全文获取类型
收费全文 | 29563篇 |
免费 | 333篇 |
国内免费 | 253篇 |
专业分类
安全科学 | 856篇 |
废物处理 | 1121篇 |
环保管理 | 4125篇 |
综合类 | 5161篇 |
基础理论 | 7766篇 |
环境理论 | 14篇 |
污染及防治 | 7444篇 |
评价与监测 | 1809篇 |
社会与环境 | 1644篇 |
灾害及防治 | 209篇 |
出版年
2022年 | 218篇 |
2021年 | 231篇 |
2020年 | 201篇 |
2019年 | 258篇 |
2018年 | 396篇 |
2017年 | 421篇 |
2016年 | 618篇 |
2015年 | 483篇 |
2014年 | 673篇 |
2013年 | 2388篇 |
2012年 | 830篇 |
2011年 | 1161篇 |
2010年 | 953篇 |
2009年 | 1010篇 |
2008年 | 1196篇 |
2007年 | 1246篇 |
2006年 | 1158篇 |
2005年 | 917篇 |
2004年 | 976篇 |
2003年 | 916篇 |
2002年 | 847篇 |
2001年 | 1127篇 |
2000年 | 802篇 |
1999年 | 477篇 |
1998年 | 403篇 |
1997年 | 368篇 |
1996年 | 401篇 |
1995年 | 427篇 |
1994年 | 438篇 |
1993年 | 390篇 |
1992年 | 414篇 |
1991年 | 387篇 |
1990年 | 413篇 |
1989年 | 380篇 |
1988年 | 318篇 |
1987年 | 279篇 |
1986年 | 290篇 |
1985年 | 299篇 |
1984年 | 320篇 |
1983年 | 313篇 |
1982年 | 312篇 |
1981年 | 315篇 |
1980年 | 268篇 |
1979年 | 270篇 |
1978年 | 215篇 |
1977年 | 210篇 |
1975年 | 182篇 |
1974年 | 210篇 |
1973年 | 188篇 |
1972年 | 221篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
171.
The effects of blooms of the cyanobacterium Trichodesmium spp. on penaeid prawn larvae were examined using in situ and laboratory rearing experiments and plankton surveys in Albatross
Bay, Gulf of Carpentaria, Australia. The in situ experiments demonstrated that, during a bloom of Trichodesmium spp., larvae of the prawn Penaeus merguiensis did not develop beyond the first protozoea stage, and survival was low compared with times when diatoms were dominant in
the same study area. Laboratory experiments confirmed the in situ results. None of the prawn larvae fed Trichodesmium sp. in laboratory experiments developed beyond the first protozoeal stage. In contrast, 94% of prawn larvae fed the green
flagellate Tetraselmis suecica successfully developed to the second protozoea stage. Electron microscopy of larvae gut-contents revealed that Trichodesmium spp. were ingested by larvae but were of no nutritional value, resulting in starvation. A 7 yr plankton survey, from 1985
to 1992, showed that minimum abundance of prawn larvae occurs during the annual summer blooms of Trichodesmium spp. and that maximum abundance of prawn larvae generally occurs just after the bloom. There was a negative correlation between
the abundance of larvae and the abundance of Trichodesmium at individual sites, one offshore and one inshore, indicating that the blooms affect the survival of larvae. We conclude that
variations in both timing and magnitude of Trichodesmium blooms are important determinants of prawn larvae abundance in Albatross Bay.
Received: 28 April 1997 / Accepted: 2 April 1998 相似文献
172.
