全文获取类型
收费全文 | 99661篇 |
免费 | 1254篇 |
国内免费 | 1149篇 |
专业分类
安全科学 | 3941篇 |
废物处理 | 3802篇 |
环保管理 | 14878篇 |
综合类 | 22052篇 |
基础理论 | 27614篇 |
环境理论 | 77篇 |
污染及防治 | 18450篇 |
评价与监测 | 6066篇 |
社会与环境 | 4571篇 |
灾害及防治 | 613篇 |
出版年
2022年 | 887篇 |
2021年 | 880篇 |
2020年 | 684篇 |
2019年 | 904篇 |
2018年 | 1328篇 |
2017年 | 1361篇 |
2016年 | 2322篇 |
2015年 | 1902篇 |
2014年 | 2656篇 |
2013年 | 9354篇 |
2012年 | 2573篇 |
2011年 | 3146篇 |
2010年 | 3515篇 |
2009年 | 3670篇 |
2008年 | 2795篇 |
2007年 | 2706篇 |
2006年 | 2867篇 |
2005年 | 2760篇 |
2004年 | 3031篇 |
2003年 | 2878篇 |
2002年 | 2423篇 |
2001年 | 2782篇 |
2000年 | 2218篇 |
1999年 | 1660篇 |
1998年 | 1428篇 |
1997年 | 1430篇 |
1996年 | 1542篇 |
1995年 | 1653篇 |
1994年 | 1543篇 |
1993年 | 1372篇 |
1992年 | 1364篇 |
1991年 | 1345篇 |
1990年 | 1296篇 |
1989年 | 1243篇 |
1988年 | 1098篇 |
1987年 | 1023篇 |
1986年 | 1006篇 |
1985年 | 1080篇 |
1984年 | 1178篇 |
1983年 | 1178篇 |
1982年 | 1186篇 |
1981年 | 1111篇 |
1980年 | 953篇 |
1979年 | 957篇 |
1978年 | 844篇 |
1977年 | 735篇 |
1976年 | 652篇 |
1974年 | 636篇 |
1973年 | 671篇 |
1972年 | 661篇 |
排序方式: 共有10000条查询结果,搜索用时 468 毫秒
421.
Protein, lipid, phosphorus, and organic carbon contents, as well as electron transport system (ETS) activity, lactatedehydrogenase activity, and gut evacuation rate, were measured in four interzonal species of Pacific copepods:Calanus australis, C. pacificus, Eucalanus inermis, andE. elongatus f.hyalinus, collected at the upwelling areas off Peru (8°S) and California (27°N), and in the middle of the North Pacific (30°N), from February to April 1987. The two Eucalanidae species —E. inermis andE. elongatus — have distinctive biochemical and elemental body composition and rates of main physiological processes. Relative protein, lipid, phosphorus, and organic carbon contents (µg mg–1 wet weight) in these species were, respectively, ca. 1/7 to 1/10, 1/5 to 1/20, 1/5 to 1/10, and 1/5 those inCalanus spp. Likewise, oxygen uptake rate per unit of wet weight (based on ETS activity) inE. inermis andE. elongatus was 5 to 10% of that in calanids; a similar difference was found in phosphorus excretion rate. In addition, gut evacuation rates inE. inermis andE. elongatus were ca. one-fifth of those inCalanus spp. Based on these data, we considered the eucalanids as belonging to a distinctive physiological group, figuratively named jelly-body copepods. In contrast with calanids, active lactatedehydrogenase has been found in the bodies ofE. inermis andE. elongatus, apparently allowing them to survive for a long time in layers of extremely low oxygen content (<0.2 ml l–1). The adaptive value of physiological features in these eucalanids and typical calanids is compared. 相似文献
422.
