全文获取类型
收费全文 | 55302篇 |
免费 | 5948篇 |
国内免费 | 8539篇 |
专业分类
测绘学 | 3870篇 |
大气科学 | 8565篇 |
地球物理 | 12118篇 |
地质学 | 26895篇 |
海洋学 | 4844篇 |
天文学 | 2966篇 |
综合类 | 5260篇 |
自然地理 | 5271篇 |
出版年
2024年 | 174篇 |
2023年 | 573篇 |
2022年 | 1484篇 |
2021年 | 1751篇 |
2020年 | 1393篇 |
2019年 | 1652篇 |
2018年 | 6084篇 |
2017年 | 5254篇 |
2016年 | 4153篇 |
2015年 | 1893篇 |
2014年 | 2141篇 |
2013年 | 1945篇 |
2012年 | 2811篇 |
2011年 | 4520篇 |
2010年 | 3903篇 |
2009年 | 4073篇 |
2008年 | 3493篇 |
2007年 | 3829篇 |
2006年 | 1355篇 |
2005年 | 1411篇 |
2004年 | 1290篇 |
2003年 | 1299篇 |
2002年 | 1137篇 |
2001年 | 979篇 |
2000年 | 1124篇 |
1999年 | 1488篇 |
1998年 | 1204篇 |
1997年 | 1124篇 |
1996年 | 1037篇 |
1995年 | 908篇 |
1994年 | 787篇 |
1993年 | 712篇 |
1992年 | 563篇 |
1991年 | 450篇 |
1990年 | 330篇 |
1989年 | 310篇 |
1988年 | 270篇 |
1987年 | 150篇 |
1986年 | 143篇 |
1985年 | 95篇 |
1984年 | 99篇 |
1983年 | 75篇 |
1982年 | 65篇 |
1981年 | 79篇 |
1980年 | 60篇 |
1979年 | 34篇 |
1978年 | 11篇 |
1977年 | 11篇 |
1976年 | 12篇 |
1958年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
321.
Fuzzy comprehensive evaluation model for water resources carrying capacity in Tarim River Basin, Xinjiang, China 总被引:12,自引:0,他引:12
This paper explores the method of comprehensive evaluation of water resources carrying capacity and sets up an evaluation model applying the fuzzy comprehensive evaluation method. Based on the data of nature, society, economics and water resources of the Tarim River Basin in 2002, we evaluated the water resources carrying capacity of the basin by means of the model. The results show that the comprehensive grades are 0.438 and 0.454 for Aksu and Kashi prefectures respectively, where the current water resources exploitation and utilization has reached a relative high degree and there is only a very limited water carrying capacity, 0.620 for Kizilsu Kirgiz Autonomous Prefecture, where water resources carrying capacity is much higher, and in between for Hotan Prefecture and Bayingolin Mongolian Autonomous Prefecture. As a whole, the comprehensive grade of the Tarim River Basin is 0.508 and the current water resources exploitation and utilization has reached a relative high degree. Thus, we suggest that the integrated management of the water resources in the basin should be strengthened in order to utilize water resources scientifically and sustainably. 相似文献
322.
Guoyan Ren Bafang Li Xue Zhao Yongliang Zhuang Mingyan Yan Hu Hou Xiukun Zhang Li Chen 《中国海洋大学学报(英文版)》2009,8(1):83-88
In order to select an optimum extraction method for the target glycoprotein (TGP) from jellyfish (Rhopilema esculentum) oral-arms, a high performance liquid chromatography (HPLC)-assay for the determination of the TGP was developed. Purified
target glycoprotein was taken as a standard glycoprotein. The results showed that the calibration curves for peak area plotted
against concentration for TGP were linear (r = 0.9984, y = 4.5895x+47.601) over concentrations ranging from 50 to 400 mgL-1. The mean extraction recovery was 97.84% (CV2.60%). The fractions
containing TGP were isolated from jellyfish (R. esculentum) oral-arms by four extraction methods: 1) water extraction (WE), 2) phosphate buffer solution (PBS) extraction (PE), 3) ultrasound-assisted
water extraction (UA-WE), 4) ultrasound-assisted PBS extraction (UA-PE). The lyophilized extract was dissolved in Milli-Q
water and analyzed directly on a short TSK-GEL G4000PWXL (7.8 mm×300 mm) column. Our results indicated that the UA-PE method
was the optimum extraction method selected by HPLC. 相似文献
323.
324.
325.