Whole-body carbon (C), nitrogen (N) and phosphorus (P) content, and stable-isotope composition (13C:12C and 15N:14N), were followed during metamorphosis of bonefish (Albula sp.) larvae (leptocephali). Metamorphosing larvae depend entirely on endogenous carbon compounds (some of which contain N and P) as an energy source. Two fundamental questions are (1) Do the demands of extensive tissue remodeling during metamorphosis require the efficient retention of N and P during the catabolism of carbon compounds? (2) What effect does the lack of feeding have on stable-isotope composition? Our results showed that both C and N decreased by ~35 to 40%, reflecting the utilization of neutral lipid (triacylglycerols) and N-containing compounds (phosphatidylethanolamine and keratan sulfate glycosaminoglycan) as energy sources, and indicating that larvae have little or no capacity to retain N. Evidence suggested that collagen breakdown, measured as a loss of hydroxyproline content, also contributed to N loss. Stable-isotope ratios, expressed as 13C and 15N, showed no statistically significant differences in early and advanced metamorphosing larvae. In contrast to C and N, phosphorus was conserved during metamorphosis and most probably is utilized in the increased bone mineralization occurring in advanced larvae. We show, however, that advanced larvae are P-limited and that normal ossification is dependent upon a supply of exogenous P obtained after the resumption of feeding. The N:P ratio of 12.3 in early larvae decreased to 8.1 in advanced larvae owing to the conservation of P as N was lost. The mean 15N value in early metamorphic larvae (11.6‰) is consistent with results from other studies, and provides further support for the view that premetamorphic leptocephali feed at a very low trophic level. 相似文献
173.
Three marine diatoms Lauderia annulata Cleve, Odontella sinensis (Greville) Grunow and Thalassiosira rotula Meunier were exposed to ultraviolet (UV) radiation of different wavebands under controlled laboratory conditions (0.035 vol%
CO2, 18 °C). Several changes in the patterns of pigments in these organisms were seen depending on the waveband of UV radiation
and species examined. UV-B and UV-B plus UV-A radiation led to a reduction in the overall pigment content of all three diatoms.
The uptake of 15N-ammonium was less affected by 5-h UV-A (WG 320) but significantly reduced after UV-B and UV-B plus UV-A exposure. The pattern
of free amino acid pools varied depending on the applied UV wavebands and the tested diatom. The main protein-bound amino
acids of T. rotula decreased after 5-h UV irradiance except leucine. Contents of adenosine 5′-mono-, di-, and triphosphate (AMP, ADP and ATP)
were affected differently by UV radiation; ATP values increased at the end of UV-B and UV-B plus UV-A exposure. These results
have been discussed with reference to the impact of the different UV sources and the influence on the nitrogen metabolism
in connection to pigments and supply with energy.
Received: 13 May 1997 / Accepted: 11 October 1997 相似文献
174.
聚苯乙烯基硫代磺酸钾树脂的合成及其与卤代烃的反应 总被引:2,自引:2,他引:0
由聚苯乙烯基磺酰氯树脂与硫化氢钾反应制备聚苯乙烯基硫代磺酸钾树脂(I),树脂I与亲电的卤代烃反应,生成聚苯乙烯基硫代磺酸酯树脂(Ⅱ),树脂Ⅱ经过乙硫醇处理,使卤代烃结构部分以不对称二硫醚的形式游离下来,用GC/MS对其结构进行鉴定。从不对称二硫醚的结构可推导出原卤代烃的结构,所制备的聚苯乙烯基硫代磺酸钾树脂的转化效率为1.11mmol·g^-1。 相似文献
175.
176.
An Ecology-Based Method for Defining Priorities for Large Mammal Conservation: The Tiger as Case Study 总被引:2,自引:0,他引:2
177.
178.
179.
180.
Nutrient transfer functions: the site of integration between feeding behaviour and nutritional physiology 总被引:6,自引:0,他引:6
Summary. We describe and extend a graphical approach to quantitative nutrition that focuses on the interplay between behavioural and
physiological components of nutritional regulation. The site of integration is the nutrient transfer function, which is the
function describing the time course of nutrient transfer between serially connected nutritional compartments (e.g., from the gut to the blood). The relationship between the shape of the nutrient transfer function and the temporal patterns
of feeding determines the values of two key quantitative parameters of nutrition: the rate ('power') and the efficiency of nutrient acquisition. The approach can be extended to consider, in addition to the short-term behavioural and physiological
decisions made by animals, some ecological determinants and longer-term, life history consequences of such decisions. Most
importantly, this category of models can provide insights into the interplay among the various nutrients in an animal's diet.
We illustrate this using hypothetical examples, and also present preliminary data for the power-efficiency relationships of
protein and digestible carbohydrates in locusts. Finally, we consider existing evidence for the various means available to
these and other insects for regulating such relationships.
Received 24 September 1997; accepted 9 December 1997. 相似文献