The present study tested the utilization of dead microbial biomass by two benthic deposit-feeders:Abra alba (Wood) (Mollusca: Bivalvia) andEupolymnia nebulosa (Montagu) (Annelida: Polychaeta). Clams were collected in the Canet lagoon during spring 1989. Worms were collected in the Port-Vendres harbour during spring 1989. The14C-labelled (glutamic acid, 24 h) sediment used during the study was sterilized with 1% chloroform, washed with sterile seawater, and dried (60°C; 48 h). This sterilisation procedure, called fumigation is the least harmful to the sediment (Novitsky 1986). Both clams and worms were incubated in the presence of the fumigated sediment for 5, 10, 20, and 50 h. At the end of each experiment we recorded the radioactivity in four compartments: (1) sediment, (2) dissolved organic matter (DOM), (3) CO2, and (4) animals. The radioactivity of the sediment was subdivided into five fractions: (i) soluble in 2N HCl, (ii) soluble in hot 5% trichloroacetic acid (TCA), (iii) soluble in 1N NaOH, (iv) soluble in hot 6N HCl, (v) residual (after combustion in a Leco carbon analyser). In the first set of experiments, after 20 h of incubation, 5.4 and 4.7% of the total radioactivity was taken up by clams and worms, respectively. However, a model revealed that this uptake could have been correlated with the release of radiolabelled DOM (33% of total radioactivity during the first 5 h). In order to test this assumption, we used the same protocol with three additional washes of the fumigated sediment. This resulted in a significantly lower uptake by the clams (1.9% of the total radioactivity byt = 50 h), whereas the worms exhibited an uptake similar to that in the initial experiment (5.1% of total radioactivity byt = 50 h). These results underline the importance of considering interactions with DOM when applying radiotracer techniques to the study of benthic food chains. The average ingestion rates of fumigated sediment byA. alba andE. nebulosa were 5.2 10–2 mg sediment dry wt mg–1 clam h–1 and 3.5 10–2 mg sediment dry wt mg–1 worm h–1, respectively, which is comparable to previous data reported for other deposit-feeding bivalves and polychaetes feeding on natural sediment or detritus. The low radioactivity recorded for CO2 together with the similarity of the changes in the partitioning of the radioactivity within the sediment between control experiments and experiments carried out in the presence of clams or worms suggest low assimilation efficiencies. Therefore, the present study supports the fact that dead microbial biomass does not constitute an important food source for benthic deposit-feeders. 相似文献
423.
Sporophytes of the brown algaLaminaria saccharina (L.) Lamour grown at 15°C contained significantly more chlorophylla (chla) than did similar plants grown at 5°C. The increase in chla in 15°C plants was due to increased numbers of photosystem II reaction centes, and possibly to increased photosynthetic unit size, compared with 5°C plants. These changes were associated with increased values (photosynthetic efficiencies) in 15°C-grownL. saccharina relative to 5°C-grown plants. The changes in together with reduced respiration rates allowed 15°C-grownL. saccharina to achieve net photosynthesis and light-saturated photosynthesis at a lower photon fluence rate (PFR) than 5°C plants when both groups were assayed at the same temperature (15°C). The photon fluence rates necessary to reach the compensation point and achieve light-saturated photosynthesis (I
c
andI
k
, respectively) increased with increasing incubation temperature inL. saccharina grown at both 5 and 15°C. However, acclimation responses to growth temperature compensated for the short-term effect of temperature onI
c
andI
k
. Consequently, plants grown at 5 and 15°C were able to achieve similar rates of light-limited photosynthesis, and similarI
c
andI
k
values at their respective growth temperatures. These responses are undoubtedly important for perennial seaweeds such asL. saccharina, which frequently grow in light-limited habitats and experience pronounced seasonal changes in water temperature.Please address all correspondence and requests for reprints to I.R. Davison 相似文献
424.
425.
