全文获取类型
收费全文 | 8933篇 |
免费 | 495篇 |
国内免费 | 6篇 |
专业分类
9434篇 |
出版年
2023年 | 76篇 |
2022年 | 123篇 |
2021年 | 256篇 |
2020年 | 152篇 |
2019年 | 172篇 |
2018年 | 240篇 |
2017年 | 219篇 |
2016年 | 279篇 |
2015年 | 359篇 |
2014年 | 418篇 |
2013年 | 588篇 |
2012年 | 605篇 |
2011年 | 574篇 |
2010年 | 349篇 |
2009年 | 283篇 |
2008年 | 401篇 |
2007年 | 360篇 |
2006年 | 350篇 |
2005年 | 348篇 |
2004年 | 287篇 |
2003年 | 236篇 |
2002年 | 238篇 |
2001年 | 209篇 |
2000年 | 181篇 |
1999年 | 165篇 |
1998年 | 65篇 |
1997年 | 59篇 |
1996年 | 68篇 |
1995年 | 53篇 |
1994年 | 60篇 |
1993年 | 38篇 |
1992年 | 118篇 |
1991年 | 120篇 |
1990年 | 89篇 |
1989年 | 96篇 |
1988年 | 90篇 |
1987年 | 91篇 |
1986年 | 88篇 |
1985年 | 95篇 |
1984年 | 85篇 |
1983年 | 53篇 |
1982年 | 49篇 |
1981年 | 47篇 |
1980年 | 50篇 |
1979年 | 79篇 |
1978年 | 61篇 |
1977年 | 51篇 |
1976年 | 46篇 |
1974年 | 39篇 |
1973年 | 44篇 |
排序方式: 共有9434条查询结果,搜索用时 15 毫秒
991.
Jing Sun Shihu Hu Keshab Raj Sharma Bing-Jie Ni Zhiguo Yuan 《Applied and environmental microbiology》2014,80(22):7042-7052
Simultaneous production of sulfide and methane by anaerobic sewer biofilms has recently been observed, suggesting that sulfate-reducing bacteria (SRB) and methanogenic archaea (MA), microorganisms known to compete for the same substrates, can coexist in this environment. This study investigated the community structures and activities of SRB and MA in anaerobic sewer biofilms (average thickness of 800 μm) using a combination of microelectrode measurements, molecular techniques, and mathematical modeling. It was seen that sulfide was mainly produced in the outer layer of the biofilm, between the depths of 0 and 300 μm, which is in good agreement with the distribution of SRB population as revealed by cryosection-fluorescence in situ hybridization (FISH). SRB had a higher relative abundance of 20% on the surface layer, which decreased gradually to below 3% at a depth of 400 μm. In contrast, MA mainly inhabited the inner layer of the biofilm. Their relative abundances increased from 10% to 75% at depths of 200 μm and 700 μm, respectively, from the biofilm surface layer. High-throughput pyrosequencing of 16S rRNA amplicons showed that SRB in the biofilm were mainly affiliated with five genera, Desulfobulbus, Desulfomicrobium, Desulfovibrio, Desulfatiferula, and Desulforegula, while about 90% of the MA population belonged to the genus Methanosaeta. The spatial organizations of SRB and MA revealed by pyrosequencing were consistent with the FISH results. A biofilm model was constructed to simulate the SRB and MA distributions in the anaerobic sewer biofilm. The good fit between model predictions and the experimental data indicate that the coexistence and spatial structure of SRB and MA in the biofilm resulted from the microbial types and their metabolic transformations and interactions with substrates. 相似文献
992.
The most common inflammatory disease of the airways is asthma among children affecting around 235 million people worldwide. 5-Lipoxygenase (5-LOX) is a crucial enzyme which helps in the conversion of arachidonic acid (AA) to leukotrienes (LTs), the lipid mediators. It is associated with several inflammation related disorders such as asthma, allergy, and atherosclerosis. Therefore, it is considered as a promising target against inflammation and asthma. Currently, the only drug against 5-LOX which is available is Zileuton, while a few inhibitors are in clinical trial stages such as Atreleuton and Setileuton. So, there is a dire requirement in the area of progress of novel 5-LOX inhibitors which necessitates an understanding of their structure activity relationship and mode of action. In this review, novel 5-LOX inhibitors reported so far, their structural design, SAR and developmental strategies along with clinical updates are discussed over the last two decades. 相似文献
993.
