全文获取类型
收费全文 | 41713篇 |
免费 | 404篇 |
国内免费 | 375篇 |
专业分类
安全科学 | 1085篇 |
废物处理 | 1652篇 |
环保管理 | 5115篇 |
综合类 | 8623篇 |
基础理论 | 10044篇 |
环境理论 | 21篇 |
污染及防治 | 10477篇 |
评价与监测 | 2832篇 |
社会与环境 | 2416篇 |
灾害及防治 | 227篇 |
出版年
2022年 | 351篇 |
2021年 | 356篇 |
2020年 | 235篇 |
2019年 | 327篇 |
2018年 | 580篇 |
2017年 | 619篇 |
2016年 | 911篇 |
2015年 | 718篇 |
2014年 | 1049篇 |
2013年 | 3237篇 |
2012年 | 1265篇 |
2011年 | 1723篇 |
2010年 | 1330篇 |
2009年 | 1456篇 |
2008年 | 1694篇 |
2007年 | 1762篇 |
2006年 | 1573篇 |
2005年 | 1353篇 |
2004年 | 1289篇 |
2003年 | 1296篇 |
2002年 | 1193篇 |
2001年 | 1543篇 |
2000年 | 1041篇 |
1999年 | 699篇 |
1998年 | 467篇 |
1997年 | 502篇 |
1996年 | 531篇 |
1995年 | 561篇 |
1994年 | 558篇 |
1993年 | 501篇 |
1992年 | 505篇 |
1991年 | 509篇 |
1990年 | 497篇 |
1989年 | 424篇 |
1988年 | 420篇 |
1987年 | 346篇 |
1986年 | 371篇 |
1985年 | 382篇 |
1984年 | 399篇 |
1983年 | 405篇 |
1982年 | 397篇 |
1981年 | 379篇 |
1980年 | 326篇 |
1979年 | 315篇 |
1978年 | 288篇 |
1977年 | 271篇 |
1974年 | 279篇 |
1972年 | 249篇 |
1971年 | 232篇 |
1967年 | 249篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
121.
122.
123.
Spilt notochord syndrome is an extremely rare form of spinal dysraphism characterized by a complete cleft of the spine and a persistent communication between endoderm and ectoderm. A variant of split notochord syndrome was diagnosed in a 25-week-old fetus showing a prolapsed congenital colostomy and a spinal cystic lesion. The final diagnosis included protruding colon segment, imperforate anus with a rectourethral fistula and lipomyelomeningocele. The ultrasound features of the condition and the post-natal management are discussed. The neonate was successfully treated with a posterior sagittal anorectoplasty, while the lipomyelomeningocele was resected at a later stage. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
124.
125.
126.
Offshore oil and gas production platforms can be a source of chronic stress that could lead to sublethal impacts on resident benthic organisms. In June 1993 and January 1994, genetic diversity of Harpacticoida (Copepoda) living proximal to operating, offshore platforms in the Gulf of Mexico was estimated to test if platforms are associated with strong selective pressures. Because harpacticoids have short generation times and direct benthic development, they are suitable organisms for examining population responses. Genetic diversity was estimated by comparing restriction fragment length polymorphisms generated from mitochondrial DNA amplified by the polymerase chain reaction on individuals of five species (Cletodes sp., Enhydrosoma pericoense, Normanella sp., Robertsonia sp., and Tachidiella sp.). Populations living at Near regions (stations<50 m from a platform) had significantly less haplotype diversity than populations of the same species living at Far regions (stations>3 km from a platform). The levels of haplotype diversity exhibited by the Far populations were similar at three different platforms located hundreds of kilometers apart. The differences in haplotype diversity between Near and Far regions were the result of a higher proportion of dominant haplotypes, and a loss of less common haplotypes. Haplotypic diversity was inversely correlated with a multivariate measurement of levels of sediment contaminants. The pattern of haplotype diversity on the Gulf of Mexico continental shelf seems to consist of a uniform level of haplotype diversity, punctuated by islands of lower diversity around oil and gas platforms. The selective pressures that lead to a loss of genetic diversity may be the result of contaminants, other differences in the physico-chemical environment, or disturbance in general. 相似文献
127.
