全文获取类型
收费全文 | 154篇 |
免费 | 4篇 |
国内免费 | 5篇 |
专业分类
化学 | 2篇 |
力学 | 2篇 |
数学 | 6篇 |
物理学 | 73篇 |
综合类 | 80篇 |
出版年
2023年 | 2篇 |
2020年 | 2篇 |
2019年 | 5篇 |
2018年 | 9篇 |
2017年 | 18篇 |
2016年 | 7篇 |
2015年 | 5篇 |
2014年 | 6篇 |
2013年 | 32篇 |
2012年 | 3篇 |
2011年 | 3篇 |
2010年 | 4篇 |
2009年 | 8篇 |
2008年 | 3篇 |
2007年 | 8篇 |
2006年 | 6篇 |
2005年 | 8篇 |
2004年 | 2篇 |
2003年 | 4篇 |
2002年 | 4篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1986年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有163条查询结果,搜索用时 15 毫秒
41.
鲁国辉 《贵州大学学报(自然科学版)》2011,28(5):29-31
马依东二井田位于贵州省盘县特区,面积69.73 km2,含煤地层为二叠系上统龙潭组,可采煤层8层,煤炭总资源量150349万t,井田除上二叠统茅口组(P2m)富水性强外,其余地层富水性均较弱.矿床属于水文地质条件中等的裂隙、溶隙充水矿床.井田的充水水源主要为龙潭组合煤地层裂隙水、第四系及古滑坡孔隙水、部分河水及冲沟水,... 相似文献
42.
C. Unnikrishnan Warrier M. Praveen Babu M. Sudheesh Rajendrakumar D. Deshpande 《Isotopes in environmental and health studies》2016,52(3):219-230
The stable isotopic compositions of all major daily rain fall samples (n?=?113) collected from Kozhikode station in Kerala, India, for the year 2010 representing the pre-monsoon, southwest and northeast monsoon seasons are examined. The isotopic variations δ18O, δ2H and d-excess in daily rainfall ranged from δ18O: ?4.4 to 2?‰, δ2H: ?25.3 to 13.8?‰, and d-excess: ?2.4 to 15.3?‰; δ18O: ?9.7 to ?0.6?‰, δ2H: ?61.7 to 5.3?‰, and d-excess 5.8 to 17.4?‰; δ18O ?11.3 to ?1.4?‰, δ2H: ?75.3 to 0.9?‰, and d-excess: 8.8 to 21.3?‰ during the pre-, southwest and northeast monsoon periods, respectively. Thus, daily rainfall events during two monsoon periods had a distinct range of isotopic variations. The daily rain events within the two monsoon seasons also exhibited periodic variations. The isotopic composition of rain events during pre-monsoon and a few low-intensity events during the southwest monsoon period had imprints of secondary evaporation. This study analysing the stable isotopic characteristics of individual rain events in southern India, which is influenced by dual monsoon rainfall, will aid in a better understanding of its mechanism. 相似文献
43.
面对新形势高等专业对人才的需求,针对水文与水资源工程专业特点,结合校实验教学中心的建设,从实验教学内容、教学方法和手段、实验考核评价机制等几个方面提出了专业实验教学改革的思路和方法。这些措施对学生学习实验的积极性、学生的团队合作能力、知识运用能力、科研能力和自学创新能力起到很大的促进作用,提高了实验教学质量,达到了专业培养目标。 相似文献
44.
Ricardo Sánchez-Murillo Erin S Brooks William J Elliot Jan Boll 《Isotopes in environmental and health studies》2013,49(2):231-254
This study presents a stable isotope hydrology and geochemical analysis in the inland Pacific Northwest (PNW) of the USA. Isotope ratios were used to estimate mean transit times (MTTs) in natural and human-altered watersheds using the FLOWPC program. Isotope ratios in precipitation resulted in a regional meteoric water line of δ2H?=?7.42·δ18O?+?0.88 (n?=?316; r2?=?0.97). Isotope compositions exhibited a strong temperature-dependent seasonality. Despite this seasonal variation, the stream δ18O variation was small. A significant regression (τ?=?0.11D?1.09; r2?=?0.83) between baseflow MTTs and the damping ratio was found. Baseflow MTTs ranged from 0.4 to 0.6 years (human-altered), 0.7 to 1.7 years (mining-altered), and 0.7 to 3.2 years (forested). Greater MTTs were represented by more homogenous aqueous chemistry whereas smaller MTTs resulted in more dynamic compositions. The isotope and geochemical data presented provide a baseline for future hydrological modelling in the inland PNW. 相似文献
45.
Christopher H. Conaway Burt Thomas Nabil Saad James J. Thordsen Yousif K. Kharaka 《Isotopes in environmental and health studies》2013,49(2):344-358
This work examines the performance and limitations of a wet chemical oxidation carbon analyser interfaced with a cavity ring-down spectrometer (WCO-CRDS) in a continuous flow (CF) configuration for measuring δ13C of dissolved organic carbon (δ13C-DOC) in natural water samples. Low-chloride matrix (<5?g Cl/L) DOC solutions were analysed with as little as 2.5?mg C/L in a 9?mL aliquot with a precision of 0.5?‰. In high-chloride matrix (10–100?g Cl/L) DOC solutions, bias towards lighter δ13C-DOC was observed because of incomplete oxidation despite using high-concentration oxidant, extended reaction time, or post-wet chemical oxidation gas-phase combustion. However, through a combination of dilution, chloride removal, and increasing the oxidant:sample ratio, high-salinity samples with sufficient DOC (>22.5?µg C/aliquot) may be analysed. The WCO-CRDS approach requires more total carbon (µg C/aliquot) than conventional CF-isotope ratio mass spectrometer, but is nonetheless applicable to a wide range of DOC concentration and water types, including brackish water, produced water, and basinal brines. 相似文献
46.
