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951.
952.
Leaños-Castañeda O Van Der Kraak G Lister A Simá-Alvarez R Gold-Bouchot G 《Marine environmental research》2002,54(3-5):703-707
In order to investigate the mechanism by which o,p'-DDT disrupts endocrine functioning of Nile tilapia in vivo, the estrogenicity of o,p'-DDT was investigated in conjunction with 17beta-estradiol (E2) and tamoxifen. Mature, male tilapia were treated intraperitoneally with o,p'-DDT (60 mg/kg, one dose) or E2 (5 mg/kg, four doses) in the presence or absence of tamoxifen (5 mg/kg, six doses) for 12 days and then plasma vitellogenin (Vtg) (measured as alkaline-labile phosphorous), E2, and testosterone (T) were measured. Vtg levels were increased dramatically by E2 (1,744 +/- 171 microg/ml) and moderately by o,p'-DDT (82 +/- 15 microg/ml) compared with controls (23 +/- 3.5 microg/ml). Tamoxifen alone had no effect on Vtg production, but inhibited both E2 and o,p'-DDT stimulated vitellogenesis. T levels were reduced with E2 administration (1,688 +/- 383 pg/ml) and declined further with the combined treatment of E2 and tamoxifen (281 +/- 70 pg/ml), compared with controls (6,558 +/- 1,438 pg/ml). Tamoxifen or o,p'-DDT alone did not affect T levels, but their combined treatment did (2,069 +/- 647 pg/ml). The results of this study suggest that o,p'-DDT is weakly estrogenic in male tilapia, and that this activity may be mediated through the estrogen receptor. 相似文献
953.
Kinetics of microbially mediated reactions: dissimilatory sulfate reduction in saltmarsh sediments (Sapelo Island, Georgia, USA) 总被引:1,自引:0,他引:1
Alakendra N. Roychoudhury Philippe Van Cappellen Joel E. Kostka Eric Viollier 《Estuarine, Coastal and Shelf Science》2003,56(5-6):1001-1010
A sediment disk reactor was tested in once flow-through mode to retrieve kinetic parameters for the Monod rate law that describes sulfate reduction. The experimental method was compared with a previously described procedure by the authors where a sediment plug-flow reactor was operated in a recirculation mode. In recirculation mode, accumulation of metabolic byproducts in certain cases may result in negative feedback, thus preventing accurate determination of kinetic information. The method described in this article provides an alternative to the recirculation sediment plug-flow-through reactor technique for retrieving kinetic parameters of microbially mediated reactions in aquatic sediments.For sulfate reduction in a saltmarsh site, a maximum estimate of the half-saturation concentration, Ks, of 204±26 μM and a maximum reaction rate, Rm, of 2846±129 nmol cm(wetsediment)3 d−1 was determined. The Ks value obtained was consistent with the one estimated previously (Ks=240±20 μM) from a different site within the same saltmarsh mud flat using a recirculating reactor. From the Rm value and reduction rates determined using 35SO42− incubation experiments, we infer that sulfate reduction is limited in the field. Substrate availability is not the main contributor for the limitation, however. Competition from other microbes, such as iron reducers affects the activity of sulfate reducers in the suboxic to anoxic zones, whereas aerobes compete in the oxic zone. High sulfide concentration in the pore water may also have acted as a toxin to the sulfate reducers in the field. 相似文献
954.
Interpretation of seismic reflection data reveal evidence of a Cenozoic fault (Walkers Cay Fault) north of Little Bahama Bank.
This fault strikes N15–30°E, perpendicular to the adjacent bank margin and offsets a late Oligocene reflector by as much as
100 m. The origin of this near-surface fault is uncertain, but its location and strike are nearly coincident with an independently
mapped basement fault. Walkers Cay Fault may be the result of recurrent faulting, implying intermittent basement fault movement
during the post-rift history of the northern Bahamian continental margin. 相似文献
955.
