全文获取类型
收费全文 | 20335篇 |
免费 | 2733篇 |
国内免费 | 4107篇 |
专业分类
测绘学 | 1432篇 |
大气科学 | 3276篇 |
地球物理 | 4081篇 |
地质学 | 10299篇 |
海洋学 | 2833篇 |
天文学 | 1969篇 |
综合类 | 1301篇 |
自然地理 | 1984篇 |
出版年
2024年 | 95篇 |
2023年 | 267篇 |
2022年 | 845篇 |
2021年 | 1101篇 |
2020年 | 973篇 |
2019年 | 1067篇 |
2018年 | 1283篇 |
2017年 | 1176篇 |
2016年 | 1204篇 |
2015年 | 965篇 |
2014年 | 1206篇 |
2013年 | 1309篇 |
2012年 | 1301篇 |
2011年 | 1384篇 |
2010年 | 1282篇 |
2009年 | 1241篇 |
2008年 | 1162篇 |
2007年 | 1181篇 |
2006年 | 1086篇 |
2005年 | 658篇 |
2004年 | 541篇 |
2003年 | 594篇 |
2002年 | 682篇 |
2001年 | 620篇 |
2000年 | 458篇 |
1999年 | 464篇 |
1998年 | 333篇 |
1997年 | 370篇 |
1996年 | 296篇 |
1995年 | 306篇 |
1994年 | 272篇 |
1993年 | 209篇 |
1992年 | 197篇 |
1991年 | 126篇 |
1990年 | 117篇 |
1989年 | 133篇 |
1988年 | 92篇 |
1987年 | 75篇 |
1986年 | 63篇 |
1985年 | 46篇 |
1984年 | 47篇 |
1983年 | 49篇 |
1982年 | 41篇 |
1981年 | 25篇 |
1980年 | 24篇 |
1979年 | 32篇 |
1978年 | 17篇 |
1977年 | 19篇 |
1975年 | 24篇 |
1973年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 515 毫秒
121.
阐述把维生素B12生产菌添加到培养水中培养褶皱臂尾轮虫BrachionusPlicatilis的买验。共18株细菌分离于轮虫培养池,其中,有一株产维生素B12的假单胞杆菌TP4对轮虫的生长繁殖有明显的促进作用。把TP4菌株培养后,加入到2L的烧杯和500L的水槽中培养泰国S型轮虫时.在9d(天)和6d(天)中,轮虫密度从124~139和242~288个体/ml增殖到4,417~5,540和1,017~1,254个体/ml,分别比对照组增加了4~6及2~3倍。 相似文献
122.
This paper considers the results of numerical experiments involving POLYMODE data assimilation by a barotropic model for synoptic ocean dynamics. The model's response the data assimilation for various space-time discretenesses of assimilation is studied. Results derived from the application of optimal interpolation algorithms and modified optimal filtration algorithms are compared. Qualitative similarity to the calculations carried out through the simulation modelling technique is noted. Optimal assimilation algorithms are determined, depending on the space-time discreteness used. An optimal sampling discreteness for the POLYMODE conditions is suggested.Translated by Vladimir A. Puchkin. 相似文献
123.
Ya. A. Virolainen Yu. M. Timofeev A. V. Polyakov H. Steele M. Newchurch 《Izvestiya Atmospheric and Oceanic Physics》2006,42(6):752-764
A statistical ensemble of microphysical parameters of the background stratospheric aerosol at altitudes of 15 to 30 km is modeled on the basis of experimental data. The aerosol attenuation coefficients (AACs) in the wavelength range 0.38–16.3 μm are calculated for all realizations of the ensemble by algorithms of the Mie theory. Analysis of correlations between the AACs and the microphysical parameters indicate that the AAC correlates most strongly with the total volume V and area S of all particles. The errors of determining the microphysical parameters from AAC measurements are analyzed via the method of linear regression. It is shown that, if the AAC is measured with an error of 5%, the errors of determining both the particle size distribution (PSD) for particles with sizes of 0.4 to 4 μm and the parameter S are an order of magnitude smaller than the prior uncertainty, whereas the error of determining V is two orders of magnitude smaller than the prior uncertainty. Schemes of AAC measurements with the SAGE III, ISAMS, CLAES, HALOE instruments and an IR interferometer in the visible and IR regions are discussed. It is shown that combining the schemes makes it possible to extend the range of particle sizes for which the PSD is retrieved with a satisfactory accuracy and to increase the accuracy of determining S and V substantially and the accuracy of determining the total number of particles N opt to a lesser extent. Examples of interpreting AAC measurements carried out simultaneously with the SAGE III and HALOE instruments within the same spatial region are presented. A systematic discrepancy between vertical profiles of S and V obtained from SAGE III and HALOE measurements is revealed. 相似文献
124.
