全文获取类型
收费全文 | 18368篇 |
免费 | 2240篇 |
国内免费 | 5696篇 |
专业分类
测绘学 | 440篇 |
大气科学 | 1289篇 |
地球物理 | 2310篇 |
地质学 | 4363篇 |
海洋学 | 14235篇 |
天文学 | 108篇 |
综合类 | 2840篇 |
自然地理 | 719篇 |
出版年
2024年 | 83篇 |
2023年 | 388篇 |
2022年 | 917篇 |
2021年 | 1103篇 |
2020年 | 1203篇 |
2019年 | 1026篇 |
2018年 | 991篇 |
2017年 | 1225篇 |
2016年 | 1090篇 |
2015年 | 1182篇 |
2014年 | 1424篇 |
2013年 | 1647篇 |
2012年 | 1462篇 |
2011年 | 1631篇 |
2010年 | 1122篇 |
2009年 | 1507篇 |
2008年 | 897篇 |
2007年 | 1318篇 |
2006年 | 1211篇 |
2005年 | 738篇 |
2004年 | 441篇 |
2003年 | 451篇 |
2002年 | 409篇 |
2001年 | 337篇 |
2000年 | 346篇 |
1999年 | 367篇 |
1998年 | 203篇 |
1997年 | 182篇 |
1996年 | 166篇 |
1995年 | 138篇 |
1994年 | 147篇 |
1993年 | 114篇 |
1992年 | 97篇 |
1991年 | 74篇 |
1990年 | 64篇 |
1989年 | 73篇 |
1988年 | 54篇 |
1987年 | 25篇 |
1986年 | 42篇 |
1985年 | 51篇 |
1984年 | 60篇 |
1983年 | 42篇 |
1982年 | 46篇 |
1981年 | 34篇 |
1980年 | 29篇 |
1979年 | 22篇 |
1978年 | 26篇 |
1977年 | 18篇 |
1976年 | 15篇 |
1973年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
61.
The new polyenzyme method for making gravy fromHarengula zunasi offal involves protein enzymolysis with flavorase after proper alkaline and neutral protease levels were established by orthogonal
trials to select the best hydrolytic conditions for processing offal with alkaline and neutral protease. The conditions for
the polyenzyme method were pH of 7.0, temperature of 50°C, alkaline and neutral protease concentration of 1.5% respectively,
hydrolysis time of 120 min, and flavorase concentration of 2.0%, for 60 min. The new gravy-making technology yields a nutritious
and delicious gravy containing 40.3% of total essential amino acids, with delicious amino acids Glu, Asp, Gly, Ala, Pro and
Ser comprising 49.5%, total and amino nitrogen being respectively 1.9 and 1.1 g/100 g (amino acid nitrogen being 61.0% of
total nitrogen), The polyenzyme method was used to make 14.8% protein gravy fromHarengula zunasi offal. In addition, inorganic elements, the phosphorus content is the highest.
This project was aided financially by the Guangdong Science and Technology Office (No. 2KM06002S). 相似文献
62.
Observation of fluid parcel pathways in the Kuroshio Stream revealed a striking crossstream pattern associated with the Kuroshio‘‘ s meanders. In order to understand the observed pattern, a two-dimensional kinematic model of a meandering jet was developed which could be used to examine the relationship between streamfunction patterns and fluid parcel trajectories. The experiments designed to investigate the dependence of the water exchanges between the Kuroshio water and its surroundings on the characteristics of the Kuroshio‘‘s meanders involved the downstream speed,phase speed and the amplitude of other propagating waves. The results suggested that fluid parcels could cross the meandering jet to and fro; and that the water exchanges between the Kuroshio and its surroundings increased with a) increasing meander amplitude, b) decreasing downstream speed, and c) increasing wave phase speed. The results also showed that when the meandering jet was disturbed by other propagating waves, more effective water exchanges could be induced. 相似文献
63.
