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   87818篇
  免费   1215篇
  国内免费   1086篇
安全科学   3713篇
废物处理   3201篇
环保管理   13555篇
综合类   21012篇
基础理论   25866篇
环境理论   74篇
污染及防治   13434篇
评价与监测   5307篇
社会与环境   3448篇
灾害及防治   509篇
  2022年   783篇
  2021年   794篇
  2020年   645篇
  2019年   860篇
  2018年   1092篇
  2017年   1121篇
  2016年   2131篇
  2015年   1824篇
  2014年   2573篇
  2013年   9224篇
  2012年   2077篇
  2011年   2207篇
  2010年   3185篇
  2009年   3332篇
  2008年   1750篇
  2007年   1609篇
  2006年   2077篇
  2005年   2112篇
  2004年   2427篇
  2003年   2296篇
  2002年   1802篇
  2001年   2077篇
  2000年   1897篇
  1999年   1469篇
  1998年   1354篇
  1997年   1336篇
  1996年   1465篇
  1995年   1555篇
  1994年   1447篇
  1993年   1301篇
  1992年   1294篇
  1991年   1265篇
  1990年   1212篇
  1989年   1180篇
  1988年   1022篇
  1987年   956篇
  1986年   985篇
  1985年   1052篇
  1984年   1152篇
  1983年   1163篇
  1982年   1171篇
  1981年   1091篇
  1980年   939篇
  1979年   911篇
  1978年   822篇
  1977年   717篇
  1976年   638篇
  1975年   602篇
  1973年   623篇
  1972年   629篇
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
141.
We report three siblings from consecutive pregnancies affected with restrictive dermopathy (RD). During the second pregnancy, fetal behavioural development and growth were studied extensively using ultrasound at 1–4 week intervals. Dramatic and sudden changes occurred in fetal body movements and growth but not until the end of the second trimester of pregnancy. Prominent at that time were prolonged periods of fetal quiescence and very low heart rate variability, together with abnormally executed body movements of short duration. Retarded femoral development and jerky abrupt fetal body movements (abnormal movement quality) were already present in the early second trimester of pregnancy. Facial anomalies emerged despite the presence of fetal mouth movements. The clinical features of RD were only partly explained by present knowledge of skin development and the fetal akinesia deformation sequence hypothesis. Quantitative assessment of fetal movements proved to be a poor early marker for antenatal diagnosis of this disorder. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   
142.
Single cell polymerase chain reaction (PCR) for preimplantation genetic diagnosis (PGD) requires high efficiency and accuracy. Allele dropout (ADO), the random amplification failure of one of the two parental alleles, remains the most significant problem in PCR-based PGD testing since it can result in serious misdiagnosis for compound heterozygous or autosomal dominant conditions. A number of different strategies (including the use of lysis buffers to break down the cell and make the DNA accessible) have been employed to combat ADO with varying degrees of success, yet there is still no consensus among PGD centres over which lysis buffer should be used (ESHRE PGD Consortium, 1999 ). To address this issue, PCR amplification of three genes (CFTR, LAMA3 and PKP1) at different chromosomal loci was investigated. Single lymphocytes from individuals heterozygous for mutations within each of the three genes were collected and lysed in either alkaline lysis buffer (ALB) or proteinase K/SDS lysis buffer (PK). PCR amplification efficiencies were comparable between alkaline lysis and proteinase K lysis for PCR products spanning each of the three mutated loci (ΔF508 in CFTR 90% vs 88%; R650X in LAMA3 82% vs 78%; and Y71X in PKP1 91% vs 87%). While there was no appreciable difference between ADO rates between the two lysis buffers for the LAMA3 PCR product (25% vs 26%), there were significant differences in ADO rates between ALB and PK for the CFTR PCR product (0% vs 23%) and the PKP1 PCR product (8% vs 56%). Based on these results, we are currently using ALB in preference to PK/SDS buffer for the lysis of cells in clinical PGD. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   
143.