Coping with riverbank erosion hazard and displacement in bangladesh: survival strategies and adjustments 总被引:2,自引:0,他引:2
As a deltaic plain, Bangladesh annually experiences riverbank erosion hazard due to sudden and rapid channel shifting, particularly in the major floodplain areas of the country. Consequently, valuable cultivable land is lost; also village settlements, markets and towns are destroyed, displacing tens of thousands of people. This paper examines the magnitude of river channel migration and encroachment on land, and the nature of human adjustment systems in the Brahmaputra–Jamuna floodplain, by investigating aspects of the social and cultural dynamics of resettlement of the displaced people. Some policy measures are recommended to improve the ability of the people in the floodplain to cope with these hazards. 相似文献
128.
This paper reviews six case studies examined as part of a project to review targetting methodologies employed by non-government organisations in Africa during the 1984-6 food crisis. Most agencies have not yet fully evaluated the role of data in informing policy decisions during their respective emergency programmes. The case studies presented reflect a wide variety of approaches to targetting emergency food aid that are based largely on the use of 'socio-economic' data. The recent emergency relief operations in Africa seem to indicate a change in relief agencies' approaches to the assessment and monitoring of needs of the affected populations. Earlier dependance on nutritional data has given way to an increasing reliance on the use of socio-economic indicators. There was a wide variation in the case studies of the type of indicators collected and utilised in needs assessment and monitoring. There were those who relied almost exclusively on nutritional data to target resources during the 1984-86 African crisis, and others whose experiences during that period lead them to attach more weight to socio-economic data. Other agencies appear to have recognised the problems of relying solely on nutritional data to target food aid during their 1984–86 emergency programmes, and thus more or less abandoned classical anthropometric surveys in their needs assessment and monitoring methodologies during this period. Thus nutritional data has a less significant role in the decision making process than previously had been the case. 相似文献
129.
A study was undertaken to establish the role of free amino acids (FAA) in aerobic energy dissipation in embryos of turbot (Scophthalmus maximus) which contain an oil globule in the egg. Laboratory-reared developing eggs and larvae (15°C, 34 salinity) were measured for oxygen uptake, ammonia excretion, contents of FAA, protein, and ammonium, and volumes of yolksac and oil globule. Newly spawned eggs from different batches contained 55 to 90 nmol egg–1 of FAA. Resorption of FAA occurred in parallel with the consumption of yolk. Resorption of the oil globule, however, occurred predominantly after hatching and mainly after yolk resorption. The combined data suggest that approximately 70% of the FAA are utilized as an energy substrate, while the rest are polymerized into body proteins. FAA become a significant energy substrate in the early egg stage and account for 100% of the aerobic energy dissipation 2 d after Fertilization then decrease to ca. 60% at the time of hatching. Lipids derived from the oil globule seem to be the main fuel after hatching and account for ca. 90% of the energy dissipation at the onset of first-feeding. Thus, the energetics of fish embryos which contain an oil globule seems to be different from those that depend exclusively on the nutritional reserves of the yolk. 相似文献
130.
Oxygen and carbon isotopic composition of the aragonite of fish otoliths was measured on 175 specimens comprising 24 different species in 1989 and 1990. All specimens but two came from the northern Adriatic Sea or the northern Tyrrhenian Sea (two freshwater specimens were studied for comparison with the marine fish). The data obtained confirm the results of previous research suggesting the existence of equilibrium conditions between the otolith aragonite and ambient water with respect to ·18O(CO3
2-) values. Examination of one of the species indicated that the CaCO3 of otoliths probably accumulates continuously over time, seasonal isotopic changes being clearly visible (from a set of radial spot samples) for both oxygen and carbon isotopes. The apparent isotopic equilibrium with ambient water suggests that the 18O(H2O) of the endolymph is equal to that of seawater and considerably different from that of fish body water. In the case of 13C(CO3
2-), isotopic equilibrium with dissolved carbon species in seawater is never reached, even though the contribution of metabolic CO2 is variable among different species and even among different individuals of the same species. This rules out the possibility of using 13C(CO3
2-) values obtained from fossil otoliths for paleoenvironmental and paleobiological conclusions. 相似文献