全文获取类型
收费全文 | 1366篇 |
免费 | 105篇 |
国内免费 | 97篇 |
出版年
2024年 | 5篇 |
2023年 | 24篇 |
2022年 | 22篇 |
2021年 | 49篇 |
2020年 | 42篇 |
2019年 | 63篇 |
2018年 | 46篇 |
2017年 | 35篇 |
2016年 | 47篇 |
2015年 | 49篇 |
2014年 | 76篇 |
2013年 | 108篇 |
2012年 | 46篇 |
2011年 | 70篇 |
2010年 | 55篇 |
2009年 | 72篇 |
2008年 | 71篇 |
2007年 | 84篇 |
2006年 | 68篇 |
2005年 | 52篇 |
2004年 | 52篇 |
2003年 | 38篇 |
2002年 | 37篇 |
2001年 | 30篇 |
2000年 | 35篇 |
1999年 | 26篇 |
1998年 | 25篇 |
1997年 | 22篇 |
1996年 | 29篇 |
1995年 | 19篇 |
1994年 | 15篇 |
1993年 | 18篇 |
1992年 | 15篇 |
1991年 | 10篇 |
1990年 | 9篇 |
1988年 | 6篇 |
1987年 | 16篇 |
1986年 | 7篇 |
1985年 | 13篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1981年 | 14篇 |
1980年 | 10篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有1568条查询结果,搜索用时 437 毫秒
141.
Extreme weather conditions correspond with localised vegetation death at Cradle Mountain,Tasmania
下载免费PDF全文
![点击此处可从《Ecological Management & Restoration》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A chance observation of a drought‐related plant mortality event in early 2014 in a normally wet and cool alpine area was matched with local weather data providing a unique insight into this event. The observed plant death was largely indiscriminate in areas that were topographically predisposed to being susceptible to drought. The weather conditions surrounding this event included 5 weeks with very little rain, an extreme heatwave and subsequent brief periods where warm temperatures and dry air combined to produce highly evaporative conditions. Extreme weather conditions such as this are expected to occur with increasing frequency as a result of climate change. Observing and reporting on real‐world examples of how extreme weather events affect native vegetation is integral to improved climate change risk assessment and to inform future management actions. 相似文献
142.
Impact of uranium (U) ore and soluble uranium (at pH 4.0) contamination on agricultural soil bacterial diversity was assessed by using laboratory microcosms for one year. Diversity and abundance of metabolically active bacterial populations in periodically collected microcosm’s samples were analyzed by extracting total RNA and preparation of cDNA followed by analysis of 16S rRNA gene by DGGE and real time PCR. DGGE analysis revealed prominent shift of soil bacterial population due to uranium ore contamination within 12 months while uranium ore along with soluble U completely destroyed the soil bacterial diversity within first six months. Real time PCR based analysis indicated 100–200 folds increase in 16S rRNA gene copies of total as well as individual bacterial taxa in both U ore amended and unamended soils in first six months while increase in incubation period upto 12 months showed reduction of the same only in U ore amended soil. Antagonistic effect of U ore contamination on soil bacterial diversity indicated the severe impact of U mining likely to have on nearby ecosystems. Role of U at acidic pH in destroying the diversity completely is noteworthy as it corroborated the disastrous consequence of acid mine drainage generated from U mine sites. 相似文献
143.
Acylation of Pseudomonas cepacia lipase with Pyromellitic dianhydride to modify 72% of total amino groups was carried out. Different organic solvents were screened for precipitation of modified lipase. It was found that 1,2-dimethoxyethane was the best precipitant which precipitated 97% protein and complete activity. PCMC (protein coated microcrystals), CLPCMC (crosslinked protein coated microcrystals), EPROS (enzyme precipitated and rinsed with organic solvents) and pH tuned preparations of modified and unmodified lipase were prepared and used for carrying out transesterification reaction with n-octane and dimethyl formamide (DMF) as reaction medium. In n-octane, among all the preparations, CLPCMC of modified lipase gave highest rate (1970 nmol min−1 mg−1) as compared to unmodified pH tuned lipase (128 nmol min−1 mg−1). In DMF, with both 1% (v/v) and 5% (v/v) water content, CLPCMC showed highest initial rate of 0.72 and 7.2 nmol min−1 mg−1, respectively. Unmodified pH tuned lipase showed no activity at all in DMF with both 1% and 5% (v/v) water content. 相似文献
144.
