全文获取类型
收费全文 | 9839篇 |
免费 | 1635篇 |
国内免费 | 2244篇 |
专业分类
测绘学 | 625篇 |
大气科学 | 1596篇 |
地球物理 | 2341篇 |
地质学 | 4230篇 |
海洋学 | 2166篇 |
天文学 | 171篇 |
综合类 | 717篇 |
自然地理 | 1872篇 |
出版年
2024年 | 45篇 |
2023年 | 151篇 |
2022年 | 323篇 |
2021年 | 382篇 |
2020年 | 406篇 |
2019年 | 498篇 |
2018年 | 382篇 |
2017年 | 436篇 |
2016年 | 456篇 |
2015年 | 503篇 |
2014年 | 619篇 |
2013年 | 695篇 |
2012年 | 646篇 |
2011年 | 628篇 |
2010年 | 573篇 |
2009年 | 628篇 |
2008年 | 576篇 |
2007年 | 660篇 |
2006年 | 601篇 |
2005年 | 512篇 |
2004年 | 455篇 |
2003年 | 420篇 |
2002年 | 369篇 |
2001年 | 326篇 |
2000年 | 337篇 |
1999年 | 283篇 |
1998年 | 249篇 |
1997年 | 268篇 |
1996年 | 223篇 |
1995年 | 172篇 |
1994年 | 169篇 |
1993年 | 137篇 |
1992年 | 148篇 |
1991年 | 93篇 |
1990年 | 76篇 |
1989年 | 61篇 |
1988年 | 44篇 |
1987年 | 27篇 |
1986年 | 33篇 |
1985年 | 25篇 |
1984年 | 17篇 |
1983年 | 20篇 |
1982年 | 11篇 |
1981年 | 9篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 8篇 |
1977年 | 3篇 |
1972年 | 2篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
Abstract. Boonea (= Odostomia) impressa is a common ectoparasite of oysters. In the laboratory, small oysters (Crassostrea virginica) parasitized by natural densities of B. impressa produced 75 % less new shell than unparasitized oysters. Shell deposition rates of previously parasitized oysters increased significantly after all B. impressa were removed. Thus, the decrease in growth rate, although significant, apparently was not permanent. B. impressa preferentially parasitized small, living oysters (≤2.5cm) in the field, even though a higher percentage of large, living oysters (>2.5cm) was available. The snails maintained an aggregated distribution on the oyster reef. The number of B. impressa per oyster clump was positively correlated with the number of living oysters per clump, however some clumps with few or no living oysters had many B. impressa. Thus, food availability only partially explained the pattern of distribution. B. impressa was very mobile. About 50 % of the population moved in one week. Reproduction occurred throughout the year with a peak period in May. Recruitment was greatest in July, however new recruits were observed throughout the year. The reduction in growth rate of parasitized oysters, the snaiľs propensity towards parasitizing small oysters and the snail's tendency to be contagiously distributed suggests that B. impressa potentially exerts a significant influence on the population structure and health of oyster populations. 相似文献
52.
53.
水溶液中聚合物在粘土上的吸附对于聚合物污染防治和污水处理等都有重要意义。Scheutjens-Fleer理论是应用范围最广的聚合物吸附理论,适应于从单体到长链高聚物,从链无相互作用的稀溶液到纯聚合物的吸附研究。本文简要介绍了有关聚合物吸附的重要参数,包括吸附量、耦合分数或直接表面覆盖、平均层厚度和链段密度,以及相应的测定方法。文中分析了影响聚合物吸附研究发展的主要问题,指出水溶液中聚合物在粘土上的吸附研究的发展方向是综合研究吸附等温线和A/V效应、耦合分数、吸附层厚度、吸附分级现象和对粘土层间的影响,并与Scheutjens-Fleer理论计算结果进行比较。 相似文献
54.
中国沿海星虫动物门名录 总被引:2,自引:0,他引:2
取1980~1989年间在我国沿海进行星虫动物区系调查的标本和有关资料做了整理、鉴定,共39种,分隶于2纲,4目,6科,12属。其中1种在我国为首次记录。 相似文献
55.
本文报道了1987年夏、冬两个航次在26°50′~32°30′N,124°30′~131°30′E海区中可溶性无机磷酸盐的调查结果,阐明了磷的分布特征和形成机制。结果表明陆架区表层测值较高,大洋区为低值区,底层则相反。大洋水常年分层,中层水有爬坡涌升现象,其浓度与Aou呈正相关,与pH和S呈负相关。夏、冬两季底层磷与Aou呈正相关,其浓度变化主要依赖于生物过程。 相似文献
56.
用自装的BET容量法装置测定了几种粒状钛型吸附剂的比表面及其孔径分布。测定是在常温减压下进行的。结果表明:钛型吸附剂在加铀海水中的吸铀量与样品的比表面及孔径分布有一定的内在联系。这种表面性质的研究对吸附剂的筛选有重要的指导意义。 相似文献
57.
Abstract. The distribution of the benthic Amphipoda was studied in the brackish-water lagoon Mazoma of Amvrakikos Bay, Ionian Sea, Greece. Eleven amphipod species typical of the sublittoral zone, some with preference for enclosed bays and lagoons, were identified. Gammarus crinicornis, Microdeutopus bifidus, C. rotundirostris , and Erichthonius difformis are mentioned for the first time for Greek waters. The distribution of amphipods in the lagoon is governed by the vegetation and is probably modified by interspecific relations. 相似文献
58.
59.
60.
Takuya Itaki Masashi Ito Hisashi Narita Naokazu Ahagon Hideo Sakai 《Deep Sea Research Part I: Oceanographic Research Papers》2003,50(12):1507
The depth distributions of the radiolarian fauna in the Chukchi and Beaufort Seas, marginal seas of the western Arctic Ocean, were examined quantitatively in depth-stratified plankton tows from 4 or 5 intervals above 500 m and in surface sediments from various depths between 163 and 2907 m. The radiolarian assemblage from the water column in September 2000 was dominated by Amphimelissa setosa and followed by the Actinomma boreale/leptoderma group, Pseudodictyophimus gracilipes and Spongotrochus glacialis. These species are related to the Arctic Surface Water shallower than 150 m. This assemblage is similar to that in the Greenland Sea relating to the ice edge, but did not contain typical Pacific radiolarians in spite of the flow of water of Pacific origin in this region. The living depth of Ceratocyrtis historicosa was restricted to the relatively warm water between 300 and 500 m corresponding to the upper Arctic Intermediate Water (AIW) originating from the Atlantic Ocean. Radiolarian assemblages in the surface sediments are similar to those in the plankton tows, except for common Cycladophora davisiana in sediment samples below 500 m. C. davisiana is probably a deep-water species adapted to the lower AIW or the Canadian Basin Deep Water ventilated from the shelves. 相似文献