全文获取类型
收费全文 | 14320篇 |
免费 | 99篇 |
国内免费 | 156篇 |
专业分类
安全科学 | 346篇 |
废物处理 | 592篇 |
环保管理 | 1557篇 |
综合类 | 3241篇 |
基础理论 | 3336篇 |
环境理论 | 6篇 |
污染及防治 | 3569篇 |
评价与监测 | 1100篇 |
社会与环境 | 758篇 |
灾害及防治 | 70篇 |
出版年
2022年 | 127篇 |
2021年 | 106篇 |
2019年 | 100篇 |
2018年 | 193篇 |
2017年 | 203篇 |
2016年 | 299篇 |
2015年 | 226篇 |
2014年 | 399篇 |
2013年 | 1023篇 |
2012年 | 447篇 |
2011年 | 583篇 |
2010年 | 467篇 |
2009年 | 522篇 |
2008年 | 562篇 |
2007年 | 576篇 |
2006年 | 536篇 |
2005年 | 492篇 |
2004年 | 450篇 |
2003年 | 455篇 |
2002年 | 430篇 |
2001年 | 595篇 |
2000年 | 372篇 |
1999年 | 260篇 |
1998年 | 147篇 |
1997年 | 164篇 |
1996年 | 171篇 |
1995年 | 188篇 |
1994年 | 179篇 |
1993年 | 131篇 |
1992年 | 164篇 |
1991年 | 173篇 |
1990年 | 168篇 |
1989年 | 141篇 |
1988年 | 156篇 |
1987年 | 96篇 |
1986年 | 128篇 |
1985年 | 127篇 |
1984年 | 122篇 |
1983年 | 114篇 |
1982年 | 120篇 |
1981年 | 121篇 |
1980年 | 87篇 |
1979年 | 99篇 |
1978年 | 101篇 |
1976年 | 92篇 |
1974年 | 104篇 |
1972年 | 87篇 |
1971年 | 85篇 |
1967年 | 100篇 |
1964年 | 92篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
501.
502.
503.
Prenatal cytogenetic diagnosis after transabdominal chorionic villus sampling in the first trimester
First trimester prenatal cytogenetic diagnosis was attempted in 350 pregnancies after trans-abdominal chorionic villus sampling. The cytogenetic investigation was performed using both a short-term method (24 h incubation) and cell culture. Adequate samples were obtained in 99·1 per cent and in all these cases the fetal karyotype was established. A chromosome abnormality was found in 2·0 per cent of cases. A discrepancy between the karyotype obtained after 24 h incubation and the karyotype in cell culture was observed in 2·3 per cent. Maternal cell contamination in the cultures was confirmed in 13 of 181 cases where the 24 h incubation revealed a male karyotype. Studies of culture morphology showed that colonies of convoluted cells may serve as a marker for contamination with maternal cells in culture. For the present, we recommend using a short-term method as well as cell culture for cytogenetic investigation until the problems with karyotype discrepancy and maternal cell contamination have been further clarified. 相似文献
504.
Dr. Linda A. Cannizzaro Barbara K. Hecht Helen A. Bixenman Stephen Pazdziorko Robert Tamis Frederick Hecht 《黑龙江环境通报》1988,8(4):297-301
We report herein a de novo unbalanced chromosome translocation in a fetus resulting from in vitro fertilization technology. Prenatal diagnostic analysis of an amniotic fluid revealed a 46,XX,4p+ karyotype. The origin of the extra material on the short arm of chromosome 4 could not be identified by a variety of banding techniques. However, examination of fetal parts did reveal some dysmorphic features. 相似文献
505.
506.
The fetal heart rate (FHR) was continuously monitored during 42 umbilical vessel punctures performed at the placental insertion of the cord in 24 diagnostic fetoscopies in which pure fetal blood was obtained. In only one patient did a deceleration first appear during puncture and aspiration of fetal blood. In two patients decelerations preceded fetoscopy and in two others they began during the fetoscopy but before puncture of an umbilical vessel. In 19 patients, the FHR did not change at all during the procedure. Fetal haemorrhage after sampling was either absent or minimal. Six pregnancies were terminated because a positive diagnosis had been made and 18 healthy babies were born. Umbilical cords were examined after 7 terminations of pregnancy and after 6 deliveries. In the former group the puncture could just be seen with the naked eye and the needle track was demonstrated histologically in 6. No traces of the puncture or other abnormalities were found in the cords after delivery. Fetal blood sampling from umbilical cord vessels, particularly at the placental insertion of the cord, is the technique of choice since pure fetal blood can be obtained without increasing the risk of fetoscopy. 相似文献
507.