《Global and Planetary Change》2006,50(1-2):112-126
Signatures between monthly global Earth gravity field solutions obtained from GRACE satellite mission data are analyzed with respect to continental water storage variability. GRACE gravity field models are derived in terms of Stokes' coefficients of a spherical harmonic expansion of the gravitational potential from the analysis of gravitational orbit perturbations of the two GRACE satellites using GPS high–low and K-band low–low intersatellite tracking and on-board accelerometry. Comparing the GRACE observations, i.e., the mass variability extracted from temporal gravity variations, with the water mass redistribution predicted by hydrological models, it is found that, when filtering with an averaging radius of 750 km, the hydrological signals generated by the world's major river basins are clearly recovered by GRACE. The analyses are based on differences in gravity and continental water mass distribution over 3- and 6-month intervals during the period April 2002 to May 2003. A background model uncertainty of some 35 mm in equivalent water column height from one month to another is estimated to be inherent in the present GRACE solutions at the selected filter length. The differences over 3 and 6 months between the GRACE monthly solutions reveal a signal of some 75 mm scattering with peak values of 400 mm in equivalent water column height changes over the continents, which is far above the uncertainty level and about 50% larger than predicted by global hydrological models. The inversion method, combining GRACE results with the signal and stochastic properties of a hydrological model as ‘a priori’ in a statistical least squares adjustment, significantly reduces the overall power in the obtained water mass estimates due to error reduction, but also reflects the current limitations in the hydrological models to represent total continental water storage change in particular for the major river basins. 相似文献
64.
Vagle S. Foote K.G. Trevorrow M.V. Farmer D.M. 《Oceanic Engineering, IEEE Journal of》1996,21(3):298-305
A calibration technique has been adapted to render complete system calibrations of high-frequency acoustical instrumentation. This is based on standard targets; specifically, precisely manufactured spheres composed of tungsten carbide with 6% cobalt binder. The use of multiple sphere sizes was found to be advantageous, both as an independent check of the calibrations, and so that resonances in the sphere responses at certain frequencies could be avoided. Complete system gains and beam patterns, which include effects of bandpass filters and finite-pulse lengths, were determined by moving the spheres individually in the transducer far-fields. Use of this procedure ensures control over the acoustical characteristics of transducers, which may change from the time of manufacture and first testing due, for example, to platform mounting. It also provides a direct means of measuring the sampling volume at relatively high and constant signal-to-noise ratios. Implementation of this technique is discussed using a multifrequency sonar system as an example 相似文献
65.
HUANGGuoqiang DONGShuanglin WANGFang 《中国海洋大学学报(英文版)》2005,4(1):56-60
Attractabilities of different diets and dietary selectivity of Chinese shrimp, Fenneropenaeus chinensis were studied through behavior observation and feeding experiment, respectively. The five diets used in the experiment are: Fish Flesh (FF), Shrimp Flesh (SF), Clam Foot (CF), Polychaete Worm (PW), and Formulated Diet (FD). No significant differences of attractability exist between any two different diets when every two natural diets or all five diets are provided simultaneously. On the other hand, significant differences of attractability exist between FD and every single natural diet when they are provided simultaneously. Results of behavioral observation indicate that natural diets are more attractive than FD. In feeding experiment, Chinese shrimp has distinct selectivity on different diets. It positively selects CF and PW, negatively selects FF and SF, and excludes FD absolutely. The results of the present studies indicate that the dietary selectivity of shrimp was based not only on the attractabilities of the diets, but also on the responses such as growth and food conversion. 相似文献
66.
Xie-Yan Song Hua-Wen Qi Paul T. Robinson Mei-Fu Zhou Zhi-Min Cao Lie-Meng Chen 《Lithos》2008,100(1-4):93-111
The Emeishan continental flood basalt (ECFB) sequence in Dongchuan, SW China comprises a basal tephrite unit overlain by an upper tholeiitic basalt unit. The upper basalts have high TiO2 contents (3.2–5.2 wt.%), relatively high rare-earth element (REE) concentrations (40 to 60 ppm La, 12.5 to 16.5 ppm Sm, and 3 to 4 ppm Yb), moderate Zr/Nb and Nb/La ratios (9.3–10.2 and 0.6–0.9, respectively) and relatively high Nd (t) values, ranging from − 0.94 to 2.3, and are comparable to the high-Ti ECFB elsewhere. The tephrites have relatively high P2O5 (1.3–2.0 wt.%), low REE concentrations (e.g., 17 to 23 ppm La, 4 to 5.3 ppm Sm, and 2 to 3 ppm Yb), high Nb/La (2.0–3.9) ratios, low Zr/Nb ratios (2.3–4.2), and extremely low Nd (t) values (mostly ranging from − 10.6 to − 11.1). The distinct compositional differences between the tephrites and the overlying tholeiitic basalts cannot be explained by either fractional crystallization or crustal contamination of a common parental magma. The tholeiitic basalts formed by partial melting of the Emeishan plume head at a depth where garnet was stable, perhaps > 80 km. We propose that the tephrites were derived from magmas formed when the base of the previously metasomatized, volatile-mineral bearing subcontinental lithospheric mantle was heated by the upwelling mantle plume. 相似文献
67.