The relative tissue accumulation of Pb, Cd and Zn were compared in two populations each of two species of slugs (Arion subfuscus and Deroceras reticulatum). One population was resident at a contaminated Pb/Zn mine site, and the other population was from an uncontaminated site and was transferred for 20 days to microcosms established at the mine site. It was found that when the experiment was conducted during late spring (May), but not in late winter (February), that the Pb and Zn concentrations in the tissues of the 'transplants', were significantly higher than in the tissues of 'residents'; the Cd concentrations in the transplants, although significantly higher in the May sample than in February, did not exceed those of their 'resident' counterparts. It was postulated that: (a) Pb and Zn tolerance in slugs is phenotypically expressed by a reduction in metal accumulation; (b) Cd tolerance, if present, may be characterized by enhanced storage capacity; and (c) the presence of local metal-tolerant ecotypes is a biotic variable that may confound the relationship between dry tissue and environmental metal concentrations that forms a basis of pollution biomonitoring. 相似文献
426.
Dominions and desert clickers (Orthoptera:Acrididae): influences of resources and male signaling on female settlement patterns 总被引:1,自引:0,他引:1
Summary Previous field work on the grasshopper Ligurotettix coquilletti revealed that females were not evenly distributed among male mating territories, Larrea tridentata (creosote) bushes, but were clustered at particular locations. These sites generally harbored several signaling males simultaneously and also possessed foliage preferred by the insects as a food source, this preference being based on the relative concentrations of various extra-foliar compounds. The clustering of females, therefore, could result from a preference for specific bushes because of the resources (i.e., food) available there and/or an orientation to groups of males per se. Here, we present the results of 3 field experiments in which we controlled the spatial distribution and intensity of male signals using a computer-operated system of loudspeakers and monitored the movement of individually marked females released in the study area. When male song was identical at high and low quality territories (all having single loudspeakers), females still aggregated at the high quality sites, indicating that variability in host plant quality alone may be sufficient to promote a skewed distribution of females. Among high quality territories, females did not discriminate between sites with one versus three loudspeakers (all broadcasting the same signal), but displayed a strong preference for sites (all having single loudspeakers) with a high intensity signal over a low intensity one. Field measurements showed that the songs of grouped males were more intense than those of lone males, implying that the signaling of grouped males may have enhanced the settlement of females at the bushes harboring male groups above and beyond that influenced by territory quality alone. We conclude that female attraction to host plants is influenced primarily by male signaling, whereas their subsequent retention is more dependent on territory quality. An experiment on male settlement failed to show an aggregative tendency, suggesting that male groups form through the passive accumulation of individuals at high quality sites. 相似文献
427.
Pleijel H Skärby L Wallin G Selldén G 《Environmental pollution (Barking, Essex : 1987)》1991,69(2-3):151-168
Spring wheat (Triticum aestivum L., cv. Drabant) was exposed to different concentrations of ozone in open-top chambers for two growing seasons, 1987 and 1988, at a site located in south-west Sweden. The chambers were placed in a field of commercially grown spring wheat. The treatments were charcoal-filtered air (CF), non-filtered air (NF) and non-filtered air plus extra ozone (NF(+)). In 1988, one additional ozone concentration (NF(++)) was used. Grain yield was affected by the ozone concentration of the air. Air filtration resulted in an increase in grain yield of about 7% in both years, compared to NF. The addition of ozone (NF(+), NF(++)) reduced grain yield and increased the content of crude protein of the grain in both years. Filtration of the air had no significant effect on the content of crude protein, compared to NF. The results showed a strong positive chamber effect on grain yield in the cold and wet summer of 1987. In 1988, there was no net chamber effect on grain yield. The relative differences between the CF, NF and NF(+) treatments with respect to grain yield were of the same magnitude in the two years, despite the very different weather conditions. 相似文献
428.
