全文获取类型
收费全文 | 26517篇 |
免费 | 585篇 |
国内免费 | 1472篇 |
专业分类
测绘学 | 1502篇 |
大气科学 | 2441篇 |
地球物理 | 5030篇 |
地质学 | 12717篇 |
海洋学 | 1242篇 |
天文学 | 1785篇 |
综合类 | 2345篇 |
自然地理 | 1512篇 |
出版年
2024年 | 5篇 |
2023年 | 47篇 |
2022年 | 130篇 |
2021年 | 151篇 |
2020年 | 105篇 |
2019年 | 123篇 |
2018年 | 4865篇 |
2017年 | 4135篇 |
2016年 | 2699篇 |
2015年 | 348篇 |
2014年 | 226篇 |
2013年 | 161篇 |
2012年 | 1096篇 |
2011年 | 2841篇 |
2010年 | 2143篇 |
2009年 | 2417篇 |
2008年 | 1985篇 |
2007年 | 2433篇 |
2006年 | 122篇 |
2005年 | 264篇 |
2004年 | 440篇 |
2003年 | 468篇 |
2002年 | 291篇 |
2001年 | 89篇 |
2000年 | 122篇 |
1999年 | 122篇 |
1998年 | 113篇 |
1997年 | 88篇 |
1996年 | 88篇 |
1995年 | 94篇 |
1994年 | 66篇 |
1993年 | 61篇 |
1992年 | 41篇 |
1991年 | 28篇 |
1990年 | 20篇 |
1989年 | 23篇 |
1988年 | 21篇 |
1987年 | 11篇 |
1986年 | 12篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 8篇 |
1982年 | 5篇 |
1981年 | 23篇 |
1980年 | 20篇 |
1979年 | 1篇 |
1976年 | 7篇 |
1958年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
171.
The upper layer (above 140 m depth) temperature in the western Philippine Sea near Taiwan was sampled using a coastal monitoring
buoy (CMB) with 15 attached thermistors during July 28–August 7, 2005. The data were collected every 10 min at 1, 3, 5, 10,
15, and 20 m using the CMB sensors, and every 15 sec at 15 different depths between 25 m and 140 m. Internal waves and solitons
were identified from the time-depth plot of the temperature field. Without the internal waves and solitons, the power spectra,
structure functions, and singular measures (representing the intermittency) of temperature field satisfy the power law with
multi-scale characteristics at all depths. The internal waves do not change the basic characteristics of the multifractal
structure. However, the internal solitons change the power exponent of the power spectra drastically, especially in the low
wave number domain; they also break down the power law of the structure function and increase the intermittency parameter.
The physical mechanisms causing these different effects need to be explored further. 相似文献
172.
Mesoscale features in the eastward extension of the Kuroshio were investigated using assimilation of TOPEX/POSEIDON (T/P)
data into a three-layer quasi-geostrophic model. The T/P data exhibited an elongated state of the southern recirculation gyre
in 1993–95 and 1997, between whose two periods the gyre had a contracted state in 1995–96. A few stationary eddies were located
in the southern gyre during the contracted state. The baroclinic instability, which was indicated by the phase shift from
the uppermost-to the lowest-layer anomalies toward the downstream side, was evident near the Kuroshio Extension (KE) path.
Since the instability never appeared in the artificial model without bottom topography, the topographic barrier for the eastward
flow in the lowest layer was a necessary condition for the instability. The instability synchronized with the transition in
the western region of the KE axis from the elongated to the contracted states. This evolution was interpreted as if the baroclinic
instability played some part in the KE states and was a trigger for the transition from the elongated to the contracted states. 相似文献
173.
