全文获取类型
收费全文 | 29942篇 |
免费 | 5886篇 |
国内免费 | 7795篇 |
专业分类
测绘学 | 1852篇 |
大气科学 | 6380篇 |
地球物理 | 7871篇 |
地质学 | 15740篇 |
海洋学 | 3503篇 |
天文学 | 1413篇 |
综合类 | 3374篇 |
自然地理 | 3490篇 |
出版年
2024年 | 176篇 |
2023年 | 655篇 |
2022年 | 1469篇 |
2021年 | 1669篇 |
2020年 | 1430篇 |
2019年 | 1569篇 |
2018年 | 1831篇 |
2017年 | 1653篇 |
2016年 | 1942篇 |
2015年 | 1552篇 |
2014年 | 1932篇 |
2013年 | 1796篇 |
2012年 | 1685篇 |
2011年 | 1680篇 |
2010年 | 1716篇 |
2009年 | 1674篇 |
2008年 | 1478篇 |
2007年 | 1404篇 |
2006年 | 1135篇 |
2005年 | 958篇 |
2004年 | 833篇 |
2003年 | 860篇 |
2002年 | 790篇 |
2001年 | 760篇 |
2000年 | 964篇 |
1999年 | 1421篇 |
1998年 | 1145篇 |
1997年 | 1142篇 |
1996年 | 1037篇 |
1995年 | 905篇 |
1994年 | 852篇 |
1993年 | 712篇 |
1992年 | 553篇 |
1991年 | 452篇 |
1990年 | 333篇 |
1989年 | 308篇 |
1988年 | 275篇 |
1987年 | 180篇 |
1986年 | 158篇 |
1985年 | 121篇 |
1984年 | 79篇 |
1983年 | 58篇 |
1982年 | 77篇 |
1981年 | 62篇 |
1980年 | 39篇 |
1979年 | 29篇 |
1978年 | 12篇 |
1977年 | 7篇 |
1976年 | 11篇 |
1958年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
ZHANG Jimin ) LIU Shuang ) SUN Xue ) YANG Guanpin ) ZHANG Xuecheng ) * GAO Zhenhui ) ) North China Sea Monitoring Center SOA Fushun Road Qingdao P..R.China) College of Marine Life Sciences Ocean University of China Qingdao P..R.China 《中国海洋大学学报(英文版)》2003,2(1)
1 Introduction Nannochloropsissp .areoneofpotentialsourcesofpolyunsaturatedfattyacids ,especiallytheeicosapen taentaenoicacid (EPA ,C2 0∶5 ) ,whichisimportantforbothanimalsandhumans . Thefattyacidcompositionofthisalgaisaffectedbyvariousenvironmentalfactors ,suchaslightintensity(Sukeniketal.,1989;Sukeniketal.,1990 ) ,imply ingthatafactorinfluencingthephotosyntheticprocessmayaffectcellularfattyacidsynthesisandtheirmetabolism .AselectionprogramofincreasingcellularEPAcontenthasbeencarriedo… 相似文献
92.
The paper provides a new stereo‐analytical method, which is a combination of the stereographic method and analytical methods, to separate finite removable blocks from the infinite and tapered blocks in discontinuous rock masses. The methodology has applicability to both convex and concave blocks. Application of the methodology is illustrated through examples. Addition of this method to the existing block theory procedures available in the literature improves the capability of block theory in solving practical problems in rock engineering. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
93.
利用高光谱数据进行植被生化成分反演方法研究 总被引:3,自引:0,他引:3
高光谱数据包含着丰富光谱信息,能够定量地分析物质成分[1]。由高光谱数据,可以运用多元逐步线性回归方法反演植被生化组分含量,从而达到监测植被生长状况的目的[2]。本文具体介绍了多元逐步线性回归方法,及其在氮、木质素和纤维素含量估算中的应用。 相似文献
94.
本文通过对成都10个重污染日进行天气学分析,将污染浓度与气象要素进行聚类、研究了重污染日形成原因及污染浓度与气象要素的关系。在此基础上,建立了SO_2、TSP日平均浓度分级预报方程。 相似文献
95.
Pavlova viridis sp. nov. is described on the basis of light and electron microscope observations. The material was collected from the coast
of haiyang county of Shandong, China. It is characterized by 1) yellowish green to green chloroplast, 2) rudimentary short
flagellum 0.3 μm long and hook-shaped, 3) long flagellum with small spherical knob-scales, 4) absence of pyrenoid and stigma,
and 5) marine habitat. This new species andP. salina seem to be most closely related to each other but their colour, the insertion of their three appendages, the shape of their
knob scales, and their cell periplasts are quite different from one another.
Contribution No. 1879 from the Institute of Oceanology, Academia Sinica 相似文献
96.
