全文获取类型
收费全文 | 37635篇 |
免费 | 6728篇 |
国内免费 | 8719篇 |
专业分类
测绘学 | 2028篇 |
大气科学 | 7734篇 |
地球物理 | 9979篇 |
地质学 | 18288篇 |
海洋学 | 4735篇 |
天文学 | 1730篇 |
综合类 | 4067篇 |
自然地理 | 4521篇 |
出版年
2024年 | 133篇 |
2023年 | 545篇 |
2022年 | 1541篇 |
2021年 | 1809篇 |
2020年 | 1477篇 |
2019年 | 1695篇 |
2018年 | 1959篇 |
2017年 | 1814篇 |
2016年 | 2099篇 |
2015年 | 1651篇 |
2014年 | 2089篇 |
2013年 | 2194篇 |
2012年 | 1998篇 |
2011年 | 2104篇 |
2010年 | 2106篇 |
2009年 | 2067篇 |
2008年 | 1804篇 |
2007年 | 1819篇 |
2006年 | 1405篇 |
2005年 | 1439篇 |
2004年 | 1013篇 |
2003年 | 1114篇 |
2002年 | 1083篇 |
2001年 | 1072篇 |
2000年 | 1294篇 |
1999年 | 1871篇 |
1998年 | 1545篇 |
1997年 | 1618篇 |
1996年 | 1512篇 |
1995年 | 1320篇 |
1994年 | 1134篇 |
1993年 | 996篇 |
1992年 | 792篇 |
1991年 | 560篇 |
1990年 | 454篇 |
1989年 | 378篇 |
1988年 | 357篇 |
1987年 | 225篇 |
1986年 | 210篇 |
1985年 | 135篇 |
1984年 | 105篇 |
1983年 | 98篇 |
1982年 | 91篇 |
1981年 | 64篇 |
1980年 | 75篇 |
1979年 | 60篇 |
1978年 | 29篇 |
1977年 | 22篇 |
1975年 | 21篇 |
1958年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
181.
分析了普通番茄(Lycopersicumesculentum)在NaCl胁迫下酯酶(EST)和过氧化物酶(PRX)同工酶的变化,考察了盐胁迫对10个同工酶位点21个等位基因在特定组织中表达的影响。发现许多EST和PRX等位基因在盐胁迫下表达,产生盐诱导同工酶;另有些等位基因的表达受盐抑制,它们在盐胁迫下的表达活性显著减弱或消失。实验表明,EST和PRX同工酶表达的变化与番茄对盐胁迫的遗传适应性有密切关系。 相似文献
182.
研究池养条件下鲻鱼MugilcephalusLinnaeus的年龄和生长特性,结果表明,鳞片新年轮主要在10—1月出现;鳞长与体长关系式为:R—0.00907L(0.7764);I—V龄鱼体长和体重相对生长率和生长指标随着年龄增长而逐渐下降;体长与体重关系式为:W=1.2716×10(-5)L(3.0695),体长与全长关系式为:LT=10.3711+1.1806LB,当年鱼体长和体重生长与月龄的关系分别为:LB=8.6669+25.5769t,W=0.1170t(3.5530),vonBertallanffy生长参数L∞=613.25mm,K=0.3412,t0=-0.825,体重生长拐点值为2.46a。 相似文献
183.
本文从江苏两万年来的气温升降与海平面变化之间的联系,展开了讨论。把两万年分成七个时段。最后一个时段,即最近2000年来,又分成四个寒期与四个暖期。寒期与暖期是交替出现。世界上已有很多学者把各地的全新世海面变化的曲线分成三种类型,我省的全新世海面变化曲线属于Fairbridge曲线。 相似文献
184.
185.
本文根据1989年4、7、10月和1990年1月(春、夏、秋、冬)秦山核电站邻近水域零点生态调查和水质监测结果的资料整理而成。经研究证明,该海域是河-海混合水域,盐度从小于3至12之间变化,受杭州湾的涌潮、风浪的影响,水体混合比较强烈,悬浮颗粒物质的含量比长江口高。由于该测区所处的海岸、海底地形,生态系统、径流输入以及水体交换状况不同,故其海洋学特征也不相同。 相似文献
186.
Recently, some results have been acquired with the Monte- Carlo statistical experiments in the design of ocean en gineering. The results show that Monte-Carlo statistical experiments can be widely used in estimating the parameters of wave statistical distributions, checking the probability model of the long- term wave extreme value distribution under a typhoon condition and calculating the failure probability of the ocean platforms. 相似文献
187.
188.
By analysing the scatter diagrams of characteristic the wave height H and the period T on the basis of instrumental data from various ocean wave stations, we found that the conditional expectation and standard deviation of wave period for a given wave height can be better predicted by using the equations of normal linear regression rather than by those based on the log- normal law. The latter was implied in Ochi' s bivariate log-normal model(Ochi. 1978) for the long-term joint distribution of H and T. With the expectation and standard deviation predicted by the normal linear regression equations and applying proper types of distribution, we have obtained the conditional distribution of T for given H. Then combining this conditional P(T / H) with long-term marginal distribution of the wave height P(H) we establish a new parameterized model for the long-term joint distribution P(H,T). As an example of the application of the new model we give a method for estimating wave period associated with an extreme w 相似文献
189.
In this study the zinc exchange process and the reason for the non-additive exchange of δ-MnO2/montmorrillonite have been investigated. The results suggest that with pH increasing from 2 to 8, the stepwise exchange of zinc occurs on δ-MnO. and montmorrillonite in their mixture.At low pH zinc ions are bound on δ-MnO2, while at high pH, the exchange on montmorrillonite dominates the surface interaction in the mixture. The study demonstrates that the stepwise exchange and the heterogeneity of the binding sites on δ-MnO2 surface are the reason for the non-additive exchange. It is also shown that when δ-MnO2 amounts to 5 %, zinc exchange on sea sediments is controlled by 8-MnO2. 相似文献
190.
Deformation Patterns of an Accretionary Wedge in the Transition Zone from Subduction to Collision Offshore Southwestern Taiwan 总被引:1,自引:0,他引:1
Char-Shine Liu Benoit Deffontaines Chia-Yu Lu Serge Lallemand 《Marine Geophysical Researches》2004,25(1-2):123-137
Swath bathymetry data and seismic reflection profiles have been used to investigate details of the deformation pattern in the area offshore southwestern Taiwan where the Luzon subduction complex encroaches on the passive Chinese continental margin. Distinctive fold-and-thrust structures of the convergent zone and horst-and-graben structures of the passive margin are separated by a deformation front that extends NNW-ward from the eastern edge of the Manila Trench to the foot of the continental slope. This deformation front gradually turns into a NNE–SSW trending direction across the continental slope and the Kaoping Shelf, and connects to the frontal thrusts of the mountain belt on land Taiwan. However, the complex Penghu submarine canyon system blurs the exact location of the deformation front and nature of many morphotectonic features offshore SW Taiwan. We suggest that the deformation front offshore SW Taiwan does not appear as a simple structural line, but is characterized by a series of N–S trending folds and thrusts that terminate sequentially in an en-echelon pattern across the passive Chinese continental slope. A number of NE–SW trending lineaments cut across the fold-and-thrust structures of the frontal accretionary wedge and exhibit prominent dextral displacement indicative of the lateral expulsion of SW Taiwan. One of the prominent lineaments, named the Yung-An lineament, forms the southeastern boundary of the upper part of the Penghu submarine canyon, and has conspicuous influence over the drainage pattern of the canyon 相似文献