J. Makowski 《Isotopes in environmental and health studies》2013,49(9):327-332
Die mit Hilfe von radioaktiven Wässern durchgeführten hydrogeologischen und hydrotechnischen Untersuchungen waren hinsichtlich der richtigen Wahl geeigneter Radionuklide und noch mehr bezüglich der Festlegung der notwendigen Aktivität mit gewissen Schwierigkeiten verbunden. Dieser Bericht umfaβt praktisch alle bisher in Polen unternommenen Versuche, ein definiertes Modell für solche vorversuche aufzustellen, damit man auf eine lergleichbare Il'eise die Faktoren fiir die verschiedenen liadionuklide unler ungleichen physiko- chemischen und hydraulischen Bedingungen festlegen kann. Die mit diesem Modell an Wassersäulen von verschiedener Dimension durchgeführten Versuche haben zu einer experimenlellen Gleichung geführt, die in einer einfachen Form die Abhäingigkeit der Konzentralions¯nderung eines radioaktiven Tracers mit dem Verlauf seiner Strömung darstellt. Der einzige in dieser Gleichung auftretende Koeffizient genügt, um die Gesamtcharakteristik der Dispersionsfaktoren, die von der Art der Nuklide, des Strömungscharakters und der physiko-chemischen Eigenschajten des Grund- und Wassermediums abluingig sind. zu kennzeichnen. 相似文献
47.
M. Krimissa L. Chery C. Fouillac J. L. Michelot 《Isotopes in environmental and health studies》2013,49(4):317-331
The thermo-mineral waters of the axial zone of the Eastern Pyrenees form a geochemically homogeneous group. They emerge in granite or orthogneiss and all have a sodium sulphide chemistry. Principal component analysis of their physico-chemical parameters has distinguished three types of fluid, 1) hot water that has evolved in a closed system and whose chemistry may reflect that of deep water, 2) water that is also of unmixed origin, but whose chemical composition has been modified during cooling by conduction, and 3) water cooled by mixing with surface water. Stable isotope (18O, 2H) contents indicate that all the waters are of meteoric origin (from oceanic and/or Mediterranean precipitation). No heavy isotope enrichment has been found that would indicate evaporation or a geothermal effect between water and the host rock. The differences in isotope contents between surface and thermo-mineral waters are attributed to a difference in recharge altitude; altitude gradients in 18O and 2H, estimated by two independent methods, are respectively 0.24‰ and 1.84° per 100m. They may, however, be lower when precipitation is in the form of snow. Applying these calculated gradients to thermo-mineral waters, taking mixing effects into account, has given an estimate of the minimum altitude of recharge of 110 springs in the Eastern Pyrenees. 相似文献
48.
Geoff Koehler 《Isotopes in environmental and health studies》2013,49(4):404-418
ABSTRACTWe investigated the influence of post-collection changes and snow gauge undercatch on the stable isotopic compositions of winter precipitation. Post-collection changes by evaporation or sublimation can be severe, and may be minimized, but not eliminated, by emptying collection gauges immediately after snowfall. Snow gauge undercatch caused two main effects: a small direct effect caused by preferential separation of snow particles during snowfall, and a much larger effect on the measured stable isotopic compositions of average annual precipitation as a result of under representation of winter precipitation. Despite these effects, however, we found little change to calculated local meteoric water lines (LMWL) for Saskatoon, SK, Canada. A comprehensive 27-year LMWL for Saskatoon which incorporates these effects can be described by δ2H?=?7.69?±?0.096?×?δ18O?–?2.22?±?1.72 (r2?=?0.97, n?=?208). 相似文献
49.
Abstract Representative water samples were collected from different oases in the western desert of Egypt to examine characteristics of Egyptian groundwater. Chemical data recognized two basic groundwater types; alkali bicarbonate and alkali chloride, where sodium has the highest concentration. For each region the median SD, δ18 0 and ionic strength of water calculated from their chemical analyses are recorded and plotted. Generally, the results of isotopic content measurements of the groundwaters from the different oases in the western desert indicate the fossile origin of these waters. The values of δD and δ18 0 of the western desert oases' waters are characteristic of old paleowaters from the Nubian sand aquifer. Modern sparse rainfall data suggest that any precipitation will exhibit moderate to large positive isotopic content enrichments and cannot be a source for these waters. They have been in no connection with the Nile water, moreover the change in isotopic composition is due to evaporation which is now ineffective at deeper levels. 相似文献
50.
Dietmar Haendel Reiner Höfling Peter Kowski 《Isotopes in environmental and health studies》2013,49(4):402-406
In 1983/1984, in the course of the 28th Soviet Antarctic Expedition, waterbody, ice cover, and surrounding glaciers of the lakes Untersee and Obersee were sampled along some depth profiles. The geochemical data of those samples, now available, show the homogeneity of both large lakes in vertical (down to the maximum depth) as well as in lateral directions. The comparison of isotope and chemical composition of lake water and adjoining glacier ice suggests strong differences in the long-term evolution between the lakes Untersee and Obersee. First data from a lakelet, embedded in the large morainic area to the west of Lake Untersee, are of special interest: the δ2H values of the lakelet water are lower than those of recent regional glacier ice by 50‰ SMOW. This fact indicates that the lakelet is fed episodically by Pleistocene dead ice, covered by the morainic material. 相似文献