Following our previous study (Sugimoto and Hanawa, 2005b), we further investigate the reason why reemergence of winter sea
surface temperature anomalies does not occur in the North Pacific eastern subtropical mode water (NPESTMW) area, despite its
occurrence in the North Pacific subtropical mode water and North Pacific central mode water areas. We use vertical temperature
and salinity profiles of the World Ocean Circulation Experiment Hydrographic Program and Argo floats with high vertical and
temporal resolution, together with heat flux data through the sea surface. We point out first that one of the causes for non-occurrence
of reemergence is that the thickness of NPESTMW is very thin. In addition to this basic cause, two major reasons are found:
a vigorous mixing in the lower portion of NPESTMW and less heat input from the atmosphere in the warming season. Since, in
the lower portion of NPESTMW and deeper, the stratification is favorable for salt-finger type convection to occur compared
with the other mode water areas, vigorous mixing takes place. This is confirmed by both a large Turner Angle there and the
existence of staircase structures in vertical temperature and salinity profiles. From the viewpoint of heat input, the NPESTMW
area gradually gains heat in the warming season compared with other mode water areas. As a result, NPESTMW cannot be capped
so quickly by the shallow summer mixed layer, and water properties of NPESTMW are to be gradually modified, even in the upper
portion. 相似文献
174.
A geomorphological and statistical analysis of slope canyons from the northern KwaZulu-Natal continental margin is documented
and compared with submarine canyons from the Atlantic margin of the USA. The northern KwaZulu-Natal margin is characterized
by increasing upslope relief, concave slope-gradient profiles and features related to upslope growth of the canyon forms.
Discounting slope-gradient profile, this morphology is strikingly similar to canyon systems of the New Jersey slope. Several
phases of canyon incision indicate that downslope erosion is also an important factor in the evolution of the northern KwaZulu-Natal
canyon systems. Despite the strong similarities between the northern KwaZulu-Natal and New Jersey slope-canyon systems, key
differences are evident: (1) the concavity of the northern KwaZulu-Natal slope, contrasting with the ∼linear New Jersey slope;
(2) the relative isolation of the northern KwaZulu-Natal canyons, rather than the dense clustering of the New Jersey canyons;
and (3) the absence of strongly shelf-breaching canyons along the northern KwaZulu-Natal margin. In comparison with the New
Jersey margin, we surmise a more youthful stage of canyon evolution, a result of either the canyons themselves being younger
or the formative processes being less active. Less complicated patterns of erosion resulting from reduced sediment availability
have developed in northern KwaZulu-Natal. The reduction in slope concavity on the New Jersey margin may be the result of grading
of the upper slope by intensive headward erosion, a process more subdued—or less evident—on the KwaZulu-Natal margin. 相似文献
175.
The effects of scattering and resonance on the energy dissipation of an internal tide were investigated using a two-dimensional
model which is a reassembled version of the theoretical generation model devised by Rattray et al. (1969) for internal tide. The basic character of the scattering process at the step bottom was first investigated with a
wide shelf model. When the internal wave incited from a deep region (Region II) into the shallow shelf region (Region I),
a passing wave into the shallow region, a reflected wave into the deep region, and a beam-like wave, i.e. a scattered wave
(SW), emanated at the step bottom. The SW, which consists of the superposition of numerous internal modes, propagated upward/downward
into both regions. The general properties of the SW were well expressed around the shelf edge, even in the present model with
viscosity effect. The amplitude of the SW decreased dramatically when the depth of the velocity maximum of the incident internal
wave in Region II corresponded with the depth of the shelf edge. In the narrow shelf model, where the decay distance of the
internal wave in Region I is longer than the shelf width, the incident internal wave reflected at the coast to form a standing
wave. When the internal wave in Region I is enhanced by the resonance, the energy of the SW in Region II is also intensified.
Furthermore, the energy of the modes in Region II predominated when the velocity maximum is identical to that of the dominant
mode in Region I. These results suggest that the spatial scale of shelf region is a very important factor governing the energy
dissipation of the internal tide through reflection and scattering in a narrow shelf. 相似文献
176.
坛紫菜(于1988年采自青岛太平角海区人工养殖筏上)的水溶性色素粗提物经过硫酸铵沉淀和羟基磷灰石(HA)柱层析后,分离出藻蓝蛋白(RPC)、藻红蛋白(RPE)和变藻蓝蛋白(APC)。在中性介质中,其吸收光谱和荧光发射光谱与文献报道基本一致;但在酸性(pH=3)或碱性(pH=12)介质中,吸收光谱较在中性介质中有明显改变,原有的荧光性质也消失。RPC和APC只分离到一种聚集体,但RPE有两种不同的聚集体。用SephadexG—100凝胶过滤方法测量藻胆蛋白的分子量分别为:RPC117000,APC112000,小分子RPE38000,大分子RPE232000。对三种藻胆蛋白的氨基酸分析的结果表明,三种藻胆蛋白中都是酸性氨基酸的含量大于碱性氨基酸的含量。 相似文献
177.
