全文获取类型
收费全文 | 4321篇 |
免费 | 30篇 |
国内免费 | 24篇 |
专业分类
安全科学 | 43篇 |
废物处理 | 168篇 |
环保管理 | 140篇 |
综合类 | 1963篇 |
基础理论 | 769篇 |
环境理论 | 7篇 |
污染及防治 | 878篇 |
评价与监测 | 242篇 |
社会与环境 | 150篇 |
灾害及防治 | 15篇 |
出版年
2022年 | 52篇 |
2021年 | 39篇 |
2019年 | 33篇 |
2018年 | 69篇 |
2017年 | 57篇 |
2016年 | 75篇 |
2015年 | 65篇 |
2014年 | 97篇 |
2013年 | 192篇 |
2012年 | 127篇 |
2011年 | 95篇 |
2010年 | 118篇 |
2009年 | 127篇 |
2008年 | 146篇 |
2007年 | 167篇 |
2006年 | 114篇 |
2005年 | 106篇 |
2004年 | 93篇 |
2003年 | 114篇 |
2002年 | 89篇 |
2001年 | 86篇 |
2000年 | 84篇 |
1999年 | 84篇 |
1998年 | 58篇 |
1997年 | 53篇 |
1996年 | 35篇 |
1995年 | 51篇 |
1994年 | 52篇 |
1991年 | 36篇 |
1990年 | 41篇 |
1985年 | 36篇 |
1979年 | 38篇 |
1978年 | 33篇 |
1977年 | 32篇 |
1969年 | 35篇 |
1968年 | 32篇 |
1967年 | 55篇 |
1966年 | 47篇 |
1965年 | 53篇 |
1964年 | 62篇 |
1963年 | 62篇 |
1962年 | 58篇 |
1961年 | 63篇 |
1960年 | 55篇 |
1959年 | 64篇 |
1958年 | 59篇 |
1957年 | 69篇 |
1956年 | 49篇 |
1955年 | 49篇 |
1954年 | 46篇 |
排序方式: 共有4375条查询结果,搜索用时 651 毫秒
641.
642.
The European Union Guideline 2001/58/EG (safety data sheet guideline) states that the safety data sheet shall enable professional users to take the necessary measures for the protection of health and safety at the workplace as well as of the environment. According to this guideline, the employer should be in the position to determine whether hazardous chemical agents do exist at the workplace, and to assesses the risk to health and safety of workers arising from their use. Can the employer actually rely on the safety data sheet? Have the present data sheets really instructed how to safely handle and manage dangerous compounds? Are the numerously arising occupational illnesses by dangerous substances just a consequence of a careless handling? This question is also important in the discussion on REACH, the new European Chemicals Policy. This paper reveals the strengths and the weaknesses as well as the potential of manufacturer information. 相似文献
643.
Differences in protein patterns of the soluble protein fraction among the sibling species Marenzelleria viridis (formerly type I) and M. neglecta (formerly type II) were investigated under common environmental conditions using two-dimensional gel electrophoresis (2D-PAGE). Protein expression was determined using general protein staining with Coomassie-blue and compared with radioactive labeling of proteins. In the well-resolved region of stained gels an average of 319 protein spots for M. viridis and 241 spots for M. neglecta could be detected. High sensitivity of radiolabeling allowed separation of an average of 517 and 496 spots for M. viridis and for M. neglecta, respectively. Differences in protein expression between both species could be attributed mainly to qualitative differences in protein patterns. Triplet pattern was used to calculate the genetic similarity of the two species. Thus, 373 protein spots were scored for this analysis; whereas 304 spots were invariant, 36 spots were specific for M. viridis, while 33 spots were specific for M. neglecta. The genetic similarity (F) of the two Marenzelleria sibling species was 0.815. Apart from presence and absence, differences between both species resulted either from slight changes in the isoelectric point or from molecular weight, but rarely from both. Genetic variability was found only among specimens of M. viridis. The experimental conditions to perform two-dimensional electrophoresis for these polychaete species were established for subsequent investigations on a proteomic level. Using 2D-PAGE we expect further insight into the evolutionary adaptation in Marenzelleria spp.Communicated by O. Kinne, Oldendorf/Luhe 相似文献
644.
