全文获取类型
收费全文 | 1094篇 |
免费 | 60篇 |
国内免费 | 3篇 |
出版年
2023年 | 14篇 |
2022年 | 32篇 |
2021年 | 46篇 |
2020年 | 27篇 |
2019年 | 49篇 |
2018年 | 42篇 |
2017年 | 28篇 |
2016年 | 51篇 |
2015年 | 58篇 |
2014年 | 69篇 |
2013年 | 85篇 |
2012年 | 89篇 |
2011年 | 76篇 |
2010年 | 31篇 |
2009年 | 42篇 |
2008年 | 41篇 |
2007年 | 50篇 |
2006年 | 48篇 |
2005年 | 35篇 |
2004年 | 25篇 |
2003年 | 33篇 |
2002年 | 25篇 |
2001年 | 16篇 |
2000年 | 6篇 |
1999年 | 6篇 |
1998年 | 7篇 |
1997年 | 2篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 3篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1974年 | 3篇 |
1972年 | 10篇 |
1970年 | 4篇 |
1969年 | 4篇 |
1966年 | 3篇 |
排序方式: 共有1157条查询结果,搜索用时 187 毫秒
991.
D. Liu T. Q. Li X. E. Yang E. Islam X. F. Jin Q. Mahmood 《Russian Journal of Plant Physiology》2008,55(1):68-76
Hydroponic experiments were conducted to study the effect of Pb on growth, leaf antioxidant enzyme activities, and ultrastructure
of the accumulating ecotype (AE) and non-accumulating ecotype (NAE) of Sedum alfredii Hance. AE was found to be more tolerant to excessive Pb levels in growth medium. Concentrations of Pb in the shoots of the
AE were 1.98 times higher than those in the NAE when 0.2 mM Pb was supplied. Both chlorophyll a and b did not decrease significantly in AE plants after Pb treatment, while a significant decrease was noted in chlorophyll a and b of NAE plants treated with Pb concentrations greater than 0.05 mM. The results showed that activities of superoxide dismutase
(SOD) and catalase (CAT) were elevated in the leaves of AE under Pb stress. However in NAE, Pb-caused enhancement was noticed
only in the activity of SOD while activity of CAT was declined as compared to the control plants. With increased Pb level,
malondialdehyde (MDA) content increased significantly in both ecotypes of S. alfredii, indicating that Pb toxicity led to lipid peroxidation and membrane damage, but MDA content in the leaves of NAE was always
higher than in AE plants. The ultrastructural analysis of the spongy mesophyll cells revealed that excessive Pb concentrations
obviously damaged the cell membrane, chloroplasts, and mitochondria of both the ecotypes but damage was more severe in NAE.
Although growth, leaf physiology, and ultrastructure of both the ecotypes were affected by Pb treatment, deleterious effects
were more pronounced in NAE.
This text was submitted by the authors in English. 相似文献
992.
Demian D. Chapman Debra L. Abercrombie Christophe J. Douady Ellen K. Pikitch Michael J. Stanhopen Mahmood S. Shivji 《Conservation Genetics》2003,4(4):415-425
The great white shark, Carcharodoncarcharias, is the most widely protectedelasmobranch in the world, and is classified asVulnerable by the IUCN and listed on AppendixIII of CITES. Monitoring of trade in whiteshark products and enforcement of harvest andtrade prohibitions is problematic, however, inlarge part due to difficulties in identifyingmarketed shark parts (e.g., dried fins, meatand processed carcasses) to species level. Toaddress these conservation and managementproblems, we have developed a rapid, moleculardiagnostic assay based on species-specific PCRprimer design for accurate identification ofwhite shark body parts, including dried fins. The assay is novel in several respects: Itemploys a multiplex PCR assay utilizing bothnuclear (ribosomal internal transcribed spacer2) and mitochondrial (cytochrome b) locisimultaneously to achieve a highly robustmeasure of diagnostic accuracy; it is verysensitive, detecting the presence of whiteshark DNA in a mixture of genomic DNAs from upto ten different commercially fished sharkspecies pooled together in a single PCR tube;and it successfully identifies white shark DNAfrom globally distributed animals. Inaddition to its utility for white shark trademonitoring and conservation applications, thishighly streamlined, bi-organelle, multiplex PCRassay may prove useful as a general model forthe design of genetic assays aimed at detectingbody parts from other protected and threatenedspecies. 相似文献
993.
