全文获取类型
收费全文 | 29733篇 |
免费 | 335篇 |
国内免费 | 247篇 |
专业分类
安全科学 | 999篇 |
废物处理 | 1453篇 |
环保管理 | 3941篇 |
综合类 | 4469篇 |
基础理论 | 7748篇 |
环境理论 | 8篇 |
污染及防治 | 7349篇 |
评价与监测 | 2125篇 |
社会与环境 | 2043篇 |
灾害及防治 | 180篇 |
出版年
2023年 | 140篇 |
2022年 | 261篇 |
2021年 | 319篇 |
2020年 | 195篇 |
2019年 | 243篇 |
2018年 | 435篇 |
2017年 | 460篇 |
2016年 | 719篇 |
2015年 | 531篇 |
2014年 | 854篇 |
2013年 | 2463篇 |
2012年 | 1015篇 |
2011年 | 1349篇 |
2010年 | 1102篇 |
2009年 | 1144篇 |
2008年 | 1411篇 |
2007年 | 1329篇 |
2006年 | 1207篇 |
2005年 | 1079篇 |
2004年 | 1037篇 |
2003年 | 990篇 |
2002年 | 933篇 |
2001年 | 1091篇 |
2000年 | 768篇 |
1999年 | 482篇 |
1998年 | 363篇 |
1997年 | 383篇 |
1996年 | 397篇 |
1995年 | 465篇 |
1994年 | 394篇 |
1993年 | 343篇 |
1992年 | 376篇 |
1991年 | 355篇 |
1990年 | 326篇 |
1989年 | 322篇 |
1988年 | 295篇 |
1987年 | 241篇 |
1986年 | 247篇 |
1985年 | 247篇 |
1984年 | 267篇 |
1983年 | 254篇 |
1982年 | 268篇 |
1981年 | 221篇 |
1980年 | 165篇 |
1979年 | 181篇 |
1978年 | 162篇 |
1977年 | 133篇 |
1975年 | 137篇 |
1973年 | 167篇 |
1972年 | 142篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
291.
N. A. Petushkova 《黑龙江环境通报》1991,11(5):279-283
Chorionic villi obtained in the first trimester from a pregnancy at risk for α-mannosidosis were shown to have reduced α-mannosidase (EC 3.2.1.24) activity. The pregnancy was terminated and subsequent enzyme studies of the fetal tissues were consistent with the diagnosis of α-mannosidosis. Like the enzyme in the child's fibroblast, α-mannosidase of the chorionic villi from a pregnancy at risk for α-mannosidosis was activated by high substrate concentration and by Zn2 +, and displayed a Km value two-fold higher than normal. Our results confirm that chorionic villi can be used for early prenatal diagnosis of α-mannosidosis. 相似文献
292.
Our aim in this study was to identify the economically optimal level of use of resources for a grazing system in tropical Australia and to compare it with the biological optimum. Grazing management trials were conducted in the Ord River irrigation area of north-western Australia. Biologists at the Commonwealth Scientific and Industrial Research Organization provided the biological data. The liveweight gains of Kimberley shorthorn steers were recorded, after a 1-year fattening period, for different grazing management strategies. Five different stocking rates were used on irrigated pangola grass (Digitaria decumbens) fertilized with nitrogen at five different rates. All other were applied at fixed, non-limiting levels.The results of the trials were modelled by a liveweight gain production function. This production function was used in an income simulation model to identify economically optimal (profit maximizing) stocking rates. This was done in two stages. First, a base analysis was undertaken on the basis o the economic conditions prevailing in September 1987. Second, sensitivity analysis was applied to the results of the base analysis. The parameters varied were the rate of interest, store cattle prices, finished cattle prices, transport costs and the length of the planning horizon.The biological optimum, when defined as maximum liveweight gain ha−1, corresponds to a much higher intensity of use of resources than the economic optimum, and yields substantially lower profits or higher losses. These discrepancies increase when economic conditions worsen, or when the planning horizon of graziers is decreased from 50 to 10 years. Therefore, the adoption of the biological optimum cannot result in an econonomically stable grazing system in the medium to long term, when it is highly likely that economic parameters will fluctuate. The economic stability of the system is increased, but is still quite weak, if the economically optimal input combination is utilized. It was not possible to determine whether this economic optimum would result in long-term ecological stability because the relevant data were not collected during the trials.The relevance of management recommendations made to graziers and land administrators would be increased if these recommendations were based on an analysis of both the economic and the ecological stability of grazing systems over the medium to long term. We show in the last part of this study how this could be accomplished. 相似文献
293.
M. L. Smith O. L. Pellett M. M. J. Cass N. G. Kennaway N. R. M. Buist J. Buckmaster M. Golbus G. S. Spear J. A. Schneider 《黑龙江环境通报》1987,7(1):23-26
The prenatal diagnosis of cystinosis is currently based on the increased amount of free-cystine present in amniotic fluid cells. Amniocyte cultures must be grown for at least 2 weeks to obtain sufficient cells for such measurements. Thus, the diagnosis cannot be made until close to 20 weeks gestational age by this method. We report a case in which chorionic villi were used for direct cystine measurement resulting in the in utero diagnosis of cystinosis at 9 weeks gestational age. The diagnosis was confirmed by the study of cultured chorionic villus cells, and of the 10-week abortus. 相似文献
294.
The prenatal diagnosis of The Turner Syndrome is described at a menstrual age of 12 weeks. Detection of cystic hygroma was followed by vaginal chorionic villous sampling (CVS) which revealed a 45,X karyotype. Early documentation of fetal karyotype in the presence of a cystic hygroma is essential for accurate diagnosis and genetic counselling. 相似文献
295.
J. H. A. M. Tuerlings MD A. S. P. M. Breed R. Vosters G. J. P. A. Anders 《黑龙江环境通报》1993,13(4):301-306
A 70,XXX, +18 karyotype was found by chorionic villus sampling, while the fetal fibroblast culture of the affected fetus revealed a 47,XX,+ 18 karyotype. From several possible mechanisms, we assume that a second gamete fusion occurred after the first cell division of the zygote. According to this interpretation, the mosaicism arose in very early pregnancy (at the two-cell stage). This discrepancy can therefore be explained by selection pressure, due to the differentiation processes in the embryonic tissues. 相似文献
296.
M. R. Verschraegen-Spae N. Van Roy A. De Perdigo A. De Paepe F. Speleman 《黑龙江环境通报》1993,13(5):385-394
The nature and origin of two de novo small marker chromosomes found at prenatal diagnosis were determined by fluorescence in situ hybridization using chromosome centromere-specific probes and chromosome-specific plasmid libraries. One marker was found in a mosaic state and was shown to be an i(18p). The second marker was characterized as an inv dup(22). We conclude that molecular cytogenetic analysis contributes to the identification of marker chromosomes and therefore facilitates genetic counselling and decision-making for the parents. 相似文献
297.
298.
299.
300.