During two expeditions of the R.V. Polarstern to the Arctic Ocean, pack ice and under-ice water samples were collected during two different seasons: late summer (September 2002) and late winter (March/April 2003). Physical and biological properties of the ice were investigated to explain seasonal differences in species composition, abundance and distribution patterns of sympagic meiofauna (in this case: heterotrophs >20 µm). In winter, the ice near the surface was characterized by extreme physical conditions (minimum ice temperature: –22°C, maximum brine salinity: 223, brine volume: 5%) and more moderate conditions in summer (minimum ice temperature: –5.6°C, maximum brine salinity: 94, most brine volumes: 5%). Conditions in the lowermost part of the ice did not differ to a high degree between summer and winter. Chlorophyll a concentrations (chl a) showed significant differences between summer and winter: during winter, concentrations were mostly <1.0 µg chl a l–1, while chl a concentrations of up to 67.4 µmol l–1 were measured during summer. The median of depth-integrated chl a concentration in summer was significantly higher than in winter. Integrated abundances of sympagic meiofauna were within the same range for both seasons and varied between 0.6 and 34.1×103 organisms m–2 in summer and between 3.7 and 24.8×103 organisms m–2 in winter. With regard to species composition, a comparison between the two seasons showed distinct differences: while copepods (42.7%) and rotifers (33.4%) were the most abundant sea-ice meiofaunal taxa during summer, copepod nauplii dominated the community, comprising 92.9% of the fauna, in winter. Low species abundances were found in the under-ice water, indicating that overwintering of the other sympagic organisms did not take place there, either. Therefore, their survival strategy over the polar winter remains unclear.Communicated by O. Kinne, Oldendorf/Luhe 相似文献
645.
In the brown alga Dictyota dichotoma Lamour the phaeoplasts move to the anticlinal walls (profile position) in strong light and to the periclinal walls (face position) in dim light. By these movements transmittance changes are caused. If the algae were grown in light:dark cycles of about natural daylengths, circadian oscillations of the amplitudes and the kinetics of these transmittance changes are initiated. The lengths of the free running periods vary between 24 and 29 h. In addition, light:dark grown thalli were transferred into continuous dim or strong light or darkness, in order to check whether or not the rhythms continued under these conditions. By taking photomicrographs of intact thalli and of isolated cortical cell layers, prepared by bisecting, it could be shown that the maxima and minima of circadian transmittance changes correspond well with the number of phaeoplasts at the periclinal cell walls. The ecological relevance of these phenomena is discussed.Presented in part by the first author at the XI. International Seaweed Symposium, Qingdao, People's Republic of China, 19 to 26 June, 1983 相似文献
646.
Sedimentation of particulate matter during a phytoplankton spring bloom in relation to the hydrographical regime 总被引:1,自引:0,他引:1
Data presented and discussed here were collected continuously during April/May 1975 in the Bornholm Basin of the Baltic Sea. Sedimentation rates of particulate matter were recorded with 5 multisample sediment traps from different depths in the water column at 2 positions 170 km apart. Current meter data collected during the same period and depths indicated that the positions remained hydrographically distinct during the investigation. Particulate matter from the euphotic zone including diatom cells formed the bulk of the material collected by all traps. This flux of organic particles to the bottom was unimpeded by the strong density stratification present in the water column. The upper traps always collected less material than lower ones. This paradox has been ascribed to diminishing current speeds with depth, concomitant with an increase in sinking rates of phytoplankton and phytodetritus. Both factors influence the sampling efficiency of sediment traps, which are thought to have underestimated actual sedimentation rates here. A time lag of 2 to 3 weeks in bloom development seemed responsible for the characteristic differences between the two positions. The phase of major sedimentation at one position covered about 18 days, and a distinct sequence in the composition of the material collected by the 6 glasses of each trap indicated phases of a progressively deteriorating phytoplankton population in the water column contributing the particulate material. A total of 6.2 g C m-2 in 34 days was recorded at this station. Apart from a trap situated in an oxygen deficient layer which collected 0.44 g C m-2 of zooplankton corpses, zooplankton mortality was overestimated by the traps. Large-scale sedimencation of fresh organic matter produced by the spring bloom is probably a regular feature in areas with low over-wintering zooplankton populations and, as such, possibly has a direct stimulatory effect on growth and reproduction of the benthos.Contribution No. 185 of the Joint Research Programme 95, Kiel University. 相似文献
647.