A. Sharma V. Kumar M. K. Kanwar A. K. Thukral R. Bhardwaj 《Russian Journal of Plant Physiology》2017,64(4):509-517
Pesticide toxicity causes oxidative stress to plants by generating reactive oxygen species (ROS). The aim of the present study was to observe the role of 24-epibrassinolide (24-EBL) in protection of Brassica juncea L. plants from oxidative stress caused by imidacloprid (IMI) pesticide. Generation of ROS, activities of antioxidative enzymes and chlorophyll contents were estimated using spectrophotometer, whereas organic acid contents were determined using gas chromatography-mass spectrometry (GC-MS). Statistical analysis of data revealed that 24-EBL significantly decreased ROS contents, accompanied by enhanced levels of shoot biomass, chlorophyll contents, organic acid contents and the activities of antioxidative enzymes in B. juncea plants under IMI toxicity. 相似文献
994.
Kawsar R. Talaat Subash Babu Pradeep Menon N. Kumarasamy Jabin Sharma Jeeva Arumugam Kalaivani Dhakshinamurthy Ramalingam Srinivasan S. Poongulali Wenjuan Gu Michael P. Fay Soumya Swaminathan Thomas B. Nutman 《PLoS neglected tropical diseases》2015,9(3)
BackgroundThe disease course of human immunodeficiency virus (HIV) is often altered by existing or newly acquired coincident infections.Conclusions/SignificanceWe were unable to find a significant effect of W. bancrofti infection or its treatment on HIV clinical course or surrogate markers of HIV disease progression though we recognized that our study was limited by the smaller than predicted sample size and by the use of ART in half of the patients. Treatment of W. bancrofti coinfection in HIV positive subjects (as is usual in mass drug administration campaigns) did not represent an increased risk to the subjects, and should therefore be considered for PLWHA living in W. bancrofti endemic areas.
Trial Registration
ClinicalTrials.gov NCT00344279相似文献995.
Interaction of Meloidogyne javanica and Fusarium oxysporum f. sp. ciceri was studied on Fusarium wilt-susceptible (JG 62 and K 850) and resistant (JG 74 and Avrodhi) chickpea cultivars. In greenhouse experiments, inoculation of M. javanica juveniles prior to F. oxysporum f. sp. ciceri caused greater wilt incidence in susceptible cultivars and induced vascular discoloration in roots of resistant cultivars. Nematode reproduction was greatest (P = 0.05) at 25 °C. Number of galls and percentage of root area galled increased when the temperature was increased from 15 °C to 25 °C. Wilt incidence was greater at 20 °C than at 25 °C. Chlorosis of leaves and vascular discoloration of plants did not occur at 15 °C. The nematode enhanced the wilt incidence in wilt-susceptible cultivars only at 25 °C. Interaction between the two pathogens on shoot and root weights was significant only at 20 °C, and F. o. ciceri suppressed the nematode density at this temperature. Wilt incidence was greater in clayey (48% clay) than in loamy sand (85% sand) soils. The nematode caused greater plant damage on loamy sand than on clayey soil. Fusarium wilt resistance in Avrodhi and JG 74 was stable in the presence of M. javanica across temperatures and soil types. 相似文献
996.
Vitul Jain Haruhisa Kikuchi Yoshiteru Oshima Amit Sharma Manickam Yogavel 《Journal of structural and functional genomics》2014,15(4):181-190
Aminoacyl-tRNA synthetases (aaRSs) drive protein translation in cells and hence these are essential enzymes across life. Inhibition of these enzymes can halt growth of an organism by stalling protein translation. Therefore, small molecule targeting of aaRS active sites is an attractive avenue from the perspective of developing anti-infectives. Febrifugine and its derivatives like halofuginone (HF) are known to inhibit prolyl-tRNA synthetase of malaria parasite Plasmodium falciparum. Here, we present functional and crystallographic data on P. falciparum prolyl-tRNA synthetase (PfPRS). Using immunofluorescence data, we show that PfPRS is exclusively resident in the parasite cytoplasm within asexual blood stage parasites. The inhibitor HF interacts strongly with PfPRS in a non-competitive binding mode in presence or absence of ATP analog. Intriguingly, the two monomers that constitute dimeric PfPRS display significantly different conformations in their active site regions. The structural analyses presented here provide a framework for development of febrifugine derivatives that can seed development of new anti-malarials. 相似文献
997.
