF-I by endothelial cells is polarized. Porcine aortic endothelial cells were cultured on permeable membranes and IGF-I measured by radioimmunoassay. Basal secretion exceeded apical secretion by a ratio of 2.3 ± 0.2:1.0 (P < 0.05). We also identified 35 kDa IGF-I binding protein activity that is preferentially secreted on the basal surface of endothelial cells. We conclude that both IGF-I and IGF-I binding protein activity secretion by endothelial cells is polarized towards the basal surface of the endothelium. A polarized secretion mechanism for IGF-I may be of importance in the normal growth and differentiation of the vasculature as well as in the development of vascular pathology. © 1993 Wiley-Liss, Inc. 相似文献
100.
Wayne A. Cass Nancy R. Zahniser Karen A. Flach Greg A. Gerhardt 《Journal of neurochemistry》1993,61(6):2269-2278
In vivo electrochemistry was used to investigate the mechanisms contributing to the clearance of locally applied dopamine in the dorsal striatum and nucleus accumbens of urethane-anesthetized rats. Chronoamperometric recordings were continuously made at 5 Hz using Nafion-coated carbon fiber electrodes. When a finite amount of dopamine was pressure-ejected at 5-min intervals from a micropipette adjacent to the electrode, transient and reproducible dopamine signals were detected. Substitution of L-a-methyldopamine, a substrate for the dopamine transporter but not for monoamine oxidase, for dopamine in the micropipette did not substantially alter the time course of the resulting signals. This indicates that metabolism of locally applied dopamine to 3,4-dihydroxyphenylacetic acid is not responsible for the decline in the dopamine signal. Similarly, changing the applied oxidation potential from ±0.45 to ±0.80 V, which allows for detection of 3-methoxytyramine formed from dopamine via catechol-O-methyltransferase, had little effect on signal amplitude or time course. In contrast, lesioning the dopamine terminals with 6-hydroxydopamine, or locally applying the dopamine uptake inhibitors cocaine or nomifensine before pressure ejection of dopamine, significantly increased the amplitude and time course of the dopamine signals in both regions. The effects of cocaine and nomifensine were greater in the nucleus accumbens than in the dorsal striatum. Local application of lidocaine and procaine had no effect on the dopamine signals. Initial attempts at modeling resulted in curves that were in qualitative agreement with our experimental findings. Taken together, these data indicate that (1) uptake of dopamine by the neuronal dopamine transporter, rather than metabolism or diffusion, is the major mechanism for clearing locally applied dopamine from the extracellular milieu of the dorsal striatum and nucleus accumbens, and (2) the nucleus accumbens is more sensitive to the effects of inhibitors of dopamine uptake than is the dorsal striatum. 相似文献