全文获取类型
收费全文 | 98125篇 |
免费 | 1604篇 |
国内免费 | 840篇 |
专业分类
测绘学 | 2296篇 |
大气科学 | 6857篇 |
地球物理 | 19601篇 |
地质学 | 35081篇 |
海洋学 | 8604篇 |
天文学 | 21939篇 |
综合类 | 282篇 |
自然地理 | 5909篇 |
出版年
2022年 | 559篇 |
2021年 | 983篇 |
2020年 | 1097篇 |
2019年 | 1193篇 |
2018年 | 2502篇 |
2017年 | 2392篇 |
2016年 | 2910篇 |
2015年 | 1699篇 |
2014年 | 2867篇 |
2013年 | 5055篇 |
2012年 | 3032篇 |
2011年 | 4155篇 |
2010年 | 3563篇 |
2009年 | 4665篇 |
2008年 | 4254篇 |
2007年 | 4132篇 |
2006年 | 3875篇 |
2005年 | 3017篇 |
2004年 | 2950篇 |
2003年 | 2871篇 |
2002年 | 2613篇 |
2001年 | 2373篇 |
2000年 | 2246篇 |
1999年 | 1852篇 |
1998年 | 1944篇 |
1997年 | 1872篇 |
1996年 | 1550篇 |
1995年 | 1542篇 |
1994年 | 1339篇 |
1993年 | 1214篇 |
1992年 | 1137篇 |
1991年 | 1094篇 |
1990年 | 1187篇 |
1989年 | 1029篇 |
1988年 | 934篇 |
1987年 | 1104篇 |
1986年 | 988篇 |
1985年 | 1244篇 |
1984年 | 1349篇 |
1983年 | 1280篇 |
1982年 | 1229篇 |
1981年 | 1072篇 |
1980年 | 1008篇 |
1979年 | 938篇 |
1978年 | 908篇 |
1977年 | 862篇 |
1976年 | 819篇 |
1975年 | 787篇 |
1974年 | 784篇 |
1973年 | 773篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
931.
M.K Vollmer R.F WeissR.T Williams K.K FalknerX Qiu E.A RalphV.V Romanovsky 《Geochimica et cosmochimica acta》2002,66(24):4235-4246
The relationships between electrical conductivity, temperature, salinity, and density are studied for brackish Lake Issyk-Kul. These studies are based on a newly determined major ion composition, which for the open lake shows a mean absolute salinity of 6.06 g kg−1. The conductivity-temperature relationship of the lake water was determined experimentally showing that the lake water is about 1.25 times less conductive than seawater diluted to the same absolute salinity as that of the lake water. Based on these results, an algorithm is presented to calculate salinity from in-situ conductivity measurements. Applied to the field data, this shows small but important vertical salinity variations in the lake with a salinity maximum at 200 m and a freshening of the surface water with increasing proximity to the shores. The algorithm we adopt to calculate density agrees well with earlier measurements and shows that at 20°C and 1 atm Lake Issyk-Kul water is about 530 g m−3 denser than seawater at the same salinity. The temperature of maximum density at 1 atm is about 0.15°C lower than that for seawater diluted to the same salinity. Despite its small variations, salinity plays an important role, together with temperature changes, in the static stability and in the production of deep-water in this lake. Changes in salinity may have had important consequences on the mixing regime and the fate of inflowing river water over geological time. Uncharged silicic acid is negligible for the stability of the water column except near an ∼15 m thick nepheloid layer observed at the bottom of the deep basin. 相似文献
932.
A problem of estimation of shock wave attenuation in an obstacle under an explosion of a high-energy material (explosive) charge on its surface is considered. An algorithm for its solution is proposed using the analytical and semiempirical dependences generally recognized in explosion physics. 相似文献
933.
CCD Photometry and Long-Term Optical Variability of 3C 345 总被引:1,自引:0,他引:1
This paper presents evidence for long-term optical variability and colour behaviour of the blazar 3C 345 (1641+399, z=0.595). Our results show that the amplitude of the optical variations of 3C 345 has been only about 3 magnitudes from its
photometric history; existent significant correlation between brightness and colours is found for 3C 345. Our recent CCD photometry
of 3C 345 in May 1996 and May 1997 showed that they are in good agreement with our prediction of the optical variability period
of about 10 years (see Zhang et al., 1998; Webb et al., 1988).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
934.
Frans J. M. Rietmeijer 《Meteoritics & planetary science》1993,28(2):242-245
Abstract I present an internally consistent reinterpretation of carbyne diffraction data making a few plausible assumptions. The results support that carbynes could be crystalline, randomly interstratified (or mixed-layered) carbons with variable C/(C+H+O+N) ratios rather than thermodynamically stable carbon allotropes. The metastable carbynes are likely the result of incomplete, kinetically-inhibited, low-temperature pyrolysis of precursor material. A renewed interest in meteoritic carbynes should seek to combine light-element chemistry and crystallography of these elusive carbons. 相似文献
935.
GPS observations in the Western Bohemia/Vogtland earthquake swarm region revealed indications of horizontal displacements
of low amplitude, and no clear long-term trend in 1993–2007. On the other hand, in 1998–2001 there was relatively significant
active movement along NNE-SSW oriented line that we called the “Cheb-Kraslice GPS Boundary” (ChKB), identical with an important
limitation of earthquake activity. The most impressive were dextral (right-lateral) movements in the 1998–1999 period followed
by reverse sinistral (left-lateral) movements in 1999–2000 that correlate with prevailing motion defined by fault plane solutions
of the Autumn 2000 earthquake swarm. Before the February 2004 micro-swarm, two points located on opposite sides of the Mariánské
Lázně fault showed extension in the order of about 7 mm in the same NNE-SSW direction of ChKB. The new NOKO permanent GPS
station in Novy Kostel showed the peak-to-peak vertical changes up to 10 mm before and during the February 2007 micro-swarm.