Wang MM 《The international journal of biochemistry & cell biology》2011,43(11):1550-1562
Originally discovered nearly a century ago, the Notch signaling pathway is critical for virtually all developmental programs and modulates an astounding variety of pathogenic processes. The DSL (Delta, Serrate, LAG-2 family) proteins have long been considered canonical activators of the core Notch pathway. More recently, a wide and expanding network of non-canonical extracellular factors has also been shown to modulate Notch signaling, conferring newly appreciated complexity to this evolutionarily conserved signal transduction system. Here, I review current concepts in Notch signaling, with a focus on work from the last decade elucidating novel extracellular proteins that up- or down-regulate signal potency. 相似文献
145.
注意缺陷多动障碍(Attention Deficit Hyperactivity Disorder,ADHD)是儿童期常见的一种发展性的异常,其病因及发生机理至今未明。低觉醒模型是ADHD成因的一种假设。本文从睡眠障碍导致的低觉醒探讨ADHD发生机理。通过对ADHD儿童的睡眠障碍进行分析以及将ADHD外在表现与睡眠剥夺后的表现进行对比分析,得出ADHD儿童存在的低觉醒是由于外显的或内隐的睡眠障碍引起的,一方面间接证明了低觉醒模型,另一方面为ADHD的成因研究开拓了新的思路。 相似文献
146.
147.
De Gregori M Pramparo T Memo L Gimelli G Messa J Rocchi M Patricelli MG Ciccone R Giorda R Zuffardi O 《Human genetics》2005,118(2):207-213
We describe the characterization of an interstitial duplication of 12p, dup(12)(p11.21p13.31), by array-CGH and FISH in a patient with mental retardation and dysmorphic features. The sequence analysis of the breakpoints revealed the presence of homologous low copy repeats (LCRs) flanking the duplication region, thus suggesting that they have mediated the rearrangement. Pip-maker analysis showed that a third cluster of homologous LCRs lie distally to the two mediating the 12p duplication. We hypothesize that this duplication might be a new recurrent rearrangement and that, thanks to the different orientations of the homologous regions lying within each cluster, the three clusters are responsible for at least some of the several 12p aneuploidies reported in the literature such as direct and inverted duplications, deletions and supernumerary analphoid chromosomes. Moreover, we excluded that polymorphic inversions between these three clusters are present in the normal population.Manuela De Gregori, Tiziano Pramparo contributed equally to this paper. 相似文献
148.
Objective: The aim of the present study was to evaluate the impact of dry mouth conditions on oral health‐related quality of life in frail old people, residents at community care centers. Further, reliability and validity of a visual analogue scale (VAS) for dry mouth symptoms were determined within the study cohort. Background: In old people functional, social and psychological impacts of oral conditions are associated with an overall sense of well being and general health. Subjective dry mouth and reduced saliva flow are common disorders in old people caused by disease and medication. Thus, dry mouth conditions may be determinants for compromised oral health‐related quality of life in old people. Method: In total, 50 old people living at service homes for the old people were asked to answer questionnaires on subjective dry mouth (VAS) and Oral Health Impact Profile (OHIP14) for oral health‐related quality of life. Saliva flow was estimated by absorbing saliva into a pre‐weighed cotton roll. Results: The final study cohort comprised 41 old people (aged 83–91 years). Significant associations were identified between both objective and subjective dry mouth and overall or specific aspects of oral health‐related quality of life. Conclusion: Dry mouth (objective and subjective) is significantly associated with oral health‐related quality of life strengthening the value of monitoring dry mouth conditions in the care of frail old people. 相似文献
149.
150.
Fresh frozen femoral heads (FH) and frozen processed bone (FP) are widely used as a source of allograft bone. The FP bone and some of the FH are terminally sterilised by the National Blood Service Tissue Services (NSBTS), via application of a minimum 25 kGy gamma radiation dose. To comply with the Guidelines for the Blood Transfusion Services in the United Kingdom (2002), frozen musculoskeletal tissue must be maintained below −40 °C during storage and transit. In practice, NBSTS stores bone long-term in −80 °C freezers. During transport for irradiation, a temperature of circa −79 °C is maintained by packing the bone in dry ice. An evaluation of the radiation dose received by bone has previously been made via dosimeters located within the tissue and dry ice, however, some evidence suggests that low temperature can influence the accuracy of the dosimeter readings. The aim of this study was to determine the actual radiation dose received by FH and FP bone during the irradiation process. This was accomplished by comparing radiation dose readings from dosimeters placed in dry ice with dosimeters placed in a dry ice substitute of similar dimensions and density i.e., polytetrafluoroethylene (PTFE) at ambient temperature. New packing formats were developed for both FH and FP bone such that 15 FH or 3 kg of FP bone could be irradiated in one transport box at any given time in a standardised fashion. The data show that low temperature consistently increased dosimeter readings 10–27%, and that radiation dose always fell within the range of 25–40 kGy (FH = 25.1–35.7 kGy; FP bone = 25.2–32.4 kGy). 相似文献