508.
Prenatal counselling for fetal agenesis of the corpus callosum is difficult as the prognosis until now has been so uncertain. We have reviewed the current world English literature to provide the best probabilistic information for prospective parents. In total, there are 70 cases where the diagnosis was made prenatally. The diagnosis of apparently isolated agenesis of the corpus callosum (in the absence of other sonographically detectable anomalies) appears to carry an excellent prognosis, with an 85 per cent chance of a normal developmental outcome and a 15 per cent risk of handicap. Fetal karyotyping is recommended as there is a 1 in 10 risk of aneuploidy. If other anomalies are detected prenatally, the outcome is very poor. Termination of pregnancy is advised in these circumstances. 相似文献
509.
Shamama Afreen Nitasha Sharma Rajiv K. Chaturvedi Ranjith Gopalakrishnan N. H. Ravindranath 《Mitigation and Adaptation Strategies for Global Change》2011,16(2):177-197
Due to large scale afforestation programs and forest conservation legislations, India’s total forest area seems to have stabilized
or even increased. In spite of such efforts, forest fragmentation and degradation continues, with forests being subject to
increased pressure due to anthropogenic factors. Such fragmentation and degradation is leading to the forest cover to change
from very dense to moderately dense and open forest and 253 km2 of very dense forest has been converted to moderately dense forest, open forest, scrub and non-forest (during 2005–2007).
Similarly, there has been a degradation of 4,120 km2 of moderately dense forest to open forest, scrub and non-forest resulting in a net loss of 936 km2 of moderately dense forest. Additionally, 4,335 km2 of open forest have degraded to scrub and non-forest. Coupled with pressure due to anthropogenic factors, climate change
is likely to be an added stress on forests. Forest sector programs and policies are major factors that determine the status
of forests and potentially resilience to projected impacts of climate change. An attempt is made to review the forest policies
and programs and their implications for the status of forests and for vulnerability of forests to projected climate change.
The study concludes that forest conservation and development policies and programs need to be oriented to incorporate climate
change impacts, vulnerability and adaptation. 相似文献
510.
N. H. Ravindranath Rajiv K. Chaturvedi N. V. Joshi R. Sukumar Jayant Sathaye 《Mitigation and Adaptation Strategies for Global Change》2011,16(2):211-227
Climate change is projected to impact forest ecosystems, including biodiversity and Net Primary Productivity (NPP). National
level carbon forest sector mitigation potential estimates are available for India; however impacts of projected climate change
are not included in the mitigation potential estimates. Change in NPP (in gC/m2/yr) is taken to represent the impacts of climate change. Long term impacts of climate change (2085) on the NPP of Indian
forests are available; however no such regional estimates are available for short and medium terms. The present study based
on GCM climatology scenarios projects the short, medium and long term impacts of climate change on forest ecosystems especially
on NPP using BIOME4 vegetation model. We estimate that under A2 scenario by the year 2030 the NPP changes by (−5) to 40% across
different agro-ecological zones (AEZ). By 2050 it increases by 15% to 59% and by 2070 it increases by 34 to 84%. However,
under B2 scenario it increases only by 3 to 25%, 3.5 to 34% and (−2.5) to 38% respectively, in the same time periods. The
cumulative mitigation potential is estimated to increase by up to 21% (by nearly 1 GtC) under A2 scenario between the years
2008 and 2108, whereas, under B2 the mitigation potential increases only by 14% (646 MtC). However, cumulative mitigation
potential estimates obtained from IBIS—a dynamic global vegetation model suggest much smaller gains, where mitigation potential
increases by only 6% and 5% during the period 2008 to 2108. 相似文献