全文获取类型
收费全文 | 1226篇 |
免费 | 123篇 |
国内免费 | 266篇 |
专业分类
测绘学 | 122篇 |
大气科学 | 129篇 |
地球物理 | 470篇 |
地质学 | 584篇 |
海洋学 | 126篇 |
天文学 | 38篇 |
综合类 | 41篇 |
自然地理 | 105篇 |
出版年
2022年 | 11篇 |
2021年 | 10篇 |
2020年 | 9篇 |
2019年 | 11篇 |
2018年 | 23篇 |
2016年 | 15篇 |
2015年 | 13篇 |
2014年 | 26篇 |
2013年 | 25篇 |
2012年 | 60篇 |
2011年 | 71篇 |
2010年 | 19篇 |
2009年 | 29篇 |
2008年 | 51篇 |
2007年 | 51篇 |
2006年 | 73篇 |
2005年 | 60篇 |
2004年 | 56篇 |
2003年 | 41篇 |
2002年 | 60篇 |
2001年 | 51篇 |
2000年 | 66篇 |
1999年 | 26篇 |
1998年 | 27篇 |
1997年 | 33篇 |
1996年 | 25篇 |
1995年 | 38篇 |
1994年 | 37篇 |
1993年 | 42篇 |
1992年 | 35篇 |
1991年 | 55篇 |
1990年 | 50篇 |
1989年 | 45篇 |
1988年 | 43篇 |
1987年 | 32篇 |
1986年 | 29篇 |
1985年 | 29篇 |
1984年 | 22篇 |
1983年 | 31篇 |
1982年 | 13篇 |
1981年 | 7篇 |
1980年 | 18篇 |
1965年 | 8篇 |
1964年 | 8篇 |
1959年 | 9篇 |
1958年 | 19篇 |
1957年 | 14篇 |
1955年 | 6篇 |
1954年 | 8篇 |
1930年 | 6篇 |
排序方式: 共有1615条查询结果,搜索用时 15 毫秒
981.
982.
Dietary metal exposure in fish is studied in native red mullet, Mullus barbatus, involving metallothionein (MT) response in the intestine, a primary site for metal uptake. Intestinal MTs (microg mg(-1) proteins), total proteins (mgml(-1) S50), Cu, Zn, Fe, Mn and Cd (microg ml(-1) S50) are considered as indicators of metal exposure in specimens from near-shore and off-shore locations of the Eastern Adriatic Sea. Metallothionein and Cu are statistically significantly higher in 68 specimens from the Kastela Bay, a near-shore area (30.0+/-6.71microg MT mg(-1) proteins; 0.30+/-0.08microg Cu ml(-1) S50), in comparison to 51 specimens from off-shore area, Solta Island (25.9+/-4.21microg MT mg(-1) proteins; 0.26+/-0.09microg Cu ml(-1) S50). Cytosolic Cu, a MT inducer, is significantly correlated (p<0.05, r=0.44) with MT in specimens from the Kastela Bay, independent on fish biometry. Our study indicates that cytosolic intestinal Cu and MT represent a measurable biochemical response in red mullet specimens, dwelling above sediments contaminated with Cu. 相似文献
983.
The benthic bivalve, Anadara trapezia, was collected from a 'clean' reference site and transplanted along a suspected trace metal contamination gradient in Lake Macquarie, NSW. At monthly intervals, Zn, Se, Cd and Pb concentrations were measured in the surficial sediments and whole tissues of the cockle as well as their physiological condition (Scope for Growth). Zinc, Cd and Pb concentrations in sediments decreased together, southward, with the highest concentrations in the Cockle Bay area, suggesting that this is the main source of contamination. Zinc, Cd and Pb concentrations were near or above [ANZECC/ARMCANZ, 2000. National water quality management strategy paper 4. Australian and New Zealand Guidelines for Fresh and Marine Water Quality, Australian and New Zealand Conservation Council and Agriculture and Resource Management Council of Australia and New Zealand. pp. 3.5.-1-3.5-10] sediment quality guidelines at Cockle Creek, Warners Bay and Koorooa Bay. Significant differences in trace metal concentrations could not be attributed to grain size or Fe concentration differences. Se concentrations were highest in fine grain Fe rich sediments of Whiteheads Lagoon, and likely to be associated with power generation operations. Trace metal concentrations did not vary significantly over time. Zinc, Cd and Pb concentrations in the tissues of A. trapezia followed a similar pattern to that of sediments. Zinc and Pb concentrations in cockles and sediments were highly correlated, indicating significant exposure-dose relationships. Selenium concentrations in the tissues of A. trapezia were higher after transplantation to the lake, however, Se concentrations were similar in all transplanted cockles, indicating that Se in contaminated sediments is not the major source of Se to organisms. There was a decline in the physiological condition of A. trapezia transplanted to Lake Macquarie after a 90-day-period with marked differences in clearance rates and respiration rates at some locations and absorption efficiencies at all locations. The mean Scope for Growth value at the most contaminated location, Cockle Bay, was markedly lower than at other locations. A significant Zn exposure-dose response relationship indicates that Zn bioaccumulation is occurring in response to sediment contamination. A significant Cd exposure-response relationship indicates that Cd may be influencing the health of cockles. Significant Pb exposure-dose, exposure-response and dose-response relationships indicate that Pb probably is affecting the health of cockles in Lake Macquarie. Therefore, Zn, Cd and Pb concentrations in sediments are likely to be affecting the health of cockles in Lake Macquarie. 相似文献
984.
