全文获取类型
收费全文 | 33594篇 |
免费 | 5150篇 |
国内免费 | 6897篇 |
专业分类
测绘学 | 4435篇 |
大气科学 | 4650篇 |
地球物理 | 9117篇 |
地质学 | 14102篇 |
海洋学 | 4278篇 |
天文学 | 1406篇 |
综合类 | 2519篇 |
自然地理 | 5134篇 |
出版年
2024年 | 123篇 |
2023年 | 373篇 |
2022年 | 938篇 |
2021年 | 1223篇 |
2020年 | 1427篇 |
2019年 | 1700篇 |
2018年 | 1227篇 |
2017年 | 1555篇 |
2016年 | 1578篇 |
2015年 | 1701篇 |
2014年 | 2057篇 |
2013年 | 2461篇 |
2012年 | 2122篇 |
2011年 | 2276篇 |
2010年 | 1781篇 |
2009年 | 2280篇 |
2008年 | 2238篇 |
2007年 | 2302篇 |
2006年 | 2263篇 |
2005年 | 1840篇 |
2004年 | 1725篇 |
2003年 | 1445篇 |
2002年 | 1178篇 |
2001年 | 998篇 |
2000年 | 914篇 |
1999年 | 858篇 |
1998年 | 853篇 |
1997年 | 735篇 |
1996年 | 598篇 |
1995年 | 528篇 |
1994年 | 440篇 |
1993年 | 417篇 |
1992年 | 291篇 |
1991年 | 234篇 |
1990年 | 176篇 |
1989年 | 176篇 |
1988年 | 123篇 |
1987年 | 80篇 |
1986年 | 68篇 |
1985年 | 69篇 |
1984年 | 39篇 |
1983年 | 19篇 |
1982年 | 29篇 |
1981年 | 21篇 |
1980年 | 24篇 |
1979年 | 16篇 |
1977年 | 19篇 |
1976年 | 25篇 |
1973年 | 17篇 |
1971年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Y. -K. Tung K. -C. Yeh J. -C. Yang 《Stochastic Environmental Research and Risk Assessment (SERRA)》1997,11(2):145-171
Hydrologic regionalization is a useful tool that allows for the transfer of hydrological information from gaged sites to ungaged
sites. This study developed regional regression equations that relate the two parameters in Nash's IUH model to the basin
characteristics for 42 major watersheds in Taiwan. In the process of developing the regional equations, different regression
procedures including the conventional univariate regression, multivariate regression, and seemingly unrelated regression were
used. Multivariate regression and seeming unrelated regression were applied because there exists a rather strong correlation
between the Nash's IUH parameters. Furthermore, a validation study was conducted to examine the predictability of regional
equations derived by different regression procedures. The study indicates that hydrologic regionalization involving several
dependent variables should consider their correlations in the process of establishing the regional equations. The consideration
of such correlation will enhance the predictability of resulting regional equations as compared with the ones from the conventional
univariate regression procedure. 相似文献
992.
Dariusz Kucharczyk Miroslaw Luczynski Roman Kujawa Piotr Czerkies 《Aquatic Sciences - Research Across Boundaries》1997,59(3):214-224
Influence of water temperature on embryonic and larval development of bream (Abramis brama L.) was stdied. Eggs of bream were incubated at eight constant water temperatures between 13.2 and 26.8°C. The temperature
of 21.1°C gave highest hatching success, with no abnormalities in the eleutheroembryos and lowest mortality observed between
eyed egg stage and the time of hatching. Developmental rate increased with increasing temperature. Duration of embryonic development
(y; hours) decreased with increasing incubation temperature (x; °C) according to the formula: y=910.1−65.88 x+1.318 x2. Larvae were reared at eight constant temperatures ranging from 13.5 to 34.0°C. The instantaneous growth rate in wet weight
increased with increasing test temperature from 13.5 to 29.9°C, and then decreased at higher temperatures. Individual growth
of fish and biomass production rate were highest at 27.9°C. This temperature is considered optimal when food availability
and photoperiod are no limiting factors. 相似文献
993.