Sulphate-related equilibria in the hypersaline brines of the Tyro and Bannock Basins, eastern Mediterranean 总被引:1,自引:0,他引:1
G.J De Lange N.A.I.M Boelrijk G Catalano C Corselli G.P Klinkhammer J.J Middelburg D.W Müller W.J Ullman P Van Gaans J.R.W Woittiez 《Marine Chemistry》1990,31(1-3)
The Tyro and Bannock Basins, which are depressions in the eastern Mediterranean, contain hypersaline anoxic brines. These brines are of different composition: Tyro brine is primarily an early-stage halite (NaCl) brine, whereas Bannock brine includes the more soluble ions of late-stage evaporite minerals. Accordingly, the Bannock brine contains a much greater sulphate concentration than the Tyro Brine. This difference in sulphate concentration is reflected in the concentrations of ions such as Ca, Sr and Ba, which form sparingly soluble sulphate minerals.Equilibrium calculations using the Pitzer specific ion interaction model indicate that the brines in both basins are saturated with respect to gypsum (CaSO4-2H2O) and supersaturated to saturated with respect to dolomite (CaMg(CO3)2). The degree of saturation with respect to dolomite is greater in the Bannock Basin than it is in the Tyro Basin. Correspondingly, recent gypsum crystals and dolomite hardgrounds have been found in the Bannock Basin but not in the Tyro Basin.The Tyro brine is homogeneous in composition, whereas the Bannock brine demonstrates a clear two-layer brine structure. At the interface of the upper and the lower brine distinct positive anomalies occur in the total alkalinity and the concentration of phosphate, and negative anomalies occur in the concentrations of Mn2+ and the rare earth elements (REE). These anomalies and the observed association of gypsum/dolomite in the sediments are all consistent with a recent precipitation of dolomite and gypsum in the Bannock Basin. The brines in both basins are also saturated with respect to barite (BaSO4).The 87Sr/86Sr and δ34S ratios of the Bannock brines are amazingly consistent but differ dramatically from the values for modern or Messinian-age seawater. The Sr concentration and Sr and S isotope ratios in the gypsum crystals indicate that most of these crystals have resulted from precipitation/recrystallization from the brine and not from seawater. The observed variations between crystals are thought to reflect the recrystallization of (sub-) outcropping Messinian gypsum with a low 87Sr/86Sr ratio in the presence of seawater or brine fluids and with different extents of diagenesis. 相似文献
956.
957.
958.
Olga Leaos-Castaeda Gerardo Gold-Bouchot Glen Van Der Kraak Andrea Lister Victor Ceja-Moreno Raul Sim-Alvarez 《Marine environmental research》2004,58(2-5):337
The objective of this study was to determine if tamoxifen or an aromatase inhibitor (4-hydroxyandrostenedione; 4-OHA) affected plasma concentrations of o,p′-DDT and its metabolites, o,p′-DDD and o,p′-DDE, in mature tilapia. Male and female tilapia were injected 6 times intraperitoneally with o,p′-DDT (40 mg/kg) alone or in combination with 4-OHA (2 mg/kg) over a 12 day period. An additional group of male fish was injected with tamoxifen (5 mg/kg) plus o,p′-DDT. At the end of the treatment period, plasma samples were extracted and analyzed by GC/ECD. Females injected only with o,p′-DDT had significantly higher levels of o,p′-DDT compared with males. Interestingly, females and males treated concomitantly with o,p′-DDT and 4-OHA or tamoxifen had significantly lower concentrations of plasma o,p′-DDT (about 50%) compared with fish treated with only o,p′-DDT. These initial results suggest that an interaction between endocrine-active compounds occurs in vivo in tilapia and may involve alterations in metabolism of o,p′-DDT. 相似文献
959.
The stable form of dissolved chromium in oxygenated seawater is Cr(VI). But Cr(III)-species are also present at an analytically significant level. It is shown that Cr(III) is oxidized only slowly by dissolved oxygen, and that manganese oxide is a strong catalyst for such oxidation. However, the low oceanic concentration of suspended MnO2 impedes the conclusion that the former process is quantitatively less important than the latter one. The distribution of dissolved chromium among Cr(VI)- and Cr(III)-species is probably kinetically controlled. 相似文献