The amounts of total NH 4 + detected in the external media in which Phascolosoma arcuatum had been exposed to various periods of anoxia were significantly greater than those in which the worms were exposed to normoxia for a similar period. The increased NH 4 + production by P. arcuatum during anoxic exposure was unlikely to be due to an increased catabolism of adenine nucleotides or urea. In contrast, there were significant decreases in the concentrations of several free amino acids in the coelomic plasma and body tissues of individuals during the 48 h of anoxic exposure. The amount of NH 4 + produced by the anoxic P. arcuatum could be accounted for by the decreases in the concentrations of aspartate or glycine. Increases in the catabolism of free amino acids (FAA), leading to the increased production of NH 4 + , in P. arcuatum during anoxia were supported by the detection of significant changes in the kinetic properties of glutamate dehydrogenase (GDH), in the deaminating direction, from worms exposed to anoxia for 48 h. The apparent increase in the affinity of GDH from the anoxic worm to glutamate would bring about a greater deaminating activity at physiological concentrations of ths substrate. P. arcuatum used in these experiments were collected from the mangrove swamp at Mandai, Singapore between 1990 and 1993.  相似文献   
144.
145.
The two studies reported further test reversal theory hypotheses concerning human psychological responses to different types of settings and environmental events on an Asian sample. In study 1, individuals in four settings representing different combinations of metamotivational state and arousal level (telic and paratelic/low arousal; telic and paratelic/high arousal) completed the telic state measure (TSM; Svebak & Murgatroyd, 1985). Significant differences between participants' mean scores across the four settings were obtained for TSM items serious–playful, planning–spontaneous, felt arousal, preferred arousal, effort and arousal discrepancy. In study 2 different environmental events in the same setting (changes in reading tasks), used in a crossover design, were used to induce reversals in individuals' operative metamotivational states. The results obtained from TSM scores pretask 1, between tasks and posttask 2. indicated significant time-of-testing interaction effects on the TSM serious–playful, planning–spontaneous and effort items. In addition, a main effect for TSM felt arousal was found. These results showed that reversals in metamotivational states were induced by the environmental event and that felt arousal scores increased across the three administrations of the TSM.  相似文献   
146.
147.
The paper draws on an empirical study of two workshops in which the issues that arise from the use of geographic information systems (GIS) as a planning tool in public participation settings were explored by local residents who take an active interest in local planning matters in their London borough. The paper demonstrates how issues concerned with the democratization of GIS and public participation GIS (PPGIS) informed the structure and conduct of the workshops and the qualitative analysis of the workshop discussions. Key themes raised by participants included: the potential of PPGIS as a means of extending knowledge networks; issues of data ownership and the responsiveness of data providers to public concerns; and the role that institutional norms and practices play in democratizing information availability and the transparency of the decision-making process. The paper concludes that the potential of PPGIS as a planning tool cannot be separated from public concerns about the legitimacy of the planning process or local government.  相似文献   
148.
In a population of crested tits in Belgium, one out of three breeding males participated in nest-building. Since variation in the amount of nest-building among 11 building males was low, analysis of male nest-building allowed a logistic regression design. The probability of building increased with male condition and for late nests. The effect of male condition decreased with date, and date was the only factor predicting nest-building for repeat broods. The effect of male condition on nest-building suggests that building entails important costs for males. Based on correlative data, we argue that building by males shortens the interval between the start of nest-building and the onset of egg-laying by about 5 days. Since clutch size, incubation and nestling time did not differ between early and late broods, male nest-building apparently affects fledging date. Since early fledgers (early dispersers) are more likely to settle in future winter flocks, building behaviour by crested tit males should be favoured by natural selection. So far, male nest-building in hole-breeding birds might have been overlooked due to the widespread use of artificial nest-boxes in behavioural studies.  相似文献   
149.
We examined the impact of stressful job demands on employee attitudes and attendance. Using Karasek's (1979) theory of job decision latitude as the conceptual foundation, we hypothesized that mental and physical work demands would interact with employee beliefs of personal control. Survey data from 90 male manufacturing employees regarding their control beliefs were combined with objective job analysis data concerning mental and physical demands and one year's worth of archival data regarding unexcused absences, sick days, and days tardy. There were significant interactions between control and objective psychological demands that indicated that these demands were associated with higher levels of tardiness and sick days only under conditions of low perceived control. In contrast, subjective workload ratings showed no relationship with tardiness and sick days, but, in interaction with control, predicted work satisfaction and voluntary absence. We discussed these results in terms of a stress process that affects health-related attendance independent of employee attitudes.  相似文献   
150.
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