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91.
Peter Högberg 《Oecologia》1990,84(2):229-231
Summary Urea (U) and ammonium nitrate (AN) had been applied to a Scots pine (Pinus sylvestris L.) forest in northern Sweden for 18 consecutive years at four doses resulting in total N applications ranging from 0 to 1980 kg ha–1. The 15N abundance ( 15N) of the grass Deschampsia flexuosa (L.) Trin. increased linearly (from –0.7 to 11.0) with application rate in the case of U. The response to AN was in the same direction but smaller. While others have shown that the initial response of nitrogen-limited systems to additions of N is a change of 15N abundance towards that of added N, this study shows that further and excessive additions leads to a retention of 15N. Monitoring 15N abundance over time in dose-response trials of this type thus opens new possibilities to estimate critical loads of N and the point of nitrogen saturation. 相似文献
92.
Nitrogen fixed in 13 provenances of Acacia albida and 11 isolines of Leucaena leucocephala inoculated with effective Rhizobium strains was measured by 15N techniques and the total N difference method. In the test soil, on the average, L. leucocephala derived about 65% of its total N from atmospheric N2 fixation compared to about 20% by A. albida. Significant differences in the percentage of N derived from atmospheric N2 (% Ndfa) occurred, between provenances or isolines within species. The % Ndfa ranged from 37 to 74% within L. leucocephala and from 6 to 37 within A. albida; (equivalent to 20–50 mg N plant–1 and 4–37 mg N plant–1 for the two species over three months, respectively) and was correlated with the nodule mass (r=0.91). The time course of N2 fixation of three selected provenances (low, intermediate and good fixers) was followed at 12 weekly intervals over a 36 week period. The % Ndfa of all provenances and isolines increased with time; and except for one of the L. leucocephala provenances, % Ndfa was similar within species at the 36 weeks harvest. There was a significant correlation between % Ndfa and the amount of N2 fixed (r=0.96). Significant interactions occurred between provenances and N treatments and often growth of uninoculated but N fertilized plants was less variable than for inoculated unfertilized plants. 相似文献
93.
A procedure for the culture in vitro of isolated small berries of Vitis vinifera L. cv. Muscat of Alexandria in a Murashige and Skoog basal medium supplemented with N6 -benzyladenine and indoleacetic acid is described. Berries developed well in culture during 60 days and tripled in size, but remained green and smaller than normal berries grown in vivo. Some callus formed on the distal end of the berry, and where major skin damage occurred, callus emerged from the cracked berries. In order to examine their biosynthetic competency, berries which were previously cultured in vitro for 60 days were incubated for 48 h in a Murashige and Skoog medium containing a [14 C]-labelled water-soluble fraction. This fraction was isolated from grape berries located adjacent to a leaf that had been exposed to gaseous 14 CO2 in full sunlight for 5 h. The berries were then recultured for 48 h after which a glycosidic fraction was isolated on a C18 reversed phase column and further separated by thin layer chromatography (TLC). The major labelled band corresponded to the geranyl-β-rutinoside marker, indicating that grape berries have the ability to synthesize monoterpene glycosides. This band also consisted of other monoterpene glycosides as revealed by the gas chromatography-mass spectrometry (GC-MS) analysis of their aglycones (released by enzymatic hydrolysis). 相似文献
94.
F. Azam 《Plant and Soil》1990,125(2):255-262
A pot experiment was conducted to study the effect of organic and inorganic nitrogen (N) sources on the yield and N uptake
of rice from applied and native soil-N. The residual effect of these N sources on a succeeding wheat crop was also studied.
Organic N was applied in the form of 15N-labelled Sesbania aculeata L., a legume, and inorganic N in the form of 15N-labelled ammonium sulphate. The two sources were applied to the soil separately or together at the time of transplanting
rice.
Recovery of N by rice from both the applied sources was quite low but both sources caused significant increases in biomass
and N yield of rice. Maximum increase was recorded in soil treated with organic N. The residual value of the two materials
as source of N for wheat was not significant; the wheat took up only a small fraction of the N initially applied. Loss of
N occurred from both applied N sources, the losses being more from inorganic N.
Both applied N sources caused a substantial increase in the availability of soil-N to rice and wheat; most of this increase
was due to organic N and was attributed to the so-called ‘priming’ effect or ANI (added nitrogen interaction) of the applied
material. 相似文献
95.