In the spring of 1988, five beaches along the coast of Beirut were surveyed for the presence of plastic pellets, tar, and megalitter--a follow-up to the studies conducted on the coast of Lebanon in 1977 for plastic pellet and tar occurrence, and in 1978 for containers and other megalitter on Beirut beaches. Plastic pellets were more abundant than they were in 1977 on three beaches and less so on two. Tar, however, seemed to occur much more abundantly on all five beaches. Megalitter, chiefly plastic but also paper, metal, and glass, had increased greatly compared with that seen 10 years ago. As in 1977, the unrestricted waste disposal practices of the plastic manufacturers, plus the possible loss of cargo from ships loading and unloading raw materials, are the most likely sources of plastic pellets. The abundance of tar is not surprising, considering that the Mediterranean Sea is tar-polluted and that two oil terminals occur on Lebanon's coast. Further, local gas stations frequently dump oil and grease onto the beaches, and numerous fires have occurred at coastal refineries over the past 10-15 years. All of these factors are likely to contribute to the presence of tar on the beaches. The main source of the vast quantities of megalitter on the beaches is undoubtedly the Lebanese people themselves, due to numerous population shifts and the lack of order and regulatory enforcement as a result of the civil chaos in the country. In addition, the ships docking or waiting for days, and sometimes weeks, to get into the Lebanese ports probably affect the abundance of megalitter (and tar) on the beaches. 相似文献
429.
The movement and digestion of food in the gut ofOligometra serripinna (Carpenter) were studied at Lizard Island (14°3842S; 145°2710E) in the austral winter of 1986. Feather stars in the laboratory were fed a brief, small meal of brine shrimp nauplii and killed at increasing time intervals thereafter. Histological reconstructions showed that the ingested nauplii progressed along the digestive tract surprisingly quickly. Some nauplii were found in the mid and hind intestine in only 30 min, and all of the nauplii had reached the hind intestine and rectum in 1 h. Digestion of the nauplii had started at 1 h, and only a few fragments of naupliar exoskeleton remained in the hind intestine and rectum 5 h after the start of feeding. Videotape analysis showed that no fecal pellets were released during this experiment. In the natural environment ofO. serripinna, ingested particles may similarly be transported quickly to the hind part of the gut and digested there — when feather stars were fixed in the field, most of the gut contents were found in the hind intestine and rectum.O. serripinna, which efficiently rejects inert particles before they are ingested, usually defecates infrequently (probably not more than once over a span of many hours) and differs from some other feather stars that ingest numerous inert particles and defecate much more frequently. When specimens ofO. serripinna were fed continuously on brine shrimp nauplii,Artemia sp. (San Francisco strain), in the laboratory, the feather stars fed gluttonously, packing their guts with several hundred nauplii in 1 to 2 h. Thereafter, superfluous feeding began (i.e., further ingestions appeared to force undigested nauplii, some of them still living, out of the anus). These observations suggest thatO. serripinna usually feeds at relatively modest rates in its natural habitat, but can feed gluttonously to take advantage of infrequent patches of highly concentrated, nutritious particles (e.g. copepod swarms, migrating demersal zooplankton, and invertebrate gametes from mass spawnings). It is likely that such patches of nutritious particles are usually small enough to drift out of reach of the feather stars before gluttonous feeding proceeds to superfluous feeding. Opportunities for superfluous feeding in nature are probably very infrequent (e.g. ingestion of coral gametes and embryos after a mass spawning), and the feather stars evidently have no behavior that stops further ingestions after the gut becomes filled to capacity. 相似文献
430.
The effect of copper on the activity of Balbiani rings (BR1 and BR2) and nucleolar organizing region (NOR) in chromosome IV of the salivary gland of the 4th instar larvae of Chironomus ninevah has been investigated. Sublethal concentrations, i.e. 0.02, 0.1, 0.15 and 0.2 mg litre(-1) suppress the activity of BR1, and are statistically significant. The same concentrations reduced the activity of BR2 and NOR, but without significant differences, except 0.1 mg litre(-1) which was significant. The purpose of this work was to evaluate the effect of chronic toxicity of Cu(2+) on the expression of gene activity of midge salivary gland chromosomes Although there may be many more aquatic organisms that are more sensitive to copper, this midge was selected as a biological indicator species because of its association with benthic sediments. 相似文献