全文获取类型
收费全文 | 60844篇 |
免费 | 462篇 |
国内免费 | 1122篇 |
专业分类
测绘学 | 2085篇 |
大气科学 | 3659篇 |
地球物理 | 11460篇 |
地质学 | 25839篇 |
海洋学 | 4517篇 |
天文学 | 10330篇 |
综合类 | 2247篇 |
自然地理 | 2291篇 |
出版年
2022年 | 487篇 |
2021年 | 705篇 |
2020年 | 757篇 |
2019年 | 827篇 |
2018年 | 6340篇 |
2017年 | 5461篇 |
2016年 | 4161篇 |
2015年 | 842篇 |
2014年 | 1496篇 |
2013年 | 2059篇 |
2012年 | 2565篇 |
2011年 | 4538篇 |
2010年 | 3752篇 |
2009年 | 4240篇 |
2008年 | 3604篇 |
2007年 | 4280篇 |
2006年 | 1787篇 |
2005年 | 1090篇 |
2004年 | 1211篇 |
2003年 | 1194篇 |
2002年 | 989篇 |
2001年 | 810篇 |
2000年 | 681篇 |
1999年 | 429篇 |
1998年 | 457篇 |
1997年 | 475篇 |
1996年 | 336篇 |
1995年 | 358篇 |
1994年 | 335篇 |
1993年 | 281篇 |
1992年 | 284篇 |
1991年 | 290篇 |
1990年 | 337篇 |
1989年 | 272篇 |
1988年 | 258篇 |
1987年 | 260篇 |
1986年 | 191篇 |
1985年 | 301篇 |
1984年 | 302篇 |
1983年 | 295篇 |
1982年 | 274篇 |
1981年 | 269篇 |
1980年 | 282篇 |
1979年 | 203篇 |
1978年 | 242篇 |
1977年 | 204篇 |
1976年 | 183篇 |
1975年 | 184篇 |
1974年 | 171篇 |
1973年 | 206篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
Based on our 1997 observations with a CCD camera and narrow-band filters attached to the 1-m Assy Obsev vatory telescope, we extensively study the latitudinal variations in limb darkening and normal albedo on Jupiter's disk at wavelengths of 387, 445, 502, 619, and 702 nm. In addition, we carried out observations in 1998 with broad-band red, green, and blue filters. Apart from a general regularity—the increase in darkening coefficient with normal albedo of Jupiter's cloud cover—there is an appreciable scatter of darkening coefficients for the same albedo, which is most pronounced in the ultraviolet. This scatter may result from differences in the optical depth of the aerosol haze above the clouds. The lack of any wavelength dependence of the darkening coefficients is confirmed for Jupiter's polar regions, while at other latitudes, they decrease with decreasing wavelength. 相似文献
172.
This study on the distribution features of petroleum hydrocarbon in water and sedi-ment off the Fujian shore using data obtained from the baseline research on oceanic contamination in Fujian showed that:during the research preiod,petroleum hydrocarbon concentrations in water varied from 5.77μg/L to 37.28μg/L,averaged 14.48 μg/L;was lower in the wet seasson than in the dry season;and was highest in the Minjiang Estuary and Jiulong Estuary in both seasons ,The petorleum hydrocarbon concentrations in shore sediment varied from 14.48 mg/kg to 784.36 mg/kg,averaged 133.3 mg/kg ,and was closely related to sediment types (granularity). 相似文献
173.
Is Precipitation the Dominant Controlling Factor of High Inorganic Nitrogen Content in the Changjiang River and Its Mouth? 总被引:1,自引:1,他引:0
沈志良 《中国海洋湖沼学报》2003,21(4):368-376
The main reasons for the high content of inorganic N and its increase by several times in the Changjiang River and its mouth during the last 40 years were analysed in this work. The inorganic N in precipitation in the Changjiang River catchment mainly comes from gaseous loss of fertilizer N, N resulting from the increases of population and livestock, and from high temperature combustions of fossil fuels. N from precipitation is the first N source in the Changjiang River water and the only direct cause of high content of inorganic N in the Changjiang River and its mouth. The lost N in gaseous form and from agriculture non-point sources fertilizer comprised about 60% of annual consumption of fertilizer N in the Changjiang River catchment and were key factors controlling the high content of inorganic N in the Changjiang River mouth. The fate of the N in precipitation and other N sources in the Changjiang River catchment are also discussed in this paper. 相似文献
174.
