全文获取类型
收费全文 | 40245篇 |
免费 | 431篇 |
国内免费 | 325篇 |
专业分类
安全科学 | 1107篇 |
废物处理 | 1513篇 |
环保管理 | 5322篇 |
综合类 | 6466篇 |
基础理论 | 11402篇 |
环境理论 | 24篇 |
污染及防治 | 10445篇 |
评价与监测 | 2495篇 |
社会与环境 | 1959篇 |
灾害及防治 | 268篇 |
出版年
2022年 | 281篇 |
2021年 | 263篇 |
2019年 | 295篇 |
2018年 | 529篇 |
2017年 | 559篇 |
2016年 | 796篇 |
2015年 | 666篇 |
2014年 | 980篇 |
2013年 | 3078篇 |
2012年 | 1191篇 |
2011年 | 1741篇 |
2010年 | 1447篇 |
2009年 | 1441篇 |
2008年 | 1694篇 |
2007年 | 1823篇 |
2006年 | 1605篇 |
2005年 | 1346篇 |
2004年 | 1333篇 |
2003年 | 1278篇 |
2002年 | 1240篇 |
2001年 | 1629篇 |
2000年 | 1164篇 |
1999年 | 721篇 |
1998年 | 538篇 |
1997年 | 563篇 |
1996年 | 575篇 |
1995年 | 632篇 |
1994年 | 576篇 |
1993年 | 510篇 |
1992年 | 537篇 |
1991年 | 491篇 |
1990年 | 501篇 |
1989年 | 532篇 |
1988年 | 443篇 |
1987年 | 404篇 |
1986年 | 384篇 |
1985年 | 403篇 |
1984年 | 401篇 |
1983年 | 422篇 |
1982年 | 410篇 |
1981年 | 351篇 |
1980年 | 324篇 |
1979年 | 353篇 |
1978年 | 309篇 |
1977年 | 266篇 |
1976年 | 245篇 |
1975年 | 245篇 |
1974年 | 234篇 |
1973年 | 245篇 |
1972年 | 264篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
251.
Fetal aspartylglucosaminuria (AGU) was studied during the first trimester of pregnancy in six at-risk pregnancies using chorionic villus samples. The activity of aspartylglucosaminidase (AGA) was high in five cases, indicating an unaffected fetus. This was confirmed through delivery of healthy newborns with a normal pattern of urinary oligosaccharides. Low enzyme activity in an uncultured biopsy specimen and in cultured amniotic fluid cells in one case demonstrated that the fetus was affected. The pregnancy was terminated and the prenatal diagnosis was confirmed by showing reduced AGA activity in cultured fibroblasts of the fetus. 相似文献
252.
253.
A Framework for Monitoring and Evaluating Carbon Mitigation by Farm Forestry Projects: Example of a Demonstration Project in Chiapas,Mexico 总被引:1,自引:0,他引:1
De Jong Ben H.J. Tipper Richard Taylor John 《Mitigation and Adaptation Strategies for Global Change》1997,2(2-3):231-246
Mitigation and Adaptation Strategies for Global Change - In Mexico an estimated 4.5 × 106ha are available for farm forestry, while up to 6.1 × 106 ha could be saved from deforestation by... 相似文献
254.
255.
P. Robbins-Furman J. T. Hecht M. Rocklin N. Maklad G. Greenhaw I. Wilkins MD 《黑龙江环境通报》1995,15(2):179-182
The diagnosis of Freeman–Sheldon syndrome was made by ultrasonographic evaluation of a 20-week fetus with a positive family history. The ultrasonographic features were abnormalities of the extremities and mouth. 相似文献
256.
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
257.
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
258.
With the advent of more stringent controls on wastewater treatment, sewage sludge production in Europe and many parts of the world is increasing. With this increase comes the problem of sludge disposal, and recycling to land arguably offers an economically and environmentally sustainable option. However, a major limitation of sewage sludge reuse is the potential release of heavy metals from the sludge and heavy metal accumulation to toxic levels in topsoils. The properties of the sludge play a crucial role in determining the initial release and subsequent availability of heavy metals in amended soils. Bioavailable forms of heavy metals in recently amended soils are most likely to be those that are bioavailable in the sewage sludge. In this paper, published research on the importance of sewage sludge characteristics on metal release and bioavailability will be reviewed and contrasted with original research. A selection of sludges from around Australia has been collected for this purpose. Through the use of incubation studies, isotope dilution techniques, ion-selective electrode measurements and 13C-NMR spectroscopy, the importance of a range of sludge properties on heavy metal behaviour in sludges and sludge-amended soils is addressed. 相似文献
259.
R Burt M.A WilsonT.J Keck B.D Dougherty D.E StromJ.A Lindahl 《Advances in Environmental Research》2003,8(1):51-67
Long-term copper smelting in the Anaconda and Deer Lodge Valley area of Montana has resulted in an extensive area of trace element contamination. Aerial extent of contamination is generally established, but total analysis of soils does not correlate to relative degree of impact on vegetation growth. Three pedons (Beaverell, Cetrack and Judco) were analyzed by routine soil characterization methods, aqua regia microwave digestion, sequential chemical extraction, and X-ray diffraction analysis with the objective of providing a better understanding of chemical forms and potential reactivity of selected trace elements (Cd, Co, Cr, Cu, Hg, Mn, Ni, P, Pb). Surface horizons of soils are more acidic than subsoils, with pH for all horizons ranging from 4.0 to 8.7. Beaverell is the most contaminated in the upper 20 cm with the sum of total extractable (SUMTE) trace elements by microwave digestion ranging from 1836 to 3605 mg kg−1, largest H2O-soluble (WS) and exchangeable (EX) fractions (e.g. 1.6 and 9.3%, respectively), and smallest residual (RES) fraction (e.g. 14.3%). Cetrack has greater SUMTE elements than Judco, though a lower WS+EX fraction due to the effects of alkaline pH, carbonates and high P. Oxide (OX), organic matter/sulfide (OM/S), and RES fractions predominate over WS, EX, and specially-sorbed/carbonate-bound fractions (SS/CAR) for all horizons. Copper, Zn, Pb and Cd are elevated in surface over subsurface horizons in these latter fractions, indicating these elements were anthropogenic additions. X-ray data indicate that Pb, Cu, Cr and Cd partially exists as both OX and sulfide mineral forms. 相似文献
260.
Gamergates (i.e. mated reproductive workers) are mostly known from ant species within the Ponerinae. We report here the discovery of gamergates in two species of the subfamily Myrmicinae. Until now, mated reproductive females in colonies of myrmicine species have been considered morphologically distinct from the worker caste. However, in two species of the myrmicine Metapone (Metapone madagascarica and a newly discovered, not yet described Metapone species) all workers have six ovarioles and a spermatheca; and some of them are mated. There are no morphological differences between mated and non-mated workers. Field observations and laboratory studies indicate that colonies of the Metapone species can reproduce with gamergates only. 相似文献