首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   41570篇
  免费   388篇
  国内免费   183篇
安全科学   1169篇
废物处理   1471篇
环保管理   5849篇
综合类   6831篇
基础理论   11657篇
环境理论   24篇
污染及防治   10553篇
评价与监测   2450篇
社会与环境   1864篇
灾害及防治   273篇
  2022年   268篇
  2021年   307篇
  2020年   283篇
  2019年   391篇
  2018年   556篇
  2017年   552篇
  2016年   823篇
  2015年   694篇
  2014年   958篇
  2013年   3081篇
  2012年   1173篇
  2011年   1714篇
  2010年   1409篇
  2009年   1410篇
  2008年   1723篇
  2007年   1805篇
  2006年   1649篇
  2005年   1363篇
  2004年   1365篇
  2003年   1296篇
  2002年   1251篇
  2001年   1669篇
  2000年   1160篇
  1999年   741篇
  1998年   605篇
  1997年   587篇
  1996年   599篇
  1995年   664篇
  1994年   632篇
  1993年   540篇
  1992年   568篇
  1991年   533篇
  1990年   553篇
  1989年   570篇
  1988年   477篇
  1987年   424篇
  1986年   384篇
  1985年   419篇
  1984年   425篇
  1983年   456篇
  1982年   452篇
  1981年   401篇
  1980年   341篇
  1979年   375篇
  1978年   320篇
  1977年   271篇
  1976年   258篇
  1975年   267篇
  1974年   256篇
  1972年   292篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
191.
Principles of good practice for collaborative resource management were derived from the literature and their use studied in a range of integrated catchment management processes. Desk-based reviews and interviews with participants allowed the principles to be refined and described within a framework that illustrates the interrelationships between core principles, enabling principles, precursors to a project and the influence of external factors on such collaborative processes. The findings illustrate the importance of these relationships in understanding how success is defined and under what conditions successful outcomes can be achieved. Understanding how these procedural aspects influence outcomes contributes to the wider literature on collaborative resource management that often treats processes separately from their context.  相似文献   
192.
193.
Nagayama J  Tsuji H  Iida T  Hirakawa H  Matsueda T  Ohki M 《Chemosphere》2001,43(4-7):1005-1010
Effects of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and coplanar polychlorinated biphenyls (Co-PCBs) on thyroid hormone and immune response systems were examined in 16 Yusho patients at about 30 years after the outbreak of the Yusho accident. Their toxic equivalent (TEQ) levels in the blood were 27.8-1048.5 pg/g fat with the median level of 222.4 pg/g fat, which was about seven times higher than that of healthy Japanese people. Even at such high blood TEQ concentrations, they seemed not to affect the serum levels of thyroid hormones, thyroid stimulating hormone (TSH), immunoglobulins (A, G and M), autoantibodies (antinuclear antibody, rheumatoid and lupus erythematosus (LE) factors), and lymphocyte subsets in the blood. However, positive rates of rheumatoid factor were considered to increase in higher blood TEQ groups. This investigation was done using rather small number of Yusho patients, so further large-scale investigations are needed to get more conclusive findings concerning their effects on thyroid hormone and immune response systems.  相似文献   
194.
Abstract

Isolates of the organic matter in the particulate, colloidal and dissolved states were obtained by tangential flow ultrafiltration through 0.40 μm polycarbonate and ~ 1 nm (1000 NMWL?) regenerated cellulose membranes and by solid-liquid reverse phase extraction techniques. the material was analyzed qualitatively by mass spectroscopy, proton nuclear magnetic resonance, Fourier transform infrared spectroscopy, high performance liquid chromatography with fluorescence detection of labelled primary amines and amino acids, and inductively coupled plasma/mass spectroscopy. All three states are characterized by similar organic chemistries. the marine colloidal state in coastal waters off the Californian coast contains primarily carbohydrates, fatty acids, minor amounts of proteinaceous compounds and electropositive elements including aluminium and iron. Aromatic molecules and olefinic functional groups are in low concentration. the colloidal state differs qualitatively from the particulate and dissolved states. Yet all three could be derived, with degradation, from algal or macroalgal surface components.  相似文献   
195.
In-situ manipulative experiments were conducted over a 3-month period (May–August 1980) to examine the rate at which meiobenthos colonizes oiled and untreated azoic fine sands at a shallow subtidal site in the lower York River, Virginia. Three concentrations of fresh Prudhoe Bay crude oil were added to sediments: 100, 2 500 and 10000 mg oil kg-1 dry wt sediment. Untreated azoic and natural sediments served as controls. Within 16 d, meiofauna densities in all treatments were comparable to natural populations in surface oxidized sediments, but densities fluctuated greatly during the remainder of the sampling period. Nematodes slowly colonized the subsurface anoxic sediments below the redox potential discontinuity (RPD); some less common species did not significantly recover below the RPD in the two more heavily oiled treatments. Analysis of nematode community composition by reciprocal averaging ordination and numerical classification revealed generally lower abundances, but no distinct differences, in species composition in the oiled substrates as compared to untreated and natural community controls. Ordination of sequential samples suggested that the nematode species assemblages in the untreated controls fully recovered from these small-scale disturbances by 90 d. Life history characteritics and frequent tidal transport combine to make estuarine meiobenthos highly resilient following disturbance. Contrary to prior recolonization studies, a successional sequence was found for the colonizing nematodes which may be analogous to models of macrobenthic colonization (e.g. McCall, 1975). The comesomatid nematode Sabatieria pulchra, which is frequently dominant in polluted sediments, colonized relatively late in the experiment. Consequently, stress resistance and resilience may not be as coincident in meiofauna as in macrofauna because of differences in factors affecting their dispersal.  相似文献   
196.
