全文获取类型
收费全文 | 26317篇 |
免费 | 421篇 |
国内免费 | 661篇 |
专业分类
安全科学 | 910篇 |
废物处理 | 1160篇 |
环保管理 | 3675篇 |
综合类 | 4347篇 |
基础理论 | 6902篇 |
环境理论 | 9篇 |
污染及防治 | 7015篇 |
评价与监测 | 1594篇 |
社会与环境 | 1588篇 |
灾害及防治 | 199篇 |
出版年
2023年 | 133篇 |
2022年 | 290篇 |
2021年 | 254篇 |
2020年 | 261篇 |
2019年 | 229篇 |
2018年 | 420篇 |
2017年 | 405篇 |
2016年 | 616篇 |
2015年 | 486篇 |
2014年 | 711篇 |
2013年 | 2092篇 |
2012年 | 920篇 |
2011年 | 1309篇 |
2010年 | 1013篇 |
2009年 | 1124篇 |
2008年 | 1239篇 |
2007年 | 1285篇 |
2006年 | 1096篇 |
2005年 | 919篇 |
2004年 | 906篇 |
2003年 | 913篇 |
2002年 | 844篇 |
2001年 | 1063篇 |
2000年 | 812篇 |
1999年 | 493篇 |
1998年 | 363篇 |
1997年 | 366篇 |
1996年 | 356篇 |
1995年 | 424篇 |
1994年 | 326篇 |
1993年 | 299篇 |
1992年 | 291篇 |
1991年 | 287篇 |
1990年 | 292篇 |
1989年 | 287篇 |
1988年 | 233篇 |
1987年 | 210篇 |
1986年 | 213篇 |
1985年 | 224篇 |
1984年 | 266篇 |
1983年 | 214篇 |
1982年 | 244篇 |
1981年 | 222篇 |
1980年 | 176篇 |
1979年 | 206篇 |
1978年 | 130篇 |
1977年 | 144篇 |
1975年 | 133篇 |
1974年 | 138篇 |
1972年 | 131篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
361.
M. Van Blerk MD J. Smitz L. De Catte C. Kumps J. Van Der Elst A. C. Van Steirteghem 《黑龙江环境通报》1992,12(12):1062-1066
This study explores if assay of cancer antigen 125 (CA 125) in maternal serum might aid the detection of Down's syndrome in the second trimester of pregnancy. CA 125 levels were determined retrospectively in stored maternal serum samples from ten Down's syndrome pregnancies and 78 controls matched for gestational and maternal age. In addition, second-trimester amniotic fluid samples from nine Down's syndrome and 109 unaffected pregnancies were analysed for CA 125. Maternal serum CA 125 values for Down's syndrome pregnancies were lower, with the median being 0.72 multiples of the unaffected population median. The medians for affected and unaffected pregnancies did not differ significantly and there was a considerable overlap in the range of values of cases and controls. The distribution of amniotic fluid CA 125 levels for Down's syndrome pregnancies resembled that for controls. From our present results, we could not find an association between Down's syndrome and second-trimester maternal serum or amniotic fluid CA 125 levels. 相似文献
362.
Mr. M. T. Rebello G. Hackett J. Smith F. E. Loeffler S. Robson N. Maclachlan R. W. Beard C. H. Rodeck R. Williamson D. V. Coleman C. Williams 《黑龙江环境通报》1991,11(1):41-46
Ten-ml samples of amniotic fluid were taken from pregnancies being terminated at 8–14 weeks' gestation. DNA was extracted from the amniotic cells by sequential centrifugation and analysed using the polymerase chain reaction (PCR). Fifteen samples were analysed for evidence of maternal contamination using Mfd5 oligo-nucleotide primers for repeat polymorphisms. Ten amniotic fluid samples were tested for the Delta-F508 deletion characteristic of cystic fibrosis to demonstrate a diagnostic application for the technique. In each case, DNA extracted from fetal tissue from the same pregnancy was included in the controls. In 14 of the 15 cases tested with the Mfd5 primers, both the amniotic fluid DNA and the fetal DNA showed no evidence of contaminating DNA. In one case, neither the amniotic fluid cells nor the fetal cells yielded results. In nine of the ten cases tested with the Delta-F508 primers, the amniotic fluid cell DNA provided accurate information about the genetic status of the fetus; in the tenth, the fetal DNA failed to amplify. The results indicate that adequate DNA can be extracted from amniotic fluid from 8 weeks' gestation onward and these samples are suitable for prenatal diagnosis using PCR. 相似文献
363.