A kerosene type hydrocarbon fraction (equivalent to 7 L m(-2)) was added to enclosures in the surface layer of high-arctic intertidal beach sediment. The experimental spill was repeated in two consecutive years in the period July-September. The rate and extent of hydrocarbon removal and the accompanying bacterial response were monitored for 79 days (2002) and 78 days (2003). The bulk of added kerosene, i.e. 94-98%, was lost from the upper 5 cm layer by putatively abiotic processes within 2 days and a residual fraction in the range 0.6-1.2mg per g dry sediment was stably retained. Concomitant addition of oleophilic fertilizer led to higher initial retention, as 24% of the kerosene remained after 2 days in the presence of a modified, cold-climate adapted version of the well-known Inipol EAP 22 bioremediation agent. In these enclosures, which showed an increase in hydrocarbon-degrader counts from 6.5 x 10(3) to 4.1 x 10(7) per g dry sediment within 8 days, a 17% contribution by biodegradation to subsequent hydrocarbon removal was estimated. Stimulation in hydrocarbon-degrader counts in fertilizer-alone control enclosures was indistinguishable from the stimulation observed with both kerosene and fertilizer present, suggesting that the dynamics in numbers of hydrocarbon-degrading bacteria was primarily impacted by the bioremediation agent. 相似文献
985.
前言
信息工艺发展到现代水平提出任务,即开发研究可保障用户在处理有关自然环境信息的整个过程——从计算机网络检索到分析结果和采取措施均能够得到计算机支持的软件技术系统。一方面是生态情况的紧张状态、自然资源利用的集约化及其监测的必要性; 相似文献
986.
J. Y. Liu Y. J. Chuo S. J. Shan Y. B. Tsai Y. I. Chen S. A. Pulinets S. B. Yu 马洁美 《国际地震动态》2005,(11):63-70
本文旨在通过全球定位系统(GPS)地面接收器得到的总电子含量(TEC)来研究地震发生前的电离层异常.利用连续15天的TEC中值和相关的四分位距(IQR)作为参考来识别1999年9月到2002年12月之间台湾地区20个M≥6.0的地震发生前的异常信号。结果表明在其中的16个地震发生的前5天18:00—22:00LT(LT=UT+8h)之间出现了电离层异常。80%的成功率表明用GPSTEC记录大地震前的电离层异常是有效的。 相似文献
987.
988.
Rainfall prediction remains one of the most challenging problems in weather forecasting. In order to improve high-resolution quantitative precipitation forecasts (QPF), a new procedure for assimilating rainfall rate derived from radar composite reflectivity has been proposed and tested in a numerical simulation of the Chicago floods of 17–18 July 1996. The methodology is based on the one-dimensional variation scheme (1DVAR) assimilation approach introduced by Fillion and Errico but applied here using the Ka... 相似文献
989.
This study investigates the use of dynamic a priori error information according to atmospheric moistness and the use of quality controls in temperature and water vapor profile retrievals from hyperspectral infrared (IR) sounders. Temperature and water vapor profiles are retrieved from Atmospheric InfraRed Sounder (AIRS) radiance measurements by applying a physical iterative method using regression retrieval as the first guess. Based on the dependency of first-guess errors on the degree of atmospheric moistness, the a priori first-guess errors classified by total precipitable water (TPW) are applied in the AIRS physical retrieval procedure. Compared to the retrieval results from a fixed a priori error, boundary layer moisture retrievals appear to be improved via TPW classification of a priori first-guess errors. Six quality control (QC) tests, which check non-converged or bad retrievals, large residuals, high terrain and desert areas, and large temperature and moisture deviations from the first guess regression retrieval, are also applied in the AIRS physical retrievals. Significantly large errors are found for the retrievals rejected by these six QCs, and the retrieval errors are substantially reduced via QC over land, which suggest the usefulness and high impact of the QCs, especially over land. In conclusion, the use of dynamic a priori error information according to atmospheric moistness, and the use of appropriate QCs dealing with the geographical information and the deviation from the first-guess as well as the conventional inverse performance are suggested to improve temperature and moisture retrievals and their applications. 相似文献
990.
This paper deals with new discovery of cosmic spherules and microdiamonds from Middle Pleistocene Selenge river basin on the Teel aggradation terrace.
The Teel aggradation terrace is located at the left edge of the Selenge River, at the pedestal of mountain Namnan uul (Dorjnamjaa et al., 2008). The Teel ter-race is those whose cusp and bench entirely composed of alluvial deposits. This indicates that the Selenge River has a long history of development, and had time to develop a flood plain and to deposit alluvium, through which it cut subsequently and left behind a Teel terrace. Alluvium studies may be of great practi-cal interest because in some areas, river terraces are veritable treasure-troves of economic minerals. With river terraces are associated most placer deposits of such important economic minerals as gold, platinum, diamond, etc. Numerous engineering projects, such as bridges(Kherlen, Tuul, Selenge, Orkhon, Baidrag, Zavkhan, etc.), dams (Ulaan Boom), hydropower plants(Durgun Nuur, Ulaan Boom) are built on alluvial deposits. Hence we need to know all the essential fea-tures of the geostructure of river terraces. Our investi-gation of the Selenge river terraces in 2006-2008 gave a possibility to discover the placer diamonds within the Teel aggradation terrace for the first time in Mongolia. 相似文献