全文获取类型
收费全文 | 322篇 |
免费 | 21篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 15篇 |
大气科学 | 15篇 |
地球物理 | 71篇 |
地质学 | 173篇 |
海洋学 | 14篇 |
天文学 | 41篇 |
综合类 | 5篇 |
自然地理 | 14篇 |
出版年
2023年 | 3篇 |
2022年 | 8篇 |
2021年 | 20篇 |
2020年 | 10篇 |
2019年 | 6篇 |
2018年 | 18篇 |
2017年 | 20篇 |
2016年 | 29篇 |
2015年 | 18篇 |
2014年 | 21篇 |
2013年 | 21篇 |
2012年 | 8篇 |
2011年 | 12篇 |
2010年 | 17篇 |
2009年 | 15篇 |
2008年 | 14篇 |
2007年 | 10篇 |
2006年 | 9篇 |
2005年 | 9篇 |
2004年 | 2篇 |
2003年 | 7篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 4篇 |
1998年 | 1篇 |
1996年 | 1篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 7篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 7篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1970年 | 2篇 |
排序方式: 共有348条查询结果,搜索用时 15 毫秒
341.
342.
A. N. Shah G. Yun-shan F. H. Shah H. U. Mughal Z. u. Rahman A. Naveed 《International Journal of Environmental Science and Technology》2014,11(2):385-394
In present study a turbocharged, medium duty compression ignition engine was alternatively fuelled with biodiesel to investigate the changes in particulate matter composition, relative to that taken with diesel fuel. The engine was operated on an AC electrical dynamometer in accordance with an 8-mode, steady-state cycle. The numbers of particles were estimated through electrical low pressure impactor, while sulfates and trace metals were analyzed by ion chromatography and inductively coupled plasma-atomic emission spectroscopy, respectively. Nitric oxides and nitrogen dioxides were measured separately using SEMTECH-DS. Experimental results revealed that, on account of elevated ratios of nitrogen dioxide to nitrogen oxides, mean accumulation mode particles were 42 % lower with biodiesel. On the other hand, nuclei mode particles were higher with biodiesel, owing to heterogeneous nucleation and accounting for an increase in sulfate emissions up to 8 % with biodiesel as compared to diesel. On the average, trace metal emissions were significantly reduced showing 65–85.4 % reduction rates with biodiesel, relative to its counterpart. Further to this, individual congeners such as iron, calcium, and sodium were the predominant elements of the trace metals emitted from engine. The mean relative decrease in iron and calcium was 89–97.8 and 77.6–87 %, respectively, while the relative rise in sodium was in the range of 29–46 % with biodiesel. Further, elements such as zinc, chromium, and aluminum showed substantial abatement, whereas potassium, magnesium, and manganese exhibited irregular trends on account of variable engine loads and speeds during the various modes of cycle. 相似文献
343.
Hidden subvertical discontinuities oriented parallel to subparallel to the exposed faces of outcropping sandstone were effectively mapped at three different study sites in central Missouri using a ground-penetrating radar system (GPR) equipped with a 400-MHz monostatic antenna and a survey wheel. At each site, a suite of 2-D ground-penetrating radar profiles were acquired along multiple closely spaced traverses on relatively smooth exposed rock surfaces. Time-zero correction was applied to the raw GPR data which were then processed using band-pass filtering, range and display gain, color transformation, and deconvolution techniques. Pseudo 3D images of each identified discontinuity at each site were constructed based on the interpretation of the nonmigrated ground-penetrating radar profiles. These pseudo 3D images were hand-migrated and transformed into true 3D images which depict variable depths at “perpendicular horizontal distance” to each discontinuity relative to the exposed rock face. The results demonstrate that GPR can be used to detect and map hidden discontinuities. This information can then be used for rock slope stability analysis and rock engineering purposes. 相似文献
344.
The electrostatic shocks and solitons are studied in weakly relativistic and collisional electron-positron-ion plasmas occurring
in polar regions of pulsar. The plasma system is composed of relativistically streaming electrons, positrons while ions are
taken to be stationary. Dissipative effects in the system are due to collision phenomena among the constituents of relativistic
plasma. Nonlinear dynamics of the dissipation and dispersion dominated relativistic plasma systems are governed by Korteweg-de
Vries Burger (KdVB) and Korteweg-de Vries (KdV) equations respectively. Numerical results, exploring the effects of plasma
parameters on the profile of nonlinear waves are expedited graphically for illustration. Positron to electron temperature
ratio plays the role of a decisive parameter. It is noticed that compressive shocks and solitons evolve in the system if the
positron to electron temperature ratio is less than a critical value. However, there exists a threshold value of positron
to electron temperature ratio beyond which the system supports the rarefactive shocks and solitons. The results may have importance
in the relativistic plasmas of pulsar magnetosphere. 相似文献
345.
The problem, significance and implications for metamorphism of 60 million years of multiple phases of staurolite growth 总被引:2,自引:0,他引:2
Microstructural measurements of FIAs in staurolite reveal at least 3 periods of growth in the Proterozoic Colorado Front Range
and 5 in the Paleozoic Western Maine. Dated monazite inclusions in staurolite have an absolute age of 1760±12 Ma (FIA 1),
1720±7 Ma (FIA 2), 1682±18 Ma (FIA 3) in Colorado, and 408±10 Ma (FIA 2), 388±8 Ma (FIA 3), 372±6 Ma (FIA 4), 352±4 Ma (FIA
5) in Maine, supporting the multiple periods of deformation and metamorphism indicated by the FIA succession in each region.
Multiple phases of growth by similar reactions in the same as well as in diverse adjacent rocks in both regions suggest that
PT and X are not the only factors controlling the commencement and cessation of metamorphic reactions. The FIAs preserved
by the staurolite porphyroblasts indicate that the local partitioning of deformation at the scale of a porphyroblast was the
eventual controlling factor on whether or not the staurolite forming reactions took place. 相似文献
346.
G. A. Shah 《Astronomische Nachrichten》1977,298(6):319-325
The colour difference between the star and the attendant reflection nebula and polarization both caused by silicate and graphite grains have been given. The properly normalized size distribution function for each type of grains has been considered within homogeneous plane parallel slab-model of the reflection nebula with the star in the rear. Contrary to some earlier results, it has been possible to show that silicate grains can certainly play a role in the phenomena of reflection nebulae. 相似文献
347.
Al-Qadami Ebrahim Hamid Hussein Mustaffa Zahiraniza Shah Syed Muzzamil Hussain Matínez-Gomariz Eduardo Yusof Khamaruzaman Wan 《Natural Hazards》2022,110(1):325-348
Natural Hazards - Vehicles can be easily swept away by floodwaters once the flow velocity and depth reach certain critical limits, with probabilities toward fatality reported to be nearly 50%.... 相似文献
348.
G. A. Shah 《Astronomische Nachrichten》1977,298(1):41-45
The extinction efficiencies for small smooth metallic particles (granules) have been calculated using rigorous MIE theory of scattering. Strong size dependent resonances for spheres composed of sodium, potassium, and calcium have been found. The results seem to have relevance to the problems of interstellar grains especially with reference to structures in the observed extinction curve, diffuse bands and anomaly of cosmic abundances of elements. 相似文献