Joe Leigh Simpson James L. Mills George G. Rhoads George C. Cunningham Howard J. Hoffman Mary R. Conley 《黑龙江环境通报》1991,11(8):641-648
No clear answer concerning whether multivitamin/folate supplementation prevents neural tube defects (NTDs) is provided by three studies in the United States. All these studies are occurrence in nature, no recurrence studies having been conducted. The Atlanta Birth Defects Study is subject to pronounced memory and recall biases, the length between event and interview being as long as 16 years. In a second study (Boston University), objections can be raised to certain aspects of the experimental design, and the claim that 22 per cent of women started vitamins sufficiently early after pregnancy diagnosis to influence NTD formation is suspicious. Our NICHD case control study of 541 women in California and Illinois revealed no evidence for multivitamins or folic acid preventing NTDs. U.S. public policy-makers face difficulties in applying results of recurrence or occurrence studies in high-risk areas to low-risk areas in the U.S. 相似文献
364.
The aim of this study was to determine whether there is increased leakage of neuron-specific enolase (NSE) and S-100 protein into amniotic fluid in pregnancies with neural tube defects, since both these proteins are produced by neural tissue, and to compare the value of these substances for detecting such defects with that of the more conventional techniques of alpha-fetoprotein (AFP) and acetylcholinesterase (AChE) gel electrophoresis. Amniotic samples from 25 mid-pregnancies (15–17 weeks' gestation) with neural tube defects (14 with open spina bifida and 11 with anencephaly) and from seven mid-pregnancies with abdominal wall defects were compared with a control material consisting of 80 amniotic fluid samples from 80 consecutive mid-pregnancy amniocenteses, with normal karyotypes and AFP concentrations. All of the above cases of abnormalities were primarily detected through increased AFP levels in the amniotic fluid. Amniotic fluid samples from 13 pregnancies with fetuses with autosomal chromosomal abnormalities and seven amniotic fluid samples contaminated with blood were also included in the investigation. It is concluded from the results that the conventional AFP assay combined with AChE gel electrophoresis is the best method for screening amniotic fluid for neural tube defects and defects of the abdominal wall. Neither NSE nor S-100 assay alone proved to be superior for the detection of these cases in mid-trimester amniotic fluid. The S-100 assay, however, could give additional information in cases where AChE gel electrophoresis is not decisive; for example, in samples contaminated with blood. 相似文献
365.
Kenneth L. Garver Miriam G. Blitzer Gladys Ibezim Sandra G. Marchese Dolores L. Pegram Anita M. Hagins Wnjing Zhang 《黑龙江环境通报》1984,4(2):109-112
Using a modified procedure by Solomons and Styner (1969), an evaluation of inorganic pyrophosphate (PPi) was performed on the amniotic fluid of two fetuses at risk for osteogenesis imperfecta (OI) at 14½ weeks gestation. The parents of both cases had a previous child with OI, Type II. The normal control group at 14–16 weeks gestation had PPi values ranging from 22.0–59.2 ug/100 ml, with a mean of 38.6±9.51 ug/100 ml. In each at-risk fetus, the amniotic fluid PPi value was within normal range. The first baby was born phenotypically normal at term. Intrauterine radiographic and fetal sonograms were done on the second fetus at approximately 19 weeks gestation. Both showed evidence of OI, Type II. The pregnancy was terminated at 21 weeks. Radiologic studies of the aborted fetus were consistent with OI, Type II. Our results indicate that the evaluation of PPi levels in amniotic fluid is not the method of choice for prenatal diagnosis of IO. 相似文献
366.
Christopher T.Perry 《Ambio-人类环境杂志》2003,32(2):134-139
引言 在过去几十年中进行的调查工作使我们对低纬度珊瑚礁的生长有了较清楚的认识.生长在这些环境(往往在温度、盐度和光照方面处于理想的条件下)中的珊瑚虫能够形成在空间上非常重要的珊瑚礁结构.在清澈的水体中,水下100m多的地方都有珊瑚生长[1,2],但据报道,在较浅的地方,碳酸盐净累积速度为0.83~0.91kg CaCO3/m2@a[3,4]. 相似文献
367.
368.
369.
370.
Mitigation and Adaptation Strategies for Global Change - Guidelines of the Intergovernmental Panel on Climate Change (IPCC) were used to assess a greenhouse gas inventory for land use change and... 相似文献