6种海洋致病性弧菌36kDa外膜蛋白特性分析 总被引:3,自引:0,他引:3
研究本着筛选和制备弧菌共同外膜蛋白亚单位疫苗,用十二烷基肌氨酸钠抽提并结合超速离心的方法提取了鳗弧菌(Vibrio anguillarum)、鱼肠道弧菌(V.ichthyoenteri)、溶藻弧菌(V.alginolyticus)、副溶血弧菌(V.parahaemolyticus)、哈维氏弧菌(V.harveyi)和创伤弧菌(V.vulnificus)6种海洋致病性弧菌的主要外膜蛋白, SDS-PAGE图谱比较发现这6种弧菌都存在36 kDa的外膜蛋白条带.通过电泳洗脱分离纯化这6种弧菌的36 kDa外膜蛋白,并制备了鳗弧菌菌株SJ060621的36 kDa外膜蛋白多抗.ELISA和Western-blot印迹结果显示,仅鳗弧菌SJ060621、S010610-1和哈维氏弧菌的36 kDa外膜蛋白存在免疫交叉反应;双向电泳分析了鳗弧菌SJ060621、S010610-1、哈维氏弧菌和溶藻弧菌的36 kDa外膜蛋白,2-DE图谱显示出鳗弧菌SJ060621和S010610-1均由3种等电点相近的蛋白组成,存在很高的同源性,2株鳗弧菌与溶藻弧菌和哈维氏弧菌在蛋白质组成数量和等电点上都存在较大的差异,结果说明通过主要外膜蛋白的分子量和免疫特性研究,可为筛选不同弧菌共同外膜蛋白的亚单位疫苗提供有利参考. 相似文献
326.
Nidhi Nagabhatla R. Wickramasuriya S. N. Prasad 《Journal of the Indian Society of Remote Sensing》2009,37(3):443-455
The present study investigates the potential of readily available and easily accessible global data sets to understand regional/local
level interactions in wetland systems. The biogeographical zones of India were used a base-frame to select three sites. The
study well fits the interests of National Wetland Committee of India to investigate and document fundamental information on
wetland extent/distribution. The national partnership with SACON represents this interest. SACON commenced the inland wetland
inventory module at national scale using geospatial data, although the provincial scale analysis is underway. In addition,
the global irrigated area mapping (GIAM-IWMI) project generated multi-scalar spatial outputs for irrigated/rain-fed areas.
With the existing information base, a multi-level geospatial analysis using Arc GIS algorithmic modelling was used to derive
comprehensive appraisal of wetland systems complementing the data from GIAM and SACON. It was observed that the overlap between
the two layers was 58 percent for Gujarat and 10 percent in Tamil Nadu. In Krishna basin the wetland’s cover 1.04 million
hectare excluding the rice agro-ecosystem. The difference in the biogeography of the case sites governs the gradient of information
derived from both data layers. Additionally, the global lakes and wetlands database (GLWD) database added thematic information
on coastal wetlands. In summary we describe the cross-scaling the global data layers to compliment the regional/national level
monitoring assignments. 相似文献
327.
Elvis A. Shukla Jagdish Prasad M. S. S. Nagaraju Rajeev Srivastava D. L. Kauraw 《Journal of the Indian Society of Remote Sensing》2009,37(1):129-137
Soil resource characterization of Dhamni micro-watershed in Chandrapur district of Maharashtra was carried out using IRS-1D
LISS-III data in conjunction with field survey and ancillary data. The study indicates that nearly 84.2 per cent of the total
geographical area of the watershed is under cultivation. Forest (mainly degraded) occupy only 4.5 per cent area Whereas wasteland
with scrub cover 9.4 per cent area of the watershed. Nine soil series were tentatively identified and mapped as soil series
association in to five mapping units. These soils belong to order Inceptisol, Vertisol and Mollisol. Except the soils of wasteland
with scrub, other soils are moderately suitable for pigeonpea and soybean and have average to good productivity. 相似文献
328.
Conventions on thermal expansion modelling of radio telescopes for geodetic and astrometric VLBI 总被引:7,自引:6,他引:1
Axel Nothnagel 《Journal of Geodesy》2009,83(8):787-792
Thermal expansion of radio telescopes has long been recognized as an effect which cannot be neglected in geodetic and astrometric
VLBI data analysis if millimeter accuracy is desired. In this article, the author documents the conventions which are being
set by the International VLBI Service for Geodesy and Astrometry (IVS) for a consistent modelling of this effect in its routine
product generation. For the largest telescopes, the annual cycle of thermal expansion may change the height of the VLBI reference
point by as much as 20 mm. However, for telescopes which are used in present-day IVS operations, the variations rather range
from 4 to 6 mm. 相似文献
329.
330.
Michiel A. F. Knaapen 《Geo-Marine Letters》2009,29(1):17-24
Sandbanks, the largest of bed patterns in shallow sandy seas, pose a potential risk to shipping. They are also valuable elements
of natural coastal protection, dissipating the energy of waves. In the Southern Bight of the North Sea, several sandbank areas
have been reported in the literature. However, based on an objective crest–trough analysis of the bathymetry of the Dutch
continental shelf, the present study shows that sandbanks are more widespread than commonly considered. These banks are relatively
low, presumably explaining why they have not been documented before. This widespread occurrence of sandbanks in the North
Sea is in agreement with theoretical predictions based on stability analysis techniques. The possible interference between
large-scale human activity and low-amplitude open-shelf ridges implies that one should be careful not to overlook these patterns
if none should appear in a preliminary (visual) assessment. The only part of the Southern Bight in which no ridges can be
seen is a circular area with a diameter of about 50 km near the mouth of the river Rhine. Here, freshwater outflow affects
the direction of tidal ellipses and residual flow, and suppresses the formation of open ridges. 相似文献