The aim of the present study was to examine if ozone produced similar effects on spring wheat growth with and without small amounts of nitrogen oxides. Two methods were used to produce ozone: the first method consisted of dry pressurized air fed to an electric discharge generator generating the byproducts, N2O5 and N2O, the second method consisted of ambient air fed to UV-lamps. Two spring wheat cultivars (Triticum aestivum L. cvs Minaret and Eridano) were exposed in small open-top chambers to charcoal-filtered air, non-filtered ambient air, and non-filtered ambient air with the addition of ozone for 8 h (0900 to 1700 h) daily, for five weeks. Plants were harvested every week. The growth of Minaret was shown to be more sensitive to O3 than that of Eridano. Leaf senescence increased with increasing ozone level in both cultivars. The total above-ground biomass dry weight decreased with increasing ozone concentration in Minaret, but not in Eridano. The Minaret plants reacted with more damaged leaf dry weight and inhibition of growth when O3 was produced by UV-lamps than when O3 was produced by air fed to an electric discharge generator. This could be explained by more nitrogen content per plant but not by increased nitrogen concentration in plant tissue in plants exposed to increased O3 and small amounts of incidental nitrogen oxides.  相似文献   
197.
Photoadaptations of zooxanthellae living within the deep water coral Leptoseris fragilis taken from the Gulf of Aqaba (Red Sea) were studied. Specimens-collected in summer 1988 between 110 and 120 m depth —were transplanted to 70 and 160 m. At each depth individuals were exposed in their natural growth position (oral side facing the surface) or in a reverse growth position (oral side facing the bottom). After 1 yr of exposure the corals were collected and the zooxanthellae were isolated. As a function of the availability of light with depth and growth position several algal parameters showed changes which are related to photoadaptations. The relatively low density of zooxanthellae of 0.15x106 cellsxcm-2 at a natural growth depth of 116 m decreased to 0.0034x106 cellsxcm-2 (2%) at 160 m in specimens growing with a natural orientation. In corals with a downward-facing oral surface at the same depth (160 m) only degenerated algae could be observed. With respect to depth dependence the volume of the algae decreased from 728 m3 at 116 m to 406 m3 at a depth of 160 m and the content of pigments increased. The augmentation of peridinin per cell was low (two times at 160 m compared to 116 m). Chlorophyll a and in particular chlorophyll c 2 concentrations per cell were enhanced. Compared to natural amounts at 116 m, chl a was five times and chl c 2 eight times higher at 160 m. At all depths the chl c 2 content per cell was higher than for chl a. The formation of chl a/chl c 2 complexes as light harvestor is discussed. Light harvesting, with chl c 2 prevailing may be explained as a special type of chromatic adaptation of L. fragilis in a double sense: (1) in the habitat light short wavelengths predominate. This light can be directly absorbed with pigments such as chl a and chl c 2. (2) Host pigments absorb visible violet light and transform these wavelengths, less suitable for photosynthesis, into longer ones by means of autofluorescence. The emitted longer wavelengths fit the absorption maxima of the algal pigments. Thus the host supports photosynthesis of his symbionts. Corals exposed at 160 m depth with a downward facing oral surface were alive after 1 yr and the host wavelength transforming pigment system was still present, but zooxanthellae were absent or degenerated. The light field at 160 m seems therefore to be critical: the combined photoadaptations of host and symbionts, allowing photosynthesis under barren light conditions, seem to be exhausted. In L. fragilis the photoadaptive strategies of host and symbionts cooperate harmoniously. In addition, the adaptations are interlocked with the particular light situation of the habitat with respect to light quantity and quality. The cooperation of physical and organismic parameters examplifies how evolution and, in particular, coevolution has led to optimal fitness.  相似文献   
198.
The feeding behavior of relatively undisturbed natural populations of tintinnids was studied in a series of experiments which utilized water samples collected in Southern California coastal waters. Dilute suspensions of corn starch were presented to the tintinnids and the rates of ingestion of this visual tracer determined after short (5 to 20 min) incubations followed by fixation in Lugol's iodine fixative. Tintinnids were observed to ingest particles of diameters up to approximately 43% of their lorica oral diameter and at rates proportional to their oral diameters. Grazing rates observed in these experiments ranged up to approximately 10 l tintinnid-1 h-1, and generally agreed well with the rates observed in experiments utilizing laboratory cultures of tintinnids. No significant diel periodicity in feeding rates was observed in the one study extending over a 24 h period.  相似文献   
199.
For about 50 years the desertion of areas by traditional activities has led to an important evolution of landscapes and environments on the island of Ouessant. The study of this evolution has been undertaken at different spatial and temporal scales. On one part of the island, a scientific investigation carried out at the scale of the parcel enabled the form of the landscape in 1850 to be compared with that of 1985. On the whole island, the evolution of spatial organization and land use was compared between 1950 and 1985. For each of three main ecological environments, vegetational successions after the decrease of agriculture have been studied along with their future potential changes. This work highlights some considerations about the present management of the environment in relation to the major objectives of island environmental policies.  相似文献   
200.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号