Mahmood S Mozaffari James L Borke 《The journal of histochemistry and cytochemistry》2002,50(4):527-532
Taurine exerts a number of actions in mammalian cells, including regulation of ion transport and osmoregulation. The production and secretion of saliva involve transepithelial ion transport, thereby making the plasma-like primary saliva hypotonic before secretion. Therefore, it is plausible to suggest modulation of salivary taurine by muscarinic agents that affect salivary gland function. One of the objectives of this study was to determine tissue content and localization of taurine in the submandibular gland of the rat. Further, we determined whether treatment with muscarinic drugs that either increase (e.g., pilocarpine) or decrease (e.g., propantheline) saliva secretion affects the submandibular gland taurine content. The results indicate that the submandibular gland contains an appreciable amount of taurine (8.9 +/- 0.3 micromoles/g wet wt). Further, acute treatment of the rats with either of the muscarinic drugs did not significantly affect tissue taurine content compared to the control group. By contrast, chronic treatment with propantheline, but not pilocarpine, reduced the tissue content of taurine compared to the control rats (p<0.05). Utilizing light microscopic immunohistochemical techniques, intense immunoreactivity was found primarily in the striated ducts of the submandibular gland. Neither pilocarpine nor propantheline treatment led to differential distribution of immunoreactivity in this tissue. In conclusion, the submandibular gland contains an appreciable amount of taurine, primarily in the striated ducts, that can be decreased by chronic muscarinic receptor blockade. 相似文献
994.
Carbamoyl phosphate synthetases (CPSs) utilize either glutamine or ammonia for the ATP-dependent generation of carbamoyl phosphate. In glutamine-utilizing CPSs (e.g. the single Escherichia coli CPS and mammalian CPS II), the hydrolysis of glutamine to yield ammonia is catalyzed at a triad-type glutamine amidotransferase domain. Non-glutamine-utilizing CPSs (e.g. rat and human CPS I), lacking the catalytic cysteine residue, can generate carbamoyl phosphate only in the presence of free ammonia. Frog CPS I (fCPS I), unlike mammalian CPS Is, retains most of the glutamine amidotransferase residues conserved in glutamine-utilizing CPSs, including an intact catalytic triad, and could therefore be expected to use glutamine. Our work with native fCPS I provides the first demonstration of the inability of this enzyme to bind/utilize glutamine. To determine why fCPS I is unable to utilize glutamine, we compared sequences of glutamine-using and non-glutamine-using CPSs to identify residues that are present or conservatively substituted in all glutamine-utilizing CPSs but absent in fCPS I. We constructed the site-directed mutants Q273E, L270K, Q273E/N240S, and Q273E/L270K in E. coli CPS and have determined that simultaneous occurrence of the two substitutions, Gln-->Glu and Leu-->Lys, found in the frog CPS I glutamine amidotransferase domain are sufficient to eliminate glutamine utilization by the E. coli enzyme. 相似文献
995.
Shazia Rehman Ejaz Aziz Wasim Akhtar Muhammad Ilyas Tariq Mahmood 《Biotechnology letters》2017,39(5):647-666
Plant proteinase inhibitor-II (PI-II) proteins are one of the promising defensive proteins that helped the plants to resist against different kinds of unfavorable conditions. Different roles for PI-II have been suggested such as regulation of endogenous proteases, modulation of plant growth and developmental processes and mediating stress responses. The basic knowledge on genetic and molecular diversity of these proteins has provided significant insight into their gene structure and evolutionary relationships in various members of this family. Phylogenetic comparisons of these family genes in different plants suggested that the high rate of retention of gene duplication and inhibitory domain multiplication may have resulted in the expansion and functional diversification of these proteins. Currently, a large number of transgenic plants expressing PI-II genes are being developed for enhancing the defensive capabilities against insects, bacteria and pathogenic fungi. Much emphasis is yet to be given to exploit this ever expanding repertoire of genes for improving abiotic stress resistance in transgenic crops. This review presents an overview about the current knowledge on PI-II family genes, their multifunctional role in plant defense and physiology with their potential applications in biotechnology. 相似文献
996.
