全文获取类型
收费全文 | 42340篇 |
免费 | 562篇 |
国内免费 | 606篇 |
专业分类
安全科学 | 1493篇 |
废物处理 | 1952篇 |
环保管理 | 5901篇 |
综合类 | 6731篇 |
基础理论 | 11052篇 |
环境理论 | 15篇 |
污染及防治 | 10624篇 |
评价与监测 | 2774篇 |
社会与环境 | 2672篇 |
灾害及防治 | 294篇 |
出版年
2022年 | 403篇 |
2021年 | 442篇 |
2020年 | 340篇 |
2019年 | 351篇 |
2018年 | 638篇 |
2017年 | 659篇 |
2016年 | 1016篇 |
2015年 | 772篇 |
2014年 | 1157篇 |
2013年 | 3489篇 |
2012年 | 1460篇 |
2011年 | 1985篇 |
2010年 | 1593篇 |
2009年 | 1688篇 |
2008年 | 1982篇 |
2007年 | 1944篇 |
2006年 | 1731篇 |
2005年 | 1498篇 |
2004年 | 1463篇 |
2003年 | 1372篇 |
2002年 | 1284篇 |
2001年 | 1524篇 |
2000年 | 1137篇 |
1999年 | 721篇 |
1998年 | 516篇 |
1997年 | 545篇 |
1996年 | 552篇 |
1995年 | 661篇 |
1994年 | 554篇 |
1993年 | 495篇 |
1992年 | 502篇 |
1991年 | 489篇 |
1990年 | 466篇 |
1989年 | 456篇 |
1988年 | 402篇 |
1987年 | 343篇 |
1986年 | 363篇 |
1985年 | 352篇 |
1984年 | 413篇 |
1983年 | 359篇 |
1982年 | 402篇 |
1981年 | 345篇 |
1980年 | 273篇 |
1979年 | 307篇 |
1978年 | 237篇 |
1977年 | 210篇 |
1975年 | 211篇 |
1974年 | 208篇 |
1973年 | 234篇 |
1972年 | 214篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
23.
This work, carried out within the framework of the PRISMA II project, aims at evaluating the effects of the Po River flow on primary productivity, measured by C with in situ sample incubations. A total of four cruises was carried out in late winter and early summer (1996-1998) along transects from the coast offshore. In both seasons, the highest primary productivity was found in the most oligohaline stations. The effects of the Po River inputs were therefore clearly evident in the westernmost area, both in high productivity values and in the shape of productivity profiles. In late winter, extensive blooms of Skeletonema costatum and Pseudo-nitzschia delicatissima resulted in productivity values that were sometimes higher than in early summer. In early summer 1996, greatly reduced river flow clearly influenced productivity which was much lower than in 1997. 相似文献
24.
Dr. J. F. Bruch P. Metezeau N. Garcia-Fonknechten Y. Richard V. Tricottet B.-L. Hsi A. Kitzis C. Julien E. Papiernik 《黑龙江环境通报》1991,11(10):787-798
Three monoclonal antibodies (MAbs) against trophoblast (GB17, GB21, and GB25) and flow cytometry were used to sort trophoblast-like cells (TLCs) from peripheral blood of pregnant women. Sorted TLCs were processed for electron microscopy and fetal DNA amplification of the Y-specific sequences from mothers carrying male fetuses. At the ultra-structural level, most of the nucleated cells had the morphology of leucocytes, suggesting maternal contaminants, and we did not find the characteristic features of the free inter-villous trophoblast cells. Nevertheless, polymerase chain reaction (PCR) analysis showed an amplification of Y-specific sequences in two out of three samples of sorted TLCs. These results suggest that besides the maternal leucocytes, sufficient trophoblast nucleated fetal cells can be obtained using cell enrichment by sorting. This sensitive method holds promise for non-invasive prenatal diagnosis of fetal sex and if sufficient Y(positive) nuclei are found, for the diagnosis of selected numerical chromosome abnormalities. 相似文献
25.
The occurrence and impact of psychological contract violations were studied among graduate management alumni (N = 128) who were surveyed twice, once at graduation (immediately following recruitment) and then two years later. Psychological contracts, reciprocal obligations in employment developed during and after recruitment, were reported by a majority of respondents (54.8 per cent) as having been violated by their employers. The impact of violations are examined using both quantitative and qualitative data. Occurrence of violations correlated positively with turnover and negatively with trust, satisfaction and intentions to remain. 相似文献
26.
The effect of mountain relief and industrial air pollution on biometric parameters of pine stands was studied. The empirical–statistical models of the dependence of biometric characteristics on the parameters of forest sites were developed using raster modeling and multivariate analysis. The possibility of predicting changes in the biometric parameters at any site on the basis of these models is shown. 相似文献
27.
We present a case of ultrasonographic prenatal diagnosis at 24 weeks of femur—fibula—ulna (FFU) complex. To our knowledge, this is the first report of an early prenatal diagnosis of FFU. 相似文献
28.
29.
Although stewardship has been widely defined and used in environmental management and planning, there is a dearth of studies
that describe how the lay public perceives this concept. A national sample of residents in 14 states who live near DOE nuclear
facilities were interviewed to delineate public understanding and awareness of the stewardship program of the U.S. Department
of Energy (DOE). This study discusses the findings of the survey and discusses how institutional trust influences public participation
and resident’s choices of potential stewards. Almost 40% of the respondents could not define stewardship; those who did, believed
that ‘responsibility,’ ‘management,’ and ‘accountability’ are key elements of stewardship. In addition, about a third of the
respondents identified Federal groups and the DOE as potential stewards.
Readers should send their comments on this paper to: BhaskarNath@aol.com within 3 months of publication of this issue 相似文献
30.
Abstract: The sustainability of seed extraction from natural populations has been questioned recently. Increased recruitment failure under intense seed harvesting suggests that seed extraction intensifies source limitation. Nevertheless, areas where more seeds are collected tend to also have more intense hunting of seed-dispersing animals. We studied whether such hunting, by limiting disperser activity, could cause quantitative dispersal limitation, especially for large crops and for crops in years of high seed abundance. In each of four Carapa procera (Meliaceae) populations in French Guiana and Surinam, two with hunting and two without, we compared seed fate for individual trees varying in crop size in years of high and low population-level seed abundance. Carapa seeds are a nontimber forest product and depend on dispersal by scatter-hoarding rodents for survival and seedling establishment. Hunting negatively affected the proportion of seeds dispersed and caused greater numbers of seeds to germinate or be infested by moths below parent trees, where they would likely die. Hunting of seed-dispersing animals disproportionally affected large seed crops, but we found no additional effect of population-level seed abundance on dispersal rates. Consistently lower rates of seed dispersal, especially for large seed crops, may translate to lower levels of seedling recruitment under hunting. Our results therefore suggest that the subsistence hunting that usually accompanies seed collection is at the cost of seed dispersal and may contribute to recruitment failure of these nontimber forest products. Seed extraction from natural populations may affect seedling recruitment less if accompanied by measures adequately incorporating and protecting seed dispersers. 相似文献