The separation of the influence of nutrients and climate on the varve time-series of baldeggersee, Switzerland 总被引:7,自引:2,他引:7
The varve data-set from a freeze-core taken in the deepest part of Baldeggersee was subjected to different multivariate statistical
analyses in order to estimate the amount of variance in the varve thickness measures explicable by past climate and by the
trophic state of the lake. A comparison of two different time-periods (1902 to1992 versus 1920 to 1980) revealed that the
lake restoration programme since 1982 has had a significant impact on the formation of the seasonal layers. Results of the
partitioning of the variance in the varve thickness measures showed that about two thirds of the variance are unexplained
by a climate and trophic state model and that trophic state explains 6%, whereas climate accounts for about 28% of the variance
before the effect of lake restoration had a strong impact on the varves. Among the climate parameters the amount of annual
precipitation is a strong predictor for explaining the thickness of both dark layer and total couplet thickness, whereas summer
precipitation is important for the thickness of the light layer. 相似文献
994.
K. -C. Yeh J. -C. Yang Y. -K. Tung 《Stochastic Environmental Research and Risk Assessment (SERRA)》1997,11(2):173-192
Hydrologic model parameters obtained from regional regression equations are subject to uncertainty. Consequently, hydrologic
model outputs based on the stochastic parameters are random. This paper presents a systematic analysis of uncertainty associated
with the two parameters, N and K, in Nash's IUH model from different regional regression equations. The uncertainty features
associated with N and K are further incorporated to assess the uncertainty of the resulting IUH. Numerical results indicate
that uncertainty of N and K from the regional regression equations are too significant to be ignored. 相似文献
995.
Federico Murrone Fabio Rossi Pierluigi Claps 《Stochastic Environmental Research and Risk Assessment (SERRA)》1997,11(6):483-510
A conceptual-stochastic approach to short time runoff data modelling is proposed, according to the aim of reproducing the
hydrological aspects of the streamflow process and of preserving as much as possible the dynamics of the process itself. This
latter task implies preservation of streamflow characteristics at higher scales of aggregation and, within a conceptual framework,
involves compatibility with models proposed for the runoff process at those scales. At a daily time scale the watershed response
to the effective rainfall is considered as deriving from the response of three linear reservoirs, respectively representing
contributions to streamflows of large deep aquifers, with over-year response lag, of aquifers which run dry by the end of
the dry season and of subsurface runoff. The surface runoff component is regarded as an uncorrelated point process. Considering
the occurrences of effective rainfall events as generated by an independent Poisson process, the output of the linear system
represents a conceptually-based multiple shot noise process. Model identification and parameter estimation are supported by
information related to the aggregated runoff process, in agreement to the conceptual framework proposed, and this allows parameter
parsimony, efficient estimation and effectiveness of the streamflow reproduction. Good performances emerged from the model
application and testing made with reference to some daily runoff series from Italian basins. 相似文献
996.
Hydrologic model parameters obtained from regional regression equations are subject to uncertainty. Consequently, hydrologic
model outputs based on the stochastic parameters are random. This paper presents a systematic analysis of uncertainty associated
with the two parameters, N and K, in Nash's IUH model from different regional regression equations. The uncertainty features
associated with N and K are further incorporated to assess the uncertainty of the resulting IUH. Numerical results indicate
that uncertainty of N and K from the regional regression equations are too significant to be ignored. 相似文献
997.
强余震持续时间的早期估计 总被引:2,自引:0,他引:2
本研究旨在解决地震序列中强余震持续时间的早期估计问题。文中首先给出了强余震的震级定义,指出:主震型与强震群型序列的强作震持续时间存在差异。使用模式识别方法对主震型序列中强余震持续时间大于1天,小于1天及无强余震等3种情况进行划分之后,给出了两类序列的强余震持续时间与序列和第一震震级的粗略相关关系。 相似文献
998.
在分散度不同的区域内进行区域采样用于水中硫酸根离子的测定,结果令人满意。应用此方法测定硫酸根离子的线性范围为200.0~3000mg/L;进样频率为120次/h;相对标准偏差为1.70% 相似文献
999.
依据东坪金矿区成矿特点进行了成矿构造的形成及应力分析,总结出一些成矿规律,并进一步对矿区一睦工作程度较低的区段进行了预测。 相似文献
1000.
孔隙流体压力与流体排驱的关系 总被引:2,自引:3,他引:2
本文讨论了在压实作用下孔隙流体压力的形成以及与流体排驱的关系,指出异常孔隙流体压力是因岩石渗透率变化引起毛细管力增加而产生的,且二者之间在流体压力孕育过程中一直维持一个动态平衡状态。对于连续沉积的盆地,只有当异常孔隙流体压力增加到超过岩石的抗剪强度时,因岩石发生剪切破裂导致毛细管力降低,流体才被排出;对于强烈构造变动的盆地,因地层大量剥蚀引起负荷压力降低,其降低幅度达到或超过岩石的抗张强度时,岩石 相似文献