The 15N isotope dilution technique and the N difference method were used to estimate N2 fixation by clover growing in a mixture with ryegrass, in a field experiment and a controlled environment experiment. Values obtained using N difference were approximately 25% lower than those estimated using 15N isotope dilution. In the field experiment there was a measured N benefit to grass growing with clover, equivalent to 42.7 kgN ha-1. The grass in the mixture had a lower atom %15N content and a higher N content than grass in a monoculture; therefore values for N2 fixation were different depending on choice of control plant i.e. monoculture or mixture grass. In the controlled environment experiment there were no significant differences between either the atom %15N contents or the N contents of monoculture grass and grass growing in a mixture with clover. It is concluded that there is a long term indirect transfer of N from clover to associated grass which can lead to errors in estimates of N2 fixation. 相似文献
96.
The pericarp of the dormant sugarbeet fruit acts as a storage reservoir for nitrate, ammonium and -amino-N. These N-reserves enable an autonomous development of the seedling for 8–10 d after imbibition. The nitrate content of the seed (1% of the whole fruit) probably induces nitrate-reductase activity in the embryo enclosed in the pericarp. Nitrate that leaks out of the pericarp is reabsorbed by the emerging radicle. Seedlings germinated from seeds (pericarp was removed) without external N-supply are able to take up nitrate immediately upon exposure via a low-capacity uptake system (vmax = 0.8 mol NO
3
-
·(g root FW)–1·h–1; Ks = 0.12 mM). We assume that this uptake system is induced by the seed nitrate (10 nmol/seed) during germination. Induction of a high-capacity nitrate-uptake system (vmax = 3.4 mol NO
3
-
·(g root FW)–1·h–1; Ks = 0.08 mM) by externally supplied nitrate occurs after a 20-min lag and requires protein synthesis. Seedlings germinated from whole fruits absorb nitrate via a highcapacity uptake mechanism induced by the pericarp nitrate (748 nmol/pericarp) during germination. The uptake rates of the high-capacity system depend only on the actual nitrate concentration of the uptake medium and not on prior nitrate pretreatments. Nitrate deprivation results in a decline of the nitrate-uptake capacity (t1/2 of vmax = 5 d) probably caused by the decay of carrier molecules. Small differences in Ks but significant differences in vmax indicate that the low- and high-capacity nitrate-uptake systems differ only in the number of identical carrier molecules.Abbreviations NR
nitrate reductase
-
pFPA
para-fluorophenylalanine
This work was supported by a grant from Bundesministerium für Forschung und Technologie and by Kleinwanzlebener Saatzucht AG, Einbeck. 相似文献
97.
Glutamine Transport in Mouse Cerebral Astrocytes 总被引:1,自引:0,他引:1
Abstract: We measured initial influx and exchange of [14 C]glutamine in primary astrocyte cultures in the presence and absence of Na+ . Kinetic analysis of transport in Na+ -free solution indicated two saturable Na+ -independent components, one of which was identifiable functionally as system L1 transport. In the presence of Na+ , multiple hyperbolic components were not resolvable from the kinetic data. Nevertheless, other evidence supported participation by at least three Na+ -dependent neutral amino acid transporters (systems A, ASC, and N). System A transport of glutamine was usually absent or minimal, based on lack of inhibition by α-(methylamino)isobutyric acid. However, vigorous system A-mediated transport emerged after derepression by substrate deprivation. Participation by system ASC was indicated by trans-acceleration of Na+ -dependent uptake, preferential inhibition of an Li+ -intolerant component of uptake by cysteine, and inhibition by cysteine of a component resistant to inhibition by histidine and α-(methylamino)isobutyric acid. Because nonsaturable transport of glutamine appeared negligible, and system L transport of glutamine was suppressed in the presence of Na+ , low-affinity system ASC transport may be the major route of export of glutamine from astrocytes. At 700 µ M glutamine, the primary uptake route was system N transport, identified on the basis of selective inhibition by histidine and asparagine, pH sensitivity, and tolerance of Li+ in place of Na+ . 相似文献
98.
99.
100.
Atmospheric CO2 concentration has increased by 25% over the preindustrial level. A parallel increase in C concentration and decreases in N
concentration and δ13C of plants grown throughout this century have been observed in plant specimens stored in herbaria. We tested our previous
results in a study of 12 more species collected in the western Mediterranean throughout this century (1920–1930, 1945–1955,
and 1985–1990) and tree rings of Quercus pubescens from the same area. These changes were accompanied by apparent increases in condensed tannin concentration. A decreasing trend
in δ15N both in herbarium material and tree rings was also found, indicating that ecosystems might cope with higher plant N demand
by decreasing N losses and increasing N fixation and mineralization. These results may contribute to a better understanding
of the effects of global change on carbon and nitrogen cycling.
Received: 12 November 1995 / Accepted: 17 May 1996 相似文献