The previously proposed (Rodin, 2002) method for calculating the microphysical properties of spatially inhomogeneous rarefied aerosol media with mixing using the lowest-order moments of the size distribution is generalized to particle coagulation. We show that when the problem is formulated in terms of moments, all of the solutions admitted by the stochastic coagulation equation lie within a narrow range whose boundaries can be determined by means of quadratic programming. We discuss the choice of an optimal solution within this range and compare the moment method with the results of our computations by the classical finite-difference method using a model of photochemical aerosols in Titan's atmosphere as an example. The moment method allows the efficiency of microphysical computations to be significantly increased by using precomputed low-dimension interpolation tables. It can be used to construct self-consistent models for the globular circulation of planetary atmospheres. 相似文献
175.
We found the equilibrium conditions for a self-gravitating toroidal vortex by taking thermal pressure into account. These conditions are shown to significantly differ from those for a disk or a sphere. The evolution of a thin vortex turns it into a compact vortex that loses mechanical stability for low masses at a polytropic index γ<4/3 but retains stability for sufficiently high masses and densities determined by the velocity circulation in the vortex. 相似文献
176.
It was found recently that fast electrons travel through the plasma of the solar corona in the form of beam-plasma structure
(BPS), which consists of electrons and Langmuir waves. In this paper the influence of scattering BPS Langmuir waves off plasma
ions (l+i=l+i) on BPS velocity is studied. We show that the maximum BPS velocity equals 0.35c, which is close to the velocity of Type III bursts sources. 相似文献
177.
DharmalingamVENUGOPAL 《山地科学学报》2004,1(1):74-80
The Nilgiri Mountains of south India is considered unique by anthropologists, geologists, climatologists, botanists as well as tourists. It has remained a subject of constant study and research over the last two centuries. Man-nature balance had continued undisturbed in the Nilgiris for thousands of years until the early 19th century when it became a British colony attracting, in due course, various developmental activities. Subsequently, the Nilgiris and its popular hill stations emerged as favourite places for the British population in India for rest and recuperation, game and for raising commercial plantations. In the process, the traditional indigenous crops were replaced by “English“ vegetables and the natural forests gave way to commercial plantations of coffee, tea and other exotic species of trees. 相似文献
178.
Andrei V. Ivanov Nataliya N. Kononkova S. Vincent Yang Michael E. Zolensky 《Meteoritics & planetary science》2003,38(5):725-737
Abstract— Clasts of alkaline (the second find in meteorites) and subalkaline rocks were found in the Kaidun meteorite. One of them (#d4A) is a large crystal of albite with inclusions of fluorapatite, arfvedsonite, aenigmatite, and wilkinsonite. The two latter minerals were previously unknown in meteorites. Another clast (#d[3–5]D) has a melt crystallization texture of mainly feldspar (oligoclase) composition and contains relict grains of both high‐Ca and low‐Ca pyroxene and fluorapatite. The mineralogical characteristics of these clasts suggest a genetic relationship and an origin from the same parent body. The textural and mineralogical characteristics of the clasts indicate origin by extensive igneous differentiation. Such processes most likely took place in a rather large differentiated body. The material of clast #d(3–5)D is similar in some mineralogical respects to basaltic shergottites. 相似文献
179.
高从堦 《中国海洋湖沼学报》2003,21(1):40-45
Seawater desalination has been people‘s fond dream since ancient times,the dream is now becoming a reality.This paper presents a brief development history of reverse osmosis.Much attention was paid to innovative development in mebranes,modules.equipments and applied technology,including asymmetric and composite membranes,spiral-wound element and hollow fiber module,energy recovery equipments and different technological processes.The extension of reverse osmosis,such as desalination,pre-concentration,integrated processes and nanofiltration,is also briefly mentioned. 相似文献
180.
Subramanian Prasad Ananthakrishnan S. Janardhan P. Kundu M.R. White S.M. Garaimov V.I. 《Solar physics》2003,218(1-2):247-259
We present the first observations of a solar flare with the GMRT. An M2.8 flare observed at 1060 MHz with the GMRT on 17 November 2001 was associated with a prominence eruption observed at 17 GHz by the Nobeyama radioheliograph and the initiation of a fast partial halo CME observed with the LASCO C2 coronagraph. Towards the start of the eruption, we find evidence for reconnection above the prominence. Subsequently, we find evidence for rapid growth of a vertical current sheet below the erupting arcade, which is accompanied by the flare and prominence eruption. 相似文献