全文获取类型
收费全文 | 25070篇 |
免费 | 237篇 |
国内免费 | 173篇 |
专业分类
安全科学 | 566篇 |
废物处理 | 1188篇 |
环保管理 | 2527篇 |
综合类 | 4008篇 |
基础理论 | 6427篇 |
环境理论 | 17篇 |
污染及防治 | 7214篇 |
评价与监测 | 1879篇 |
社会与环境 | 1528篇 |
灾害及防治 | 126篇 |
出版年
2023年 | 156篇 |
2022年 | 381篇 |
2021年 | 382篇 |
2020年 | 226篇 |
2019年 | 248篇 |
2018年 | 528篇 |
2017年 | 569篇 |
2016年 | 807篇 |
2015年 | 565篇 |
2014年 | 953篇 |
2013年 | 2036篇 |
2012年 | 1059篇 |
2011年 | 1337篇 |
2010年 | 1064篇 |
2009年 | 966篇 |
2008年 | 1223篇 |
2007年 | 1266篇 |
2006年 | 1045篇 |
2005年 | 851篇 |
2004年 | 821篇 |
2003年 | 748篇 |
2002年 | 726篇 |
2001年 | 772篇 |
2000年 | 575篇 |
1999年 | 328篇 |
1998年 | 220篇 |
1997年 | 250篇 |
1996年 | 233篇 |
1995年 | 298篇 |
1994年 | 279篇 |
1993年 | 202篇 |
1992年 | 234篇 |
1991年 | 209篇 |
1990年 | 228篇 |
1989年 | 208篇 |
1988年 | 169篇 |
1987年 | 175篇 |
1986年 | 175篇 |
1985年 | 171篇 |
1984年 | 156篇 |
1983年 | 155篇 |
1982年 | 145篇 |
1981年 | 128篇 |
1980年 | 125篇 |
1979年 | 135篇 |
1978年 | 107篇 |
1977年 | 118篇 |
1975年 | 98篇 |
1973年 | 98篇 |
1972年 | 91篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
341.
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
342.
343.
344.
Reverse phase HPLC of radioactive globin chains has been compared to classical carboxy methyl cellulose chromatography for the prenatal diagnosis of β thalassaemia. The two methods correlated highly (r = 0.97 p < 0.0005) and provided an identical diagnosis for 40 fetal blood samples of fetuses homozygous or heterozygous for β thalassaemia. The HPLC procedure was much faster and required fewer biochemical steps (no globin preparation). It was at least as accurate and more sensitive than the classical chromatography. A single column can be used for 150 analyses and is always ready to be used. Last but not least it is much less expensive than CMC chromatography. 相似文献
345.
IntroductionFertilizationisessentialforagriculturalproduction ,butunreasonablyapplyingfertilizerscouldresultinseriesofproblemssuchascropqualitydecline,fertilizeruseefficiencydecrease,residualfertilizerspollution groundwaterandriversandnitrogencontented … 相似文献
346.
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
347.
W. F. Carey A. Poulos P. Sharp P. V. Nelson E. F. Robertson J. L. Hughes A. Gill 《黑龙江环境通报》1994,14(9):813-819
Variability in the level of expression of very long chain fatty acids (VLCFAs) is documented in cultured chorionic villus (CV) cells derived from two fetuses, one at risk for an unusual peroxisomal fatty acid β-oxidation defect, and the other at risk for the X-linked form of adrenoleucodystrophy (ALD). Cells from early subcultures of chorionic cells from both cases gave normal values for VLCFA ratios. The results for the fetus at risk for the β-oxidation defect were interpreted to indicate that the fetus was not affected; however, at birth, the infant was clinically and biochemically affected. In the case of the fetus at risk for X-linked ALD, although VLCFAs were normal in subculture 1, the levels of these fatty acids increased dramatically in subculture 3, suggesting an abnormal fetus. Termination of the pregnancy and subsequent biochemical and morphological follow-up confirmed that the fetus was indeed affected by ALD. 相似文献
348.
A survey was carried out to determine the effect of prenatal screening and therapeutic abortion on births in 1985 with anencephaly and spina bifida in England and Wales. Maternal serum alpha-fetoprotein tests were done on 399 288 women (60 per cent of pregnant women): 4 per cent were reported as being screen-positive and 1 per cent had an amniocentesis. An estimated 534 pregnancies associated with anencephaly were terminated and an estimated 445 pregnancies associated with spina bifida (but without anencephaly) were terminated. Most (63 per cent) of the anencephalic pregnancies were first suspected from an ultrasound examination; 57 per cent of the spina bifida pregnancies were first suspected from a positive maternal serum alpha-fetoprotein test, 35 per cent by ultrasound, and the remaining 8 per cent by other means. The birth prevalence of anencephaly declined by 94 per cent between 1964–1972 and 1985, but when the terminations of pregnancy on account of having a fetus with anencephaly are added to the births the decline in prevalence was only 50 per cent. The birth prevalence of spina bifida declined by 68 per cent over the same period but when the terminations were added to the births the decline in prevalence was only 32 per cent. Among births with anencephaly 66 per cent had had no screening or diagnostic tests in early pregnancy, but in those that did nearly all were positive–usually in twin pregnancies where one fetus was affected but not the other. Among births with spina bifida, 48 per cent had no tests and in those that did the results were mainly negative. We conclude that in order to monitor adequately the national screening programme for anencephaly and spina bifida a special neural tube defects register should be formed. 相似文献
349.
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
350.
Enrique Castelán 《Ambio-人类环境杂志》2003,32(2):124-129
引言 墨西哥城大都市区(MCMA)位于被称作"墨西哥谷(Valle deMexico)"的天然围合的盆地里,海拔2240m.它下辖联邦区和墨西哥州的34个自治市.墨西哥城是墨西哥的首都,位于联邦区(DistritoFederal,DF),四面环山,海拔高度超过5000m.墨西哥州是墨西哥人口最稠密的地区(据报道有1300万居民),人口仅次于它的是墨西哥城,大约有860万人[1]. 相似文献