We studied the behavior of magnetic field, horizontal motion and helicity in a fast emerging flux region NOAA 10488 which
eventually forms a δ spot. It is found that the rotation of photospheric footpoints forms in the earlier stage of magnetic
flux emergence and the relative shear motion of different magnetic flux systems appears later in this active region (AR).
Therefore the emerging process of the AR can be separated into two phases: rotation and shear. We have computed the magnetic
helicity injected into the corona using the local correlation tracking (LCT) technique. Furthermore we determined the vertical
component of current helicity density and the vertical component of induction electric fields Ez = (V× B)z in the photosphere. Particularly we have presented the comparison of the injection rate of magnetic helicity and the variation
of the current helicity density. The main results are as follows: (1) The strong shear motion (SSM) between the new emerging
flux system and the old one brings more magnetic helicity into the corona than the twisting motions. (2) After the maturity
of the main bipolar spots, their twist decreases and the SSM becomes dominant and the major contributor of magnetic non-potentiality
in the solar atmosphere in this AR. (3) The positions of the maxima of Ez (about 0.1 ∼ 0.2 V cm−1) shift from the twisting areas to the areas showing SSMs as the AR evolved from the rotation phase to the shear one, but
no obvious correlation is found between the kernels of Hα flare and Ez for the M1.6 flare in this AR. (4) The coronal helicity inferred from the horizontal motion of this AR amounts to −6 × 1043 Mx2. It is comparable with the coronal helicity of ARs producing flares with coronal mass ejections (CMEs) or helicity carried
away by magnetic clouds (MCs) reported in previous studies (Nindos, Zhang, and Zhang, 2003; Nindos and Andrews, 2004). In
addition, the formation of the δ configuration in this AR belongs to the third formation type indicated by Zirin and Liggett
(1987), i.e., collision of opposite polarities from different dipoles, and can be naturally explained by the SSM. 相似文献
97.
FUZZY COMPREHENSIVE EVALUATION OF CONTAINER TRANSPORTATION MODES ALONG THE CHANGJIANG RIVER MAIN LINE AND ITS DELTA AREA 总被引:1,自引:0,他引:1
ZHANGShi-yu XIAOHan-liang 《中国地理科学(英文版)》2003,13(3):259-261
The Changjiang River (Yangtze) is one of the fastest growth areas of container transportation in Chi-na. Rail, road and water transportation have competed against each other for container transportation in the Chang-jiang River main line and its delta area. It is of significance to assess these different transportation modes scientifi-cally in order to organize container transportation efficiently in this area and make decision for integral plan and construction of transportation system in this area. This paper outlines application of fuzzy comprehensive evaluation to appraise different modes of typical direction of containers. Twelve assessment indexes were decided. Membership functions were formulated. Evaluation results indicated that road transportation was optimal mode in the Changjiang River delta area, however water transportation was the primary way in the Changjiang River main line. 相似文献
98.
We describe how a local plasma structure can be changed by a transverse shear flow using numerical simulation to investigate the disturbance process near the magnetopause. The results show that magnetic field lines are bent by transverse shear flow disturbance near the current sheet region. There are multiple bipolar structures of the normal magnetic field in the numerical simulation. We term this new feature as K-point magnetic reconnection, realistic for discussing space observations. 相似文献
99.
On September 14–18, 2000, a medium-small solar active region was observed at Ganyu Station of Purple Mountain Observatory. Its spots were not large, but it had a peculiar active filament. On Sep.16, a flare of importance IIIb with rather intense geophysical effects was produced. Our computation of the magnetic structure of the active region reveals that the rope-shaped filament was concerned with a low magnetic arc close to magnetic neutral line. An intense shear of magnetic field occurred near magnetic rope. The QSL analysis shows that a 3-D magnetic reconnection might appear in the vicinity of filament, and this can be used to interpret the formation of a large flare. 相似文献
100.
Z. Q. Qu C. L. Xu X. Y. Zhang X. L. Yan C. L. Jin 《Monthly notices of the Royal Astronomical Society》2006,370(4):1790-1796
The influence of magnetic fields on the energy level populations of atoms is firstly studied by analysing the Stokes profiles of Fe i 6302.5 forming in the solar magnetized atmosphere, with the aid of a departure factor defined to evaluate the deviation from the normal Boltzmann distribution without a magnetic field. This factor is directly related to the ratio of line-source function to the continuum one. The relationship between the departure and the magnetic field reveals an effect that the magnetic field induces an exponential increase in the level population of the lower level of Fe i 6302.5 (Landé factor g = 2.5 ) with the field strength. This indicates that the magnetic field can cause the redistribution of populations of those levels whose Landé factors are non-zero. Therefore, this effect should be included in the calculation of the statistical equilibrium. Secondly, an experiment utilizing the Hg5461 line in the laboratory on the Earth is carried out to reveal that the exponential relation is independent of variations in temperature, and the excitation is completely magneto-induced. Finally, the exponential relation is explained by taking account of the magnetic energy in the Boltzmann distribution. 相似文献