Numerous investigations have been carried out on the spectral distribution of the light of different species of fireflies. Here we record the emission spectrum of the Indian species of the firefly Luciola praeusta Kiesenwetter 1874 (Coleoptera : Lampyridae : Luciolinae) on a color film. Green and red color-sectors, with an intense yellow one in between, appear in this spectrum. Intensity profile of this spectrum reveals a hitherto undetected strong narrow yellow line, which lies within the full-width-at-half maximum (FWHM) of the intensity profile. The spectrum recorded in a high-resolution spectrometer confirms the presence of this sharp intense line. This finding lends support to an earlier drawn analogy between the in vivo emission of the firefly and laser light. 相似文献
998.
Vijay K. Sharma Pradeep K. Jain Satish C. Maheshwari Jitendra P. Khurana 《Journal of plant biochemistry and biotechnology.》1999,8(2):87-92
The polypeptides of etioplast and chloroplast fractions, purified on Percoll discontinuous gradient, were phosphorylated in vitro using (γ-32P)ATP, resolved by SDS-PAGE and autoradiographed. In general, about 15-18 phosphopolypeptides in the range of 14-150 kD were distinctly visible in autoradiograms of both organelle fractions with varying degree of radiolabel incorporation. Although short-term irradiation with red or far-red light did not have any significant effect on phosphorylation status of etioplast polypeptides, in vivo irradiation with 1 h white light, followed by in vitro phosphorylation, decreased phosphorylation of a 116 kD polypeptide and increased the phosphorylation of polypeptides of 38 kD and a doublet around 20 kD. Strikingly, the phosphorylation status of 116 kD etioplast polypeptide was adversely affected by Ca2+ as well, and this phosphopolypeptlde was not distinctly visible in the autoradiogram of the chloroplast fraction proteins. However, in vitro phosphorylation of 98, 57 and 50 kD polypeptides of both etioplast and chloroplast fractions was found to be Ca2+ dependent. Unlike Ca2+, 3′,5′-cyclic AMP down-regulated the phosphorylation of several polypeptides of both etioplasts and chloroplasts, including 98 and 50 kD, and up-regulated the phosphorylation of 32 and 57 kD polypeptides. The significance of these observations on changes in phosphoprotein profile of etioplasts and chloroplasts, as influenced by light, Ca2+ and cyclic nucleotides, has been discussed. 相似文献
999.
1000.
Gulshan B. Sharma Richard E. Debski Patrick J. McMahon Douglas D. Robertson 《Journal of biomechanics》2009,42(10):1460-1468
Glenoid prosthesis loosening is the most common cause for revision total shoulder arthroplasty. Stress-induced bone remodeling may compromise long-term prosthesis fixation and significantly contribute to loosening. Realistic, robust analysis of bone-prosthesis constructs need to look beyond initial post-implantation mechanics provided by static finite element (FE) simulation. Adaptive bone remodeling simulations based on Wolff's law are needed for evaluating long-term glenoid prostheses fixation. The purpose of this study was to take a first step towards this goal and create and validate two-dimensional FE simulations, using the intact glenoid, for computing subject-specific adaptive glenoid remodeling. Two-dimensional glenoid FE models were created from scapulae computed tomography images. Two distinct processes, “element” and “node” simulations, used the forward-Euler method to compute bone remodeling. Initial bone density was homogeneous. Center and offset load combinations were iteratively applied. To validate the simulations we performed location-specific statistical comparisons between predicted and actual bone density, load combinations, and “element” and “node” processes. Visually and quantitatively “element” simulations produced better results (p>0.22), and correlation coefficients ranged 0.51–0.69 (p<0.001). Having met this initial work's goals, we expect subject-specific FE glenoid bone remodeling simulations together with static FE stress analyses to be effective tools for designing and evaluating glenoid prostheses. 相似文献