首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   88681篇
  免费   1229篇
  国内免费   1091篇
安全科学   3508篇
废物处理   3187篇
环保管理   13738篇
综合类   21017篇
基础理论   26115篇
环境理论   72篇
污染及防治   13857篇
评价与监测   5375篇
社会与环境   3593篇
灾害及防治   539篇
  2022年   726篇
  2021年   797篇
  2020年   641篇
  2019年   855篇
  2018年   1102篇
  2017年   1158篇
  2016年   2125篇
  2015年   1816篇
  2014年   2560篇
  2013年   9221篇
  2012年   2143篇
  2011年   2349篇
  2010年   3220篇
  2009年   3382篇
  2008年   1887篇
  2007年   1737篇
  2006年   2197篇
  2005年   2175篇
  2004年   2474篇
  2003年   2327篇
  2002年   1862篇
  2001年   2097篇
  2000年   1819篇
  1999年   1417篇
  1998年   1324篇
  1997年   1311篇
  1996年   1440篇
  1995年   1566篇
  1994年   1459篇
  1993年   1301篇
  1992年   1307篇
  1991年   1275篇
  1990年   1229篇
  1989年   1198篇
  1988年   1033篇
  1987年   964篇
  1986年   990篇
  1985年   1060篇
  1984年   1151篇
  1983年   1174篇
  1982年   1175篇
  1981年   1095篇
  1980年   941篇
  1979年   929篇
  1978年   817篇
  1977年   719篇
  1976年   638篇
  1975年   610篇
  1973年   637篇
  1972年   650篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
The change in the composition of the bryophyte component of succession communities that occur in the process of natural regeneration at the site of clear felling of the indigenous elm—maple–linden forests of the Bashkir Cis-Ural Region has been studied. The vulnerability of species to the consequences of felling is affected by their substrate confinement, ecological amplitude in relation to the factors of temperature, humidity, variability of soil moisture, and type of life strategy. In the secondary aspen forests, the absence or low constancy of nemoral epiphytic and ground mosses was noted.  相似文献   
52.
This study investigates the energy–growth nexus for transition countries analysing Granger causality between GDP growth per capita and energy use per capita. For this purpose, 17 countries located at Central and Eastern Europe and Caucasian region are chosen and a panel dataset consisting of these countries for the available period of 1990–2011 is studied. In the study, Granger causality is investigated using bootstrapped panel causality approach proposed by Konya (Econ Modell 23(6):978–992, 2006). The approach gives consistent results in case of cross-sectional dependency and heterogeneity of slope coefficients between countries. Causality is examined for two scenarios: one with a trend and one without a trend. The results reveal that, in general, there is no causality running between energy consumption and economic growth, yet there is causality running from energy consumption to economic growth for some countries and sign of the relationship is always negative. Therefore, increases in energy consumption harm economic growth.  相似文献   
53.
Journal of Material Cycles and Waste Management - The amount of biomass-derived ashes is expected to rise in the EU due to targets to increase the use of renewable energy resources. To promote the...  相似文献   
54.
The high surface area of porous nanofibers enhances their performance for many applications. The present study investigated electrospinning and dye adsorption properties of polymeric nanofibers which were porous by various types of salts. The salt/polyacrylonitrile/polyvinylidene fluoride composite nanofibers were electrospun, and the inexpensive salts such as sodium chloride (NaCl), sodium bicarbonate (NaHCO3), or calcium chloride (CaCl2) was used to manufacture the porous fibers. Subsequently, the salt was removed by a selective dissolution, and salt extraction of nanofibers was performed with the solution of hydrochloric acid (10 wt%). Salt/PVDF/PAN and porous PVDF/PAN composite nanofibers have been applied to dye adsorption of solution. The characteristics of nanofibers were studied by Fourier transform infrared microscopy (FTIR) and scanning electron microscopy (SEM) analysis. FTIR showed that the salt was extracted from PVDF/PAN nanofibers successfully, and SEM indicated that many pores were aligned with the nanofibers. The adsorption capacity of salt nanofibers webs and porous nanofibers webs for Basic Blue 41 were compared with each other, and porous fibers were obtained from NaHCO3 having the highest dye adsorption value. Adsorption of dyes follows the Langmuir isotherm and pseudo-second order kinetics.  相似文献   
55.
Objective. Bad posture increases the risk that a musician may suffer from musculoskeletal disorders. This study compared posture quality required by different instruments or families of instruments. Methods. Using an ad-hoc postural observation instrument embracing 11 postural variables, four experts evaluated the postures of 100 students attending a Spanish higher conservatory of music. Results. The agreement of the experts’ evaluations was statistically confirmed by a Cohen's κ value between 0.855 and 1.000 and a Kendall value between 0.709 and 1.000 (p?χ2 tests revealed significant association between instrument families and seated posture with respect to pelvic attitude, dorsal curvature and head alignment in both sagittal and frontal planes. This analysis also showed an association between instrument families and standing posture with respect to the frontal plane of the axis of gravity, pelvic attitude, head alignment in the frontal plane, the sagittal plane of the shoulders and overall posture. Conclusions. While certain postural defects appear to be common to all families of instruments, others are more characteristic of some families than others. The instrument associated with the best posture quality was the bagpipe, followed by percussion and strings.  相似文献   
56.
Objectives: In this study, we sought to accomplish the following objectives: to (1) calculate the percentage of children considered appropriately restrained across 8 criteria of increasing restrictiveness; (2) examine agreement between age- and size-based appropriateness criteria; (3) assess for changes in the percentage of children considered appropriately restrained by the 8 criteria between 2011 (shortly after updates to U.S. guidelines) and 2015.