Annual precise levelling campaigns in the local network around Novy Kostel revealed regular vertical displacements during
the 1994, 1997 and 2000 earthquake swarms. The points around the Novy Kostel seismological station showed uplift during the
active periods, including the micro-swarm February 2004. However, no such indication was observed on levelling points in the
period of the February 2007 swarm. Long-term vertical displacements depend on the same direction NNE-SSW (ChKB) as the GPS
displacements. Both geodetic techniques have revealed oscillating displacements, GPS horizontal, and levelling vertical, rather
than any long-term trends in the study period 1993–2007. The displacements exhibited significant spatial and temporal relation
to tectonic activity (earthquake swarms) including their coincidence with the seismologically determined sense of motion along
the fault plane during earthquakes. 相似文献
936.
M. deCastro M. Gómez-Gesteira I. Alvarez J.L.G. Gesteira 《Continental Shelf Research》2009,29(8):1053-1059
The warming trend observed during the last decades in the Bay of Biscay is put within the context of sea surface temperature (SST) changes observed in the area since 1854. Macroscopically, two consecutive warming–cooling cycles were detected during this period of time: cooling from 1867 to 1910; warming from 1910 to 1945; cooling from 1945 to 1974; and warming from 1974 to nowadays. Warming rates of 0.17 and 0.22 °C per decade were measured during the warming sub-periods and cooling rates of ?0.14 and ?0.10 °C per decade were measured during the cooling sub-periods. The present warming period is on the same order of magnitude although slightly more intense than the one observed from 1910 to 1945, which is consistent with previous analysis carried for the North Atlantic. Finally, the thermal amplitude defined as the difference between the maximum and minimum annual values has increased since 1974 at a rate of 0.06 °C per decade due to the different increasing rates of the maximum (0.26 °C per decade) and minimum (0.20 °C per decade) SSTs. 相似文献
937.
Kaare L. Rasmussen Hans J. F. Olsen Raymond Gwozdz Evgeniy M. Kolesnikov 《Meteoritics & planetary science》2001,36(7):1001-1006
Abstract— Jull et al. propose an alternative interpretation of our depth vs. 14C data measured on a peat core from the central Tunguska impact site (Rasmussen et al., 1999). We find that the proposed alternative is untenable. 相似文献
938.
I. Xanthakis I. Liritzis B. Petropoulos C. Banos E. Sarris 《Earth, Moon, and Planets》1994,66(2):189-212
The atmospheric activity of Jupiter exhibits quasi-periodic character attributed to the stochastic nature of the involved mechanisms. Periodicities between 4–33 years are obtained employing four spectrum analysis methods, (power spectrum employing the Blackman-Tukey window, maximum entropy, Fourier, autocorrelation), whilst, their significance and their stationarity has been established with the application of general statistical tests (Kolmogorov-Smirnov, one sample and two sample test, randomness test, chi-square, various orders of autoregressive process, analysis of truncated records).Deceased. 相似文献
939.
Ele Vahtm?e Tiit Kutser Jonne Kotta Merli P?rnoja Tiia M?ller Lennart Lennuk 《Oceanology》2012,52(6):803-809
It is known that the structure of benthic macrophyte and invertebrate habitats indicate the quality of coastal water. Thus, a large-scale analysis of the spatial patterns of coastal marine habitats makes it possible to adequately estimate the status of valuable coastal marine habitats, provide better evidence for environmental changes, and describe the processes behind the changes. Knowing the spatial distribution of benthic habitats is also important from the coastal management point of view. Our previous results clearly demonstrated that remote sensing methods can be used to map water depth and distribution of taxonomic groups of benthic algae (e.g., red, green, and brown algae) in the optically complex coastal waters of the Baltic Sea. We have as well shown that benthic habitat mapping should be done at high spatial resolution owing to the small-scale heterogeneity of such habitats in Estonian coastal waters. Here we tested the capability of high spatial resolution hyperspectral airborne image in its application for mapping benthic habitats. A big challenge is to define appropriate mapping classes that are also meaningful from the ecological point of view. In this study two benthic habitat classification schemes??broader level and finer level??were defined for the study area. The broader level classes were relatively well classified, but discrimination among the units of the finer classification scheme posed a considerable challenge and required a careful approach. Benthic habitat classification provided the highest accuracy in the case of the Spectral Angle Mapper classification method applied to a radiometrically corrected image. Further processing levels, such as spatial filtering and glint correction, decreased the classification accuracy. 相似文献
940.
V. M. Kushnir 《Physical Oceanography》2005,15(6):370-382
The comparison of six well-known models of the wave bottom boundary layer shows that they are identical in the case of a smooth
bottom but exhibit serious differences for the other types of conditions. The thickness of the wave bottom boundary layer
and the coefficient of vertical diffusion of momentum are studied by using the relations of the k-ε-model. The validity of these estimates is checked by comparing the measured and computed values of the friction velocity.
This comparison demonstrates fairly good agreement between the results characterized by a coefficient of correlation equal
to 0.851.
__________
Translated from Morskoi Gidrofizicheskii Zhurnal, No. 6, pp. 54–67, November–December, 2005. 相似文献