Bushra Jabeen S. M. Saqlan Naqvi Tariq Mahmood Tasawar Sultana Madiha Arif Fariha Khan 《Molecular biotechnology》2017,59(2-3):66-72
Members of the plant glycine-rich RNA-binding proteins (GR-RBPs) family have been reported in flowering, development, circadian rhythms, biotic and abiotic stresses. Particularly, GR-RBPs are reported to function as RNA chaperones, promoting growth and acclimation during cold shock. It is indispensable to further question the efficacy and mechanism of GR-RBPs under various environmental strains. Monitoring the expression of stress-regulated proteins under stress conditions has been a beneficial strategy to study their functional roles. In an effort to elucidate the NtGR-RBP1 function, stress markers such as salinity, drought, low temperature and heat stresses were studied. The NtGR-RBP1 gene was expressed in E. coli followed by the exposure to stress conditions. Recombinant E. coli expressing NtGR-RBP1 were more tolerant to stresses, e.g., salinity, drought, cold and heat shock. Recombinants exhibited higher growth rates compared to control in spot assays. The tolerance was further confirmed by monitoring the growth in liquid culture assays. Cells expressing NtGR-RBP1 under salt (500 mM NaCl), drought (20% PEG), cold (4 and 20 °C) and heat stresses (50 °C) had enhanced growing ability and better endurance. Our study supports the notion that the protective role of NtGR-RBP1 may contribute to growth and survival during diverse environmental stresses. 相似文献
997.
Hasnain?Sajid Tariq?Mahmood Khurshid?AyubEmail author 《Journal of molecular modeling》2017,23(10):295
An accurate comparison of the interaction of furan, pyrrole, and thiophene with different gaseous analytes is vital not only for understanding the sensing mechanism of corresponding polymers but also for rational design of new materials. In the present study, DFT calculations at (M05-2X/Aug-cc-PVDZ) have been performed to investigate the interaction behavior of furan, pyrrole, and thiophene (as models for their corresponding polymers) with different analytes (NH3, CO2, CO, N2H4, HCN, H2O2, H2S, CH4, CH3OH, SO2, SO3, H2O). The interaction of heterocycles with analytes is illustrated by changes in geometric, energetic, and electronic properties. SAPT calculations were performed for energy decomposition analysis to study the contribution of non-covalent components of the total interaction energy for each complex. Analysis of energetic and electronic properties reveals that all heterocycles are highly sensitive to SO3. The results suggest that sensing ability of polypyrrole is higher than polyfuran and polythiophene for all analytes. 相似文献
998.
999.
Bacterial microbiomes of individual ectomycorrhizal Pinus sylvestris roots are shaped by soil horizon and differentially sensitive to nitrogen addition 下载免费PDF全文
Srisailam Marupakula Shahid Mahmood Johanna Jernberg Srivathsa Nallanchakravarthula Zaenab A. Fahad Roger D. Finlay 《Environmental microbiology》2017,19(11):4736-4753
Plant roots select non‐random communities of fungi and bacteria from the surrounding soil that have effects on their health and growth, but we know little about the factors influencing their composition. We profiled bacterial microbiomes associated with individual ectomycorrhizal Pinus sylvestris roots colonized by different fungi and analyzed differences in microbiome structure related to soils from distinct podzol horizons and effects of short‐term additions of N, a growth‐limiting nutrient commonly applied as a fertilizer, but known to influence patterns of carbon allocation to roots. Ectomycorrhizal roots growing in soil from different horizons harboured distinct bacterial communities. The fungi colonizing individual roots had a strong effect on the associated bacterial communities. Even closely related species within the same ectomycorrhizal genus had distinct bacterial microbiomes in unfertilized soil, but fertilization removed this specificity. Effects of N were rapid and context dependent, being influenced by both soil type and the particular ectomycorrhizal fungi involved. Fungal community composition changed in soil from all horizons, but bacteria only responded strongly to N in soil from the B horizon where community structure was different and bacterial diversity was significantly reduced, possibly reflecting changed carbon allocation patterns. 相似文献
1000.
Muhammad Imran Naseer Mahmood Rasool Osama Yousef Muthaffar Abdulrahman J. Sabbagh Adeel G. Chaudhary Mohammad H. Al-Qahtani 《Genes & genomics.》2017,39(12):1317-1323
Primary microcephaly (MCPH) is a rare developmental defect characterized by impaired cognitive functions, retarded neurodevelopment and reduced brain size. It is genetically heterogeneous and so far more than 17 genes associated with this disease have been identified. Primary microcephaly type 1 (MCPH1) gene encodes a protein called microcephalin, which is implicated in chromosome condensation and DNA damage induced cellular responses. It is suggested to play a role in neurogenesis and regulation of the size of the cerebral cortex. Whole exome sequencing revealed a novel, homozygous frameshift mutation (c.373_374delAA) in MCPH1 gene in exon 5 resulting in frameshift change from p.Lys125Glusfs*7. Our report presents the results of the simultaneous analysis of the trio exome data of both unaffected parents and their affected son. A homozygous frameshift variant in the MCPH1 gene was identified as a plausible candidate causal variant for the clinical phenotype in this family. 相似文献