杆状病毒感染越冬亲虾(Penaeus chenesis)的研究——越冬亲虾感染及其垂直传播的可能性 总被引:2,自引:0,他引:2
在中国对虾越冬亲虾中检出杆状病毒。经对病虾鳃、前中肠、卵巢组织进行电镜观察,在这些组织中发现大量有囊膜的杆状病毒。病毒粒子大小约为367nm×128nm,核衣壳为324nm×92nm。病毒在细胞内不形成包涵体,在核内或在细胞质的发生基质中装配。从病毒的形态特征、感染组织以及典型的发病症状和病理变化,初步认为亲虾感染的病毒与近年广泛报道的造成养殖对虾大规模流行病的主要原因——中国对虾杆状病毒为同一种。卵巢组织也是病毒的主要靶器官之一,亲虾卵巢组织的被感染暗示着该病毒有可能通过生殖细胞而垂直传播 相似文献
125.
研究了青岛市南、市北、四方三区交警在服用排铅奶粉(LeadExcretingMilkPow-der,LEMP)前后,体内粪铅含量变化情况。实验结果表明,服用LEMP后,粪铅含量先呈上升趋势,达到最高值后,又呈下降趋势。在整个实验过程中,粪铅含量四方区最高,而市南区最低。服用LEMP前,三区交警粪铅平均含量为0.687mg/kg,服用7d后达到峰值(1.96mg/kg,P<0.01),第15d降到1.61(mg/kg)(P<0.05),表明LEMP能排除体内铅起到预防铅中毒的作用 相似文献
126.
根据作者导得的AfKdV方程,理论上确定了先锋孤立子生成问题的理论平均波阻,能量劈分及能量劈分比。本文的能量劈分是确定先锋孤立子生成参数的理论基础。同时,本理论确定了现有理论中的自由未知参数问题,从而使先锋孤立子生成参数得到理论预报。 相似文献
127.
128.
Total dissolved selenium and selenium species have been measured in the Rhône river delta and the Gulf of Lions within the framework of the EROS-2000 project. The Rhône river concentration of total selenium averages 2.30 nM with important variations related to river discharge. During estuar-ine mixing, the concentrations of total dissolved selenium, selenite and selenate (calculated as the difference between total dissolved and selenite) decrease linearly with increasing salinity, without significant interconversion between selenium species. In the open Mediterranean waters of the Gulf of Lions the total dissolved selenium increases from 0.5 nM in the surface waters to 0.9 nM in the deep waters. Organic selenium has been observed in Mediterranean deep water, an observation which is different from those from the Atlantic and the Pacific Oceans. The distributions of total inorganic selenium (Σ5e), selenite and selenate are strongly related to phosphate and silicate concentrations as observed previously for the major oceans. 相似文献
129.
V. A. Frol’kis I. L. Karol’ A. A. Kiselev Yu. E. Ozolin V. A. Zubov 《Izvestiya Atmospheric and Oceanic Physics》2007,43(4):413-422
This is a study of the sensitivity of model results (atmospheric content of main gas constituents and radiative characteristics of the atmosphere) to errors in emissions of a number of atmospheric gaseous pollutants. Groups of the model variables most dependent on these errors are selected. Two variants of emissions are considered: one without their evolution and the other with their variation according to the IPCC scenario. The estimates are made on the basis of standard statistical methods for the results obtained with the detailed onedimensional radiative—photochemical model of the Main Geophysical Observatory (MGO). Some approaches to such estimations with models of higher complexity and to the solution of the inverse problem (i.e., the estimation of the necessary accuracy of external model parameters for obtaining the given accuracy of model results) are outlined. 相似文献
130.
IwrincrIONOn the evolution of palcoenvironment, salt-water encroachmnt and the distributionof subsurface brine in the LaizhOu Bay area, many researches had been carried out, and muchknowledge abeut the gcolOgical features in this area since Late QUaternary was aCquired' ) (H8nand Wu, l992; Han and Meng, l994; Wen et al. l989). However there was IittIe studyon the sediment geOChemical characteristics since Quaternary. In this Paper, the element strati-graphic characteristics and evolut… 相似文献