全文获取类型
收费全文 | 49181篇 |
免费 | 456篇 |
国内免费 | 324篇 |
专业分类
安全科学 | 1212篇 |
废物处理 | 2197篇 |
环保管理 | 6675篇 |
综合类 | 7763篇 |
基础理论 | 13853篇 |
环境理论 | 31篇 |
污染及防治 | 11860篇 |
评价与监测 | 3328篇 |
社会与环境 | 2749篇 |
灾害及防治 | 293篇 |
出版年
2022年 | 266篇 |
2021年 | 273篇 |
2019年 | 308篇 |
2018年 | 1878篇 |
2017年 | 1766篇 |
2016年 | 1874篇 |
2015年 | 791篇 |
2014年 | 955篇 |
2013年 | 3134篇 |
2012年 | 1597篇 |
2011年 | 2816篇 |
2010年 | 1983篇 |
2009年 | 1903篇 |
2008年 | 2433篇 |
2007年 | 2814篇 |
2006年 | 1602篇 |
2005年 | 1373篇 |
2004年 | 1355篇 |
2003年 | 1335篇 |
2002年 | 1298篇 |
2001年 | 1610篇 |
2000年 | 1134篇 |
1999年 | 716篇 |
1998年 | 569篇 |
1997年 | 556篇 |
1996年 | 588篇 |
1995年 | 632篇 |
1994年 | 582篇 |
1993年 | 538篇 |
1992年 | 560篇 |
1991年 | 512篇 |
1990年 | 513篇 |
1989年 | 523篇 |
1988年 | 454篇 |
1987年 | 395篇 |
1986年 | 388篇 |
1985年 | 417篇 |
1984年 | 416篇 |
1983年 | 437篇 |
1982年 | 428篇 |
1981年 | 395篇 |
1980年 | 368篇 |
1979年 | 372篇 |
1978年 | 317篇 |
1977年 | 278篇 |
1976年 | 256篇 |
1975年 | 242篇 |
1974年 | 248篇 |
1973年 | 245篇 |
1972年 | 274篇 |
排序方式: 共有10000条查询结果,搜索用时 52 毫秒
591.
In the case-control study of 118 women with autosomal trisomy identified at prenatal diagnosis and their 442 karyotypically normal matched controls, we found that there was no overall association between risk of trisomy and the presence of vaginal bleeding during pregnancy. However, a lengthy duration of bleeding appears to predict increased risk of trisorny. 相似文献
592.
Citrullinaemia was presumed to be excluded in a fetus at risk by the direct assay of argininosuccinate synthetase in chorionic villi. The diagnosis was confirmed after amniocentesis by normal argininosuccinate synthetase activity in the cultured amniotic fluid cells and by a normal citrulline concentration in the amniotic fluid. The prediction of a normal fetus was confirmed at term by the birth of a non-citrullinaemic boy. 相似文献
593.
594.
Pregnancies with fetal trisomy 21 have been associated with low amniotic fluid alpha-fetoprotein levels (AFAFP). This observation led to the suggestion that low AFAFP levels be used as a criterion for completion of a chromosomal analysis in patients who are not otherwise at increased risk for a fetal chromosome abnormality and in whom karyotyping might not have been completed for economic reasons. In order to assess the usefulness of such criteria, we reviewed the AFAFP levels of 90 cases of fetal trisomy 21, 23 cases of trisomy 18, and 10 cases of trisomy 13. These were compared with 2400 control samples with normal chromosome constitution. AFAFP levels were generally lower in pregnancies with trisomy 21, showing a median value of 0·72 MoM. However, 40 per cent of the trisomy 21 samples had AFAFP values greater than 0·8 MoM and 20 per cent were over 1·0 MoM. These data imply that over 50 per cent of Down syndrome cases might have been missed using a cut-off level of 0·70 MoM for completion of chromosome analysis. Using a higher cut-off level will leave only a small percentage of samples unkaryotyped. The distribution of AFP levels in trisomy 13 and 18 is no different from controls; we therefore believe that fetal karyotyping should be completed in every amniotic fluid sample obtained. 相似文献
595.
596.
597.
Manganese-oxidizing fungi and bacteria 总被引:1,自引:0,他引:1
The Science of Nature - 相似文献
598.
599.
Bosch J 《Die Naturwissenschaften》2002,89(12):575-578
Female midwife toads (genus Alytes) emit highly variable reciprocal calls of unclear function prior to and during courtship. In some species, female-female competition, expressed as physical fighting, has been reported. Males of Majorcan midwife toads (Alytes muletensis) show phonotactic response to female calls, and females of Iberian midwife toads (Alytes cisternasii) respond differently according to the male call characteristics. In this study, I test the hypothesis of female-female acoustic competition as an additional function of female reciprocal calls. Playback tests indicate that female calls are not clearly involved in female acoustic competition in the Iberian midwife toad, therefore female calls could be directed at males rather than towards competitive females. 相似文献
600.