Kersten Roselt Christoph Scheibert Jürgen W. Einax Jörg Kraft 《Environmental Sciences Europe》2004,16(2):99-104
Goal and Scope
By means of Geographical Information Systems (GIS) and other geostatistical methods, the extensive heterogeneous data materials of large area soil contaminations are re-evaluated to eliminate exploitation conflicts and investment obstacles.Methods
The mapping of relevant frame criteria generates the basis to solve the conflicts, such as types of exploitation of field areas, development plans, protected areas, flooded areas, etc. as well as their geo-referencing in the Geographical Information System. The critical examination of data age and quality as well as the geostatistical evaluation by means of semivariogram analysis and Kriging technique are essential prerequisites for the determination of areas related to utility and exceeding test values.Results and Conclusions
As a result, one can modify the hazardous situation and can provide recommendations for an optimal elimination of hazards, mostly in the framework of scheduled measures in terms of town planning.Outlook
On the basis of the results obtained, further exploitation or monitoring work can clearly be optimized. 相似文献648.
Karsten Grunewald Christiana Unger Heinz -Jürgen Brauch Wido Schmidt 《Environmental Sciences Europe》2004,16(1):7-14
Objective
Flood sediments were investigated due to the extreme flood situation around Dresden in August 2002Method
The samples have been analyzed by screening inorganic and organic pollutants.Results
It was observed that As, Pb, Cd, Zn, Cu, B and other heavy metals as well as DDT, PCB and Benzo [a] pyren were significantly enriched.Conclusion
Depending on geogenic and anthropogenic impacts, the spatial distribution of these contaminants was different. Organic compounds were dislocated down stream from Czech Republic along the Elbe River. Because of the old ore mining, samples near the Mulde and Wei\eritz Rivers showed high metal pollution.Perspective
More detailed and systematic investigations should be undertaken in the Elbe and Mulde river systems. 相似文献649.
Peter D. Dijkstra Renske Hekman Rüdiger W. Schulz Ton G. G. Groothuis 《Behavioral ecology and sociobiology》2007,61(4):599-609
The nature of the costs maintaining honesty of sexual signalling in inter- and intrasexual interactions remains a contentious
issue. For carotenoid-based colour ornaments, it has been hypothesized that the honesty of the signal is enforced when carotenoid
allocation to colour expression is traded off against carotenoid availability for immunocompetence. In addition, honesty is
enforced if androgens required for colour expression are immunosuppressive. We tested whether there is a trade-off between
colour expression and immunocompetence in a lek-breeding haplochromine cichlid fish, Pundamilia nyererei, from Lake Victoria with a carotenoid-based nuptial dress. First, we showed that expression of red nuptial colouration and
social rank in a group were positively correlated. We then successfully manipulated the level of colour advertisement by socially
stimulating individually housed males with a rival male: Stimulated males developed larger areas of red nuptial colouration
and had higher levels of circulating 11-ketotestosterone (11-KT) than non-stimulated males. We subsequently tested the humoral
immune response to a novel antigen (sheep red blood cells). There was no overall significant effect of social stimulation
on antibody production, but in the stimulated males, the degree of red colouration and the antibody response were negatively
correlated. This significant interaction between colour and treatment thus shows that the negative correlation between colouration
and antibody production is dependent on the (manipulated) social environment. This study provides correlational and experimental
evidence for a trade-off between expression of a sexual trait and one component of immune function in fish. We found no evidence
for a direct effect of 11-KT on antibody production, and we discuss alternative mechanisms that could mediate the trade-off. 相似文献
650.
Summary The vibratory courtship signal generated by abdominal and leg movements of male Cupiennius salei on plants consists of impulses, which in groups of about ten form syllables. A syllable together with the preceding silent pause is called a sequence. Up to 50 sequences chained together form a series. A series together with the preceding silent period is called an interseries. A complete courtship is built up from a row of successive interseries. An additional signal produced by palpal drumming only occurs between syllables. Females respond to ca. 40% of the male signal series with a single irregular signal produced by leg oscillations and lasting for 113–1790 ms. Their response reduces the duration of the male interseries significantly from an average of 27.9 s to 20.6 s. The female signal follows a male signal series within a narrow time frame of 0.89±0.53 s. Analysis over long periods of time and of complete courtships showed the male signalling to be highly structured in the time domain and to contain many cues potentially usable by the female for both such precise timing and conspecific recognition: (1) On average, the interval between the last two syllables is significantly longer than the preceding ones. (2) During the course of a series, syllable durations increase nearly linearly from 93 ms to 123 ms. (3) The twelfth sequence (T-12) prior to the final one (T) is outstanding since here, roughly 4 s before the end of a series, the duration of sequences and pauses, the signal amplitudes and the occurrence of palpal drumming abruptly start to increase. Also, the frequencies contained in the syllables shift to higher values. (4) Between sequences T-4 and T-6 pause duration and sequence duration reach their minimum whereas the values for signal acceleration and the occurrence of palpal drumming are highest. 相似文献