全文获取类型
收费全文 | 30625篇 |
免费 | 510篇 |
国内免费 | 319篇 |
专业分类
测绘学 | 738篇 |
大气科学 | 2393篇 |
地球物理 | 6611篇 |
地质学 | 10606篇 |
海洋学 | 2562篇 |
天文学 | 6233篇 |
综合类 | 51篇 |
自然地理 | 2260篇 |
出版年
2020年 | 196篇 |
2019年 | 191篇 |
2018年 | 386篇 |
2017年 | 376篇 |
2016年 | 529篇 |
2015年 | 394篇 |
2014年 | 538篇 |
2013年 | 1466篇 |
2012年 | 661篇 |
2011年 | 1008篇 |
2010年 | 855篇 |
2009年 | 1123篇 |
2008年 | 1058篇 |
2007年 | 984篇 |
2006年 | 1039篇 |
2005年 | 881篇 |
2004年 | 913篇 |
2003年 | 860篇 |
2002年 | 854篇 |
2001年 | 691篇 |
2000年 | 696篇 |
1999年 | 668篇 |
1998年 | 635篇 |
1997年 | 637篇 |
1996年 | 539篇 |
1995年 | 533篇 |
1994年 | 506篇 |
1993年 | 475篇 |
1992年 | 453篇 |
1991年 | 388篇 |
1990年 | 469篇 |
1989年 | 375篇 |
1988年 | 414篇 |
1987年 | 465篇 |
1986年 | 391篇 |
1985年 | 564篇 |
1984年 | 649篇 |
1983年 | 626篇 |
1982年 | 510篇 |
1981年 | 503篇 |
1980年 | 511篇 |
1979年 | 470篇 |
1978年 | 457篇 |
1977年 | 427篇 |
1976年 | 444篇 |
1975年 | 396篇 |
1974年 | 429篇 |
1973年 | 421篇 |
1972年 | 262篇 |
1971年 | 207篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Möglichkeiten der photometrischen Untersuchung von Kugelhaufen mittels photographischer Äquidensiten
A method of estimating the surface-brightness of globular cluster with equidensity curves is described. (Russian abstract) 相似文献
62.
W. Fehlmann 《Aquatic Sciences - Research Across Boundaries》1931,5(1-2):130-141
Ohne Zusammenfassung 相似文献
63.
64.
65.
Robert Kreuzig 《洁净——土壤、空气、水》2010,38(8):697-705
Veterinary medicines and biocides are frequently applied in animal houses of livestock husbandry. Due to these application patterns, they reach liquid manure. So far these substances are not transformed during manure storage, they enter soil by the application of manure as organic fertilizer. Therefore, biodegradability of veterinary medicines and biocides in manure is in the focus of regulatory procedures of environmental risk assessment. Since the representative and reproducible sampling of manures from high volume tanks is considered impossible due to high matrix variabilities, the reference manure concept was developed to utilize liquid bovine and pig manures for reproducible laboratory testing. Accordingly, excrement samples of cattle and pigs individually kept at experimental and conventional animal houses were taken. Tap water was added to matrix characterized excrements in order to prepare bovine and pig reference manures of 10 and 5% dry substance contents, respectively. Subsequently, the long‐term transformation of selected 14C‐labeled test substances was investigated under strictly anaerobic conditions. The application of different batches of bovine or pig reference manures indicated that extrapolation of transformation rates within the same animal species was possible. However, results cannot be transferred from bovine to pig manure because of substance specific interactions with the different manure matrices. The dependency of metabolic dynamics on different dry substance contents (2.5, 5, 10%) was additionally investigated in both manure matrices. These tests clearly showed that the dry substance content of the reference manure is one of the most relevant factors affecting the transformation of veterinary medicines and biocides. In contrast to highly variable tank manures, the reference manure concept allows for the exact adjustment of this parameter to guarantee reproducible laboratory testing. 相似文献
66.
The modified time-to-failure method for intermediate-term earthquake prediction utilizes empirical relationships to reduce the number of unknown parameters providing a stable and unique solution set. The only unknown parameters in the modified time-to-failure method are the time and size of the impending main shock. The modified time-to-failure equation is used to model the precursory events and a prediction contour diagram is constructed with the magnitude and time-of-failure as the axes of the diagram. The root-mean-square (rms) is calculated for each set of time and magnitude on the prediction diagram representing the difference between the model (calculated) acceleration and the actual accelerated energy release of the precursory events. A small region, corresponding to the low rms region on the diagram, defines the prediction. The prediction has been shown to consistently under-estimate the magnitude and over-estimate the time-of-failure. These shortcomings are caused by an underestimation in energy release of the modified time-to-failure equation at the very end of the sequence. An empirical correction can be applied to the predicted results to minimize this problem. A main shock location search technique has been developed for use with the modified time-to-failure method. The location technique is used to systematically search an earthquake catalog and identify locations corresponding to precursory sequences that display accelerated energy releases. It has shown good results when applied in retrospective predictions, and is essential for the practical application of the modified time-to-failure method. In addition, an observed linear characteristic in long-term energy release can be used to minimize false predictions. The refined empirical relationships that eliminate or constrain unknown constants used in the modified time-to-failure method and the main shock location search technique are used in a practical application in the New Madrid Seismic Zone (NMSZ). The NMSZ, which is over due for a magnitude 6 event according to recurrence rates (Johnston and Nava, 1985), makes this region ideal for testing the method. One location was identified in the NMSZ as a high risk area for an event in the magnitude 4.5 range. The prediction, if accurate, is of scientific interest only because of the relatively small size of the main shock. 相似文献
67.
68.
Robert G. Garrett 《Journal of Geochemical Exploration》1974,3(3):277-289
Data for the mean mercury contents of some granitoid rocks of the Yukon are presented. A correlation of high mercury content with plutons postulated to be the sources, or genetically related to the sources, of the alluvial gold deposits of the McQuesten area is established. In addition a relation is indicated between high mercury content in one intrusion and high content in the Palaeozoic shale host rock. A limited amount of data is presented on the mercury content of the Proterozoic and Palaeozoic rocks of the sampled area. 相似文献
69.
70.
The Cryogenian succession of the Northern Flinders Ranges reveals a complex sedimentary record between the Sturtian and Marinoan glacial deposits. A major unconformity separates the Sturtian and Marinoan-aged sedimentary successions in the area. This forms a subaerial erosion surface with terrestrial and marginal marine infill directly above the Angepena and Balcanoona Formations in their respective localities. This exposure surface is here correlated with the previously documented submarine unconformity between the Yankaninna Formation and the underlying deep marine Tapley Hill Formation. This erosional event provides a chronostratigraphic marker horizon that coincides approximately with thepreviously defined Sturtian–Marinoan Time Series boundary in the Northern Flinders Ranges. These stratigraphic relationships also constrain lateral facies relationships between the Oodnaminta ReefComplex (Balcanoona Formation) and the Angepena Formation. Similarly, the shallow-water Weetootla Dolomite is correlated with the deeper water carbonates of the Yankaninna Formation. 相似文献