全文获取类型
收费全文 | 7383篇 |
免费 | 315篇 |
国内免费 | 25篇 |
专业分类
测绘学 | 236篇 |
大气科学 | 462篇 |
地球物理 | 2803篇 |
地质学 | 2331篇 |
海洋学 | 250篇 |
天文学 | 1329篇 |
综合类 | 30篇 |
自然地理 | 282篇 |
出版年
2022年 | 55篇 |
2021年 | 111篇 |
2020年 | 115篇 |
2019年 | 97篇 |
2018年 | 278篇 |
2017年 | 270篇 |
2016年 | 425篇 |
2015年 | 283篇 |
2014年 | 321篇 |
2013年 | 419篇 |
2012年 | 349篇 |
2011年 | 296篇 |
2010年 | 303篇 |
2009年 | 308篇 |
2008年 | 240篇 |
2007年 | 209篇 |
2006年 | 189篇 |
2005年 | 156篇 |
2004年 | 156篇 |
2003年 | 148篇 |
2002年 | 137篇 |
2001年 | 121篇 |
2000年 | 115篇 |
1999年 | 83篇 |
1998年 | 109篇 |
1997年 | 97篇 |
1996年 | 85篇 |
1995年 | 99篇 |
1994年 | 111篇 |
1993年 | 90篇 |
1992年 | 77篇 |
1991年 | 68篇 |
1990年 | 80篇 |
1989年 | 75篇 |
1988年 | 63篇 |
1987年 | 72篇 |
1986年 | 67篇 |
1985年 | 70篇 |
1984年 | 64篇 |
1983年 | 78篇 |
1982年 | 83篇 |
1981年 | 73篇 |
1980年 | 72篇 |
1979年 | 68篇 |
1978年 | 74篇 |
1977年 | 67篇 |
1976年 | 57篇 |
1975年 | 60篇 |
1973年 | 62篇 |
1971年 | 71篇 |
排序方式: 共有7723条查询结果,搜索用时 15 毫秒
51.
A. Tárczy-Hornoch 《Pure and Applied Geophysics》1962,52(1):53-58
Zusammenfassung Es werden mit Hilfe der sphärischen Trigonometrie und der Ausgleichsrechnung Methoden angegeben, die die Berechnung der bestanschmiegenden Ebene an eine Anzahl von Geraden mit einem gemeinsamen Punkt ermöglichen.
Summary With the aid of the spherical trigonometry and the adjustment, methods are given to determin the best-fitting plane for a given set of directions through a common point.相似文献
52.
53.
54.
55.
Karel Kučera 《Studia Geophysica et Geodaetica》1966,10(4):411-421
Summary In [1] the author has put forward a three-direction method, a general way of adjustment of angular observations in incomplete
sets by the method of extending into angular combinations, and the definition of mean weightP
*. In this article the question is dealt with as a whole. In the three-direction methods>3 triangulation directions are measured in direction triplets 123, 234, 345,… …,s12, while in the method of measuring single angles at the station they are measured in angles 12, 23, 34, 45, …,s1. The advantage of transition from angles to direction triplets rests, besides in saving 31% of pointings, above all in certain
possibility of elimination of the horizontal refraction, which follows from this. The treatise of the relation between the
method of measurement and the refraction is not included into this article, as it would go beyond its scope. The fact that
adjusted directions, with the exception of the stations having four directions, are not of equal weight, is proper not only
to the three-direction method. The non-equality of weights is even more conspicuous in the method of measuring single angles
at the station, and it appears already at the stations having four directions. In author's view the homogeneity of observation
elements is more important than the homogeneity of weights from the point of view of adjustment at the station; therefore
the direction triplets ought not to exist abreast with the angles in one programme, and especially the number of observations
ought to be constant at one station with adjusted direction of homogeneous mean weight in the net.
This transition from angles to direction triplets could also provoke a comment that simultaneous visibility of three adjoining
directions occurs less often than of two such directions. The author adds to this that nowadays the causes of this phenomenon,
following from unsuitable technique, must be eliminated. It is just air limpidity that ought to define the visibility, not
unsufficient or everywhere equal intensity of light of reflectors, or too long sides of the triangulation net. Recent approach
to this problem requires simultaneous visibility of all directions during most of the days of observation. In connection with
the out-of=date technique, the methods of angular observation often have one unfavourable character: they are the cause of
the accumulation of observations of “always visible” directions. The supposed merit of angles thus turns into their imperfection.
Адрес: Politickych vězňů 12, Praha 1-Nové Město 相似文献
Адрес: Politickych vězňů 12, Praha 1-Nové Město 相似文献
56.
Резюме С помощью принятия простых кинематических предположений и на основании ω—уравнения выла определена конфигурация полос облаков
в полностью окклюдированном циклоне без фронтов. Облачная система определяется полем скрытой теплоты, выделяемой в процессах
конденсации. Полосы облаков теоретически представляют собой в основном листы синусоидальной спирали.
Address: Boční II, Praha 4-Spořilov. 相似文献
Address: Boční II, Praha 4-Spořilov. 相似文献
57.
58.
P. Cobo C. Ranz A. Fernández M. Cuesta D.K. Anthony M. Siguero 《Marine Geophysical Researches》2005,26(2-4):87-95
Vertical resolution is of fundamental importance in sonar exploration and is directly related to the duration of the acoustic
pulse generated by the transducer. The shorter the radiated pulse, the higher the vertical resolution. Many sub-bottom profiling
sonar systems use piezoelectric transducers because they are reversible and well understood. Piezoelectric projectors are
normally resonant transducers, which are intrinsically narrowband. A piezoelectric transducer is usually driven by a tone-burst.
However, it is possible to use Fourier techniques to find a pre-compensated electrical driving function so that the transducer
radiates a prescribed wider band acoustic waveform. This technique can be applied to synthesize zero-phase cosine-magnitude,
Gaussian, and bionic pulses, with a conventional sandwich transducer. Zero-phase cosine-magnitude waveforms provide minimum
length pulses (and therefore maximum resolution) within a prescribed frequency band.The aim of this paper is to illustrate
the synthesis of wideband acoustic pulses using an underwater piezoelectric projector. The conventional acoustic waveform
radiated when a Tonpiltz transducer is transiently excited using a “click” and allows its frequency response function to be
measured. This function is used to design the electrical signal which then drives the transducer so that it radiates the shortest
pulse compatible with its mechanical response. The significant resolution enhancement of the waveform shaping process is illustrated
by its application to a sediment wedge model. 相似文献
59.
Periáñez R 《Marine environmental research》2005,60(1):35-49
The presence and temporal evolution (1990-2001) of (226)Ra in a tidal estuary affected by the phosphate industry has been investigated. Water samples collected in the course of four separate sampling campaigns were analysed for (226)Ra content using a gas flow proportional counter following Ba coprecipitation. Two (226)Ra sources have been identified: direct discharges from the industrial complex and run-off from a phosphogypsum pile. Although activity levels are similar, or even higher, than those found in other environments affected by the phosphate industry, there has been a general decrease in contamination since direct discharges ceased in 1998 due to new regulations from the EU. However, sediments are now acting as a source of Ra to the water column due to redissolution processes. A numerical model of the estuary has been developed to describe quantitatively the experimental results. The model solves the hydrodynamics and the dispersion equation of (226)Ra including interactions with sediments. Model results are, in general, in good agreement with observations. 相似文献
60.