JÜRGEN TITSCHACK CAMPBELL S. NELSON TIM BECK ANDRÉ FREIWALD ULRICH RADTKE 《Sedimentology》2008,55(6):1747-1776
Autochthonous red algal structures known as coralligène de plateau occur in the modern warm‐temperate Mediterranean Sea at water depths from 20 to 120 m, but fossil counterparts are not so well‐known. This study describes, from an uplifted coastal section at Plimiri on the island of Rhodes, a 450 m long by 10 m thick Late Pleistocene red algal reef (Coralligène Facies), interpreted as being a coralligène de plateau, and its associated deposits. The Coralligène Facies, constructed mainly by Lithophyllum and Titanoderma, sits unconformably upon the Plio‐Pleistocene Rhodes Formation and is overlain by a Maerl Facies (2 m), a Mixed Siliciclastic‐Carbonate Facies (0·2 m) and an Aeolian Sand Facies (2·5 m). The three calcareous facies, of Heterozoan character, are correlated with established members in the Lindos Acropolis Formation in the north of the island, while the aeolian facies is assigned to the new Plimiri Aeolianite Formation. The palaeoenvironmental and genetic‐stratigraphic interpretations of these mixed siliciclastic‐carbonate temperate water deposits involved consideration of certain characteristics associated with siliciclastic shelf and tropical carbonate shelf models, such as vertical grain‐size trends and the stratigraphic position of zooxanthellate coral growths. Integration of these results with electron spin resonance dates of bivalve shells indicates that the Coralligène Facies was deposited during Marine Isotope Stage 6 to 5e transgressive event (ca 135 to 120 ka), in water depths of 20 to 50 m, and the overlying Maerl Facies was deposited during regression from Marine Isotope Stage 5e to 5d (ca 120 to 110 ka), at water depths of 25 to 40 m. The capping Aeolian Sand Facies, involving dual terrestrial subunits, is interpreted as having formed during each of the glacial intervals Marine Isotope Stages 4 (71 to 59 ka) and 2 (24 to 12 ka), with soil formation during the subsequent interglacial periods of Marine Isotope Stages 3 and 1, respectively. Accumulation rates of about 0·7 mm year?1 are estimated for the Coralligène Facies and minimum accumulation rates of 0·2 mm year?1 are estimated for the Maerl Facies. The existence of older red algal reefs in the Plimiri region during at least Marine Isotope Stages 7 (245 to 186 ka) and 9 (339 to 303 ka) is inferred from the occurrence of reworked coralligène‐type lithoclasts in the basal part of the section and from the electron spin resonance ages of transported bivalve shells. 相似文献
68.
《Cretaceous Research》2008,29(1):87-99
The first carbon and oxygen isotope curves for the Valanginian to Early Barremian (Early Cretaceous) interval obtained from outcrops in the Southern Hemisphere are presented. They were obtained from well-dated (by ammonites) sediments from the Neuquén Basin, Argentina. Measurements were acquired by the innovative method of analysing fossil oyster laminae. The occurrence of the well-established mid-Valanginian positive carbon isotope excursion is documented, while less well-marked positive events may also correlate with peaks identified in the well-known successions of SE France. The mid-Valanginian positive carbon isotope event in the Neuquén Basin is possibly associated with organic-rich sediments. A similar relationship is seen in the European Alps and in oceanic cores in some areas of the world. 相似文献
69.
The shallow water wave simulation model-SWAN incorporated with a simple fine sediment erosion model is applied to Hangzhou
Bay, China, to model the horizontal distribution of the maximum bottom orbital velocity and corresponding fine sediment erosion
rates induced by: (1) southeasterly steady winds (5, 20 and 30 m/s), (2) southwesterly steady winds (5 and 20 m/s); (3) northwesterly
steady winds (5 and 20 m/s); (4) east-southeasterly steady winds (5 and 20 m/s); (5) easterly steady winds (5 and 20 m/s)
under closed and unclosed boundaries; and (6) unsteady winds during the slack water periods. Results suggest: (1) the steady
wind wave-induced maximum bottom orbital velocities and corresponding fine sediment erosion rates generally increased with
the increasing steady winds; (2) closed and unclosed boundary conditions had more significant influences on modeled fine sediment
erosion rates under 5 m/s easterly steady winds than 20 m/s; and (3) steady and unsteady wind wave-induced maximum bottom
currents could be significant in eroding fine sediment bed in Hangzhou Bay. The results show implications for geomorphology,
sedimentology, coastal erosion, and environmental pollution mitigation in Hangzhou Bay. 相似文献
70.