Methods: Data from 2 cross-sectional surveys of 928 parents of children younger than 12 years old (n = 591 in 2011, n = 337 in 2015) were analyzed in 2017. Child age, weight, and height were measured at an emergency department visit and used to determine whether the parent-reported child passenger restraint was considered appropriate according to 8 criteria. Age-based criteria were derived from Michigan law and U.S. guidelines. Weight, height, and size-based criteria were derived from typical restraints available in the United States in 2007 and 2011. The percentage appropriate restraint use was calculated for each criterion. The kappa statistic was used to measure agreement between criteria. Change in appropriateness from 2011 to 2015 was assessed with chi-square statistics.

Results: Percentage appropriate restraint use varied from a low of 19% for higher weight limits in 2011 to a high of 91% for Michigan law in 2015. Agreement between criteria was slight to moderate. The lowest kappa was for Michigan law and higher weight limits in 2011 (κ = 0.06) and highest for U.S. guidelines and lower weight limits in 2011 (κ = 0.60). Percentage appropriate restraint use was higher in 2015 than 2011 for the following criteria: U.S. guidelines (74 vs. 58%, P < .001), lower weight (57 vs. 47%, P = .005), higher weight (25 vs. 19%, P = .03), greater height (39 vs. 26%, P < .001), and greater size (42 vs. 30%, P = .001).

Conclusions: The percentage of children considered to be using an appropriate restraint varied substantially across criteria. Aligning the definition of appropriate restraint use with current U.S. guidelines would increase consistency in reporting results from studies of child passenger safety in the United States. Potential explanations for the increased percentage of children considered appropriately restrained between 2011 and 2015 include adoption of the updated U.S. guidelines and the use of child passenger restraints with higher weight and height limits.  相似文献   
57.
In this paper, we assert and test the proposition that environmental disclosure (ED) is structured by institutionalised myths and that is why ED is decoupled from environmental performance and media pressures. Focusing on firms from Canada, France and Germany, findings show that ED mimetic isomorphism for different topics varies among countries and by industry sensitiveness to the environment. The results corroborate the institutional presumption that institutionalised myths vary among different contexts. Our findings also suggest that institutionalised ED structures may not reflect environmental performance, mimetic patterns being affected by environmental performance. However, the decoupling between ED mimetic isomorphism and environmental performance decrease when firms’ ED credibility is questioned by the media.  相似文献   
58.
Regional Environmental Change - The rapid environmental changes currently underway in many dry regions of the world, and the deep uncertainty about their consequences, underscore a critical...  相似文献   
59.
Regional Environmental Change - Research that projects biophysical changes under climate change is more advanced than research that projects socio-economic changes. There is a need in adaptation...  相似文献   
60.
Controlling invasive species is critical for conservation but can have unintended consequences for native species and divert resources away from other efforts. This dilemma occurs on a grand scale in the North American Great Lakes, where dams and culverts block tributary access to habitat of desirable fish species and are a lynchpin of long‐standing efforts to limit ecological damage inflicted by the invasive, parasitic sea lamprey (Petromyzon marinus). Habitat restoration and sea‐lamprey control create conflicting goals for managing aging infrastructure. We used optimization to minimize opportunity costs of habitat gains for 37 desirable migratory fishes that arose from restricting sea lamprey access (0–25% increase) when selecting barriers for removal under a limited budget (US$1–105 million). Imposing limits on sea lamprey habitat reduced gains in tributary access for desirable species by 15–50% relative to an unconstrained scenario. Additional investment to offset the effect of limiting sea‐lamprey access resulted in high opportunity costs for 30 of 37 species (e.g., an additional US$20–80 million for lake sturgeon [Acipenser fulvescens]) and often required ≥5% increase in sea‐lamprey access to identify barrier‐removal solutions adhering to the budget and limiting access. Narrowly distributed species exhibited the highest opportunity costs but benefited more at less cost when small increases in sea‐lamprey access were allowed. Our results illustrate the value of optimization in limiting opportunity costs when balancing invasion control against restoration benefits for diverse desirable species. Such trade‐off analyses are essential to the restoration of connectivity within fragmented rivers without unleashing invaders.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号