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   239篇
  免费   11篇
  国内免费   7篇
化学   98篇
数学   44篇
物理学   28篇
综合类   87篇
  2024年   1篇
  2023年   3篇
  2022年   22篇
  2021年   16篇
  2020年   9篇
  2019年   11篇
  2018年   4篇
  2017年   7篇
  2016年   3篇
  2015年   11篇
  2014年   10篇
  2013年   16篇
  2012年   12篇
  2011年   11篇
  2010年   4篇
  2009年   13篇
  2008年   12篇
  2007年   12篇
  2006年   4篇
  2005年   8篇
  2004年   7篇
  2003年   11篇
  2002年   9篇
  2001年   1篇
  2000年   11篇
  1999年   6篇
  1998年   1篇
  1997年   10篇
  1995年   2篇
  1994年   1篇
  1993年   3篇
  1990年   2篇
  1989年   1篇
  1988年   1篇
  1987年   2篇
排序方式: 共有257条查询结果,搜索用时 15 毫秒
81.
A rapid epifluorescence staining method using the LIVE/DEAD® BacLight Bacterial Viability kit was applied to differentiate both viable and total counts of acetic acid bacteria in vinegar fermentation. The results obtained were compared with those from other measurement techniques: 4,6-diamidine-2phenyl indole (DAPI) and 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) and colony counts. BacLight total counts were comparable to DAPI (differing by <3.5%). BacLight viable counts were similar to CTC counts but considerable higher than colony-forming cells in plates.  相似文献   
82.
The total yield of shrimp farming industry declined after WSSV broke out. It was only at the last 20 years that production had again begun to increase[1]. So far, shrimp farming industries mostly depend on capturing wild shrimps or wild post-larvae to sto…  相似文献   
83.
最小存活种群的确定与生物多样性保护   总被引:9,自引:3,他引:6  
以Allee的集群理论为基础,从种群内部的生态学机制出发,把物种划分为补偿物种(compensations species)、中性物种(middle species)与退偿物种(depensation species)三个类别,同时应用数学生态方法进行了种群生存力分析(PVA)的理论探讨,提出了最小存活种群(MVP)与物种濒危度的新观点,最后,对环境保护与生物多样性的保护提出了合理化建议。  相似文献   
84.
《Electroanalysis》2017,29(6):1498-1505
In bioelectrochemical systems (BESs), living microorganisms are capable of converting the chemical energy of degradable organic matters into bioelectricity. The electrical current outputs are dependent on the microbial cell viability and the biodegradation rates. Therefore, monitoring the current generative through the BES is promising for the microbial activity assessments. As compared to conventional microbiological methods, BESs are considered as non‐invasive techniques that offer rapid and sensitive detection of cellular functions (extra‐ and/or intracellular). Therefore, several progressions were made in the last 100 years in order to develop effective BESs. In this review, the involvements of materials sciences, microbiology, and electrochemistry in the effective designing and developments of BESs were intensively discussed. Due to the nanotechnology revolutions, manipulation of electrode materials led to the creation of different BES generations. Therefore, the impact of nanomaterials on the developments of the second and third generations of BESs is still the outlook of this promising research area.  相似文献   
85.
Abstract The success a species may have invading a patch previously unoccupied is of considerable interest for pest managers and conservation ecologists. The purpose here is to present a mechanistic approach to analyze reproductive Allee effects appearing through the failure in the process of fertilization in a two‐sex population and observe how the survival in an invaded patch is affected. This is in contrast to the usually employed stochastic models with a deterministic skeleton that describe the presence of Allee effects. A Poisson–Ricker model, which includes stochastic demography and sex determination with females classified as successfully fertilized or not fertilized, is used. Numerical approximations to the probabilities of extinction and the mean time to extinction are presented, for fixed parameter values, suggesting how stochasticity in the mating process combined with random fluctuations in the male and female densities, at each generation, contribute to the risk of extinction of a population which started an invasion at a low density.  相似文献   
86.
87.
Biofabrication of three dimensional tissues by Laser-Assisted Bioprinting (LAB) implies to develop specific strategies for assembling the extracellular matrix (ECM) and cells. Possible strategies consist in (i) printing cells onto or in the depth of ECM layer and/or (ii) printing bioinks containing both cells and ECM-like printable biomaterial. The aim of this article was to evaluate combinatorial effects of laser pulse energy, ECM thickness and viscosity of the bioink on cell viability. A LAB workstation was used to print Ea.hy926 endothelial cells onto a quartz substrate covered with a film of ECM mimicking Matrigel™. Hence, effect of laser energy, Matrigel™ film thickness and bioink viscosity was addressed for different experimental conditions (8-24 μJ, 20-100 μm and 40-110 mPa s, respectively). Cell viability was assessed by live/dead assay performed 24 h post-printing. Results show that increasing the laser energy tends to augment the cell mortality while increasing the thickness of the Matrigel™ film and the viscosity of the bioink support cell viability. Hence, critical printing parameters influencing high cell viability have been related to the cell landing conditions and more specifically to the intensity of the cell impacts occurring at the air-ECM interface and at the ECM-glass interface.  相似文献   
88.
以华山松种子为研究材料,通过研究不同质量分数(0.2%、0.5%)四唑溶液、不同染色温度和不同染色时间对华山松 种子生活力的影响,探索出测定华山松种子生活力的最佳条件。 通过萌发率对比,得出:在 30 ℃下用质量分数为 0.5%的四唑 溶液染色为最佳染色条件,且染色时间仅需要 5 h;胚全部染色,胚乳未染色面积小于 1 / 3 的种子具有生活力。  相似文献   
89.
心脏心肌功能的判断对疾病的治疗和预后极为重要。心肌存活属于可逆性心肌损害,故冠状动脉血运重建术可获益。存活心肌的检测,区分可逆性和不可逆性心肌损害,具有决策价值和预后价值。通过回顾近年来单光子心肌断层显像(SPECT)评价心肌存活的各种方法以及对比研究,以综合阐述SPECT对心肌存活评价的价值和最新进展,并对SPECT的未来作一初步探讨。  相似文献   
90.
本文通过引用生存定理,Lyapunov第二方法和比较定理,首先证明了微分包含的整体存在定理,然后讨论了微分包含解的稳定性  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