二色桌片参酶解液对转化细胞的效应 总被引:3,自引:2,他引:3
用二色桌片参(Mensamariaintercedens)酶解液处理转化的人胚肺成纤维细胞(NLF)后,细胞生长受到显著抑制,抑制率达64.84%,光镜下细胞透光性加强,铺展较好,细胞核形更为规则,核畸形现象减少;线粒体结构趋于正常;软琼脂集落实验表明,细胞集落形成率由23x10-5下降至12.5x10-5,裸小鼠致瘤实验显示抑瘤率为82.39%,差异显著(p<5%)。结果提示,二色桌片参酶解液可能逆转转化的HLF细胞的恶性表型,对其有一定的诱导分化作用。 相似文献
178.
Takushi Niki Miwa Shimizu Ayako Fujishiro Junji Kinoshita 《Journal of Oceanography》2007,63(5):873-877
During time-series observations in Sagami Bay, Japan, the concentration of dissolved dimethylsulfoniopropionate (DMSPd), a precursor of dimethylsulfide (DMS), was negatively correlated with salinity. In the laboratory, low-salinity shock reduced
DMS production rates of the natural bacterial community and induced rapid DMSP release from a dinophyte, Heterocapsa triquetra, suggesting that low-salinity shock reduced DMSPd consumption but enhanced DMSPd production, which agrees with the negative correlation between DMSPd and salinity observed in Sagami bay. In addition, low-salinity shock did not affect DMSP lyase activity of H. triquetra. Low-salinity shock would increase the contribution from algae in DMS production, leading to an increase in potential DMS
productivity in the environment. 相似文献
179.
Algorithm for HF radar vector current measurements 总被引:1,自引:0,他引:1
A new algorithm is proposed, called the stream function method (SFM) for producing vector current maps from radial data measured
by dual-site high frequency surface wave radar (HFSWR). In SFM, a scalar stream function is constructed under some oceanographic
assumptions. The function describes the two-dimensional (2-D) ocean surface water motion and is used to obtain the distribution
of vector currents. The performance of SFM is evaluated using simulated radial data, which demonstrates that SFM has advantages
over typical vectorial combination methods (VCM) both in error acceptance and robustness, and excels another method based
on least-squares fitting (LSF) in recovering the complicated current models. Furthermore, SFM is capable of providing the
total currents based on radials from single-site radar. We also test the assumptions of horizontal non-divergence in the simulation.
The new algorithm is applied to the field experiment data of Wuhan University’s ocean state measuring and analyzing radar
(OSMAR), collected in the coastal East China Sea during April 11–17, 2004. Quantitative comparisons are given between radar
results by three current algorithms and in-situ current meter measurements. Preliminary analysis of the vertical current shear is given based on the current meter measurements. 相似文献
180.
The Blake Outer Ridge is a 480–kilometer long linear sedimentary drift ridge striking perpendicular to the North American
coastline. By modeling free-air gravity anomalies we tested for the presence of a crustal feature that may control the location
and orientation of the Blake Outer Ridge. Most of our crustal density models that match observed gravity anomalies require
an increase in oceanic crustal thickness of 1–3 km on the southwest side of the Blake Outer Ridge relative to the northeast
side. Most of these models also require 1–4 km of crustal thinning in zone 20–30 km southwest of the crest of the Blake Outer
Ridge. Although these features are consistent with the structure of oceanic fracture zones, the Blake Outer Ridge is not parallel
to adjacent known fracture zones. Magnetic anomalies suggest that the ocean crust beneath this feature formed during a period
of mid-ocean ridge reorganization, and that the Blake Outer Ridge may be built upon the bathymetric expression of an oblique
extensional feature associated with ridge propagation. It is likely that the orientation of this trough acted as a catalyst
for sediment deposition with the start of the Western Boundary Undercurrent in the mid-Oligocene. 相似文献