全文获取类型
收费全文 | 26148篇 |
免费 | 366篇 |
国内免费 | 214篇 |
专业分类
测绘学 | 521篇 |
大气科学 | 1950篇 |
地球物理 | 5207篇 |
地质学 | 9154篇 |
海洋学 | 2111篇 |
天文学 | 6011篇 |
综合类 | 47篇 |
自然地理 | 1727篇 |
出版年
2021年 | 161篇 |
2020年 | 197篇 |
2019年 | 209篇 |
2018年 | 497篇 |
2017年 | 462篇 |
2016年 | 567篇 |
2015年 | 436篇 |
2014年 | 606篇 |
2013年 | 1222篇 |
2012年 | 737篇 |
2011年 | 1020篇 |
2010年 | 880篇 |
2009年 | 1224篇 |
2008年 | 1059篇 |
2007年 | 1053篇 |
2006年 | 983篇 |
2005年 | 825篇 |
2004年 | 845篇 |
2003年 | 799篇 |
2002年 | 743篇 |
2001年 | 690篇 |
2000年 | 641篇 |
1999年 | 574篇 |
1998年 | 583篇 |
1997年 | 582篇 |
1996年 | 446篇 |
1995年 | 424篇 |
1994年 | 384篇 |
1993年 | 340篇 |
1992年 | 315篇 |
1991年 | 287篇 |
1990年 | 309篇 |
1989年 | 285篇 |
1988年 | 238篇 |
1987年 | 314篇 |
1986年 | 258篇 |
1985年 | 348篇 |
1984年 | 386篇 |
1983年 | 373篇 |
1982年 | 336篇 |
1981年 | 311篇 |
1980年 | 314篇 |
1979年 | 284篇 |
1978年 | 311篇 |
1977年 | 267篇 |
1976年 | 271篇 |
1975年 | 275篇 |
1974年 | 235篇 |
1973年 | 239篇 |
1972年 | 158篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
471.
Community-based coastal resource management projects facilitated by non-governmental organizations (NGOs) in the Philippines have explored approaches to decrease poverty-driven over-exploitation of coastal resources. There has been little reporting and analysis of such activities until recently. Nine case studies have recently been published and this paper presents a brief summary of these, along with an analysis of the trends and themes identified. Though diverse and covering the Philippines from Mindanao to Luzon, the case studies highlight the value of community commitment and participation in decisions regarding, and in the implementation of, resource management in ways that consider not only the bio-physical aspects of resource management but the social, economic and legal implications. Experience in working with local government has been both successful and limited. Successful projects raise hopes for further progress through education and organization of communities to improve livelihoods and protect coastal resources. 相似文献
472.
Glauconitic minerals range from green smectite to 10Å glauconite, occur mainly in peloids (most of which were fecal pellets), and apparently were produced largely by neoformation replacing several kinds of substrate. Chamositic minerals, berthierine and chamosite, occur in Recent and ancient peloids, but mostly in ancient ooids, and they developed by alteration of a precursor Al-rich clay mineral. Ooid sheaths were built by rolling of cores on ue sea floor. Glauconitic greensands and chamositic oolitic ironstones are condensed sequences deposited as sandwaves during long periods of reduced influx of sediment. Some are associated with hardgrounds. 相似文献
473.
The hepatic mixed function oxidase system in the fish differs from that in mammals in its responses to the two classic mammalian inducers. The cytochrome P-448-type inducers (polycyclic aromatic hydrocarbons) stimulate monooxygenase activity, but phenobarbital, a P-450-type inducer, does not.1 We have compared the effects of phenobarbital (PB) and polychlorinated biphenyls (PCB) on the turnover of hepatic microsomal hemoproteins in trout (PCB's are P-448- and P-450-type inducers in mammals, which in fish induce only cytochrome P-448). We show here that neither PCB nor PB treatment changed the turnover rate. However, both the rates of synthesis and degradation were much slower than in the rat. 相似文献
474.
S. F. Dotsenko 《Physical Oceanography》1993,4(1):1-8
The process of generation of two-dimensional (2D) wave motions during small elliptical displacements of the bottom which occur for a finite time interval is considered within the framework of the linear theory of long waves in a basin of constant depth. The spatial structure and the amplitudinal and energy characteristics of the emerging directional surface wave are analysed for bottom deformations of a special form.Translated by Mikhail M. Trufanov. 相似文献
475.
476.
477.
Stable carbon isotope ratios have been used to study the sources of particulate organic carbon (POC) and total dissolved inorganic carbon in the Orinoco Basin. The isotopic composition of total dissolved inorganic carbon shows a range of from -8·1 to -23·0 ppt, an indication of dominance of biological processes. The isotopic composition of POC exhibits a range of from -24·1 to -34·6 ppt with little seasonal variation. The isotopic evidence indicates that the POC is predominantly of terrestrial origin rather than a result of in situ planktonic production. The similarity of isotopic composition of POC and coastal sediments suggests that riverine organic detritus has been transported 30-50 km offshore in a direction parallel to the Orinoco river channel. 相似文献
478.
479.
480.
S. F. Dotsenko 《Physical Oceanography》2000,10(4):287-295
Within the framework of the general linear statement of the problem, we determine the conditions of generation of a geostrophic
current in a layer of uniform rotating fluid for small displacements of the bottom of a basin. We deduce an equation relating
the equilibrium shape of the surface of the fluid with residual deformations of the bottom and find its general solution.
It is shown that the geostrophic current is generated only in the presence of residual deformations. We present numerical
estimates of the intensity of the generated geostrophic formation for a model of motion of the bottom. The investigated mechanism
of generation of geostrophic vortex fields is especially efficient in the shelf zone of the ocean.
Translated by Peter V. Malyshev and Dmitry V. Malyshev 相似文献